What is the term for a test method employing two separate search units on opposite surfaces of the material being tested?

The term for a test method employing two separate search units on opposite surfaces of the material being tested is through-transmission testing. In this technique, one search unit (transmitter) generates ultrasonic waves that travel through the test material, and another search unit (receiver) detects those waves after they have passed through the material. This method is particularly useful for evaluating materials that may have internal flaws or inconsistencies, as it allows for a comprehensive assessment of the material’s characteristics based on how sound waves propagate through it.

Through-transmission testing is distinct from other methods, such as reflection testing, where waves are sent into the material and reflected back to the same surface, and surface testing, which focuses on detecting flaws only on or near the surface of the material. The proper understanding of these methods is critical in NDT applications, particularly in determining the integrity of materials in various engineering contexts.