The internal quality of fruit can be non-invasively tested using systems based on vibrational characteristics. In this work, acoustic impulses were used to detect internal hollows in watermelons; the change in the signal revealing the problem. Frequency spectrum variables were analysed for their potential as non-destructive predictors of this defect. The band magnitude variables, obtained from the integral of the spectrum magnitudes between two frequencies, best predicted internal disorders. Experimental modal analysis was used to investigate the vibrational performance of watermelons and to determine the best positions for the impact point and response measurement microphone. A first-type spherical mode and its resonant frequency was the best indicator of internal quality problems. Finite element modal analysis was performed to establish a watermelon shape/characteristics model and to compare theoretical and experimental results.
Additional key words: acoustic impulse response, experimental modal analysis, non-destructive methods.
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