This invention relates to composite self-supporting structures.

By "self-supporting structures" is meant structures that are capable of maintaining their form under the action of Earth's gravity.

Composite materials are well known and include such everyday materials as plywood, glass fibre reinforced plastics [GFRP] and carbon fibre reinforced composites. Reasons for using composite materials over other materials may include strength, rigidity, toughness, or weight. Applications in which composite materials are becoming more prevalent include, without limitation :-

• aerospace and automotive applications;

• building applications;

• armour applications, for example in helmets.

It is known to provide composite materials comprising electrically conductive pathways. For example :-

• US2015083709 discloses a shapeable heating panel system in which a non- woven fabric comprising electrically conductive fibres is laminated between layers, at least one of which comprises a thermoplastic shapeable material, with electrodes provided to enable current to pass through the non-woven fabric. Such an arrangement effectively passes electricity through the entirety of the layer comprising the non- woven fabric;

• US 8029295 discloses electrical circuits embedded in a laminated composite structure, and describes forms of connector for such circuits. Such an arrangement is vulnerable to damage to the conductors, and in addition the conductors can provide regions of weakness through poor bonding of the layers either side of the conductors and the introduction of stresses in layers adjacent the conductors;

• US 2014/0097011 discloses a composite comprising a plurality of electrical lines embedded therein;

• WO2010/004262 discloses a hybrid material comprising a plurality of spaced isolated electrically conducting fibres extending in a first direction with electrically insulating fibres extending in a second direction to define a material having a plurality of insulated electrically conductive tracks.

In the above documents electrical conduction is either through the entirety of a conductive layer, or through a plurality of separate spaced tracks. Such an approach does not provide for branched circuits.

The applicants have realised that fabrics comprising electrically conductive yarns arranged to provide fabric electrical circuits can be used in composite materials to provide for transmission of data and/or power to connectors embedded in or mounted to the composite material, and thereby provide fault tolerant electrical circuitry embedded in a composite self- supporting structure. The inventors have further realised that woven or knitted textiles may provide advantages over non- woven fabrics.

Woven or knitted textiles comprising electrically conductive yarns arranged to provide electrical circuits are known for example from WO01/75778, WO2005/083164, the Broadsword "Spine" products for soldiers

and from "Intelligent Textiles: Reducing the Burden", RUSI Defence Systems February 2010

https://www.rusi.org/downloads/assets/swallow RDS feb2010.pdf.

Such textiles have become known as "e-textiles". However such textiles have only been considered in the context of flexible fabrics (for example, for clothing) where emphasis is on replacing heavy and stiff cables.

By incorporating textiles comprising electrically conductive yarns arranged to provide electrical circuits into a composite material, power and/or data can be distributed:-

• in a manner providing redundancy of pathways, so providing a defence against damage;

• in a manner providing lesser weight than the use of cables;

• with improved composite integrity as bonding between the materials of layers either side of the textile can take place through the natural interstices present in the textile and so can be relatively uniformly distributed;

• with further improved composite integrity, as the majority composition of the electrically conductive textile may be so selected to be similar to the existing layers that conventionally compose the composite material, for example aramid fibres or glass fibres;

• with simplified manufacturing, as the electrically conductive textile may be handled, processed and formed in a manner largely akin to that of the existing layers.

The present invention is as set out in the claims, and in its broadest aspect provides a self- supporting composite structure comprising electrically conductive fabric circuit patterns embedded in an electrically insulating matrix, the fabric circuit patterns providing a plurality of discrete conductive pathways..

By "discrete conductive pathways" is meant separate and distinct pathways as opposed to the random or homogeneous conduction provided by a uniform sheet of electrically conductive material.

In a second aspect, the present invention provides a self-supporting composite structure comprising at least one layer of fabric embedded in an electrically insulating matrix, the fabric comprising electrically conductive fibres arranged to provide a plurality of discrete conductive pathways, at least one of said pathways being a branched pathway.

The invention is exemplified by way of example in the following description with reference to the drawings in which :-

Fig. 1 is a schematic illustration of printed circuit method not in accordance with the present invention;

Fig. 2 is a schematic illustration of the use of a fabric circuit; and

Fig. 3 is a schematic illustration of the use of a different fabric circuit; and

Fig. 4 is a schematic illustration of a helmet incorporating a fabric circuit.

In the drawings, like integers are described using the same references.

The purpose of the invention is to provide a self-supporting structure comprising integral pathways capable of transferring power and/or data. The inventive concept may be thought of as the incorporation of a conductive flexible fabric layer within the structure of a rigid composite structure such that the conductive flexible fabric layer can be connected to by external devices. In Fig. 1 a portion of a composite article 1 is shown in plan section and part transverse section and comprises printed circuit patterns formed in conventional manner forming pathways 2,3 leading to connectors 4,5 for connection to an electrical device (not shown). As can be seen the pathways 2,3 are embedded in the matrix 6 of the composite article, which matrix may be a laminated structure. The pathways 2,3 provide regions of weakness in the composite, since the matrix 6 can only bond around the pathways 2,3 and not through them. Additionally, when the composite article is manufactured in a lay-up method, the variable thickness of the layer comprising the pathways 2,3 can introduce stresses in the composite article. The higher the current required to be carried, the larger the conductive pathway has to be [in depth or width or both], which exacerbates the bonding and/or stress problems.

In Fig.2, a portion of a composite article 7 is shown in plan section and part transverse section and comprises circuit patterns (analogous to the printed circuit patterns of Fig. 1) formed from a fabric comprising electrically conductive fibres, the fabric being cut to form pathways 8,9 leading to connectors 4,5 for connection to an electrical device (not shown). As can be seen the pathways 8,9 are embedded in the matrix 6 of the composite article, which matrix may be a laminated structure. Pathway 9 is a branched pathway. The pathways 8,9 provide less of a region of weakness than in the article of Fig, 1 since the matrix 6 can bond through interstices in the fabric. Such an article is complex to make however, since the individual pathways require handling, and so the pathways may be mounted on a scrim 10. Such arrangements may have problems in use, since when the composite article is manufactured in a lay-up method, the variable thickness of the layer comprising the pathways 8,9 can introduce stresses in the composite article.

In Fig. 3, a portion of a composite article 11 is shown in plan section and part transverse section and comprises circuit patterns (analogous to the printed circuit patterns of Fig. 1) formed from a fabric comprising conductive fibres arranged to form pathways 12,13 (including branched pathway 13) leading to connectors 4,5 for connection to an electrical device (not shown). As can be seen the pathways 12,13 are embedded in the matrix 6 of the composite article, which matrix may be a laminated structure. The pathways 12,13 provide regions of weakness in the composite, but less than in the composite article 1 of Fig, 1 since material of the matrix 6 can bond through interstices in the fabric. Since the fabric is of a relatively uniform thickness, the layer comprising the pathways 12,13 is less likely to introduce stresses in the composite article than the products of Fig. 1 or Fig. 2. The fabric comprising electrically conductive fibres may be a non-woven fabric with electrically conductive fibres provided in selected regions either by addition or by selective lay down of fibres in manufacture of the non-woven fabric. However, non-woven fabrics comprising electrically conductive fibres may have a relatively high resistance compared to woven or knitted textiles such as the woven or knitted textiles comprising electrically conductive yarns described above. In such woven or knitted textiles textiles conductive fibres may extend throughout the textile and be selectively connected in the desired pathways. Woven or knitted fabrics may be made with defined width interstices between the conductive fibres, and this permits tailoring of the fabric to provide optimum bonding of the matrix through the interstices consistent with the desired pathway distribution.

In an alternative approach, a non-conductive fabric may be printed with a conductive material to form conductive tracks. However this approach is less preferred, as liable to having poor conductivity and poor robustness during handling. In both the structures of Fig. 2 and Fig. 3, high current requirements can be dealt with by providing a wide pathway without causing the bonding problems of the structure of Fig. 1.

The incorporated fabric layer can transfer power or data, or be woven or knitted such that it can carry both power and data. The fabrics may be of the type described in Intelligent Textiles Ltd patent US8298968, WO01/75778, WO2005/083164, or the Broadsword "Spine" products for soldiers. The fabric may consist of yarns traditionally used in composites (.e.g. aramid or glass) interwoven with conductive yarns which may be in the form of nickel or silver coated yarns, carbon yarns or other such conductive yarn. Almost any weave style can be used to produce these fabrics.

Where required multiple layers of fabric may be used to provide pathways on separate levels. The fabric may be incorporated into the composite structure either as a post-process [the fabric being moulded to a pre-existing article] or as an integral moulding. The moulding can be a lay-up process in which successive layers of material are assembled and hardened to form a composite structure.

Layers of material may comprise fabrics other than the fabric comprising electrically conductive fibres, for example comprising aramid, glass, or other insulating fibres.

The connectors can be incorporated with the fabric, the fabric and connectors being moulded into the composite structure at the same time, or by moulding the fabric into the structure and attaching the connectors post moulding.

The connectors themselves can form both the attachment method for external devices, as well as the means of transferring power and data.

In addition to connectors, electrical components connected to the fabric may be integrated into the composite structure [examples include, without limitation: control circuitry and components, induction loops, lighting components, and audio components]. The fabric layer can be placed at any point in the layers of material making up the composite structure, but optimal structural performance for mounting devices is achieved by placing the conductive fabric somewhere from the middle of the structure to the surface of the structure furthest from the mounted device. Further features, variants and applications of self-supporting structures comprising such embedded pathways include:-

Rigid composite panels incorporating power and/or data pathways have much utility. This invention allows the moulding of complex shapes incorporating such pathways. The fabric can be woven such that there are many different routes for power and data to travel from point A to point B, making the fabric fault tolerant, a key advantage of this approach. Potential application of this technology include:

• Electrical circuitry

• Building panels

• Automotive applications

• Ballistic structures

The last aspect includes static or moveable ballistic structures and also ballistic structures for personal protection, e.g. helmets. The following example illustrates the application to helmets with reference to Fig. 4. In Fig 4 a helmet 14 is shown comprising an e-textile system of pathways 15 (shown separately for convenience) which is embedded into the helmet to provide a composite structure comprising an embedded fabric having conductive pathways.

The pathways 15 connect to a helmet module 16 comprising a data hub and battery that can recharge from a torso power supply via cable 17 that can act as a data and audio feed too. Connectors 18 embedded in the helmet or helmet cover are used to connect to peripherals 19, including for example, night vision systems, illuminators, cameras, audio equipment.

In constructing a ballistic helmet, a typical construction might be:

Kevlar 258 HPP is a plain woven Kevlar fabric of 3140 dtex yarns, woven at 64 yarns / 10cm to a fabric weight of 400gsm. This is impregnated on one side with a pvb-phenolic resin film of 50gsm. Kevlar 258 HPD is the same base fabric with a double- sided layer of pvb-phenolic resin applied i.e. a 50gsm layer of phenolic is laminated on each side of the fabric.

Connectors [e.g. Glenair® "Mighty Mouse" connectors from Glenair Inc.] may be used to connect to the conductive fabric layer. Accessories can then be mounted to the connectors in order to connect to the helmet. Different connector types would require the conductive fabric to be placed at different points throughout the thickness.

Further modifications and variants to the invention are possible while still remaining within the scope of the claims. In particular it should be noted that optical fibres may be embedded to provide optical data connectivity as an alternative to or in addition to the use of electrically conductive fibres for this purpose.