The effect of Resonator Configurations on the optimized sensitivity in the Wireless Resistive Analog Passive (WRAP) sensors

Body signal monitoring during normal daily activities requires wireless wearable devices. Furthermore, fully passive body-worn wireless sensors can provide significant advantages by eliminating the need for batteries. With this goal, we have previously proposed a novel Wireless Resistive Analog Passive (WRAP) sensor concept that captures body signals via modulation of carrier signals sent from the primary Planar Spiral Coil (PSC) using the inductive loading principal. Additionally, we reported the optimization methods for the PSC design to maximize the inductive link sensitivity for the wireless signal transmission. A higher efficiency and sensitivity can he achieved when both the primary and secondary circuits are in resonance with the carrier frequency (at 13.56 MHz ISM band in this work). There are four configurations for these resonator arrangement in the primary and secondary circuits according to the series or parallel arrangement of the tuning capacitors, namely: series in primary/secondary (called SS), parallel in primary/secondary (PP), series/parallel in primary/secondary (SP), and vice versa (PS). A Genetic Algorithm (GA) based method is employed to maximize the sensitivity by optimizing the components for each arrangement. It is shown that the PP structure, with the sensitivity of 6.3 M(sic), has the highest sensitivity. Moreover, the susceptibility of PP structure vs primary and secondary self-inductance variations is minimum among the other configurations.