A new thermometer measures temperature with sound

A new device eavesdrops on objects to take their temperatures.

Hot objects not only glow, but also softly hum. The hum is generated by the rapid jitters of particles that make up the hot object. If human ears were keen enough to hear this noise, “it would sound like radio static,” says Tom Purdy of the University of Pittsburgh. “The hotter [an object] gets, the louder it gets.”

Purdy, along with Robinjeet Singh of the University of Maryland in College Park, created an acoustic thermometer that senses the intensity of heat-generated sound emanating from nearby objects. The heart of the device is a one-square-millimeter sheet of silicon nitride. That sheet is suspended within a window cut in the center of a silicon chip, which transmits sound waves better than air.

In experiments, the physicists deposited blobs of an epoxy material on the chip’s surface around the silicon nitride sheet. When

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Seismic sound waves crossing the deep ocean could be a new thermometer

A seismometer on the atoll of Diego Garcia (left) can calculate ocean temperature with earthquakes near Sumatra (right).
Enlarge / A seismometer on the atoll of Diego Garcia (left) can calculate ocean temperature with earthquakes near Sumatra (right).

Geophysics has shown that precise measurements and a little modeling can perform wonders, like showing us the detailed structure of the Earth’s interior despite the fact that it is inaccessibly buried beneath hundreds of kilometers of rock. This is possible because seismic waves produced by earthquakes subtly change velocity or direction as they pass through different materials. A new paper shows that something similar can actually measure small temperature changes in the deep ocean.

An idea to use acoustic waves from man-made sources was actually floated several decades ago but died out after some trials. A team led by Wenbo Wu at the University of Toronto realized that earthquakes could be taken advantage of in the same way, removing the expensive logistics of constantly setting off booms to get

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