What does it mean when a signal is "reflected" in Ultrasonic Testing?

When a signal is labeled as "reflected" in Ultrasonic Testing, it specifically refers to the phenomenon whereby an ultrasonic wave encounters an interface or a flaw within the material being tested. This interaction leads to a portion of the wave being redirected back toward the transducer, where it can be detected and analyzed.

In the context of NDT, interfaces could include boundaries between different materials, such as metal and air, or varying densities within a material, including disbonds, cracks, or inclusions. The reflected signal often provides critical information about the location, size, and nature of these discontinuities. By analyzing the time it takes for the reflection to return and its amplitude, technicians can determine the characteristics of the material and identify any potential defects.

The other options do not accurately describe what happens during the reflection of the ultrasonic signal. While spreading of the wave, decrease in testing power, or successful propagation through the medium are all relevant concepts in ultrasonic testing, they do not specifically relate to the message conveyed when a signal is reflected. The reflection is pivotal to evaluating the integrity of the material and is integral in the overall assessment process during Ultrasonic Testing.