All-dielectric Electromagnetic Encoders based on Permittivity Contrast for Displacement/Velocity Sensors and Chipless-RFID Tags

Electromagnetic encoders exclusively made of a dielectric material are presented in this paper. The proposed encoders consist of a grid (chain) of apertures, which can be arranged circularly (rotary encoders) or linearly (linear encoders) on the considered substrate, a dielectric material. Such encoders can be useful for the measurement of angular or linear displacements and velocities based on pulse counting (similar to optical encoders). Alternatively, the encoder can be used as a near-field chipless-RFID tag based on the presence or absence of apertures at predefined positions in the chain (hence providing an identification code). In both applications, encoder reading is based on the detection of the apertures (pulses) as the encoder moves on top of a dedicated sensing element (reader). In this work, the reader is a microstrip line loaded with a complementary spiral resonator (CSR) etched in the ground plane, and encoder reading is based on the variation of the transmission coefficient caused by encoder motion. Specifically, the notch generated by the CSR shifts up each time an aperture lies on top of the CSR (due to permittivity variation). Thus, the apertures can be detected from the amplitude modulated (AM) signal generated at the output port of the CSR-loaded line, when it is fed by a properly tuned harmonic (interrogation) signal. The main originality of the work is the working principle for encoder reading (permittivity contrast), as well as the lack of metallic elements in the encoder (representing a reduction in fabrication costs).