Metasurfaces with actively tunable features are highly demanded for advanced applications in electronic and electromagnetic systems. However, realizing independent dual-tunability remains challenging and requires more efforts. In this paper, we present an active metasurface where the magnitude and frequency of the resonant absorption can be continuously and independently tuned through application of voltage biases. Such a dual-tunability is accomplished at microwave frequencies by combining a varactor-loaded high-impedance surface and a graphene-based sandwich structure. By electrically controlling the Fermi energy of graphene and the capacitance of varactor diodes, we experimentally demonstrate the independent shifting of the working frequency from 3.41 to 4.55 GHz and tuning of the reflection amplitude between −3 and −30 dB, which is in excellent agreement with full-wave numerical simulations. We further employed an equivalent lumped circuit model to elucidate the mechanism of the dual-tunability resulting from the graphene-based sandwich structure and the active high-impedance surface. We speculate that such a dual-tunability scheme can be potentially extended to terahertz and optical regimes by employing different active/dynamical tuning methods and materials integration, thereby enabling a variety of practical applications.

中文翻译：

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具有独立频率和振幅调制的电可调超颖表面

具有主动可调特征的超表面对于电子和电磁系统中的高级应用有很高的要求。但是，实现独立的双可调性仍然具有挑战性，需要更多的努力。在本文中，我们介绍了一个有源超表面，可以通过施加电压偏置来连续且独立地调节谐振吸收的幅度和频率。通过将负载变容二极管的高阻抗表面和基于石墨烯的夹心结构相结合，可以在微波频率上实现这种双重可调性。通过电气控制石墨烯的费米能量和变容二极管的电容，我们通过实验证明了工作频率从3.41到4.55 GHz的独立偏移，以及在-3和-30 dB之间的反射幅度的调整，这与全波数值模拟非常吻合。我们还采用了等效集总电路模型来阐明由基于石墨烯的夹心结构和有源高阻抗表面产生的双可调性机制。我们推测，通过采用不同的主动/动态调谐方法和材料集成，可以将这种双重可调性方案潜在地扩展到太赫兹和光学方案，从而实现各种实际应用。