sonar

A standard home audio speaker converts electrical signals into sound pulses in the air (via a somewhat cumbersome cone). Those sound waves in turn cause tiny variations in air temperature, as waves disrupt surrounding air. So, scientists reasoned, why not create sound waves through those temperature fluctuations themselves?

In 2008 researchers built a loudspeaker from carbon nanotubes that creates sound from this thermoacoustic effect. Now Finnish researchers have created a far more simple thermoacoustic device using tiny aluminum wires suspended over a substrate, opening thermoacoustics to a far broader range of applications.

Imaging an unborn fetus and and spotting a lurking submarine could both become much easier with the world's first acoustic hyperlens. The device manipulates imaging sound waves to provide an eightfold increase in the magnification power of technologies such as ultrasound and sonar.

Today's stealth fighters, such as the F-22 Raptor, may do pretty well in concealing their radar signature, but mathematicians say that a new active cloaking technique could someday generate electromagnetic fields to hide submarines from sonar, or even protect buildings from earthquakes.

This past week we happened to cover both dolphin echolocation and facial recognition. Today comes a report on a study that may bring the two concepts a little closer together. German researchers have devised a computer algorithm which is able to identify plant species using sonar echoes, in the same way bats are able to find fruit and insects. If the technology is one day sufficiently refined, it could ultimately be used for facial recognition.

In the past decade, navies have been roundly criticized for extensively testing active sonar due to its potentially detrimental affect on marine life. Military-grade active sonar sends out a powerfully loud low-frequency signal with a range anywhere from tens to hundreds of miles under water. The effect on whales has been well documented—its akin to you or I standing next to a jet engine without ear protection.

Nobody ever accused the bat of being beautiful. But its ugliest features—its freakishly ornate ears and intricately furrowed mouth—play a key part in the animals uncanny ability to track its prey. The mystery is how.