Frequency-Coded and Programmable Synchronous Electromagnetic Encoders Based on Linear Strips

This letter presents electromagnetic encoders where encoding is achieved by considering four different inclusions, particularly linear strips of different length, etched at the predefined positions of the encoder chain, and transversely oriented with regard to the chain axis. Since the length of the strips determines their resonance frequencies, it follows that the 2-bits per inclusion, corresponding to the four possible different states (strip lengths), are frequency-coded. Thus, the reader is a microstrip line with a series gap fed by four harmonic (carrier) signals tuned to the resonance frequencies of the four considered encoder strips. By encoder motion over the reader, each carrier signal is amplitude modulated, with envelope functions exhibiting a peak each time a strip of the encoder chain tuned to the resonance frequency of the considered carrier signal crosses the axis of the reader line. The functionality of the system is experimentally validated in this letter. It is also shown that the encoders can be programmed by considering identical strips and by cutting them appropriately, according to the desired code. The proposed encoders are intrinsically synchronous. Such encoders are useful for measuring displacements and velocities, as well as for the implementation of synchronous near-field chipless radiofrequency identification tags with sequential bit reading.