Miniature Pressure Sensor Research Articles

Fiber optic-based in-cylinder pressure sensor for advanced engine control and monitoring

This paper describes the design and performance of a miniature cylinder pressure sensor packaged either as a stand-alone device or integrated with a cylinder head gasket, glow plug, fuel injector, or spark plug. Benefitting from a fiber-optic based design the sensing element can operate at ultra-high temperatures and is not affected by EMI. This low cost device utilizes the principle of light intensity changes transmitted by two optical fibers upon reflection from a metal diaphragm deflecting under the effect of pressure. When the diaphragm thickness and shape are optimized, the sensor can operate up to 5 billion pressure cycles. The device is compensated for all temperature effects encountered in combustion engines, resulting from the thermal shock, engine load changes, and under-hood temperature fluctuations. Due to the diaphragm small thermal mass the sensor is subject to the thermal shock error if no heat shield is employed. While a suitable shield can almost eliminate the thermal shock error, it can get clogged in engines fuelled by diesel or landfill gas. For such engines a dual diaphragm construction offers a robust solution against soot and other combustion deposits as well as minimum thermal shock error. In comparison to a water cooled piezoelectric quartz transducer the present sensor offers the accuracy of ±1.5% of reading at pressures above 5 bars, ±0.1 bar error at pressure below 5 bars during compression, and the thermal shock error ranging from 0.1 bar to 0.3 bar dependent if a single or dual diaphragm is used. Such accuracy is possible with both stand-alone sensors as well as those 1.7 mm in diameter used in the “pressure sensing” cylinder head gaskets, glow plugs, fuel injectors, or spark plugs. This accuracy is maintained under all combustion conditions, sensor tip continuous temperatures up to 380 oC, signal conditioner temperature range of –40 oC to 140 oC, pressures up to 350 bar, and over frequency range of 0.1 Hz to 30 kHz. Such remarkable accuracy allows advanced engine controls based on highly accurate values of the Indicated Mean Effective Pressure, Mass Fraction Burned, Maximum Pressure Gradient, and Peak Pressure. Benefitting from sensor’s high accuracy at both low and high pressures the device enables closed-loop control of fuel injection as well as in-cylinder prediction of mass air flow and engine NOx emission levels.

Miniature Fabry-Perot pressure sensor created by using UV-molding process with an optical fiber based mold

We present a miniature Fabry-Perot pressure sensor fabricated at the tip of an optical fiber with a pre-written Bragg grating by using UV-molding polymer process. The mold is constructed by integrating an optical fiber of 80 μm diameter with a zirconia ferrule. The optical fiber based mold makes it possible to use optical aligning method to monitor the coupled intensity between the mold-side and replica-side fibers, rendering a maskless alignment process with a submicrometer accuracy. A polymer-metal composite thin diaphragm is employed as the pressure transducer. The overall sensor size is around 200 μm in diameter. Experimental study shows that the sensor exhibits a good linearity over a pressure range of 1.9-7.9 psi, with a sensitivity of 0.0106 μm/psi. The fiber Bragg grating is exploited for simultaneous temperature measurements or compensation for temperature effects in pressure readings. The sensor is expected to benefit many fronts that require miniature and inexpensive sensors for reliable pressure measurement, especially biomedical applications.

Miniature Absolute Optical Pressure Sensor at a Fiber Tip for High Temperature Applications

Abstract Fiber optic pressure sensors have attracted considerable attention because of their small size, high sensitivity and immunity to electromagnetic interference. Here, a miniature absolute pressure sensor at the edge of a fiber is presented. Contradictory to earlier pressure sensors with membranes at the fiber tip (in a co-axial configuration), we present a sensor in a cross-axial configuration. It is optimized for aerodynamic pressure measurements in turbo–machinery. The sensor is fabricated by thin film deposition techniques and focused ion beam (FIB) microfabrication and uses multilayer Fabry-Perot (FP) interferometry as sensing principle. The reflected power intensity of the prototype is experimentally verified to be 0.77%/bar.

Miniature fiber pressure sensor based on fiber etching

A miniature fiber optic pressure sensor based on Fabry–Perot interference fabricated on the tip of a single mode (SM) fiber is presented. The sensor measures only 125μm in diameter. A Fabry–Perot cavity and a thin silica diaphragm are fabricated by simple techniques involving only cleaving, wet chemical etching and fusion splicing. Interference pattern of the sensor is analyzed and issues in sensor design are discussed. The overall chemical reaction of the fiber wet etching is specifically represented. Pressure testing system is carried out. By tracing a peak point in the interference spectrum, the gap length of the sensor can be demodulated. Experimental results show the sensor has a good linearity. The sensor is made entirely of fused silica, whose structure has good stability, cabinet, simple for fabrication and low cost.

Polymer-based miniature flexible capacitive pressure sensor for intraocular pressure (IOP) monitoring inside a mouse eye

This paper presents an ultra-thin and flexible polymer-based capacitive pressure sensor for intraocular pressure (IOP) monitoring in a mouse eye. Due to the size limitation of the anterior chamber in the mouse eye, a volume of approximately 700 × 700 × 150μm(3) on a small substrate is available for the MEMS capacitive pressure sensor. Moreover, the sensor would ideally be easily injectable into place. Further complicating the sensing is the need to operate the device on the curved surface of the anterior chamber with minimum damage to the eye tissue. Therefore, a thin and flexible substrate is required. We fabricate sensors by exploiting Parylene as a biocompatible structural material in a suitable form factor and 25μm thick liquid crystal polymer (LCP) as a soft and flexible host substrate. Using our approach, the flexibility and small form factor necessary for a mouse eye implant is achieved, along with the sensitivity required to monitor IOP fluctuations. This device will allow better study of glaucoma through close monitoring in mice after integration with other components.

High-temperature high-frequency turbine exit flow field measurements in a military engine with a cooled unsteady total pressure probe

The measurement of unsteady pressures within the hot components of gas turbine engines still remains a true challenge for test engineers. Several high-temperature pressure sensors have been developed, but so far, their applications are restricted to unsteady wall static pressure measurements. Because of the severe flow conditions such as turbine inlet temperatures of 1700 °C and pressures of 50 bar or more in the most advanced aero-engine designs, few (if any) experimental techniques exist to measure the time-resolved flow total pressure inside the gas path. This article describes the measurements performed at the turbine exit of a military engine with a cooled fast response total pressure probe. The probe concept is based on the use of a conventional miniature piezo-resistive pressure sensor, located in the probe tip to achieve a bandwidth of at least 40 kHz. Due to the extremely harsh conditions, the probe and sensor are heavily water cooled. The probe was designed to be continuously immersed into the hot gas stream to obtain time series of pressure with a high bandwidth and therefore statistically representative average fluctuations at the blade passing frequency (BPV). The experimental results obtained with a second-generation prototype are presented. The probe was immersed into the engine through the bypass duct between turbine exit and flame-holders of the afterburner of a Volvo RM12 engine, at exhaust temperatures above 900 °C. The probe was able to resolve the BPV (∼17 kHz) and several harmonics up to 100 kHz.

Low-cost rapid miniature optical pressure sensors for blast wave measurements

This paper presents an optical pressure sensor based on a Fabry-Perot (FP) interferometer formed by a 45° angle polished single mode fiber and an external silicon nitride diaphragm. The sensor is comprised of two V-shape grooves with different widths on a silicon chip, a silicon nitride diaphragm released on the surface of the wider V-groove, and a 45° angle polished single mode fiber. The sensor is especially suitable for blast wave measurements: its compact structure ensures a high spatial resolution; its thin diaphragm based design and the optical demodulation scheme allow a fast response to the rapid changing signals experienced during blast events. The sensor shows linearity with the correlation coefficient of 0.9999 as well as a hysteresis of less than 0.3%. The shock tube test demonstrated that the sensor has a rise time of less than 2 µs from 0 kPa to 140 kPa.

Miniature Fiber-Optic Tip High Pressure Sensors Micromachined by 157 nm Laser

Two miniature all-fiber in-line tip pressure sensors fabricated by 157 nm laser are demonstrated. First, a sensor without any reflective coating been tested for pressure response in the range of 0-60 MPa, showing a sensitivity of ~0.01 rad/MPa, a linearity of 99.998%, and a long-term stability of ±0.04 MPa, respectively. For improving the sensor stability, sensor with high reflective coating is also demonstrated for comparison, which shows a long-term stability of less than ±0.02 MPa. Tolerance of the sensitivity of the sensors for 60 Mpa measurement range is ±5% for ten samples. These sensors could find important applications in automotive and aerospace indus tries, and down-hole monitoring, etc.

Investigation of flow structures and transport phenomena in bubble columns using particle image velocimetry and miniature pressure sensors

The bubble column reactors are usually operated in a heterogeneous regime where the liquid phase turbulence is generated by the bubble motion and the velocity gradients in the mean motion. The turbulent flow comprises of fluid elements moving in a random fashion with different sizes and energies, called ‘flow structures’. Both the large and small scale flow structures within a reactor play an important role in governing the local momentum, heat and mass transfer. The current work is focused on the estimation of the time averaged flow pattern and flow structures. The experimental data has been collected using miniature pressure sensors, PIV+shadowgraphy and LDA. The data was subjected/analyzed to/with multipoint linear stochastic estimation (MLSE), wavelet transforms, image processing and eddy isolation (EIM) to identify the flow structures. Two bubble columns have been used: a narrow rectangular (2D) column and a cylindrical (3D) column. Wavelet transforms (WT) were applied to isolate individual structures from PIV data to get their shape, size and energy in the 2D column. MLSE has been used to obtain the velocity profiles from pressure fluctuation signals. This data, augmented by PIV and LDA data, is subjected to WT and EIM to get the eddy age and its energy distribution. The data of the eddy shape size and energy was used to predict the mass transfer coefficient in the cylindrical bubble column as a test case. Overall, in this work we present a methodology to utilize the experimental data to get a better insight of the dynamics of flow structures, and propose a path forward for the deeper understanding of transport phenomena in bubble columns.

Unsteady Pressure Measurements With a Fast Response Cooled Probe in High Temperature Gas Turbine Environments

This paper presents the first experimental engine and test rig results obtained from a fast response cooled total pressure probe. The first objective of the probe design was to favor continuous immersion of the probe into the engine to obtain a time series of pressure with a high bandwidth and, therefore, statistically representative average fluctuations at the blade passing frequency. The probe is water cooled by a high pressure cooling system and uses a conventional piezoresistive pressure sensor, which yields, therefore, both time-averaged and time-resolved pressures. The initial design target was to gain the capability of performing measurements at the temperature conditions typically found at high pressure turbine exit (800–1100°C) with a bandwidth of at least 40 kHz and in the long term at combustor exit (2000 K or higher). The probe was first traversed at the turbine exit of a Rolls-Royce Viper turbojet engine at exhaust temperatures around 750°C and absolute pressure of 2.1 bars. The probe was able to resolve the high blade passing frequency (≈23 kHz) and several harmonics of up to 100 kHz. Besides the average total pressure distributions rom the radial traverses, phase-locked averages and random unsteadiness are presented. The probe was also used in a virtual three-hole mode yielding unsteady yaw angle, static pressure, and Mach number. The same probe was used for measurements in a Rolls-Royce intermediate pressure burner rig. Traverses were performed inside the flame tube of a kerosene burner at temperatures above 1600°C. The probe successfully measured the total pressure distribution in the flame tube and typical frequencies of combustion instabilities were identified during rumble conditions. The cooling performance of the probe is compared with estimations at the design stage and found to be in good agreement. The frequency response of the probe is compared with cold shock-tube results and a significant increase in the natural frequency of the line-cavity system formed by the conduction cooled screen in front of the miniature pressure sensor were observed.

A Design of Amplifying Circuit Based on Pt Resistance Strain Pressure Sensor

This topic takes the miniature Pt resistance strain pressure sensor made by Institute of Electronics, Chinese Academy of Sciences, as the core sensing element, and designs corresponding high-precision, low cost, low power amplifying circuit so as to realize accurate detection of atmospheric pressure in time. In this topic, a new design of amplifying circuit is taken, which first connects the digital potentiometer to the bridge circuit to adjust its balance, and then amplifies the output signal of the bridge circuit once to ideal value. This design not only meets the requirement of measurement, but also is feasible and reduces the cost. At the same time, in order to improve the precision of the potentiometer adjusting the bridge balancing, paralleled resistances are creatively used beside the digital potentiometer and its influence to the bridge balance adjustment and the accuracy of the bridge measurement is analyzed in detail.

Fabrication of a miniature all-glass fibre optic pressure and temperature sensor

In this paper the fabrication of a miniature all-glass fibre optic pressure and temperature sensor is presented. The sensor combines the functionality of a miniature all-silica diaphragm based Extrinsic Fabry Perot Interferometric (EFPI) Fibre Optic Pressure Sensor (FOPS) and an in-Fibre Bragg Grating (FBG) sensor. The reported fibre optic sensor has several advantages such as being cost-effective, simple to fabricate, miniature in size, mechanically robust and can be designed to withstand high temperatures or/and pressures.

Association between intraoral pressure and molar position and inclination in subjects with facial asymmetry

Although it has been suggested that an imbalance in buccolingual pressure may play a role in dental compensation of the molars and asymmetry in the mandibular dental arch in subjects with facial asymmetry, it is still unclear whether buccolingual pressure is associated with this phenomenon. Thus, the purpose of this study was to test the null hypothesis that there are no differences in cheek and tongue pressure between the shifted and non-shifted sides in 12 (8 females and 4 males, mean age: 24.9 years) subjects with facial asymmetry defined as 4 mm or more deviation of the midline in the mandibular incisors. The resting buccolingual pressure on the bilateral mandibular first molars was measured simultaneously using four miniature pressure sensors. Moreover, a postero-anterior (PA) cephalogram was used to determine the buccolingual positions and the inclination of the mandibular first molars. Wilcoxon t-, Kruskal-Wallis H-, and Mann-Whitney U-tests and Spearman correlation coefficient by rank were used for statistical analysis. Significance was set at P < 0.05. Cheek pressure was significantly greater on the shifted than that on the non-shifted side, while tongue pressure on the shifted side was significantly less than that on the non-shifted side. On the other hand, tongue/cheek pressure ratio on the shifted side was significantly less than that on the non-shifted side. There were significant differences between the shifted and non-shifted sides in the buccolingual positions and inclination of the mandibular first molars. Regardless of the side, there were significant negative correlations between the buccolingual position of the mandibular first molars and cheek pressure and significant positive correlations between the buccolingual position of the mandibular first molars and tongue/cheek pressure ratio. There were also significant negative correlations between tongue/cheek pressure ratio and inclination of the mandibular first molars on both the shifted and the non-shifted sides. Thus, the present findings reject the null hypothesis. The imbalance in buccolingual pressure in subjects with facial asymmetry appears to be related to dental compensation of the molars and mandibular asymmetry.

Miniature all-silica optical fiber pressure sensor with an ultrathin uniform diaphragm

This paper presents an all-silica miniature optical fiber pressure/acoustic sensor based on the Fabry-Perot (FP) interferometric principle. The endface of the etched optical fiber tip and silica thin diaphragm on it form the FP structure. The uniform and thin silica diaphragm was fabricated by etching away the silicon substrate from a commercial silicon wafer that has a thermal oxide layer. The thin film was directly thermally bonded to the endface of the optical fiber thus creating the Fabry-Perot cavity. Thin films with a thickness from 1microm to 3microm have been bonded successfully. The sensor shows good linearity and hysteresis during measurement. A sensor with 0.75 microm-thick diaphragm thinned by post silica etching was demonstrated to have a sensitivity of 11 nm/kPa. The new sensor has great potential to be used as a non-intrusive pressure sensor in a variety of sensing applications.

Hydrodynamic Forces Generated on a Spherical Sediment Particle during Entrainment

The objective of this research is to study the relationship between the coherent flow structures and the hydrodynamic forces leading to entrainment of a spherical bed sediment particle for a rough bed uniform turbulent flow. Two types of experiments, namely, movable and fixed balls, were conducted using spherical roughness-element beds with particle image velocimetry to measure the instantaneous flow-velocity field. Miniature piezoelectric pressure sensors were used to capture the instantaneous pressure on the surface of the sphere. Movable ball experiments reveal the predominance of large sweep structures at the instant of entrainment. Fixed ball experiments carried out at entrainment conditions show the importance of both vertical and horizontal pressure gradients on the ball leading to entrainment. Probability distribution function plots of pressures based on quadrant analysis of velocities also reveal the higher probability of occurrence of high magnitude force induced by sweep ( Q4 ) events.

Estimation of a three-dimensional tyre footprint using dynamic soil–tyre contact pressures

A method for estimating the three-dimensional (3D) footprint of a 16.9R38 pneumatic tyre was developed. The method was based on measured values of contact pressure at the soil–tyre interface and wheel contact length determined from the contact pressures and the depths and widths of ruts formed in the soil. The 3D footprint was investigated in an area of the field where the pressure sensors of the tyre passed in a soft clay soil. The tyre was instrumented with six miniature pressure sensors, three on the lug face and the remaining three on the under-tread region between two lugs. The instrumented tyre was run at a constant forward speed of 0.27 m/s and 23% slip on a soft soil, 0.48 MPa cone index, 25.6% d.b. moisture content for four wheel load and tyre pressure combination treatments. The 3D footprint assessment derived from soil–tyre interface stress used in this research is a unique methodology, which could precisely relate the trend profile of the 3D footprint to the measured rut depth. The tyre–soil interface contact pressure distributions results showed that as inflation pressure increased the soil strength increased significantly near the centre of the tyre as a compaction increase sensed with the cone penetrometer.

A study of violent sloshing wave impacts using an improved SPH method

The flip-through phenomenon has been observed in several conditions characterized by a steep wave approaching a vertical wall (Peregrine 2003). One of the cases where this phenomenon has been observed and studied experimentally is the sloshing in a partially filled tank. This case has been described in Lugni et al. (2006) and in Faltinsen and Timoka (2009). Those experiments detail the features of the flip-through dynamics with an ad hoc distributions of miniaturized pressure sensors and with the records of a fast video-camera. Here, the same flow conditions have been reproduced numerically with an improved SPH method (cSPH), i.e. with MLS integral interpolators (Fries and Matthies 2003). This allows to solve the Euler equations in the case of free surfaces impacting at a wall. The extremely intense local features of the phenomenon highlight the capabilities and limits of the numerical algorithms proposed.

Unsteady Blade Loading with Clocking in Multistage Axial Compressors, Part 1

This two-part paper presents numerical and experimental investigations of clocking effects of stator blade rows on the blade loading in the third stage of the four-stage low-speed research compressor at Technische Universitat Dresden. In Part 1 of the paper, the results of the numerical investigations are presented. The unsteady flowfield of the four-stage low-speed research compressor at several clocking configurations is investigated using a three-dimensional time-accurate viscous solver. The unsteady pressure distributions on the rotor and stator blades in the third stage at midspan at several clocking configurations are presented and discussed. Furthermore, the clocking effects in the rotor blade tip region will also be discussed. In Part 2 (Muller, L., Mailach, R., Vogeler, K., Jia, H. X., and Xi, G., Unsteady Blade Loading with Clocking in Multistage Axial Compressors, Part 2, Journal ofPropulsion and Power, Vol. 26, No. 1, 2009, pp. 36-45.), the experimental investigations are analyzed, which were performed using time-resolving piezoresistive miniature pressure sensors. The measurements were carried out on the pressure side and suction side of the rotor and stator blades in the first and third stages at midspan. Exemplary results for the third stage and design point will be discussed both for the numerical and experimental investigations.

Unsteady Blade Loading with Clocking in Multistage Axial Compressors, Part 2

This two-part paper presents numerical and experimental investigations of clocking effects of stator blade rows on the blade loading in the third stage of the four-stage low-speed research compressor at Technische Universitat Dresden. In Part 1 (Muller, L., Mailach, R., Vogeler, K., Jia, H. X., and Xi, G., Unsteady Blade Loading with Clocking in Multistage Axial Compressors, Part 1, Journal of Propulsion and Power, Vol. 26, No.1, 2009, pp. 25-35.) of the paper, the results of the numerical investigations are presented. The unsteady flowfield of the four-stage low-speed research compressor at several clocking configurations is investigated using a three-dimensional time-accurate viscous solver. The unsteady pressure distributions on the rotor and stator blades in the third stage at midspan at several clocking configurations are presented and discussed. Furthermore, the clocking effects in the rotor blade tip region will also be discussed. In Part 2, the experimental investigations are analyzed, which were performed using time-resolving piezoresistive miniature pressure sensors. The measurements were carried out on the pressure side and suction side of the rotor and stator blades in the first and third stages at midspan. Exemplary results for the third stage and design point will be discussed both for the numerical and experimental investigations.

From piezoelectric sensor to measuring system

In 1959, Hans Conrad Sonderegger established Kistler Instrumente AG in Switzerland. In 1957, Walter P. Kistler and Hans Conrad Sonderegger had already founded Kistler Instrument Corp. in the USA and Hans Conrad Sonderegger had established Kistler Instruments in Switzerland. In 1958, Kistler launched the first universal miniature pressure sensor. In the years that followed Kistler set milestones in the field of sensor technology with its innovations and expanded its global presence. In 2009, its jubilee year, Kistler is adding the new KiBox, the mobile in-vehicle combustion analysis system, to its range of products.