U.S. Military Looks to Beetles for New Sensors

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"Incoming infrared radiation is absorbed by the outer sphere and absorption causes the sphere to expand a little bit," said Schmitz. "This micromechanical event is measured by the mechanoreceptor and a neuronal signal is generated."

So when a forest goes up in flames, the infrared radiation excites the little sensors, which alert the beetles to an imminent opportunity to mate. The beetles take off urgently for the flames.

Once Schmitz and his colleagues figured out how the sensor on the beetle functions, they started to work on mimicking this natural approach to engineer what they call a photomechanic infrared sensor.

To date the researchers have built a prototype that can detect the heat put off by a human hand or a lit match from a distance of 12 to 16 inches (30 to 40 centimeters).

"Studies indicate that animals have extremely sensitive systems, but progress in reproducing that sensitivity is slower," said DeLong.

The sensors made by Schmitz and colleagues consist of a little metallic disc that acts as the infrared absorber. The metal chosen depends on the wavelength of infrared that is being detected. For example, Teflon is good for detecting heat put off by a human hand. Polyethylene—the common plastic used in grocery bags—is good for detecting the heat of a fire.

The metallic disc is connected to a mechanosensor, which is currently an inexpensive crystal that gives off an electric charge when disturbed by the expanding metal. "We now want to make it much more sensitive," said Schmitz.

The next step will involve the addition of a highly sensitive so-called capacitive sensor that can measure the expansion of just a few nanometers. As well, they hope to make the sensor smaller, making it faster and thus more sensitive.

Schmitz says the applications of this technology are many, including every field of application where other technical infrared sensors are used today.

"That means we could detect infrared radiation emitted from low-temperature infrared sources like animals or humans as well as infrared radiation emitted from very hot surfaces or fires," he said.

Note: Melanophila acuminata beetles are not the only animals equipped with biological receptors capable of detecting infrared sources at even great distances. Scientists are also studying how blood-sucking insects such as mosquitoes detect warm-blooded animals as well as how IR-sensitive snakes find their prey.

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