Pulsed fourier-transform ultrasonic

In practice ultrasound is usually propagated through materials in the form of pulses rather than continuous sinusoidal waves. Pulses contain a spectrum of frequencies, and so if they are used to test materials that have frequency dependent properties the measured velocity and attenuation coefficient will be average values. This problem can be overcome by using Fourier Transform analysis of pulses to determine the frequency dependence of the ultrasonic properties. 

Before the tensile test the samples were investigated by ultrasonic transmission measurements as described in Section 25.2. The peak power of the RF-car-rier pulse (again 10-30 cycles, center frequency 2.25 MHz) was swept from 0 up to 3.6 kW and back to zero. The transmitted ultrasonic signal was detected by a broadband receiver probe, recorded, and Fourier-transformed. The dependence of the resulting amplitude and phase spectra on the transmitting pulse power was recorded. Figs. 25.11 and 25.12 show the results obtained for two of the specimens, one with a weak and one with a strong bond of 5.5 and... 

The pnnaide of the novd ultrasonic spectro%opy utilizing a wide-band polymeric transducer and the FFT (fast Fourier transformation) analysis of a single pulse is introduced and its application to various polymraic matenals is reviewed Ultrasonic analysis of mechanical rdaxation processes and phase transitioiis m solid polymers as wdl as practical non-destructive inspection of defects m composite materials are described... 

The modern and realistic approach would be to record digitally and subsequently analyze numerically the ultrasonic pulse by means of Fast Fourier Transformation (FFT). The development of piezoelectric polymer films as wide-band transducers and digital data analysis by computer have enabled this technique to be used easily [9],... 

Ultrasonic correlation analysis in frequency (Fourier transformation of frequency) domain analysis was utilized to measure a thickness of the sample and to image the structure of the material. This technique comprises four processes (1) calculation of the spectrum, (2) division by the power spectrum of a pulse or other component, (3) Fourier transformation into the frequency domain, and (4) analysis and imaging in the frequency domain. Here we obtain much higher resolution in the imaging and thickness measurements by applying the echo analysis developed in earthquake theory [12] and the thickness measurements methods for a thin layer [13,14]. 

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