Ultrasonic testing is preferred widely for the evaluation of material properties. However, ultrasonic signals are highly affected by the characteristics of the piezoelectric transducers employed for the measurements. Since ultrasonic transducers are mostly used to measure the travel time of waves only, their non-flat frequency response does not affect the results. On the other hand, the analyses based on the full-waveform provide more reliable results, as thousands of additional data points in the measured signals are taken into account to determine the material properties (e.g., material damping). To perform such analyses, however, the transfer function of the transducer is required in order to normalize the recorded signals. In this paper, a new calibration approach was proposed to determine the transfer function of the piezo-electric accelerometers that are used beyond their nominal frequency range. A nano-laser vibrometer was utilized to measure the high frequency ultrasonic vibrations generated by the piezoelectric transmitter employed as the excitation source for the accelerometers. The transfer functions of two accelerometers with different nominal frequency ranges were determined for frequencies between 20 and 70 kHz, which were then used to capture the ultrasonic waves on a lightly cemented-sand medium. The original signals and the ones corrected by eliminating the effect of the transfer functions were processed to determine the material damping of the medium. Improvement in the accuracy of the material damping is achieved with the corrected signals compared to the uncorrected ones.
|Number of pages||10|
|Journal||Geotechnical Testing Journal|
|Publication status||Published - 1 Jan 2017|
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