Getting Walls to Talk... and Passengers to Shut Up

A new "magic crystal" can make windows whisper, church pews sermonize... and hog manure smell sweeter. Another new technology might be able to get that cell phone user to lower his voice.

Not many places in Iowa are under as much security as the headquarters of Etrema, located in the Iowa State University Research Park in the college town of Ames.

Etrema is carefully guarding the secrets of Terfenol-D, an exotic metal alloy that can do magic tricks. Technically a "solid-state transducer" capable of "magnetostriction," informally it is called a type of "smart metal."

What makes Terfenol-D so smart? It can change shape rapidly, more than 10,000 times per second, when hit with a magnetic field. And it can be precisely controlled by such a field, which means it can create all sorts of useful sounds. Etrema's first product, Whispering Windows, is a $1,500 device that can turn any flat surface into stereo speakers. Walls, tabletops, counters, and even windows can radiate clear, balanced sound. An early commercial test recently came in London, where a department store window was wired for sound. The increase in attention the display received from visitors also turned executive heads, so the store is now installing the technology at more locations around the UK. Etrema also fitted a church pew with a device that permits hearing impaired worshippers to hear the sermon through their tailbones. The company hopes it will have success in the consumer market with Soundbug (price expected to be around $20), which links to any headphone socket and attaches to flat surfaces via a suction cup. Impromptu parties and business presentations should be enhanced with better audio, leaping out of whatever surfaces happen to be at hand.

Terfenol-D industrial applications under development include welding (Ford hopes to make aluminum vehicles), improved fuel economy (Ford again, tweaking fuel injectors), mountain tunneling (early detection of granite ahead), metal work (Briggs & Stratton - precise lathing of machine parts), and animal waste (bursting bacteria cells in hog manure to prevent odor).

And there are military applications, as well. The U.S. Navy originally developed Terfenol in the 1940s to improve control over sonar. Etrema is tight-lipped about current research, but it is understood that improved Terfenol-D technologies can permit lower-volume sonar, which is harder to detect and less harmful to sea creatures.

Which has led to some new accusations of spying. The Chinese military is alleged to have developed its Terfenol technologies through spying -- using Chinese students at Iowa State University and some computer hacking. As it happens, China holds the world's largest reserves of the rare earth elements terbium and dysprosium, key ingredients of Terfenol-D.

Also on the subject of "hush, hush" technologies, the journal Nature reports that some Korean engineers have designed a tiny microphone that is an expert in hearing whispers.

Whispering is ineffective with most microphones because it exaggerates sounds like "s," "t," "p," and "b" (what linguists call sibilants and plosives) and because, obviously, it is soft and easily overwhelmed by background sounds.  That's why that guy who rides the bus with you has to YELL SO LOUD TO BE UNDERSTOOD.

The new microphone maximizes speech recognition through clever signal processing, and it filters away the exaggerated sounds using a precisely-sized and -located hole to re-route whispering's extra air flow. It's small enough to fit in a mobile phone, so [try whispering this on your current cell phone:] someday soon cell shouters should seem softer.

Visit Etrema and learn about their acoustics technologies

Read about Whispering Windows via the Toronto Globe & Mail

Read about the test installation of Whispering Windows at the UK's Peter Jones department store

Read about the spying allegations via the Ames Tribune

Read the news feature from Nature magazine, or read the original Nature article's abstract [for complete article, subscription required]