Novel FSS-Based Sensor for Concurrent Temperature and Strain Sensing

Frequency selective surfaces (FSSs) are periodic arrays of conductive elements (or patches). When illuminated with electromagnetic energy, FSSs have specific reflection and/or transmission properties including resonant frequency, Q-factor, etc. Since the FSS response is sensitive to changes in FSS geometry and dielectric properties (local to the FSS), FSS-based sensors have strong potential for a variety of sensing applications including strain and temperature. In this paper, a new FSS-based sensor, capable of concurrent temperature and (unidirectional) strain sensing, is presented. This sensor is based on the cross-loop FSS and includes two different sizes of cross-loop elements. In this way, the FSS sensor response features two different resonant frequencies. In order to utilize changes in one resonant frequency for temperature sensing and changes in the other resonant frequency for strain sensing, each resonant frequency must be affected by only one sensing parameter. This design constrain was accomplished by selective placement of a temperature sensitive dielectric on the larger cross-loop elements, making the lower resonant frequency sensitive to temperature, and through utilizing a properly polarized interrogation signal (with respect to the strain direction) such that the upper resonant frequency is sensitive to strain.