A Sapphire Based Fiber Optic Dynamic Pressure Sensor for Harsh Environments: Fabrication and Characterization

Dynamic calibration is one of the important ways to obtain the dynamic performance parameters of pressure sensors, and shock tube calibration is a common method for dynamic calibration of pressure sensors. To study the dynamic calibration method of the shock tube of the blast pressure pencil probes, such as free-field pressure sensors and dynamic pressure sensors, a convenient and adjustable PVC-U (unplasticized polyvinyl chloride) shock tube is developed. Taking the dynamic pressure sensor as the research object, the feasibility of dynamic calibration of shock tube based on CFD (Computational Fluid Dynamics) techniques is discussed. Finally, the dynamic calibration experiment based on shock tube is carried out, and the time-domain and frequency-domain signals are analyzed. The results are in good agreement with the theoretical analysis. The results show that the shock tube can effectively excite the natural frequency of the dynamic pressure sensor, and the developed shock tube can indeed achieve the dynamic calibration and dynamic experiments of pencil probes.

An all-fiber dynamic sound pressure sensor based on Mach-Zehnder interferometer(MZI) encapsulated with the Poly Ethylene Terephthalate (PET) diaphragm is composed. The relationships between the material, size, thickness of the diaphragm and sensitivity are analyzed theoretically. The simulation results show that the shape variable of the diaphragm increases as the diaphragm radius increases and the thickness decrease under the condition of the small deflection theorem, resulting in a good linear relationship between sound pressure and the shape of the diaphragm. The sensor can be widely used in dynamic sound pressure detection, sound signal collection, and recovery.

This paper develops a new method to estimate IRI using a dynamic tire pressure sensor (DTPS) inside the tire with an axle accelerometer. This method is based on a physical 2-D dynamic tire model. This paper verifies that speeds above 40 km/h (25 mph) are suitable for both highways and urban roads. Feasibility and repeatability tests were hereby conducted and reported on an airport runway through a certification test that was administered by the Massachusetts Department of Transportation (MassDOT), highways and urban roads. During testing, the accuracy of the new method was equivalent to IRI values measured using the laser profilometers and accelerometers. The newly developed method has the potential to be integrated into vehicle computer systems to form a network wide global health monitoring system of roadways to make the right repair, at the right time, in the right place.

Optical fibre pressure sensors have potential performance advantages over electrical sensors in measuring rapid transients such as shock waves from explosive blasts. We report the development of micromachined optical fibre Fabry–Pérot pressure sensors using a silicon dioxide or nitride diaphragm and detail the fabrication stages of the sensor body and diaphragm. The planar technology used is based on silicon deep etching and direct fusion bonding of silicon wafers. Test results for both types of diaphragm are presented. Sensors with rise times better than 3 µs, range 0.1 to 1 MPa and resolution ∼500 Pa have been demonstrated in explosives trials. Despite the difference in the sign of stress for the two diaphragm types, both demonstrated excellent high-speed response to explosively generated air shocks.

As the performance of GaN- and SiC-based power devices becomes limited by fundamental material properties, semiconductors with larger bandgaps are appealing due to their superior material properties. Most notable is that the critical electrical field scales as the bandgap to the 2.0-2.5 power. Thus, diodes employing wide bandgap semiconductors are expected to operate at higher breakdown voltages with thinner and more heavily-doped drift regions, leading to lower resistive losses. AlGaN alloys with their much larger bandgap compared to SiC and GaN are thus appealing for high voltage pn diodes and transistors. Additionally, the formation of AlGaN-based heterojunctions and the utilization of polarization fields offer design options not possible for devices based on materials such as SiC and diamond. Here we report on the growth and performance of pn diodes fabricated from Al0.30Ga0.70N (Eg=4.1eV) and Al0.74Ga0.26N (Eg=5.3eV) alloys, illustrating the potential for AlGaN alloys as a viable material for next-generation power diodes. Quasi-vertical pn diodes consisting of Al0.30Ga0.70N epilayers were grown by metalorganic vapor phase epitaxy on 1.3 mm thick sapphire substrates. The added stiffness of such thick sapphire substrates (3x thicker than typical sapphire) reduces wafer bow and eliminates cracking in epitaxial structures up to 19 μm thick. Thick epitaxial structures are needed to achieve the > 4 microns thick drift layers necessary for multi-kilovolt breakdown voltages. A series of pn diode structures were grown where the thickness of the lightly doped drift layer (No = 2-5x1016 cm-3) was varied from 4.3 to 11 μm. All structures were completed with a 0.35 μm thick Mg-doped Al0.30Ga0.70N p-layer followed by a compositional grade to a p-GaN contact layer. Diodes employed a junction edge termination structure around the p-contact to reduce the peak electric field at the contact metal to avoid premature breakdown. Breakdown voltages from 1600 to 3000V were achieved in reverse bias and a forward turn-on voltage of 6 to 8 volts was recorded. To our knowledge, this is the first vertical AlGaN-based pn diode exhibiting a breakdown voltage in excess of 1 kilovolt. The differential specific on-resistance was higher than expected based on consideration of the drift region only (typically 16-20 mΩ-cm2), which is tentatively attributed to the resistance due to lateral current spreading in these front-contacted, quasi-vertical diodes. An effective critical electric field of 5.9 MV/cm was determined from the reverse current-voltage characteristics based on a punch-through, as dictated by the doping and thickness of the drift region. We have also investigated quasi-vertical pn diodes consisting of Al0.74Ga0.26N epilayers to exploit the expected higher critical electric field in higher aluminum mole fraction alloys. These diodes consisted of 4.5 μm thick AlN epilayers grown on sapphire followed by a heavily doped n-type contact layer. Next a lightly doped (No = 2-4x1016 cm-3) 5 or 8 μm thick drift layer was grown. The combination of a thick AlN buffer and Al0.74Ga0.26N layers resulted in x-ray diffraction linewidths of 164-197 (237–284) arc seconds for the (0002) and (10-12) reflections for the drift layer, respectively. By optimizing the growth conditions used for the drift layer, the density of electron compensating defects can be reduced to ~ 1x1016 cm-3 — a level reported for GaN pn diodes. Unlike GaN diodes where drift layer doping at mid to low 1015 cm-3 is necessary for breakdown voltages of several kilovolts, the free electron concentration in these Al0.74Ga0.26N pn diodes is significantly higher than the level of compensation, making doping much easier to control and illustrating the benefit of higher critical electric field. The drift layer was followed by p-type AlGaN and finally a compositional grade to a p-GaN contact layer. It is the p-AlGaN layer that is a significant challenge in Al-rich pn diodes. Unlike pn diodes based on Al0.30Ga0.70N epilayers, simple homojunction pn diodes are not practical in Al-rich AlGaN alloys due to the low hole concentration owing to the very deep (Ea > 400 meV) acceptor level. Consequently, other approaches must be considered for hole transport to the pn junction. We will report on the current-voltage characteristics of pn heterojunction diodes where a Mg-doped p-type Al0.30Ga0.70N layer is grown on the n-type Al0.74Ga0.26N drift layer. Additionally, the current-voltage characteristics of pn diodes where holes are generated in the p-region by field ionization of Mg acceptors will also be presented. Finally, practical pn diodes require specific on-resistance lower than what is inherent for front-contacted quasi-vertical device architectures grown on insulating substrates. We will report an approach that has realized vertically conducting AlGaN pn diodes employing AlGaN overgrowth on conducting GaN substrates.

In this paper, Poly-crystalline silicon carbide (poly-sic) Micro-electromechanical systems (MEMS) capacitive pressure sensor operating in harsh environment in touch mode is proposed, The principle of the paper is to design, obtain analytical solution and compare the results with the simulation for a circular diaphragm deflection before and after touch point. The sensor demonstrated a high temperature sensing capability up to 400°C, the device achieves a linear characteristic response and consists of a circular clamped-edges poly-sic diaphragm suspended over sealed cavity on a silicon carbide substrate. The sensor is operating in touch mode capacitive pressure sensor, The advantages of a touch mode are the robust structure that make the sensor to withstand harsh environment, near linear output, and large over-range protection, operating in wide range of pressure, higher sensitivity than the near linear operation in normal mode, The material is considered to be used for harsh environment is SiC (Silicon Carbide), Because of SiC owing excellent electrical stability, mechanical robustness, and chemical inertness properties and the application of pressure sensors in harsh environments are, such as automotive industries, aerospace, oil/logging equipments, nuclear station, and power station. We are simulating MEMS capacitive pressure sensor to optimize the design, improve the performance and reduce the time of fabricating process of the device. The proposed touch mode MEMS capacitive pressure sensor demonstrated diaphragm ranging from 150 μm to 360 μm in diameter, with the gap depth from 0.5 μm to 7.5 μm and the sensor exhibit a linear response with pressure from 0.05 Mpa to 10 Mpa.

Experimental study on effect of density ratio and phase transition during sloshing impact in rectangular tank

Infrasound measurement devices like low frequency microphones and dynamic pressure sensors are widely used in many branches of trade like aerospace industries (airflow mechanics) or acoustical engineering (infrasound measurements of geophysical events, emissions of wind energy plants, etc.). This paper presents a calibration system that allows the calibration of such devices in a frequency range as low as 0.1 Hz to 31.5 Hz. It is based on a special low frequency pressure chamber that uses a similar working principle as a pistonphone but is adapted to the requirements of this low frequency range. The chamber has a size that allows to place the whole device under test (DUT) inside the chamber. So no mechanical adaption between DUT and pressure chamber is required and thus the DUT can have a nearly arbitrary shape. Other than a pistonphone which is based on the assumption that the sound level can be calculated from the physical dimensions of the chamber by means of the adiabatic gas law, this calibration system requires the use of a reference standard sensor. This is due to the fact that in the low frequency range the gas compression becomes more and more an isothermal process the lower the applied frequency gets. Thus a pressure sensor is used as reference standard allowing high precision measurements (uncertainty < 0.05 dB). The paper discusses the question how the measurement uncertainty over the whole frequency can be determined although the reference pressure sensor is only calibrated by static pressure calibration. It also shows how other parameters like the homogeneity of the pressure field can be determined that contribute to the measurement uncertainty. Finally some calibration results will be presented.

Approximate constant volume combustion (aCVC) is a promising way to achieve a step change in the efficiency of gas turbines. This work investigates a recently proposed approach to implement aCVC in a gas turbine combustion system: shockless explosion combustion (SEC). The new concept overcomes several disadvantages such as sharp pressure transitions, entropy generation due to shock waves, and exergy losses due to kinetic energy which are associated with other aCVC approaches like, e.g., pulsed detonation combustion. The combustion is controlled via the the fuel/air mixture distribution which is adjusted such that the entire fuel/air volume undergoes a spatially quasi-homogeneous autoignition. Accordingly, no shock waves occur and the losses associated with a detonation wave are not present in the proposed system. Instead, a smooth pressure rise is created due to the heat release of the homogeneous combustion. An atmospheric combustion test rig is designed to investigate the autoignition behavior of relevant fuels under intermittent operation, currently up to a frequency of 2Hz. Application of OH*- and dynamic pressure sensors allows for a spatially- and time-resolved detection of ignition delay times and locations. Dimethyl ether (DME) is used as fuel since it exhibits reliable autoignition already at 920K mixture temperature and ambient pressure. First, a model-based control algorithm is used to demonstrate that the fuel valve can produce arbitrary fuel profiles in the combustion tube. Next, the control algorithm is used to achieve the desired fuel stratification, resulting in a significant reduction in spatial variance of the auto-ignition delay times. This proves that the control approach is a useful tool for increasing the homogeneity of the autoignition.

We describe a wireless wearable system that was developed to provide quantitative gait analysis outside the confines of the traditional motion laboratory. The sensor suite includes three orthogonal accelerometers, three orthogonal gyroscopes, four force sensors, two bidirectional bend sensors, two dynamic pressure sensors, as well as electric field height sensors. The "GaitShoe" was built to be worn in any shoe, without interfering with gait and was designed to collect data unobtrusively, in any environment, and over long periods. The calibrated sensor outputs were analyzed and validated with results obtained simultaneously from the Massachusetts General Hospital, Biomotion Laboratory. The GaitShoe proved highly capable of detecting heel-strike and toe-off, as well as estimating foot orientation and position, inter alia.

This work aims at studying the influence of adding splitter blades on the performance of a hydraulic centrifugal pump. The studied machine is an ENSIVAL-MORET MP 250.200.400 pump (diameter=408 mm, 5 blades, specific speed=32), whose impeller is designed with and without splitter blades. Velocity and pressure fields are computed using unsteady Reynolds-averaged Navier-Stokes (URANS) approach at different flow rates. The sliding mesh method is used to model the rotor zone motion in order to simulate the impeller-volute casing interaction. The flow morphology analysis shows that, when adding splitter blades to the impeller, the impeller periphery velocities and pressures become more homogeneous. An evaluation of the static pressure values all around the impeller is performed and their integration leads to the radial thrust. Global and local experimental validations are carried out at the rotating speed of 900 rpm, for both the original and the splitter blade impellers. The head is evaluated at various flow rates: 50%, 80%, 100%, and 120%of the flow rate at the best efficiency point (BEP). The pressure fluctuations are measured at four locations at the BEP using dynamic pressure sensors. The experimental results match the numerical predictions, so that the effect of adding splitter blades on the pump is acknowledged. Adding splitters has a positive effect on the pressure fluctuations which decrease at the canal duct.

The dynamic performance of the typical spark discharge plasma synthetic jet (SPJ) has been studied. The dynamic change of the SPJ jet velocity was measured by a dynamic pressure sensor in different loading electric parameters and structure parameters of the actuator. The experimental results showed that the jet speed waveform of SPJ was similar to sine wave. The SPJ peak velocity increased with the rise of the loading voltage amplitude, duty cycle and electrode gap, but it decreased with the increase of the loading frequency and SPJ orifice diameter. There was a best cavity volume for SPJ to achieve the maximum peak velocity.

In the present study, an actuator with the ability to generate spatially oscillating jets, known as the sweeping jet actuator (SJA), is employed to manage the corner separation in a CDA profile. Experiments were performed in a low-speed wind tunnel with an inflow Mach number of 0.23. Measurements using a five-hole probe, dynamic pressure sensors, and oil flow visualizations were carried out to get insight into the performance and physics of the flow field. SJA was integrated into the cascade endwall through 3D printing, with dimensions constrained within 15mm, and reaching a maximum operating frequency of approximately 1400Hz. Parameters such as axial injection location, jet momentum, and operating frequency were systematically investigated to determine the optimal active flow control strategy. The results show that the spatially sweeping jet significantly suppresses the migration of low-energy fluids on the endwall surface, leading to a reduction of more than 30% in the spanwise extent of corner separation and a 14.2% decrease in the integrated total pressure loss coefficient, with 0.13% of the cascade throughflow. The study of the influence of jet momentum on control effect indicates that the sweeping jet could enforce the low-energy fluids without a significant increase in mixing losses between jets and mainstream even at a large jet momentum, which is attributing to the rapid decay of the unsteady sweeping jet velocity in mainstream. The results highlight the superior characteristics of the SJA in managing the corner separation.

Rotating detonation engines have been studied due to their better theoretical propulsion performance than that of deflagration-based engines. In this experimental study, the Laval nozzle throat width was varied to study combustion features in rotating detonation engines with different air flow rates and equivalence ratios. The detonation channel had an outer diameter of 100 mm and an inner diameter of 80 mm. Air and hydrogen were injected into the combustor from 60 cylindrical orifices each of 2 mm in diameter and a circular channel with a width of 1 mm, respectively. Four different widths of the plug nozzle were used: 2, 4, 6, and 8 mm. Three dynamic pressure sensors were used to obtain the detonation pressure. A standard speed camera was used to observe the exhaust from the combustion process. The results show that rotating detonation never occurred for a throat width of 4 mm. Rotating detonation waves with high speeds above 2300 m/s were obtained for a throat width of 2 mm. The mode of combustion in the engine was highly dependent on equivalence ratio and throat width. Probabilities of occurrences of longitudinal pulsed detonation increased first and then decreased with the decreased throat width.

An experimental study was performed to investigate the combustion instability characteristics of swirl-stabilized combustors. A premixed gas composed of ethylene and air was burned under various flow and geometric conditions. Experiments were conducted by changing the inlet mean velocity, equivalence ratio, swirler vane angle, and combustor length. Two dynamic pressure sensors, a hot-wire anemometer, and a photomultiplier tube were installed to detect the pressure oscillations, velocity perturbations, and heat release fluctuations in the inlet and combustion chambers, respectively. An ICCD camera was used to capture the time-averaged flame structure. The objective was to understand the relationship between combustion instability and the Rayleigh criterion/the flame structure. When combustion instability occurred, the pressure oscillations were in-phase with the heat release oscillations. Even if the Rayleigh criterion between the pressure and heat release oscillations was satisfied, stable combustion with low pressure fluctuations was possible. This was explained by analyzing the dynamic flow and combustion data. The root-mean-square value of the heat release fluctuations was observed to predict the combustion instability region better than that of the inlet velocity fluctuations. The bifurcation of the flame structure was a necessary condition for combustion instability in this combustor. The results shed new insight into combustion instability in swirl-stabilized combustors.