Meta-mirror: Enabling Frequency-Selective Reflection Through Phase -Dispersion Tailoring of a Metasurface

Presently, metasurfaces have enabled full control of the electromagnetic waves thus leading to implementation of numerous applications such as flat lenses based on electromagnetic properties. Going with the current trends, future demand for efficient metasurfaces designs have attracted significant attention of researchers. Among the available metasurfaces, the reflective type, or called meta-mirror, enables full control of the reflected and scattered wavefronts. Unfortunately, for most natural materials, the dispersion characteristics depend on molecules that have little manipulation freedom. This makes it difficult to realize more advanced functions. Existing literature shows several attempts to develop advanced applications based on the dispersion properties of the meta-mirrors. However, existing metasurfaces are often limited by the difficulty of finding suitable meta-atoms with desired dispersion control.

To this note, Nanjing University researchers led by Professor Yijun Feng from the School of Electronic Science and Engineering developed a frequency-selective concept for coding of the meta-mirrors. They showed how to tailor the phase dispersion of the meta-mirror to perform the scattering properties of various frequency bands. Their work is currently published in the journal, Physical Review Applied.

In brief, the research team commenced their experimental work by designing a resonant meta-atom which was used as a binary coding element to achieve the desired in-phase function at the center frequency and out-of-phase function at the sidebands. Next, the meta-atoms in the metasurface were randomly distributed to obtain the back scattering reduction both numerically and experimentally in the two outside bands. Eventually, a comparison between the full-wave simulation and the experimental results were conducted to validate the feasibility of the newly developed meta-mirror.

The authors observed that the developed concept exhibited frequency-selective effects as compared to conventional metasurface designs for scattering reductions. Specifically, it could achieve high-efficient mirror reflection at center frequency window around 10.7 GHz and low diffusive scatterings in two sidebands with a frequency ranging from 7.5-9.5 GHz and 11.6-15 GHz. Additionally, it was worth noting that the functionality of the metasurfaces was not limited only to scattering reduction. In fact, it enabled full control of other wavefronts by simply tailoring the phase dispersion characteristics of the meta-atoms in question.

In summary, the study by Nanjing University scientists presented a combined frequency-selective scattering and specular reflection approach for reflective metasurface that utilizes tailored phase dispersion characteristics. Generally, the achieved frequency-selective scattering effects would advance the development of numerous electromagnetic devices such as the ground planes for antennas with the desired capacity to retain good in-band characteristics and reduce the out-of-band radar cross-section. Furthermore, Professor Yijun Feng and his research team aspire to enhance the impact of the frequency coding metasurface by taking into consideration the active materials.