Electromagnetic field absorbing composition

Patent metadata

Field	Value
Publication number	US-9806426-B2
Application number	US-201013260612-A
Country	US
Kind code	B2
Filing date	Mar 24, 2010
Priority date	Mar 27, 2009
Publication date	Oct 31, 2017
Grant date	Oct 31, 2017

Abstract

This invention relates to the field of an electromagnetic (EM) field absorbing composition, in particular, those capable of providing absorbance in the frequency of commercial radar. The composition finds particular use as a radar absorbing coating for wind turbines, in particular for use in onshore and offshore environments. There are further provided coated surfaces comprising the composition, methods of absorbing EM radiation, and methods of use of such a composition, such that a surface coated in the composition is capable of absorbing EM radiation. There is provided an electromagnetic radiation absorbing composition comprising elongate carbon elements with an average longest dimension in the range of 50 to 1 000 microns, with a thickness in the range of 1 to 15 microns and present in the range of from 0.5 to 20 volume % dried, in a non conductive binder.

First claim

The invention claimed is:

1. A method of providing absorption of electromagnetic radiation at a selected frequency on a surface structure or body or portions thereof, comprising the steps of
determining the selected frequency,
applying at least one coat of electromagnetic radiation absorbing composition at a thickness which selectively absorbs at said frequency or an appliqué film comprising the electromagnetic radiation absorbing composition, to a first side of said surface structure or body or portions thereof,
and drying the electromagnetic radiation absorbing composition,
wherein the electromagnetic radiation absorbing composition comprises a carbon filler substantially consisting of machined elongate carbon elements with an average longest dimension in the range of 100 to 150 microns, with a thickness in the range of 1 to 15 microns, wherein the total carbon filler content is present in the range of from 2 to 10 volume % dried, in a non conductive binder, and wherein the binder is selected from an acrylate, an epoxy binder, an acrylic, a urethane and epoxy-modified acrylic, a polyurethane, an alkyd, a modified alkyd, a fluoropolymer, and mixtures thereof,
wherein the electromagnetic radiation absorbing composition after the drying step has a dielectric loss tangent that is configured to absorb microwave radiation, the dielectric loss tangent being a ratio of an imaginary component of complex permittivity to a real component of complex permittivity,
wherein the method further comprises applying at least one or more sub-layers, each of which have been separately applied in an orthogonal direction to the preceding layer.

2. The method according to claim 1 , wherein the elongate carbon elements are cylindrical and have a diameter in the range of from 5 to 10 microns.

3. The method according to claim 1 , wherein the elongate carbon elements have an average thickness to average longest dimension ratio of from 1:10 to 1:25.

4. The method according to claim 1 , wherein the binder is selected from a water based dispersion comprising a binder selected from an acrylic, or polyurethane based latex.

5. The method according to claim 1 , wherein the composition is a liquid formulation.

6. The method according to claim 1 , wherein the thickness of said coating is one quarter of the wavelength (λ/4) of the resonant frequency of the incident radiation to be absorbed.

7. The method according to claim 1 further comprising providing an electromagnetic reflective backplane between the surface, structure or body and the at least one dried coating.

8. The method according to claim 1 , wherein the machined elongate carbon elements are milled carbon fibers.

9. The method according to claim 5 , wherein the composition comprises a solvent.

10. The method according to claim 1 , further comprising applying at least one coat of electromagnetic radiation absorbing composition at a thickness which selectively absorbs at said frequency or an appliqué film comprising the electromagnetic radiation absorbing composition, to a second side of said surface structure or body or portions thereof.

Assignees

• Bryant Richard
• Fixter Greg Pw
• Hussain Shahid
• Vaughan Adrian St
• Qinetiq Ltd

Inventors

• Bryant Richard
• Fixter Greg Pw
• Hussain Shahid
• Vaughan Adrian St

Classifications

• F05B2260/99

  Radar absorption · CPC title

• C08K7/06

  Elements · CPC title

• Y10T156/10

  Methods of surface bonding and/or assembly therefor · CPC title

• H01Q17/002 Primary

  using short elongated elements as dissipative material, e.g. metallic threads or flake-like particles · CPC title

• C09D5/32 Primary

  Radiation-absorbing paints {(protection against X-, gamma- or corpuscular radiation G21F)} · CPC title