A tiny microphone diaphragm

Based on fly ears has been built. Ronald Miles (SUNY Binghamton) and his colleagues based their diaphragm on Ormia ochracea, a small parasitic fly that uses sound to track down its cricket host even in complete darkness. The fly can detect changes as small as two degrees in a sound’s direction. Such directional sensitivity—as good as humans’—is unexpected, since the fly’s ears are just a few hundred microns apart. Mammals’ ears, in contrast, are well separated from one another, so that differences in sound signals at the ears provide localization cues (see Physics Today, November 1999, page 24 ). The fly’s hearing organs are a pair of mechanically coupled membranes: Sound waves incident on one membrane can deflect the other. With this coupling, the fly can obtain both the average pressure of an incoming sound and its pressure gradient, which together provide localization information. The Binghamton researchers’ 2-mm² prototype microphone diaphragm, shown above, closely reproduced the fly ears’ characteristics. This unconventional approach to localizing sound may lead to new applications, such as a compact hearing aid that responds only to sound in front of the wearer. The work was presented at last December’s Acoustical Society of America meeting in Ft. Lauderdale, Florida, as paper number 2aEA1.