Homma Haruki, Akram Muhammad Rizwan, Fathnan Ashif Aminulloh, Lee Jiyeon, Christopoulos Christos, Wakatsuchi Hiroki
Department of Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Aichi, 466-8555, Japan.
Electrical and Computer Engineering Department, University of California San Diego, La Jolla, CA, 92093, USA.
Nanophotonics. 2022 Feb 7;11(9):1989-2000. doi: 10.1515/nanoph-2021-0659. eCollection 2022 Apr.
Anisotropic impedance surfaces have been used to control surface wave propagation, which has benefited applications across a variety of fields including radio-frequency (RF) and optical devices, sensing, electromagnetic compatibility, wireless power transfer, and communications. However, the responses of these surfaces are fixed once they are fabricated. Although tunable impedance surfaces have been introduced by utilizing power-dependent nonlinear components, such a tuning mechanism is generally limited to specific applications. Here we propose an additional mechanism to achieve tunable anisotropic impedance surfaces by embedding transient circuits that are controllable via the type of incident waveform. By switching between the open and short states of the circuits, it is possible to separately control the unit-cell impedances in two orthogonal directions, thereby changing from an isotropic impedance surface to an anisotropic impedance surface. Our simulation results show that a short pulse strongly propagates for both and directions at 3 GHz. However, when the waveform changes to a continuous wave, the transmittance for direction is reduced to 26%, although still the transmittance for direction achieves 77%. Therefore, the proposed metasurfaces are capable of guiding a surface wave in a specific direction based on the incident waveform even with the same power level and at the same frequency. Our study paves new avenues regarding the use of surface wave control in applications ranging from wireless communications to sensing and cloaking devices.
各向异性阻抗表面已被用于控制表面波传播，这有益于包括射频（RF）和光学器件、传感、电磁兼容性、无线电力传输及通信在内的各种领域的应用。然而，这些表面一旦制造完成，其响应就固定了。尽管通过利用功率相关的非线性元件引入了可调谐阻抗表面，但这种调谐机制通常仅限于特定应用。在此，我们提出一种额外的机制，通过嵌入可根据入射波形类型进行控制的瞬态电路来实现可调谐各向异性阻抗表面。通过在电路的开路和短路状态之间切换，可以分别控制两个正交方向上的单元胞阻抗，从而从各向同性阻抗表面转变为各向异性阻抗表面。我们的仿真结果表明，在3GHz时，短脉冲在两个方向上都能强烈传播。然而，当波形变为连续波时，方向的透射率降至26%，尽管方向的透射率仍达到77%。因此，即使在相同功率水平和相同频率下，所提出的超表面也能够根据入射波形在特定方向上引导表面波。我们的研究为从无线通信到传感和隐身装置等应用中表面波控制的使用开辟了新途径。
