Spectral Shifts of Ultrasonic Propagation: A Study of Theoretical and Experimental Models

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Abstract
The theoretical relationship between center frequency downshift and the spectral bandwidth was investigated for pulses with a sinc (x) spectrum propagating through lossy media. Power law and exponential models for frequency dependence of attenuation were used. Six target materials encompassing a range of attenuation parameters were used to verify the theoretical model. The frequency downshift data from these materials was used to calculate their respective attenuation parameters. It was shown theoretically and verified experimentally that for small frequency downshifts, the sinc (x) model yields the same material parameters as the Gaussian model. The choice of the model for the attenuation of the material was found to be inconsequential.