design, fabrication and testing of exponential horn for measuring ultrasonic attributes of agricultural produce

non-destructive ultrasonic testing is one of the methods utilized to evaluate quality of agricultural produce. transducers used in this method are made for basically industrial applications. since ultrasonic attenuation of waves in agricultural produce is very high, industrial transducers cannot be used in agriculture and needs to be modified. this is done with horns that concentrate energy on a small area at a certain distance from the transducer. in this paper, an exponential horn was designed, fabricated and tested using theoretical and computer-aided methods. results showed that highly sophisticated horns can be designed using computer-aided method with a high accuracy. analysis of the number of elements on the natural frequency of horn proved that the analysis was not precise at the low number of elements. therefore, the number of elements should be increased when natural frequency of horn is almost fixed. the minimum number of elements was obtained to be 300. a comparison between theoretical and computer-aided methods showed a desirable performance of the computer-aided method with an error less than 1% without solving very complicated equations. based on statistical analysis of the data, the effect of produce thickness (potato and carrot) on the velocity of ultrasonic waves in the horned probe was not significant. however, for the un-horned probe, velocity changed significantly with the sample thickness which is not desirable. therefore, horned probe is more suitable for non-destructive ultrasonic tests than the un-horned probe.