Researchers at the US Department of Energy’s Idaho National Laboratory (INL), have devised an inexpensive way to produce plastic sheets containing billions of nanoantennas that collect heat energy generated by the sun and other sources.

While methods to convert the energy into useable electricity still need to be developed, the sheets could one day be manufactured as lightweight ‘skins’ that power everything from hybrid cars to iPods with higher efficiency than traditional solar cells, say the researchers. The nanoantennas also have the potential to act as cooling devices that draw waste heat from buildings or electronics without using electricity.

The nanoantennas target mid-infrared rays, which the Earth continuously radiates as heat after absorbing energy from the sun during the day. In contrast, traditional solar cells can only use visible light, rendering them idle after dark. Infrared radiation is an especially rich energy source because it is also generated by industrial processes such as coal-fired plants.

The nanoantennas are tiny gold squares or spirals set in a specially treated form of polyethylene, a material used in plastic bags. While others have successfully invented antennas that collect energy from lower-frequency regions of the electromagnetic spectrum, such as microwaves, infrared rays have proven more elusive. Part of the reason is that materials’ properties change drastically at high-frequency wavelengths, says INL engineer Dale Kotter.

The nanoantenna’s ability to absorb infrared radition makes them promising cooling devices. Since objects give off heat as infrared rays, the nanoantennas could collect those rays and e0emit the energy at harmless wavelengths. Such a system could cool down buildings and computers without the external power source required by air-conditioners such as fans.

But more technological advances are needed before the nanoantennas can funnel their energy into usable electricity. The infrared rays create alternating currents in the nanoantennas that oscillate trillions of times per second, so a rectifier is needed to convert the alternating current to direct current, but today’s rectifiers can’t handle such high frequencies.

Kotter continued: “We need to design nanorectifiers that go with out nanoantennas”
Kotter calculated that a nanoscale rectifier would need to be about 1,000 times smaller than current commercial devices and will require new manufacturing methods. Another possibility is to develop electrical circuitry that might slow down the current to usable frequencies.

According to the researchers, of these technical hurdles can be overcome, nanoantennas have the potential to be a cheaper more efficient alternative to solar cells.