ELECTROMAGNETIC WAVE ATTENUATING DEVICE

• US 3,568,195 A
• Filed: 11/23/1959
• Issued: 03/02/1971
• Est. Priority Date: 12/04/1958
• Status: Expired due to Term

• Current Assignee: Hans H. Meinke, Wesch Ludwig
• Original Assignee: Hans H. Meinke, Wesch Ludwig
• Inventors: WESCH LUDWIG, Meinke, Hans H.
• Application Number:
  US03/854,979
• Time in Patent Office: 4,117 Days
• US Class Current: 342/1
• CPC Class Codes: H01Q 17/004 using non-directional dissipative particles, e.g. ferrite powders H01Q17/005 takes precedence; flake-like H01Q17/002

Abstract

A radar wave absorber is disclosed which does not require a metal backing layer. The absorber operates according to interference principles, with a portion of the wave reflected from the absorber'"'"''"'"'s back layer interfering with the wave reflected from the surface layer. The backing material must exhibit a high relative dielectric constant, or a high relative magnetic permeability and dielectric loss tangent, or a high magnetic loss tangent, or a combination of these properties.

Claims

1. An improved device for attenuating impinging radar waves by interference, consisting of the combination of an outer radar wave attenuating layer means having a surface reflecting one part of the impinging waves and a wave reflecting backing reflecting the other part of the impinging waves, which have penetrated into the layer means, said backing being a nonmetallic sheet having a relative dielectric constant of between 20 and 600, and a relative permeability of between 0.9 and 10.

2. The device of claim 1, wherein the relative dielectric constant of the nonmetallic backing is between 100 and 200, and the relative permeability is about 1.

3. The device of claim 1, wherein the nonmetallic backing consists of a dielectric binder material containing a particulate filler controlling the high frequency constant of the backing.

4. The device of claim 1, wherein the nonmetallic backing consists of a dielectric base material selected from the group consisting of concrete and cement containing a particulate filler controlling the high frequency constant of the backing.

5. The device of claim 1, wherein the nonmetallic backing consists of a dielectric base material containing a particulate filler selected from the group consisting of iron, ferrites, magnetites and mixtures thereof, having a grain size of 0.1 to 100 microns.

6. The device of claim 1, wherein the nonmetallic backing is composed essentially of a synthetic resin containing a particulate filler imparting a high high frequency loss to the backing.

7. The device of claim 6, wherein said synthetic resin is a synthetic rubber.

8. The device of claim 7, wherein said synthetic rubber is selected from the group consisting of butyl rubber and a butadiene-base rubber.

9. The device of claim 6, wherein at least the major portion of the particulate filler consists of graphite.

10. The device of claim 6, wherein at least the major portion of the particulate filler consists of carbon black.

11. The device of claim 6, wherein at least the major portion of the particulate filler consists of graphite and carbon black.

12. An improved device for attenuating impinging radar waves by interference, consisting of the combination of an outer radar wave attenuating layer means having a surface reflecting one part of the impinging waves and a wave reflecting backing reflecting the other part of the impinging waves, which have penetrated into the layer means, saId backing being a sheet composed essentially of polyisobutylene and a particulate filler of graphite and carbon black, the backing sheet having a thickness of the order or magnitude of a few millimeters.

13. The device of claim 12, wherein the weight ratio of the polyisobutylene, graphite and carbon black is about 2 :

4 ;

4.

14. An improved device for attenuating impinging radar waves by interference, consisting of the combination of an outer radar wave attenuating layer means having a surface reflecting one part of the impinging waves and a wave reflecting backing reflecting the other part of the impinging waves, which have penetrated into the layer means, said backing being a sheet composed essentially of a synthetic resin containing from about 30 percent to about 80 percent, by weight, of a particulate filler imparting a high high frequency loss to the backing sheet, at least a major portion of said filler consisting of a mixture of graphite and carbon black.

15. The device of claim 14, wherein the filler includes a minor portion of at least one permeable high frequency iron powder.

16. An improved device for attenuating impinging radar waves by interference, consisting of the combination of an outer radar wave attenuating layer means having a surface reflecting one part of the impinging waves and a wave reflecting backing reflecting the other part of the impinging waves, which have penetrated into the layer means, said backing being a sheet composed essentially of a vulcanized butadiene acrylonitrile copolymer, graphite and carbon black.

17. The device of claim 16, wherein the butadiene acrylonitrile copolymer, graphite and carbon black are present in about equal proportion, by weight.

18. An improved device for attenuating impinging radar waves by interference, consisting of the combination of (1) a radar wave attenuating layer means having a surface reflecting one part of the impinging waves, said layer means having a thickness of approximately n lambda /4, wherein n is any odd integer and lambda is the wavelength of the impinging waves measured in the layer means, and (2) a wave reflecting backing reflecting the other part of the impinging waves, which have penetrated into the layer means, said backing being a nonmetallic sheet having a relative dielectric constant of between 20 and 600, and a relative permeability of between 0.9 and 10.

19. The device of claim 18, further comprising an outer conductive coating having a resistance of 377 ohms cm. on the wave absorbing layer structure.