Nonlinear Acoustics, a Technique to Determine Microstructural Changes in Materials

Acoustic Harmonic Generation Measurements for Materials Characterization

“…5, where ~ is plotted as a function of fundamental amplitude. It is common to see ~ values to increase very quickly below a particular level of the fundamental [8,10], as seen in the curves of Fig 5. This artificial increase in ~ is known to be the result of the second hannonic amplitude falling below the noise floor, appearing to remain constant for ever decreasing levels of the fundamental amplitude. From Eq.…”

“…This broadband technique establishes the empirical conversion efficiency for the receiving transducer as a function of frequency and includes the effects of the coupling media, allowing the calculation of absolute displacement amplitudes. Details of the calibration technique have been described elsewhere [7,8]. This contact transducer technique was chosen because sensitivity and signal-to-noise are reasonable and sample preparation is relatively easy, with reasonable results obtained from surfaces prepared by polishing with 600 grit abrasives.…”

Experimental comparison of nonlinear parameters obtained from absolute measurement and relative measurement

“…The calibration was conducted to obtain the transfer function that converts the electrical output of the receiving transducer into displacement amplitude. The transfer function was obtained using the broadband pulse-echo technique [10]. The calibration was conducted only for the 10 MHz transducer that was used as the receiver in the nonlinear measurement.…”

“…Received signal was processed through fast Fourier transform (FFT) to obtain ( ). From the experimental results of calibration and nonlinear measurement, the displacement amplitude spectrum of the current output spectrum ( ) as follows [5], ( ) …”

“…The piezo-electric detection method [5] measures the displacement amplitude using a contact piezo-electric transducer in a roundabout way with the calibration process, which converts a measured electrical current into the acoustic displacement amplitude. This 060007-1 method has the advantage that the signal-to-noise ratio is high, and the measurement result is less affected by surface roughness of the material compared with other methods such as capacitive detection method and laser interferometer method [6,7].…”