Ultralow-Metal-Content Epsilon-Mu-Near-Zero Metamaterials for Optically Transparent EMI Shielding

Conventional electromagnetic interference (EMI) shielding films rely on high loadings of conductive materials to achieve strong shielding effectiveness, but this approach inevitably reduces optical transmittance, increases haze, and compromises visual fidelity. Here, we report an optically transparent EMI shielding metamaterial, configured as an array of double-shell hexagonal resonators with symmetric capacitive gaps. The metamaterial, implemented as a single thin Cu layer (300 nm) on bare glass, featured a 0.7% metal filling fraction yet attained an average visible transmittance of 91.2%, practically indistinguishable from that of uncoated glass. Despite this ultralow metal content, the metamaterial-coated glass exhibited moderate EMI shielding, with reflection (∣S₁₁∣²) and transmission (∣S₂₁∣²) levels of −2.1 and −16.1 dB, respectively, at the target microwave frequency of 14.9 GHz. This shielding performance originated from an epsilon-mu-near-zero resonance, as confirmed by extracted permittivity and permeability dispersions. Practical validation is demonstrated by integrating the metamaterial into a commercial radar system, where it completely blocked microwave signal detection. We believe that optically transparent EMI shielding will become crucial for emerging technologies that require visual access through the shielding layer, such as semiconductor inspection platforms and transparent displays.