3D printed metamaterials offer novel optical properties

Engineers at Tufts University have developed 3D printed metamaterials with microwave or optical properties that are claimed to go beyond what is possible using conventional materials.

According to Tufts, the fabrication methods demonstrate how 3D printing can expand the range of geometric designs and material composites that lead to devices with novel optical properties, including a hemispherical device inspired by the compound eye of a moth that absorbs electromagnetic signals from any direction at selected wavelengths. The research is published in Microsystems & Nanoengineering.

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.

In one 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 at Tufts University's School of Engineering who heads the Nano Lab at Tufts and is corresponding author of the study. "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 utilises stereolithography, which focuses light to polymerize photo-curable resins into the desired shapes. Other 3D printing technologies, such as two photon polymerisation, can provide printing resolution down to 200nm, 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 realised," said Aydin Sadeqi, graduate student in Sankusale's lab at Tufts University School of Engineering and lead author of the study. "There is much more we can do with the current technology, and a vast potential as 3D printing inevitably evolves."

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