Diffraction correction in the measurement of ultrasonic attenuation

The ultrasonic attenuation of ductile cast-iron specimens with different dimensions was measured by a pulse-echo system with introduction of a buffer rod between the transducer and the specimen. The amplitude spectra of echo waveforms without and with diffraction (or beam spreading) correction and the power spectra of echo waveforms were used to characterize the ultrasonic attenuation. The results show that the ultrasonic attenuation evaluated from the amplitude spectra of echo waveforms with diffraction correction was independent of both the specimen length and the buffer-rod length in the range of present frequencies. Besides, it was more reliable than the ultrasonic attenuation evaluated from the power spectra of echo waveforms. Therefore, the amplitude spectra of echo waveforms with diffraction correction are preferred for measuring the ultrasonic attenuation.