Chipless Image-Based System for Spatial-Frequency Data Encoding

This article discusses a bistatic reading configuration that employs a spatial-frequency encoding strategy to enhance the data encoding capacity in chipless radio frequency identification (RFID) systems. The proposed method allows for the estimation of resonant frequencies associated with each scatterer and the determination of relative resonator positions. The approach relies on an imaging algorithm that evaluates the positions of the resonators by considering a single-frequency point corresponding to the resonant frequency of each scatterer. Consequently, the proposed method does not seek to image the shape of the metal scatterers but rather to locate their positions geometrically for different frequencies. Indeed, once the resonance frequencies have been detected, a geometric representation of the backscattered field is created by limiting the observable frequency band to the resonance frequencies. The use of individual processing with single-frequency steps enables the distinction of the side-by-side gap between resonators, even at resolutions below the conventional image resolution. Furthermore, this method has the capability to differentiate the gap spacing, which can be as small as
${\lambda /8}$
, between resonators operating at different resonance frequencies. This technique significantly increases the coding capacity associated with the chipless tag. A proof of concept (PoC) is evaluated based on loop resonators for identification (ID) purposes. Then, anechoic and real scenario measurements (3-D displacement table and conveyor belt) are considered in different acquisition configurations. An office environment reading range of up to 20 cm has been reported.