This paper presents a novel method to inspect the levels of vulcanization of natural rubber by ultrasonic testing. In the research, test specimens are natural rubbers of type ‘cis-1,4-polyisoprene’ vulcanized at different durations. Piezoelectric contact transducers were used to transmit and receive ultrasonic to/from each sample. Longitudinal waves at nominal frequency of 2, 2.25 and 5 MHz were used to investigate the samples. Experiments were conducted using two techniques: pulse echo and through transmission. The pulse echo technique was applied to inspect the ultrasonic attenuation and the velocity of longitudinal wave of natural rubber. The through transmission technique was implemented to identify the shape and amplitude of the frequency spectrum. The results from both time and frequency domains can be employed to classify the levels of the vulcanization. From the experiments, this ultrasonic testing provides an effective way to inspect the vulcanization of natural rubber with repeatability and allows faster inspection rate than other methods.

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