Showing papers on "Pressure measurement published in 2012"

Patterning piezoelectric thin film PVDF–TrFE based pressure sensor for catheter application

Abstract: We report a thin PVDF–TrFE (polyvinyledenedifluoride–trifluoroethylene) copolymer film pressure sensor, fabricated using standard lithography process for cost-effective batch process, film uniformity, and high resolution of polymer patterning. PVDF–TrFE copolymer, a semi-crystalline material, was spin-coated into thin films (1 μm thick) to tap the near β-phase formation. Pressure measurements demonstrated that the thin film (1 μm) show better performance compared to thick film (6 μm) with no electrical poling or mechanical stretching. Thin film devices showed higher β phase formation from Raman spectroscopy measurements, which translate into high piezoelectricity for sensing. The sensors can operate over a broad pressure range of 0–300 mmHg, with fast recovery time of 0.17 s, suitable for real time flow measurements in catheter applications.

Miniature all-fiber Fabry-Perot sensor for simultaneous measurement of pressure and temperature.

Abstract: This article presents a miniature, high-sensitivity, all-silica Fabry–Perot fiber-optic sensor suitable for simultaneous measurements of pressure and temperature. The proposed sensor diameter does not exceed 125 μm and consists of two low-finesse Fabry–Perot resonators created at the tip of an optical fiber. The first resonator is embodied in the form of a short air cavity positioned at the tip of the fiber. This resonator utilizes a thin silica diaphragm to achieve the sensor’s pressure response. The second resonator exploits the refractive index dependence of silica fiber in order to provide the proposed sensor’s temperature measurement function. Both resonators have substantially different lengths that permit straightforward spectrally resolved signal processing and unambiguous determination of the applied pressure and temperature.

Wavelet analysis of near-field pressure fluctuations generated by a subsonic jet

Abstract: An experimental study of the pressure field generated by a subsonic, single stream, round jet is presented. The investigation is conducted in the near-field region at subsonic Mach numbers (up to 0.9) and Reynolds numbers . The main task of the present work is the analysis of the near-field acoustic pressure and the characterization of its spectral properties. To this aim, a novel post-processing technique based on the application of wavelet transforms is presented. The method accomplishes the separation of nearly Gaussian background fluctuations, interpreted as acoustic pressure, from intermittent pressure peaks induced by the hydrodynamic components. With respect to more standard approaches based on Fourier filtering, the new technique permits one to recover the whole frequency content of both the acoustic and the hydrodynamic contributions and to reconstruct them as independent signals in the time domain. The near-field acoustic pressure is characterized in terms of spectral content, sound pressure level and directivity. The effects of both the Mach number and the distance from the jet axis are analysed and the results are compared with published far-field observations and theoretical predictions. Simultaneous velocity/pressure measurements have been also performed using a hot-wire probe and a microphone pair in the near field. It is shown that the cross-correlation between the near-field acoustic pressure and the axial velocity is large (of the order of 0.2) in the potential core region whereas large velocity/hydrodynamic pressure correlations are located at the nozzle exit and downstream of the potential core.

Unsteady Pressure Analysis of a Swirling Flow With Vortex Rope and Axial Water Injection in a Discharge Cone

Abstract: The variable demand of the energy market requires that hydraulic turbines operate atvariable conditions, which includes regimes far from the best efficiency point. The vortexrope developed at partial discharges in the conical diffuser is responsible for large pres-sure pulsations, runner blades breakdowns and may lead to power swing phenomena. Anovel method introduced by Resiga et al. (2006, “Jet Control of the Draft Tube in FrancisTurbines at Partial Discharge,” Proceedings of the 23rd IAHR Symposium on HydraulicMachinery and Systems, Yokohama, Japan, Paper No. F192) injects an axial water jetfrom the runner crown downstream in the draft tube cone to mitigate the vortex rope andits consequences. A special test rig was developed at “Politehnica” University of Timi-soara in order to investigate different flow control techniques. Consequently, a vortexrope similar to the one developed in a Francis turbine cone at 70% partial discharge isgenerated in the rig’s test section. In order to investigate the new jet control method anauxiliary hydraulic circuit was designed in order to supply the jet. The experimentalinvestigations presented in this paper are concerned with pressure measurements at thewall of the conical diffuser. The pressure fluctuations’ Fourier spectra are analyzed inorder to assess how the amplitude and dominating frequency are modified by the waterinjection. It is shown that the water jet injection significantly reduces both the amplitudeand the frequency of pressure fluctuations, while improving the pressure recovery in theconical diffuser. [DOI: 10.1115/1.4007074]Keywords: decelerated swirling flow, vortex rope, water injection method, unsteadypressure, experimental investigation

PIV-based pressure fluctuations in the turbulent boundary layer

Abstract: The unsteady pressure field is obtained from time-resolved tomographic particle image velocimetry (Tomo-PIV) measurement within a fully developed turbulent boundary layer at free stream velocity of U ∞ = 9.3 m/s and Reθ = 2,400. The pressure field is evaluated from the velocity fields measured by Tomo-PIV at 10 kHz invoking the momentum equation for unsteady incompressible flows. The spatial integration of the pressure gradient is conducted by solving the Poisson pressure equation with fixed boundary conditions at the outer edge of the boundary layer. The PIV-based evaluation of the pressure field is validated against simultaneous surface pressure measurement using calibrated condenser microphones mounted behind a pinhole orifice. The comparison shows agreement between the two pressure signals obtained from the Tomo-PIV and the microphones with a cross-correlation coefficient of 0.6 while their power spectral densities (PSD) overlap up to 3 kHz. The impact of several parameters governing the pressure evaluation from the PIV data is evaluated. The use of the Tomo-PIV system with the application of three-dimensional momentum equation shows higher accuracy compared to the planar version of the technique. The results show that the evaluation of the wall pressure can be conducted using a domain as small as half the boundary layer thickness (0.5δ99) in both the streamwise and the wall normal directions. The combination of a correlation sliding-average technique, the Lagrangian approach to the evaluation of the material derivative and the planar integration of the Poisson pressure equation results in the best agreement with the pressure measurement of the surface microphones.

High-temperature piezoresistive pressure sensor based on implantation of oxygen into silicon wafer

Abstract: Silicon on insulator (SOI) substrates can be prepared using ion implantation of oxygen. For piezoresistive detection, the top layer (0.2 μm thickness) of silicon is used as the active material due to its excellent monocrystalline properties. The piezoresistive effect of the top silicon layer of the SOI wafer is analyzed using a cantilever structure. Results show that under certain doping concentration conditions, the longitudinal piezoresistive coefficients of 〈1 1 0〉 crystal direction silicon decrease with temperature, while transverse piezoresistive coefficients are less affected by temperature. At 300 °C, Si 〈1 1 0〉 crystal direction has larger longitudinal and transverse piezoresistive coefficients, which make it suitable for high temperature piezoresistive pressure sensor production. The pressure sensor chip structure is simulated and analyzed using the finite element method. The pressure gauge chips are manufactured using MEMS techniques. The manufactured sensors are measured with an applied pressure from 0 to 6.0 MPa at 300 °C. The test results show that the sensitivity is approximately 30 mV/(mA MPa), the non-linearity is less than 1.5‰FS, and the repeatability is less than 0.3‰FS. This research shows that the SOI piezoresistive pressure sensor could reliably work at high temperatures up to 300 °C.

Modern Gas-Based Temperature and Pressure Measurements

Abstract: The concept of temperature.- Gas-based fixed points for thermometry.- Gas thermometry between 0.5 K and 273.16 K.- Vapor-pressure thermometry.- Thermometry based on the melting line of 3He.- Cryostats for thermometry and gas-based temperature control.- Primary standards for pressure measurements.- Pressure transducers for gaseous media.- Gas based pressure fixed points.- The thermomolecular pressure difference effect.- The Mutual Recognition Arrangement and its implementation in Temperature and Pressure.- Appendix A - The international Temperature Scale of 1990.- Appendix B - List of temperature and pressure fixed points - Appendix C - Reference data on gases.- Appendix D - Vapor pressure equations.- Appendix E - Reference data for liquid-column manometers.- Appendix F - Reference data for pressure balances.- Appendix G - The text of the Mutual Recognition Arrangement.- Appendix H - General terminology in measurements.- INDEX.

A nano-opto-mechanical pressure sensor via ring resonator

Abstract: This paper reports a nano-opto-mechanical pressure sensor based on nano-scaled ring resonator. The pressure is measured through the output spectrum shift which is induced via mechanical deformation of the ring resonator. The sensitivity as high as 1.47 pm/kPa has been experimentally achieved which agrees with numerical prediction. Due to the strong variation of sensitivity with different ring radius and thickness of the diaphragm, the pressure sensor can be used to form an array structure to detect the pressure distribution in highly accurate measurement with low-cost advantages. The nano-opto-mechanical pressure sensor has potential applications such as shear stress displacement detection, pressure wave detector and pressure mapping etc.

Intermodal coupling of supermodes in a twin-core photonic crystal fiber and its application as a pressure sensor.

Abstract: In this paper, we experimentally demonstrated the fabrication and hydrostatic pressure characteristics of a twin-core photonic crystal fiber (TC-PCF). Mode couplings in the TC-PCF for x- and y-polarizations were analyzed simultaneously using group effective index of guiding modes. The output spectrum of the TC-PCF was modulated due to the combined couplings of the two polarizations. To the best of our knowledge, it is the first time to measure hydrostatic pressure through the dual-polarization mode coupling in a TC-PCF. The measured sensitivity of the pressure sensor was −21pm/MPa. The length of the TC-PCF used for pressure measurement was 20cm, which is much shorter than pressure sensor based on PM-PCF, and does not require any external polarizing components, meaning that it is a good candidate for compact pressure sensor.

Isobaric Specific Heat Capacity Measurement for Kerosene RP-3 in the Near-Critical and Supercritical Regions

Abstract: The isobaric specific heat capacity of kerosene RP-3 was experimentally measured using a vacuum flow-calorimeter in the near-critical and supercritical regions. During the experiments, the qualitative temperature changed from (292.1 to 823.9) K, and the operation pressure changed from (2.40 to 5.98) MPa. The operation pressure, fuel inlet and outlet bulk temperatures, mass flow rate, and heat power were measured using a pressure gauge transducer, K-type sheathed thermocouples, a Coriolis-force flow meter, and current and voltage meters, respectively. The estimated uncertainty of the measurement was lower than 2.11 %. The expanded accuracy of the measured method for the low temperature region was verified by the water at the pressure of 3.01 MPa; the high-temperature region was verified by comparing the temperatures calculated from Cp integrating enthalpy with the temperatures measured in the experiments.

The design and analysis of beam-membrane structure sensors for micro-pressure measurement.

Abstract: This paper reports the design and analysis of a type of piezoresistive pressure sensor for micro-pressure measurement with a cross beam-membrane (CBM) structure. This new silicon substrate-based sensor has the advantages of a miniature structure and high sensitivity, linearity, and accuracy. By using the finite element method to analyze the stress distribution of the new structure and subsequently deducing the relationship between structural dimensions and mechanical performances, equations used to determine the CBM structure are established. Based on the CBM model and our stress and deflections equations, sensor fabrication is then performed on the silicon wafer via a process including anisotropy chemical etching and inductively coupled plasma. The structure's merits, such as linearity, sensitivity, and repeatability, have been investigated under the pressure of 5 kPa. Our results show that the precision of these equations is ±0.19%FS, indicating that this new small-sized structure offers easy preparation, high sensitivity, and high accuracy for micro-pressure measurement.

Optical coherence tomography and pressure based systems and methods

Abstract: In part, the invention relates to methods, apparatus, and systems suitable for determining a fractional flow reserve (FFR) and variations of modifications thereof One embodiment relates to a method and apparatus for obtaining a corrected FFR in a vessel having a stenosis. In one aspect, the invention relates to an apparatus for measuring corrected FFR of a vessel having a stenosis. In one embodiment, the apparatus includes a probe comprising an optical coherence tomography assembly and a pressure assembly; and a processor in communication with the optical coherence tomography assembly and the pressure assembly. In one embodiment, the pressure assembly measures values of pressure in predetermined locations the vessel and communicates them to the processor. In one embodiment, a dual guidewire is used to reduce the interference in the pressure measurement.

Measurements of void fraction distribution in cavitating pipe flow using x-ray CT

Abstract: Measuring the void fraction distribution is still one of the greatest challenges in cavitation research. In this paper, a measurement technique for the quantitative void fraction characterization in a cavitating pipe flow is presented. While it is almost impossible to visualize the inside of the cavitation region with visible light, it is shown that with x-ray computed tomography (CT) it is possible to capture the time-averaged void fraction distribution in a quasi-steady pipe flow. Different types of cavitation have been investigated including cloud-like cavitation, bubble cavitation and film cavitation at very high flow rates. A specially designed nozzle was employed to induce very stable quasi-steady cavitation. The obtained results demonstrate the advantages of the measurement technique compared to other ones; for example, structures were observed inside the cavitation region that could not be visualized by photographic images. Furthermore, photographic images and pressure measurements were used to allow comparisons to be made and to prove the superiority of the CT measurement technique.

In situ pressure measurement within deformable rectangular polydimethylsiloxane microfluidic devices.

Abstract: In this paper, we present a simple procedure to incorporate commercially available external pressure transducers into existing microfluidic devices, to monitor pressure-drop in real-time, with minimal design modifications to pre-existing channel designs. We focus on the detailed fabrication steps and assembly to make the process straightforward and robust. The work presented here will benefit those interested in adding pressure drop measurements in polydimethylsiloxane (PDMS) based microchannels without having to modify existing channel designs or requiring additional fabrication steps. By using three different devices with varying aspect ratio channels (wh0, width/depth), we demonstrate that our approach can easily be adapted into existing channel designs inexpensively. Furthermore, our approach can achieve steady state measurements within a matter of minutes (depending on the fluid) and can easily be used to investigate dynamic pressure drops. In order to validate the accuracy of the measured pressure d...

Development of high total pressure scramjet flow conditions using the X2 expansion tube

Abstract: The objective of this thesis was to use the X2 expansion tube to produce the high Mach number and high total pressure scramjet flow conditions associated with access to space. Initial experimental attempts to produce a Mach 13 condition indicated that the existing free-piston driver arrangement, based on a 35 kg piston and 100% helium driver gas, did not produce high pressure driver gas for sufficient duration. Following expansion of the driver gas, the expansion wave processing the driver gas reflected off the piston face, interfering with the test gas prior to its arrival in the test section. The result was significant attenuation of the primary shock prior to its arrival in the test section. It was determined that a tuned driver condition could provide a significantly longer duration of high pressure driver gas; achieving this operating condition subsequently became the first major task of the investigation. Tuned operation involves configuring the driver so that the piston is moving sufficiently fast following primary diaphragm rupture that the piston displacement compensates for driver gas loss to the driven tube. This can result in approximately constant driver pressures for a relatively long duration of time. An analysis of X2's free-piston driver indicated that for X2's relatively short (4.5 m) compression tube, tuned operation requires a very lightweight piston (approximately 10 kg). The tuned piston must be light so that it can be first accelerated to a high speed (>200 m/s), and then brought to rest, over the short compression tube length. A new 10.5 kg lightweight piston for X2 was developed, and three new tuned driver conditions were developed. The theoretical performance envelope of X2 with the new driver was then investigated, and a set of new scramjet flow conditions was proposed based on analytical relations which were later refined using the 1-D CFD code L1d2. The final task in this study was to assess the new flow conditions both experimentally in X2, and numerically using a hybrid 1-D L1d2/2-D axisymmetric Eilmer3 CFD model. Four flow conditions were considered: Mach 10, 12.5, and 15 conditions in X2 without a nozzle, and a Mach 10 condition with a nozzle. The experimental and numerical results indicated that the predicted primary wave processes were achieved. The detailed CFD analysis further predicted that the target test flow Mach number, velocity, temperature, and static pressure, were all approximately achieved at each condition. It is estimated that the maximum test flow total pressures were 3.75, 8.79, and 10.4 GPa, at Mach 10, 12.5, and 15 respectively. At these relatively low enthalpies (4.05, 6.68, and 10.4 MJ/kg respectively), these are the highest total pressure scramjet flows that have been reported in the literature to date. Several challenges remain to be addressed following this experimental campaign. Satisfactory experimental Pitot pressure measurements could not be achieved in these harsh, short duration test flows, and therefore CFD Pitot calculations could not be experimentally validated. Partial impact pressure measurements with 15 deg half angle cone probes, specially developed for this experimental campaign, did demonstrate reasonable correlation with an equivalent pressure calculation from the CFD simulation results. Hence, there are reasons to be confident that better measurement techniques will demonstrate that good agreement exists with the experiment. This is based on a) matched wave processes, b) matched and steady tube wall static pressure measurements, c) correlation with cone probe pressure measurements, and d) the high fidelity of the CFD simulations. Two other obvious limiting features of these test flows are the short test times and small core flow diameters (40-80 mm). X2 is a medium sized facility, and test time and core flow size are directly dependent on tube length and diameter. The purpose of this investigation was to demonstrate proof of concept, and this has been achieved. UQ's X3 facility is much larger than X2, and when these conditions are scaled upwards it is expected that test flow duration and core flow diameter will correspondingly increase to meet the requirements for actual scramjet testing. In summary, this study has shown, for the first time, that an expansion tube can be configured to achieve the high Mach number, GPa total pressure, flow conditions associated with scramjet access to space. The CFD predicts some unsteadiness in these test flows; in the worst case, future testing may simply need to adapt to these imperfect test flows, since no ground testing technique, other than the expansion tube, is currently conceived which can produce flows even close to these total pressures. One of ground testing's most important functions is validation of CFD models, and these test flows can provide experimental data which permit validation of CFD models very close to the true flight conditions.

Noninvasive studies of central aortic pressure.

Abstract: Our purpose is to review noninvasive methods for measuring central arterial pressure. Indices of central arterial pressure measured from central aortic and peripheral arterial waveforms have shown value in predicting cardiovascular events and death, as well as in guiding therapeutic management. This article reviews noninvasive techniques of measuring central arterial pressure that have been validated against intra-arterial pressure. This paper explains methods to derive central (aortic and carotid) pressure from radial and brachial sites. It focuses on specific issues of brachial calibration applied to carotid pressure waveforms, which were regarded as a surrogate of aortic pressures used in three major studies (Framingham, Asklepios, and Australian National Blood Pressure 2 studies). We explain why radial-based methods are superior to carotid-based methods for estimating central pressure. Physiological principles of pressure measurement need be satisfied to ensure accurate recording.

Motion-deblurred, fast-response pressure-sensitive paint on a rotor in forward flight

Abstract: A pressure-sensitive paint (PSP) system capable of measuring the global, unsteady pressure distribution on a rotating surface without resorting to phase averaging is applied to a two-bladed model propeller in edgewise freestream flow. A gated lifetime-based technique captures the paint luminescence after a single pulse of high-energy laser excitation, yielding a signal-to-noise ratio sufficient to avoid image averaging. The selection of a porous polymer/ceramic matrix base with platinum tetra(pentafluorophenyl) porphyrin (PtTFPP) as the luminophore afforded high frequency response and pressure sensitivity, but the long lifetime of PtTFPP caused blurring in the long-exposure image of the rotating blade. An approach to deblurring based on the lifetime of the paint and surface motion is described and validated by results obtained from a disc of 17.8 cm diameter spinning at 70 Hz. An infrared camera recorded wind-on and -off temperature maps to provide a temperature correction for the PSP. The single-shot PSP technique with motion deblurring and temperature correction is then applied to a vertically mounted model propeller with a 25.4 cm diameter and 10.2 cm pitch. Surface pressure maps for the advancing and retreating blades are presented for a spin rate of 70 Hz and advance ratio of 0.3. The higher suction peak and other features on the advancing blade due to its larger effective velocity are detected by the paint system, while the retreating blade shows a qualitatively different distribution.

A comparative evaluation of three hydrophones and a numerical model in high intensity focused ultrasound fields.

Abstract: The pressure fields of two different high intensity focused ultrasound (HIFU) transducers operated in burst mode were measured at acoustical power levels of 25 and 50 W (continuous wave equivalent) with three different hydrophones: A fiber-optic displacement sensor, a commercial HIFU needle hydrophone, and a prototype of a membrane hydrophone with a protective coating against cavitation effects. Additionally, the fields were modeled using a freely available simulations software package. The measured waveforms, the peak pressure profiles, as well as the spatial-peak temporal-average intensities from the different devices and from the modeling are compared and possible reasons for differences are discussed. The results clearly show that reliable pressure measurements in HIFU fields remain a difficult task concerning both the reliability of the measured values and the robustness of the sensors used: Only the fiber-optic hydrophone survived all four exposure regimes and the measured spatial-peak temporal-aver...

Ultra-miniature fiber-optic pressure sensor system and method of fabrication

Abstract: Ultra-miniature surface-mountable Fabry-Perot pressure sensor is constructed on an optical fiber which utilizes a 45° angled fiber tip covered with a reflective layer which steers the optical axis of the fiber by 90°. The Fabry-Perot cavity is formed on the sidewall of the fiber and a polymer-metal composite diaphragm is formed on the top of the Fabry-Perot cavity to operate as a pressure transducer. The sensor exhibits a sufficient linearity over the broad pressure range with a high sensitivity. The sensitivity of the sensor may be tuned by controlling the thickness of the diaphragm. The sensor may be used in a wide range of applications, including reliable in vivo low invasive pressure measurements of biological fluids, single sensor systems, as well as integral spatial-division-multiplexing sensor networks. Methods of batch production of uniform device-to-device Fabry-Perot pressure sensors of co-axial and cross-axial configurations are presented.

Side-Hole Dual-Core Photonic Crystal Fiber for Hydrostatic Pressure Sensing

Abstract: We propose a novel side-hole dual-core photonic crystal fiber (SHDC-PCF) which is used as the sensing element of the hydrostatic pressure sensor. There are two solid fiber cores separated by one small air hole in the triangular lattice photonic crystal structure region. Two large air holes are employed in the cross-section outside of the photonic crystal structure region, which essentially provides a built-in transducing mechanism to enhance the pressure-induced index change for the SHDC-PCF. The mode coupling between two fiber cores of the SHDC-PCF under different hydrostatic pressure is numerically investigated. The SHDC-PCF based pressure sensor is simply formed by using a segment of SHDC-PCF spliced to two single mode fibers. Our simulations show that there is a linear relationship between the hydrostatic pressure applied on the SHDC-PCF and the peak wavelength shift of the sensor output spectrum. A hydrostatic pressure sensor based on a 10-cm SHDC-PCF has shown a sensing range from 0 to 500 MPa and a sensitivity of 32 pm/MPa. The performances of hydrostatic pressure sensors based on SHDC-PCFs with different structure parameters are presented.

Apparatus, system and methods for measuring a blood pressure gradient

Abstract: An apparatus (100), control system (150) and methods are provided for directly measuring a pressure gradient, i.e. by real-time pressure measurements, with particular application for in situ measurement of transvalvular blood pressure gradients for the aortic valve and other heart valves, using minimally-invasive techniques. The apparatus takes the form of a multi-sensor assembly, e.g. enclosed within a micro-catheter or a steerable guidewire, and comprises a plurality of optical pressure sensors (10) is arranged along a length of the distal end portion (101), for measuring pressure simultaneously at each sensor location. For example, four MOMS optical pressure sensors (10), and optionally, a flow sensor (20), are incorporated into a distal end portion (101) having a diameter of 0.89 mm or less, and preferably 0.46 mm or less. Beneficially, all sensors are optically coupled, via respective optical fibers (11), to an optical coupler (112) at the proximal end of the multi-sensor apparatus, without requiring electrical connections.

Static and cyclic performance evaluation of sensors for human interface pressure measurement

Abstract: Researchers and clinicians often desire to monitor pressure distributions on soft tissues at interfaces to mechanical devices such as prosthetics, orthotics or shoes. The most common type of sensor used for this type of applications is a Force Sensitive Resistor (FSR) as these are convenient to use and inexpensive. Several other types of sensors exist that may have superior sensing performance but are less ubiquitous or more expensive, such as optical or capacitive sensors. We tested five sensors (two FSRs, one optical, one capacitive and one fluid pressure) in a static drift and cyclic loading configuration. The results show that relative to the important performance characteristics for soft tissue pressure monitoring (i.e. hysteresis, drift), many of the sensors tested have significant limitations. The FSRs exhibited hysteresis, drift and loss of sensitivity under cyclic loading. The capacitive sensor had substantial drift. The optical sensor had some hysteresis and temperature-related drift. The fluid pressure sensor performed well in these tests but is not as flat as the other sensors and is not commercially available. Researchers and clinicians should carefully consider the convenience and performance trade-offs when choosing a sensor for soft-tissue pressure monitoring.

Polyimide/SU-8 catheter-tip MEMS gauge pressure sensor

Abstract: This paper describes the development of a polyimide/SU-8 catheter-tip MEMS gauge pressure sensor. Finite element analysis was used to investigate critical parameters, impacting on the device design and sensing characteristics. The sensing element of the device was fabricated by polyimide-based micromachining on a flexible membrane, using embedded thin-film metallic wires as piezoresistive elements. A chamber containing this flexible membrane was sealed using an adapted SU-8 bonding technique. The device was evaluated experimentally and its overall performance compared with a commercial silicon-based pressure sensor. Furthermore, the device use was demonstrated by measuring blood pressure and heart rate in vivo.

Tuned Pressure Sensitivity of Dual Resonant Long-Period Gratings Written in Boron Co-Doped Optical Fiber

Abstract: This paper presents a pressure sensor based on a long-period grating (LPG) written in boron co-doped photosensitive fiber and operating at the phase-matching turning point. It is shown that the pressure sensitivity can be tuned by varying the UV exposure time during the LPG fabrication process as well as by varying ambient temperature during pressure measurements. The achieved pressure sensitivity in certain pressure range can reach over 1 nm·bar- 1, and is at least four times higher than for previously presented gratings working away from the double-resonance regime. In terms of an intensity-based measurement, the sensitivity at the turning point can reach 0.212 dB ·bar - 1.

Novel Time-Resolved Pressure Measurements on an Airfoil at a Low Reynolds Number

Abstract: 2This work focuses on time-resolved surface pressure measurements on an airfoil operating in low Reynolds number flows. The experiments were performed on a NACA 0018 airfoil at a chord Reynolds number of 100,000. The results are presented for two angles of attack, eight and twelve degrees, representative of two flow regimes common to airfoil operation at low Reynolds numbers, separation bubble formation and separation without subsequent reattachment. An array of twenty-five microphones was embedded into the airfoil model to facilitate multi-point, time-resolved surface pressure measurements. A comparative analysis of mean pressure, velocity, and time-resolved pressure measurements is presented to determine what flow characteristics can be estimated using embedded pressure sensors. The results show that surface pressure fluctuations increase markedly past the separation location, reflecting the increase in the magnitude of velocity fluctuations in the separated shear layer undergoing laminar-to-turbulent transition. In the separation bubble, surface pressure fluctuations peak just upstream of reattachment, suggesting that time- resolved surface pressure measurements can be used to identify the presence and estimate the length of the separation region. The analysis of simultaneous velocity and pressure measurements shows that the characteristics of flow disturbances growing in the separated shear layer can be estimated from microphone measurements. In particular, the dominant frequency, convective speed, and growth rate of disturbances can be estimated without performing the extensive tests typically required when conventional velocity measurement techniques are used. However, when separation occurs without reattachment, the relatively large distance between the transitioning separated shear layer and the airfoil surface results in lower magnitude surface pressure fluctuations, which substantially increases the uncertainty of estimating flow characteristics based on microphone measurements for this flow regime.

Free-Surface Profiles, Velocity and Pressure Distributions on a Broad-Crested Weir: A Physical Study

Abstract: Basic experiments were conducted on a large-size broad-crested weir with a rounded corner. Detailed free-surface, velocity, and pressure measurements were performed for a range of flow conditions. The results showed the rapid flow distribution at the upstream end of the weir and next to the weir brink at large flow rates. The flow properties above the crest were analyzed taking into account the nonuniform velocity and nonhydrostatic pressure distributions. Introducing some velocity and pressure correction coefficients, it is shown that critical flow conditions were achieved above the weir crest for 0.1

A Flexible Underwater Pressure Sensor Array Using a Conductive Elastomer Strain Gauge

Abstract: This paper presents a flexible pressure sensor array which is demonstrated to transduce underwater pressure variations produced by moving objects and surface waves. The sensors exhibit a 0.0014 fractional resistance change per 100 Pa, achieving a high 1.5-Pa pressure resolution. The measurement has a repeatability of 22% of the peak amplitude of the pressure waveform, due to creep. Additionally, sensor operation while bent to a 0.5-m radius of curvature is demonstrated. Each sensor consists of a strain-concentrating polydimethylsiloxane (PDMS) diaphragm and a resistive strain gauge made of a conductive carbon-black-PDMS composite. A 1-D array of four sensors with a 15-mm center-to-center spacing is fabricated, and the dynamic response of the sensors is characterized and modeled.