Highly sensitive surface acoustic wave strain sensor for the measurement of tire deformation

We developed a surface acoustic wave (SAW) strain sensor system with high sensitivity for real-time monitoring tire deformation. The SAW sensor utilizes a shear horizontal wave and split interdigital transducer (IDT). After the SAW sensor was attached to the tire specimen, the characteristics of the SAW sensor were investigated using tensile and three-point bending tests, respectively. When external deformation is applied to the SAW sensor, the strain of the piezoelectric substrate changes the distance between the two IDTs and alters the velocity of the propagating SAW, resulting in a change in the center frequency of the SAW sensor. Based on the degree of changes in the center frequency, we can evaluate the extent of the tire deformation. The center frequency linearly decreases by 20 kHz as the tire is strained to 20%. As the tire specimen with SAW sensor was bent upto 2 mm, the center frequency linearly decreased by 25 kHz. The sensitivity and linearity of the SAW strain sensor were measured to be 2.5 kHz/% and 0.97. These results indicate that the developed SAW sensor has excellent sensitivity for external deformation and it is capable of measuring tire deformation.