EMI-Suppression from transmission lines

• US 4,371,742 A
• Filed: 07/19/1979
• Issued: 02/01/1983
• Est. Priority Date: 12/20/1977
• Status: Expired due to Term

• Current Assignee: Vistatech Corporation
• Original Assignee: Graham Magnetics, Inc.
• Inventors: Manly, William A.
• Primary Examiner(s): Reynolds, B. A.
• Assistant Examiner(s): Leung, Philip H.
• Application Number:
  US06/059,047
• Time in Patent Office: 1,293 Days
• Field of Search: 174/36, 174/35 MS, 343/18 A, 333/243, 333/244, 333/12, 252/62.51, 252/62.54, 252/62.55, 252/62.56, 106/290
• US Class Current: 174/36
• CPC Class Codes: H01B 11/146 using magnetically loaded coatings
• CPC Class Codes: H01B 11/1869 Construction of the layers on the outer side of the outer conductor
• CPC Class Codes: H05K 9/0098 for shielding electrical cables

Abstract

Absorptive shields for transmission lines, especially those tending to radiate electromagnetic wave lengths within a frequency range of from about 10⁶ to about 10¹⁰ hertz, especially 10⁷ to 10¹⁰ hertz. The shields are flexible materials filled with ferromagnetic, or ferrimagnetic, powders of selected particle size and distribution.

Claims

1. A flexible transmission line of the type utilized to transmit electric current in the frequency range of 10⁶ to 10¹⁰ hertz and comprising

(a) an electrical conductor

(b) electrical insulation around said conductor

(c) a metallic sheathing around said electrical insulation

and a coating means placed around said sheathing to absorb electromagnetic radiation emanating from said line, in the range of 10⁶ to 10¹⁰ hertz, said means being formed of a shielding composition comprising ferromagnetic particles of above 20 microns in average maximum dimension in a resin matrix and said coating means being of such thickness that it has no substantial interference with the flexibility of said transmission line.

2. A transmission line as described in claim 1 wherein said average maximum particle dimension is between 20 micrometers and 500 micrometers.

3. A transmission line as described in claim 2 wherein the division of said average maximum particle dimension in micrometers by the said shield thickness in inches gives a number of about 5000.

4. A transmission line as defined in claim 3 wherein said composition forming means to absorb electromagnetic radiation forms means to reduce Q for current in said metal sheathing by a factor of about 5 or more.

5. A transmission line as defined in claim 3 which transmission line is a coaxial cable.

6. A transmission line as defined in claim 3 wherein the volume conductivity of said composition is such that the skin depth factor thereof is from about 0.2 to 5 times the thickness of the coating means.

7. A transmission line as defined in claim 3 wherein said shielding composition is non-conductive.

8. A transmission line as defined in claim 3 wherein said composition forming means to absorb electromagnetic radiation forms means to reduce Q for current in said metal sheathing by a factor of about 5 or more.

9. A transmission line as defined in claim 2 wherein said particles are iron particles.

10. A transmission line as defined in claim 9 which transmission line is a coaxial cable.

11. A transmission line as defined in claim 9 wherein the volume conductivity of said composition is such that the skin depth factor thereof is from about 0.2 to 5 times the thickness of the coating means.

12. A transmission line as defined in claim 9 wherein said shielding composition is non-conductive.

13. A transmission line as defined in claim 2 wherein said particles are nickel particles.

14. A transmission line as defined in claim 13 which transmission line is a coaxial cable.

15. A transmission line as defined in claim 13 wherein the volume conductivity of said composition is such that the

16. A transmission lines as defined in claim 13 wherein said shielding composition is non-conductive.

17. A transmission line as described in claim 2 wherein said composition forming means to absorb electromagnetic radiation forms means to reduce Q for current in said metal sheathing by a factor of about 5 or more.

18. A transmission line as defined in claim 17 which transmission line is a coaxial cable.

19. A transmission line as defined in claim 17 wherein the volume conductivity of said composition is such that the skin depth factor thereof is from about 0.2 to 5 times the thickness of the coating means.

20. A transmission line as defined in claim 17 wherein said shielding composition is non-conductive.

21. A transmission line as defined in claim 2 wherein the volume conductivity of said composition is such that the skin depth factor thereof is from about 0.2 to 5 times the

22. A transmission line as defined in claim 2 wherein said shielding composition is non-conductive.

23. A transmission lines as defined in claim 1 wherein the volume conductivity of said composition is such that the skin depth factor thereof is from about 0.2 to 5 times the thickness of the coating means.

24. A transmission as defined in claim 1 wherein said composition forming means to absorb electromagnetic radiatin forms means to reduce Q for current in said metal sheathing by a factor of about 5 or more.

25. In electronic apparatus comprising a means to absorb the electromagnetic radiation in the range of 10⁶ hertz to 10⁹ hertz passing into or out of said apparatus, the improvement wherein said means to absorb is a thin coating comprising therein ferromagnetic metal particles having an average maximum dimension of from 38 micrometers to 50 micrometers.

26. A flexible, radiation-absorptive, sheet material comprising a flexible substrate and coated thereupon a flexible organic resin based coating comprising therein ferromagnetic metal particles having an av

27. A process for absorbing electromagnetic radiation in the frequency range of from about 10⁷ to 10¹⁰ hertz from a metal-shielded transmission line of the type transmitting at a frequency of from about 10⁷ to 10¹⁰ hertz, said process comprising the steps of overcoating said metal shield with a layer of a radiation-absorbing composition comprising small ferromagnetic particles dispersed in a resin matrix such that the volume conductivity of said composition is such that the skin depth factor is from about 0.2 to five times the thickness of said layer.

28. A process as defined in claim 27 wherein said particles are nickel, iron, or cobalt particles.

29. A process as described in claim 28 wherein said particles are ferromagnetic and have an average maximum particle dimension of between about 20 micrometers to about 500 micrometers.

30. A process as defined in claim 29 wherein said frequency range is from about 10⁷ hertz to about 10⁸ hertz and said maximum particle dimension is in a range of about from about 160 micrometers to 500 micrometers.

31. A process as defined in claim 30 wherein the Q factor at said transmitted frequency is reduced by a factor of 5 or more by said layer of radiation-absorbing composition comprising small magnetic particles dispersed in a resin matrix.

32. A process as defined in claim 30 wherein the principal wavelength of radiation to be absorbed is at least about 1/6 of the length of said transmission line and said transmission line is approximately an even multiple of half the wavelength of said radiation to be absorbed.

33. A process as defined in claim 30 wherein said layer of radiation-absorbing composition is nonconductive.

34. A process as defined in claim 29 wherein said frequency range is from about 10⁸ hertz to about 10⁹ hertz and said maximum particle dimension is within a range of about from about 50 micrometers to 160 micrometers.

35. A process as defined in claim 34 wherein the Q factor at said transmitted frequency is reduced by a factor of 5 or more by said layer of radiation-absorbing composition comprising small magnetic particles dispersed in a resin matrix.

36. A process as defined in claim 34 wherein the principal wavelength of radiation to be absorbed is at least about 1/6 of the length of said transmission line and said transmission line is approximately an even multiple of half the wavelength of said radiation to be absorbed.

37. A process as defined in claim 34 wherein said layer of radiation-absorbing composition is nonconductive.

38. A process as defined in claim 29 wherein said frequency range is from about 10⁹ hertz to about 10¹⁰ hertz and said average maximum particle dimension is between about 20 and about 50 micrometers.

39. A process as defined in claim 38 wherein the Q factor at said transmitted frequency is reduced by a factor of 5 or more by said layer of radiation-absorbing composition comprising small magnetic particles dispersed in a resin matrix.

40. A process as defined in claim 38 wherein the principal wavelength of radiation to be absorbed is at least about 1/6 of the length of said transmission line and said transmission line is approximately an even multiple of half the wavelength of said radiation to be absorbed.

41. A process as defined in claim 38 wherein said layer of radiation-absorbing composition is nonconductive.

42. A process as defined in claim 29 wherein the Q factor at said transmitted frequency is reduced by a factor of 5 or more by said layer of radiation-absorbing composition comprising small magnetic particles dispersed in a resin matrix.

43. A process as defined in claim 29 wherein the principal wavelength of radiation to be absorbed is at least about 1/6 of the length of said transmission line and said transmission line is approximately an even multiple of half the wavelength of said radiation to be absorbed.

44. A process as defined in claim 29 wherein said layer of radiation-absorbing composition is nonconductive.

45. A process as defined in claim 28 wherein the Q factor at said transmitted frequency is reduced by a factor of 5 or more by said layer of radiation-absorbing composition comprising small magnetic particles dispersed in a resin matrix.

46. A process as defined in claim 28 wherein the principal wavelength of radiation to be absorbed is at least about 1/6 of the length of said transmission line and said transmission line is approximately an even multiple of half the wavelength of said radiation to be absorbed.

47. A process as defined in claim 27 wherein the Q factor at said transmitted frequency is reduced by a factor of 5 or more by said layer of radiation-absorbing composition comprising small magnetic particles dispersed in a resin matrix.

48. A process as defined in claim 27 wherein the principal wavelength of radiation to be absorbed is at least about 1/6 of the length of said transmission line and said transmission line is approximately an even multiple of half the wavelength of said radiation to be absorbed.