Whereas the sound is propagated in a rectilinear fashion in homogeneous media, it will reveal interfaces between different materials (e.g. inclusions or defects) by reflection, scattering, or absorption of the sound waves. Ultrasound waves can therefore pinpoint acoustic resistances (impedances) within a sample and therefore errors and irregularities with a very high degree of accuracy.
For instance, if ultrasound waves encounter an air inclusion inside a sample, a very bright contrast associated with a phase inversion will be recorded. Other material defects such as microcracks, inclusions, and delamination can also be shown in the same way at resolutions equivalent to that of a light microscope.
All systems of Analytical Systems GmbH operate using the pulse reflection method, also referred to as the pulse-echo method.
At the heart of our ultrasound microscopes is an ultrasound probe consisting of a special acoustic lens (usually a sapphire crystal in cylindrical form) that is connected to a transducer—a piezoelectric crystal that can consist of different materials depending on the frequency range used.
The piezoelectric element in the transducer converts electrical signals into sound waves. The downstream lens focuses and bundles these as acoustic waves on the specimen under investigation. The de-ionized water serves primarily as a coupling medium to transmits the ultrasound waves to the probe. These sound waves are ultimately reflected by the sample back to the ultrasonic transmitter, where they are evaluated by an analog-digital converter (ADC) and suitable software and presented as a gray-level image.