Comparison of Time-Domain and Frequency-Domain Contact Resonant Ultrasound Spectroscopy

Abstract

In this work, two contact resonant ultrasound spectroscopy arrangements, one measuring in the frequency- and the other in the time-domain, are compared. Both set-ups use the same shear wave piezoelectric transducers for excitation and detection. Frequency-scan and acquisition with a lock-in amplifier is used for the frequency-domain measurement. As for the time-domain measurement, narrow square-pulse excitation and oscilloscope signal acquisition are employed. Output-to-input ultrasonic amplitude spectra are obtained with both arrangements for two samples of brass and polymethyl methacrylate. Fits of the more distinctive peaks of the spectra to Lorentzians yields limits of agreement between time- and frequency-domain measurements of the order of 5 × 10^–2 kHz for most of the peaks considered. For brass, the full widths at half maximum of the frequency-domain peaks are of the order of 69 to 85% smaller than those of the corresponding time-domain peaks. For polymethyl methacrylate the differences in full widths at half maximum between corresponding frequency- and time-domain peaks fall into the range of error.