Abstract
GMR sensors are widely used in many industrial segments such as information technology, automotive, automation and production, and safety applications. Each area requires an adaption of the sensor arrangement in terms of size adaption and alignment with respect to the field source involved. This paper deals with an analysis of geometric sensor parameters and the arrangement of GMR sensors providing a design roadmap for non-destructive testing (NDT) applications. For this purpose we use an analytical model simulating the magnetic flux leakage (MFL) distribution of surface breaking defects and investigate the flux leakage signal as a function of various sensor parameters. Our calculations show both the influence of sensor length and height and that when detecting the magnetic flux leakage of μm sized defects a gradiometer base line of 250 μm leads to a signal strength loss of less than 10% in comparison with a magnetometer response. To validate the simulation results we finally performed measurements with a GMR magnetometer sensor on a test plate with artificial μm-range cracks. The differences between simulation and measurement are below 6%. We report on the routes for a GMR gradiometer design as a basis for the fabrication of NDT-adapted sensor arrays. The results are also helpful for the use of GMR in other application when it comes to measure positions, lengths, angles or electrical currents.
Highlights
Since its discovery in 1988 [1,2] the giant magneto resistance (GMR) effect has been intensively investigated
GMR sensors are prevalent in many different measurement applications such as proximity, position, rotational speed, angle, and electrical current
GMR sensors have been intensively used as magnetic field sensors in magnetic flux leakage (MFL) [6,7] and in eddy current (EC) testing [8–12]
Summary
Since its discovery in 1988 [1,2] the giant magneto resistance (GMR) effect has been intensively investigated. GMR sensors are prevalent in many different measurement applications such as proximity, position, rotational speed, angle, and electrical current They can be miniaturized and their low power consumption is a further promising feature. GMR sensors have been intensively used as magnetic field sensors in magnetic flux leakage (MFL) [6,7] and in eddy current (EC) testing [8–12] Due to their main promising properties-the high field sensitivity and the high spatial resolution- small defects can be quantitatively detected paving the way for automation of the testing process. Most commercially available GMR sensors are not designed for NDT applications They are integrated in encapsulations, resulting in a large, detrimental distance between their active layers and the surface of the component to be tested. We present a comparison of simulated results with measurements carried out using a GMR magnetometer
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