New Sensors Detect Speech Without Sound

April 19, 2005 — -- Annoyed by cell phone users who believe they need to yell into their mobiles in order to be heard? Such loud and obnoxious talkers may become extinct, thanks in part to the military's need for sure -- and sometimes silent -- communications.

For years, scientists at the U.S. military's Defense Advanced Research Projects Agency, have been investigating ways to improve radio communications among troopers in noisy environments such as inside a rumbling tank or clattering helicopter.

Under its Advanced Speech Encoding project, DARPA hopes the answer may lie in refinement of so-called "non-acoustic sensors," experimental devices that can pick up a person's voice without a single syllable shouted, spoken or otherwise uttered.

One such device, the Tuned Electromagnetic Resonance Collar or TERC, being developed by a team of researchers at Worcester Polytechnic Institute in Massachusetts uses a unique approach to creating speech from an unspoken voice.

TERC is a plastic strip embedded with thin copper foil and other small electronic components. When strapped around a person's neck, the collar acts as a big capacitor -- an electronic component that can be charged to hold a small amount of electricity.

As a person speaks, the tiny movement of the vocal chords changes the collar's capacitance. Microchips can measure and process these shifting electronic signals and turn them into synthesized human speech using computers equipped with specially crafted software.

The main advantage of non-acoustical sensors such as TERC is that they pick up only the sound of only the speaker wearing the device. Conventional microphones, by contrast, pick up the speaker's voice as well as every other sound within its range.

It's a novel approach to battling background noise, says Donald R. Brown, a principal investigator with the research team developing the sensor at WPI. But human capacitance is a technology that is well understood and already employed in other devices.