Abstract
Abstract 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 x and y directions at 3 GHz. However, when the waveform changes to a continuous wave, the transmittance for x direction is reduced to 26%, although still the transmittance for y 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.
Highlights
Surface waves are waves bound with a surface, and they decay exponentially the farther away they are from the surface plane [1]
We propose switchable anisotropic impedance surfaces that can change the direction of surface wave propagation depending on the incident waveform type
We have demonstrated switching mechanisms between an isotropic impedance surface and an anisotropic impedance surface
Summary
Surface waves are waves bound with a surface, and they decay exponentially the farther away they are from the surface plane [1]. By introducing additional lumped elements such as resistors and inductors to control the transient response of incoming signals, a new tunability method based on waveform selectivity was reported [37, 38]. These nonlinear and transient surfaces are called waveform-selective surfaces which can distinguish between pulses and continuous waves. H. Homma et al.: Anisotropic impedance surfaces | 3 the simple power-dependent surface, secondly, the waveform-selective impedance surfaces are designed using four diodes, a resistor, and an inductor in each unit cell; these components are configured as a nonlinear and transient circuit. Such an operation is not possible to realize with current conventional filters or frequency-selective surfaces [43]
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