Multi-layer absorber

A multi-layer absorber, comprising:

• a plurality of polymeric layers disposed relative to one another to form a polymeric stack having an input layer and an output layer such that said input layer includes a radiation-receiving surface for receiving incident electromagnetic radiation and said output layer includes an exit surface through which at least a portion of the received radiation, if any, exits the stack, wherein the number of the polymeric layers is greater than 2 and equal to or less than 20,
• a plurality of radiation-absorbing additives distributed within at least one of said polymeric layers, wherein said additives are capable of absorbing electromagnetic energy at one or more frequencies in a range of about 20 GHz to about 110 GHz,
• wherein real dielectric constants of said polymeric layers for one or more frequencies in a range of about 20 GHz to about 110 GHz progressively increase from said input layer to said output layer,
• wherein a difference in real index of refraction of any two adjacent layers at one or more of said frequencies satisfy the following relation:
• 1≦(nrd−nrp)≦20
• wherein
• nrd denotes the real part of the index of refraction of a distal layer,
• nrp denotes the real part of the index of refraction of a proximal layer, and
• f (in units of GHz) denotes the frequency at which the difference in real parts of the indices of refraction of the proximal and distal layers is determined, and
• wherein said absorber exhibits a reflectance coefficient less than about 0.3 and a transmission coefficient less than about 0.3 for incident radiation in a frequency band within said frequency range of about 20 GHz to about 110 GHz.