Scientists have developed a new technology involving a new infrared-emitting device that can help us turn waste energy into usable energy.
The work by researchers at Duke University, North Carolina, has been published in The Optical Society’s journal for high impact research, Optica. The new technology effectively paves way for possible improvement of thermophotovoltaics, a type of solar cell that uses infrared light, or heat, rather than the visible light absorbed by traditional solar cells.
For a long time now researchers and scientists around the world have been working towards a practical solution that harvests heat energy found in hot areas, such as around furnaces and kilns used by the glass industry and turn it into usable energy. Scientists explain that as infrared energy emission, or intensity, is controllable, their new technology could provide a tailored way to collect and use energy from waste heat.
The new device is based on metamaterials, synthetic materials that exhibit exotic properties not available from natural materials. Researchers used a metamaterial engineered to absorb and emit infrared wavelengths with very high efficiency. By combining it with the electronically controlled movement available from microelectromechanical systems (MEMS), the researchers created the first metamaterial device with infrared emission properties that can be quickly changed on a pixel-by-pixel basis.
The new infrared-emitting device consists of an 8 × 8 array of individually controllable pixels, each measuring 120 X 120 microns. The team behind the study demonstrated the MEMS metamaterial device by creating a “D” that is visible with an infrared camera.
Researchers report that their infrared emitter can achieve a range of infrared intensities and can display patterns at speeds of up to 110 kHz, or more than 100,000 times per second. Scaling up the technology could allow it to be used to create dynamic infrared patterns for friend or foe identification during combat.
No heat involved
In contrast to methods typically used to achieve variable infrared emission, the new technology emits tunable infrared energies without any change in temperature. Since the material is neither heated nor cooled, the device can be used at room temperature while other methods require high operating temperatures. Although experiments with natural materials have been successful at room-temperature, they are limited to narrow infrared spectral ranges.
The new reconfigurable infrared emitter consists of a movable top layer of patterned metallic metamaterial and a bottom metallic layer that remains stationary. The device absorbs infrared photons and emits them with high efficiency when the two layers are touching but emits less infrared energy when the two layers are apart. An applied voltage controls the movement of the top layer, and the amount of infrared energy emitted depends on the exact voltage applied.
Dynamic infrared emission
Using an infrared camera, the researchers demonstrated that they could dynamically modify the number of infrared photons coming off the surface of the MEMS metamaterial over a range of intensities equivalent to a temperature change of nearly 20 degrees Celsius.
The researchers say that they could modify the metamaterial patterns used in the top layer to create different colored infrared pixels that would be each be tunable in intensity. This could allow the creation of infrared pixels that are similar to the RGB pixels used in a TV. They are now working to scale up the technology by making a device with more pixels — as many as 128 X 128 — and increasing the size of the pixels.