Electromagnetic shielding of Optically-Transparent and Electrically-Insulating ionic solutions

High-tech electronic and communication devices require advanced materials for their protection against electromagnetic interference (EMI). Electrically conductive solid materials, such as metals, are typically employed as EMI shields owing to their high shielding performance caused by their high electronic conductivity. Herein, electrically insulative and ionically conducting aqueous ionic solutions of KBr, NaCl, and CaCl₂ salts are investigated with a focus on their effective EMI shielding performance, which is mechanistically different from that of conventional solid materials. A 5M KBr solution exhibits an optimal EMI shielding effectiveness of 61.3 dB at 5-mm thickness. Debye and Drude theoretical models, which describe polarization of dipolar water molecules and ionic conduction of mobile ions, respectively, are invoked to elucidate the absorption-dominant EMI shielding mechanism of the optically transparent aqueous ionic solutions in X-band (8.2–12.4 GHz) frequency range. Cost-effective aqueous ionic solutions can be used as efficient and lightweight EMI shielding materials providing strong optical transparency in advanced electronic systems.