A Depolarizing Chipless RF Label for Dielectric Permittivity Sensing

A novel depolarizing chipless radio-frequency identification tag is employed to estimate the variation of the dielectric properties of materials. The tag, comprising two 45° tilted dipoles printed on a thin substrate, is accommodated on the top of the target material, and it is interrogated wirelessly at radio frequency with a narrowband signal. Once interrogated, the tag radiates back a frequency-selective response in cross-polarization. The depolarizing property of the tag allows employing it on materials characterized by arbitrary large size, thus avoiding the conceling effect of the large radar echo of the platform. The properties of the target material are estimated by resorting to the amount of frequency shift detected on the backscattered signal. The operation principle of the tag is initially illustrated by using simulations, and then measurements are performed on various materials to show the reliability of the proposed procedure.