Fractional flow reserve (FFR) has proven to be very useful in diagnosis of narrowed coronary arteries. It is a technique
that is used in coronary catheterization to measure blood pressure difference across a coronary artery stenosis in maximal
flow. In-vivo blood pressure measurement is critical in FFR diagnosis. This paper presents a novel miniature all-optical
fiber blood pressure sensor. It is based on Fabry-Perot (FP) interferometry principle. The FP cavity was fabricated by
directly wet etching the fiber tip. Then, a diaphragm with well-controlled thickness was bonded to the end face of the
fiber using the thermal bonding technique. Finally, the sensor was packaged with a bio-compatible and flexible coil for
animal tests. A 25-50 kg Yorkshire swine model was introduced as the animal test target. The left anterior descending
coronary artery (LAD) was exposed, and beyond the takeoff of the largest diagonal branch, a 3.0 mm vascular occluder
was secured. Firstly, standard invasive manometry was used to obtain the blood pressure as baseline. Next, a guiding
catheter was introduced into the ostium of the left main coronary artery, and the miniature blood pressure sensor was
advanced into the LAD at a point beyond the vascular occlude. The blood pressure beyond the vascular occlude was
recorded. The sensor successfully recorded the blood pressure at both near-end and far-end of the vascular occluder.
The low energy-conversion efficiency in photoacoustic generation is the most critical hurdle preventing its wide
applications. In recent studies, it was found that the selection of the energy-absorbing layer material and design of the
acoustic generator structure both determine the photoacoustic conversion efficiency. The selection of the absorbing
material is based on its optical, thermal, and mechanical properties. In this research, we calculated and compared the
conversion efficiencies of six different absorbing film materials: bulk aluminum, bulk gold, graphite foil, graphite
powder-resin mixture, gold nanospheres, and gold nanorods. The calculations were carried out by a finite element
modeling (FEM) software, COMSOL Multiphysics. A 2D-axisymmetric model in COMSOL was built up to simulate a
3-layer structure: optical fiber tip, light absorbing film, and surrounding water. Three equations governed the thermo-elastic
generation of ultrasonic waves: the heat conduction, thermal expansion and acoustic wave equations. In "thick-film"
generation regime, majority of the laser energy is absorbed by the film and converted to high-frequency film
vibration, and the vibration excites the ultrasound wave in the adjacent water, while the water would not be heated
directly by the laser. From the results of this FEM simulation, the acoustic signal generated by gold nanosphere (or
nanorod) film is over two times stronger than that generated by graphite powder-resin film of the same thickness. This
simulation provides a strong support to the absorbing material selection for our proposed fiber ultrasound generator.
A 2D-axisymmetric finite element analysis (FEA) model was built to simulate an optical fiber-based photoacoustic
generator. A layer of absorbing film deposited on the tip of an optical fiber converts the pulsed-laser energy into
vibrations, which excite broadband ultrasound waves in the adjacent fluid. Instead of 1D or simplified 2D theoretical
solution, this multi-physics FEA model successfully calculates the ultrasound generated by film vibration and fluid
heating. Another advantage of this numerical calculation is that the dimensions of fiber and film can be optimized to
achieve high photoacoustic conversion efficiency. Two major conclusions were obtained from the simulation: 1) Thicker
absorbing film has higher photoacoustic conversion efficiency than thinner film; 2) Shorter laser pulse leads to higher
conversion efficiency and higher ultrasound central-frequency. The FEA results provide a practical support to the design
of this type of optical fiber photoacoustic generator, and make it possible to have a miniaturized non-destructive testing
transducer in the intravascular and intraluminal applications.
Ultrasound transducers have been used in various applications such as nondestructive testing, acoustic response analysis
of vascular tissues, and medical imaging. Most recent applications lead to a demand of more advanced ultrasound
generators featuring higher central frequency, wider bandwidth and miniature size. In this paper, a novel ultrasound
generator on an optical fiber tip is designed, fabricated and characterized. The ultrasound generator was fabricated by
coating several layers of gold nanoparticles (Au NPs) on the end face of a piece of commercially available optical fiber
via a layer-by-layer (L-b-L) technique. The Au NPs were synthesized by a traditional sodium citrate reduction method
and the diameter of Au NPs was controlled at 20 nm. The ultrasound is generated through photoacoustic procedure. By
introducing excitation laser pulses on the Au NPs layer, the energy of laser is converted into the heat through
photothermal mechanism. Then, the heat transforms into kinetic energy through thermalelastic mechanism. Thus,
ultrasound can be generated. The experiment results showed that this kind of ultrasound generator shows wide
bandwidth, high frequency and miniature size. By comparing to the conventional energy absorption material such as
graphite, the Au NPs show high energy absorption efficiency and high thermal expansion rate. Therefore, the generator
exhibits great potentials in intravascular imaging due to its miniature size.
The adaptive neural network is a standard technique used in nonlinear system estimation and learning applications for
dynamic models. In this paper, we introduced an adaptive sensor fusion algorithm for a helmet structure health
monitoring system. The helmet structure health monitoring system is used to study the effects of ballistic/blast events on
the helmet and human skull. Installed inside the helmet system, there is an optical fiber pressure sensors array. After
implementing the adaptive estimation algorithm into helmet system, a dynamic model for the sensor array has been
developed. The dynamic response characteristics of the sensor network are estimated from the pressure data by applying
an adaptive control algorithm using artificial neural network. With the estimated parameters and position data from the
dynamic model, the pressure distribution of the whole helmet can be calculated following the Bazier Surface
interpolation method. The distribution pattern inside the helmet will be very helpful for improving helmet design to
provide better protection to soldiers from head injuries.
GaN and AlN compounds have been proven useful in wide bandgap microelectronics and optoelectronics. Also
properties of bulk GaN and AlN have been studied extensively. However, many characteristics of AlGaN/GaN
superlattices are not well known. In particular, the properties of phonons have not been determined. In order
to determine phonon properties, this study measured infrared reflectivity spectra on short period superlattices,
which were grown by high quality molecular beam epitaxy. The superlattices consisted of 300 periods of alternating
layers of GaN and AlGaN, each containing between 1 and 8 monolayers. Next, the reflectivity of each sample
was measured using a Bruker IFS-66V spectrometer. From these experimental spectra the dielectric function,
and hence the optical phonon properties (namely phonon frequency and phonon damping), were determined.
Mapping the experimental spectra with theoretical calculations determined the longitudinal and transverse optical
phonon energies present in the AlGaN/GaN superlattices. Through the examination of different AlGaN/GaN
superlattice combinations, plots of phonon energies versus material composition were obtained. Furthermore,
new phonons, that were not present in bulk AlN and GaN, were discovered. Finally, phonon characteristics were
measured as a function of temperature, confirming that phonon energies decrease with increasing temperature.
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