2D measurements of magnetic field near an oscillating interface between two fluids carrying an electrical current

An experimental technique is presented to measure two-dimensional magnetic fields outside a cylindrical cell containing two electrically conducting fluids as the primary step of magnetic field tomography (MFT). The magnetic field is induced by a direct current through the fluids. Under a periodic, vertical vibration driven by a pneumatic shaker, Faraday instabilities are generated, which lead to a series of non-axisymmetrical wave modes, and the non-axisymmetrical interface shape introduces a perturbation to the magnetic field which can be measured by eight two-dimensional fluxgate sensors fixed concentrically and uniformly around the cell. The original signals from the sensors are collected by a Keithley data acquisition board and processed by fast Fourier transform (FFT). The amplitude and frequency of the magnetic flux density are extracted successfully. Based on the measured magnetic field distribution, the maximum of the interface displacement is reconstructed by an evolutionary strategy, which is in good agreement with the optical measurement. This MFT system can be applied to study the interface movements in aluminium reduction cells, in iron/steel making, in glass melts, and in other electromagnetic processing of materials.