Electroless Plating on Coiled Algae to Copper Microcoils and Their Terahertz Electromagnetic Wave Absorption

Mass production of Cu microcoils, spring-shaped with ca. 30 μm diameter and 100-200 μm length, was developed by performing a batch surface treatment by electroless plating on mass-cultured coiled algae, Spirulina. The polyurethane sheet containing only 0.76 w/v% of Cu microcoil shows an intense and broad absorption band around 0.35 THz (-38 dB of transmission, 220 GHz of FWHM) over a gently downward-sloping transmission of the polyurethane foam itself. The Cu microcoils work as filler crucial for efficient THz wave absorption around 0.3-0.4 THz, well matched with allocated frequency of the next generation communication.