Hybrid time/phase/frequency domain linear electromagnetic encoders for displacement sensing and near-field chipless-RFID

Hybrid time/phase/frequency domain linear electromagnetic encoders are presented in this paper for the first time. The encoders consist of a linear chain of electric-LC (ELC) resonators etched in a dielectric substrate. Encoding is achieved by phase and frequency modulation simultaneously, namely, by considering different transverse positions and dimensions of the ELC resonators in the chain. The reader is a simple matched microstrip transmission line terminated with a matched load, and encoder reading proceeds by displacing the encoder over the reader line, at short distance, in the direction orthogonal to the line axis. When an ELC resonator lies on top of the line, the phase of the reflection coefficient at resonance depends on the distance to the input port and hence on the transverse position of the resonator in the chain (phase modulation). Moreover, the size of the resonator determines its resonance frequency (frequency modulation). This means that the reader line should be fed by as many harmonic signals as ELC resonator sizes considered, to identify the phase and the resonance frequency of the inclusion (ELC) on top of the line. In this paper, we consider 16 different transverse positions and 4 different sizes of the ELC resonators, which are read sequentially, in a time-division multiplexing scheme. Thus, 6 bits per encoder position (or row) in the chain are achieved. These encoders, with a per-unit-length density of bits of DPL = 6 bit/cm, can be applied to the implementation of synchronous near-field chipless-RFID systems with high data capacity, as well as long-range displacement sensors. In the latter case, the number of bits per encoder row can be doubled (i.e., 12 bits) by considering two chains and two readers, allowing for the discrimination of 212 (= 4096) absolute positions.