Estimating the age-dependent physical parameters of kiwifruit with non-contact acoustic measurements

We present non-contact acoustic measurements of the mechanical properties of a golden kiwifruit. With a laser source in emission, we measure the transmitted acoustic waves using a rotating laser ultrasound detector with a fibre head. Two main propagating waves are observed; a low-frequency Rayleigh wave, and a high frequency wave which propagates through the outer flesh of the fruit. Theoretical modeling of this second wave enables estimates of the wave velocity in the two outer layers of the fruit flesh, and of several viscoelastic parameters. In particular, we find that both acoustic wave velocities, Young's modulus $E$, and bulk modulus $K$ evolve with fruit age, while the high-frequency wave velocity and $K$ also differ between outer and inner fruit layers.