Fully Passive Coupling-Robust Wireless 3-D Force Sensor Based on Nonlinear Parity-Time Symmetry

As an essential component of intelligent robots, wearable devices, and so on, 3-D force sensors have seen continuous advancements. However, most existing 3-D force sensors rely on wired readout circuits, limiting the application in narrow spaces or harsh environments, where wired readout circuit is hard to achieve. Recently, parity-time (PT) symmetric theory has been applied to LC passive wireless senser to enhance sensitivity and performance, which holds potential applications in 3-D force sensing. In this work, we propose a fully passive, flexible 3-D force sensor with a coplanar electrode layer and four piezoresistive sensing units, which are made from polydimethylsiloxane (PDMS) doped with multiwalled carbon nanotubes (MWCNTs). Through the design of four channel nonlinear PT symmetric wireless sensing circuit, a coupling-robust sensing distance is achieved in PT symmetric phase, enhancing the robustness of near-field coupling. Additionally, a neural network-based decoupling algorithm is implemented to output the 3-D force. This fully passive wireless 3-D force sensor system demonstrates good applications in the field of smart wearable devices, especially in narrow or enclosed spaces.