Research on damage detection of freeze-dried apples based on terahertz meta-surface

freeze-dried apple damage are among the most common commercial apple products, and detecting damage in freeze-dried apples is a crucial step in ensuring product quality. Terahertz technology, as a safe, non-ionizing, and non-destructive technique, is highly sensitive to structural variations. In this paper, the terahertz time-domain spectroscopy system enhanced by a flexible meta-surface was employed to detect damage in freeze-dried apples. The results showed that terahertz images could clearly distinguish damaged regions from undamaged ones. Moreover, as the degree of damage increases, the THz frequency domain amplitude of the damaged area decreased, and this trend became more pronounced with meta-surface enhancement. By performing nonlinear polynomial fitting on the spectral data, it was found that the normalized amplitudes in both the time and frequency domains of the damaged regions decreased progressively with increasing damage degree. After meta-surface enhancement, the variation rate increased by at least 20.2 %. Therefore, this study not only achieved highly sensitive detection of freeze-dried apple damage but also established a correlation between the damage duration of fresh apples and the damage degree of their freeze-dried counterparts. These findings verify the high sensitivity and reliability of the meta-surface terahertz technology in detecting damage in freeze-dried apples and provide an efficient new approach for agricultural product quality evaluation.