Pulse-Echo Ultrasonic Testing

The pulse-echo technique operates on a simple principle of timing sound waves. A specialized device called a pulser-receiver generates a high-voltage electrical pulse. This pulse is sent to a transducer, which contains a piezoelectric element that vibrates in response, creating a high-frequency ultrasonic wave. This wave propagates through the test material. When it encounters an interface with a different acoustic impedance, such as a crack, void, or the back wall of the material, a portion of the wave’s energy is reflected.

The reflected wave, or echo, travels back to the transducer. The piezoelectric element converts this returning acoustic energy back into an electrical signal. The receiver component of the pulser-receiver amplifies this weak signal. The system’s internal clock measures the precise time elapsed between the initial pulse transmission and the reception of the echo. This is known as the ‘time-of-flight’ (ToF).

Knowing the velocity of sound in the specific material being tested (\(c\)), the distance (\(d\)) to the reflector can be calculated using the formula \(d = (c times ToF) / 2\). The division by two is necessary because the measured time accounts for the sound traveling to the reflector and back again. The results are typically displayed on a screen as an A-scan, which plots signal amplitude versus time, allowing a trained operator to identify the location, size, and orientation of internal flaws.