High Data Density Absolute Electromagnetic Encoders Based on Hybrid Time/Frequency Domain Encoding

This article presents a novel concept for the implementation of electromagnetic encoders exhibiting very high data density per unit length (DPL), a figure of merit (FoM) of such systems. Encoding is based on a hybrid scheme that exploits both the frequency and time domains. The encoders consist of rows of inclusions (linear strips) of different sizes, periodically arranged to form a chain (with four columns). The bits corresponding to each row are read sequentially in a time-division multiplexing scheme, whereas the size of the inclusions provides frequency encoding. The main relevant aspect of the proposed system concerns the reader, based on a power splitter architecture with either two outputs (prototype A) or four outputs (prototype B). It is shown that the data capacity per row in one of the encoders read through prototype B is 8.78 bits, whereas the data density is as high as DPL = 29.26 bit/cm, an unprecedented value in this type of encoders. The proposed system can be used as a near-field synchronous chipless-radio frequency identification (RFID) system, or as a position and velocity sensor. In the latter case, the system is able to provide the absolute encoder position, provided the number of bits per row (or position) is enough to discern the different number of encoder positions (up to 440 different positions for prototype B, corresponding to the indicated number of bits).