Naftali Galili

Determination of fruit and vegetable properties by ultrasonic excitation

ABSTRACT Problems involved in non-desctructive quality determination of fresh food products through sonic and ultrasonic excitation were discussed. An experimental setup for basic measurements of acoustic properties of fruits and vegetables was described. Preliminary tests were made with tissue specimens of some fruit and vegetables; the velocity of wave propagation, the attenuation rate, and the reflection properties of these products were calculated. The results demonstrate the feasibility of low frequency ultrasonic testing of agricultural products.

Detection of fruit firmness by frequency analysis

High-value fresh agricultural products must maintain high quality standards and a predetermined shelf-life. Dynamic excitation and response sensing is an accepted method for the evaluation of fruit’s physical properties, quality, and shelf life. The purpose of the present study was to develop and evaluate a new nondestructive measuring technique of fruit firmness. The technique was based on mechanical impulse excitation, flexible piezoelectric film sensors and an FFT signal analysis method which was used to obtain the fruit’s resonance frequencies. Experiments with different geometrical configurations of the sensing elements, fruit mass, and impulse location were tested on three apple varieties. Results showed the potential of the new method to detect fruit firmness. The findings confirmed previous works on acoustical response of fruits and vegetables. The measuring technique was found to be simple, fast, and repeatable. Additional tests of large sample size and analysis by individual item are needed in order to develop reliable classification algorithms for various fruit species. Due to its simplicity, applications of the new technique may include on-line determination of firmness and shelf-life of fruit and vegetables.

ACOUSTICAL, MECHANICAL, AND QUALITY PARAMETERS OF WINTER-GROWN MELON TISSUE

ABSTRACT Acoustical, mechanical, and quality parameters of ripe winter-grown melons were tested in sample fruit sectors from different depths, and the relationships among them were analyzed. The modulus of elasticity and the tangent modulus of the sample tissues decreased ckastically with the sample depth; the acoustical attenuation of a transmitted pulse, as well as the quality characteristics tested in this study, strongly increased with the depth of the fruit sample. This strong dependence on depth (R = 0.842) indicates the potential for using the attenuation coefficient for the identification of internal fruit quality. Wave propagation velocity was found to be a poor predictor for internal properties of ripe winter grown melons.

Ultrasonic evaluation of some ripening parameters of autumn and winter-grown Galia melons

Abstract Autumn-grown (without internal breakdown) and winter-grown (with internal breakdown) melons were evaluated for firmness, dry weight (DW) and total soluble solids (TSS) content in sample fruit sectors from different depths within the fruit. Acoustical and quality parameters of the samples were tested, and the relationships between them analyzed. In the fruit of both seasons, the DW and TSS showed increasing gradients toward the center of the fruit, although winter-grown fruits had much higher values of the two parameters. The acoustical attenuation of transmitted pulse in ripe wintergrown melons, as well as the DW and TSS characteristics, increased drastically with the depth of the fruit sample. The dependence on depth (R = 0.842) indicates the potential for using the attenuation coefficient to predict internal fruit quality.

3-D Model of sound pressure field in a meridinal section plane of fruit.

A theoretical model was suggested for qualitative evaluation of a sound pressure field in fruit tissue, as affected by ultrasonic probe dimensions and fruit properties. The classic directivity pattern of an ideal fluid model, expressed by Bessel function of the first kind, was extended to include energy dissipation of a real material. The directional characteristics of wave propagation, as influenced by transmitter frequency and diameter, and by fruit properties, were discussed. The model indicates how to select the parameters of the ultrasonic transducer (transducer diameter, frequency and excitation power) to control the magnitude and directivity of the ultrasonic waves in the fruit tissue. The suggested theoretical model represented fairly well the experimental sound wave distribution over the half-cut surface of potato and avocado (R(2)>0.862 and 0.977, respectively); the same theoretical model could not represent the sound wave distribution over a half-cut melon. Results of the study were applied in a new probe design for ultrasonic testing of whole fruit.

Two-dimensional model of a multi-jointed mobile truss system

A two-dimensional simulation model was developed for a multi-jointed mobile truss system. The model takes into account machine and soil parameters, such as maximum power, traction limits and soil rolling resistance. The model was used for the simulation of a multi-variable proportional integral derivative (PID) control method and its effect on the dynamic performance of a cable-drawn tillage system and irrigation machine. The proportional gain was found to be the dominant factor of the control operation. When soil resistance was not neglected or when other external unpredicted forces exist, the integration operator was essential in the control system for proper steady-state operation. The simulated results of the PID control with proper gain were found to be much better than results of field tests with existing on/off and proportional control methods.