Full Scale Pressure Range Research Articles

Passive Wireless Pressure Gradient Measurement System for Fluid Flow Analysis

Using distributed MEMS pressure sensors to measure small flow rates in high resistance fluidic channels is fraught with challenges far beyond the performance of the pressure sensing element. In a typical core-flood experiment, which may last several months, flow-induced pressure gradients are generated in porous rock core samples wrapped in a polymer sheath. Measuring these pressure gradients along the flow path requires high resolution pressure measurement while contending with difficult test conditions such as large bias pressures (up to 20 bar) and temperatures (up to 125 °C), as well as the presence of corrosive fluids. This work is directed at a system for using passive wireless inductive-capacitive (LC) pressure sensors that are distributed along the flow path to measure the pressure gradient. The sensors are wirelessly interrogated with readout electronics placed exterior to the polymer sheath for continuous monitoring of experiments. Using microfabricated pressure sensors that are smaller than ø15 × 3.0 mm3, an LC sensor design model for minimizing pressure resolution, accounting for sensor packaging and environmental artifacts is investigated and experimentally validated. A test setup, built to provide fluid-flow pressure differentials to LC sensors with conditions that mimic placement of the sensors within the wall of the sheath, is used to test the system. Experimental results show the microsystem operating over full-scale pressure range of 20,700 mbar and temperatures up to 125 °C, while achieving pressure resolution of <1 mbar, and resolving gradients of 10-30 mL/min, which are typical in core-flood experiments.

Fabry-Perot Pressure Sensors Based on Polycrystalline Diamond Membranes.

Pressure sensors based on diamond membranes were designed and tested for gas pressure measurement up to 6.8 MPa. The diamond film (2” diameter, 6 μm thickness)—grown by microwave plasma chemical vapor deposition on a silicon substrate—was a starting material to produce an array of membranes with different diameters in the 130–400 μm range, in order to optimize the sensor performance. Each 5 mm × 5 mm sensing element was obtained by subsequent silicon slicing. The fixed film thickness, full-scale pressure range, and sensor sensitivity were established by a proper design of the diameter of diamond membrane which represents the sensing element for differential pressure measurement. The pressure-induced deflection of the membrane was optically measured using a Fabry-Pérot interferometer formed by a single mode optical fiber front surface and the deflecting diamond film surface. The optical response of the system was numerically simulated using geometry and the elastic properties of the diamond diaphragm, and was compared with the experiments. Depending on the diamond membrane’s diameter, the fabricated sensors displayed a good modulation depth of response over different full-scale ranges, from 3 to 300 bar. In view of the excellent mechanical, thermal, and chemical properties of diamond, such pressure sensors could be useful for performance in a harsh environment.

Characterization of CMOS-MEMS Resonant Pressure Sensors

Comprehensive characterization results of CMOS-microelectromechanical systems resonant pressure sensor are presented. We have extensively evaluated the key performance parameters of our device in terms of quality factor ( $Q$ ) variations under variable conditions of temperature and pressure, characterized by Knudsen number ( $K_{n}$ ). The fundamental frequency of the reported device is 104.3 kHz. Over the full-scale pressure range of 0.1 to 100 kPa and a temperature range of −10 °C to 85 °C, $Q$ from 450 to 62.6 have been obtained. Besides, static variations of the device capacitance have been measured and analyzed with temperature to evaluate the spring softening and the pull-in effects. A nonlinearity analysis has been performed to assess the device stability. Furthermore, a statistical mismatch analysis has been carried out to determine the deviation of resonance with etching time and ascertain maximum device yield. With our in-house back-end of line metal-layer release, this sensor can be monolithically embedded in the same substrate as standard CMOS integrated circuits, resulting in a significant cost and area reduction.

A Micromachined Pressure Sensor with Integrated Resonator Operating at Atmospheric Pressure

A novel resonant pressure sensor with an improved micromechanical double-ended tuning fork resonator packaged in dry air at atmospheric pressure is presented. The resonator is electrostatically driven and capacitively detected, and the sensor is designed to realize a low cost resonant pressure sensor with medium accuracy. Various damping mechanisms in a resonator that is vibrating at atmospheric pressure are analyzed in detail, and a formula is developed to predict the overall quality factor. A trade-off has been reached between the quality factor, stress sensitivity and drive capability of the resonator. Furthermore, differential sense elements and the method of electromechanical amplitude modulation are used for capacitive detection to obtain a large signal-to-noise ratio. The prototype sensor chip is successfully fabricated using a micromachining process based on a commercially available silicon-on-insulator wafer and is hermetically encapsulated in a custom 16-pin Kovar package. Preliminary measurements show that the fundamental frequency of the resonant pressure sensor is approximately 34.55 kHz with a pressure sensitivity of 20.77 Hz/kPa. Over the full scale pressure range of 100–400 kPa and the whole temperature range of −20–60 °C, high quality factors from 1,146 to 1,772 are obtained. The characterization of the prototype sensor reveals the feasibility of a resonant pressure sensor packaged at atmospheric pressure.

An optimized high-sensitivity capacitive MEMS for blood pressure measurement

A high-sensitivity capacitive pressure transducer with active processing circuit on the chip has been demonstrated and evaluated. The transducer configuration has been optimized by computer-aided simulation and design to achieve highest sensitivity for a given maximum dimension. The measured sensitivity of the devices is in the range of 50-150 MV/V mmHg, which is approximately one order of magnitude higher than the sensitivity of the piezoresistive pressure transducer of comparable size. Theoretical analysis also shows that sensitivity of the order of 1000 pV/V mmHg is also possible using the capacitive approach if the dimension of the device can be enlarged and the full-scale pressure range is lowered.

Performance Evaluation of Honeywell Silicon Piezoresistive Pressure Transducers for Oceanographic and Limnological Measurements*

Abstract Simultaneous calibrations of three temperature-compensated piezoresistive ruggedized precision “absolute” pressure transducers (Honeywell model PPTR0040AP5VB-BD), which have been designed specially for long-term coastal oceanographic and limnological measurements, have been carried out at four differing temperatures (10°, 20°, 30°, and 40°C) to evaluate their suitability for such applications. The full-scale pressure range of these shallow water absolute pressure sensors is ≈ 2800 hPa (equivalent to water depth of ≈ 18 m). Measurement results have been used to examine the transducers’ performance indicators, such as zero-point offset, accuracy, linearity, hysteresis, temperature sensitivity, and slope. Differing piezoresistive ruggedized precision absolute pressure transducers (PPTRs) exhibited differing zero-point offset values, ranging from 2 to −79 hPa. Temperature sensitivity of zero-point offset was ≈0.3 hPa over the temperature range 10°–40°C. The mean hysteresis over the full-scale absolute pressure range (≈2800 hPa) varied from approximately 2 to 8 hPa over the temperature range 10°–40°C. The slope of the least squares–fitted linear graph (taking the mean of ascending and descending pressures) was close to the ideal value of unity (deviation from 1 over the temperature range 10°–40°C was in the range of −0.001 to +0.005). Linearity was excellent, its mean over the entire pressure range being between ≈ −0.006% and 0.008% of full-scale (FS) over the above temperature range. The worst performance was exhibited at input pressures below ≈1500 hPa. Zero-point offset has played a significant role in deteriorating the accuracy of the PPTR, the mean accuracy (within ≈0.1% and −5%) having been exhibited by those transducers having offsets of 2 and −79 hPa, respectively. The mean accuracy exhibited temperature sensitivity of ≈1% in the range 10°–20°C and negligible sensitivity beyond 20°C. Use of a calibration equation significantly improved the mean static accuracy obtainable from the PPTR, to between −0.04% and 0.01% of FS. Evaluation results have indicated that a suitably calibrated temperature-compensated Honeywell PPTR provides an alternate cost-effective means for pressure measurements for coastal oceanographic and limnological studies.

Modeling, design and fabrication of a triple-layered capacitive pressure sensor

A novel triple-layered capacitive pressure sensor (TCPS) is presented. It consists of a polysilicon/nitride/polysilicon composite-membrane sandwich structure, and was fabricated by surface micromachining technology. The operation principle of TCPS is based on the combination of variations of the capacitor area and distance of electrodes with the applied pressure. A load-deflection model for the triple-layered composite-membrane is derived by the improved energy method for the analysis and design optimization of TCPS, which is in good agreement with finite element analysis performed by ANSYS™. Test results show the sensitivity of the device is about 40 fF/Torr (1 Torr = 133.32 Pa = 1 mm Hg) and the nonlinearity is about 0.32%. The pressure sensor described here has a full scale pressure range of 110 kPa. A sensor structure array with 10×10 cells was fabricated and the side length of each cell is 100 μm.

Force balanced micromachined pressure sensors

This paper discusses the fabrication and testing of two low-voltage force-balanced pressure sensors. In these devices the force acting on a diaphragm under external pressure and its corresponding deflection are counterbalanced with the force and deflection generated in a parallel plate electrostatic actuator mechanically coupled to the diaphragm. The low balancing voltage is attained using a force multiplication scheme. The first device is implemented using an open gap actuator constructed on top of a vacuum sealed sense diaphragm. The open gap design is exposed to the measurement environment hence susceptible to contamination. The second device eliminates this problem by enclosing the actuator in an hermetically-sealed cavity. Both devices have a full scale pressure range of 1 atmosphere (1.013 bar). The open actuator device has a nominal capacitance of 0.34 pF and a full scale range of 70 fF. The sealed actuator device a nominal capacitance of 2.12 pF and a full scale range of 100 fF. The pressure is balanced by voltages in the range of 12-25 V demonstrating the feasibility of force balanced pressure sensor compatible with low-voltage electronics.

High temperature pressure sensor using double SOIstructure with two Al2O3 films

Abstract A high temperature pressure sensor using double silicon-on-insulator (SOI) structures stacked by double heteroepitaxial growth, Si//δ-Al2O3//Si//δ-Al2O3//Si-substrate structures, has been developed. This sensor consists of a thin rectangular diaphragm and a single-elementfour-terminal piezoresistor produced by micromachininh technology with a standard IC process. The diagphragm size is 360X1080 μm and 5 μm in thickness. The diagphragm thickness was precisely controlled by the Al2O3 films of the first SOI layer. A second Al2O3 film on the first SOI layer was used as a dielectrically isolated single-element four-terminal piezoresistor that was placed at the center of the diagphragm. The pressure sensitivity was 6.5 mV/V kgf/cm2 full scale pressure range. The thermal sensitivity shift was less than 2.7% in the temperature range from 20 to 300 °C. These values are acceptable for many applications, and indicate that the sensor can be operated stably up to temperatures as high as 300 °C.

Effect of Line Pressure on the Zero Stability of a Differential Quartz Bourdon Gauge for Various Gases

In this paper results obtained on the effect of line pressure on the zero stability of a differential quartz Bourdon gauge are presented. The gauge studied has a helical fused-quartz Bourdon tube as the pressure-sensing element with an electromagnetic nulling device. The full scale pressure range of the gauge is 110 kPa. Zero shift values at different line pressures for various gases under different conditions have been measured. It is observed that when the line pressure is increased from an initial pressure of zero, the zero shift is negative: conversely, it is positive for decreasing line pressures. The magnitude of the zero shift for all the gases under different experimental conditions is found to be directly proportional to the change in the line pressure. The results obtained for helium and hydrogen show a completely different behaviour of the quartz Bourdon gauge from those observed for nitrogen, argon and oxygen. An analysis of the experimental results reveals that this gauge behaves in different ways with different gases. The possible causes of this behaviour are briefly discussed.

Novel Pressure Sensors Using Epitaxially Stacked Si/Al2O3/Si Structures for High-Precision Thickness Control of Silicon Diaphragms

Using epitaxial Al2O3 films as an etch-stop layer, Si-on-insulator (SOI) pressure sensors have been fabricated on a heteroepitaxially grown Si(100)/Al2O3(100)/Si(100) substrate. The epitaxially stacked SOI structure was formed by successive chemical vapor deposition of Al2O3 and Si on a 2-inch Si(100) substrate. The implemented sensors have a high sensitivity of 0.28 mV/V·kPa for a 93.3 kPa full-scale pressure range, with a nonlinearity and hysteresis of less than +0.2%FS and +0.09%FS, respectively. The pressure sensitivity variation can be controlled to within a standard deviation of ±2.0%. The shifts in sensitivity and offset voltage of the fabricated pressure sensors are less than -0.36% and +0.22%, respectively, in the temperature ranges of from -20°C to +100°C. The epitaxially stacked SOI structure is a highly promising material for the development of high-resolution pressure sensors with no-variation pressure sensitivity.

High-performance pressure sensors using double silicon-on-insulator structures

A high performance pressure sensor using double silicon-on-insulator (SOI) structures, a (100) Si// (100) Al2O3// (100) Si/ SiO2/ (100) Si substrate, has been developed that is capable of very accurate operation at temperatures as high as 350 °C. A first SOI layer made by bonding two oxidized Si wafers together was employed as an etch-stop layer during KOH selective anisotropic etching and for controlling the thickness of the thin diaphragm. A double-heteroepitaxially grown second SOI layer on the first SOI layer was used as a dielectrically isolated single-element four terminal strain gauge that was placed at the center of a rectangular diaphragm. The dimensions of the diaphragm and its thickness were 360 μm ×1140 μm and 5 μm, respectively. This sensor has high sensitivity (0.04 mV/V⋅mmHg) for 700 mmHg full scale pressure range, with a nonlinearity less than +0.15% full scale. In the temperature range from −20 °C to +350 °C, the shift in sensitivity and offset voltage are less than −0.2% and +0.1%, respectively. Moreover, the implemented sensor is very useful for the miniaturization and integration of the sensor.

A high-sensitivity integrated-circuit capacitive pressure transducer

A high-sensitivity capacitive pressure transducer with active processing circuit on the chip has been demonstrated and evaluated. The transducer configuration has been optimized by computer-aided design to achieve highest sensitivity for a given maximum dimension. The measured sensitivity of the devices is in the range of 50-150 µV/ V . mmHg, which is approximately one order of magnitude higher than the sensitivity of the piezoresistive pressure transducer of comparable size. Theoretical analysis also shows that a sensitivity on the order of 1000 µV/V . mmHg is also possible using the capacitive approach if the dimension of the device can be enlarged and the full scale pressure range is lowered. Other characteristics of the devices have been investigated and are presented.

Transient Pressure Recording with a High-Speed Interferometer Camera

This paper describes a transient-pressure recording camera with a full scale pressure range (by changing diaphragms) of 3 psi to 50,000 psi, and an accuracy of one-half per cent of full scale for any range. Its stability and hysteresis are such that a single static calibration suffices for years of dynamic measurements, and its frequency response varies from 10,000 cycle/sec to 100,000 cycle/sec, depending on the pressure range of the diaphragm used. The paper includes records of interesting applications.