A flux concentrator, or pole piece, is a ferrous material used to significantly increase the performance of a Hall Effect Sensor System. When a flux concentrator is placed opposite the pole face of a magnet, the magnetic field channels through the concentrator, thereby increasing the flux density between the concentrator and the pole face.

The reason this magnetic flux channels through the concentrator is because of the reluctance of the ferrous material. Reluctance is the resistance that magnetic flux lines experience as they flow from the North pole into the South pole of a magnet. Ferromagnetic materials have lower reluctance than air, therefore a pole piece provides an easier path for the flux to flow through, while increasing the flux density at the same time. There are three benefits to adding a flux concentrator to a magnetic circuit. First, a less sensitive Hall Effect Sensor can be implemented, a result of the increased flux density. The second benefit of using a flux concentrator is that Hall Effect Sensor with a specific operate level can be actuated a greater distance from the magnet, than if one were not in use. The addition of a pole piece also allows the use of a magnet with a lower field intensity. A flux concentrator makes it possible to use a smaller magnet or a magnet of different material to achieve the same operating characteristics as one with higher flux density or a larger size. When choosing materials for a pole piece, pay attention to the following characteristics: The permeability and reluctance of the material will affect its performance as a flux concentrator. Also, pay close attention to the mechanical characteristics of machining and corrosion. These properties are very important when selecting an alloy.