Experimental evaluation of frequency response and firmness of apples based on an excitation technique using a dielectric elastomer actuator

A vibration experiment technique based on a dielectric elastomer actuator (DEA) excitation for apples is proposed. The characteristics of DEAs such as flexibility, lightweight, large deformation, and a fast response are conducive to vibration applications. Moreover, DEAs composed of soft rubber-like materials should be compatible with diverse objects. They can be applied to structures with curved surfaces and transfer excitation forces effectively. Herein, as an agricultural application, a DEA excitation technique is applied to assess the quality of apples, which have a spherical shape, using quality-related indices. Firmness is a function of the fruit's mass and its second-lowest resonance frequency. To evaluate the frequency responses and firmness of apples, we developed a vibration experiment system and the appropriate DEA composition. Then, the vibration responses of apples were measured by laser Doppler vibrometer (LDV) and evaluated by a spectrum analyzer to obtain the frequency responses. By assessing the firmness index of apples upon storing, we experimentally demonstrate the effectiveness of the proposed measurement technique based on the DEA excitation.