Wireless Pulse Monitoring Using Nonlinear Parity-Time-Symmetric Circuits

Flexible, skin-mounted sensors have broad applications in continuous health monitoring and personalized medicine. To enable their battery-free operation and reduce sensor cost, wireless techniques to remotely read out data from the sensor are desired. A key challenge associated with such wireless readout techniques is the limited sensitivity of the system with respect to a change in the passive circuit parameters (resistance or capacitance), which constrains the range and robustness of the sensor. Here, we show that wireless readout sensitivity of a resistance-based flexible sensor can be enhanced by operating the system near an exceptional point. Using a parity-time-symmetric circuit operating at about 13.56 MHz, we show that because of the occurrence of the exceptional point, our system has a significantly higher sensing coefficient compared to the circuit with the dirac point. In addition, the operating frequency of this circuit can be adjusted, which has a broad application prospect such as in combination with near-field communication. We also show that wireless pulse monitoring can be successfully performed with this circuit.