Low density dielectric having low microwave loss

• US 6,562,448 B1
• Filed: 04/06/2000
• Issued: 05/13/2003
• Est. Priority Date: 04/06/2000
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Brennan, Joan V., Gettinger, Constance L., Wilson, Robert W., Chamberlain, Craig S.
• Primary Examiner(s): Thibodeau, Paul
• Assistant Examiner(s): UHLIR, NIKOLAS J
• Application Number:
  US09/544,067
• Time in Patent Office: 1,132 Days
• Field of Search: 428/323, 428/402, 428/403, 428/332, 428/312.6, 428/313.9
• US Class Current: 428/312.6
• CPC Class Codes: C08K 9/02 Ingredients treated with inorganic substances
• CPC Class Codes: H01Q 15/08 formed of solid dielectric material
• CPC Class Codes: Y10T 428/249969 Of silicon-containing material [e.g., glass, etc.]
• CPC Class Codes: Y10T 428/249974 Metal- or silicon-containing element
• CPC Class Codes: Y10T 428/26 Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
• CPC Class Codes: Y10T 428/2982 Particulate matter [e.g., sphere, flake, etc.]
• CPC Class Codes: Y10T 428/2991 Coated

Abstract

Disclosed is a composite material comprising a matrix material comprising a microwave transmissive polymer; and from about 1 to 65 volume percent of a particulate filler dispersed in the matrix. This particulate filler is characterized by an electrically conductive coating on the filler particles, particles selected from spheroids and ellipsoids having a major dimension below about 0.5 mm and particles having an aspect ratio greater than about 2 to 1 having a minor dimension below 100 μm, and a combination of particle size and coating thickness sufficient to yield a combination of a composite material dielectric constant between about 1.2 to 100, and a composite material microwave loss tangent no greater than about 0.10 at 1 GHz.

Claims

1. A composite material comprising:

a matrix material comprising a microwave transmissive polymer; and

from about 1 to 65 volume percent of a particulate filler dispersed in the matrix, the particulate filler being characterized by;

an electrically conductive coating 5 to 500 nanometers thick on the filler particles,

particles which are spheroids having a particle size in the range of 10-350 μ

m and a density below 3.5 g/cc, the combination of particle size and coating thickness being sufficient to yield a composite material dielectric constant from 1.2 to 100, and a composite material microwave loss tangent no greater than 0.10 at 1 GHz.

2. The composite material of claim 1 wherein the composite material has a density less than about 95% of the density of a reference composite material which is the same as the composite material except that the particulate filler is replaced with a sufficient quantity of particulate barium titanate to provide a dielectric constant within about 5% of that of the composite material.

3. The composite material of claim 1 wherein the filler is in a form selected from microspheres, fibers, or flakes.

4. The composite material of claim 1 further comprising a substantially electrically insulating coating on the electrically conductive coating of the particulate filler.

5. The composite material of claim 1 wherein the matrix comprises a polymer selected from cellulose acetates, natural rubbers, polyethylenes, polypropylenes, fluoropolymers, synthetic rubbers, and silicones.

6. A lens comprising the composite material of claim 1 having a planar, convex, concave, hemispherical, or spherical shape.

7. An antenna comprising the composite material of claim 1.

15. The composite material of claim 7, wherein the microwave transmissive polymer matrix contains a chemical blowing agent.

8. A composite material comprising:

a matrix material comprising a microwave transmissive polymer; and

from about 1 to 65 volume percent of a filler comprising microspheres dispersed in the matrix, the filler microspheres being characterized by;

a metal coating 5 to 500 nanometers thick and selected from the group consisting of aluminum, stainless steel, titanium, and tungsten,

an average particle size in the range of 10 to 350 μ

m,

a density below 3.5 g/cc, the combination of particle size and coating thickness being sufficient to yield of a composite material dielectric constant from 1.2 to 100, and a composite material microwave loss tangent no greater than 0.10 at 1 GHz.

9. The composite material of claim 8 wherein the polymer is selected from cellulose acetates, natural rubbers, polyethylenes, polypropylenes, fluoropolymers, synthetic rubbers, and silicones.

10. The composite material of claim 8 further comprising another component having a dielectric constant lower than the polymer of which the matrix is comprised.

11. The composite material of claim 8 wherein the matrix is continuous, discontinuous, or foamed.

12. A lens comprising the composite material of claim 8 having a planar, convex, concave, hemispherical, or spherical shape.

13. The lens of claim 12 comprised of at least 2 layers each comprising a composite material.

14. An antenna comprising the composite material of claim 8.

16. The composite material of claim 8 wherein the filler comprises hollow microspheres capable of withstanding hydrostatic pressures of at least 6.9 MPa without the microspheres being significantly ruptured and having a density of at least 0.29 g/cc.

17. The composite material of claim 16 wherein the filler microspheres have an average particle size in the range of about 10 to 60 μ

m.

18. The composite material of claim 16 further comprising a substantially electrically insulating coating on the electrically conductive coating on the particulate filler.