Electrically conductive tungsten silicide coatings for EMI/RFI shielding of optically transparent windows

Conductive metal mesh coatings on external surfaces of infrared (IR) windows reduce the electromagnetic and radio frequency interference (EMI/RFI) but are mechanically soft and easily damaged. Surface-doped semiconductors, such as gallium arsenide, have optical absorption and emission problems, while semiconducting carbide coatings, such as germanium carbide, suffer performance loss at the low end of the required temperature range. Electrically conductive tungsten silicide have been investigated for use in erosion-resistant EMI/RFI protective coatings for IR windows and radomes. Tungsten silicide films were sputtered on zinc sulphide substrates, electrical properties were evaluated, and shielding effectiveness was measured over 400 MHz to 18 GHz. The relevant results are presented and discussed.