Demonstrate the typical ultrasonic flaw detector in transmission mode?

A typical ultrasonic flaw detector into its transmission mode is as demonstrated below.

In this way the transmitting probe is placed within contact with the test piece surface onto one side and an acquiring probe is placed precisely onto the opposite side of the test piece as demonstrated in the figure given above. Both the transmitting probe and obtaining probe are moved together. While there is no defect, the receiving probe receives complete signal and while there is a defect between the transmitter and receiver the amplitude of the received signal is reduced due to partial reflection at the defective area.