Bionic Metamaterials with Novel Optical Properties

3D-printed hemispherical metamaterial can absorb microwaves at select frequencies. (Source: H. R. Nejad, Nano Lab, Tufts U.)

A team of engineers at Tufts University has developed a series of 3D printed meta­materials with unique microwave or optical properties that go beyond what is possible using conven­tional optical or electronic materials. The fabrication methods developed by the researchers demon­strate the potential, both present and future, of 3D printing to expand the range of geometric designs and material composites that lead to devices with novel optical properties. In one case, the researchers drew inspi­ration from the compound eye of a moth to create a hemi­spherical device that can absorb electro­magnetic signals from any direction at selected wavelengths.

Meta­materials extend the capa­bilities of conventional materials in devices by making use of geometric features arranged in repeating patterns at scales smaller than the wavelengths of energy being detected or influenced. New develop­ments in 3D printing tech­nology are making it possible to create many more shapes and patterns of metamaterials, and at ever smaller scales. In the study, researchers at the Nano Lab at Tufts describe a hybrid fabri­cation approach using 3D printing, metal coating and etching to create meta­materials with complex geometries and novel func­tionalities for wave­lengths in the microwave range.

For example, they created an array of tiny mushroom shaped structures, each holding a small patterned metal resonator at the top of a stalk. This particular arrange­ment permits microwaves of specific frequencies to be absorbed, depending on the chosen geometry of the mushrooms and their spacing. Use of such meta­materials could be valuable in appli­cations such as sensors in medical diagnosis and as antennas in telecommu­nications or detectors in imaging appli­cations.

Other devices developed by the authors include para­bolic reflectors that selectively absorb and transmit certain frequencies. Such concepts could simplify optical devices by combining the functions of reflection and fil­tering into one unit. “The ability to conso­lidate functions using meta­materials could be incredibly useful,” said Sameer Sonkusale, professor of electrical and computer engi­neering, who heads the Nano Lab at Tufts. “It’s possible that we could use these materials to reduce the size of spectro­meters and other optical measuring devices so they can be designed for portable field study.”

The products of combining optical/electronic patter­ning with 3D fabrication of the underlying substrate are referred to by the authors as meta­materials embedded with geometric optics, or MEGOs. Other shapes, sizes, and orienta­tions of patterned 3D printing can be conceived to create MEGOs that absorb, enhance, reflect or bend waves in ways that would be difficult to achieve with conven­tional fabri­cation methods.

There are a number of tech­nologies now available for 3D printing, and the current study utilizes stereo­lithography, which focuses light to polymerize photo-curable resins into the desired shapes. Other 3D printing technologies, such as two photon poly­merization, can provide printing resolution down to 200 nano­meters, which enables the fabri­cation of even finer meta­materials that can detect and mani­pulate electro­magnetic signals of even smaller wave­lengths, potentially including visible light. “The full potential of 3D printing for MEGOs has not yet been realized,” said Aydin Sadeqi, graduate student in Sankusale’s lab. “There is much more we can do with the current tech­nology, and a vast potential as 3D printing inevitably evolves.” (Source: Tufts U.)

Reference: A. Sadeqi et al.: Three dimensional printing of metamaterial embedded geometrical optics (MEGO), Microsys. & Nanoeng. 5, 16 (2019); DOI: 10.1038/s41378-019-0053-6

Link: Nano Lab, Dept. of Electrical and Computer Engineering, Tufts University, Medford, USA

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