Magnetostriction and the Advantages of Using Noncontact Measurements

Magnetic noise in electrical machines and transformers are a large portion of the total noise of the device. Part of this magnetic noise is caused by the deformation of the ferromagnetic laminations due to the magnetic field. This effect is called magnetostriction, and it strongly depends on the applied magnetic field, the material properties and external pressure to the material. A strain gauge measurement setup has been applied before to measure the magnetostrictive behaviour of ferromagnetic materials. The results obtained by this setup suffered from some limitations such as the need to filter highfrequency harmonics. Also the measurement results for excitation below 0.8T were not easily distinguished from the present noise. Therefore, a new setup using heterodyne laser interferometers has been built. With this new setup, on the contrary to the strain gauge setup, the sample preparation is simple. This new setup and the gradual improvements toward the optimal performance of the setup are presented in this paper.