Non-Contact Ultrasonic Based Stiffness Evaluation System for Tomatoesduring Shelf-Life Storage

摘要

This paper addresses a use of the non-contact ultrasonic based stiffness or firmness measurement technique for tomatoes quality judgment. Here, both the change in received acoustic signal attenuation and its propagation delay due to variation in stiffness of tomatoes are recorded over a time period from fresh to full ripen cycle of tomato. The experimental setup consist of ultrasonic transducer (400EP14D) have center frequency 40 KHz with 1350 typical beam angle, interface circuit to connect with ARM9 processor using the Linux OS with qtopia based GUI for data acquisition and further analysis purpose. The data obtained by the developed system is also transferred to PC using Zigbee wireless network for further processing and training using various pattern recognitions techniques under the developed system software package. A second order nonlinear relationship between the attenuation, propagation delay was observed until the end of shelf life of tomatoes under test. The ARM9 based developed system helps both in linearization and auto calibration of the measured data well as has advantage of multiple sensor connectivity for different analysis like temperature and humidity compensation. The results obtained are also validated using standard Alpha-Mos system consists of 12 gas sensors using odor sensing technique. Thus the developed noncontact ultrasonic based system is cost effective, low power and compact system to differentiate between quality (mature and immature) of tomatoes as well as prediction of different factors like chilling injury, TSWV (tomato spotted wilt virus), sunscald and it can be further applied to other types of fruits where stiffness change is major factor for quality of the fruit.