Engineers developed new methods to more efficiently fabricate materials that behave in unusual ways when interacting with microwave energy, with potential implications for telecommunications, GPS, radar, mobile devices, and medical devices. Known as metamaterials, they are sometimes referred to as “impossible materials” because they could, in theory, bend energy around objects to make them appear invisible, concentrate the transmission of energy into focused beams, or have chameleon like abilities to reconfigure their absorption or transmission of different frequency ranges.
The innovation constructs the metamaterials using low-cost inkjet printing, making the method widely accessible and scalable while also providing benefits, such as the ability to be applied to large conformable surfaces or interface with a biological environment. It is also the first demonstration that organic polymers can be used to electrically “tune” the properties of the metamaterials.
Electromagnetic metamaterials and metasurfaces — their two-dimensional counterparts — are composite structures that interact with electromagnetic waves in peculiar ways. The materials are composed of tiny structures — smaller than the wavelengths of the energy they influence — carefully arranged in repeating patterns. The ordered structures display unique wave interaction capabilities that enable the design of unconventional mirrors, lenses, and filters able to either block, enhance, reflect, transmit, or bend waves beyond the possibilities offered by conventional materials.
The engineers fabricated the metamaterials by using conducting polymers as a substrate, then inkjet printing specific patterns of electrodes to create microwave resonators. Resonators are important components used in communications devices that can help filter select frequencies of energy that are either absorbed or transmitted. The printed devices can be electrically tuned to adjust the range of frequencies that the modulators can filter.
Metamaterial devices operating in the microwave spectrum could have widespread applications to telecommunications, GPS, radar, and mobile devices, where metamaterials can significantly boost their signal sensitivity and transmission power. The metamaterials produced in this work could also be applied to medical device communications because the biocompatible nature of the thin film organic polymer could enable the incorporation of enzyme-coupled sensors, while its inherent flexibility could permit devices to be fashioned into conformable surfaces appropriate for use on or in the body.
The tuning strategy relies entirely on thin-film materials that can be processed and deposited through mass-scalable techniques, such as printing and coating, on a variety of substrates. The ability to tune the electrical properties of the substrate polymers enabled the team to operate the devices within a much wider range of microwave energies and up to higher frequencies (5 GHz) than was assumed to be possible with conventional non-metamaterials (<0.1 GHz).
Development of metamaterials for visible light, which has nanometer-scale wavelength, is still in its early stages due to the technical challenges of making tiny arrays of substructures at that scale but metamaterials for microwave energy, which has centimeter-scale wavelengths, are more amenable to the resolution of common fabrication methods.