Metafilm shrinks resonant cavity

US researchers have made metafilms of both copper squares etched on a wafer and yttrium iron spheres embedded in a matrix.

The US National Institute of Standards and Technology (NIST) has metamaterial thin films that can reduce the size of microwave resonators.

"Other research groups have shown that filling part of the cavity with bulk metamaterials allows resonators to be shrunk beyond the usual size limit," said NIST. "Our team showed the same effect can be achieved with a single metafilm, which consumes less space, thus allowing for the possibility of smaller resonators."

The organisation goes on to claim that more sophisticated metafilm designs would enhance the effect further, so that in principle resonators could be made as small as desired.

Although NIST is making metafilms - two-dimensional arrays of structures that result in a negative refractive index for particular wavelengths - the NIST predictions are based on calculations and simulations of metallic patch or dielectric puck arrays.

To resonate, a microwave cavity's main dimension must be at least half the wavelength.


The metafilm creates an illusion that the resonator is longer than its physical size by shifting the phase of the electromagnetic energy as it passes through the metafilm, said researcher Chris Holloway explains, as if space were expanded in the middle of the cavity.

This occurs, said NIST, because the metafilm's scattering structures - like atoms or molecules in conventional dielectric or magnetic materials - trap electric and magnetic energy locally. The microwaves respond to this uneven energy landscape by adjusting their phases to achieve stable resonance conditions inside the cavity.

In the debit side, metafilms are predicted to introduce losses which will drop the Q of a device using them.

Researchers from the Universities of Pennsylvania and Colorado participated in the work.