The touch sensor is made with a polymer substrate between two metal-coated polyethylene terephthalate films. Credit: Vikram Maharshi
A polymer-based touch sensor can detect the ripeness of various fruits during harvest and transportation. The device can discriminate between the firmness of tomatoes at different ripeness levels1.
The sensor could be embedded in a robotic system and used to assess the ripeness of mangoes, kiwis, pears, avocados and sapodillas, say researchers at the Indian Institute of Technology Jodhpur in Rajasthan.
Many existing sensors are complex, expensive and can damage fruit. To devise a better, cheaper sensor, scientists led by Ajay Agarwal used a porous alumina film to make a nanoneedle-patterned polymer substrate. They then made the sensor by placing the polymer substrate between two metal-coated polyethylene terephthalate films.
The team, which included Bhaskar Mitra at the Indian Institute of Technology Delhi and CSIR Central Electronics Engineering Research Institute in Pilani, tested the sensor on four tomatoes at different levels of ripeness. They used a specific machine to mount the sensor on each tomato, which found that their firmness decreased as they ripened.
The researchers also observed a change in the sensor’s capacitance depending on the stiffness of the tomato – a firmer tomato induced a large change in capacitance, whereas a softer tomato caused a smaller change.
The sensor was fabricated without using lithography. It retained stability and performance when exposed to consecutive taps for over 500 cycles. Its sensitivity is higher than sensors based on graphene and carbon nanotube, the researchers say.
