Technology: Microscopic Microphone

A microphone as small as a pinhead? It is on its way. A Raytheon Co. scientist has discovered that transistors, which are far smaller than any ordinary microphones, have areas that can detect fantastically faint mechanical forces and translate them into sizable changes of voltage —just as a microphone does.

The discovery was made by Dr. Wilhelm Rindner while he was poking under a microscope with a delicate probe, studying surface defects on a tiny transistor. The transistor was hooked up to a voltmeter, and Dr. Rindner soon noticed something peculiar: even his gentlest pokes at the transistor made the voltmeter fluctuate. He concluded that the transistor was sensitive to pressure as well as to electrical effects.

Dropping his regular research to investigate, Dr. Rindner led a Raytheon task force in painstakingly devising a tiny bit of metal shaped like a thumb tack and mounting it so that its stem pressed on a transistor’s sensitive spot. This device, smaller than a pinhead, performed as an excellent microphone. It can be made to transmit music faithfully, and can even pick up ultrasonic sounds to which the human ear does not respond.

Raytheon has high hopes for its near-microscopic microphone. Aside from countless possible uses in industry or the entertainment world or even in spacecraft, the microphone could certainly be used to great advantage in hearing aids, which could be made small enough to fit invisibly inside the ear. A hearing aid could be made even smaller, but the scientists feel that too small a device might get lost in the ear canal.