A Piezo-Resonator Method for Shear Attenuation Measurement of Rubber

Determination of shear wave attenuation coefficient in rubbers has significance in many applications, for example in non-destructive evaluation of bonding of rubber linings, acoustic absorbing/transparent coatings in air and underwater acoustic devices, shear wave attenuation tissue characterization, etc. Generally an elaborate and expensive acoustic test setup is used for measurement of acoustic properties of rubber and other acoustic materials. In the present work, a piezoelectric resonator method based on bandwidth of a radial mode piezoelectric disc is proposed. Piezoelectric resonators like quartz controlled microbalance (QCM) are well-known for their use in thin film thickness monitor in vacuum coating units based on based on resonance of quartz element. Likewise, quartz oscillator has also been deployed for viscosity determination. The present work describes a radial mode piezoelectric resonator coupled with rubber pads, wherein the radial oscillations excite shear waves into the rubber. The bandwidth of the resonator is related to the penetration depth (attenuation coefficient) of the shear waves. Bandwidth based on data from literature on decay time constant of a damped piezoelectric resonator has been used to compute the shear wave attenuation coefficient in rubbers. A good degree of agreement is observed between the calculated attenuation coefficient and the experimental value from the literature. The proposed method would provide a simple solution to measure shear wave attenuation coefficient in rubbers or other visco-elastic media at discrete frequencies.