In principle, a metal shield can be inserted between a sensor’s Target and an Antenna.
The skin depth through which the excitation signals can permeate limits the thickness of the metal shield. The lower the excitation frequency, the greater the thickness of permissible metal.
The maximum thickness of metal depends on the actual metal. If a metal shield is to be used then non-magnetic stainless steel is most preferred with aluminium, steel, copper or brass least preferred. Practically, metal thicknesses of <1.6mm are necessary.