A 2.5-Dimensional Frequency Selective Sensor for Detecting Strain Magnitude and Direction

In the past decade, there have been numerous potential applications for Frequency selective surface (FSS) based sensors. A new 2.5-dimensional (2.5D) FSS sensor design is proposed for strain sensing in this work. The proposed FSS unit cell is composed of multiple metal wires and dielectric layers, and metallic blind via holes are used to connect the metal wires between the different layers. Compared to the conventional single-layer dipole unit cell, the proposed multi-layer FSS structure can significantly reduce the unit cell size. The simulation results show that the FSS sensor's resonance frequency decreases from 14.996 GHz to 14.379 GHz as the horizontal strain increases from 0% to 4%. The FSS sensor's resonance frequency increases from 14.996 GHz to 15.192 GHz as the vertical strain increases from 0% to 4%. The sensitivities of the FSS sensor in the horizontal direction and vertical direction are −15.425 kHz/microstrain and 4.9 kHz/microstrain, respectively. Due to the FSS sensor's resonance frequency shift direction and the value of sensitivity are different in the two strain directions, the magnitude and direction of the strain can be quantitatively detected by the proposed FSS sensor.