Structurally integrable electrode and associated assembly and fabrication method

A structurally integrable electrode, an assembly with an integrated electrode, and an associated method are provided. The electrode is configured to provide an electrically conductive path between nodes of an electrical circuit of a structural member. In particular, the electrode includes at least one conductive tow having a core and a conductive coating thereon. Electrically conductive contacts are connected to the ends of the tow, and at least one dielectric ply extends parallel to the tow to at least partially insulate the tow. Thus, the first and second contacts can be connected to the nodes of the circuit, and the tow can be structurally integrated with the structural member so that the tow provides an electrically conductive path between the nodes.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to electrodes and, in particular, to an elongate electrode that is integrated with a structural member and provides a path of electrical conductivity, for example, for transmitting signals or power through the structural member.

2) Description of Related Art

Electrical devices are often used in conjunction with a structural member. For example, electrical devices such as sensors and actuators can be embedded within, mounted on, or otherwise structurally integrated with the structure of a vehicle such as an airplane, spacecraft, land vehicle, ship, and the like. Other examples of electrical devices mounted in conjunction with a structural member can include machinery, buildings, and the like. The sensors can be used to detect temperature, motion, stress, strain, damage, and the like at different locations throughout the structure. The actuators can be used to adjust various control portions of the structure such as an elevator, rudder, aileron, helicopter rotor, door, or valve. Data generated by the electrical devices is typically communicated via electrical wires from the devices to a computer or other circuit device for processing. Similarly, control signals and electrical power are typically transmitted via electrical wires from the computer, power supply, and/or other circuit device to the actuators and sensors. Thus, a network of wires is often required for controlling and monitoring the electrical devices. Each wire usually includes one or more conductive strands, for example, copper strands, which are covered with an insulative jacket. Parallel wires can be held in groups with bundle fasteners, such as cable tie straps or shrink tubing. Fasteners such as clips, ties, and the like are often used to connect the wires or bundles of wires to the structural member at successive locations along the length of the wires so that the position of the wires is maintained.

In some applications, however, it is difficult or impractical to connect the wires to the structural member. For example, the structural member may not define any interior cavities through which the wires can be passed, and the environmental conditions outside the structural member may be harsh, for example, excessively warm or cold or subject to mechanical stress, moisture, or corrosive agents. Further, in applications where the structural member undergoes significant or repeated mechanical stress, the resulting strains in the wires can break the wires regardless of whether the wires are connected to the structural member.

One illustrative example is a blade of a helicopter rotor, which is rotated quickly around a hub of the rotor. In some cases, it may be desirable to provide wires that extend along the length of the blade, for example, to monitor sensors or control actuators in or on the blade. The wires cannot be connected to the outside of the blade because of the external conditions, e.g., wind, moisture, and the like. Further, the blade undergoes significant stress due to centripetal force when rotated at high speeds. If the wires are not connected successively or continuously along the length of the blade, each wire will also be strained due to the centripetal force that results from the rotation. On the other hand, if the wires are connected to the blade, the wires will be strained at the same rate as the blade. In either case, the stress that results in the wires can break or fatigue the wires, rendering the electrical devices ineffective.

Thus, there exists a need for an electrode device that can be provided in a structural member for transmitting electrical signals or power. The electrode should be capable of being integrated with structural members and functioning in harsh environmental conditions that include strain and temperature variations, moisture, and corrosive agents. The electrode should also be adaptable and formable to structural members without internal passages for wiring. Further, the electrode should resist failure, even when the structural member is subjected to significant or repeated stresses.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a structurally integrable electrode for providing an electrically conductive path between first and second nodes of an electrical circuit of a structural member. The electrode includes at least one conductive tow having a core and a conductive coating thereon. The tow can be formed of a plurality of reinforcement fibers extending in the longitudinal direction of the tow. The tow can include a core formed of a relatively strong material that is coated with a conductive material. Thus, the tow can resist failure, even if stressed, e.g., with the structural member. First and second electrically conductive contacts, which can be formed of fabric that is coated with a conductive metal, are connected to the ends of the tow. At least one dielectric ply extends generally parallel to the tow and electrically insulates the tow between the first and second ends. Thus, the first and second contacts can be connected to the first and second nodes of the circuit, and the tow can be structurally integrated with the structural member so that the tow provides an electrically conductive path between the first and second nodes. Further, the dielectric material can be formed of polyimide film or another dielectric material (non-reinforced or fiber renforced) compatible with the structural member, e.g., so that the electrode adhesive (which can be conductive or nonconductive) used in the electrode may be integrated into the structural member and cured before or during curing of the structural member.

According to another embodiment, the present invention provides an assembly having a structurally integrated electrode. The assembly includes a structural member defining first and second nodes of an electrical circuit, and the electrode is embedded in the structural member to provide an electrically conductive path between the nodes. For example, the structural member can be formed of a composite material that includes a reinforcement material disposed in a matrix material. In some cases, the electrode and/or bonds between the electrode and the rest of the circuit can be cured with the structural member.

According to yet another embodiment, the present invention provides a method of fabricating a structurally integrable electrode for providing an electrically conductive path between first and second nodes of an electrical circuit of a structural member. The method includes providing at least one conductive tow having a core and a conductive coating thereon, the tow extending along a longitudinal direction from a first end to a second end, and the core being formed of a plurality of reinforcement fibers extending in the longitudinal direction of the tow. First and second electrically conductive contacts are connected to the ends of the tow so that each contact can provide an electrical connection between the tow and one of the nodes. At least one dielectric ply is also disposed generally parallel to the tow and at least partially around the tow so that the ply electrically insulates the tow between the first and second ends. The electrode can be disposed in a structural member, e.g., by embedding the electrode in a composite material of the structural member such as by co-curing the electrode and the structural member, with the electrode connected between nodes of the structural member.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures, and in particular toFIGS. 1-5, there is shown a structurally integrable electrode10during various stages of manufacture according to one embodiment of the present invention. As shown inFIG. 5, the electrode10includes a conductive tow20that extends along a longitudinal direction of the electrode10. The tow20is disposed on a first dielectric ply30, and a second dielectric ply32can be disposed opposite the tow20from the first ply30so that the tow20is sandwiched between the plies30,32. Each of the dielectric plies30,32is configured to electrically insulate at least a portion of the tow20, and the plies30,32can be formed of a variety of dielectric materials, which can be reinforced or non-reinforced. For example, the plies30,32can be formed of E-glass or quartz glass composite materials, or the plies30,32can be formed of a flexible film, such as Kapton® polyimide film, a registered trademark of E. I. du Pont de Nemours and Company. In some cases, the dielectric plies30,32are provided with a contoured surface, e.g., by plasma etching one or both sides of the plies30,32so that the plies are roughened to facilitate bonding of the plies to the adhesive.

First and/or second layers of adhesive material34,36can also be provided between the plies30,32to secure the tow20to the plies30,32. In some cases, the dielectric plies30,32are provided with a contoured surface, e.g., by plasma etching one or both sides of the plies30,32so that the plies are roughened to facilitate bonding of the plies to the adhesive. In addition, contacts40are electrically connected to opposite ends22,24of the tow20. Thus, the contacts40can be connected to nodes of an electrical circuit so that the electrode10provides an electrically conductive path between the nodes.

FIGS. 1–3illustrate the operations of forming the electrode10according to one embodiment of the present invention. As shown, the tow20is disposed on the first dielectric ply30, typically with the layer of adhesive material34therebetween. For example, the adhesive material34can be an unreinforced thin film adhesive such as FM94 from Cytec Industries Inc. of West Paterson, N.J., or other similar material. Alternative adhesive materials include reinforced or thin film adhesives with or without a carrier. If present, the adhesive, reinforcement material, and carrier are typically insulative dielectric materials. Other adhesive materials can similarly be used. In some cases, the second layer of the adhesive material36is provided between the tow20and the second ply32, though one layer of the adhesive material can be sufficient in some cases for securing the plies30,32with the tow20therebetween.

The contacts40are provided at the ends22,24of the tow20and electrically connected thereto. For example, a deformable and/or adhesive conductive material42can be applied to the ends22,24of the tow20to form the electrical connection between the tow20and the respective contact40. The conductive material42can be a conductive epoxy, such as Ablebond® 84-1 LMIT, a registered trademark of National Starch and Chemical Investment Holding Corporation of Wilmington, Del. For purposes of illustrative clarity, the conductive material42is shown applied to only one end22of the tow20inFIG. 1, though the conductive material42is typically applied to both ends22,24in order to connect each end22,24of the tow20to a respective one of the contacts40. The contacts40can be formed of a variety of materials. According to one embodiment of the present invention, the contacts40are formed of pieces of woven fabric, which can be formed of a nonconductive material that is coated with a conductive material. For example, the contacts can be formed of a fabric formed of woven strands of nylon, graphite, Kevlar®, a registered trademark of E. I. du Pont de Nemours and Company, or the like, and the fabric can be coated with conductive materials such as silver, copper, gold, or other metals. The conductive material42and the fabric of the contacts can be cured while the electrode10is partially assembled, e.g., by oven curing the electrode10before the second dielectric ply32is disposed thereon.

As shown inFIGS. 2 and 3, the contacts40can be smaller than the width of the first dielectric ply30so that the ply30extends peripherally from each contact40. In addition, or alternative, the contacts40can be configured inward of the longitudinal ends of the first dielectric ply30so that the ply30extends longitudinally from the contacts40, as shown inFIGS. 2 and 3. Thus, the electrical contacts40can be at least partially insulated by the ply30so that the contacts40do not make unintended electrical contact with other devices or structures. As shown inFIG. 3, the tow20is also insulated by the plies30,32. In fact, both of the plies30,32can extend longitudinally to sandwich part of the contacts40so that the tow20is completely insulated on one side by the first ply30, and the second ply32and the contacts40cover the opposite side of the tow20. As shown inFIGS. 2 and 3, the conductive material42and the contacts40can be disposed before the second layer of the adhesive material36and the second dielectric ply32.

With the electrode10assembled as shown inFIG. 5, the electrode10can be cured by heat and pressure to form the electrode10as a unified structure. For example, the electrode can be cured in an autoclave according to a temperature and pressure schedule that is conventionally used for curing composite structures. Alternatively, the electrode10can be oven cured under vacuum or cured at room temperature. Preferably, the electrode10is able to support a subsequent composite cure cycle without the formation of bubbles due to outgassing, and such a composite cure cycle typically occurs at a temperature of between about 250° F. and 350° F. or higher. In some cases, the electrode10can be disposed in a vacuum bag, i.e., a bladder that is evacuated, during the curing process. As a result of the curing process, the plies30,32of the electrode10are adhered with the tow20therebetween, as shown inFIG. 4. While the layers of adhesive material34,36are shown as distinct layers inFIG. 4, the adhesive material may instead be diffused into the plies30,32and the tow20. In this cured, unified form, the electrode10can be easily handled, stored, transported, and disposed in or on a structural member without disturbing the configuration of the electrode10.

While the electrode illustrated inFIGS. 1–5includes a single tow20, the electrode10can alternatively include multiple tows20in other embodiments of the invention. For example,FIG. 6illustrates the electrode10according to another embodiment of the present invention in which the electrode10includes two of the tows20, each extending generally in the longitudinal direction of the electrode10. In some cases, additional adhesive, such as the first and second layers of the adhesive material34,36, can be provided so that each of the tows20is sufficiently wetted by the adhesive. Each tow20typically extends between the contacts40independently of the other tows20. That is, typically the tows20are not braided, woven, or otherwise interlaced. However, in some cases, the tows20can be interlaced. For example, a wire with interlaced tows is further described in U.S. application Ser. No. 10/369,906, filed Feb. 20, 2003, which application is assigned to the assignee of the present application, and which application is incorporated herein in its entirety by reference. As also shown inFIG. 6, the contacts40can extend to one or more of the edges of the first ply30, in which case the contacts40may be partially exposed at the edges of the electrode10. Further, in other cases, the second dielectric ply32can be omitted.

Each tow20can be formed of a plurality of fibers or filaments26, as generally illustrated inFIGS. 4 and 5. In some cases, each tow20can include thousands of the individual fibers26, which can be formed of materials including, but not limited to, carbon, graphite, nylon, fiberglass, and aramids such as Kevlar® fibers. The use of tows formed of materials such as carbon or graphite fibers for forming composite materials is known in the art. Carbon fibers and other fibers can be formed according to a variety of methods, which are sufficiently known to those skilled in the art that a description herein is unnecessary for a thorough understanding of the present invention. Typically, the fibers26of each tow20are arranged generally parallel to each other and extend longitudinally between the ends22,24of the tow20.

The electrode10is electrically conductive such that the electrode10can be used for transmitting an electrical signal or electrical power along its length. In particular, a conductive material is provided as a conductive coating28on the outer surface of the tow20, and the core of the tow is formed of a nonconductive, semi-conductive, or conductive material. The conductive coating28can include various metals such as silver, nickel, gold, copper, beryllium, aluminum, and alloys thereof. For example, the coating28of the conductive material can be disposed on each tow20by electroplating, vapor deposition, or other coating methods. In one embodiment, the tow20is formed of a metal-plated aramid fiber, e.g., Aracon® fiber, a registered trademark of E.I. du Pont de Nemours and Company, which includes metal-plated Kevlar® fibers. A conductive Aracon® tow can include a plurality of fine metal-clad fibers, such as aromatic polyamides, that are twisted together into a yarn. In other embodiments, the fibers26of the tow20can be formed of a material, such as carbon, that provides some degree of electrical conductivity. For example, conductive core can be provided for the tow20so that the tow20is conductive even without the coating28, and the core can thus provide an alternate path for current flow besides through the coating28.

FIG. 7illustrates a manufacturing assembly50for forming fourteen of the electrodes10according to one embodiment of the present invention. In particular, the assembly50includes seven of the tows20, which are disposed on the first dielectric ply30. The first layer of the adhesive material34is disposed in two portions, indicated by reference numerals34a,34b. The assembly50can be cut where indicated by dashed lines52a,52bto form the individual electrodes10. In particular, the assembly50can be cut along lines52aso that each tow20is separated from the other tows20, and each electrode includes a single one of the tows20. As described above in connection withFIG. 6, the electrodes10can alternatively include multiple tows20, e.g., by making fewer than all of the cuts along lines52a. As indicated by dashed line52b, the assembly50can also be cut to form electrodes10of various lengths. In any case, it is appreciated that other assemblies can be formed for manufacturing any number of the electrodes, each electrode having similar or different configurations. Further, additional elements of each electrode10, such as the conductive material42, the contacts40, the second layer of adhesive material36, the second dielectric ply32, and the like can be disposed before or after the assembly50is cut to form the individual electrodes10. In any case, the assembly50can be cured before or after cutting. Typically, the dielectric plies30,32are disposed in the assembly50in combination with the tow20. That is, the electrode10is assembled and then disposed as a single member into the assembly50.

As illustrated inFIGS. 8 and 9, the electrode10can be integrated into a structural member60so that the electrode10provides a conductive path along the structural member60and between nodes62,64of the structural member60. In this regard, the electrode10can be integrated with various types of structural members and, in some cases, multiple structural members of similar or different compositions. The term “structural member” is not meant to be limiting, and the structural member60can be a single component or multiple assembled members, for example, building components or machinery. Further, the structural member60can be used in any type of structure including vehicles such as aerospace vehicles, aircraft, marine vehicles, automobiles and other land vehicles, and the like. For example, as shown inFIGS. 8 and 9, the structural member60is a helicopter rotor blade with three wire buses66a,66b,66cextending along the length of the member60. The buses66a,66b,66ccan be various types of electrical conductors, e.g., woven or braided conductive wires such as are described in U.S. application Ser. No. 10/369,906. As shown inFIG. 9, the buses66a,66b,66ccan extend to an end of the structural member60, and each bus66a,66b,66ccan be connected to a circuit device70such as a controller mounted in the helicopter. The buses66a,66b,66ccan extend to the circuit device70, or intermediate connection devices68such as wires or other conductive elements can be provided therebetween.

Two electrical devices72,74are disposed in the structural member60, and the electrical devices72,74are electrically connected to the buses66a,66b,66cby electrodes10a,10b,10c,10d, which are referred to collectively by reference numeral10. Thus, the circuit device70is connected to the electrical devices72,74via the buses66a,66b,66cand electrodes10a,10b,10c,10dso that the circuit device70can monitor, actuate, and/or power the electrical devices72,74. In particular, the first bus66ais connected to the first electrical device72by the first electrode10a. Both of the electrical devices72,74are connected to the second bus66bby electrodes10b,10c, respectively. Electrode10dconnects the third bus66cto the second electrical device74. In this configuration, the second bus66bprovides a connection to both electrical devices72,74, while the first and third buses66a,66cprovide independent connections to the respective devices72,74.

Each of the electrical devices72,74can be an active or passive electrical device. For example, each electrical device72,74can be an actuator such as a piezo-fiber actuator pack that can be used to provide active aerodynamic control and vibration reduction of the structural member60. In other embodiments, each of the electrical devices72,74can be a sensor, such a strain gauge that senses deformation in the structural member60, a light-emitting device, a computer, a processor, a power supply, or any other circuit device. The structural member60can include any number of the electrical devices72,74, each of which can be controlled independently or in combination. Each electrode10can communicate data, transmit control signals, and/or supply power between the electrical devices72,74and the buses66a,66b,66c. The electrodes10and/or the buses66a,66b,66ccan also provide an electrical ground path for the devices72,74. Typically, the electrical devices72,74are also integrated with the structural member60, e.g., by mounting the devices72,74in or on the structural member60.

One of the contacts40of each electrode10can be connected to the respective bus66a,66b,66cby a conductive material such as conductive epoxy that can be cured before or during the curing of the structural member60. Similarly, conductive epoxy can be used to connect the opposite contact40of each electrode10to a lead or electrical contact of the respective electrical device72,74. Alternatively, the electrodes10can be connected by other materials, such as solder, or by a device such as a mechanical connector.

According to one embodiment of the present invention, the structural member60is formed of a composite material including fibers or tows that are impregnated with a matrix of a cured resin, and each electrode10and/or the buses66a,66b,66ccan be structurally integrated with the structural member60. For example, each electrode10can be embedded between the reinforcement materials of a composite structural member. Typically, the electrode is embedded into the structural member60before the composite material of the structural member60is cured so that as the structural member60is cured, the electrode10is integrated with the structural member60to form a substantially continuous structure. As noted above, the electrode10can be cured before or during the curing of the structural member60. Integration of electrodes, electrical devices, wire buses, and the like is further described in U.S. application Ser. No. 10/848,703, titled “STRUCTURALLY INTEGRATED CIRCUIT AND ASSOCIATED METHOD,” filed concurrently herewith, assigned to the assignee of the present application, and which application is incorporated herein in its entirety by reference.

In some cases, the electrode10can be partially or completely embedded or encapsulated in the material of the structural member60. Thus, during operation of the structural member60, the electrode10can be subjected to substantially the same strains as the structural member60. Typically, the tow20of the electrode10is formed of a material that is about as strong as, or stronger than, the structural member60so that the electrode10is unlikely to break or otherwise fail during operation of the structural member60. For example, the structural member60can include reinforcement materials that are the same as the tow20. In other embodiments, the electrode10can be integrated with a structural member formed of other conventional materials including polymers, metals, and the like. Further, the electrode10can alternatively be secured to the structural member60in other manners, such as by bonding the electrode thereto with adhesive, mechanical connectors, and the like.

As noted above, the electrodes10, buses66a,66b,66c, and/or the electrical devices72,74can be disposed within the structural member60. Each of the components10,66a,66b,66c,72,74can be disposed during the assembly of the structural member60. For example, as shown inFIG. 10, the structural member60can be formed of a composite material having a plurality of layers76formed of sheets, tows, fibers, or the like, that are impregnated with a matrix of a thermoset or thermoplastic matrix material such as a resin. The electrodes10, buses66a,66b,66c, and/or the electrical devices72,74can be disposed during the lay-up of the various layers76of the structural member60, e.g., by laying the components10,66a,66b,66c,72,74between the layers76of the structural member60as a stacked layup on a mandrel or other tool and then compressing and curing the structural member60with the components therein. As the composite structural member60is cured, the electrode10is joined to the structural member60, or integrated with the structural member60, so that fasteners such as clips are not required. In some cases, multiple electrodes10can be layered within the structural member60, as shown inFIG. 10.

In addition, layers78can be disposed adjacent the electrodes10for reinforcement and/or insulation. For example, one or more of the layers78can be disposed between the electrodes10a,10band between the electrodes10c,10dto electrically isolate the respective electrodes10and prevent electrical communication therebetween. The layers78can be formed of the same reinforcement material of the layers76or the same material as the dielectric layers30,32of the electrodes10. Alternatively, the layers78can be formed of a different material, which can be chosen, e.g., to provide a particular electromagnetic shielding between the adjacent electrodes10. The layers78can be any size. For example, according to one embodiment, the layers78can correspond in size to the adjacent electrodes10a,10b,10c,10dso that the layers78generally isolate the electrodes10but do not extend to positions remote from the electrodes10. Alternatively, the layers78can extend from the electrodes10, e.g., so that each layer78can isolate multiple electrodes10disposed along the length of the structural member60.

The electrode10can extend in a generally longitudinal direction between the various nodes62,64of a circuit of the structural member60, e.g., between the buses66a,66b,66cand the electrical devices72,74, so that the electrodes10electrically connect the electrical devices72,74to the buses66a,66b,66c. The term “longitudinal” is intended to indicate generally that the electrode10extends generally between the two or more nodes62,64that are spaced apart in, though the particular path of the electrode10need not be a straight or direct path. That is, each electrode10is configured in a predetermined pattern and interconnected into a circuit to obtain the desired performance, and the electrodes10can be spaced as necessary to obtain the desired electrical conduction and isolation. For example, as shown inFIGS. 8–10, the integrated electrode10may be routed in a nonlinear configuration according to a variety of design factors that are particular to the structural member60including, for example, the shape of the structural member60, the placement of the electrical devices72,74, the anticipated variation of stress and strain throughout the structural member72,74, and the like. Further, in some cases, more than two of the electrical devices72,74can be connected by the electrode10, and the devices72,74can also be connected at different locations along the electrode10.

While the electrode10discussed above is described as being electrically conductive, the electrode10could alternatively be configured to otherwise conduct or transmit energy. For example, the tow20of the electrode10can be a fiber optic member that is configured to optically conduct, such that the electrode10can be used to transmit light, such as for communicating a signal to and/or from devices disposed throughout the structural member60. While fiber optic fibers can be disposed in the electrode10and subsequently in the structural member60in a manner generally similar to that described above, the connections between optic fibers and the buses, devices, and the like are configured to transmit light.