Key Engineering Materials Vols. 562-565

Abstract: In this paper, a new structure of polyimide-based humidity sensor is developed, which can work better at low temperature environment. In this humidity sensor, the capacitive part is sputtered on a suspended membrane, the lower electrode is also a controllable heater, used to control the temperature on the surface of the sensor through the external circuits. The results of experiment suggest that the sensor has a wide range of sensing ambient relative humidity from 10%RH to 90%RH with a controllable constant temperature and at a lower temperature it shows a good linearity.

Abstract: The influence of temperature’s variation upon the resonant frequency and damping of the Micro-Electro- Mechanical-System (MEMS) gyroscope’s silicon structure in the vacuum package is investigated in this article. The gyroscope’s working principle and the dual-mass decoupled gyroscope structure are introduced, the drive and sense modes’ frequencies are analyzed. The ideal models of resonant frequency and damping are established and the dominate elements of impacting the resonant frequency and damping are Young Modulus, air viscosity coefficient and ambient pressure respectively. The experiments and the results proved that the frequency model works well, and the damping model only can simulate the tendency because of the air getter’s influence.

Abstract: A liquid floating rotational micro-gyroscope is proposed in this paper, whose stability is improved by liquid suspension. High rotor velocity is needed to improve its sensitivity. Edge effect is the phenomenon that sharp edges cause much more viscous drag. This work researches edge effect's influence on viscous drag to speed up the rotor. Flow field models of the sharp edge structure and fillet structure are established separately. Viscous drag is measured by simulation and experiment. Edge effect causes a lot of viscous drag and it can be reduced significantly by filleting the rotor. The maximal reduction is one third relative to the sharp edge structure, and it is reached when fillet curvature radius is half of rotor thickness.

Abstract: This paper presents a micro-displacement sensing circuit, which can detect sensing capacitors of levitated rotor. To ensure the high resolution, noise analysis of pre-amplifier of micro-displacement sensing circuit is conducted. The results show that choosing low noise amp and decreasing Cf /C1 can reduce the electronic noise.

Abstract: Liquid-suspended rotor micro-mechanical gyroscope uses a high-speed rotating hollow rotor in response to the density of the liquid as the mass to do the angular velocity detection. In order to improve the liquid-suspended gyroscope's performance, this paper suggested a new high performance magnetic driving technology. In this technology, the driving performance is optimized by applying six-phase overlapped driving signal to the twelve driving coils of the stator. With this driving technology, the rotating speed of rotor in 3# industrial white oil can go up to 8700rpm.

Abstract: A hall speed sensor detection system is designed in this paper. The system consists of the controlling circuit part, the detecting circuit part and the microcomputer part. The system’s structure is simple. It has the advantages such as lower cost, intuitive display and user-friendly. The detecting accuracy can meet the requirements of industrial production, and be suitable for mass production.

Abstract: Field emission accelerometer work in vacuum environment, the negative exponential relationship between the current and the distance of the cathode and anode electrode make the accelerometer has high sensitivity and serious non-linearity. A system simulation method by using SIMULINK tools was put forward, and the system simulation model was proposed. The system simulation was carried out under low vacuum and high vacuum environment. On the guidance of the simulation result, the circuit was designed and the performance of accelerometer was tested. The result indicated that the accelerometer have good linearity and sensitivity.

Abstract: The theory of a Sigma-Delta modulator is introduced in this paper. Based on this theory, a feedback 2-1-1 multi-stage-noise-shaping (MASH) sigma-delta modulator is designed, and the coefficients of the modulator are calculated. The system-level simulation results show that the effective number of bits (ENOB) is 24 bits when the signal bandwidth is 1 kHz and the over-sampling (OSR) rate is 128. Then the circuits of modulator are designed, including integrator, comparator, multi-phase clock and the noise cancelling logic. The whole modulator is simulated in Cadence, the signal to noise ratio (SNR) of the modulator is 125.4dB, and the ENOB is 21.1bits, which meet the technical requirements of the sensor.

Abstract: Based on the principle of catalytic combustion type gas sensor, a kerosene gas sensor with micro twin-bridge structure is fabricated using silicon micromachining technology. A pair of platinum film resistor is fabricated by film processing, and its nominal resistance is 20Ω at 0°C. The nano-alumina catalytic carrier and noble metal catalyst are coated on the surface of sensitive resistance in order to form the sensitive bridge and compensating bridge. The monolithic integration of catalytic element and compensating element is achieved on the silicon micro twin-bridge for fabrication of kerosene sensor. The simulation result shows that once temperature of one bridge rises to 650K, the other bridge may increases about 10°C. The test on kerosene sensor by calibration device indicates that the sensor can detect the kerosene volume fraction ranging from 0 to 7000×10-6 and the sensor output property is linear.

Abstract: The electrode layout determines the piezoelectric performance of quartz resonator and directly affects the precision of the quartz VBA. We presented a novel monolithic differential quartz VBA with optimized electrode layout and solved the lock-in problem due to mechanical coupling. Based on the mass-equivalent system, an analytical model was developed and the uncoupling condition of the monolithic differential quartz VBA was deduced. Then we proposed five different electrode layouts and the optimum one was determined via simulation of piezoelectric and harmonic characteristics of quartz resonator with ANSYS. As a result, the mechanical coupling can be eliminated and at the same time, ±100 g measurement range and 80Hz/g scale factor can be achieved. The optimum electrode layout can drive quartz resonator in the desired modal. The presented device with advantages of miniaturization, low mechanical coupling, none assembly errors and high electromechanical coupling efficiency is very promising in the high-precision quartz VBA.