Formal method for PSC design optimization of 13.56 MHz resistive Wireless Analog Passive Sensors (rWAPS)

Fully passive wireless body-worn sensors that collect physiological signals in natural settings is practical for seamless and unobtrusive monitoring of patients for medical cyber physical systems (CPS). In this regard, we have previously presented a novel Resistive Wireless Analog Passive Sensor (rWAPS), which is fully-passive, fast, low cost, and operates on the near field induction coupling method. Printed spiral coils (PSC) are one of the best solutions for near-field wireless communication for this fully-passive sensor. This paper describes a formal method to implement and optimize PSC coil pairs for such a system. Iterative process is required to reach optimal solutions of this complex multivariate optimization problem. After optimum design based on coil dimension, track size, and number of turns, a coil pair was fabricated on 2-layer PCB. The secondary coil size was restricted to a small footprint of 20mm, while the carrier frequency was selected as 13.56 MHz within ISM frequency band. Evaluation of the measurement from the prototypes and theoretically calculated results were found to be in agreement. This approach of PSC design optimization is practical for its application in our previously reported resistive transducer based wireless analog passive sensors (rWAPS) for body worn and wearable medical CPS.