A Dual-Layer Reverse-Helical Inductive Wireless Passive Flexible Temperature Sensor Integrated With Ferrite for Bearings Monitoring

A wireless passive flexible sensor has been developed to measure the surface temperature of bearings and transmit wireless signals. The sensor employs a dielectric film sandwiched by a double-layer reverse-helical inductor structure to enhance magnetic field coupling with a ferrite composite material at the bottom of the layers. Both the permittivity of the dielectric material and the permeability of the ferrite demonstrate temperature-sensitive characteristics. This configuration establishes a synergistic mechanism that enables both inductance–capacitance (LC) sensitive to the change in temperature simultaneously. The ferrite substrate effectively prevents the spiral inductor antenna from electromagnetic absorption caused by metallic components. The type of dual-layer reverse-helical inductive wireless passive sensor enables efficient wireless transmission in a metallic environment. The sensitivity of this configuration can reach 237.34 kHz/°C with the maximal coupling distance extending to 21 mm. The exceptional stability of the resonant frequency of this dual-layer reverse-helical inductive structure was achieved through the mutual inhibition of LC variations when the flexible sensor is subjected to bending on the surface of the bearing. The sensor of composite structure establishes dual-sensitive units and optimizes electromagnetic field coupling, achieving an integrated system with electromagnetically synergistic properties. The integration of ferrite into a dual-layer reverse-helical inductor represents a novel approach to wireless passive sensing technology for temperature monitoring in metallic environments and a wider range of applications.