Absorbing electromagnetic energy without heating

1 min read

Electrical engineers at Duke University have created an electromagnetic metamaterial made without metal. The device's ability to absorb electromagnetic energy without heating has applications in imaging, sensing and lighting.

"Heat propagates fast in metals, which is problematic for thermal imagers," said doctoral student Xinyu Liu. "There are tricks to isolate the metal during fabrication, but that becomes cumbersome and costly."

The researchers claim to have demonstrated the first completely dielectric electromagnetic metamaterial – a surface dimpled with cylinders that is designed to absorb terahertz waves.

While this frequency range sits between infrared waves and microwaves, the approach should be applicable for most of the electromagnetic spectrum, according to the engineers.

The team created its metamaterial with boron-doped silicon. Using computer simulations, they calculated how terahertz waves would interact with cylinders of varying heights and widths.

The researchers then manufactured a prototype consisting of hundreds of these optimised cylinders aligned in rows on a flat surface. Tests showed that the metasurface absorbed 97.5% of the energy produced by waves at 1.011THz.

"People have created these types of devices before, but previous attempts with dielectrics have always been paired with at least some metal," said Professor Willie Padilla. "We still need to optimise the technology, but the path forward to several applications is much easier than with metal-based approaches."

"We can produce a dielectric metasurface designed to emit light, without producing waste heat," Prof Padilla said. "Although we could already do this with metal-based metamaterials, you need to operate at high temperature for the whole thing to work. Dielectric materials have melting points much higher than metals, and we're now trying to move this technology into the infrared to demonstrate a lighting system."