Three-Dimensional Frequency Selective Surface Displacement Sensor Using Complementary Dielectrics

A novel displacement sensor using a frequency-selective surface (FSS) with a removable substrate complement is proposed. The new concept sensor is based on modifying the effective permittivity of the FSS when the substrate complement is gradually withdrawn. The change in the effective permittivity produces a change in capacitance, and thus in the resonant frequency. The FSS consists of an array of square loop elements in a square lattice. A 3-D convoluted version of the FSS sensor improves the angle of incident behavior and increases the displacement range. The dielectric layers of the 3-D FSS sensor were 3-D printed while the metal layers were painted using silver conductive paint. The transmission response, ${S}_{{21}}$ , has been employed as the validation parameter. The proposed sensor operates in a frequency range between 2.0 and 2.8 GHz and has achieved a 0.052 GHz/mm sensitivity and 12 mm dynamic range and has a dimension of 207 mm by 207 mm. The sensor is passive, compact, inexpensive, and easy to operate. The envisaged application is the wireless detection of structural movement, which can be critical in civil structures such as bridges or buildings or earthquake monitoring.