Metafilms promise to shrink electronic devices

Metafilms promise to shrink electronic devices

Thin films made of metamaterial can reduce the size of resonating circuits that generate microwaves

A team of scientists from the National Institute of Standards (NIST) recently showed that thin films made of “metamaterials” — engineering materials that offer a unique combination of electromagnetic properties—can reduce the size of resonating circuits that generate microwaves. With this development, the team hopes to further reduce the size of electronic devices such as mobile phones, radios, and other radio equipment.

NIST researcher have made metafilms of both yttrium iron spheres (bottom, each about 50 mm in diameter) embedded in a matrix, and tiny copper squares etched on a wafer (top). Photo on top courtesy of C. Holloway/NIST;, photo on bottom courtesy of Geoffrey Wheeler/NIST.

The team performed calculations and simulations of two-dimensional surface version, dubbed metafilms, composed of metallic patches or dielectric pucks. The vibrating particles in these metafilms caused electromagnetic energy to behave in unique ways.

The metafilm was placed across the inside center of a resonator—a cavity in which microwaves continuously jump back and forth. The resonant cavities are used to tune microwave systems to radiate or detect specific frequencies. In order to resonate, the cavity must be a least half the wavelength of the desired frequency. As an example, for 1-GHz cell phones, the resonator would need to be about 15 cm long.

Other research teams showed that by filling most of the cavity with bulk metamaterials will reduce the size of the resonators more than the usual limit. The same effect was demonstrated by the NIST group by using a single metafilm, which uses less space and less energy loss.

Basically the metafilm creates an illusion that the resonator is longer than it normally is by shifting the phase of the electromagnetic energy as it passes through the metafilm. This phenomenon occurs due to the metafilm’s scattering particles, which like atoms or molecules in conventional dielectric or magnetic materials, trap electric and magnetic energy locally. The microwaves act to this uneven energy landscape by adjusting their phases to achieve stable resonance conditions inside the cavity.

On the con side, the team claims that smaller resonator size is achieved at the expense of lower Q (quality factor). According to the paper, tradeoffs need to be made in device design in regards to operating frequency, resonator size, and quality factor. For more information, call Laura Ost at 303-497-4880 or e-mail laura.ost@nist.gov.

Christina Nickolas