A new device eavesdrops on objects to measure their temperatures. Hot objects not only glow, but also softly hum. The hum is generated by the rapid jitters of particles that made-up hot object. If human ears were keen enough to listen to this noise, “it would sound like radio static,” says Tom Purdy of University of Pittsburgh. “The hotter gets (object) , the louder it gets.”
Purdy, along side Robinjeet Singh of University of Maryland in College Park, created an acoustic thermometer that senses the intensity of heat-generated sound emanating from nearby objects. The main of the device may be a one-square-millimeter sheet of silicon nitride. That sheet is suspended within a window cut within the center of a chip , which transmits sound waves better than air.
In experiments, the physicists deposited blobs of an epoxy material on the chip’s surface round the silicon nitride sheet. When heated with a laser, each epoxy blob gave off sound waves that rippled through the chip to the sheet, causing the sheet to vibrate. The warmer the epoxy blob, the stronger its sound waves, and therefore the more intense the silicon nitride’s vibrations.
Bouncing a beam off the sheet & measuring beam’s angle of reflection allowed the researchers to trace the sheet’s motion, and thus the temperatures of the epoxy blobs, Singh & Purdy report in Sept 18 Physical Review Letters.