Experimental demonstration of an electrically tunable broadband coherent perfect absorber based on a graphene-electrolyte-graphene sandwich structure

We propose and experimentally demonstrate the operation of an electrically tunable, broadband coherent perfect absorption (CPA) at microwave frequencies by harnessing the CPA features of a graphene-electrolyte-graphene sandwich structure (GSS). Using both a simplified lumped circuit model and full-wave numerical simulation, it is found that the microwave coherent absorptivity of the GSS can be tuned dynamically from nearly 50% to 100% by changing the Fermi level of the graphene. Strikingly, our simplified lumped circuit model agrees very well with the full-wave numerical model, offering valuable insight into the CPA operation of the device. The angle dependency of coherent absorption in the GSS is further investigated, making suggestions for achieving CPA at wide angles up to 80 degrees. To show the validity and accuracy of our theory and numerical simulations, a GSS prototype is fabricated and measured in a C-band waveguide system. The reasonably good agreement between the experimental and the simulated results confirms that the tunable coherent absorption in GSS can be electrically controlled by changing the Fermi level of the graphene. (C) 2019 Chinese Laser Press