Evaluation of microwave propagation control by plasma-metamaterial composite using pattern comparison*

Up to now the level of cloaking, which is achieved by installation of metamaterial that is an artificial structure that control permittivity and permeability, is evaluated by observing electromagnetic waves going around a given object and suppression of scattering waves. Following those studies, we aim to visualize the levels of total wave manipulation schemes which includes not only cloaking but also absorption and scattering of waves. In this study, we used plasma that makes its composite with metamaterial more functional, and experimentally investigated this wave manipulation [1]. Changing electron density in the center by adjusting electric power of RF plasma at 27.12 MHz, we controlled spatial gradient of permittivity. And we introduced anisotropic permeability with directional metamaterial composed of split-ring resonators. We launched microwave at 2.89 GHz [1] and evaluated uniformity of detected signals in each case of Ar pressure by installing receiving antenna at each spatial point and scanning transmitting antenna. According to measurement results, the variation of the signals was reduced in comparison with the case in free space as the Ar pressure increased in the range from 50 to 200 Pa. The similar measurements are applicable to level estimation of absorption and scattering. [1] C. Inami et al., J. Appl. Phys 130, 043301 (2021).