  The absorption of electromagnetic radiation by a planar structure, consisting
of a three-layer dielectric-metal-dielectric coating on a metal back-reflector
is analysed. The conditions for total absorption are derived. Our analysis
shows that, in contrast with bi-layer structures, the calculated layer
thicknesses are feasible to fabricate for any metal. The proposed absorber
design is of potential use in infrared and longer wavelength detectors and for
radiant energy harvesting devices.
