Researchers at Duke University’s Department of Electrical and Computer Engineering have created the first material whose ability to capture and emit infrared radiation can be used in a number of applications. This material combines two very recent scientific advances, namely microelectromechanics (MEMS) and metamaterials. These two technologies will contribute to the miniaturization, reduction and empowerment of certain electronic device components.
Applications of Metamaterials
This new technology can be used to optimize the yield of thermophotovoltaic cells by absorbing heat or infrared radiation (IR) instead of the visible spectrum of sunlight, like the more customary photovoltaic cells. With this material, it is also possible to create an efficient system capable of recovering the heat emitted by appliances, particularly in industrial environments using ovens, like the glass industries. It can be used in smaller systems, such as vehicles, where it can harvest and transform heat from the engines into energy to charge the batteries.
What is a Metamaterial?
A metamaterial is an artificial three-dimensional composite material whose periodic architecture is designed “to achieve an optimized combination of two or more responses to a specific excitation“. This type of material is endowed with electromagnetic and mechanical, microscopic and macroscopic properties not found in a natural material. Its mechanical properties have earned it the name of machine material.
The History of Metamaterials
A monoblock motion mechanism made with a metamaterial
The researchers created a metamaterial whose elements function as MEMS. This internal structure allows it to absorb and emit IR waves very effectively. Moreover, the emitted waves follow the shape of a pixelated pattern. The material has a network of 8 × 8 individually controlled pixels, each measuring 120 X 120 microns. It can emit a wide range of IR radiation and make moving images visible at a frequency up to 110 kHz. Scaling the technology will make it possible to create dynamic IR cameras capable of identifying people in a moving crowd.
How do MEMS work?
MEMS are components that have very small mechanical elements whose dimensions can reach sub-micron scales. They can function as actuators or as sensors. MEMS are used, for example, to communicate the orientation of an image by detecting the displacement of a smart phone.
MEMS Operation and Applications
In addition to its ability to operate at ambient temperature, unlike other IR transmitters, this metamaterial allows the range of wavelengths and emitted frequencies to be varied, this modulation being possible because of the geometry of the device and not the chemical nature of the constituent substances.
The material comprises a movable openwork upper layer with tile pattern perforations and a lower metallic sheet coated with a dielectric layer (aluminum oxide). The two layers are connected by eight cantilever arms running along the perimeter.
The top layer is removable and the lower layer is fixed. Electrical voltage applied to the upper layer provides an electrostatic force that activates absorption and IR emissions. The material does not in fact require a heat source to operate. The intensity of the emitted IR waves is modulated depending on the distance separating the two layers. The device absorbs the IR photons and emits them at a high intensity when the two layers touch, and emits less energy when the two layers are separated. The voltage controls the movement of the upper layer as well as the amount of energy emitted. The researchers tested the device by projecting the letter “D” visible through an IR camera.
Using an IR camera, researchers have demonstrated that they can modify the number of IR photons emitted from the surface of the MEMS metamaterial over a range of intensities equivalent to a temperature change of nearly 20 degrees Celsius.
The researchers stressed that they can vary the pattern types of the upper layer metamaterial to create different projections of IR radiation according to the arrangement of the pixels. They are now working on scaling the technology by creating a prototype with more pixels—up to 128 X 128—and by increasing their sizes.
Co-authored by Xinyu Liu and Willie J. Padilla, this study, entitled “Reconfigurable room temperature metamaterial infrared emitter”, was published April 13, 2017 in The Optical Society.