Sixth sense: probing the world by means of electric auras

Science News, June 19, 2004 by Peter Weiss

A decade ago, Philip H. Rittmueller was a man on a mission. By the early 1990s, the automobile industry knew that airbags, while successful at saving lives in crashes, could also prove deadly to children and small adults (SN: 9/26/98, p. 206). As an engineer with NEC Technologies Automotive Electronics Division at that time, Rittmueller was looking for a technological fix for this lethal threat.

Yet none of the approaches Rittmueller knew about for the automatic sizing up of car seat occupants--including weight sensing, ultrasonic scanning, and optical imaging--seemed good enough. "I was looking under all sorts of rocks," Rittmueller recalls.

Then, in the fall of 1994 at the Massachusetts Institute of Technology, Rittmueller found the right rock. He was visiting the university's hotbed of invention, known as the Media Lab, when he saw what looked like a throne flanked by two lighted Plexiglas poles, and he viewed a startling video showing how such a "spirit chair" was used in magic shows by the famous duo Penn and Teller.

In the video, Penn sat in the chair. As he gestured wildly with both hands and feet, drums, trumpets, cymbals, and other musical sounds blared out. No wires linked Penn to the synthesizers making the sounds, yet the device sensed his every move

When Rittmueller tried the gadget in the lab, its speed and three-dimensional awareness were "amazing," he recalls. If such a wireless-sensing system could be adapted to track an occupant of an automobile, he figured, he would be on his way to a superior airbag-controller that could determine the size and position of a passenger or driver and then judge whether it was dangerous to fire the airbag to its full extent.

On the spot, Rittmueller and the chair's designers started sketching possible airbag-related designs. Today, that collaboration between MIT and Rittmueller's Suwanee, Ga.-based automotive-electronics company, now called Elesys North America, is bearing its first fruit--an airbag controller that's already in some cars and soon to be introduced in many more.

The commercial use of the technology is expected to mushroom beyond the airbag niche, say developers of electric field imaging, the heart of the new technology. "Where letting objects know what's around them," says Media Lab physicist Neil A. Gershenfeld. In this increasingly automated world, any technology that can do that reliably, cheaply, and autonomously could be useful in many places.

TAKING CHARGE Imaging things in the world by means of electric fields actually started out as nature's own technology.

Several species offish in South America and Africa generate and detect weak electric fields. Because small fish, larvae, and other prey perturb the electric fields around the field-generating fish, voltage-sensitive cells in their skin can detect the objects. Weakly electric fish, as they are called, also use electric signals to recognize and attract potential mates.

Electric field sensing has made it into the technoscape too. Anyone who has pushed one of those elevator buttons that responds to a finger's touch without itself moving has triggered an electric field sensor. A weak electric field continuously emanates from such buttons. When a finger contacts the button, that field becomes distorted. This causes an electric current increase in the buttons circuit that's then interpreted by the elevator's control circuitry as, say, the "go to floor 10" command.

Similar ways of using electric fields to sense nearby objects have been in use for roughly a century. Back in the 1920s, the Russian inventor Leon Theremin created one of the first electronic musical instruments, and it was based on electric field sensing.

Today, in addition to elevators, electric field sensing shows up in touch screens and pads on computers and stud finders that locate wooden supports in walls. Still, "That's the old-fashioned measurement," notes Media Lab physicist Joseph A. Paradiso.

Media Lab researchers in the early 1990s realized that it might be possible to use electric fields to image objects, not just to detect their presence. The scientists weren't looking for crisp optical imaging, but rather a fuzzier result that would be good enough to make out sizes, shapes, and positions of objects. This imprecise approach saves processing time and resources, says Joshua R. Smith of Intel Research in Seattle. In 1991, the MIT researchers began adding electronics to conventional musical instruments, such as cellos and violins, so that computers could detect players' bowing or other movements and produce electronic sounds to accompany the natural tones of the instrument. Tod Machover, a Media Lab composer and electronic-instrument developer, and Gershenfeld built the first such hyperinstrument, a hypercello for Yo-Yo Ma.

Working on a wireless bow for a hyperviolin in 1993, Gershenfeld, Paradiso, and their colleagues ran into some puzzling observations stemming from unexpected ways that objects, including people, can perturb electric fields.