Design and Simulation of Interdigital Capacitive (IDC) Sensing for Daily Non-Destructive Ripeness Monitoring of Manilkara zapota (Ciku) at Frequencies Below 1 kHz

ASM Sc. J., 21(2), 2026

Published on July 16, 2026

https://doi.org/10.32802/asmscj.2026.1006

Author: Nur Syafikah Najiha Mohd Hanafi, Rafidah Rosman, Kumar Velaiyudam, Anees Abdul Aziz

Abstract

Postharvest handling of tropical fruits requires a reliable and non -destructive method for assessing the degree of ripeness. This paper proposes an IDC sensing technology to address the limitations of the conventional subjective methods used in the Malaysian fruit industry. IDC sensor measures changes in capacitance during fruit ripening based on a correlation between fruit maturity and dielectric properties. Capacitance values are obtained via a voltage divider at 340 Hz, 500 Hz and 1 kHz frequencies and a 10 Vpp supply and then compared with traditional destructive analysis of firmness, Brix and pH. CST Studio Suite was used to simulate four IDC sensor designs to demonstrate their performance. Design 2 (finger length = 11 mm, finger width = 5 mm, finger gap = 2 mm) and Design 4 (finger length = 7 mm, finger width = 5 mm, finger gap = 1 mm) were selected for further study as the best field performance design. Capacitance of Design 4 at 340 Hz was most closely related (R²= 0.9771) to markers of ripeness. The experimental results show that the IDC sensor offers fast and accurate ripeness estimation, 25% more accurate compared to visual inspection. The combination of sensor data and known destructive methods helps to establish firm predictive models. The non-destructive nature of the IDC technique brings great benefit to the preservation, quality and reduction of postharvest waste of fruit.

Keywords: interdigital capacitive sensing, Manilkara zapota, non-destructive, postharvest