M.Ing. (Electrical And Electronic Engineering) / A need was established for the development of a acoustical sensor in silicon. The acoustical sensor is based on the silicon pressure sensor. This sensor consists of a silicon membrane which is formed from silicon bulk material by means of etching. By transforming the movement of the membrane into a variation of capacitance, it is possible to detect a change in pressure. Signal processing is needed to insure that the : information, received from the sensor, is useable and accurate. The physical aspects of sound was investigated. An important relationship was derived between the intensity of a sound and the pressure associated with it. Because silicon was used in a mechanical environment, the mechanical properties of the material were investigated. A model was developed to simplify the design of the senor. A expression was derived for the movement of the membrane for any uniform load applied to it. The variation in capacitance was given by integrating over the area of the membrane. The condense microphone was used as a example of a design of a acoustical sensor. Arising from the example, the natural frequency of the silicon membrane was looked into. A variety of diaphragms were made to provide for a wide working area. Some of the manufacturingprocesses were individually examincd and changed to comply with the manufacturing of the diaphragms. The important process of etching was thoroughly investigated. An excellent etching agent was found with which accurate micro machining could be done. Using this etching agent, a variety of silicon and poll silicon diaphragms were made. Most of the silicon diaphragms were suceossfully formed. The. poli silicon diaphragms were however deformed because of internal stress which developed during the forming process. A signal processing circuit was developed to perform the task of transforming the variation in capacitance to a variation in voltage. The circuit utilised the current through the capacitor to establish the variation in capacitance. The current was transferred to a voltage by a differencing current amplifier. Further signal processing is done by a analogue multiplier.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:11246 |
| Date | 29 May 2014 |
| Creators | Ferreira, Daniel Nicolaas Paul |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Johannesburg |
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