An Optically Transparent Water-Based Metamaterial Absorber for Ultra-Broadband EMI Shielding in Coal Mines.

Electromagnetic interference (EMI) in underground coal mines, generated by large-scale machinery and electronic devices, severely disrupts the operation of sensitive electronics, leading to performance degradation, equipment failure, and significant safety hazards. To address these challenges, we propose an ultra-wideband, ultra-thin, and optically transparent metamaterial absorber (MA) that combines patterned indium tin oxide (ITO) films with a water-filled resin shell. This design, independent of the incident polarization maintains high absorption efficiency over a wide range of incident angles. The absorber achieves over 90% microwave absorption efficiency across an ultra-wide frequency ranging from 0.52 to 40 GHz, corresponding to a remarkable relative bandwidth of 194.9%, with a thickness of only 1/50 of the maximum operating wavelength. Experimental evaluations conducted in a simulated coal mine tunnel environment demonstrate its exceptional EMI shielding performance: the MA effectively stabilized digital tube displays that previously flickered under strong interference and restored normal operation to analog multimeters exhibiting erratic behavior. These results confirm the capability of our absorber to enhance the operational reliability and measurement accuracy of sensitive electronic equipment in high-EMI conditions while preserving optical transparency for real-time visual monitoring. The proposed MA offers a promising solution for robust electromagnetic protection in complex and harsh electromagnetic environments.