Development of an Ultrasonic System and Evaluation of Effective Parameters in Ultrasonic Measurement of Agricultural Products

Ultrasonic testing (UT), a nondestructive testing (NDT) method, is under development for quality determination of agricultural products, although it has long been used in the food industry. Determination and measurement of product quality are important in modern agricultural research. Noninvasive/nondestructive quality determination is a novel aspect of the postharvest process in which parameters measured by NDT methods are correlated with product quality. Reviews show that the “through-transmission method” is better than other UT methods for examination of agricultural products. The main parameters of the through-transmission method are wave velocity and attenuation.In this research, a UT system was designed and developed to analyze a signal passing through a product. The system consisted of a set of fabricated pulser/receiver units with ultrasonic transducers, control software and a data acquisition system. The system semi-automatically determined the two important ultrasonic parameters of wave velocity and attenuation coefficient by signal processing. The effect of couplant type, contact force, enveloping, delay line, and sample thickness were investigated using the signal. Several types of fruits and vegetables having differing tissue types (apple, potato, nectarine, banana, carrot, cucumber and quince) were selected for testing. The thicknesses of thesamples were 5cm to 12cm. Results demonstrated that using couplant, enveloping signal, low contact force (5N) and suitable sample thickness, the ultrasonic measurement system could measure ultrasonic parameters effectively at a suitable response speed. The ultrasonic wave was transmitted through most of these products using a pulse signal with 40kHz excited frequency at low power. The precision of the time-of-flight measurement increased with enveloping of the transmitted signal.