Magnetic shielding in a planar geometry: using ferromagnetic washers to screen in-plane fields

Magnetic shielding is a crucial aspect for many electronic devices and sensors. In this paper, we investigate the magnetic shielding properties of ferromagnetic washers in a planar geometry in view of an integration with on-chip devices, focussing on the transverse configuration, i.e. with the applied field parallel to the plane of the washer. We show that, in this configuration, the shielding factor of a washer can exceed the predictions of previous studies. We argue that the magnetic shielding results from the capture of the external magnetic flux by the upper and lower faces of the washer, and its subsequent channeling through the washer material and around the central hole. We present experimental results and numerical simulations, and discuss the influence of the geometry of the washer, the permeability and the saturation of the ferromagnetic material. We propose an explanation for the observed behaviour and provide empirical formulae to estimate different quantities characterizing the shielding properties of washers in the transverse configuration.