Wireless strain monitoring using electrical capacitance change of tire: part II—passive

In-service strain monitoring of tires of automobiles is quite effective for improving the reliability of tires and design tools. In a previous study, the authors proposed a new wireless strain monitoring method that adopts the tire itself as a sensor, with an oscillator circuit. In the method, steel wires are employed as electrodes to measure electrical capacitance changes of tires. A specimen cut from a commercial tire is connected to an oscillator circuit, and the oscillation frequency changes with the capacitance changes of the tire. This method is very simple and useful, but it requires a battery to activate the oscillator circuit. In the present study, a new passive strain measurement system utilizing electrical capacitance changes of steel-wire-reinforced tires is proposed and experimentally investigated. The passive wireless strain monitoring method makes use of the specimen cut from the tire as a condenser of a passive filter circuit. Deformation of the tire causes capacitance changes of the tire comprised of steel wire and rubber; the change of the capacitance causes a change of the filtering frequency of a radio wave. Measurement of the frequency of a radio wave passed through the filter circuit enables us to measure the strain of the tire wirelessly. A rectangular specimen cut from a commercially available tire is adopted as a specimen. Tension testing is performed and the change of the filtering frequency is measured during the test. As a result, the method is experimentally proved to be effective for the passive wireless strain monitoring of tires.