Liquid crystal based miniaturized tunable FSS design

Abstract

Reconfigurable FSS is an important research direction of FSS research. The reconfigurable FSS can be changed to a suitable resonant frequency, bandwidth or resonant characteristic according to the changing electromagnetic environment, which has wide application value in many electromagnetic engineering environments. The current reconfigurable FSS design can be roughly classified into mechanical and electronically controlled reconfigurable FSS according to the control method. The liquid crystal-based tunable FSS is a kind of electronically controlled reconfigurable FSS. The equivalent dielectric constant of the liquid crystal changes under the action of the bias voltage, thereby changing the resonance characteristics of the FSS. At present, liquid crystal-based tunable FSS is generally tuned by covering a layer of liquid crystal on the FSS unit. This method uses a large amount of liquid crystal material, and the dielectric loss and material cost are high. In this paper, two miniaturized tunable FSS units are designed by loading a small number of liquid crystal cells. The first structure is based on the Jerusalem cross metal patch and the cross metal slit, and is miniaturized by the fractal of the cross-shaped structure, working in the C-band. The size of the structural unit is equivalent to ten of the working wavelength. In one part, the equivalent dielectric constant of the liquid crystal is changed by changing the voltage between the FSS layers, thereby changing the overall resonance frequency of the unit. The results show that the continuous adjustable range of the resonant frequency is 11.8% (compared to the lower resonant frequency). The second structure is based on a fractal mutual-coupled metal patch, which is miniaturized by loading the lumped element capacitance and inductance, and operates in the X-band. The size of the structural unit is equivalent to one-sixteenth of the operating wavelength. The resonance frequency is also adjusted by changing the voltage between the FSS layers. The results show that the continuous adjustable range of the resonant frequency is 11.5% (compared to the lower resonant frequency). The feasibility and rationality of this loading method are verified by two FSS structural designs, which can achieve tunability with less liquid crystal, reduce dielectric loss and material cost, and provide a new design idea for liquid crystal-based tunable FSS design.