High-Performance Transparent Broadband Microwave Absorbers

The ability to absorb a broad frequency range of microwaves is essential for improving the performance of various electromagnetic interference shielding applications. However, the achievement of broadband microwave absorption with high optical transparency remains a long-standing and unsolved challenge. Here, a simple and powerful method for high-efficiency broadband microwave absorption is presented by introducing strongly overlapped multi-cavity resonances, which is supported by multi-layer structures comprising of alternating graphene/silica pairs and ultrathin silver films. A design guideline for achieving broadband absorption in multi-layer structures is proposed and, more importantly, the complementary effect of different graphene layers on the microwave absorption mechanism is revealed for the first time, providing a new analytical perspective. Experiments show that the absorption efficiency of the proposed multi-layer structures is near unity (≈100%) at resonant peaks with absorption bandwidths (≥50%) up to ≈30 GHz within the measured range of 32 GHz. In addition, the multi-layer structures exhibit highly visible transmittance ranging from ≈85.8% to 68.0%. The proposed general theoretical framework and physical insights in combination with experimental demonstrations lay the foundation for designing a new type of transparent broadband microwave absorber.