10-01-2019 | | By Rob Coppinger
A material called a Weyl sonic crystal that can reflect sound or light is expected to aid photonic electronics because it can reflect a beam light back to its source as a mirror image of itself.
This mirror image reflection is called negative refraction. Refraction is when sound or light waves change their direction, being bent, as they travel from one medium to another, for example air and glass. Refraction is used in optics for microscopes and cameras to focus the light to create a clear image. Negative refraction is when this does not happen and instead the light is reflected directly back. One possible application to photonics that has already been proposed is a super lens for a biosensor that uses negative refraction photonic crystals. These superlensing properties could provide images in dimensions at the nano and micro scale.
Dr. Fan Zhang, assistant professor of physics at the University of Texas at Dallas, said: “This new knowledge could open up some important applications not only in acoustics but also in photonics and electronics.”
Negative refraction does not occur in nature, so researchers have to engineer artificial substances that have its characteristics, and these are considered a metamaterial. Metamaterials are a class of materials engineered to produce properties that do not occur in nature. The Weyl sonic crystal that has the negative refraction properties was made by the UT Dallas physicists using 3D printing. Between Zhang and his fellow researchers at Wuhan University in China they were able to print a Weyl sonic crystal that is a cube about the size of a desktop computer. “To test our theory, we created an artificial crystal that is structurally simple and can be fabricated by a 3D printer,” Zhang said.
The cube was made from 3D-printed polymer rectangular rods that are stacked in layers, which the researchers describe as a, “woodpile configuration”. Each layer consisted of several rods placed parallel to each other but offset by 120 degrees from the layer beneath it. This cube is for sound, not light, and the researchers transmitted sound towards the surface. Microphones inserted inside the structure mapped how the sound wave was dispersed as it travelled along different facets of the negative refraction crystal.
The efforts of the researchers at Wuhan University were supported by China’s National Science Foundation. Zhang’s work received funding from the UT Dallas school of natural sciences and mathematics research enhancement funds and a grant from the United States Army Research Office to explore exotic physics in 2D materials and to develop innovative concepts in electronics.