Tensile tests are to be carried out when evaluating the strength of metallic materials. In order to detect small changes in metal cracks or shape, you can measure the AC resistance of sample (called AC potential method).

Turbine flaw detectors used by smelters are a type of device similar to metal detectors that can automatically check for metal body damage.

The metal detector measures the small change in the sensor's transfer function with a lock-in amplifier.