Sensitivity maps for metal detector design

Eddy-current or permeability-contrast based metal detectors may be characterized by static sensitivity maps, a new graphic representation that maps detector response to a standardized infinitesimal object in a static field. A sphere is shown to be a suitable standard object because its behavior describes, to within multiplicative constants, objects of arbitrary conductivity and permeability. Static sensitivity maps take full account of both the excitation and detection coil shapes. They are compact, easy to understand, closely related to industrial testing procedures, and likely to prove a useful design tool. Their usefulness is illustrated by examples based on a metal detector for which published data exist.