Wireless strain monitoring using electrical capacitance change of tire: part I—with oscillating circuit

Strain monitoring of tires of automobiles in service is quite effective to improve the reliability of tires and design tools. Since conventional strain gages have high stiffness and require lead wires, the conventional strain gages are cumbersome for the strain measurement of tires. Sensors of micro-electro-mechanical systems are also usually of high stiffness themselves, and those are not applied to tires. The background requires a new low cost wireless sensor for tires. In the present study, a new strain measurement system utilizing the electric capacitance change of steel wire reinforced tires is proposed and experimentally investigated. A small oscillating circuit is embedded in the tire; deformation of the tire induces a capacitance change of the tire comprising steel wire and rubber; the change of the capacitance makes a change in oscillating frequency of the oscillating circuit. Measurement of the frequency of the oscillating 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. A tension test is performed and the frequency of the oscillating circuit is measured during the test. As a result, the method is experimentally proved to be effective for the wireless strain monitoring of tires.