An external charger for an implantable medical device (IMD) includes a multi-layer shield to direct the magnetic field generated by its charging coil towards the IMD. Each of the shield's multiple layers includes a ferromagnetic material that increases the permeance of the magnetic field's flux paths. The layers decrease in magnetic saturation point with increasing distance from the external charger's charging coil. That is, the layer closest to the charging coil has a higher saturation point than the next layer further from the charging coil, and so on. Layers that are positioned closer to the charging coil shield layers that are further from the charging coil, which generally have higher magnetic permeabilities, such that the magnetic intensity does not exceed any layer's saturation point. In this way, the multi-layer shield provides a beneficial balance between permeability and saturation, which can limit the required dimensions of the shield.
