What term describes the effect observed from a change in electromagnetic coupling as the distance between a test specimen and a probe coil is varied?

The term that describes the effect observed from a change in electromagnetic coupling as the distance between a test specimen and a probe coil is varied is lift-off. This phenomenon refers to the separation distance between the probe coil and the test specimen, which can significantly influence the strength of the electromagnetic coupling.

As the lift-off increases, the electromagnetic field's effectiveness diminishes, leading to a decrease in the induced signal within the probe coil. This is critical in non-destructive testing because it affects the accuracy of measurements and the interpretation of results. Operators must account for lift-off to ensure that they maintain consistent and reliable measurements during inspections.

Understanding lift-off is essential in the electromagnetic testing process as it helps technicians adjust their test configurations for optimal sensitivity and accuracy, making it a pivotal concept in this field.