Monitoring physiological signals during regular life might provide many benefits including early detection of abnormalities and tracking the severities of diseases. A wireless connection between the passive sensor and the scanner eliminates the obtrusive wires, resolves battery‐related issues, and makes it easy‐to‐use. We have previously proposed a wireless resistive analogue passive sensor technique that operates with the help of inductive coupling. The variation of resistive physiological transducer (secondary side) leads to amplitude modulation on the scanner coil (primary side). The design of printed spiral coil (PSC) on printed circuit board, significantly affects the performance of the overall system in terms of sensitivity, the output voltage change as a reflection of the transducer change. To optimize the PSC's profile and maximize the sensitivity, we employ three methods: iterative, analytical, and genetic algorithm (GA). The GA optimized PSCs, as the best result, have been fabricated and the measurement showed a sensitivity of 0.72 mƱ which has 5% (8.8%) deviation from the simulation (theoretical) results. This method can be utilized to design a PSC pair in near‐field applications to transfer amplitude modulation with various sizes and fabrication constraints.

Continuous patient monitoring in the normal daily life can be realized with body-worn wireless and fully passive sensors. We have previously developed and optimized a novel Wireless Resistive Analog Passive (WRAP) sensor technology with inductive link between a secondary Printed Spiral Coil (PSC) attached to the body and a wearable scanner with the primary PSC to continuously monitor physiological signal. The flexible and unobtrusive nature of wireless connection between primary and secondary coils causes the distance and the angle between the PSCs to change in real-life operation that can influence the mutual inductance and alter the sensitivity of the whole system. In this paper, we use COMSOL Multiphysics to simulate the effects of varying PSC separation and angle on the mutual inductance for our 13.56 MHz WRAP sensors. We simulate a pair of optimized coil in the cubic infinite boundaries (for magnetic and electric fields) using mef (magnetic and electric field) physics in a stationary study. The results show a decrease of 82% in coupling factor with increasing the tilting angle from 0° to 60°. The coupling factor decreases with increasing separation and angle (center-to-edge) in a quadratic function basis.

Body-worn battery-less Wireless Resistive Analog Passive (WRAP) sensor can be unobtrusive while collecting physiological data continuously. Inductive connection between a pair of Printed Spiral Coils (PSC) eliminates the intrusive wires. Inductive connection of primary and secondary PSC enabled us to probe the body signals using the inductive link. The primary side voltage is modulated by the sensed body signal at the secondary PSC. The coil physical characteristics influence the sensitivity which is defined as observed voltage changes over the sensor variation. We have previously reported an iterative method to optimize the coil specifications for maximum sensitivity with constrained coil prof ile size by maximizing the power transfer efficiency from primary to secondary. In this study sensitivity is maximized by first, driving an analytical multivariable equation of circuit components and physical characteristics, and then using Genetic Algorithm (GA) to maximize it with considering the size and fabrication constraints. The results are compared to the other methods that shows a higher result in the range of 10 ² comparing to the best alternate methods (sqp). It helps us to detect smaller physiological signals in the noisy environment.

Inductive coupling between two coils is becoming an important technique for wireless power and data transfer in near-field for a variety of applications such as wireless charging and passive (zero-power) sensors. We have previously employed a pair of printed spiral coils (PSC) to collect the physiological signals via our novel Wireless Resistive Analog Passive (WRAP) skin attachable sensors. The pair of PSCs and the circuit components have been optimized to maximize the probed biosignals where the mutual inductance (or coupling factor) was kept constant. However, the coils' relative positions in the wearables can vary in real-life scenarios, which makes the mutual inductance to change, compromising optimal results. To design a system with maximum robustness against these PSC alignment variations, the effects of primary coil size on the coupling factor variability to axial and lateral displacements are studied. We limited the maximum self-inductance to 5 µH and 7 µH for primary and secondary coils, respectively that ensures the results are not affected by the coils' self-inductance variation. Our simulation shows that larger primary coils create magnetic fields with reduced sensitivity to the coupling factor for lateral and axial displacements. The resultant coupling factor behavior indicates robust coil designs for applications where the axial and lateral displacements can occur in real-life.