A method of testing pear fruit firmness with dielectric elastomer actuator excitation

The quality of pear fruits is correlated with their firmness, which is assessed by a firmness index derived from the resonance frequency and mass. Postharvest pear fruits ripen during storage, which affects the firmness. A nondestructive measurement technique is necessary to predict fruit firmness without causing any damage. Thus, this study proposes a vibration experiment technique based on dielectric elastomer actuator (DEA) excitation to determine the resonance frequency of pear fruits without any damage. Therefore, DEAs can be attached directly on fruits with curved surfaces because of their stretchability, light weight, and responsiveness and can be used to transfer the excitation force effectively. For our experiments, thin laminated DEAs were fabricated to obtain sufficient vibration excitation force, and resonance frequencies of the pear fruits were confirmed. Subsequently, the firmness indices of each target fruit were calculated and assessed. Finally, the variations in firmness indices of pear fruits during storage were confirmed, and the effectiveness of the proposed technique was validated.