The first indication that a machine is not working properly is often a strange noise. However, our human hearing is not precise enough to hear all frequencies. We cannot hear all sound waves above 20 Khz. However, even those sounds often indicate a malfunction.
Our ultrasonic measurements record sounds that cannot be perceived by the human ear. Thanks to the directional operation of US sound waves, we can exactly determine the origins of anomalous signals.
Ultrasonic measurements are essential in these cases: