Jinjun Deng

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.

Flexible thermal sensor array on PI film substrate for underwater applications

Fully flexible thermal sensor array was developed for underwater applications. To minimize conductive heat loss to substrate and shorten response time nickel thin film resistors are fabricated on polyimide film substrate. This flexible sensing belt can be applied onto highly curved non-planar surfaces to measure flow with minimal invasion. Polymer compatible micromachining technology with consideration of waterproof coating was developed. Through calibration performed under constant-current excitation, high temperature coefficient of resistance (TCR) and low time constant of sensor were obtained. Hydrodynamic experiments in water channels were carried out, and it indicates dynamic wave flow can be sensed promptly with this sensing belt.

Design and fabrication of a Piezoelectric Micro Synthetic Jet Actuator

Synthetic Jet Actuator (SJA) is a new type actuator for active flow control applications. A Piezoelectric Micro SJA based on MEMS technology was present in this work. The simulation of device performance was carried out through a multi-domain coupled analysis model, and the relative error of jet velocity between simulation results and experiment data is less than 8%. A batch fabrication process was proposed to integrated fabrication of piezoelectric film and silicon structure. And using this process, prototype of micro SJA was gained. Preliminary tests of SJAs performance show that the max synthetic jet velocity (8.2m/s) is obtained as driving voltage is 25V and driving frequency close to the first-order natural frequency (10500Hz).

ITO thin film thermocouple for transient high temperature measurement in scramjet combustor

Thin film thermocouples have high respond speed and measuring accuracy of the dynamic surface temperature for their negligible thermal mass. In this paper, ITO thin film thermocouples were used to capture the transient wall temperature in supersonic combustor. A protective bilayer was used to improve the sensors thermal stability and durability. Calibration results show that the sensor exhibit high thermal stability over 1600K for 300 minutes. And a relationship was established to describe the thermoelectricity of ITO thin film thermocouples. The dynamic temperature of scramjets inner wall was successfully captured and the combustion procedure was characterized clearly.

High temperature thin film thermocouples on different ceramic substrates

This paper was directed at the effect of ceramic substrate on NiCr/NiSi film thermocouples fabricated on two ceramics substrate. One was on smooth Al2O3 substrate. The other was on silicon carbide ceramic reinforced by carbon fiber (CFCC-SiC). Since the CFCC-SiC has rough surface, the stress between the layer was greater and the thin film was easier to crack. With experiments the measure temperature of the thin film thermocouples on both of them could reach 700°C. Calibrate test data showed that the high-temperature stability of the thin film thermocouple on smooth Al2O3 substrate was much better than the other.

Microfabricated SOI pressure sensor using dynamically balanced lateral resonator

A resonant pressure sensor using a dynamically balanced lateral resonator is presented, which employs differential electrostatic comb structure for linear driving and sensing. The sensor is successfully microfabricated through a simple yet reliable micromachining process based on a commercially available silicon-on-insulator wafer with only two masks. Special anchor structure is developed to suppress the vertical position shift of the resonator when the diaphragm deflects, which using suspended connecting trusses to attach the stress-sensitive beam ends of the resonator. The sensor chip is mounted into a custom 16-pin Kovar package with epoxy resin for preliminary measurements. Testing results show that the resonator has a fundamental resonant frequency of 34.17 kHz, and the quality factor is about 1253 at atmospheric pressure, which rises to above 50 000 below 5 Pa. Over the pressure range of 100-380 kPa, the static pressure sensitivity is approximately 10.17 Hz/kPa, with the nonlinearity of 0.02%FS, the hysteresis error of 0.05%FS, and the repeatability error of 0.17%FS.

Fully flexible hot film sensor array for underwater applications

Flexible hot film sensor array was developed for underwater applications. To minimize conductive heat loss to substrate, heighten sensitivity and shorten response time nickel thin film resistors are fabricated on polyimide substrate. Fully flexible structure and very low thickness of the sensing belt enable it possible to be taped on highly curved surfaces to measure fluid parameters with minimal invasion. Polymer compatible micromachining technologies with further consideration of waterproof coating were developed. High temperature coefficient of resistance (TCR) and low time constant of sensor were obtained. A hydrodynamic experimental setup was established, and a demonstration indicated flow velocity can be measured with the sensor.

METHOD AND SIMULATION OF THE USE OF MICRO SHEAR STRESS SENSOR ARRAY IN DETECTING BOUNDARY-LAYER SEPARATION POINT

At the boundary layers separation point, the mean of the shear stress drops to a small value while its fluctuation increases dramatically. Based on the thermal method, we can fabricate a MEMS-based shear stress sensor array to bend with the curved surface, which can measure the shear stress profile of the boundary layer. This paper presents two methods, mean and RMS of the shear stress difference max value and the second order of the array signals difference algorithm, to calculate the location of the flow separation point. Through combination of the two methods and analyzing the 2D circular column CFD simulation data, the position of the separation point can be determined accurately.

Accurate Measurements of Wall Shear Stress on a Plate with Elliptic Leading Edge

A micro-floating element wall shear stress sensor with backside connections has been developed for accurate measurements of wall shear stress under the turbulent boundary layer. The micro-sensor was designed and fabricated on a 10.16 cm SOI (Silicon on Insulator) wafer by MEMS (Micro-Electro-Mechanical System) processing technology. Then, it was calibrated by a wind tunnel setup over a range of 0 Pa to 65 Pa. The measurements of wall shear stress on a smooth plate were carried out in a 0.6 m × 0.6 m transonic wind tunnel. Flow speed ranges from 0.4 Ma to 0.8 Ma, with a corresponding Reynold number of 1.05 × 106~1.55 × 106 at the micro-sensor location. Wall shear stress measured by the micro-sensor has a range of about 34 Pa to 93 Pa, which is consistent with theoretical values. For comparisons, a Preston tube was also used to measure wall shear stress at the same time. The results show that wall shear stress obtained by three methods (the micro-sensor, a Preston tube, and theoretical results) are well agreed with each other.

A Flexible Hot-Film Sensor Array for Underwater Shear Stress and Transition Measurement

A flexible hot-film sensor array for wall shear stress, flow separation, and transition measurement has been fabricated and implemented in experiments. Parylene C waterproof layer is vapor phase deposited to encapsulate the sensor. Experimental studies of shear stress and flow transition on a flat plate have been undertaken in a water tunnel with the sensor array. Compared with the shear stress derived from velocity profile and empirical formulas, the measuring errors of the hot-film sensors are less than 5%. In addition, boundary layer transition of the flat plate has also been detected successfully. Ensemble-averaged mean, normalized root mean square, and power spectra of the sensor output voltage indicate that the Reynolds number when transition begins at where the sensor array located is 1.82 × 105, 50% intermittency transition is 2.52 × 105, and transition finishes is 3.96 × 105. These results have a good agreement with the transition Reynolds numbers, as measured by the Laser Doppler Velocimetry (LDV) system.