The Development Of Particle Velocity Sensor Based On MEMS

There are two important means in field of acoustic measurement,that sound pressure measurement and particle velocity measurement.Compared to the research of sound pressure measurement technology,the research of particle velocity measurement has always been more important and difficult.In this dissertation,a particle velocity sensor is proposed and implemented,based on MEMS nano-wires structure,with the feature of figure-of-eight directivity independent,which could be widely used to measure noise vibration,to test acoustic material,to fulfill sound localization and underwater acoustic measurement.On the design of the MEMS particle velocity sensor,a microstructure of sensor named "bulk silicon cavity-double nano-wires" has been proposed.We will use the MEMS micro processing technology to fabricate two sensitive nano-wires with thickness of 450 nm and wideness of 5nm in the central area of the silicon cavity?depth of 200 ?m and wideness of 1 mm?.The outstanding of this sensor design lies in:?1?simple technology,easy to process;?2?good sensitivity,especially in the low frequency area;?3?high reliability and low stress.A physical heat-transfer model of particle velocity sensor has been built.?1?To discuss the influence of sensitivity determine the geometry of nano-wires especially on the spacing.Determine the geometry of nano-wires.?2?To analyze frequency characteristic of the sensor,and to present the relationship between material and geometry of nano-wire.?3?To determine working condition by testing the electrical parameters.A particle velocity sensor will be fabricated by using bulk micro-machining technology.Bulk-silicon cavity is made by etching technology.And corrosion and lift – off technology is used to build nano-wire.A set of suitable processing technology parameters of the sensor will be obtained by optimizing parameters from key part-corrosion and life-off technology,and by analyzing the influence of magnetron sputter technology of the metal layer.Design for signal processing circuit,including R-V conversion,frequency compensation and preamplifier.Circuit noise is the key which should be taken into consideration when to process the signal.In R-V conversion section,analyzed three kinds of noise characteristics,including mirror current bridge,differential bridge,common emitter.Given advantages like strong controllability,high signal-to-noise,mirror current bridge is chosen as the final R-V conversion plan.In frequency compensation part,first order frequency characteristic of the particle velocity sensor is compensated by RC,and the circuit will be gained 6db/oct when frequency is more than 1 kHz.In preamplifier part,low noise preamplifier circuit is realized by reducing the noise of the bias circuit.Result of tests indicates that requirements of sensor can be satisfied when the equivalent input noise voltage reaches 5nV/?Hz.The MEMS particle vibration velocity sensor was tested in air.?1?The method of standing wave tube is applied to the test of sensitivity,with measure theory and built testing system,to realize the sensitivity measure of the acoustic frequency range from 100 Hz to 3 kHz.?2?The results show that the MEMS particle velocity sensor has a sensitivity of 4.9mV/m·s^-1 @250 Hz.