The Amazing Diversity of Acoustic Energy
Who isn't fascinated by the ability of bats and dolphins to navigate and find food using sound waves? Who isn't marveled by the low-frequency love songs sung by courting whales over miles of open ocean? Or, for that matter, who isn't thrilled to see a 3D sonogram in real time of a human fetus yawning or sucking their thumb at 24 weeks gestational age? "Look---she has your nose Mom!"
I first learned about diagnostic medical sonography when I was a sailor in the 1970s. When I enlisted in the U.S. Navy I had four electronics-based specializations (what the Navy calls ratings) from which to choose. Sonar operator was my first choice and, as luck would have it, after boot camp I was selected to attend sonar school in San Diego, Calif. Since that time, I've been fascinated with the utility of acoustic energy and the wide variety of new applications being discovered all the time.
Sure, we've all seen the submarine movies and heard the "pings" of the surface ship's sonar as it bears down on the killers beneath the surface, and we certainly know the usefulness of sound energy as a diagnostic medical tool. But have you ever stopped to think of how many other uses of acoustic energy there are? It's used for everything from cleaning jewelry to focusing cameras and repelling rodents---simply amazing.
A few years ago I thought my sons were pulling my leg when they said our oldest (14 at the time) had down-loaded a "supersonic ring tone" to his cell phone. In case you haven't heard about it, apparently someone got the great idea that a ring tone in the higher frequencies of the human audible range (somewhere upwards of 16 or 18 kilo Hertz) could be heard by children and teens but not by adults, who progressively lose their ability to hear high frequencies as they age. "Ha ha ha---look at Dad---he can't hear it but we can!" Very funny---just wait, you're turn will come. The idea is that kids could have their cell phones on in classrooms and the unknowing teacher wouldn't know when a student got a call or text message.
Well, the adults are having their turn now. Recently a device was developed that took the same selective hearing concept and turned it against those rotten little bra... I mean rambunctious young adults. The device, called a "Mosquito," emits a high-pitched sound to disperse congregating groups of teenagers. In this case, the high-frequency acoustic energy causes discomfort to the youngsters' ears, which forces them leave the area. Of course us old-timers aren't affected by the noise simply because we can't hear it.
As you might imagine, the reception in the United Kingdom, where the Mosquito is being used with some regularity to curb unruly teen gatherings (an estimated 3,500 are in use) has been mixed. Some shop owners applaud its use since gangs of kids sometimes cause problems for their patrons, and the police like it as a way to disperse kid-crowds. But others, including civil rights activists, are calling for the device to be banned because they say too many people can use it indiscriminately. Other critics say the Mosquito affects all young people and not just those who are causing the problems. Hmmm---I can think of a few occasions when the Mosquito would come in handy in my own home as well as in our usually quiet suburban neighborhood.
Like I said, the variety of new applications for acoustic energy never ceases to amaze me. If you'd like to read more about the Mosquito, read the article at BBC News.