This PDF file contains the front matter associated with SPIE Proceedings Volume 7295, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee and Symposium Committee listings.

The use of permanently attached arrays of sensors has made it clear that guided waves can be used for the SHM of structures. The approaches developed have relied on the use of reference signal subtraction to indicate changes to the state of the structure, such as the appearance of damage. The limit of performance of any system is defined by the post subtraction noise. In order to confirm the basic principles at work the majority of this work has been carried out on simple metallic plates. While important to confirm the levels of understanding, this is not sufficient for practical use. This paper looks at the application of SHM techniques in more complex structures, more typical of those any system would be used on in practise. A rib from a BaE 146 aircraft is used to demonstrate the practical difficulties of applying guided wave SHM methods to densely featured structures. A model system comprising a plate with a single stringer is used to demonstrate a method for normalizing signals to give responses directly related to the scattering properties of the change in the system, mitigating the effect of the position of the change, and a method is proposed to generalize the approach to complex systems. Preliminary tests in the region of the stringer are used to identify the experimental challenges to realizing the calibration on complex systems.

With the goal to detect relatively small damage while minimizing signal processing burden, an approach in the medium frequency range (10 kHz - 50 kHz) is proposed for the characterization of a damage in a complex assembly structure and more specifically, a lap joint. The approach is based on the identification of the parameters of a reference transmission line model of a damaged lap joint structure through the experimental measurement of a reflection coefficient. The transmission line model of the lap joint is first presented, where symmetrical thickness variations on a beam are used to represent the lap joint region and a notch within this region. The cost function used in the model identification approach is then defined as the squared difference between simulated and measured reflection coefficients in a given frequency range. A sensitivity analysis is conducted using the Hessian of the cost function and simulation results are presented to demonstrate the sensitivity of the cost function to variations in the sought parameters, i.e. location and depth of the notch, in the frequency domain. Experimental results are then presented to assess the sensitivity of the cost function to the variation of the depth of the notch. These experimental results confirm the simulation results which indicate that the sensitivity of the cost function to the depth of the notch increases as this depth increases. Moreover, cross-sensitivity results indicate that the sensitivity of the cost function to the location of the notch also increases as the depth of the notch increases.

Rotor health monitoring and on-line damage detection have been increasingly gaining interest to manufacturers of aircraft engines, primarily to increase safety of operation and lower the high maintenance costs. But health monitoring in the presence of scatter in the loading conditions, crack size, disk geometry, and material property is rather challenging. However, detection factors that cause fractures and hidden internal cracks can be implemented via noninvasive types of health monitoring and or nondestructive evaluation techniques. These evaluations go further to inspect materials discontinuities and other anomalies that have grown to become critical defects that can lead to failure. To address the bulk of these concerning issues and understand the technical aspects leading to these outcomes, a combined analytical and experimental study is being thought. Results produced from the experiments such as blade tip displacement and other data collected from tests conducted at the NASA Glenn Research Center's Rotordynamics Laboratory, a high precision spin rig, are evaluated, discussed and compared with data predicted from finite element analysis simulating the engine rotor disk spinning at various rotational speeds. Further computations using the progressive failure analysis (PFA) approach with GENOA code [6] to additionally assess the structural response, damage initiation, propagation, and failure criterion are also performed. This study presents an inclusive evaluation of an on-line health monitoring of a rotating disk and an examination for the capability of the in-house spin system in support of ongoing research under the NASA Integrated Vehicle Health Management (IVHM) program.

Composites are increasingly used in numerous structural applications because of their low weight-to-strength and weight-to-stiffness ratios. However, the performance and behavior characteristics of nearly all in-service composite structures can be affected by degradation resulting from sustained use as well as from exposure to severe environmental conditions or damage resulting from external conditions such as impact, loading abrasion, operator abuse. These factors can have serious consequences on the structures relative to safety, cost, and operational capability. In this paper, a SmartComposite system is introduced for monitoring the integrity of large composite structures. Key features of the system include miniaturized lightweight hardware, self-diagnostics and an adaptive algorithm to automatically compensate for damaged sensors, reliable damage detection under different environmental conditions, and generation of POD curves. Tests were conducted on composite test article with sensor network embedded inside the composite skin or surface mounted to demonstrate the impact damage detection capability of the SmartComposite System. It is clear from the test results that the SmartComposite system can successfully detect impact damages, including both damage location and probability of damage size.

Maintenance is an important issue for aerospace systems, since they are in service beyond their designed lifetime. This requires scheduled inspections and damage repair before failure. Research is in progress to develop a structural health monitoring system (SHMS) to improve this maintenance routine. Ultrasonic testing, utilizing a system of piezoelectric actuators and sensors, is a promising concept Measured wave signals are compared with signals for previously scanned states. Changes to the signal could be the result of damage to the component. This paper focuses on analyzing the differences of states, using artificial neural networks. Neural network analysis has the potential of creating a SHMS of greater ability and processing. Experiments were performed on a thin, flat aluminum panel. Ultrasonic actuators and sensors were installed and a baseline scan was performed on the undamaged panel. Simulated damage was introduced in specific areas, and scans were conducted for several damaged states. Neural networks were created to assess the changing conditions of the panel. The system was later tested on a lap joint specimen to confirm the abilities of the neural network. This form of analysis performed well at locating and quantifying areas of change within the structure. The neural network performance indicated that it has a role in the SHMS of aerospace structures.

One of the key issues in enabling fast and reliable deployment of space systems is structural qualification before launch. The current qualification process is rather long and may span many months. It is envisioned that structural health monitoring (SHM) could assist with verification of structural assembly during pre-launch procedures and enable diagnosis of satellite components. The proposed satellite SHM system utilizes active sensors to launch and receive elastic waves carrying elasticity information about the structural material. Sensor signatures are analyzed for variation of the elastic behavior due to damage. Satellite structural components typically feature complex geometries involving isogrids and bolted joints. Simple representations of complex structures are studied first, followed by investigation of elastic wave propagation in a realistic satellite panel. The sensor network approach is utilized to detect and locate structural damage. The acousto-elastic method is implemented for diagnosis of bolted joints in the satellite panel. Sensitivity of the method is explored for various damage scenarios and a practical damage detection algorithm is suggested. It is shown that the acousto-elastic method allows for assessment of the structural integrity of complex structural elements with bolted joints.

In present years, surface mounted piezoelectric wafer active sensors (PWAS) or piezoelectric patches are gaining popularity for onboard Structural Health Monitoring (SHM) systems. Through experimental investigations, it is apparent that several uncertainties are associated with the sensor signals. Proper understanding of the influence factors may provide insight to such uncertainties. Optimal placement of sensors is also a big challenge. In this paper, we have tried to report the pattern of wave field generated by the surface mounted actuators and the pattern of wave field developed near the sensors using a semi-analytical modeling technique called Distributed Point Source Method (DPSM). The surface mounted sensors/actuators are glued to the surface of the structure. Therefore, the contact between sensors and the host material is of utmost importance in transmitting energy into the host material. Long term interest of this research is to show the feature based differences in generated signals due to various types of contacts and debondings. However, in this paper we have addressed the most common type of contact called Gaussian contact which has a practical significance. In the near future, through this research, we can address issues related to other types of contact that frequently occur. This will help us to better understand the generated signals and quantify the uncertainties due to contact condition.

This paper presents results of an experiment designed to determine the impact of repeated strain cycles on lead ziconate titanate (PZT) transducers affixed to an aluminum test specimen. The goal of this research effort is to determine the impact of three cyclic strain levels on PZTs affixed with two different glue types. PZT transducers are evaluated because they are one of the leading health monitoring technologies used in aircraft structures due to their ability to transmit and receive Lamb Waves. Analysis of changes in the received signals can indicate the presence of structural damage. This monitoring paradigm can only be successful if signal changes due to exposure to aircraft environmental factors (temperature/strain/pressure cycles, etc) over time can be clearly identified and characterized. This paper presents the results and initial analysis of experiments to determine the changes in signal responses due to cyclic mechanical strain. Results indicate cyclic strain at 800 με has no effect to 510K cycles, while cyclic strain at 1700 and 2600 με both cause signal loss to varying degrees.

Deminsys is the world's fastest multi sensor / multi channel FBG interrogator, identifies one till four channels with typically 8 sensors per channel. The system is especially developed for the interrogation of signals up to 19,3 kHz for each sensor and the sample frequency is independent of the number of sensors. By having multiple sensors per fibre you can create a very compact network of sensors. Due to its revolutionary (light weight, compact and solid state) design, Deminsys seems to fit perfectly into (research) programs for aerospace, medic & life science, maritime, industrial, crash test and all other fast detection applications. Technobis Fibre Technologies (TFT) and NLR made a first test flight with the Deminsys optical fibre measurement system using the NLR test aircraft on October 24th 2008. This flight was a first step in the further development of the current system in order to make it suitable for operation on-board an aircraft and bring it from TRL3 towards TRL5, a functional model for aerospace applications.

This study characterizes the performance of embedded optical fiber Bragg gratings (FBGs) used as strain sensors. Focus is provided to FBGs embedded in a quasi-isotropic lay-up of carbon fiber epoxy lamina both parallel and perpendicular to adjacent structural fibers. It studies the birefringence induced during curing and quantifies the residual transverse strain differences on the fibers by measuring the split from a single reflected Bragg wavelength into two. The association between light polarization and loading directions relative to the optical fiber (in-plane parallel, in-plane transverse, and out-of-plane transverse) are analyzed. Birefringence was seen to increase when a compressive out-of-plane load was applied to the embedded optical fiber. In contrast, in-plane loads did not lead to an increase in birefringence as indicated by reflected wavelengths that split during curing shifting equally and linearly during tensile load tests. An effective strain-optic coefficient was determined that resulted in strong correlations between FBG and surface mounted electrical strain gauge measurements.

Analytical models have shown that local damage in a structure can be detected by studying changes in the curvature of the structure's displaced shape while under an applied load. In order for damage to be detected, located, and quantified using curvature methods, a spatially dense set of measurement points is required on the structure of interest and the change in curvature must be measurable. Experimental testing done to validate the theory is often plagued by sparse data sets and experimental noise. Furthermore, the type of load, the location and severity of the damage, and the mechanical properties (material and geometry) of the structure have a significant effect on how much the curvature will change. Within this paper, three-dimensional (3D) Digital Image Correlation (DIC) as one possible method for detecting damage through curvature methods is investigated. 3D DIC is a non-contacting full-field measurement technique which uses a stereo pair of digital cameras to capture surface shape. This approach allows for an extremely dense data set across the entire visible surface of an object. A test is performed to validate the approach on an aluminum cantilever beam. A dynamic load is applied to the beam which allows for measurements to be made of the beam's response at each of its first three resonant frequencies, corresponding to the first three bending modes of the structure. DIC measurements are used with damage detection algorithms to predict damage location with varying levels of damage inflicted in the form of a crack with a prescribed depth. The testing demonstrated that this technique will likely only work with structures where a large displaced shape is easily achieved and in cases where the damage is relatively severe. Practical applications and limitations of the technique are discussed.

Embedded ultrasonics has demonstrated considerable utility in structural health monitoring of aeronautical vehicle. This active sensing approach has been widely used to detect and monitor cracks, delaminations, and disbonds in a broad spectrum of metallic and composite structures. However, application of the embedded ultrasonics for active sensing of incipient damage before fracture has received limited attention. The aim of this study was to investigate the suitability of embedded ultrasonics and nonlinear acoustic signatures for monitoring pre-crack fatigue damage in aerospace structural material. A harmonic load was applied to structural specimens in order to induce fatigue damage accumulation and growth. Specimens of simple geometry were considered and piezoelectric active sensors were employed for generation and reception of elastic waves. The elastic wave signatures were analyzed in the frequency domain using nonlinear impedance and nonlinear resonance methods. A relationship between fatigue severity and linear as well as nonlinear acoustic signatures was investigated and considered in the damage classification procedure. Practical aspects of the active sensing of the fatigue damage before fracture were discussed and prospective avenues for future research were suggested.

As part of an on-going, multi-year effort focused on developing a practical structural health monitoring (SHM) sensor for critical structural components in aircraft, a miniature Rayleigh surface wave sensor has been developed and tested. The sensor was specifically designed to detect localized, deterministic cracking in targeted locations in critical locations where fatigue cracking is prevalent. A representative aircraft component was used in the present investigation. Miniature interdigital transducers (IDTs) operating in the low megahertz frequency range were designed, fabricated, and tested on compact tension (CT) fatigue specimens in the laboratory before they were strategically placed on the structure, where surface wave signals were monitored in both pitch-catch and pulse-echo detection modes simultaneously. Under a high-cycle fatigue loading to the structure, the IDT sensors performed well with three of the sensors successfully detecting the existence of a critical fatigue crack. Visual and eddy current inspection methods subsequently verified the presence of the crack and its location. In this paper, the entire effort from the design and characterization of the IDT sensors to the final fatigue test on an actual aircraft part is discussed.

Advanced composites are being used increasingly in state-of-the-art aircraft and aerospace structures. In spite of their many advantages, composite materials are highly susceptible to hidden flaws that may occur at any time during the life cycle of a structure, and if undetected, may cause sudden and catastrophic failure of the entire structure. This paper is concerned with the detection and characterization of hidden defects in composite structures before they grow to a critical size. A methodology for automatic damage identification and localization is developed using a combination of vibration and wave propagation data. The structure is assumed to be instrumented with an array of actuators and sensors to excite and record its dynamic response, including vibration and wave propagation effects. A damage index, calculated from the measured dynamical response of the structure in a previous (reference) state and the current state, is introduced as a determinant of structural damage. The indices are used to identify low velocity impact damages in increasingly complex composite structural components. The potential application of the approach in developing health monitoring systems in defects-critical structures is indicated.

Fiber Bragg gratings (FBGs) are excellent tools for monitoring mechanical and thermal strains, and have widespread application in the structural health monitoring (SHM) of aerospace, civil, and mechanical structures. A common approach used for interrogating FBG sensors involves the illumination of the sensor with a broadband laser source and the narrowband reflected light reflected from the FBG is monitored with a wavelength sensitive optical detection system. The thermal or mechanical perturbations experienced by the FBG sensor lead to a shift in its reflectivity spectrum. In this work, an alternative interrogation scheme is presented that uses an FBG based narrowband tunable laser source produced by incorporating the FBG into a fiber ring laser cavity as an optical feedback element. The laser cavity consists an erbium doped fiber (EDF) connected to the FBG at the output of the fiber ring, which allows for the generation of the required amplified stimulated emission (ASE) in the C-band and lasing at the center wavelength of the FBG reflectivity spectrum. With this interrogation scheme, the wavelength of the resulting narrowband laser source tracks the center wavelength of the FBG sensor as it drifts due to quasi-static and/or dynamic mechanical and thermal strains. In addition, the instantaneous spectral line-width of the laser source is effectively narrowed owing to the long length of the laser cavity, which facilitates highly sensitive demodulation of dynamic shifts of the lasing wavelength with a high coherence optical interferometer.

The paper presents the application of the nonlinear acoustic technique for fatigue crack detection. The method uses frequency modulation of the high-frequency ultrasonic wave by the low-frequency modal excitation. Low-profile, surface-bonded piezoceramic transducers are used for acousto-vibration actuation and sensing. The paper investigates the application of the broad-band low-frequency modal excitation. The study demonstrates that small fatigue cracks can be detected in an aluminum plate by the increase of amplitude level of modulation sidebands in the ultrasonic spectra. However, the sidebands can be also observed when the crack is not present in the plate due intrinsic nonlinear effects. Further studies are recommended to investigate these findings.

Magnetostrictive sensor (MsS) technology is an emerging method to cost-effectively inspect large structures using ultrasonic guided waves. Recent research focuses on applications demanding small, robust sensors. To adapt to these applications, SwRI has extended MsS capabilities to generating bulk and surface wave modes. Bulk wave applications are demonstrated on a laboratory specimen with artificial damage. Surface wave inspections are demonstrated to monitor large areas of a thick-walled containment type structure.

This paper explores the feasibility of detecting and quantifying corrosion and delamination (separation) at the interface between reinforcing steel bars and concrete using ultrasonic guided waves. The problem of corrosion of the reinforcing steel in structures has increased significantly with time. Concrete is strengthened by the inclusion of the reinforcement steel such as deformed or corrugated steel bars. Bonding between the two materials plays a vital role in maximizing performance capacity of the structural members. Corrosion of reinforcing steel has led to premature deterioration of many concrete members before their design life is attained. It is therefore, important to be able to detect and measure the level of corrosion in reinforcing steel or delamination at the interface. The development and implementation of damage detection strategies, and the continuous health assessment of concrete structures then become a matter of utmost importance. The ultimate goal is to develop a nondestructive testing technique to quantify the amount of corrosion in the reinforcing steel. The guided mechanical wave approach has been explored towards the development of such methodology. The ultrasonic waves, specifically cylindrical guided waves, can propagate a long distance along the reinforcing steel bars and have been found to be sensitive to the interface conditions between steel bars and concrete. Ultrasonic transducers are used to launch and detect cylindrical guided waves along the steel bar.

In-situ measurements of specimens in research reactors and the health monitoring of commercial nuclear power plants are difficult because of high operating temperatures and the presence of radiation. One possible solution is to transmit ultrasonic guided waves into the harsh environment from a remote transducer. However, it is well known that large changes in temperature can significantly alter guided-wave propagation. The work presented in this paper examines how temperature, up to 700 K, influences guided-waves in a bar specimen of rectangular cross-section. The measurement setup consists of a bar specimen connected to a magnetostrictive transducer via a long wire waveguide. This allows the transducer to be located outside of the high temperature environment. Theoretical dispersion curve calculations as well as time-domain finite element models have been used to predict the behavior of group velocity. Preliminary results indicate that each wave mode has a unique response to temperature at a given frequency. Although higher order modes are generally more sensitive to temperature, the results also suggest the possibility of selecting wave mode and frequency to minimize the change in group velocity due to temperature.

There is a need to better understand the effect of temperature changes on the response of ultrasonic guided-wave pitchcatch systems used for Structural Health Monitoring. A model is proposed to account for all relevant temperaturedependent parameters of a pitch-catch system on an isotropic plate and a fiber-reinforced composite laminate, including the actuator-plate and plate-sensor interactions through shear-lag behavior, the piezoelectric and dielectric permittivity properties of the transducers, and the Lamb wave dispersion properties of the substrate plate. The model is used to predict the S₀ response spectra in for the temperature range of -40°C to +60°C which accounts for normal aircraft operations. The transducers examined are flexible Macro-Fiber Composite type P1 patches. The study shows substantial changes in Lamb wave amplitude response caused solely by temperature excursions. It is also shown that, for the transducers considered, the response amplitude changes follow two opposite trends below and above ambient temperature (20°C), respectively. These results can provide a basis for the compensation of temperature effects in guided-wave damage detection systems.

Fatigue damage sensing and measurement in aluminum alloys is critical to estimating the residual useful lifetime of a range of aircraft structural components. In this work, we present electrical impedance and ultrasonic measurements in aluminum alloy 2024 that has been fatigued under high cycle conditions. While ultrasonic measurements can indicate fatigue-induced damage through changes in stiffness, the primary indicator is ultrasonic attenuation. We have used laser ultrasonic methods to investigate changes in ultrasonic attenuation since simultaneous measurement of longitudinal and shear properties provides opportunities to develop classification algorithms that can estimate the degree of damage. Electrical impedance measurements are sensitive to changes in the conductivity and permittivity of materials - both are affected by the microstructural damage processes related to fatigue. By employing spectral analysis of impedance over a range of frequencies, resonance peaks can be identified that directly reflect the damage state in the material. In order to compare the impedance and ultrasonic measurements for samples subjected to tension testing, we use processing and classification tools that are matched to the time-varying spectral nature of the measurements. Specifically, we process the measurements to extract time-frequency features and estimate stochastic variation properties to be used in robust classification algorithms. Results are presented for fatigue damage identification in aluminum lug joint specimens.

The scope of this paper is the investigation of reliable damage indicators obtained from Lamb wave responses on a multi-riveted strap joint aluminium panel representing a standard joint in aviation. Damage indices based on amplitude and cross-correlation are assessed by examining two data sets. The first set was taken 8 years ago, while the second set was obtained recently. The resumption of the experiment on the aircraft riveted panel after 8 years required a new clamping, a different data acquisition system and involved a new operator amongst other changes. Those variations inevitably caused deviations in the gathered data. The deviations obtained will be examined in the context of the derived damage indices. The application of a second baseline is carried out and its necessity discussed. Additional temperature measurements were recorded for the second phase of the experiment which showed high correlation with the variation of the waveforms and hence with the damage indices. This study gives a good indication of the sensitivity and reliability of a SHM system based on guided waves in complex joint structures. It also provides information about the robustness of the chosen method, as in real-world applications it is more likely that operators will change too.

Ultrasonic Guided Waves (UGWs) are a useful tool in structural health monitoring (SHM) applications that can benefit from built-in transduction, moderately large inspection ranges and high sensitivity to small flaws. This paper describes a SHM method based on UGWs, discrete wavelet transform (DWT), outlier analysis and principal component analysis (PCA) able to detect and quantify the onset and propagation of fatigue cracks in structural waveguides. The method combines the advantages of guided wave signals processed through the DWT with the outcomes of selecting defectsensitive features to perform a multivariate diagnosis of damage. The framework presented in this paper is applied to the detection of fatigue cracks in a steel beam. The probing hardware consists of a PXI platform that controls the generation and measurement of the ultrasonic signals by means of piezoelectric transducers made of Lead Zirconate Titanate. Although the approach is demonstrated in a beam test, it is argued that the proposed method is general and applicable to any structure that can sustain the propagation of UGWs.

Sudden crack growth has the potential to cause catastrophic failure when a crack reaches a critical crack size. Early detection of crack formation helps to minimize this potential. This research focuses on the use of guided ultrasonic waves (GUWs) to detect crack formation. Experiments are conducted on test specimens in which fatigue cracks are grown through cyclic loading. Macro Fiber Composite (MFC) and piezoelectric disc actuators are used as sensors to induce and receive various GUWs ranging in frequency from 25 to 100 kHz. Preliminary experimental results are given.

Acoustic-wave velocity is strongly direction dependent in an anisotropic medium. This can be used to design composites with preferred acoustic-energy transport characteristics. In a unidirectional fiber-glass composite, for example, the preferred direction corresponds to the fiber orientation which is associated with the highest stiffness and which can be used to guide the momentum and energy of the acoustic waves either away from or toward a region within the material, depending on whether one wishes to avoid or harvest the corresponding stress waves. The main focus of this work is to illustrate this phenomenon using numerical simulations and then check the results experimentally.

Commercial guided wave inspection systems provide rapid screening of pipes, but limited sizing capability for small defects. However, accurate detection and sizing of small defects is essential for assessing the integrity of inaccessible pipe regions where guided waves provide the only possible inspection mechanism. In this paper an array-based approach is presented that allows guided waves to be focused on both transmission and reception to produce a high resolution image of a length of pipe. In the image, it is shown that a signal to coherent noise ratio of over 40 dB with respect to the reflected signal from a free end of pipe can be obtained, even taking into account typical levels of experimental uncertainty in terms of transducer positioning, wave velocity etc. The combination of an image with high resolution and a 40 dB dynamic range enables the detection of very small defects. It also allows the in-plane shape of defects over a certain size to be observed directly. Simulations are used to estimate the detection and sizing capability of the system for crack-like defects. Results are presented from a prototype system that uses EMATs to fully focus pipe guided wave modes on both transmission and reception in a 12 inch diameter stainless steel pipe. The 40 dB signal to coherent noise ratio is obtained experimentally and a 2 mm diameter (0.08 wavelengths) half-thickness hole is shown to be detectable.

Structural health monitoring (SHM) systems often rely on propagating elastic waves through complex structures, which can result in the formation of diffuse-fields. Diffuse fields fill the whole structure with energy and are characterized by energy equi-partition among all propagation modes. Due to their apparent complexity, diffuse-fields are not commonly used by conventional SHM systems. However, recent theoretical and experimental studies have demonstrated that the local Green's functions (GF) can be estimated from the cross-correlation of diffuse wavefields recorded between points of a sensor grid and generated by sources located remotely from the monitoring area. The Diffuse Field Interferometry (DFI) concept yields the GF between all measured points (e.g. nominal response of the structure), effectively transforming each measurement point into a virtual source. The resulting local GFs provide detailed information on the dynamic behavior of the material/structure under investigation. In this work, Green's functions are estimated experimentally from DFI using full-field measurements obtained with a scanning laser vibrometer.

In recent years, nondestructive testing (NDT) has gained popularity for structural health monitoring and damage detection applications. Among the NDT methods, guided wave based NDT techniques have attracted the attention of many researchers due to their relatively long sensing range. These guided waves can be generated in a structure and sensed by a variety of techniques. The present study proposes a new scheme for PZT excitation and sensing based on laser and optoelectronic technologies, where power as well as data can be transmitted via laser. This paper mainly focuses on the excitation aspect. An arbitrary waveform is generated using a light source and transmitted to the PZT. A photodiode connected to the PZT then converts the light into an electrical signal and excites the PZT. The technique can be configured either for wired or wireless PZT excitations. Finally, the feasibility of the proposed power transmission scheme has been experimentally demonstrated in a laboratory setup.

The characterization of the dispersive behaviour of stress guided waves (GWs) from a time transient measurement is generally attempted by means of time-frequency representations (TFRs). Unfortunately, any TFR is subjected to the time-frequency uncertainty principle that limits the capability of the TFR to distinguish multiple, closely spaced guided modes, over a wide frequency range. To this aim we implemented a new Warped Frequency Transform (WFT) that in force of a more flexible tiling of the time-frequency domain presents enhanced modes extraction capabilities. Such tiling, composed by non linearly modulated atoms, is built on the dispersive group velocity curve of a particular propagating mode. The resulting TFR thus emphasizes the energy content associated to that particular guided mode within the recorded time waveform. Here we propose an application of the WFT to numerically simulated Lamb Waves propagating in an aluminum plate. The results show that the proposed WFT limits interference patterns which appears with others TFRs and produces a sparse representation of the dispersive Lamb wave pattern that can be suitable for identification and characterization purposes.

Honeycomb composite structures have been widely used in aerospace and aeronautic industries due to their unique characteristics. Due to the complex nature of honeycomb composite with the celled core, structural health monitoring (SHM) of honeycomb composite panels inherently imposes many challenges, which requires a detailed knowledge of dynamic elastic responses of such complex structures in a broad frequency domain. This paper gives numerical and experimental analyses of elastic wave propagation phenomena in sandwich panels with a honeycomb core, especially when the frequency domain of interest is relative high. Numerical simulation based on the Finite Element (FE) method is first performed to investigate wave generation and reception using piezoelectric actuators/sensors. The effectiveness of homogenized core model is discussed, compared with the dynamic responses based on honeycomb celled core model. The reliability of the simulated wave will be verified with the experimental results. Specific attention will be paid on core effects on group wave velocity. This research will establish a solid theoretical foundation for the future study of the structural health monitoring in the composites.

Ultrasonic chaotic excitations combined with sensor prediction algorithms have shown the ability to identify incipient damage (loss of preload) in a bolted joint. In this study we examine the capability of this damage detection scheme to identify disbonds and poorly cured bonds in a composite-to-composite adhesive joint. The test structure consists of a carbon fiber reinforced polymer (CFRP) plate that has been bonded to a CFRP rectangular tube/spar with several sizes of disbond as well as a poorly cured section. Each excitation signal is imparted to the CFRP plate through a macro-fiber composite (MFC) patch on one side of the adhesive joint and sensed using an equivalent MFC patch on the opposite side of the joint. A novel statistical classification feature is developed from information theory concepts of cross-prediction and interdependence. Temperature dependence of this newly developed feature will also be examined.

Shape memory alloy (SMA) washers expand axially when heated, and the expansion for the one-way type SMA is permanent even if the heat is removed. We investigated a method to repair bolted joint loosening defects using SMA washers. We incorporated such a feature into our impedance-based structural health monitoring (SHM) system. An SMA washer wrapped with a heater is installed between a bolt and the nut. Upon detection of a loosening defect, the heater is turned on to expand the SMA washer, which in turn repairs the defect. Our experimental results show that (i) our enhanced SHM system can detect bolted-joint loosening defects, and (ii) it can repair such defects effectively. Our system suggests that self-repairing of some structural defects is feasible without human interventions.

Full acoustic wavefield data were acquired from an aluminum plate with various structural discontinuities and artificial defects using an air-coupled transducer mounted on a scanning stage. Piezoelectric transducers permanently mounted on the specimen were used as wave sources. These source transducers were elements of a permanently attached sparse array. A time series of wavefield images clearly shows details of guided waves as they propagate outward from the source, reflect from specimen boundaries, and scatter from discontinuities within the structure. Distinct S₀ and A₀ Lamb wave modes are directly visible on constant time snapshots of the captured wavefield. However, the waves propagating outward from the source, and waves reflected from boundaries, obscure the weaker waves that are scattered from defects. To facilitate analysis of weaker scattered waves, source waves are removed from the full wavefield data using both time and frequency domain methods. The effectiveness of each method is evaluated in the wavenumber-wavenumber domain and results are fused to obtain images of scattered wavefields. The method is demonstrated on a through hole, to which a notch is added to simulate a crack. The angular dependence of the scattered wavefield is experimentally determined for source waves incident on the notch from two directions, one toward the side of the notch and the other toward the end of the notch.

The ultrasonic guided wave phased array technique offers an efficient means to interrogate damages in plate-like structures. When applying this technique to multilayer composite plates, however, the anisotropic behavior of the composite materials leads to significant influences on the beam steering performances of the phased arrays. This paper investigates the beam steering performances of guided wave phased arrays for multilayer composite plates in terms of phased array directivity profiles under influences of anisotropy. Angular dependences of guided wave amplitudes and phase variations in composite plates obtained through a Green's function based method are implemented into directivity profile calculations to account for the influences of anisotropy in a quantitative way. Guided wave phased array experiments are carried out to validate the directivity profile calculations.

Several imaging algorithms are being considered for localizing damage in plate-like structures by analyzing changes in signals recorded from permanently mounted guided wave sensor arrays. Delay-and-sum type algorithms have been shown to be effective for damage localization, but exhibit side lobes that significantly reduce the signal-to-noise ratio. Adaptive algorithms such as MVDR (minimum variance distortionless response) can provide significant reduction in the amplitude of side lobes. Additional improvements in image quality are possible if assumptions can be made concerning the scattering characteristics of the damage site. In the work presented here, the efficacy of the adaptive imaging algorithms is evaluated using both simulated and experimental waveform data. The simulated waveform data is generated by ray tracing and incorporates edge reflections, nominal dispersion curves, and a variety of angular scattering patterns for scatterers with cylindrical symmetry. The effect on image quality of mismatch between actual and assumed scattering patterns is evaluated. Images generated from the simulated waveform data are compared to those generated from experimental data for scattering from a 6 mm through-hole in an aluminum plate. The images are in good agreement, and knowledge of scattering characteristics is shown to significantly improve imaging results.

Lamb-wave testing for structural health monitoring is complicated by the dispersion nature of the wave modes. The dispersion effect will result in a propagated wave with longer time duration, deformed envelop shape as compared to its excitation counterpart, and hard to be interpreted. This paper first reviews the dispersion compensation and removal algorithms. Second, it compares these two methods by applying them to two widely used low-frequency Lamb wave modes: S0 and A0. Numerical simulations are compared in parallel with experimental results. Finally, the dispersion compensation algorithm is applied to 1-D PWAS phased array and demonstrated to improve the phase array's spatial resolution.

Distributed array systems for guided ultrasonic waves offer an efficient way for the long-term monitoring of the structural integrity of large plate-like structures. The measurement concept involving baseline subtraction has been demonstrated under laboratory conditions. For the application to real technical structures it needs to be shown that the methodology works equally well in the presence of structural and surface features. Problems employing this structural health monitoring concept can occur due to the presence of additional changes in the signal reflected at undamaged parts of the structure. The influence of the signal processing parameters and transducer placement on the damage detection and localization accuracy is discussed. The use of permanently attached, distributed sensors for the A0 Lamb wave mode has been investigated. Results are presented using experimental data obtained from laboratory measurements and Finite Element simulated signals for a large steel plate with a welded stiffener.

The detection of stress in bolts based on acoustic bulk waves of longitudinal and transversal polarization is well introduced and respective detection schemes are commercially available. Whereas the time-of-flight of bulk waves observed for detection varies under stress due to non-linear elastic properties, 1- or 2-dimensionally guided waves can in addition and for suitable modes even be dominantly influenced by geometric effects. Even though geometric effects are well known and used for example to tune string instruments, little if any attention has so far been given to similar effects for Lamb waves and other guided modes. The basic effects including anomalous stress dependencies if compared to bulk waves are presented and discussed including a comparison to expectations based on analytical modeling. Novel detection schemes including developments suitable for in-flight detections of stress in structural components of aircrafts are demonstrated.

This article theoretically studies the symmetry characteristics of Rayleigh-Lamb guided waves in nonlinear, isotropic plates. It has been known that the nonlinearity driven double harmonic in Lamb waves does not support antisymmetric motion. However the proof of this has not been obvious. Moreover, little is known on nonlinearity driven Lamb harmonics higher than double. These gaps were here studied by the method of perturbation coupled with wavemode orthogonality and forced response. This reduced the nonlinear problem to a forced linear problem which was subsequently investigated to formulate an energy level constraint as the defining factor for the absence of antisymmetry at any order of higher harmonic. This constraint was then used to explain the reason behind the absence of antisymmetric Lamb waves at the double harmonic. Further, it was shown that antisymmetric motion is prohibited at all the higher-order even harmonics, whereas all the higher order odd harmonics allow both symmetric and antisymmetric motions. Finally, experimental results corroborating theoretical conclusions are presented.

A new concept of reference-free damage detection methodology is developed using transfer impedances to detect crack damage in a plate-like structure without using previously collected baseline data. Conventional impedance-based damage detection techniques have been shown to be vulnerable to other types of changes such as temperature variation that may not be relevant to defects of interest. One of potential disadvantages of the conventional techniques is frequent falsealarms due to these undesirable variations that may occur particularly for field applications. In order to reduce these false-alarms, this paper proposes a new methodology that utilizes transfer impedances obtained between two pairs of collocated PZT patches instead of the electromechanical impedance obtained at one PZT patch. The proposed technique seeks Lamb mode conversion effects caused by the presence of crack damage in plate structures. Furthermore, an instantaneous damage classification is carried out by comparing mode conversion energy among several combinations of measured signals without any user-specified threshold or relying on the baseline data. The feasibility of the proposed reference-free methodology using transfer impedances is investigated via a series of experiments conducted on an aluminum plate.

A circular array of Piezoelectric Wafer Active Sensor (PWAS) has been employed to detect surface damages like corrosion using lamb waves. The array consists of a number of small PWASs of 10 mm diameter and 1 mm thickness. The advantage of a circular array is its compact arrangement and large area of coverage for monitoring with small area of physical access. Growth of corrosion is monitored in a laboratory-scale set-up using the PWAS array and the nature of reflected and transmitted Lamb wave patterns due to corrosion is investigated. The wavelet time-frequency maps of the sensor signals are employed and a damage index is plotted against the damage parameters and varying frequency of the actuation signal (a windowed sine signal). The variation of wavelet coefficient for different growth of corrosion is studied. Wavelet coefficient as function of time gives an insight into the effect of corrosion in time-frequency scale. We present here a method to eliminate the time scale effect which helps in identifying easily the signature of damage in the measured signals. The proposed method becomes useful in determining the approximate location of the corrosion with respect to the location of three neighboring sensors in the circular array. A cumulative damage index is computed for varying damage sizes and the results appear promising.

The scattering of elastic waves by defects is the physical basis of ultrasonic NDE. Although analytical models exist for some canonical problems, the general case of scattering from an arbitrarily-shaped defect requires numerical methods such as finite elements (FE). In this paper, a robust and efficient FE technique is presented that is based on the premise of meshing a relatively small domain sufficient to enclose the scatterer. Plane waves are then excited from a particular direction by a numerical implementation of the Helmholtz-Kirchhoff integral that uses an encircling array of uni-modal point sources. The scattered field displacements are recorded at the same points and the field decomposed into plane waves of different modes at different angles. By repeating this procedure for different incident angles it is possible to generate the scattering- or S-matrix for the scatterer. For a given size of scatterer, all the information in an S-matrix can be represented in the Fourier domain by a limited number of complex coefficients. Thus the complete scattering behavior of an arbitrary-shaped scatterer can be characterized by a finite number of complex coefficients, that can be obtained from a relatively small number of FE model executions.

The ultrasonic field generated by a Micro Intereferometric Acoustic Lens used for high precision Rayleigh wave velocity measurements is modeled by the recently developed mesh-free technique called Distributed Point Source Method (DPSM). The field generated by the three individual ultrasonic transducer elements forming the micro intereferometric acoustic lens are computed and compared with experimental measurements. Qualitative agreement between the theoretical and experimental results is observed; both results show converging beams up to the focal point and then the beams diverge. However, some of the minute detailed features in the generated ultrasonic field could only be observed in the computed results. Effects of non-uniform surface of the transducer and its contribution to the non-uniform ultrasonic source strength are investigated to understand and optimize the acoustic lens for localized quantitative elastic property measurements.

This paper investigates the use of finite element to model frictional heating based vibrothermography for the detection of fatigue cracks in steel specimens. First, a finite element modal analysis is carried out to predict the optimal excitation frequencies. Some thermographic experiments using an infrared camera are carried out to help updating a coupled thermo-mechanical model built to simulate the thermographic inspection process and to explain the heat generation and transfer related to it. Experimental investigations also confirmed that the technique is able to detect cracks as short as 0.1 mm. The developed model is able to simulate the thermographic inspection process with a maximum error of 2.13 % on the temperature distribution. The Fourier transform applied to numerical data reveals that the temperature evolution at the crack face changes according to the excitation frequency and is modulated due to the nonlinearity induced by the crack. The model also serves to confirm that the test is non-destructive since the calculated stress at the crack tip is less than the specimen material's yield stress.

It has been shown that guided waves can be used with sparse arrays of permanently attached sensors to detect the presence of damage in structures. When applied with temperature compensation strategies complex structures can be inspected over time and in the presence of varying conditions. Current analysis suggests a series of relationships for individual sensor pairs but is difficult to expand to predict the signal to noise performance of a real world large network of sensors. The result of this is that it is unclear as to what is the best sensor layout to detect damage. This paper quantitatively and qualitatively investigates the performance of different sensor geometries to determine the signal to noise ratio of different configurations. It is shown that using more than two sensors not only offers the ability to localize damage but also produces enhanced signal to noise ratio over a single pair of transducers. It is shown that there is no single optimum sensor layout, with the optimum layout dependant on the type of damage that is to be detected. However a network of squares or hexagons offers excellent performance.

Bio-inspired design to make artificial flappers fly does not just imitate biological systems as closely as possible, but also transferring the flappers' own functionalities to engineering solutions. This paper summarizes some key technical issues and the states-of-art of bio-inspired design of flapping UAVs with an introduction to authors' recent research results in this field.

ONERA - The French Aerospace Lab - has launched an internal program on biologically-inspired Micro Air Vehicles (MAVs), covering many research topics such as unsteady aerodynamics, actuation, structural dynamics or control. The aim is to better understand the flapping flight performed in nature by insects, and to control state of the art technologies and applications in this field. For that purpose, a flight-dynamics oriented simulation model of a flapping-wing concept has been developed. This model, called OSCAB, features a body and two wings along which the aerodynamics efforts are integrated, so as to determine the global motion of the MAV. The model has been improved by taking into account the flexibility of the wings (flexion of the leading edge and passive torsion of the wings, induced by the flapping motion itself under wing inertia). Thus, it becomes possible to estimate the coupling between flexibility and the aerodynamic forces. Furthermore, the model shows that using elastic properties of the wings allows a diminution of the mechanical energy needed for wings motion, and a reduction of the number of actuators to be implanted into the MAV.

Various experimental studies have demonstrated that an impedance-based approach to structural health monitoring can be an effective means of damage detection. Using the self-sensing and active-sensing capabilities of piezoelectric materials, the electromechanical impedance response can be monitored to provide a qualitative indication of the overall health of a structure. Although impedance analyzers are commonly used to collect such data, they are bulky and impractical for long-term field implementation, so a smaller and more portable device is desired. However, impedance measurements often contain a sizeable number of data points, and a smaller device may not possess enough memory to store the required information, particularly for real-time analysis. Therefore, the amount of data used to assess the integrity of a structure must be significantly reduced. A new type of cross correlation analysis, for which impedance data is instantaneously correlated between different sensor sets and different frequency ranges, as opposed to be correlated to pre-stored baseline data, is proposed to drastically reduce the amount of data to a single correlation coefficient and provide a quantitative means of detecting damage relative to the sensor positions. The proposed analysis is carried out on a 3-story representative structure and its efficiency is demonstrated.

This paper presents and evaluates in detail a harmonics tracking method (HTM) for tracking the instantaneous frequency and amplitude of a vibration signal by processing only three most recent data points. Teager-Kaiser algorithm (TKA) is a popular 4-point method for online frequency tracking, but its accuracy is easily destroyed by measurement noise due to the use of finite difference. Moreover, because a signal is assumed to be a pure harmonic in TKA, any moving average in the signal can destroy the accuracy of TKA. On the other hand, HTM uses a constant and a pair of harmonics to fit three recent data points and estimate the instantaneous frequency and amplitude, and it dramatically reduces the influence of any moving average. Moreover, noise filtering is an implicit capability of HTM if more than three points are processed, and this capability increases with the number of processed data points. However, HTM depends on TKA to provide the first frequency estimation in order to start online tracking. To compare HTM and TKA and evaluate the accuracy of HTM, Hilbert-Huang transform (HHT) is used to extract accurate time-varying frequency and amplitude by processing the whole data set without assuming the signal to be harmonic. Frequency and amplitude tracking of different amplitude- and/or frequency-modulated signals, nonlinear dynamic signals, and transient signals due to damage propagation is studied. Results show that HTM is more accurate, robust, and versatile than TKA for online frequency tracking. Moreover, the frequencies and amplitudes tracked by HTM have about the same accuracy as those extracted by HHT but without the edge effect that HHT suffers from. Hence, HTM is valuable for structural health monitoring by online frequency tracking.

Dimensionality reduction is an essential data preprocessing technique for feature extraction, clustering and data classification in the area of Structural Health Monitoring (SHM). This paper presents a novel data-driven model for feature extraction and its application to damage identification by means of experimental case studies. The method obtains similarity matrix indices for individual dimensional reduction techniques whereby maximum compression of information is obtained and redundancy therein is removed by creating an ensemble of these indices. A systematic comparison of this novel technique to existing linear and nonlinear dimensional reduction methods is given. First case study investigates the aeroacoustic properties of a scaled wing model with penetrating impact damage. In the experimental vibration case study, we use the response of surface mounted accelerometers to detect and quantify damage of an aluminum plate. The dimensional reduction methods will be used to improve the efficiency and effectiveness of damage classifier. In this study, damage identification performances are evaluated using a one-class k-Nearest Neighbor classifier. Classification performance is measured in terms of rate of detection and false alarm via receiver operating characteristic (ROC) curves. The robustness of the damage detection approach to uncertainty in the input data is investigated using probabilistic-based confidence bounds of prediction accuracy. Experimental results show that proposed approach yields significant reduction of false-diagnosis and increasing confidence levels in damage detection.

This study focuses on embeddable algorithms that operate within multi-scale wireless sensor networks for damage detection in civil infrastructure systems, and in specific, the Bivariate Regressive Adaptive INdex (BRAIN) to detect damage in structures by examining the changes in regressive coefficients of time series models. As its name suggests, BRAIN exploits heterogeneous sensor arrays by a data-driven damage feature (DSF) to enhance detection capability through the use of two types of response data, each with its own unique sensitivities to damage. While previous studies have shown that BRAIN offers more reliable damage detection, a number of factors contributing to its performance are explored herein, including observability, damage proximity/severity, and relative signal strength. These investigations also include an experimental program to determine if performance is maintained when implementing the approaches in physical systems. The results of these investigations will be used to further verify that the use of heterogeneous sensing enhances overall detection capability of such data-driven damage metrics.

In current physical medicine, specific manual forces are applied to patients for diagnosis, treatment, and evaluation, but these forces remain largely qualitiative. No universal tool exists to measure these forces and display them in real-time. To provide real-time quantitative feedback to clinicians, we have developed a disposable glove with a force sensor embedded in the fingertips or palm. The sensor is based on the fiberoptic bendloss effect whereby light intensity from an infrared source is attenuated as the fiber is bent between a series of corrugated teeth. The sensor fabricated has a very low profile (10 × 7 × 1 mm) and has demonstrated high sensitivity, accuracy, range, and durability. Forces as low as 0.1 N and up to 90 N have been measured with high signal to noise ratios. Good agreement with theoretical predictions of bendloss has been demonstrated. Current trials have obtained data from 20 ACL reconstruction patients demonstrating a significant increase in range of motion recovery for patients who consistently stretch at home over those who do not.

The use of flat panels based on amorphous silicon technology (a-Si) for digital radiography has been accepted by the medical community as having advantages over film-based systems. Radiation treatment planning employs computed tomographic (CT) data sets and projection images to delineate tumor targets and normal structures that are to be spared from radiation treatment. The accuracy of CT numbers is crucial for radiotherapy dose calculations in general but is even more important for charged particle therapy. Conventional CT scanners operating at kilovoltage X-ray energies typically exhibit significant image reconstruction artifacts in the presence of metal implants in human body. We demonstrate a significant improvement in metal artifact reductions and electron density measurements using an amorphous silicon a-Si imager obtained with an X-ray source that can operate at energies up to 1 MeV. The data collected with the higher energy system will be compared and contrasted to CT results obtained at standard kilovoltage energies.

Beside of changes in the shape of contracting and relaxing muscle, which can be monitored with ultrasound, also changes in the velocity of ultrasound are expected. To observe such changes with high resolution for the gastrocnemius muscle of athletes a novel detection scheme has been developed. As already introduced for the detection of sideways expansion of the muscle, ultrasonic transducers are mounted sideways on opposing positions of the skin. To detect variations of the speed of sound, the expansion of the muscle is suppressed by mechanical clamping. Under this condition, any variation in the time-of-flight of ultrasonic signals can only be introduced by a variation of the speed of sound along the path of the ultrasound transit signal. The observed rather small variations of the speed of sound are compared to the signals obtained by ultrasound monitoring for the extension and contraction observed for free sideways motion (unclamped muscle). Opposite to the general behavior of a free muscle the clamped muscle shows a diminishing time-of-flight under contraction relating to an increase in the sound velocity. Since clamping also reduces effects of inertia, the influence of inertia on muscle dynamics can be illustrated by comparison of measurements on clamped and free muscle.

Results on a designed piezo resistive transducer (PZR) are presented in this work. The PZR will be specially manufactured for accurately measuring human blood pressure levels. Such transducer consists of four indifussed piezoresistors within a 10-μm Si membrane. The voltage signal response (VSR) is predicted when pressure is applied to the membrane, using a MEMS design tool that includes Finite Element Analysis (FEA). This transducer has the purpose of serving as a basis for the integration of an implantable Bio-MEMS BP sensor.

Despite the wide variety of effective disinfection and wastewater treatment techniques for removing organic and inorganic wastes, pollutants such as nitrogen remain in wastewater effluents. If left untreated, these nitrogenous wastes can adversely impact the environment by promoting the overgrowth of aquatic plants, depleting dissolved oxygen, and causing eutrophication. Although nitrification/denitrification processes are employed during advanced wastewater treatment, effective and efficient operation of these facilities require information of the pH, dissolved oxygen content, among many other parameters, of the wastewater effluent. In this preliminary study, a biocompatible CNT-based nanocomposite is proposed and validated for monitoring the biological metabolic activity of nitrifying bacteria in wastewater effluent environments (i.e., to monitor the nitrification process). Using carbon nanotubes and a pH-sensitive conductive polymer (i.e., poly(aniline) emeraldine base), a layer-by-layer fabrication technique is employed to fabricate a novel thin film pH sensor that changes its electrical properties in response to variations in ambient pH environments. Laboratory studies are conducted to evaluate the proposed nanocomposite's biocompatibility with wastewater effluent environments and its pH sensing performance.

In introductory and even some advanced textbooks covering ultrasonic transducers including piezoelectric discs, the transducers used for excitation are normally introduced as electrically driven mechanical oscillators operated reversely for detection. A refined treatment based on original work from the early 60's of the last century demonstrates that even in this simple case, electromagnetic-mechanical coupling is restricted to interfaces with the volume of transducer discs operating in part as inertial mass, which can also be provided by suitable backing with improved results. Geometrical effects in combination with the oscillating masses lead to resonances of the transducers limiting the applications. Thin transducer discs or film transducers, which are in comparison to the oscillating masses in the generated or detected acoustic waves approximately mass free, can be operated such that inertial effects in the transducer are reduced respectively almost avoided. Even though such transducers are available on a commercial basis and are well introduced for the generation and detection of Lamb waves, the basic underlying principles are usually not highlighted. These effects are experimentally demonstrated and compared to expectations based on basic principles. Schemes suitable to overcome bandwidth restrictions given by geometrical effects are discussed and an application of wideband transducers for Lamb waves used for stress detection is exemplified.

A diamagnetically stabilized levitating rotor demonstrates feasibility of creating small a low friction and low maintenance generator. The planar rotor described in this paper uses a triangular configuration of magnets that generate EMF by passing over coils placed below the rotor. Equations were developed to predict the generated EMF from a series of arc segmented coils. Additionally, this paper provides a method for estimating optimal coil size and position for this planar rotor. Experiments demonstrated that the EMF generated in the coils matches well with the predicted wave forms for each case and the optimization theory is close enough to be useful for design.

Due to their increased angular coverage around body surfaces, conformal ultrasound transducers may potentially provide increased signal acquisition relative to rigid medical ultrasound probes and eliminate the need for mechanical scanning. This paper describes a novel, high efficiency, and robust conformal ultrasound transducer array based on a flexible substrate of silicon islands joined together using polyimide joints. The array incorporated diced bulk lead zirconate titanate (PZT) mounted atop the silicon islands as its piezoelectric material for its desirable electromechanical coupling factor and high piezoelectric coefficients. Parylene thin films deposited over the array reinforced the bendable joints, encapsulated the metal film interconnects, and formed, in conjunction with the silicon, an acoustical match between the PZT and soft tissue. Eight element linear arrays were fabricated with a pitch of 3.5 mm, operating at a center frequency of 12 MHz with a 6dB bandwidth of 27%. The robustness of the transducer was demonstrated by iterative bending around a 1 cm diameter cylinder, and the durability of the electrical traces and the frequency performance was measured using a vector network analyzer. This paper presents a robust, durable conformal ultrasound array with the versatility to scale to enable new applications in diagnostic ultrasound imaging.

In this paper, a structural health monitoring (SHM) methodology that can detect and characterize local structural damages in early stage is developed, by merging the concepts of two existing SHM principles, a piezoelectric impedance-based methodology and a nonlinear wave modulation spectroscopy. The presented SHM system mainly consists of a piezoelectric element bonded on the structural surface, a high-frequency harmonic voltage source, and a current detector. When the structure is subjected to a dynamic load at low-frequencies, it vibrates, and the scattering conditions for the high-frequency elastic waves in the vicinity of the inherent damages will change in synchronization with the structural vibration. This nonlinear effects of vibro-acoustic interaction between the low-frequency vibration and the high-frequency wave field causes the change in the driving-point impedance at the high frequency range, which can significantly modulate the coupled electro-mechanical impedance (or admittance) of the piezoelectric element. Therefore, if the piezoelectric element is driven by a fixed amplitude high-frequency harmonic voltage source, the nonlinear modulation of the coupled admittance can be observed as the amplitude and phase modulation of the current flowing through the piezoelectric element. A simplified modeling study of the above-mentioned nonlinear piezoelectric impedance modulation successfully leads to a damage evaluation index that assesses the intensity of the modulation of the modal stiffness. Experiments using a cracked beam are conducted to see how the impedance modulation can be observed and to examine the performance of the proposed method.

Viscosity measurement by bend loss of fiber is presented. The sensing principle makes use of the damping characteristic of a vibrating optical fiber probe with fix-free end configuration. By measuring the displacement of the fiber probe, the viscosity can be determined by matching the probe's displacement with the displacement built in the database obtained by either experimental method or Finite element calculation. Experimental results are presented by measuring the sucrose and glycerol solutions of different concentrations with a viscosity varying from 1 to 15 cP. Stokes' flow assumption is utilized to attenuate the mass density effect and simplify the viscosity measurement.

In complex structures such as lap joints, extracting the information associated with damage from the measured signal can be challenging. An approach is presented, based on the use of high frequency bursts injected into a structure using an actuator and the measurement of structural intensity using a compact array of sensors, located remotely from the damage. The approach implements structural intensity estimation using the Timoshenko beam formulation, including dual-mode propagation above the cut-off frequency of the A1 Lamb mode. The structural intensity is first expressed within Timoshenko beam theory and the use of the wave decomposition approach is proposed to allow its measurement. Simulations are then conducted to illustrate localized time-domain structural intensity measurement for a burst propagating in a semi-infinite beam with a notch represented by a thickness variation. Results show that below the cut-off frequency, the burst propagates as a shear-dominated wave (mode A0) while a moment-dominated burst also propagates above the cut-off frequency (mode A1). Experimental results show that both shear and moment components of intensity can be measured for frequencies below and above the cut-off frequency and that the notch can be detected. Structural intensity measurement is then applied to the detection of a notch in a simulated lap joint region of a beam. The results demonstrate the potential benefit of using the structural intensity to extract useful information from the dual-mode interference for characterizing the location and depth of the notch.

Residuals that capture the difference between anticipated behavior and actual observations are often used to identify damage. Wanting to control the influence of unmeasured disturbances and noise in residuals, it is common to generate reference signals using feedback from measured outputs. Since there is much flexibility in the gains a wide range of models that react differently to changes are possible. This paper examines two questions: 1) how damage residuals generated by different closed loop models relate to each other and 2) how to rank the expected efficiency of alternative models. On the first question examination shows that the residuals from any model can be viewed as sums of filtered open loop residuals where the filter coefficients depend on the model structure but not on the damage. On the second item a general procedure based on Bayesian decision-making is proposed to quantify the economical benefit in adopting a specific autoregressive model.

This paper addresses the problem of piezoelectric conversion enhancement from mechanical to electrical energy and illustrates this improvement on vibration control and health monitoring applications. Considering a mechanical structure equipped with piezoelements, it can be shown that a non-linear processing (SSHI) of the piezoelement output voltage improves significantly the energy conversion. This non-linear processing simply corresponds to short-circuit the voltage for a brief period of time when the voltage reaches a maximum or minimum. Technically, a non-linear switch is added in parallel with the piezoelement, thus the piezovoltage, in front of the rectifier, increases and consequently more energy flows to the storage capacitance. The harvested energy is nine times higher than the standard approach. The influence of piezo-material characteristics will be described. Extension of the non-linear approach to harvesting in the pulse regime leads also to a performance increase specifically for low coupled structure which is mostly the case. After an overview of the basic principles, the presentation will go over new extensions of the SSHI approach to increase the output power, to make it independent of the resistive load or to minimize the voltage drop effect in the rectifier. The SSHI extension to heat harvesting will be also introduced.

A steady technology development of such high-tech sensor system as optical fiber sensor, GPS sensor and laser sensor has led to increasingly utilizing them for monitoring the civil structure including the bridge. The state-of-the-art monitoring system making a great commitment to improving the stability and accuracy of the system has been effectively used for enhancing the efficiency of existing monitoring system. Optical fiber strain sensor, among those high-tech sensors, functions to measure the strain of the members using a contact method, like the existing strain sensor, because of the common characteristics of the strain sensors, but, compared to the existing electrical resistance strain sensor, it proved to be less affected by temperature as well as able to effectively correct the effect by temperature itself. The study, in an attempt to identify the temperature effect on FBG optical fiber strain sensor, among the sensors being used to monitoring system in bridges, evaluated the data from long-term measurement by real time monitoring system using optical fiber strain sensors. To that end, the real time monitoring system using optical fiber sensors were installed on Sapgyo Bridge (560m-long steel box girder composite bridge with maximum span of 80m) built in 1998 at Dang-jin, South Choong-chung Province and the monitoring continued for a certain period. The optical fiber sensors used was os310 of MOI (Micron Optic, Inc). The existing electrical resistance sensor was also set up under the same conditions for the purpose of comparing the temperature effect. In the wake of the analysis, the effect by temperature on measurement using optical fiber sensors under the condition of actual bridge could be identified.

To attain high accuracy results from GPS, the carrier phase observables have to be used to update the filter's states. However, a cycle slip that remains uncorrected will significantly degrade the filter's performance. In this paper, a novel method that can effectively detect and identify the small cycle slip is presented. First, the location of the cycle slip is detected by ascertaining the point of modulus maximal value of the wavelet coefficients since the cycle slip can be regarded as the singular point of the signal. Secondly, two kinds of prediction models based on artificial neural network (ANN) are established to correct the cycle slip. Experimental results with real data sets indicate that the method is effective and feasible.

The paper investigates innovative designs of piezoelectric actuators for Structural Health Monitoring (SHM). Periodic, configurations are proposed as effective means to provide actuators and sensors with strong, frequency dependent directional characteristics, which allow beam steering through a sweep of the excitation frequency. The concept has the potential to enable in-situ monitoring of critical components through strongly focused actuation (and/or sensing) and directional scanning capability, which may be achieved with very limited hardware requirements. Beam steering is achieved by exploiting interference phenomena generated by the spatial periodicity of the array and the simultaneous activation of its components. Such interference phenomena produce waves with frequency dependent directional characteristics, which allow directional scanning to be performed simply through a frequency sweep. The need for beam-forming algorithms and associated hardware is thus avoided. The concept is illustrated by considering 2D arrays of point sources of various topologies. The case of a thin membrane supporting the propagation of SV waves is first presented to provide a simple frame work of analysis. The case of Lamb waves in a thin plate is then considered to demonstrate the validity and the practicality of the proposed approach.

A number of structural health monitoring strategies have been proposed recently that can be implemented in smart sensor networks. Many are based on changes in the experimentally determined flexibility matrix for the structure under consideration. However, the flexibility matrix contains only static information; much richer information is potentially available by considering the dynamic flexibility, or receptance, of the structure. Recently, the stochastic dynamic DLV method was proposed based on the changes in the dynamic flexibility matrix employing centrally collected output-only measurements. This paper extends the stochastic dynamic DLV method so that it can be implemented on a decentralized network of smart sensors. New damage indices are derived that provide robustness estimates of damage location. The smart sensor network is emulated with wired sensors to demonstrate the potential of the proposed method. The efficacy of the proposed approach is demonstrated experimentally using a model truss structure.

In this study, an output-only modal analysis approach for wireless sensor nodes is proposed on the basis of assumption that a target structure is a linear system. In order to achieve the objective, the following approaches are implemented. Firstly, an output-only modal analysis method is selected for the wireless sensor networks. Secondly, the effect of time unsynchronization on the modal analysis method is mathematically derived. Thirdly, a new modal analysis approach using complex mode-shapes is proposed to extract modal parameters from unsynchronized signals. Finally, the proposed approach is evaluated by numerical tests and experimental tests.

After an extensive analysis, the Río Papaloapan Bridge in the state of Veracruz, Mexico, was scheduled for maintenance to replace the upper anchorage element of 20 cables that were identified as structurally deficient. For this rehabilitation, an extensive monitoring was implemented to ensure the integrity of the bridge. As a result, abnormal vibration levels were detected in one cable (cable 9 in semi-harp 1), particularly for winds over 50 km/h. To determine the origin of this behavior, additional vibration measurements were implemented to evaluate the dynamic vibrations of the different elements involved. Comparison of the frequency spectrum of different cables with same characteristics and tensions, it was found that the abnormal cable had high vibration levels within the range of 10 to 20 Hz. At the same time, the frequency spectrum for their corresponding upper anchorage of the cable also showed significant differences for the same range of frequencies and higher levels were detected for the same atypical cable in the semi-harp plane (xy plane). Analysis from the vibration data concluded that the tension of the cable was within specifications and the abnormal behavior was not due to distension. Simulation studies confirmed that reduction in the structural stiffness for the anchorage element induced high vibration levels in the range within 20 Hz and the dynamic coupling with the higher vibration modes of the cable was the most probable cause for the extensive vibration in the cable. Also, simulation analysis showed that a damping system could minimize significantly the vibration levels between 8 and 25 Hz. The foregoing gave us the opportunity to conclude that the cable # 9 o semi-harp 1, is under an abnormal conditions due to a dynamic vibration coupling to its upper anchorage element and the higher vibration in the xy plane in this anchorage element was most probably to stiffness reduction. Based on the previous, monitoring and detailed inspection of the anchorage element was recommended, and at the same time, consideration of a damping system is highly recommended to reduce vibration damage.

Rising energy prices and carbon emission standards are driving a fundamental shift from fossil fuels to alternative sources of energy such as biofuel, solar, wind, clean coal and nuclear. In 2008, the U.S. installed 8,358 MW of new wind capacity increasing the total installed wind power by 50% to 25,170 MW. A key technology to improve the efficiency of wind turbines is smart rotor blades that can monitor the physical loads being applied by the wind and then adapt the airfoil for increased energy capture. For extreme wind and gust events, the airfoil could be changed to reduce the loads to prevent excessive fatigue or catastrophic failure. Knowledge of the actual loading to the turbine is also useful for maintenance planning and design improvements. In this work, an array of uniaxial and triaxial accelerometers was integrally manufactured into a 9m smart rotor blade. DC type accelerometers were utilized in order to estimate the loading and deflection from both quasi-steady-state and dynamic events. A method is presented that designs an estimator of the rotor blade static deflection and loading and then optimizes the placement of the sensor(s). Example results show that the method can identify the optimal location for the sensor for both simple example cases and realistic complex loading. The optimal location of a single sensor shifts towards the tip as the curvature of the blade deflection increases with increasingly complex wind loading. The framework developed is practical for the expansion of sensor optimization in more complex blade models and for higher numbers of sensors.

Intelligent tires, equipped with sensors for monitoring applied strain, are effective in improving reliability and control systems such as anti-lock braking systems (ABSs). However, since a conventional foil strain gage has high stiffness, it causes the analyzed region to behave unnaturally. The present study proposes a novel rubber-based strain sensor fabricated using photolithography. The rubber base has the same mechanical properties as the tire surface; thereby the sensor does not interfere with the tire deformation and can accurately monitor the behavior of the tire. We also investigate the application of strain data for an optimized braking control and road condition warning system. Finally, we suggested the possibility of optimized braking control and road condition warning systems. Optimized braking control can be achieved by keeping the slip ratio constant. The road condition warning would be actuated if the recorded friction coefficient at a certain slip ratio is lower than a 'safe' reference value.

Early results and status of a research effort to frame the possibility in compressing the time scale of structural health monitoring to the impulsive transient domain are presented. Output only modal methods using a frequency domain decomposition technique are used to extract the operational modes of a plate subject to impulsive loading. A strain energy method for plates is the used to detect the damage on the plate. The method detects damage, but the location of damages is not very precise. The development of an extremely short duration, transient structural health monitoring algorithm will be discussed. Challenges in studying this new domain of health monitoring will also be highlighted.

This paper presents an innovative technique for structural damage detection that is based on principal component analysis when feedback controllers are incorporated into the structure. The use of feedback control can generate additional modal parameters of closed-loop systems and also enhance the sensitivity of modal parameters to structural damage. Principal component analysis (PCA) is used to extract the features of parameter changes due to damage for open-loop and closed-loop systems. The effect of uncertainty, such as measurement noise, on damage identification is studied based on PCA. The objective of this research is to develop methodologies, based on feedback control with PCA, to improve structural damage identification under model uncertainty.

Two modifications to an ultrasonic camera system have been performed in an effort to reduce setup time and post inspection image processing. Current production ultrasonic cameras have image gates that are adjusted manually. The process to adjust them prior to each inspection consumes large amounts of time and requires a skilled operator. The authors have overcome this by integrating the A-Scan and image together such that the image gating is automatically adjusted using the A-Scan data. The system monitors the A-scan signal which is in the center of the camera's field of view (FOV) and adjusts the image gating accordingly. This integration will allow for defect detection at any depth of the inspected area. Ultrasonic camera operation requires the inspector to scan the surface manually while observing the cameras FOV in the monitor. If the monitor image indicates a defect the operator then stores that image manually and marks an index on the surface as to where the image has been acquired. The second modification automates this effort by employing a digital encoder and image capture card. The encoder is used to track movement of the camera on the structures surface, record positions, and trigger the image capture device. The images are stored real time in the buffer memory rather than on the hard drive. The storing of images in the buffer enables for a more rapid acquisition time compared to storing the images individually to the hard drive. Once the images are stored, an algorithm tracks the movement of the camera through the encoder and accordingly displays the image to the inspector. Upon completion of the scan, an algorithm digitally stitches all the images to create a single full field image. The modifications were tested on a aerospace composite laminate with known defects and the results are discussed.

Fiberglass sandwich panels are tested to study a vibration-based method for locating damage in composite materials. This method does not rely on a direct comparison of the natural frequencies, mode shapes, or residues in the forced vibration response data. Specifically, a nonlinear system identification based method for damage detection is sought that reduces the sensitivity of damage detection results to changes in vibration measurements due to variations in boundary conditions, environmental conditions, and material properties of the panel. Damage mechanisms considered include a disbond between the core and face sheet and a crack within the core. A panel is excited by a skewed piezoelectric actuator over a broad frequency range while a three-dimensional scanning laser vibrometer measures the surface velocity of the panel along three orthogonal axes. The forced frequency response data measured using the scanning laser vibrometer at multiple excitation amplitudes is processed to identify areas of the panel that exhibit significant nonlinear response characteristics. It is demonstrated that these localized nonlinearities in the panel coincide with the damaged areas of the composite material. Because changes in the measured frequency response functions due to nonlinear distortions associated with the damage can be identified without comparing the vibration data to a reference (baseline) signature of the undamaged material, this vibration technique for damage detection in composite materials exhibits less sensitivity to variations in the underlying linear characteristics than traditional methods. It is also demonstrated that the damage at a given location can be classified as either due to a disbond or core crack because these two types of damage produce difference signatures when comparing the multi-amplitude frequency response functions.

This paper investigates the potential of a novel SHM method for the detection of delamination cracks in composites which exploits the nonlinear ultrasonic response with in-situ d31 piezoceramic actuators and sensors. Composite beam specimens with artificially created delamination cracks are tested, entailing two piezoceramic actuator patches, the first to generate a low frequency, high power modal excitation and the second a high frequency acoustical wave, as well as a piezoceramic sensor. Nonlinearities induced at the high-frequency signal, such as sidebands at the spectral components as long as modulations at the measured sensory voltage are evaluated as damage indicators. Experimental results quantify the potential of the method in detecting small delamination cracks through spectral sideband components. The influence of high-frequency on the effectiveness of the method is shown. Additionally, the effect of the magnitude of applied voltage on the low frequency actuator on the formation of spectral components is investigated. Finally, the obtained results of the present method are compared with a guided wave based pitch and catch SHM method using the same actuator-sensor pair to excite and monitor the propagation of the first symmetric and asymmetric Lamb waves.

This contribution deals with the implementation of a PC-controlled structural health monitoring system for continuous damage detection. The system is implemented in a real size demonstrator component made of carbon fiber reinforced polymer (CFRP). The component is equipped with an actuator array of piezoelectric patches which are driven by power amplifiers. With the appropriate test signals elastic Lamb waves are emitted into the continuum in a specific direction. Vibrometer measurements of reflections which are caused by delaminations make it possible to observe the size and position of the defect areas.

Since 2004, Shandong Binzhou Yellow River highway bridge health monitoring (SHM) system has started to operate. Abundance data has been acquired during these years. To make full use of these data, a 1/40 scale laboratorial model has been built based on the design information of Shandong Binzhou Yellow River highway bridge. And a health monitoring system of the laboratorial model, which included loading system, local response monitoring subsystem and global response monitoring subsystem, has been designed and implemented. The dynamic performance of bridge model and prototype has been compared and the error analysis has been provided also. The numeric simulation of cable damage localization utilizing damage location vectors (DLVs) has been demonstrated. And the results indicated that using DLVs to localize the cable damage is feasible and accurate. The goal of these efforts is to utilize the convenience of the laboratorial environment to obtain the structural information in ideal state which is hard to get in field.

The structure of concrete bridge is usually large in dimension and the structural state information is heavily impacted by many complicated factors. Especially, the influence of temperature to the structural responses is very significant and this influence varies distinctly with the sun shine, sharp descent of temperature and season changing. Consequently, the existence of temperature effect will result in a greatly complicated variation of the structural responses, adding great difficulty in the effective extraction of structural health information for safety assessment of bridges. In this paper, In order to realize the effective assessment of the structural safety of concrete bridges, according to the correlating characteristic between temperature and structural response (such as strain or deflection) of the bridge, the experiential regressive equation is decided by regressive analysis of temperature and structural response, and further more the temperature effect is separated from the total response. Finally, an application example is given out for demonstration. The results indicate that the response residual after elimination of temperature effect remains only the effect of structural variety under loads (including dead load and live load), which can be used as the foundation information for structural safety assessment of concrete bridges.

More and more large span structures have been built or are being built and their health is concerned about by civil engineers and investors, which arises to the problem of studying on several damage identification methods to give estimation on the health of the structure and the identification on damage location and damage degree. The damage identification methods in civil engineering are mostly based on dynamic characteristics, which have difficulties when applied to practical structures. Meanwhile, the strains of the structural important elements can give more exactly and more directly information for damage identification on damage location and damage degree. The information fusion for acceleration sensors and strain sensors is used for making a strategic decision on damage identification and the Dempster-Shafer evidence theory is used as the information fusion strategic decision, in which the strategic decision information fusion is a method to give the final decision based on the decision made by each kind of sensors according to some principle and some synthesized evaluation, that is, the final damage identification results are given based on the damage identification results using the structural dynamic characteristics and strain measurements. In addition, a finite element model of large span space shell structure is built and several damage cases of it are simulated, in the example, the structural dynamic characteristics damage index and strain measurements damage index are used to give the damage identification results, combining which the final damage identification result by strategic decision fusion is given too, while the method presented in the paper is proofed to be reliable and effective according to comparing the three kinds of damage identification results mentioned above.

During an MR procedure, the patient absorbs a portion of the transmitted RF energy, which may result in tissue heating and other adverse effects, such as alterations in visual, auditory and neural functions. The Specific Absorption Rate (SAR), in W/kg, is the RF power absorbed per unit mass of tissue and is one of the most important parameters related with thermal effects and acts as a guideline for MRI safety. Strict limits to the SAR levels are imposed by patient safety international regulations (CEI - EN 60601 - 2 - 33) and SAR measurements are required in order to verify its respect. The recommended methods for mean SAR measurement are quite problematic and often require a maintenance man intervention and long stop machine. For example, in the CEI recommended pulse energy method, the presence of a maintenance man is required in order to correctly connect the required instrumentation; furthermore, the procedure is complex and requires remarkable processing and calculus. Simpler are the calorimetric methods, also if in this case long acquisition times are required in order to have significant temperature variations and accurate heat capacity knowledge (CEI - EN 60601 - 2- 33). The phase transition method is a new method to measure SAR in MRI which has the advantages to be very simple and to overcome all the typical calorimetric method problems. It does not require in gantry temperature measurements, any specific heat or heat capacity knowledge, but only mass and time measurement. Furthermore, in this method, it is possible to show that all deposited SAR power can be considered acquired and measured.

Quantitative information from multidimensional NMR experiments can be obtained by peak volume integration. The standard procedure (selection of a region around the chosen peak and addition of all values) is often biased by poor peak definition because of peak overlap. Here we describe a simple method, called CAKE, for volume integration of (partially) overlapping peaks. Assuming the axial symmetry of two-dimensional NMR peaks, as it occurs in NOESY and TOCSY when Lorentz-Gauss transformation of the signals is carried out, CAKE estimates the peak volume by multiplying a volume fraction by a factor R. It represents a proportionality ratio between the total and the fractional volume, which is identified as a slice in an exposed region of the overlapping peaks. The volume fraction is obtained via Monte Carlo Hit-or-Miss technique, which proved to be the most efficient because of the small region and the limited number of points within the selected area. Tests on simulated and experimental peaks, with different degrees of overlap and signal-to-noise ratios, show that CAKE results in improved volume estimates. A main advantage of CAKE is that the volume fraction can be flexibly chosen so as to minimize the effect of overlap, frequently observed in two-dimensional spectra.

Study is performed of the weekly cycle of temperature indices (its diurnal range, mean, maximum and minimum) as well as cloudiness, solar radiation and air pollution index based on 1996-2005 surface observations and air pollution indexes from four big cities over the Yangtze River Delta of China. Results suggest that these temperature variations are featured by significant weekend effect (WE) in that these temperatures are higher at weekends than on workdays in summer as opposed to those in other seasons; the WE of diurnal maximum and minimum temperatures is much bigger at weekends and can be utilized as the WE index; during the long spell of holidays or festivities in China WE is remarkable, and especially in the Spring Festival and National Day holidays these temperatures are smaller compared to those 7 day before and after as opposed to the values during, and 7 days before/after, the May Day holidays; the temperature WE bears a close relation to aerosol concentration thanks to anthropogenic activities; in summer the indirect impacts of aerosols (aerosol - cloud interactions) due to abundant vapor play a dominant role and at weekends little aerosol is responsible for reduced cloudiness, allowing more solar radiation to strike the ground for the rise in all the temperatures; in the other seasons the direct and semi-direct effect of aerosol plays a predominant part, with the concentration of aerosols declining at weekends for reducing its ability to heat air and increasing cloudiness, thus leading to the decrease in all the temperature elements.

We present a technique for biomedical imaging without radiation. The technique is based on the principles of thermal radiation and RF radiometry, which can be used to generate tomographic images for medical diagnosis such as early detection of breast cancer. Thermal radiation refers to the blackbody radiation emitted by matter, which extends all through the electromagnetic spectrum. By wirelessly measuring this thermal radiation transmitted by the patient's body and internal tissues at RF frequencies using RF radiometry, a mapping of the temperature distribution can be established, from which information such as images of the body and internal tissues can be formed. Biomedical imaging using RF radiometry is valuable for biomedical imaging applications as it promises to retain the full benefits of RF imaging without exposing patients to radiation, thus benefiting not only patients but also health-care professionals and industries.

We present a technique for measuring human's heart beat and blood flow. The technique is based on interferometry at radio frequency (RF) and can produce very fine resolution and fast response. RF interferometry is a process detecting the change of phase and capable of resolving any physical quantity being measured within a fraction of the operating wavelength. It has relatively faster system response time than other techniques due to the fact that it is typically operated with a single-frequency source rather than across a frequency range. In measurement of heart beat and blood flow in the human body, a RF signal is used as the irradiating source and the change of the phase of the return signal over time is detected in the signal processing. This phase change is processed to extract the Doppler frequency shift used for calculating the heart beat or blood flow. Accurate wireless non-contact measurement of human's heart beat and blood flow with RF interferometry will advance the practice of medicine and promise substantial benefits to patients and medical professionals.