Study On THz Metal Mesh Bandpass Filters

Every unit of metal mesh composed of holes array couples with each other. Free electrons in metal will strongly resonate with incident photons, which results in enhanced transmission. The resonated transmission depends on the structure of metal mesh and incident frequency. Therefore, metal mesh structures are usually used as bandpass filters. However, this type bandpass filter has obvious sidelobes, which are mainly induced by diffraction, F-P effect, and high-order resonance. In this paper a new type metal mesh structure is designed to suppress sidelobes and the fabrication processes are explored.Firstly, a fold-cross shape holes array is designed. Combined with existing theories such as surface plasmon, spoof surface plasmon, Wood anomaly, F-P cavity effect, waveguide effect, etc., the metal mesh structure is analyzed and investigated using FEM simulation. We can know diffraction, F-P effect, and high-order resonance are found to take responsibility for the sidelobe problem. The fold-cross shape holes array we designed is to make the main transmission peak keep away from the sidelobes caused by diffraction as far as possible.Secondly, the fabrication process of substrate-free metal mesh is investigated. A maskless photolithography system based upon DMD (digital mirror devices) is used in this paper. We construct the experimental photolithography system with DMD-based projection. Then we develop the control system for arrays scanning using PI motors. Finally, by the process that nickel electroplating follows photolithography, a small-scale arrays metal mesh is fabricated successfully.