Method of Incorporating Microwave Structures within Reinforced Composites by Overstitching Patterns of Conductive Fibers onto Reinforcement Fabric

Abstract

A method of attaching conductive fiber to composite laminate reinforcement fabric and to other fabrics utilizing stitching which comprises: a means of precisely arranging said conductive fiber on the surface of said reinforcement fabric to minimize radio frequency losses; an overstitching means wherein said conductive fiber is attached to said reinforcement fabric by a non-conductive retention thread.

Description

FIELD OF INVENTION

This invention relates to methods of constructing radio frequency antennas, transmission lines and other structures such as filters.

BACKGROUND OF INVENTION

In many radar and communications systems, it is desirable to employ an antenna or transmission line that is lightweight and flexible. For example, an antenna may be incorporated into a fabric structure such as a garment or a tent. In other applications, an antenna may be incorporated into a composite laminate. This laminate is first comprised of a reinforcement fabric which is then impregnated with a resin. This prepreg structure is often merged with other prepreg structures and then cured to produce a final assembly. Prior to merging and curing, it is desirable to incorporate said antenna structures into the laminate reinforcement fabric and thereby obtain a durable, low cost, integrated antenna structure.

In the past, several methods of constructing radio frequency structures from textile materials have been proposed. See “Method for constructing microwave antennas from textile fabrics and components”, Provisional Patent Application, U.S. application Ser. No. 60/557,431, Mar. 29, 2004 and “The Characterization of Conductive Textile Materials Intended for Radio Frequency Applications”, Robert K. Shaw, et. al., IEEE Antennas and Propagation Magazine, Vol. 49, No. 3, June 2007, pp. 28-40. Structures have been built using conductive foil or fabric attached to a laminate or conductive ink printed onto a laminate. However, under fatigue stress, such embedded radio frequency (RF) structures can cause delamination.

Also in the past, methods of incorporating conductive fibers into reinforcement fabric by direct stitching of said fiber have resulted in undesirable radio frequency losses due to propagation disturbances. The inventors have tried that method and the data for that method is included in FIG. 3.

SUMMARY OF INVENTION

It is therefore the object of this invention to provide methods of constructing RF structures by attaching conductive fiber to the reinforcement fabrics of composite laminates.

It is a further object of this invention to provide a means of constructing RF structures by attaching conductive fiber to the surface of fabric structures so that propagation losses are reduced.

It is another object of this invention to provide a means of construction of microwave antennas on a reinforcing fabric for later incorporation into laminated structures.

It is another object of this invention to provide a means of constructing RF structures and to incorporate said structures into clothing in a way that allows said RF structures to look like fashion designs or appliques.

It is the realization of these-objects that an RF structure can be incorporated into ordinary fabrics, non-woven fabrics and even clothing so that said RF structures are flexible, not subject to delamination and the basic structure can also be incorporated in to laminate prepeg structures for other applications.

This invention features conductive fiber such as copper wire, stainless steel wire or other conductive fibers that is attached to fabric such as composite laminate reinforcement fabric by means of zigzag overstitching. This overstitching is accomplished by use of cording embroidery and can be implemented with, for example, Schiffley or Cornelly Embroidery machine or with cording attachments to lock-stitch embroidery machines or by other similar means. It is important that the fibers be attached onto the reinforcing fabric as opposed to being stitched through said fabric as stitching through the fabric diminishes the microwave properties of the antenna.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a depiction of the working parts of an embroidery or overstitching sewing machine used to manufacture a microwave structure such as an antenna, feed or filter.

FIG. 2 shows a transmission line constructed by said methods.

FIG. 3 shows performance data for an antenna produced by a stitched through method of incorporating conductive fabric within non-conductive fabric.

FIG. 4 is a graph of performance data for the overstitched method of constructing a microwave fabric antenna.

DISCLOSURE OF PREFERRED EMBODIMENT

Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings in which:

There is shown in FIG. 1 an overstitching sewing machine incorporating a foot and platen 4 lock stitch overstitching needle 7 and a wire feed. Said overstitching feature feeds the fabric along the sewing machine base 5 though the stitching mechanism in a regular zigzag pattern 6 onto the reinforced fabric 8. Simultaneously, the conductive fiber 9 is precisely fed in front of the stitching mechanism coming off a spool 2 and wire feed 3. Not shown is a means of computer control, so that a precisely planned pattern of conductive fiber 9 can be attached to the reinforced fabric 8.

FIG. 2 is a rendition of the completed antenna with the zigzag pattern 6 holding the conductive fabric 9 in place. The reinforced fabric 8 provides the backing for the antenna.

FIG. 3 shows the data for the cross-stitched antenna with curve 12 representing the S₁₂ and the S₂₁ overlapping data for insertion loss. Curve 11 represents the S₁₁ data for power from the input port and represents the reflected energy Curve 22 represents the S₂₂ data for power. This data is can easily be compared to that of the overstitched antenna in FIG. 4. Here the insertion loss data is less as represented by curve 12 and the energy output is greater as shown by curves 11 and 22.

Claims

1. A method of attaching conductive fiber to composite laminate reinforcement fabric and to other fabrics utilizing stitching which comprises:

a means of precisely arranging said conductive fiber on the surface of said reinforcement fabric to minimize radio frequency losses;

an overstitching means wherein said conductive fiber is attached to said reinforcement fabric by a non-conductive retention thread.

2. The method of claim 1 wherein the arranging means and stitching means are accomplished by a person skilled in the art of embroidery.

3. The method of claim 1 wherein the arranging means and the stitching means are accomplished by a person skilled in the art of operating a stitching or embroidery machine.

4. The method of claim 3 wherein the operation of the stitching or embroidery machine is controlled by a computer or other electronic control device