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Three-dimensional frequency selective fabric, based on textile or textile composite materials, is formed by adding another dimension in the longitude along the two-dimensional (2D) plane, and has the characteristics of miniaturization and multi-resonant frequency compared to the traditional 2D frequency selective fabric. In this paper, tunable three-dimensional frequency selective fabric (3D TFSF) forming a U-shaped array is proposed. The U-shaped unit is composed of two velvets and a dipole at the bottom. Through analysis of the physical samples, the geometric model of the 3D TFSF stretched along the x-axis and the y-axis during the stretching process was established. The velvets of the 3D TFSF were studied in both oblique and upright states during stretching. The 3D TFSF has good tunability, while the velvets remain upright when stretched, and it has the characteristics of stable resonance frequency under small strain and adjustable resonance frequency under large strain. By stretching, because the shape and size of the U-shaped conductive units can be changed, the equivalent inductance ( L) and capacitance ( C) of 3D TFSF can change during stretching to realize the tuning of resonant frequency. The 3D TFSF offers more design freedom and possibilities. Significant effects of wave absorption or selective filtering by the periodic structure can be achieved by regulating the structural parameters and material parameters together.

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The development of tunable frequency selective surfaces that can respond to changing electromagnetic environments is a crucial area for the development of intelligent EM devices. In this research paper, a new displacement-type tunable frequency selective fabric (dTFSF) that can adjust its resonant frequency by external force is presented. The dTFSF is constructed by two identical plane frequency selective fabrics that contain periodic arranged cross-shaped conductive units. The resonance frequency of the dTFSF can be changed by displacing the two fabrics relative to each other, causing a change in the shape and size of the conductive units. The displacement is quantitatively related to the resonance frequency, allowing for precise control of the resonance frequency. Particle swarm optimization (PSO) and equivalent circuit analysis were used to obtain the equivalent EM parameters of the dTFSF. Overall, the dTFSF with lightweight and flexible nature making it an ideal candidate for integration into communication devices.

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