Abstract
Strain gauges and optical methods are commonly used to measure the magnetostriction coefficient of a sample. All these methods require a specific size sample and can only realize offline measurement, which is time-consuming. Therefore, we propose a new method using a magnetostriction-based electromagnetic acoustic transducer (EMAT) to measure the magnetostriction coefficient. The amplitude of the ultrasonic waves generated by the EMAT is applied to characterize the magnetostriction coefficient of a sample. A nonlinear magnetostriction finite element model is established, and the simulation results show that the amplitude of the ultrasonic wave generated by the magnetostriction-based EMAT is proportional to the magnetostriction coefficient of the material. Experiments are carried out on silicon steel strips with different silicon contents. The results show that the method can effectively measure their relative magnetostriction coefficients. Furthermore, the structure of the magnetostriction-based EMAT is optimized to maximize efficiency. The excitation and receiving transducers reach their maximum efficiency when the static magnetic flux densities are 3.5 mT and 6.8 mT, respectively. Moreover, the relative error caused by the vibration reaches the minimal size when the lift-off of the receiving coil is set to 3 mm around. This method is fast and can be applied to online measurement.
Highlights
It is always desirable to keep the magnetostriction coefficient of electrical steel as low as possible to reduce the operating noise of the transformer or motor [1]
The results reveal that the relative error rises with the increment of the vibration amplitude
A 2-D nonlinear magnetostriction finite element model was established to simulate the Lamb S0 waves generated by magnetostriction-based electromagnetic acoustic transducer (EMAT) in silicon steel strips with different magnetostriction coefficients
Summary
It is always desirable to keep the magnetostriction coefficient of electrical steel as low as possible to reduce the operating noise of the transformer or motor [1]. The magnetostriction coefficient of electrical steel can be reduced by increasing the silicon content [2]. It is usually necessary to sample and measure their products to ensure that their magnetostriction coefficients meet the requirements. A two-dimensional (2-D) model based on a mechanical elasticity analogy is proposed to calculate the magnetostriction of electrical steel [7]. These methods are generally inefficient and require destructive sampling for the larger sized specimens. It is difficult to achieve an accurate measurement through the strain gauge method due to their
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