This paper presents, for the first time, an absolute linear electromagnetic encoder consisting of a rubber belt with two chains of screen-printed metallic inclusions (rectangular patches). The position, velocity, and direction of the belt (the moving part) is determined by detecting the inclusions when they cross the stator (the static part). The stator is a microstrip line loaded with three complementary split ring resonators (CSRRs), resonant elements exhibiting a resonance frequency perturbed by the presence of inclusions on top of them (contactless). The line is fed by three harmonic signals tuned to the resonance frequencies of the CSRRs. Such signals are generated by a voltage-controlled oscillator (VCO) managed by a microcontroller. The sensed data are retrieved from the pulses contained in the envelope functions of the respective amplitude modulated (AM) signals (caused by the belt motion) generated at the output port of the line. One of the signals provides the absolute belt position, determined by one of the chains, the encoded one. The information relative to the velocity and motion direction is contained in the other AM signals generated by the motion of the other chain, periodic, and thereby, uncoded. The spatial resolution of the system, a figure of merit, is 4 mm. Special emphasis is devoted to the printing process of the belt inclusions.

Hydrogel materials offer many advantages for chemical and biological sensoring due to their response to a small change in their environment with a related change in volume. Several designs have been outlined in the literature in the specific field of hydrogel-based optical sensors, reporting a large number of steps for their fabrication. In this work we present a three-dimensional, hydrogel-based sensor the structure of which is fabricated in a single step using thermal nanoimprint lithography. The sensor is based on a waveguide with a grating readout section. A specific hydrogel formulation, based on a combination of PEGDMA (Poly(Ethylene Glycol DiMethAcrylate)), NIPAAm (N-IsoPropylAcrylAmide), and AA (Acrylic Acid), was developed. This stimulus-responsive hydrogel is sensitive to pH and to water. Moreover, the hydrogel has been modified to be suitable for fabrication by thermal nanoimprint lithography. Once stimulated, the hydrogel-based sensor changes its topography, which is characterised physically by AFM and SEM, and optically using a specific optical set-up.

In this paper, a complete system useful for the measurement of the absolute position, velocity, and acceleration of moving objects in industrial scenarios (such as conveyor transport devices, elevators, escalators, and other mechanical systems) is presented. The proposed system contains an electromagnetic encoder consisting of a pair of chains of metallic patches screen-printed on a rubber belt. In one of the chains (designated as clock/velocity chain), the patches are printed at predefined periodic positions. Such clock chain generates also the clock signal necessary to read the other chain (position chain), with patches either present (binary state ‘1’) or absent (binary state ‘0’) at their predefined positions. The system includes a reader based on a transmission line with three resonators etched on the ground plane and fed with three harmonic signals. Such three elements are complementary split ring resonators (CSRRs), which are sensitive to the presence of patches at short distance on top of them, and therefore they are used to detect the patches as the encoder moves with regard to the reader. By encoder motion, the patches generate three amplitude modulation (AM) signals, providing the velocity (and acceleration), the absolute encoder position, and the motion direction. A prototype system, including the encoder, the reader and the associated electronics is designed, fabricated and validated.