Method allows for dual harmonic control in smart surfaces

Tunable reflective metasurfaces provide a way to dynamically control the electromagnetic waves that reflect off them. The surface’s arrangement and phase of atoms can determine the direction and polarization of the reflected wave with precision. Being able to manipulate the meta-atoms in both space and time simultaneously expanded the potential of these surfaces, but only one set of harmonic frequencies could be controlled at a time. Cui et. al, some of the original pioneers of space-time coding metasurfaces, have expanded the potential of this technology by developing and demonstrating a method of controlling two harmonics.

The researchers demonstrated this experimentally, selectively tuning the original phase of the meta-atoms and the time delay between control signals that manipulate the location and phase of the meta-atoms. These two variables affect the reflected light differently depending on its harmonic orders and having two independent variables allows for flexible control of two harmonics simultaneously. They were able to experimentally demonstrate control of arbitrary pairs between the -1^st, 1^st, and 2^nd harmonics of an incident monochromatic wave.

“Our control signal can also control the original phase of the meta-atoms,” said Jun Yan Dai, member of the research team. “That was what we had not considered before, and that was the key.”

Being able to control more than one harmonic with a space-time coding metasurface opens the doors to more advanced sensing and communication technologies, such as radar that adjusts its frequencies based on what it sees and more advanced multiuser wireless communication.

Source: “Arbitrary manipulations of dual harmonics and their wave behaviors based on space-time-coding digital metasurface,” by Jun Yan Dai, Jin Yang, Wankai Tang, Ming Zheng Chen, Jun Chen Ke, Qiang Cheng, Shi Jin, and Tie Jun Cui, Applied Physics Reviews (2020). The article can be accessed at https://doi.org/10.1063/5.0017885 .