Synchronous Electromagnetic Encoders Based on Step-Impedance Resonators

This article presents a new type of electromagnetic encoders based on step-impedance resonators (SIRs). The encoders consist of a linear chain of transversely oriented SIRs etched on a dielectric substrate, whereas the reader is a simple microstrip transmission line fed by a certain number of single-tone signals, i.e., three in one prototype, and four in another prototype, tuned to specific predefined frequencies. System functionality is based on detecting at which of such predefined frequencies (considering all possible combinations), each SIR of the chain resonates. Thus, the number of combinations (or states) per encoder position (or row) corresponding to the prototype fed with three single-tone signals is seven, whereas it is 15 for the prototype fed with four single-tone signals, corresponding to 2.81 and 3.91 bits, respectively, per encoder row. Although there are other synchronous electromagnetic encoders exhibiting a higher number of bits per row, the number of chains of those encoders is at least two, and the readers are complex microwave structures based on power splitters, contrary to the prototypes reported in this article. Enhancing the number of bits per row in these encoders is a fundamental aspect toward the implementation of true absolute electromagnetic encoders able to determine the position relative to the reader at any instant of time without the need to know the previous stages of encoder motion (a need in the incremental type and in the so-called quasi-absolute encoders).