Determination of Acoustic Vibration Modes in Apples

Abstract

Theoretical analysis and experimental measurements were conducted to determine the vibration modes in apples. Comparison of experimental results with theoretical solutions governing the free vibration of an elastic sphere showed that the vibration modes at the three lowest resonant frequencies are the spheroidal modes, denoted by Auld (1973) as S20, S30, and S40. The S20 mode, often called the oblate-prolate mode, has two nodal lines located on the parallels of latitude at q = 54.7 and 125.3. For the S30 mode, there are three nodal lines located at 39.2, 90, and 140.8, and the four nodal lines for the S40 mode are located at 30.6, 70.1109.9, and 149.4.