A Liquid Sensor Based on Frequency Selective Surfaces

Abstract

A novel, simple and easy-to-fabricate liquid sensor using frequency selective surfaces (FSS) is proposed. The new sensor concept is based on modifying the capacitance between adjacent FSS elements when materials of different electrical characteristics are inserted. The change in capacitance produces a change in resonant frequency. The FSS design consists of a 9 x 9 array of square loops on 0.31λ x 0.31λ square unit cells with trenches between the loops. The trenches are filled with liquids under test (LTU). The structure operates at 4.6 GHz without any liquid. When liquids are inserted in the trenches, the resonance frequency varies in relation to the dielectric constant of the liquid. This is observed by measuring the transmission coefficient (S21).Butan-1-ol, ethanol, methanol, propan-2-ol, and Xylene are used to demonstrate the sensing function. A maximum sensitivity of 8.65 % for Xylene was achieved. Further, very low differences were observed between the measured and expected dielectric constant and loss tangent, thus validating the design. The device is inexpensive, compact, and easy to make and scalable for large area operations in liquid detection for microwave sensing applications. This technique has potential applications in reconfigurable FSS.

Bandpass frequency selective surfaces with fast roll-off characteristics

“…Based on the structure, the FSSs commonly employed in millimeter and submillimeter wave bands can be classified into three categories: single-layer [11][12][13][14][15][16], multi-layer [17][18][19][20][21][22], and 3D FSSs [23][24][25][26][27]. Due to the simplicity of production and analysis, single-layer FSSs are widely utilized, particularly in the design of sensors and conformal FSSs [28,29], wireless and satellite communication [30,31], radio telescope systems [12,32], etc. About multi-layer FSSs, because of their compactness and versatility, common design solutions of stacked multi-layer FSSs include coded FSSs [33,34], resonant FSSs [35], and non-resonant FSSs [36][37][38][39].…”

A Review on Through-Wall Communications: Wall Characterization, Applications, Technologies, and Prospects

“…Another technology that can be applied in combination with antennas is frequency selective surfaces (FSSs) [75]- [78]. FSSs are periodic planar structures that consist of metallic surfaces on dielectric substrates [79], [80].…”