Chipless Dielectric Constant Sensor for Structural Health Testing

A low-cost chipless RFID sensor tag to determine the dielectric properties of materials is presented. The sensor is based on a depolarizing dipole resonator loaded with printed capacitors whose capacitance depends on the permittivity of the material located on contact with the tag. The permittivity is obtained from the shift of the resonance frequency. The resonator is tested both individually as well as placed on a periodic arrangement so as to form a frequency selective structure (FSS) to increase the cross- polar radar cross section, thus facilitating the tag detection. The proposed structure and measurement procedure is particularly suitable for the characterization of civil materials as a nondestructive testing (NDT).