Gathering dust: a new technique for rapid measurement of magnetic fluid concentration

A new technique has been developed to measure magnetic particle concentration using magnetic sedimentation and computer vision. The concentration of magnetic fluid used in the well-established technique of magnetic particle inspection (MPI) must conform to a standard range and is commonly measured after a slow process of sedimentation in a conical flask. In the new method, a ring magnet is used to gather particles to form a uniform profile through manual swilling. This is then imaged and analysed digitally to compute the proportion of a selected area in which particles are present. Custom software uses a binary threshold to separate darker pixels containing particles from lighter pixels without particles. Three ring magnets of various sizes are shown to exhibit a linear relationship between particle concentration and the proportion of dark to light pixels. This low-cost method allows measurements to be made and analysed within minutes, facilitating rapid conformity testing.