Fortunately, this time everything went according to plan... but it doesn't mean that the results are satisfying.
As it turned out, there's no difference between water and USG gel as a couplant. We supposed improved transfer of energy from the probe to the sample in case of using gel, but it doesn't happen. After testing couplants we spent most of the time trying to find the value of attenuation factor for different samples. The result are different than these published in literature (for aluminium and brass or copper). We decided to resign the measurement of mentioned physical quantity. Moreover, the problem of unidentified echoes is still open. We have assumpton that they come from the rear side of probe: the wave propagates through the probe, then it reflects, comes back and enters sample. As a result we observe fake bottom echo behind the correct one. But it's still unconfirmed.
After the consultation with academic teachers, we obtained some useful information concerning ultrasonic testing. Now we need to consider the possibility of producing additional samples with intentionally introduced flaws. It will give us a chance to expand the list of tasks for our exercise.
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