Sound is all around us, to the point where those of us blessed with good hearing take it for granted. But there is a thriving field of science for whose researchers sound is more than just background noise. They see sound as a potential tool for everything from new forms of transportation to new military weapons.
Sound, according to my encylopedia, is “a physical phenomenon that stimulates the sense of hearing.” That physical phenomenon is a compression wave passing through a medium, usually air (although it can also be water or a solid). The molecules of the medium bunch up, then move apart again, as the waves of sound pass through them. This all begins with the vibration of the source of the sound; it bumps into the molecules of the medium surrounding it, pushing those molecules up against other molecules further out, which are then pushed up against the molecules further out yet, and so on.
That’s sound, and as physical phenomena go, it’s pretty straightforward. But you might be surprised by what some scientists are trying to do with it. I know I was when I ran across an article in the online version of England’s Daily Telegraph newspaper detailing some of the work being done around the globe.
For instance, the article says, in one military test, laboratory animals bombarded with high-powered infrasound (very low frequency sound, too low-pitched for humans to hear) suffered internal bleeding and tissue damage. This could eventually lead to sound-based weapons that could incapacitate enemy troops without a single shot being fired.
Fortunately there are more constructive uses being researched. At the Los Alamos National Laboratory, researchers have developed an environmentally friendly engine with no moving parts that is powered by sound waves. The Backhaus-Swift engine is constructed of inexpensive steel pipe and filled with compressed helium. Applying heat to the helium through a heat exchanger at the lower end of the baseball-bat-shaped engine generates intense sound waves within the engine, which can then be used to drive a generator and produce electricity. The Los Alamos inventors think their engine, which would be very cheap to build and, they hope, can be made to work on solar power, could be used in homes, both generating electricity and producing heat.
Another innovative use of sound is to cancel out other sounds. Because sound is a wave, you can cancel it out by creating an opposing wave whose peaks exactly match the valleys of the original sound wave. In Japan, the Public Works Research Institute has unveiled a special wall that cancels out highway and railway noise this way way. It measures the sound waves being generated by traffic and then generates sound waves to cancel them out. Right now, it only reduces traffic noise by about five percent–but it’s an intriguing beginning.
It sounds like magic, but sound waves can also be used to achieve levitation. Yoshiki Hashimoto, a researcher at Tokyo’s Kaijo Corporation, has been able to keep a small silicon wafer hovering one millimetre above the surface of his acoustic levitator, which fires off sound waves that vibrate at 20,000 times per second. By changing the direction and speed of the sound waves, he can move the wafer in any direction.
This could have immediate application in the semiconductor industry. Microchips don’t take well to handling, and the acoustic levitator could move them along an assembly line from station to station while minimizing the possibility for damage.
Of course, there’s also lots of research being done into more traditional uses for sound. At the University of Southampton, in England, they’re working on virtual reality sound to accompany virtual reality displays. In other words, the sound could seem to come from anywhere–behind you, above your head, or to one side–and wouldn’t require headphones. The system uses two loudspeakers placed very close together. This enables the system to cancel out the sound in one or the other of the listener’s ears–the key to providing the illusion of a specific location for a sound.
The necessary signal processing can either be carried out by a computer at the time a recording is made, or built into a special chip that in turn could be installed in TVs, computers and portable stereo systems. Yamaha Corporation is already making chips to implement this system, called Stereo Dipole.
Weapon, energy source, method of transportation or entertainment, sound has become a multipurpose phenomenon.
Sound: it’s not just for hearing any more.
