Improvement in FSS-Based Sensor Sensitivity by Miniaturization Technique

Frequency selective surfaces are a planar array of elements (or unit cells) that, when illuminated externally, have a frequency response that depends on element geometry and spacing, and the dielectric properties and thickness of the substrate. Thus, FSSs are good candidates for wireless sensing for numerous nondestructive testing applications. As sensitivity is an important sensing issue, detection sensitivity of FSS-based sensors can be improved by increasing the number of unit cells within a given (physical) space. This is a result of the fact that more unit cells will contribute to the frequency response within a given physical area (i.e., the illuminating footprint upon the sensor) in addition to smaller inter-element spacing (e.g., higher mutual coupling). Both of these aspects increase the sensitivity of the sensor to geometrical changes, and can be physically realized through implementation of FSS miniaturization techniques. To this end, in this work, two FSS-based sensors have been designed; one of which is the miniaturized version of the other. Measurement results indicate that the miniaturized FSS sensor is more sensitive to geometrical variations.