Key Engineering Materials Vols. 562-565

Abstract: Unlike the solid-solid contact of traditional micro acceleration switch, liquid metal can be utilized to solve the disadvantage of solid-solid contact, such as contact wear and signal bounce. Liquid-metal micro switches have demonstrated no contact bounce, low switch-on time, low contact resistance, long life, and the capability to handle large currents. So the liquid-metal micro acceleration switches have attracted researcher’s attentions increasingly. To investigate the flow characteristics of mercury droplet in micro acceleration switch, this paper establishes numerical models of micro acceleration switch by using FLUENT. The effect of contact angle, droplet volume and temperature are discussed in this paper. Based on the VOF-CSF model of FLUENT, a serial of simulations were performed. The simulation results show that the influence of contact angle and droplet volume on flow characteristics is serious, and the influence of temperature is small. As compared with theoretical analysis, simulations are in good agreement with theoretical analysis.

Abstract: Surface stress-based biosensors as a crucial part of micro-scale and label-free system, use free energy change, the underlying concept in any binding reaction, have been investigated extensively in recent years. In this paper, a new bi-micro-cantilever surface stress biosensor is proposed which can be used to detect cells. Some fundamental study has been done, especially for the micro-cantilever due to its crucial role in the whole system. To acquiring the optimal material for more sensitive sensor, four material, Si, SiN, AlN, PMMA(polymethylmethacrylate), were contrastively analyzed under the same conditions (loads, size, environmental factor. etc) by finite element (FE) method. This study could provide some foundation for the biosensor design and fabrication.

Abstract: Based on magnetoelastic biosensor for the heavy ion detection, this paper is committed to study the influence of the excitations and detection positions on the sensitivity of magnetoelastic biosensors. The frequency response of biosensors with different excitations and different detection positions were studied. The numerical simulation software ANSYS [TM] Ansoft Maxwell was applied to calculate the distribution of magnetic field around the coil. The optimal excitation value was determined by this simulation. The frequency test of the magnetoelastic sensor was analyzed by a network analyzer, which showed the frequency in the middle of coil is better than in the two ends.

Abstract: Previous research on MWNTs/SiO2 humidity sensing film by our work group has proved that MWNTs sensor has a different response mechanism to humidity at AC testing signals and shows greater testing stability and higher sensitivity, compared with traditional DC signal measurement. An interface circuit for conductive MWNTs/SiO2 humidity sensor is designed in this paper for humidity detection and prospection in miniaturization and integration. It aims at detecting the sensor’s humidity sensitive conductance signal at AC testing signals, and inhibiting the interference of capacitance signals. The ASIC demodulates the two signals by their phase difference and outputs a direct voltage proportional to conductance. The layout for ASIC is drawn by standard 0.5um P2M2 CMOS process and has a total area of 4*2mm2. In circuit level simulation by HSPICE which introduces practical data of the sensor’s humidity sensing characteristics, the relation of circuit output to conductance turns out to have great linearity at no more than 300 kHz and zero offset can be neglected at less than 100 kHz frequency. It is feasible to select proper testing frequency for high sensitivity and stability and make further investigations on the sensor’s frequency property.

Abstract: Along with the development of MEMS technology, the precision of MEMS-Gyro is increasing and the range of application of MEMS-Gyro is expanding. The accuracy of centroid determination of the spot directly relates to the precision of star tracker, but, when the exposure time is shorter or the satellite is in an unstable state, the noise of detector limits the accuracy greatly in the traditional approach of centroid determination. In view of these issues, this paper presents an approach which is based on high-precision MEMS-Gyro to determine the centroid of spot. This approach references EKF to estimate the position of centroid optimally. So, when the SNR is reduced because of shorter exposure and unstable state, this approach can help to increase the accuracy of centroid determination by introducing MEMS-Gyro. Further, it improves the precision and dynamic performance of the star tracker. In the end of this article, the feasibility of the approach is verified by the numerical simulation.

Abstract: As a typical inertial sensor, vibration micro-gyro is extensively studied. According to its working principle, drive control system is an important element for the gyro system. The role of drive control system is to keep the drive modal stability including stable vibration frequency and amplitude. The PLL method is usually used to realize the drive system. However, it has some shortcomings used to high Q vibration micro-gyro. In this paper, the problems of the PLL method are analyzed, and a PID & AGC control system is introduced. By simulating and measuring, it is indicated that this method is fit for driving high Q vibration micro-gyro.

Abstract: In order to detect the tool-substrate contact force and the tool-target interaction force during nano-manipulation process, a novel MEMS based 2D piezoresistive micro-force sensor structure was proposed. This structure can realize the 3D hardware decoupling for the X，Y and Z axis. Thus, the force detection in the vertical direction (Z axis) and parallel direction reference to base (X axis) can be done simultaneously. Theoretical analysis shows that this structure has a good structural sensitivity. The rationality and feasibility of the structure were confirmed by simulation results.

Abstract: In this paper a fourth-order single-loop sigma-delta modulator applied in micro-gyroscope is designed. The modulator system chose the fully feedforword structure. The signal bandwidth is 200KHz, oversampling ratio is 64 and sampling frequency is 25.6MHz. By system simulation result in Matlab, the signal to noise ratio (SNR) is 92.3dB and effective number of bits (ENOB) is 15.03bits. The whole circuit of modulator is designed and simulated in Cadence Spectre. It is gotten that the SNR is 78.6dB and changes linearly with input level. When input level is bigger than -4dBFs, the modulator becomes overload.

Abstract: Nonlinearities of the resonator in silicon resonant accelerometer (SRA) limit the ultimate short term frequency stability. In SRA, this stability is a measure of the achievable resolution. This paper discusses the nonlinear vibration phenomenon of micro-resonator considering the impact of the entire structure of SRA and builds a model to calculate the micro-resonator nonlinear stiffness K_3,eff of the SRA prototype. The dies of SRA were fabricated by Silicon on Insulator (SOI) process. The equivalent model of the micro-resonator is built and the analytical value of the elastic constraint stiffness K_a of micro-resonator is derived as 8.91×10⁴ N/m. It is calculated that K_3,eff is equal to 5×10¹¹ N/m³,and as a comparison, the simulation result is 5.026×10¹¹ N/m³. The error between them is 0.52%. The nonlinear vibration experiments show that the maximum error between the theoretical and experimental value of resonance frequency is 2.1%. The prediction for the nonlinear stiffness contributes to further research on nonlinear vibration of the resonant beam. The model in this paper could also provide guidance and reference for optimal design of SRA.

Abstract: A high-order interface circuit based on sigma-delta (ΣΔ) modulation is advantageous to enhance the resolution and reduce the quantization noise of micro-accelerometer, while the performance is restricted by the effect of nonlinearity of op-amp, electrostatic force feedback and quantizer. A fifth-order closed-loop ΣΔ capacitive accelerometer is proposed in this paper and a theoretic nonlinearity of the accelerometer was investigated. The nonlinear behavioral models based on SIMULINK are given in the paper. The simulation and test result are presented through optimization based on the nonlinearity analysis at last.