Abstract
Acoustic impulse response of muskmelons was studied to evaluate their quality. First, linearity and the effects of supporting conditions on the acoustic signals were examined. Secondly we obtained acoustic signals at points which divide the equator of the sample into 24 equal parts. These signals were displayed in a three-dimensional diagram with axes of time, location and sound intensity, and in a two-dimensional map with a gradation of 257 colors. For a more complete visual comprehension, an animation display which shows time changes of the distribution of sound intensity was presented. As a result of these analyses, it became evident that the impulse waveform of acoustic signals induced by impact was transmitted along the surface of the equator with uniform velocity. This transmission velocity became lower as the muskmelon ripened. The lower transmission velocity in the time domain agreed with the lower peak frequency in the frequency domain, both theoretically and practically. Because the wave equation suggests that the transmission velocity depends on the tensile force of the sample, the nondestructive evaluation provides a more direct index of the quality of muskmelons.
