Ultra Resolution in Acoustic Imaging of Bulk Microstructure in Solids

AbstractImpulse acoustic visualization of bulk microstructure in solid specimens is performed in the dark-field regime. Dark-field regime images display small details of microstructure and their distribution over the specimen bulk - spatial resolution of the method is derived by efficiency of ultrasonic scattering at small obstacles and sensitivity of an ultrasonic radiation-reception system, but not by the probe radiation wavelength (ultramicroscopic technique). The technique is attractive when efforts are concentrated at revealing presence and location of small bulk microstructure elements (microdefects, particles distribution in composite media and so on). Detailed knowledge of their shape could not be reached with this regime. In the paper theoretical analysis of interaction of probe ultrasonic radiation with diverse types of small inclusions, both acoustically soft and hard, has been done. It was shown ultrasound interaction with soft obstacles is much more effective than it is for hard inclusions. It is the main source of the contrast in acoustic images of the bulk microstructure for diverse types of solids. Performed theoretical assessments have been employed for interpreting acoustic images of bulk microstructure in the graphite-epoxy nanocomposites