Radar absorbing material compatible with lightning protection systems

Patent metadata

Field	Value
Publication number	US-9422914-B2
Application number	US-201214002656-A
Country	US
Kind code	B2
Filing date	Feb 23, 2012
Priority date	Mar 1, 2011
Publication date	Aug 23, 2016
Grant date	Aug 23, 2016

Abstract

A wind turbine component incorporating radar-absorbing material having increased compatibility with lightning protection systems is described. The radar absorbing material includes a ground plane having an electrical conductivity and/or a dielectric constant that is higher in the presence of an electric field having a frequency of 1 GHz and above than in the presence of an electric field having a frequency of 10 MHz and below. Suitable materials for the ground plane include ferroelectric and ferrimagnetic materials and percolating material combinations, all of which have frequency-dependent properties that can be tuned to make the ground plane highly reflective at radar frequencies and benign at lightning discharge frequencies.

First claim

The invention claimed is:

1. A wind turbine component incorporating radar absorbing material, wherein the radar absorbing material includes a ground plane having an electrical conductivity and/or a dielectric constant that is higher in the presence of an electric field having a frequency of 1 GHz and above than in the presence of an electric field having a frequency of 10 MHz and below.

2. The wind turbine component of claim 1 , wherein the ground plane comprises a ferroelectric material.

3. The wind turbine component of claim 2 , wherein the ferroelectric material is selected from barium titanate (BaTiO 3 ), lead titanate (PbTiO 3 ), sodium nitrite (NaNO 2 ) and lead zirconate titanate (PZT).

4. The wind turbine component of claim 1 , wherein the ground plane comprises a ferrimagnetic material.

5. The wind turbine component of claim 4 , wherein the ferrimagnetic material is selected from magnetite; a hexaferrite or other ferrites composed of iron oxides and other elements.

6. The wind turbine component of claim 1 , wherein the ground plane comprises a percolating material combination.

7. The wind turbine component of claim 6 , wherein the percolating material combination comprises particles of conductive material dispersed in a non-metallic host.

8. The wind turbine component of claim 7 , wherein the non-metallic host comprises a polymer matrix.

9. The wind turbine component of claim 7 , wherein the conductive particles are particles of metal or carbon.

10. The wind turbine component of claim 1 , wherein the ground plane is optimised to reflect radar signals having a frequency in the range of 1-10 GHz.

11. The wind turbine component of claim 1 , wherein the ground plane has a sheet resistance of less than 0.02 Ω/sq in the presence of an electric field having a frequency of 1 GHz and above.

12. The wind turbine component of claim 1 , wherein the ground plane has a dielectric constant of 80-120 in the presence of an electric field having a frequency of 1 GHz and above.

13. The wind turbine component of claim 1 , wherein the ground plane has a dielectric constant of 90-110 in the presence of an electric field having a frequency of 1 GHz and above.

14. The wind turbine component of claim 1 , wherein the ground plane has a dielectric constant of 95-105 in the presence of an electric field having a frequency of 1 GHz and above.

15. The wind turbine component of claim 1 , wherein the ground plane has a sheet resistance that is greater than 100,000 Ω/sq in the presence of an electric field having a frequency of 10 MHz and below.

16. The wind turbine component of claim 1 , wherein the ground plane has a dielectric constant of 1-10 in the presence of an electric field having a frequency of 10 MHz and below.

17. The wind turbine component of claim 1 , wherein the ground plane has a dielectric constant of 2-6 in the presence of an electric field having a frequency of 10 MHz and below.

18. The wind turbine component of claim 1 , wherein the ground plane has a dielectric constant of 3-5 in the presence of an electric field having a frequency of 10 MHz and below.

19. The wind turbine component of claim 1 , wherein the component includes at least part of a lightning protection system.

20. The wind turbine component of claim 1 , wherein the component includes one or more lightning receptors.

21. The wind turbine component of claim 20 , wherein the ground plane abuts the one or more lightning receptors.

22. The wind turbine component of claim 1 , wherein the radar absorbing material further comprises an impedance layer spaced apart from the ground plane.

23. The wind turbine component of claim 22 , wherein the impedance layer is a circuit analogue layer.

24. The wind turbine component of claim 22 , wherein the radar absorbing material further comprises at least one dielectric layer between the impedance layer and the ground plane.

25. The wind turbine component of claim 1 , wherein the wind turbine component is a rotor blade.

26. A wind turbine comprising the component of claim 1 .

27. A wind farm including the wind turbine of claim 26 .

28. A radar-reflecting ground plane for incorporating into a composite structure, the ground plane having an electrical conductivity and/or a dielectric constant that is higher in the presence of an electric field having a frequency of 1 GHz and above than in the presence of an electric field having a frequency of 10 MHz and below.

Assignees

• Appleton Steve
• Vestas Wind Sys As

Inventors

• Appleton Steve

Classifications

• Y02E10/722

  Cross-Sectional Technologies · mapped topic

• H01Q15/14

  Reflecting surfaces; Equivalent structures {(electromagnetic shields H01Q1/526)} · CPC title

• F03D1/0675 Primary

  of the blades · CPC title

• F03D80/30

  Lightning protection · CPC title

• H01Q17/004

  using non-directional dissipative particles, e.g. ferrite powders (H01Q17/005 takes precedence; flake-like H01Q17/002) · CPC title