Modes of Vibration of Spheroids at the First and Second Resonant Frequencies

Abstract

ABSTRACT FRUITS and vegetables of approximately spheroidal shape undergo many resonances when sinusoidally excited over the acoustical range of frequencies. The two lowest resonant frequencies are the most significant in the quality-detection of intact fruits and vegetables. The mode of vibration at the first resonance is characterized by the Kelvin model of the one-degree-of-freedom vibra-tional system. At the second resonance, the intact fruit or vegetable vibrates in the spheroidal mode. Fruits like the apple, peach and nectarine exhibit the same behavior. At the first resonance, the intact fruit oscillates on a spring formed by its skin, and adjacent tissues, at the point of contact with the vibrating table. This fact enables proper measurement of the first resonant fre-quencies for application in the design of vibratory quality sorters.