Multi-layer absorber
In one aspect, a multi-layer absorber is disclosed, which comprises a proximal layer having a radiation-receiving surface adapted for receiving electromagnetic radiation, and a distal layer disposed adjacent the proximal layer to receive at least a portion of the received radiation, if any, transmitted through said proximal layer, wherein said proximal layer exhibits an index of refraction having a real part that is less than the real part of an index of refraction of the said distal layer for at least one frequency of the electromagnetic radiation in a range of about 1 GHz to about 110 GHz.
1. 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 plurality of 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 plurality of polymeric layers, wherein a concentration of the plurality of radiation-absorbing additives is greater in said input layer relative to a concentration of said radiation-absorbing additives in said output layer, wherein said plurality of radiation-absorbing additives is capable of absorbing electromagnetic energy at one or more frequencies in a range of about 1 GHz to about 110 GHz,
wherein the real dielectric constants of said polymeric layers progressively increase from the input layer to the output layer for one or more frequencies in a range of about 1 GHz to about 110 GHz, and
wherein the absorber exhibits a coefficient of reflection equal to or less than about 0.3 and a coefficient of transmission equal to or less than about 0.3 for at least one incident radiation frequency in the range of about 1 GHz to about 110 GHz.
2. The multi-layer absorber of claim 1 , wherein each of said layers exhibits a real dielectric constant in a range of about 0 to about 50 for at least one frequency in said range of about 1 GHz to about 110 GHz.
3. The multi-layer absorber of claim 2 , wherein said at least one frequency is any of 24 GHz and 77 GHz.
4. The multi-layer absorber of claim 1 , wherein said real dielectric constants of said polymeric layers progressively increase from said input layer to said output layer for frequencies within a frequency band in a range of about 20 GHz to about 80 GHz.
5. The multi-layer absorber of claim 4 , wherein said frequency band has a bandwidth of at least about 20 GHz.
6. The multi-layer absorber of claim 4 , wherein said frequency band has a bandwidth of at least about 50 GHz.
7. The multi-layer absorber of claim 4 , wherein said absorbing additives are formed of a material exhibiting a coefficient of absorption greater than about 0.5 for at least one frequency in the range of about 20 GHz to about 100 GHz.
8. The multi-layer absorber of claim 1 , wherein said additives comprise a plurality of carbon particles.
9. The multi-layer absorber of claim 1 , wherein said radiation-absorbing additives are distributed within each of said polymeric layers.
10. The multi-layer absorber of claim 1 , wherein a volume fraction of said radiation-absorbing additives in at least one of said layers is in a range of about 1% to about 50%.
11. The multi-layer absorber of claim 1 , wherein the plurality of polymeric layers comprises different polymeric materials.
12. The multi-layer absorber of claim 11 , wherein the polymeric materials are selected from the group consisting of thermoset elastomers, thermoplastic elastomers, liquid crystal polymers, polyamide, polyester, polycarbonate, polypropylene, polystyrene, acrylonitrile butadiene styrene, polyurethane, epoxy, polyethylene, ethylene vinyl acetate, and silicone.
13. The multi-layer absorber of claim 12 , wherein a thickness of the input layer is greater than a thickness of the output layer.