A scanning acoustic microscope works on the principle of propagation and reflection of acoustic waves at interfaces where a change of acoustic impedance (AI = density x velocity) occurs.
It is similar to going to a doctor's office for an ultrasound test. We use the same principle to investigate rocks, concrete, and other man-made materials. The sound wave is propagated through water into the sample. At positions where an impedance (equals velocity times density) change occurs, the sound waves are reflected back. We map distribution of these reflected waves we receive at the sample surface. The map of reflected waves gives us an idea of how impedance changes within our sample.
SAM applications to Petrophysics
is from a paper published in the journal "The Leading Edge".
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This is an acoustic image of a coal sample made at 50 MHz. The left hand image shows dull and bright coal layers. The right hand image shows cleats in coal. The image size is 40 mm x 40 mm.
Some other results (not acoustic microscopy but pulse transmission)