Electric and magnetic resonances inducing triple-stopband terahertz metamaterial filter

A polarization insensitive triple-stopband terahertz metamaterial filter is proposed. This filter consists of a flexible polyimide substrate and periodically arranged copper structures on its top. The shape of the metal unit is a “田” inside a square ring. The simulation results show that the resonant frequencies of the filter are 0.107, 0.23, and 0.271 THz; the stopband depths are −35.56 dB, −42.7 dB, and −37.485 dB; the 3 dB bandwidths are 34, 53, and 32 GHz; and the relative bandwidths are 31.78%, 23%, and 11.8%, respectively. Effective parameter analysis demonstrates that the first resonance originates from the negative effective permittivity and positive effective permeability, but the reason for the latter two resonances is opposite to the first. The surface current distributions indicate that the first resonance is electric type, while the latter two resonances are the lower and higher orders magnetic resonances, respectively. Then, we verify the triple-stopband characteristic of the filter based on the equivalent circuit. Finally, the analysis reveals that the performance of the filter is independent of the incident polarization angle. This filter has the characteristics of multi-frequency, broadband, deep stopband, polarization insensitivity, and simple structure, which can be used in terahertz communication, detection, and other fields.