In this article, we review our recent progress on the development of a multifunctional optical system-on-a-chip platform, which can be used for achieving heterogeneous wireless fiber optical sensor networks. A multifunctional optical sensor platform based on the micro-electromechanical systems (MEMS) technology is developed. The key component of the multifunctional optical sensor platform is a MEMS based tunable Fabry-Pérot (FP) filter, which can be used as a phase modulator or a wavelength tuning device in a multifunctional optical sensing system. Mechanics model of the FP filter and optics model of the multifunctional optical sensing system are developed to facilitate the design of the filter. The MEMS FP filter is implemented in a multifunctional optical sensing system including both Fabry-Perot interferometer based sensors and Fiber Bragg grating sensors. The experimental results indicate that this large dynamic range tunable filter can enable high performance heterogeneous optical sensing for many applications.
A novel miniature dual cavity Fabry–Perot sensor is presented for simultaneous measurements of pressure and temperature in this work. Both of the pressure and the temperature sensing cavities are fabricated by using a single step UV molding process which is simple, cost-effective, and safe procedure. The pressure sensor is composed of an UV molded cavity covered by a metal/polymer composite diaphragm for a high pressure sensitivity with a miniature sensor size. The temperature sensor is made of a short segment of UV curable polymer, which renders a high temperature sensitivity due to the material’s large thermal expansion. By exploiting the material characteristic of the polymer around 90% of size-reduction could be achieved with 88.5% of temperature sensitivity of the previously reported sensor made of pure silica. The overall sensor size is around 150 μm in diameter and 55 μm in length. Experimental studies show that the sensor has a good linearity over a pressure range of 1.0 to 4.0 psi with a pressure sensitivity of 0.137 μm/psi at 28 °C, and a temperature range of 28.0 °C to 42.4 °C with a temperature sensitivity of 0.0026 μm/◦C. The sensor can be applied to many biomedical applications that require pressure and temperature simultaneous measurements with minimum intrusiveness.
We present a surface-mountable miniature Fabry-Perot (FP) pressure sensor that exploits the total internal reflection at a
polished 45° angled fiber end face to swerve the optical axis by 90°. Optical analysis of the sensor system is performed
based in ABCD method in terms of intensity of the beams reflected from each mirror and visibility of the sensor
compared to conventional sensor system. One unique feature of the surface-mountable sensor is its embeddability with
minimum intrusiveness to the system. By using the fiber as a waveguide, as well as an inherent mask for
photolithography, a self-aligned FP cavity is constructed. A polymer-metal composite diaphragm is employed as a
deflection diaphragm for pressure sensing which enables achieving higher sensitivity and low-cost fabrication over
silicon diaphragm. The sensor exhibits a good linearity over the designed pressure range. Fiber Bragg grating is
embedded in the vicinity of the pressure sensor to solve the problem of cross sensitivity between pressure and
temperature by measuring the temperature of the system and compensating the temperature effect. This sensor is
expected to impact many fronts where temperature effect should be considered to perform reliable and accurate pressure
measurement with minimum intrusiveness.
The superacute ear of the parasitoid fly Ormia ochracea has inspired the development of a variety of novel miniature
directional microphones for sound source localization, in which the effects of air cavity backing the eardrums are often
neglected without validation. In the original testing on the fly ear, the integrity of the air space is shown not to be the key
to the intertympnal coupling. However, it does not necessarily mean that the tympanum can be treated as in vacuo, and
the effects of the air cavity backing the eardrums have yet to be fully understood. In this article, a normalized version of
our previous model of air-backed circular membranes is derived to study the conditions under which the air cavity can be
indeed neglected. This model is then used to study a fly-ear inspired directional microphone design with two clamped
circular membranes mechanically coupled by a bridge. The performance of the directional microphone with air cavity is
evaluated in comparison to its counterpart in vacuo. This article not only provides more insights into the fly ear
phenomena, but builds a theoretical foundation on whether and how to take the air cavity into account in the design of
pressure sensors and directional microphones in general.
We present an improved microfabricated sound localization sensor for unobtrusive surveillance systems inspired by the
tympanic membranes of the parasitoid fly, Ormia ochracea. The device consists of two silicon diaphragms mechanically
coupled by a suspended beam that amplifies the difference in time response, dependent on the incident angle of the
sound source. Fabrication techniques were modified to reduce residual stresses and improve device uniformity.
Enhanced acoustic cues for devices with central pivoting anchors were measured with laser Doppler vibrometry. Device
responses to weak excitations demonstrated good sensitivity over environmental noise. An order of magnitude in time
difference amplification was measured at 90° incident angles with a directional sensitivity of .39μs/degree. These results
provide a foundation for realizing an accurate bio-inspired MEMS directional microphone.
When using microphone array for sound source localization, the most fundamental step is to estimate the time difference
of arrival (TDOA) between different microphones. Since TDOA is proportional to the microphone separation, the
localization performance degrades with decreasing size relative to the sound wavelength. To address the size constraint
of conventional directional microphones, a new approach is sought by utilizing the mechanical coupling mechanism
found in the superacute ears of the parasitic fly Ormia ochracea. Previously, we have presented a novel bio-inspired
directional microphone consisting of two circular clamped membranes structurally coupled by a center pivoted bridge,
and demonstrated both theoretically and experimentally that the fly ear mechanism is replicable in a man-made structure.
The emphasis of this article is on theoretical analysis of the thermal noise floor of the bio-inspired directional
microphones. Using an equivalent two degrees-of-freedom model, the mechanical-thermal noise limit of the structurally
coupled microphone is estimated and compared with those obtained for a single omni-directional microphone and a
conventional microphone pair. Parametric studies are also conducted to investigate the effects of key normalized
parameters on the noise floor and the signal-to-noise ratio (SNR).
Inclined dual-fiber optical tweezers (DFOTs) are investigated both numerically and experimentally. In simulations, the
trapping forces of the inclined DFOTs and the single-fiber optical tweezers (SFOTs) are studied along two directions. By
comparing the simulation results of the inclined DFOTs and the SFOTs, the inclined DFOTs are found to have more
symmetric performance, stronger trapping forces, and more reliable functionality. The spring constant of the DFOTs was
calibrated experimentally along one direction. The calibration results agree with those obtained in simulations. Moreover,
we created multiple optical traps with an inclined dual-fiber optical tweezers setup. Multiple optical traps were formed at
different vertical levels. We demonstrated that this fiber-based trapping system can perform multiple functions, such as
particle grouping and stacking. Compared with those formed with objective-based optical tweezers, the multiple traps
presented here are small in size and independent of the objective or the substrate, and hence hold the promise to be
integrated in microfluidic systems. The inclined DFOTs capable of multiple trapping can be used for on-chip parallel
manipulation.
The supersensitive ears of the parasitoid fly Ormia ochracea have inspired researchers to develop bio-inspired
directional microphone for sound localization. Although the fly ear is optimized for localizing the narrow-band calling
song of crickets at 5 kHz, experiments and simulation have shown that it can amplify directional cues for a wide
frequency range. In this article, a theoretical investigation is presented to study the use of fly-ear inspired directional
microphones for gunshot localization. Using an equivalent 2-DOF model of the fly ear, the time responses of the fly ear
structure to a typical shock wave are obtained and the associated time delay is estimated by using cross-correlation. Both
near-field and far-field scenarios are considered. The simulation shows that the fly ear can greatly amplify the time delay
by ~20 times, which indicates that with an interaural distance of only 1.2 mm the fly ear is able to generate a time delay
comparable to that obtained by a conventional microphone pair with a separation as large as 24 mm. Since the
parameters of the fly ear structure can also be tuned for muzzle blast and other impulse stimulus, fly-ear inspired acoustic
sensors offers great potential for developing portable gunshot localization systems.
We present a microscale implementation of an acoustic localization device inspired by the auditory organ of the parasitic
fly Ormia Ochracea. The device consists of a pair of circular membranes coupled together with a beam. The coupling
serves to amplify the difference in magnitude and phase between the response of the two membranes as the incident
angle of the sound changes, allowing directional information to be deduced from the coupled device response. The
device was fabricated using MEMS technology and tested with laser Doppler vibrometery. Amplification factors of up to
7 times were observed in the phase difference between the membranes at 90 degree incident sound angles, with
directional sensitivity of up to 0.3μs/degree.
In this article, the equivalent two-degree-of-freedom (2-DOF) model for the hypersensitive ear of fly Ormia
ocharacea is revisited. It is found that in addition to the mechanical coupling between the ears, the key to
the remarkable directional hearing ability of the fly is the proper contributions of the rocking mode and
bending mode of the ear structure. This can serve as the basis for the development of fly-ear inspired
directional microphones. New insights are also provided to establish the connection between the mechanics
of the fly ear and the prior biological experiments, which reveals that the fly ear is a nature-designed
optimal structure that might have evolved to best perform its localization task at 5 kHz. Based on this
understanding, a new design of the fly-ear inspired directional microphone is presented and a
corresponding normalized continuum mechanics model is derived. Parametric studies are carried out to
study the influence of the identified non-dimensional parameters on the microphone performance.
Directional microphones are developed to verify the understanding and concept. This study provides a
theoretical guidance to develop miniature bio-inspired directional microphones, and can impact many
fronts that require miniature directional microphones.
We developed a miniature fiber optic pressure sensor system and utilized it for in vitro intradiscal pressure measurements for rodents. One of the unique features of this work is the design and fabrication of a sensor element with a multilayer polymer-metal diaphragm. This diaphragm consists of a base polyimide layer (150 nm thick), a metal reflective layer (1 µm thick), and another polyimide layer for protection and isolation (150 nm thick). The sensor element is biocompatible and can be fabricated by simple, batch-fabrication methods in a non-cleanroom environment with good device-to-device uniformity. The fabricated sensor element has an outer diameter of only 366 µm, which is small enough to be inserted into the rodent discs without disrupting the structure or altering the intradiscal pressures. In the calibration and in vitro rodent intradiscal pressure measurements, the sensor element exhibits a linear response to the applied pressure over the range of 0–70 kPa, with a sensitivity of 0.0206 µm/kPa and a resolution of 0.17 kPa. To our best knowledge, this work is the first successful demonstration of rodent intradiscal pressure measurements.
In this article, the design of a biology-inspired miniature directional microphone is presented. This microphone consists of two clamped circular diaphragms, which are mechanically coupled by a connecting bridge that is pivoted at its center. A theoretical model is constructed to determine the microphone response to sound incident from an arbitrary direction. Both the simulation and preliminary experimental results show that the proposed microphone provides a remarkable amplification of the time delay associated with the sound induced diaphragm responses. This study should be relevant to various sound source localization applications.
Experimental measurements of the strain and pressure of rotor blades are important for understanding the aerodynamics
and dynamics of a rotorcraft. This understanding can help in solving on-blade problems as well as in designing and
optimizing the blade profiles for improved aerodynamics and noise attenuation in the next generation rotorcraft. The
overall goal of our research is to develop a miniature wireless optical sensor system for helicopter on-blade pressure and
strain measurements. In this paper, leveraging past and current experiences with fiber optic sensor development, a proof-of-
concept of fiber optic pressure/strain sensor system with wireless data acquisition and transfer capability is
demonstrated. The recently developed high-speed, real-time fiber optic sensor demodulation techniques based on low
coherence interferometry and phase-shifting interferometry is used. This scheme enables a Spatial Division Multiplexing
configuration that consists of multiple Fabry-Perot strain and pressure sensors. Calibration of the strain and pressure
sensors is carried out by using commercially available sensors as references. Spin chamber testing of the sensor system
for simultaneous on-blade pressure and strain field measurements is also performed. It is expected that such a sensor
system will result in enhanced robustness and performance for on-blade pressure and strain field measurements.
In this paper, recent efforts conducted to analyze the dynamic behavior of a biology-inspired miniature directional
microphone are presented. Inspired by the tiny ears of the fly Ormia, the proposed directional microphone consists of two
circular diaphragms coupled by a beam. The numerical study has shown that the biology-inspired directional microphone
enables the amplification of the time delay between the sound pressure induced displacement responses of the two
diaphragms. Factors such as the beam stiffness and the air backed cavity, which influence the performance of the
directional microphone, are investigated. These analyses and results are expected to be valuable for the development of
biology-inspired miniature directional microphones for various applications.
Three dimensional cell manipulation using two inclined fibers with lensed tips is demonstrated. For the first time, the
relationship between optical forces and cell positions is experimentally characterized in such an optical fiber trap, which
exhibits a good linearity in the vicinity of the equilibrium. The system is capable of being a force sensor with a
resolution of around 1 pN/&mgr;m. The spring constant is found to be dependent on the cell's shape: a prolate cell entails a
larger spring constant than that of a round cell with a similar size. Numerical analysis is carried out by using a modified
ray optics model with a spheroidal object in the trap. The spring constant obtained from the analysis also depends on the
shape of a cell, which agrees with the experimental results. The fiber optical tweezers have great potential for threedimensional
manipulation and force measurement of cells.
Lower back pain continues to be a leading cause of disability in people of all ages, and has been associated with
degenerative disc disease. It is well accepted that mechanical stress, among other factors, can play a role in the
development of disc degeneration. Pressures generated in the intervertebral disc have been measured both in vivo and in
vitro for humans and animals. However, thus far it has been difficult to measure pressure experimentally in rodent discs
due to their small size. With the prevalent use of rodent tail disc models in mechanobiology, it is important to
characterize the intradiscal pressures generated with externally applied stresses.
In this paper, a miniature fiber optic Fabry-Perot interferometric pressure sensor with an outer diameter of 360 &mgr;m was
developed to measure intradiscal pressures in rat caudal discs. A low coherence interferometer based optical system was
used, which includes a broadband light source, a high-speed spectrometer, and a Fabry-Perot sensor. The sensor employs
a capillary tube, a flexible, polymer diaphragm coated with titanium as a partial mirror, and a fiber tip as another mirror.
The pressure induced deformation of the diaphragm results in a cavity length change of the Fabry-Perot interferometer
which can be calculated from the wavelength shift of interference fringes. The sensor exhibited good linearity with small
applied pressures. Our validation experiments show that owing to the small size, inserting the sensor does not disrupt
the annulus fibrosus and will not alter intradiscal pressures generated. Measurements also demonstrate the feasibility of
using this sensor to quantify external load intradiscal pressure relationships in small animal discs.
In this article, recently developed high-speed, real-time fiber optic sensor demodulation techniques based on low coherence interferometry and phase-shifting interferometry are presented. The demodulation schemes are used in a pressure sensor system that consists of a Fabry-Perot sensing interferometer and an integrated optical circuit (IOC) phase modulator that is used as a reference interferometer. Various conventional phase-stepping algorithms and novel algorithms with error compensations are investigated in order to reduce the errors in the demodulated phase signals. The errors introduced in the phase demodulation arise from many sources, including random intensity measurement errors, phase-shifting errors, and signal-related errors associated with time delays. Numerical analyses are conducted to compare the performances of the demodulation schemes based on different phase-shifting algorithms. These analyses will provide guidelines for choosing appropriate algorithms in sensor demodulation schemes and improving the sensor accuracy and bandwidth.
In this paper, recent efforts conducted to investigate the dynamic behavior of a pressure sensor diaphragm coupled with a cylindrical air-backed cavity are presented. Our study shows that a careful consideration of the coupling effect between the plate and the air-backed cavity is necessary to determine the design parameters of a pressure sensor, such as sensitivity and bandwidth. In the case of strong coupling, based on linear analysis of the coupled system, the model of the diaphragm center displacement and natural frequencies are found to be significantly different from the corresponding quantities obtained for a pure plate model. These analyses and results are expected to be valuable for carrying out the design of small pressure sensors (e.g., MEMS pressure sensors) for various applications.
Wind profiling systems are critical for next generation, free space laser communication systems and laser designation systems, which are required to operate in the presence of severe atmospheric turbulence. The precision of the received laser beam depends greatly on the accuracy of estimation of the transversal wind along the laser beam propagation path. Two types of wind profiling techniques are investigated here. One technique is based on the reconstruction of wind velocity information from spatio-temporal intensity scintillation data measured at the optical receiver telescope. For the case of multiple phase-distorting layers located at different distances, the observed intensity scintillation pattern contains intensity spots of different spatial scales. The determination of the wind velocity for each spatial scale allows reconstruction of the wind profile along the entire propagation path. The second technique is based on simultaneous real-time characterization of the transversal wind velocity along the propagation path from the output image streams of a differential nonlinear Zernike wavefront sensor. This sensor consists of an optically addressed spatial light modulator that enables high-speed, high-resolution visualization of wind flow at each distant phase-distorting layer along the propagation path. Both preliminary experimental results and numerical simulation results are shown to validate the performance of the two types of techniques.
In this article, recent investigations into the dynamic behavior of a sensor diaphragm under initial tension are presented. A comprehensive mechanics model based on a plate with in-plane tension is presented and analyzed to examine the transition from plate behavior to membrane behavior. It is shown that, for certain tension parameter values, it is appropriate to model the diaphragm as a plate-membrane structure rather than as a membrane. In the nonlinear analysis, the effect of cubic nonlinearity is studied when the excitation frequency is either close to one-third of the first natural frequency or the first natural frequency. The nonlinear effects limit the sensor bandwidth and dynamic range. The study shows that both of the nonlinear effects can be attenuated by decreasing the diaphragm thickness and applying an appropriate tension to realize the desired first natural frequency while reducing the strength of the nonlinearity. The analyses and related results should be valuable for carrying out the design of circular diaphragms for various sensor applications, in particular, for designing sensors on small scales.
Phase modulated fiber-optic sensors based on Fabry-Perot interferometers have been widely used in many applications. In this paper, a novel digital phase-stepping demodulation technique is developed, which is based on combining the principle of low coherence fiber-optic interferometry (LCFOI) and phase-measurement interferometry (PMI). An integrated optical circuit (IOC) phase modulator that enables a high frequency modulation is used to acquire multi-step phase shifts that are applicable to each sensing interferometer in a spatial division multiplexing system. The phase retrieval algorithm along with phase unwrapping technique is detailed and phase error associated with this technique is discussed. A multichannel acoustic measurement system was demonstrated using this technique. Experimental results show that this technique is especially useful for Fabry-Perot sensors with sensor cavity length in micrometer range and sensor bandwidth requirements in kHz to MHz range.
Analysis and numerical modeling of "exotic" laser beam propagation through inhomogeneous atmospheric media is performed. The exotic beam is synthesized by introducing an additional periodical dynamically changing phase modulation to a conventional outgoing beam base. The propagation media model includes a set of thin phase distorting layers corresponding to atmospheric turbulence-induced distortions and non-stationary nonlinear layers describing the thermal blooming effects that accompany high-energy laser beam propagation in a moving propagation medium. The exotic beam structure is optimized to have maximum energy inside the diffraction-limited size area on the target plane. Compared with propagation of conventional laser beams, the exotic beam exhibits better beam quality metrics on the target plane such as maximum intensity, centroid intensity, and energy in the vicinity of the maximum beam intensity and the centroid.
KEYWORDS: Control systems, Sensors, Wavefronts, Adaptive optics, Near field, Stochastic processes, Receivers, Wavefront sensors, Near field optics, Telescopes
Adaptive system bandwidth estimation techniques that can be applied to the adaptive optical systems based on stochastic parallel gradient descent (SPGD) optimizations are described. A useful parameter characterizing temporal dynamics of phase fluctuations resulting from the pupil-plane phase distorting layer moving at a certain velocity (wind velocity) is the Greenwood frequency. The knowledge of the Greenwood frequency and clock frequency of the adaptive control system (first order controller) allows simple estimation of the performance metric Strehl ratio. The numerical analyses indicate that the system performance can be characterized through the ratio of the Greenwood frequency and the system iterative process clock-frequency. A formula that estimates how the degradation of the adaptation performance in SPGD based compensators are derived and analyzed numerically. The bandwidth estimation for SPGD control systems with different resolution and decoupled SPGD (D-SPGD) control system is detailed.
In this paper, analytical and experimental investigations conducted into the design and use of fiber-tip based Fabry-Perot sensors for control of structural acoustics are presented. Noise is transmitted into the enclosure through a flexible boundary, and the fiber-tip sensors are designed for acoustic pressure and air particle velocity measurements inside and outside the enclosure as well as panel acceleration measurements. The benefits of these sensors for realizing zero spillover control schemes and other schemes are discussed.
Two kinds ofsmart force sensors for the force distribution measurements are presented in this paper. The force distribution testing technique is widely used in intelligent control of robot and biomechanics. Usually a sensor matrix that includes hundreds to thousands micro sensor elements is adopted and that will provides the precise force distribution information for the different requirements. Two kinds of sensor material the piezoelectric ceramic, PVDF and piezo-resistance sensor conducting rubber are introduced in this paper. The requirements ofthe smart structure and the signal processing technique are discussed. Three smart force sensor systems are developed for the robot and biomechanics applications. Some image processing techniques are developed for the signal analysis and data processing.
We report recent work on acoustic measurements using a Bragg grating based Fabry-Perot sensor system. A single Fabry-Perot sensor using a path matched Michelson interferometer was developed, and a digital demodulation scheme based on the phase stepping technique was used to measure acoustic sound pressure from 100 Hz to 600 Hz. This sensor is designed to work in a multiplexed architecture to provide inputs to a feed-forward adaptive control system. This control system will be used to actively control the sound pressure level within an enclosure. A series of experiments were performed to investigate the possibility and potential use of this sensor system for acoustic noise detection. In this paper, we present initial test data from the prototype optical sensor microphone. We also illustrate the envisioned multiplexed sensor scheme and control system.
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