Here's why:

* Pulse: The ultrasonic waves are sent out in short, distinct bursts (pulses).

* Echo: The pulses travel through the material and reflect (echo) back from internal boundaries or defects.

* Receive: The reflected echoes are received by the same transducer that sent the pulses.

By analyzing the time it takes for the echoes to return and the intensity of the echoes, pulse-echo ultrasound can be used to:

* Measure thickness: By measuring the time between the pulse and the echo from the back surface of the material.

* Detect flaws: Flaws like cracks, voids, or inclusions reflect the ultrasound differently than the surrounding material, creating unique echo patterns.

* Characterize materials: The speed of sound and attenuation of ultrasound within a material can provide information about its properties.

Pulse-echo ultrasound is a widely used non-destructive testing (NDT) method in various industries, including manufacturing, construction, and medical diagnostics.