Method for making a material with artificial dielectric constant

• US 5,385,623 A
• Filed: 05/29/1992
• Issued: 01/31/1995
• Est. Priority Date: 05/29/1992
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Corporation
• Original Assignee: Hexcel Corporation
• Inventors: Diaz, Rodolfo E.
• Primary Examiner(s): Barry, Chester T.
• Application Number:
  US07/890,757
• Time in Patent Office: 977 Days
• Field of Search: 343/911 R, 156/197, 156/272.2, 156/277, 156/278, 342/1-4, 428/118, 428/116
• US Class Current: 156/197
• CPC Class Codes: B29K 2995/0006 Dielectric
• CPC Class Codes: H01Q 1/38 formed by a conductive layer on an insulating support patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface H01Q15/142
• CPC Class Codes: H01Q 15/0013 said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
• CPC Class Codes: H01Q 17/00 Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
• CPC Class Codes: Y10T 156/1003 by separating laminae between spaced secured areas [e.g., honeycomb expanding]
• CPC Class Codes: Y10T 428/24149 Honeycomb-like
• CPC Class Codes: Y10T 428/24165 Hexagonally shaped cavities

Abstract

A method for making a material with an artificial dielectric constant is carried out by choosing the desired dielectric constant for a particular electromagnetic field, selecting a substantially non-electrically conductive sheet material (2) from which the cellular core material (26) is to be made, applying an electrically conductive material (8) to selected areas on the sheet material and thereafter forming a cellular core material from layers of the sheet material having the conductive material already applied thereto.

Claims

1. Method for making a material with a first frequency dependent complex permittivity along a first principal axis, a second frequency dependent complex permittivity along a second principal axis, and a third frequency dependent complex permittivity along a third principal axis, said method comprising the following steps:

choosing a frequency of interest for each principal axis;

choosing a polarization for a wave of interest relative to each principal axis;

determining the frequency dependent complex permittivity along each principal axis such that the wave of interest for the chosen polarization encounters the desired frequency dependent complex permittivity;

designing a pattern and a cellular core structure in which the dimensions, geometry and conductivity characteristics of the pattern and the dimensions and the geometry of the cellular core structure are chosen to achieve the desired frequency dependent complex permittivity along each principal axis;

selecting a substantially non-electrically conductive sheet material;

applying an electrically conductive material to the sheet material according to said pattern design; and

thereafter

forming a cellular core structure from layers of the sheet material according to said cellular core structure design, said structure defining said first principal axis, said second principal axis, and said third principal axis.

2. The method of claim 1 wherein the selecting step is carried out by selecting sheets of resin impregnated fabric.

3. The method of claim 2 wherein the resin impregnated fabric is made of woven or felted fabric impregnated with a phenolic resin.

4. The method of claim 1 wherein said pattern is comprised of a plurality of continuous parallel lines, said lines having preselected widths and conductivities and gap spacings.

5. The method of claim 4 wherein the forming step is carried out by forming the layers of the sheet material into a honeycomb type cellular core material having hexagonal cells, said hexagonal cells defining an open interior and orthogonal L, W and T directions, said T direction coaxial with said first principal axis and passing axially through the open interior, said L direction coaxial with said second principal axis and oriented generally parallel to the sheet material and the W direction coaxial with said third principal axis and oriented generally perpendicular to the sheet material.

6. The method of claim 5 wherein the lines are generally parallel to the L direction.

7. The method of claim 5 wherein the lines are generally parallel to the T direction.

8. The method of claim 1 wherein the forming step is carried out by forming the layers of the sheet material into a honeycomb type cellular core material having hexagonal cells, said hexagonal cells defining an open interior and orthogonal L, W and T directions, said T direction coaxial with said first principal axis and passing axially through the open interior, said L direction coaxial with said second principal axis and oriented generally parallel to the sheet material and the W direction coaxial with said third principal axis and oriented generally perpendicular to the sheet material.

9. The method of claim 8 wherein the hexagonal cells are defined as follows:

sizing each of two opposite sides as length X;

sizing each of the other four sides as length Xe⁰.5 ; and

forming the included angles between first and second adjacent sets of said other four sides as 2.3π

.

10. The method of claim 6 wherein said pattern is comprised of a grid of first and second sets of spaced-apart, continuous parallel lines intersecting generally at right angles to one another, said first set of parallel lines having a first line width and a first line conductivity and said second set of parallel lines having a second line width and a second line conductivity.

11. The method of claim 10 wherein the applying step includes the step of aligning the first set of parallel lines with the L direction and the second set of parallel lines with the T direction, said first and second sets of parallel lines creating repeating unit cell lengths in the T and L directions respectively.

12. The method of claim 11 wherein the first and second sets of parallel lines have equal line widths and equal conductivities, and the unit cell length in the L direction is about 2 to 2.5 times the unit cell length in the T direction in order to create the cellular core material which exhibits approximately twice the conductivity for an electric field aligned in the L direction compared to the electric field aligned in the T direction.

13. The method of claim 1 wherein said pattern is comprised of first and second sets of parallel, spaced-apart grid elements oriented transversely to one another, the first and second sets of grid elements having preselected widths and conductivities.

14. The method of claim 13 wherein the sets of grid elements are approximately perpendicular to one another.

15. The method of claim 13 wherein the widths of the grid elements are varied according to the desired conductance of the grid elements.

16. The method of claim 13 wherein the thicknesses of the grid elements are varied according to the desired conductance of the grid elements.

17. The method of claim 16 wherein the thickness of the first set of grid elements is thicker than the second set of grid elements.

18. The method of claim 1 wherein said pattern is comprised of an array of unit cells, each said unit cell having a chosen pattern of said electrically conductive material, said chosen pattern such that the electrically conductive material in one said unit cell does not contact the electrically conductive material in an adjacent unit cell.

19. The method of claim 18 wherein said chosen pattern has an undulating shape.

20. The method of claim 1 wherein said electrically conductive material includes finely divided carbon suspended within a carrier fluid.

21. The method of claim 1 wherein said applying step is carried out using a rotogravure process.