Wireless strain monitoring of tires using electrical capacitance changes with an oscillating circuit

In-service strain monitoring of automobile tires is quite effective to improve reliability of tires and design tools. Conventional strain gages have high stiffness and require lead wires. For those reasons, they are cumbersome for strain measurement of tires. Therefore, a new low cost wireless sensor is required for tires. The present study proposes and experimentally investigates a new wireless strain measurement system using the electric capacitance change of steel-wire reinforced tires. A small CR oscillating circuit is embedded in the tire. Thereby, tire deformation engenders a capacitance change of the tire, which comprises steel wire and rubber. In turn, these changes in capacitance alter the oscillating frequency of the oscillating circuit. Measurement of the oscillating circuit frequency indicates the tire strain wirelessly. A rectangular specimen cut from a truck tire is adopted as a specimen for this study. Finally, feasibility of the proposed system is examined using a commercially available passenger car tire through performing static compression and a dynamic rotation test. Experimental results prove that the method is effective for wireless strain monitoring of tires.