Resonant Coupling Effects in a Double-Layer THz Bandpass Filter

Abstract

Cascading similar frequency selective surfaces (FSSs) improves the roll-off rate and frequency selectivity of THz bandpass filters. However, resonant coupling between FSS layers causes anomalous transmission peaks. In this work, we have employed an equivalent circuit model to analyze a double-layer FSS structure with periodic cross apertures at different interlayer spacing. We found that the anomalous peaks can be attributed to the resonant coupling between the upper and lower layer FSSs, and their periodic appearance with changing interlayer spacing is related to the half-wavelength repeatability of the circuit. We have fabricated a double-layer FSS sample using femtosecond laser micromachining and measured it using time-domain THz spectroscopy. The results using the equivalent circuit model agree with the Finite-Difference Time-Domain (FDTD) and experimental results.

Design, simulation and fabrication of a new terahertz cross-shaped metamaterial bandpass filter to obtain a narrow frequency bandwidth

“…An experimental equation has been proposed to calculate terahertz bandpass cross-shaped apertures [1]. Müller et al also proposed the following experimental equation to determine approximate central wavelengths [1][2][3][4][5]:…”

“…Figure 1. Schematic diagram of a THz bandpass filter with a cross-shaped aperture: the parameters L, W, P and T represent the arm length, arm width, period and thickness of the cross structure respectively [ 5 ] Where P is the period, L is the width, and W is the length of the cross-shaped aperture. Those researchers also summarized several experimental equations with different coefficients for L, W and P, as compared to Equation (2).…”

“…Those researchers also summarized several experimental equations with different coefficients for L, W and P, as compared to Equation (2). However, Equation ( 2) has been used more in recent works in which terahertz crossshaped metamaterials are constructed [4][5][6].…”

“…In recent years, researchers have successfully demonstrated that surface structures of appropriate characteristic wavelengths can have extraordinary transmissions in the terahertz field. Those structures have also found applications in such areas as terahertz measurement and imaging [1][2][3][4][5]…”

A double layer FSS filter for sub-THz applications

“…Previously, a double metamaterial layer resonator with semiconductor (GaAs) material has been studied by tuning the distances of the layers, for THz-TDS with an operation frequency of 0.35 THz 32 . Also, a similar study has been conducted on a double layer cross frequency selective surface (FSS) unit cell using only metal material (aluminum), fabricated by femtosecond laser machining, for an operating frequency of 0.55 THz 33 .…”