Frequency Dependent Ultrasound Absorption In Solid Disks Determined By Means Of Radiation Force Based Power Measurements

Two key quantities for material characterization for ultrasound applications are the speed of sound and the frequency dependent acoustic absorption. The two standard approaches to determine the amplitude absorption coefficient either use subsequent rear surface reflections of one sample or multiple samples of the same material but with different thicknesses. Our new approach uses the total temporal averaged ultrasonic power. It is determined using a radiation force balance. The power values of "long" bursts with and without the sample are compared. In this paper we specifically look at when a burst is "long" enough and what this means for the uncertainty of the measurement. Information about the thickness and speed of sound of the sample, as well as the amplitude reflection and transmission coefficients are required a priori and were obtained within the same measurement setup. The effects of half-wave layers on the transmission coefficient are incorporated in the analyzing routines. Determining ultrasound absorption by means of radiation force based power measurements takes advantage of the low uncertainty of the method, but requires an extended time frame for measurement.