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1、Optimized Design of a Stacked Diaphragm MEMS Pressure Sensor for Tsunami Warning SystemSuja K J, Santo Mathew, Rama KomaragiriDepartment of Electronics and Communication engineering National Institute of Technology Calicut, Kerala. ramanitc.ac.inAbstractTsunami is a large scale, short duration verti
2、cal dis-placement of water column. Tsunami results in a pressure change in the sea bed. The Tsunami warning system (TWS) con-sist of a series of sensors which detect the change in pressure at the sea bed when tsunami waves are generated. Micro electro mechanical system based silicon pressure sensors
3、 have under-gone a significant growth in the last few years. The sensitivity, maximum measurable pressure and linear range over the deflec-tion of pressure sensor highly depend upon the diaphragm struc-ture. In this work, a stacked diaphragm pressure sensor is de-signed and simulated which can be us
4、ed for under water pres-sure measurements. A novel method for sensitivity enhancement by optimizing the thickness of various layers for stacked dia-phragms is presented. Also a study of the bulk micro machined silicon piezoresistive pressure sensor and a surface micro ma-chined stacked diaphragm pre
5、ssure sensor is presented, simulat-ed and compared with respect of sensitivity and deflection.Keywords Tsunami Monitoring, MEMS, Piezoresistive Pres-sure Sensor, Surface micromachining, Bulk micro machining.1. INTRODUCTIONTsunamis generally consist of a series of waves with periods ranging from minu
6、tes to hours, arriving in a so-called wave train. Wave heights of tens of metres can be gen-erated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enor-mous has huge impact on economy, lives and environment and even can result in catastrop
7、hes. The principal generation mechanism of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is usually attributed to earthquakes, landslides, vol-canic eruptions and glacier calving or more rarely by meteor-ites and nuclear tests.
8、The waves formed in this way are then sustained by gravity. Tsunamis have a small amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometres long, whereas normal ocean waves have a wave-length of only 30 or 40 metres), which is why they generally pass unnoticed at sea
9、, forming only a slight swell usually about 300 millimetres (12 in) above the normal sea surface. They grow in height when they reach shallower water, ina wave shoaling process. A tsunami warning system (TWS) is used to detect tsunamis in advance and issue warnings to pre-vent loss of life and damag
10、e. It is made up of two equally im-portant components: a network of sensors to detect tsunamis and a communications infrastructure to issue timely alarms to permit evacuation of the coastal areas 1. A TWS consists of a seafloor Bottom Pressure Recording (BPR) system capable ofdetecting tsunamis, and
11、 a moored surface buoy for real-time communications. An acoustic link is used to transmit data from the BPR on the seafloor to the surface buoy. The data are then relayed via a GOES (Geostationary Operational Envi-ronmental Satellites) link to ground stations. Figure 1 shows NOAA (National Oceanic a
12、nd Atmospheric Administration) tsunami warning system.Figure 1. NOAA tsunami warning system 1The sensor detects the presence of a Tsunami by detecting the pressure variation in the sea bed 2. Ordinary wind waves disturb only a very thin layer of water at the surface of the sea, and so dont affect th
13、e sea floor far, far below. Tsunami moves the entire water column, which in the open sea is thousands of meters thick. So when a tsunami rolls over a sensor on the sea floor, it will cause a noticeable change in water pressure.978-1-4799-1095-3/13/$31.00 2013 IEEE346Pressure sensors are one of the m
14、ost common Micro Electro Mechanical System (MEMS) devices. The MEMS sensor fab-rication technology enables miniaturization of complex sys-tems by integrating the sensing, controlling and actuating functions on a single chip. Diaphragm dimensions are deter-mined by the pressure range and maximum pres
15、sure that needs to be measured. MEMS based pressure sensors are clas-sified into piezoresistive and capacitive based depending upon the on pressure sensing mechanism. The piezoresistive pres-sure sensor utilises the piezoresistive property of silicon to measure applied pressure. The piezoresistive d
16、evice works on the principle of change in resistance with the deflection of the diaphragm due to applied pressure. Generally Wheatstone bridge configuration is formed by using four different resistors.Figure 2. Structure of a piezoresistive silicon pressure sensorty are reported 2. The load deflection method that describes
