Published on Jan 02, 2017
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.
Description of Nanoantenna
Part of the reason is that materials' properties change drastically at high-frequency wavelengths. The researchers studied the behavior of various materials -- including gold, manganese and copper -- under infrared rays and used the resulting data to build computer models of nanoantennas. They found that with the right materials, shape and size, the simulated nanoantennas could harvest up to 92 percent of the energy at infrared wavelengths.
The nanoantennas' ability to absorb infrared radiation makes them promising cooling devices. Since objects give off heat as infrared rays, the nanoantennas could collect those rays and re-emit the energy at harmless wavelengths. Such a system could cool down buildings and computers without the external power source required by air-conditioners and 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, requiring a component called a rectifier to convert the alternating current to direct current. Today's rectifiers can't handle such high frequencies. The 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.
If these technical hurdles can be overcome, nanoantennas have the potential to be a cheaper, more efficient alternative to solar cells.
The nanoantenna, as the normal antenna, receives electromagnetic radiation. But the characteristic thing, nanoantenna receives higher frequency and shorter wavelength. Therefore, it can deal with light (frequency of light higher than frequency of radio wave). In fact, light is defined as the portion of electromagnetic radiation that is visible to the human eye, responsible for the sense of sight.
Visible light has a wavelength in a range from about 380 or 400 nanometres to about 760 or 780 nm, with a frequency range of about 405 THz to 790 THz. It is worthily to mention that electromagnetic radiation has both electric and magnetic field components, which oscillate in phase perpendicular to each other (see figure 1) and perpendicular to the direction of energy propagation. The behavior of EM radiation depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths ( Frequency and wavelength has a versus relation).
When EM radiation interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries.
The nanoantenna consists of three main parts: the ground plane, the optical resonance cavity, and the antenna. The antenna absorbs the electromagnetic wave, the ground plane acts to reflect the light back towards the antenna, and the optical resonance cavity bends and concentrates the light back towards the antenna via the ground plane.