Nondestructive Evaluation/Nondestructive Testing/Nondestructive Inspection (NDE/NDT/NDI) Sensors—Eddy Current, Ultrasonic, and Acoustic Emission Sensors

Abstract Material state characterization is often performed using nondestructive evaluation (NDE) techniques with an objective to either understand or evaluate the microstructural state of the material or indirectly determine the damage that may have occurred in the material during manufacturing or service. Understanding material state is crucial, since material properties define the material's ability to perform its designed function. A number of nondestructive evaluation/nondestructive testing/nondestructive inspection (NDE/NDT/NDI) sensors are available to measure properties of a material. Basic laws of physics dictate the function of the sensor. This article attempts to explain the physics behind eddy current, ultrasonic, and acoustic emission sensors routinely used in NDI of aircraft structures.