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Transistor Microphone Small Signal h Parameters

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The results of studying the h parameters of stressed transistors of the 2N706 type are presented. For this transistor type, the stress characteristics can be predicted by knowing the initial parameter values. The optimum stress location on the transistor surface is detrmined for a practical transducer.

JAES Volume 15 Issue 1 pp. 60-62; January 1967
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Scott Dorsey
Scott Dorsey

Comment posted May 31, 2020 @ 13:42:21 UTC (Comment permalink)

Engineers at Bell Labs working on planar silicon transistors discovered that flexing the transistor die changed the beta, and since Bell was always looking for new sources of inexpensive communications microphones for telephone use, a lot of research has been done trying to put this effect to use to create a "Transistor Microphone." There are several other papers in the AES library on this.

This paper comes from Automatic Electric, which was one of the big competitors to the Bell System, showing that they were doing serious research into this microphone design as well.

In the end, the whole thing didn't amount to much, and when Sony started coming out with stable jellybean electret capsules a couple of years afterward, the research in this direction was abandoned.

So this is an interesting look at an effect that was never made into a practical product.

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