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

Abstract

In-service strain monitoring of tires of automobiles is quite effective for improvingthe reliability of tires and design tools. In a previous study, the authors proposeda 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 tomeasure electrical capacitance changes of tires. A specimen cut from acommercial tire is connected to an oscillator circuit, and the oscillationfrequency changes with the capacitance changes of the tire. This method isvery simple and useful, but it requires a battery to activate the oscillatorcircuit. In the present study, a new passive strain measurement systemutilizing electrical capacitance changes of steel-wire-reinforced tires isproposed and experimentally investigated. The passive wireless strainmonitoring method makes use of the specimen cut from the tire as acondenser of a passive filter circuit. Deformation of the tire causes capacitancechanges of the tire comprised of steel wire and rubber; the change of thecapacitance causes a change of the filtering frequency of a radio wave.Measurement of the frequency of a radio wave passed through the filtercircuit enables us to measure the strain of the tire wirelessly. A rectangularspecimen cut from a commercially available tire is adopted as a specimen.Tension testing is performed and the change of the filtering frequencyis measured during the test. As a result, the method is experimentallyproved to be effective for the passive wireless strain monitoring of tires.