Magnetic field measurements are critical in electromagnetic nondestructive testing (NDT) and evaluation modalities used widely for quality control and failure prevention in several industries. In the application of these techniques, the material under examination is excited electromagnetically, and the response of the interaction between the field and material is monitored and measured. Magnetic fields can be measured using a variety of different sensor technologies, including pick up coils. Each sensor technology has unique properties with respect to sensitivity, range, resolution, bandwidth, cost, and operational environment that make it suitable for different applications. For instance, hall effect sensors have been widely used for measuring magnetic fields in magnetic flux leakage (MFL) methods, where high magnetization levels are applied to saturate magnetic test magnetic (steel) samples, and leakage magnetic flux, due to defects and metal loss, is measured. Magnetic field components measured near the test sample typically contain information about material anomalies that affect electrical conductivity, magnetic permeability, or dielectric permittivity. The magnetoresistive (MR) sensor offers an attractive choice for midrange application in terms of sensitivity, cost, and measurement range. This article focuses on the basics of MR sensors, which are new and promising for obtaining magnetic field measurements for NDT.
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