Attenuation of Electromagnetic Pulse Using High Temperature Superconductor

A high-speed thin-film resistive type fault current limiter (FCL) manufactured from YBCO thin film has been developed. It is designed to protect the front-end of the communication systems from damage due to electromagnetic pulses caused by thunder strikes or unexpected radiations. A 50 Omega coplanar waveguide (CPW), fabricated on an YBCO thin film coated on an MgO or LaAlO₃ substrate up to 3 inch diameter, is used as the FCL. The resistivity of the YBCO central stripe will raise many orders of magnitude in a very short time automatically if the current pulse exceeds the critical current (I_c ) of the superconductor film. We design a meandering pattern to increase the effective length of the CPW, and also the normal state resistance. This FCL design is shown to have a switching time less than 10 ns, and the capability of tackling electromagnetic pulses with very large magnitude. The samples were cooled below 89 K in vacuum by a closed-cycle refrigerator, and tested with pulse-modulated 2 GHz electromagnetic signals of power up to 50 dBm. Our results show an 18 dB power attenuation while the input power exceeds 34~44 dBm at various temperatures slightly below T_c.