ULTRASONIC MEASUREMENTS FOR DETECTING DAMAGE ON AGRICULTURAL PRODUCTS (BRUISE, NONDESTRUCTIVE)

Scanning electron micrographs showed differences in the tissue macrostructure for unbruised and bruised apple tissue which might be detectable with ultrasonics. Damaged tissue contained fluid in the intercellular spaces, whereas, air occupied these spaces for undamaged tissue. The acoustic impedance and attenuation coefficient for unbruised apple tissue were measured. Apple tissue had a very high acoustic impedance and attenuation coefficient. In addition, to tissue measurements, the acoustic impedance and attenuation properties of the apple periderm were evaluated. The cuticle was a major reason for the high impedance of the periderm. A model demonstrating an ultrasonic technique was developed and tested for distinguishing bruised and unbruised tissue. The number of frequency nulls in the power spectrum of the reflected signal provided a feature for distinguishing the simulated tissue. This technique was applied to intact fruit with and without the cuticle. In comparing undamaged and damaged tissue at the same site, signals reflected from damaged areas did not contain two reflections as described in the model. The only difference was a shift in the maximum frequency. The results on apples indicated that the technique was not as successful as the model