An electromagnetic test is a class of non-destructive testing used to find defects in an object. Each type of test has a different application and methodology. All tests use electricity or magnetic fields, with some using both. Depending on the specific type of testing used, the amount of electrical current that is reflected, refracted or otherwise conducted through the piece is measured. Changes in the current or magnetic field, as it moves through or around an object being tested, point to possible flaws or defects.
In the past, the term "electromagnetic test" typically referred to eddy-current testing. Eddy-current testing finds defects close to the surface of metal objects. Improvements in testing capabilities, however, have resulted in an ever-expanding number of electromagnetic test options. Other tests such as remote field testing, magnetic flux leakage testing, wire-rope testing and magnetic particle inspection allow users to test for defects in a variety materials, shapes and locations. Using electricity and magnetic fields, each type of electromagnetic test produces a response that points to cracks, heat damage, corrosion or other flaws in a broad range of materials and environments.
Aside from detecting defects, the use of electricity in magnetic fields can also help determine the other unseen properties of metal, earth and soft tissue. Results indicate material thickness, electrical conductivity, the presence of foreign objects and other information. The purpose of any electromagnetic test is to provide the ability to gather information before embarking on expensive or unnecessary digging, dissembling or surgery or to ensure the safety of a manufactured component.
Examples of the many uses of various types of electromagnetic testing can be found in commercial construction and the medical field. For example, pulsed eddy-current testing is used on pipes to determine metal loss without the need to expose the actual pipe. This type of electromagnetic testing can be done from a considerable distance when direct access to the pipe in question is not practical.
When applied to metal storage tanks, airplane fuselages and similar metal containers, an electromagnetic test such as the magnetic flux leakage test can locate interior damage to metal. Such tests employ a magnetic field that passes over the test object, producing different results over areas suffering from corrosion or pitting. Tests of this nature can be performed on a completed airplane, on tanks already mounted for storage or during the manufacturing process.
Although typically used on metal test objects, electromagnetic testing also is useful in medical applications, topographical research and specific niche applications. Magnetic resonance imaging (MRI), for example, is a type of electromagnetic test used to view inside the human body. Ground penetrating radar is a similar electromagnetic testing method used to create a geophysical map of underground areas. Radar can sense buried objects and determine subsurface conditions. Likewise, Barkhausen noise analysis uses a magnetic field combined with noise signals to test ferromagnetic, or naturally magnetic, samples.