Magnetic particle tracking enabled by planar Hall effect sensors

Foam processes are essential in many industrial applications e.g., in froth flotation for material
separation. A detailed understanding of foam flows is vital for improvements in process efficiency. X-
Ray and Neutron imaging can measure flow fields in foam, but require a complex setup and cannot be
performed in-situ. Magnetic particle tracking (MPT) is an alternative approach, that measures the
trajectory of a small magnetic tracer particle inside the foam as a representation of its movement.
Different magnetic field sensors can be applied to detect the magnetic tracer particle. We chose thin film
sensors based on the planar Hall effect (PHE) due to their small size, high sensitivity, high signal-to-
noise ratio and low cost. Our sensors have a size of only 2 mm x 2 mm and are capable of measuring
magnetic fields as low as 10 nT at a sampling frequency of 1 Hz. A sensitivity of 20 V/T at a driving
current of 1 mA was achieved by means of sensor bridging. Our PHE-sensors are almost as precise as
currently used Fluxgate probes, but offer several advantages due to their reduced size. This includes
being installed closer to the area to be measured, enabling finer grids of sensors and decreasing the
detection volume, which increases the precision of the MPT as well as other tomographic methods.