Hybrid fabrication technique enhances optical functionality

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Combining 3D printing with metal-coating and wet-etching processes enables metamaterial geometrical optics with unique properties

The geometry of a moth's eye has inspired a 3D printed antenna that absorbs specific microwave frequencies from any direction. Credit: Hojat Nejad

A team of engineers at Tufts University in the United States has produced a series of 3D-printed metamaterials with novel optical properties that cannot be produced using conventional processes. The technique has been used to create metamaterial embedded geometrical optics (MEGO) devices such as a moth-eye-like lens that can absorb electromagnetic signals from any direction at selected wavelengths, in addition to an optical parabolic mirror with both reflecting and filtering functionalities.

The research was released on 8 April in Microsystems & Nanoengineering, published by Springer Nature.

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 developed devices such as 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 and 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 (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 uses stereolithography, which focuses light to polymerise 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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