Cellphones and other electronic devices involve the generation of microwaves and the US National Institute of Standards and Technology (NIST) researchers have made “metamaterials” that can reduce the size of resonating circuits that generate microwaves.
The metamaterials or metafilms of tiny copper squares etched on a wafer are manmade composites engineered to offer strange combinations of electromagnetic properties. They are widely known as a possible means of “cloaking” to produce an illusion of invisibility, like the low-reflectivity coatings that help stealth fighter jets evade radar.
In their study, led by Chris Holloway, NIST researchers performed calculations and simulations of two-dimensional surface versions, or “metafilms”, composed of metallic patches or dielectric pucks. Vibrating particles in these metafilms cause incoming electromagnetic energy to behave in unique ways.
The team construed the effects of placing a metafilm across the inside centre of a common type of resonator, a cavity in which microwaves continuously recoil back and forth. Resonant cavities are used to tune microwave systems to radiate or detect specific frequencies.
For resonating, the cavity’s main dimension should be at least half the wavelength of the desired frequency, thus for a mobile phone operating at a frequency of one gigahertz, the resonator would be about 15 cms long. Other research groups have shown that filling part of the cavity with bulk metamaterials allows resonators to be shrunk beyond the usual size limit.
However, NIST researchers showed the same effect can be achieved with a single metafilm, which consumes less space, thus allowing for the possibility of smaller resonators, as well as less energy loss. They mentioned that more sophisticated metafilm designs would enhance the effect further so that, in principle, resonators could be made as small as desired.
Holloway explained that the metafilm creates an illusion that the resonator is longer than its small physical size by shifting the phase of the electromagnetic energy as it passes through the metafilm, as if space were expanded in the middle of the cavity.
This happens because the metafilm’s scattering structures, like atoms or molecules in conventional dielectric or magnetic materials, trap electric and magnetic energy locally.
The researchers also found one of the consequences of using these materials as due to losses in the metafilm, smaller resonators have a lower quality factor, or ability to store energy. Consequently, trade-offs need to be made in device design with respect to operating frequency, resonator size and quality factor, according to the paper.
