Ultrathin optically transparent metamaterial absorber for broadband microwave invisibility of solar panels

In this paper, we propose an ultrathin optically transparent metamaterial absorber (OTMMA) for broadband microwave invisibility of solar panels. The OTMMA is a multi-layered structure consists of a continuous indium tin oxide (ITO) film layer, a polymethyl methacrylate substrate layer, and an ITO film layer etched with periodic square split resonance rings. Under normal incidence, the OTMMA exhibits more than 90% absorptivity from 7.82 to 17.15 GHz with arbitrary polarization. At oblique incidence, the absorptivity of the OTMMA reaches over 75% for transverse electric polarization when the incident angle is not more than 50 degrees, whereas it is over 80% for transverse magnetic polarization with an incident angle not greater than 75 degrees. An OTMMA sample with a thickness of lambda (0)/11 is fabricated and attached to the surface of a 300 x 300 mm(2) solar panel for measurement. Excellent agreement between the simulated and measured absorptivity verify our design, showing that the OTMMA can achieve 93%-99% absorption of electromagnetic waves in the whole X-band while ensuring the efficient light transmittance of the solar panels.