Ultrasonic Attenuation Measurement by Spectral Ratios Utilizing Signal Processing Techniques

A new approach using signal averaging and signal processing is described for measuring ultrasonic attenuation of compressional (P) and shear (S) waves in highly attenuative (low Q) materials. Broadband ultrasonic pulses in the frequency range of 0.7-1.1 MHz are transmitted through a specimen to be characterized for comparison to a reference with low dissipation. Attenuation is calculated from the ratio of spectral amplitudes which are corrected for diffraction effects. An experimental example is given based upon measurements made on dry polycrystalline sodium chloride (halite or rock salt) from Avery Island, LA. The measured QP of compressional waves is 46 ± 5.5 and QS of shear waves is 12 ± 0.3. This is a through transmission technique which gives results for materials so lossy that multiple echoes cannot be detected.