Depending on the shape of the test piece and the purpose of the test, different types of coils can be used. There are usually three types of through-type, probe-type, and insertion-type coils.

Pass-through coils are used to detect tubes, rods, and wires. Its inner diameter is slightly larger than the object to be inspected. When used, the object under inspection passes through the coil at a certain speed. Cracks, inclusions, pits, and other defects can be found.

Probe coils are suitable for local detection of test pieces. During application, the coil is placed on a metal plate, tube, or other parts to check for fatigue cracks on the inner cylinder of the aircraft landing strut and turbine engine blades.

Plug-in coils are also called internal probes. They are placed in the holes of pipes or parts for inner wall inspection. They can be used to check the degree of corrosion of various pipe inner walls. In order to improve the detection sensitivity, the probe-type and plug-in coils are mostly equipped with magnetic cores. The eddy current method is mainly used for the rapid detection of metal pipes, rods, and wires on the production line, as well as the flaw detection, material sorting, and hardness measurement of large quantities of parts such as bearing steel balls and steam valves. It can also be used to measure the thickness of coatings and coatings.