The Influence of Microcracking Degree of Feldspars on the Spectral Power of Backscattered Broadband Pulses of Longitudinal Ultrasonic Waves

In this work, we study the influence of microcracks in laboratory samples of feldspars on the spectral power of broadband pulses of longitudinal ultrasonic waves backscattered in a studied sample (so-called “structural noise power”). An optoacoustic transducer is used for this purpose, which combines laser excitation of probe broadband ultrasonic pulses in a black polyethylene film and piezoelectric detection of both probe pulses and those scattered in the sample. The orthoclase and plagioclase samples with the zones of the microcrack agglomerations nonuniformly distributed over the sample volume are studied. These zones were found using optical microscopy of the sample surface, as well as using the data of measurements of the attenuation coefficient of longitudinal ultrasonic waves in the 1–15 MHz frequency range. The zones with a higher ultrasonic attenuation exhibited an increased structural noise power. The revealed correlation between the concentration of microcracks and the structural noise power can serve as a basis for the development of a technique of nondestructive optoacoustic monitoring of the occurrence and evolution of local microcracks in samples of rocks and minerals under various external loadings.