Patent Description:
<CIT>, according to its abstract, states a composite ice protection heater for an aircraft. The composite heater includes at least one electrically insulating layer, and at least one electric heater element comprising an electrically conductive layer bonded to the insulating layer. The conductive layer may include a pre-impregnated woven fabric that includes a plurality of threads that include an electrically conductive material, such as carbon or graphite fibers. The composite heater can be incorporated into a composite surface structure of an aircraft. The conductive layer and insulating layer may include a plurality of spaced openings through the layers that cooperate with an underlying open-cell matrix to attenuate noise at the associated surface of an aircraft. A desired electrical resistance of the conductive layer may be obtained by introducing a plurality of discontinuities in the layer, such as spaced holes or slits.

<CIT>, according to its abstract, states an electrically conductive structural composite which can be heated by application of an electrical current. The structural composite includes a plurality of layers of structural fabric which have been treated and prepreged with a laminating resin and cured into a laminate structure. At least one of the layers of fabric is rendered conductive by being treated with conductive polymer produced by the steps of contacting an electrically insulating porous structural fabric with a liquid pyrrole; contacting the electrically insulating porous structural fabric with a solution of a strong oxidant capable of oxidizing pyrrole to a pyrrole polymer; and, oxidizing the pyrrole by the strong oxidant in the presence of a substantially nonnucleophilic anion and precipitating a conductive pyrrole polymer in the pores of the structural fabric. Electrical conducting means in electrical contact with the conductive layer are utilized for providing passage of electrical current for joule heating of the structural composite. The structural composite has been found to be particularly useful as an airplane surface which is capable of anti-icing and de-icing.

In examples, a conductive polymer is produced by an emulsion polymerization method to form an organically soluble conductive polymer. The soluble conductive polymer can then be cast into a film having a particular electrical conductivity. Electrical conductivity (or specific conductance) is a measure of the film's ability to conduct electricity. Electrical conductivity can be measured in units of Siemens per meter (S/m) or Siemens per centimeter meter (S/cm), for example. Electrical conductivity is the reciprocal of electrical resistivity, which is measured in (Ohm. m) or (Ohm. For example, the film of conductive polymer may have electrical conductivity on the order of 1E-<NUM>/cm.

Electrical conductivity of the film may be increased by treating the film with a conductivity enhancer (e.g., isopropanol). For instance, conductivity of the film made of the conductive polymer may be increased to approximately <NUM>/cm, which amounts to <NUM> orders of magnitude increase from the film before treatment with isopropanol.

The conductive polymer may be brittle and not suitable to some applications. To make the conductive polymer usable in particular applications, it is first rendered flexible and compatible with other materials by, for example, formulating the conductive polymer in polyurethane, epoxy, or phenoxy resins, among other example resins. Formulating conductive polymer in a resin may, for example, involve dispersing the conductive polymer in the resin to form a network of the conductive polymer therein.

However, formulating the conductive polymer in the resin reduces or degrades electrical conductivity of the conductive polymer. For instance, electrical conductivity of the conductive polymer may be reduced to lower than 1E-<NUM>/cm despite treatment with isopropanol. Such reduction or degradation in electrical conductivity may be undesirable.

It may thus be desirable to have films or layers of a conductive polymer that are usable in various applications without degradation to electrical conductivity of the conductive polymer films or layers.

The present disclosure describes examples that relate to multilayer stack with enhanced conductivity and stability. In one aspect, the present disclosure describes a method as defined in claim <NUM>.

In another aspect, the present disclosure describes a device as defined in claim <NUM>.

In still another aspect, the present disclosure describes a component of a vehicle such as an aircraft. The component includes a multilayer stack of conductive polymer layers and insulating layers disposed on or proximate to a surface of the component. The multilayer stack includes a plurality of conductive polymer layers, each conductive polymer layer being interposed between respective insulating layers. Each conductive polymer layer has a respective electrical resistance, such that when the respective conductive polymer layers are connected in parallel to a power source coupled to the aircraft, a resultant electrical resistance of the respective conductive polymer layers is less than each respective electrical resistance.

The novel features believed characteristic of the illustrative examples are set forth in the appended claims. The illustrative examples, however, as well as a preferred mode of use, further objectives and descriptions thereof, will best be understood by reference to the following detailed description of an illustrative example of the present disclosure when read in conjunction with the accompanying Figures.

Formulating a conductive polymer in an insulating material such as resin reduces or degrades electrical conductivity of the conductive polymer despite treatment with a conductivity enhancer such as isopropanol (IPA). Such reduction or degradation in electrical conductivity may be undesirable. Within examples described herein is a multilayer stack having a conductive polymer layer treated with a conductivity enhancer and "sandwiched" or interposed between two insulating layers. An example process disclosed herein involves casting and curing a film of an insulating material such as resin (e.g., polyurethane (PUR)) followed by applying a coating of conductive polymer. The conductive polymer can then be treated with a conductivity enhancer to increase electrical conductivity of the conductive polymer layer. The treated conductive polymer layer may then be dried, and another insulating layer is applied and cured. This layer-by-layer stack-up provides a protective encapsulation of the conductive polymer from the environment and maintains the level of electrical conductivity of the conductive polymer layer.

Further, this process allows for forming a multilayer stack of conductive polymer layers and can lower overall electrical resistance of the multilayer stack. In particular, as the number of layers increases, the electrical resistance decreases per Ohm's law. As such, a multilayer stack of conductive polymer layers interposed between insulation layers can be fabricated to have a particular electrical resistance.

<FIG> illustrate stages of fabricating a multilayer stack, in accordance with an example implementation. The illustrations shown in <FIG> are generally shown in cross-sectional views to illustrate sequentially formed layers developed to create the multilayer stack. The layers can be developed by microfabrication and/or manufacturing techniques such as, for example, electroplating, photolithography, deposition, and/or evaporation fabrication processes, spin coating, spray coating, roll-to-roll coating, ink jet, direct-write, among other possible deposition or forming techniques.

Further, in examples, the various materials of the layers may be formed according to patterns using photoresists and/or masks to pattern materials in particular arrangements. Additionally, electroplating techniques can also be employed to coat ends or edges of conductive polymer layers with electrical contacts (e.g., metallic pads or electrical leads). For example, an arrangement of conductive material formed by a deposition and/or photolithography process can be plated with a metallic material to create a conductive electrical contact.

The dimensions, including relative thicknesses and widths, of the various layers illustrated and described in connection with <FIG> to create a multilayer stack are not illustrated to scale. Rather, the drawings in <FIG> schematically illustrate the ordering of the various layers for purposes of explanation only.

<FIG> illustrates a substrate <NUM> with an insulating layer <NUM> formed on the substrate <NUM> to provide a partially-fabricated multilayer stack <NUM>, in accordance with an example implementation. In some examples, the insulating layer <NUM> can adhere to the substrate <NUM>. In examples, the insulating layer <NUM> can be configured to facilitate forming a conductive polymer layer thereon, such that the conductive polymer layer adheres to the insulating layer <NUM>.

As examples, the substrate <NUM> can be made out of an epoxy resin, a composite structural material (e.g., of a wing, blade, or any component of an aircraft), thermoplastic resin, thermoset material, a polycarbonate material, etc. The substrate <NUM> can be cleaned before forming the insulating layer <NUM>. The substrate <NUM> may be cleaned in a variety of ways such as soaking in a first fluid, rinsing with a second fluid, and drying with a gas. In some examples, the first fluid can include a solvent, such as acetone. Moreover, in some examples, the second fluid can include isopropyl alcohol. Further, in some examples, the gas can include nitrogen. Rinsing may be performed in a variety ways, such as soaking in a bath in a tank, an automated spray, manually via a squirt bottle, etc..

In examples, the substrate <NUM> can be baked before forming the insulating layer <NUM>. The substrate <NUM> may be baked at a particular temperature for a time period. For example, the temperature can be <NUM> degrees Celsius (C) and the time period may be <NUM> minutes. In other examples, the substrate <NUM> can be plasma cleaned before forming the insulating layer <NUM>. The substrate <NUM> may be plasma-cleaned at a particular power level for a time period.

The insulating layer <NUM> can be formed, for example, of a resin material. Example resin materials include epoxy, thermoplastic resins, phenolic resins, or silicone resins, which are characterized in being durable and operable under elevated temperatures. It may be desirable to configure the insulating layer <NUM> of a thermostable resin material. As a specific example, the insulating layer <NUM> can be made of PUR, which is a polymer composed of organic units joined by carbamate (urethane) links. PUR can be a thermosetting polymer or a thermoplastic polymer. PUR can be formed by reacting a di- or poly-isocyanate with a polyol. PUR is described herein as an example for illustration, and other types of resin could be used to make the insulating layer <NUM>.

The insulating layer <NUM> can be deposited on the substrate <NUM> in a variety of ways such as brushing, painting, patterning, printing, any additive manufacturing method, etc. In examples, after forming the insulating layer <NUM> on the substrate <NUM>, the insulating layer <NUM> may be cured (e.g., cured at a particular temperature such as <NUM> C). Curing may involve toughening or hardening of the insulating material by heat or chemical additives, among other processes. Curing can be partial or can be full depending on the application and implementation. The insulating layer <NUM> can have a surface <NUM> configured to receive a conductive polymer layer as described next.

<FIG> illustrates a conductive polymer layer <NUM> formed on the insulating layer <NUM> to provide a partially-fabricated multilayer stack <NUM>, in accordance with an example implementation. The conductive polymer layer <NUM> can be made of any of several conductive polymers. For example, the conductive polymer layer <NUM> can be made of polyaniline (PANI), poly(ethylenedioxythiophene) (PEDOT), poly(styrenesulfonate) (PSS), dodecylbenzene sulfonic acid (DBSA), Dinonylnaphthylsulfonic acid (DNNSA), Polypyrrole (PPy), mixtures thereof, or salts thereof. In other examples, the conductive polymer layer <NUM> could be made of graphene paint, carbon nanotubes paint, carbon black paint, conductive oxides, or conductive paints containing metal or metallic particles.

In examples, the conductive polymer layer <NUM> could be made of an intrinsically conducting polymer (ICP). ICPs include synthetic organic polymers configured to conduct electricity. In other examples, the conductive polymer layer <NUM> could be made of an extrinsically conducting polymer. An extrinsically conducting polymer is obtained by adding specific additives (e.g., metallic particle fillers) to a naturally insulating polymer to render such an insulting polymer electrically conductive.

As a specific example for illustration, the conductive polymer layer <NUM> can be made of Polyaniline-Dinonylnaphthalene sulfonic acid (PANI-DNNSA). PANI is a conducting polymer of the semi-flexible rod polymer family, and is characterized by high electrical conductivity. DNNSA is an organic chemical, e.g., an aryl sulfonic acid. In examples, DNNSA has a melting point of <NUM> C and a boiling point of <NUM> C. DNNSA is stable above <NUM> C. DNNSA can be prepared by reaction of naphthalene with nonene, yielding diisononylnaphthalene. Diisononylnaphthalene then undergoes sulfonation. DNNSA can be added to a PANI fluid to increase the electrical conductivity of the fluid. PANI-DNNSA is used herein as example; however, any other conductive polymer, such as the conductive polymers, mentioned above could be used.

In an example, the conductive polymer can be produced by an emulsion polymerization method to form an organically soluble conductive polymer. The organically soluble conductive polymer can then be mixed with toluene, for example. Toluene is a colorless, water-insoluble liquid that operates as a solvent. Toluene is a mono-substituted benzene derivative, having a CH<NUM> group attached to a phenyl group. In this example, the conductive polymer in toluene may be applied or deposited to the surface <NUM> of the insulating layer <NUM> to form the conductive polymer layer <NUM> shown in <FIG>.

In an example, the conductive polymer layer <NUM> in toluene may be brushed on the surface <NUM> of the insulating layer <NUM> to form a uniform layer thereon so as to have consistent electrical resistance over the substrate <NUM>. Other depositing techniques could be used to form the conductive polymer layer <NUM> on the insulating layer <NUM>. For instance, the conductive polymer layer <NUM> may be formed by a microfabrication process such as chemical vapor deposition, spin coating, spray coating, roll-to-roll coating, ink jet printing, patterning, direct-write. For example, the conductive polymer material may be spin coated by placing the conductive polymer material on the partially-fabricated multilayer stack <NUM>, applying a spread cycle, applying a spin cycle, and applying a deceleration cycle.

In examples, the conductive polymer layer <NUM> may be deposited onto the insulating layer <NUM> with a substantially uniform thickness such that a surface of the conductive polymer layer <NUM> is substantially flat. In some examples, the conductive polymer layer <NUM> can be configured as a conformal coat.

An adhesion promoter can be applied to the surface <NUM> of the insulating layer <NUM> before the conductive polymer layer <NUM> is formed. With such an arrangement, adhesion of the conductive polymer layer <NUM> to the insulating layer <NUM> may be improved. In some examples, the adhesion promoter can comprise <NUM>-methacryloyloxypropyltrimethoxysilane, and in other examples, the adhesion promoter may comprise hexamethyldisilazane (HDMS), which can enhance adhesion of the conductive polymer layer <NUM> to the insulating layer <NUM>. Other adhesion promoters are possible as well.

The adhesion promoter may be applied in a variety of ways such as spin coating at a particular rate (e.g., <NUM> rpm), baking at a temperature for a first time period, rinsing with a fluid (e.g., IPA), and baking at the temperature for a second time period. In such examples, applying the adhesion promoter by spin coating may involve accelerating and/or decelerating the partially-fabricated multilayer stack <NUM>. Other application methods of the adhesion promoter are possible. Moreover, the partially-fabricated multilayer stack <NUM> can be cleaned (e.g., via rinsing or plasma cleaning) before applying the adhesion promoter to the surface <NUM> of the insulating layer <NUM>.

The surface <NUM> of the insulating layer <NUM> can be treated, such that the conductive polymer layer <NUM> bonds to the treated surface during formation of the conductive polymer layer <NUM>. The surface <NUM> may be treated in a variety of ways such as by etching using an inductively coupled plasma.

The conductive polymer layer <NUM> can be dried at a particular temperature, and treated with a conductivity enhancer to enhance electrical conductivity of the conductive polymer layer <NUM>. An example conductivity enhancer can include a morphology enhancer such as IPA. In this example, to enhance electrical conductivity of the conductive polymer layer <NUM>, the conductive polymer layer <NUM> may be rinsed several times with IPA. The conductive polymer layer <NUM> (e.g., PANI-DNNSA) can be treated with IPA using other methods. In other examples, the conductive polymer layer <NUM> can be treated with a band modifier to enhance electron hole mobility, and thus enhance electrical conductivity of the conductive polymer layer <NUM>. Other conductivity enhancers could be used as well.

As described above, the conductive polymer layer <NUM> is formed on the insulating layer <NUM> such that the conductive polymer layer <NUM> adheres to the insulating layer <NUM>. Because the insulating layer <NUM> is interposed between the conductive polymer layer <NUM> and the substrate <NUM>, the conductive polymer layer <NUM> need not be configured to adhere to a material of the substrate <NUM>. With this configuration, the conductive polymer layer <NUM> is not formulated in a resin, and thus the electrical conductivity of the conductive polymer layer <NUM>, which may be enhanced by treatment with a conductivity enhancer, is not degraded.

In examples, the conductive polymer layer <NUM> may have a thickness less than <NUM> one thousandth of an inch (i.e., less than <NUM> mil. However, other thicknesses are possible. The conductive polymer layer <NUM> can have a surface <NUM> configured to receive another insulating layer as described next.

<FIG> illustrates another insulating layer <NUM> formed on the conductive polymer layer <NUM> to provide a partially-fabricated multilayer stack <NUM>, in accordance with an example implementation. The insulating layer <NUM> can comprise another resin layer similar to the insulating layer <NUM>. In an example, the insulating layer <NUM> may be diluted with a solvent such as dimethylcarbonate to give a <NUM>% mass/mass (w/w) solution.

The insulating layer <NUM> can be applied to the surface <NUM> of the conductive polymer layer <NUM> in a similar manner to applying the insulating layer <NUM> to the substrate <NUM>. As such, the insulating layer <NUM> may be spin coated, brushed, patterned, printed, etc. on the surface <NUM>. An adhesion promoter can be applied to the surface <NUM> to facilitate adhesion of the insulating layer <NUM> to the surface <NUM> of the conductive polymer layer <NUM>. The insulating layer <NUM> can then be cured at a particular temperature (e.g., <NUM> C).

<FIG> illustrates electrical contacts <NUM>, <NUM> formed on edges of the conductive polymer layer <NUM> to provide a multilayer stack <NUM>, in accordance with an example implementation. The electrical contact <NUM> can be formed at a first lateral edge or end of the conductive polymer layer <NUM>, whereas the electrical contact <NUM> can be formed at a second lateral edge or end, opposite the first lateral edge or end, of the conductive polymer layer <NUM>.

Each of the electrical contacts <NUM>, <NUM> can be formed independently as a piece of electrically conductive material made of a metal. For instance, the electrical contacts <NUM>, <NUM> could be configured as metal (e.g., silver or gold alloy) pads. However, the electrical contacts <NUM>, <NUM> could take other forms such as an electrical lead or a wire.

The electrical contacts <NUM>, <NUM> may be sprayed, brushed, patterned (printed) or deposited at the lateral ends or edges of the conductive polymer layer <NUM> via other techniques. The electrical contacts <NUM>, <NUM> can then be used to connect a power source (direct current or alternating current source) to the conductive polymer layer <NUM>. In examples, electrical connections between the electrical contacts <NUM>, <NUM> and the power source could be made using conductive inks or metals applied with evaporation or cold-spray techniques.

<FIG> illustrates a power source <NUM> coupled to the multilayer stack <NUM>, in accordance with an example implementation. The power source <NUM> is depicted as an alternating current (AC) source; however, other types of power sources could be used.

With this configuration, the conductive polymer layer <NUM> can operate as an electrical resistance. In other words, the conductive polymer layer <NUM> has a particular electrical conductivity based on the amount of conductive material in the conductive polymer layer <NUM>, a thickness of the conductive polymer layer <NUM>, and treatment with a conductivity enhancer. As electric current flows through the conductive polymer layer <NUM>, heat is generated. In particular, due to the electrical resistance of the conductive polymer layer <NUM> (i.e., resistance to motion of electrons), electrons of the electric current bump into atoms within the conductive polymer layer <NUM>, and thus some of the kinetic energy of the electrons is transferred to the atoms of the conductive polymer layer <NUM> as thermal energy. This thermal energy causes the conductive polymer layer <NUM> to be heated. As such, electric power from the power source <NUM> is dissipated as thermal energy from the conductive polymer layer <NUM>.

In a specific experimental implementation, the substrate <NUM> is made of a <NUM> inches by <NUM> inches polycarbonate substrate. The insulating layer <NUM> is then applied as a PUR coating via a brush to the polycarbonate substrate, and the PUR coating is then cured at <NUM> degrees C. PANI-DNNSA in toluene is then applied via a brush to the surface of the PUR coating to form the conductive polymer layer <NUM>, and then the PANI-DNNSA layer is dried at <NUM> degrees C. Another layer of PUR (diluted with dimethylcarbonate to give a <NUM>% weight per weight (% w/w) solution) is then applied to the surface of the PANI-DNNSA layer to form the insulating layer <NUM>, and is then cured at <NUM> degrees C. Silver contacts are then applied to edges of the PANI-DNNSA layer. With this specific implementation, the PANI-DNNSA layer may have or may cause an electrical resistance of approximately <NUM>,<NUM> ohms between the silver contacts.

With this specific experimental implementation, the multilayer stack is connected to an AC voltage power source to test its electrical heating capability. The voltage applied is <NUM> volts and the current measured is <NUM> mill amperes, thus yielding a <NUM> watt heater. These numbers and configurations are examples for illustration only. Other dimensions, sizes, and techniques could be used based on an application in which the multilayer stack is to be used and the electrical resistance to be generated.

<FIG> illustrates a variation of temperature at a particular location on the multilayer stack as a power source is cycled, in accordance to an example implementation. In particular, <FIG> depicts a plot <NUM> with temperature in Celsius represented on the y-axis and absolute time on the x-axis. Curve <NUM> illustrates temperature variation at the particular location as voltage of the power source is cycled on and off at <NUM> second intervals and the temperature monitored with a thermal camera. No degradation is detected over a two hour cycling period. In other words, the temperature level reached for each cycle is not varied or reduced over time.

This layer-by-layer stack-up shown in <FIG> provides several advantages. For example, with the configuration shown in <FIG>, the conductive polymer layer <NUM> is provided in a protective encapsulation between two insulating layers <NUM>, <NUM> to protect the conductive polymer layer <NUM> from its environment. Also, with this configuration, the conductive polymer layer <NUM> is not formulated in a resin, but is rather formed as an independent polymer layer interposed between the two insulating layers <NUM>, <NUM>. Thus, if the conductive polymer layer <NUM> is treated by a conductive enhancer to increase its electrical conductivity, the enhanced electrical conductivity is not degraded because the conductive polymer layer <NUM> is no formulated in a resin.

Moreover, as mentioned above, the conductive polymer layer <NUM> is adhered to the insulating layers <NUM>, <NUM> rather than the substrate <NUM>, and thus the conductive polymer layer <NUM> need not be configured to adhere to a material of the substrate <NUM>. In other words, the conductive polymer layer <NUM> is configured to adhere to the material of the insulating layers <NUM>, <NUM>, whereas the insulating layers <NUM>, <NUM> are configured to adhere to the material of the substrate <NUM>. As such, the chemical composition and processing of the conductive polymer layer <NUM> may be simplified because the conductive polymer layer <NUM> need not have chemical formulations that facilitate adhesion to the substrate <NUM>.

Further, the multilayer stack <NUM> represents a modular stack-up that can be repeated to reduce electrical resistance level to a particular or predetermined electrical resistance. <FIG> illustrates a device <NUM> having a multilayer stack of respective conductive polymer layers and respective insulating layers, in accordance with an example implementation. The multilayer stack of the device <NUM> includes several modular multilayer stacks similar to the multilayer stack <NUM>. In other words, several multilayer stacks similar to the multilayer stack <NUM> can be stacked. As shown in <FIG>, in addition to the multilayer stack <NUM>, other multilayer stacks could be added to achieve a particular electrical resistance. For instance, multilayer stack <NUM> could be stacked above the multilayer stack <NUM> to achieve a lower electrical resistance as described below. The multilayer stack <NUM> includes a conductive polymer layer <NUM> "sandwiched" or interposed between the insulating layer <NUM> and an insulating layer <NUM>.

The conductive polymer layer <NUM> may have electrical contacts <NUM>, <NUM> formed on edges of the conductive polymer layer <NUM>. The electrical contacts <NUM>, <NUM> may be similar to the electrical contact <NUM>, <NUM>. In examples, electrical connections can be made between the electrical contacts <NUM>, <NUM> and the power source <NUM> using conductive inks or metals applied with evaporation or cold-spray technologies.

With the configuration shown in <FIG>, the conductive polymer layer <NUM> and the conductive polymer layer <NUM> operate as two electrical resistances that are connected in parallel to the power source <NUM>. As such, a total or resultant resistance Rt of the conductive polymer layer <NUM> and the conductive polymer layer <NUM> can be calculated using Ohm's law as follows: <MAT> where R<NUM> is the electrical resistance of the conductive polymer layer <NUM> and R<NUM> is the electrical resistance of the conductive polymer layer <NUM>. For example, if R<NUM> is <NUM>,<NUM> Ohms and R<NUM> is <NUM>,<NUM> Ohms, then Rt can be calculated as <NUM> Ohms, which is half the electrical resistance of R<NUM> or R<NUM>.

By stacking more multilayer stacks similar to the multilayer stack <NUM>, the total or resultant electrical resistance can further be reduced. For example, a multilayer stack <NUM> could be stacked above the multilayer stack <NUM>. The multilayer stack <NUM> includes a conductive polymer layer <NUM> "sandwiched" or interposed between the insulating layer <NUM> of the multilayer stack <NUM> and an insulating layer <NUM>. The insulating layers <NUM>, <NUM>, <NUM>, and <NUM> could be referred to as respective insulating layers to indicate that the insulating layers are separate and can be formed subsequent to each other. For instance, the insulating layer <NUM> can be formed subsequent to forming the insulating layer <NUM>; the insulating layer <NUM> can be formed subsequent to forming the insulating layer <NUM>; and the insulating layer <NUM> can be formed subsequent to forming the insulating layer <NUM>.

The conductive polymer layer <NUM> may have electrical contacts <NUM>, <NUM> formed on edges of the conductive polymer layer <NUM>. The electrical contacts <NUM>, <NUM> may be similar to the electrical contact <NUM>, <NUM> and the electrical contacts <NUM>, <NUM>. In examples, electrical connections can be made between the electrical contacts <NUM>, <NUM> and the power source <NUM> using conductive inks or metals applied with evaporation or cold-spray technologies.

With the configuration shown in <FIG>, the conductive polymer layer <NUM>, the conductive polymer layer <NUM>, and the conductive polymer layer <NUM> operate as three electrical resistances that are connected in parallel to the power source <NUM>. As such, the total or resultant resistance Rt of the conductive polymer layer <NUM>, the conductive polymer layer <NUM>, and the conductive polymer layer <NUM> can be calculated using Ohm's law as follows: <MAT> where R<NUM> is the electrical resistance of the conductive polymer layer <NUM>. For example, if R<NUM> = R<NUM> = R<NUM> = <NUM>,<NUM> Ohms, then Rt can be calculated by equation (<NUM>) as approximately <NUM> Ohms, which is one third the electrical resistance of R<NUM>, R<NUM>, or R<NUM>.

Thus, with this configuration, a predetermined resultant electrical resistance can be achieved by stacking more multilayer stacks. In other words the steps of depositing an insulating layer and forming a conductive polymer layer can be repeated to add more multilayer stacks to cause the device <NUM> to have the predetermined resultant electrical resistance when the power source <NUM> is connected thereto.

Adding more multilayer stacks is depicted schematically in Figure by dots <NUM>. More multilayer stacks can be added on top of the multilayer stack <NUM> until a predetermined electrical resistance or predetermined electrical conductivity is achieved. As the number of multilayer stacks increases, the overall resultant electrical resistance decreases per Ohm's law: <MAT> where Rt is the total or resultant resistance and R<NUM>. Rn are the resistances of the individual multilayer stacks <NUM>, <NUM>, <NUM>. etc. The resultant resistance is less than each respective electrical resistance R<NUM>.

As such, the multilayer stacks <NUM>, <NUM>, <NUM> shown in <FIG> comprise a plurality of conductive polymer layers <NUM>, <NUM>, <NUM> sandwiched or interposed between insulating layers <NUM>, <NUM>, <NUM>, <NUM>. This configuration enables using multiple conductive polymer layers rather than a single thick conductive polymer layer. A thin conductive polymer layer is easier to cast into uniform-thickness layer compared to a thick conductive polymer layer. Further, a thin conductive polymer layer is more flexible and has less electric resistance compared to a thick conductive polymer layer. The configuration allows for tuning electrical resistance and electrical conductivity. By adding more stacks, electrical resistance is decreased and electrical conductivity is increased, and vice versa.

The device <NUM> is configured to have different resistivity, and thus different amounts of heat generated, at different locations of the device <NUM> (e.g., at different locations on the substrate <NUM>). For example, a different number of layers can be used at different locations. Having more conductive polymer layers at one location may indicate that the electrical resistance at that location can be lower than a respective electrical resistance at a different location having fewer conductive polymer layers. As a result of using different number of layers at different locations, a heating gradient can be generated across the substrate <NUM>. Such arrangement can be implemented by patterning (e.g., printing) a different number of layers at various locations to enable some locations to be hotter than others.

In another example, the same number of layers can be used across the device <NUM>; however, according to the present invention, different conductive polymer materials having different electrical conductivities are used at different locations to provide different electrical resistance. As a result, different electrical resistance can be generated at different locations of the device <NUM> and a heating gradient can be generated, e.g., to generate a different amount of heat at different locations of the device <NUM>.

In another example, a thickness of a conductive polymer layer at one location of the device <NUM> may be different than a respective thickness of a conductive layer at another location. The different thickness can indicate different electrical conductivity and different electrical resistances at different locations of the device <NUM>. In another example, the conductive polymer layers at one location can be treated by a conductivity enhancer while conductive polymer layers at another location might not be treated with, or may be treated with a different conductivity enhancer. Thus, several techniques can be used to modify the conductivity and resistivity over the substrate <NUM> including using different number of layers, in particular according to the invention different materials for the conductive polymer layers, different thicknesses for the conductive polymer layers, using a conductivity enhancer at some locations while using no or a different conductivity enhancer at other locations, among other possible techniques.

Further, the device <NUM> can be configured as an addressable matrix of conductive polymer layers to selectively activate a subset of conductive polymer layers as desired. For example, electrical connections can be made between the electrical contacts of the conductive polymer layers and the power source <NUM> using independently actuatable switches. For instance, a controller of the device <NUM> may be coupled to the switches that connect individual electrical contacts (e.g., the electrical contacts <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc.) to the power source <NUM>. The controller may then activate a particular number of switches to connect a particular number of conductive polymer layers to the power source <NUM> and achieve a predetermined or a target electrical resistance. If more switches, and thus more conductive polymer layers, are activated, then a lower electrical resistance and a lower amount of heat are generated compared to when fewer switches are activated.

In some examples, an encapsulation layer or encapsulation package <NUM> may be formed about the device <NUM>. The encapsulation package <NUM> can provide protection to the device <NUM> from its environment. In an example, the encapsulation package <NUM> may be configured as a conformal insulating coating of polyurethane, polyimide, polyester, or epoxy that is applied to a surface of the multilayer stack by spray, dip coating, screen printing, etc. The encapsulation package <NUM> can then be cured via ultraviolet light or may be thermally cured. In another example, the encapsulation package <NUM> can comprise a polymer film (e.g., polyurethane, polyimide, polyester, etc.) that is to a surface of the multilayer stack using a pressure sensitive adhesive that bonds to the surface of the multilayer stack. These examples are for illustration only and other materials and configuration are possible for the encapsulation package <NUM>.

In the implementation described above, and shown in <FIG> and <FIG>, the substrate <NUM> is shown to be flat. However, this is not meant to be limiting. In examples, the substrate could be configured to be non-flexible and flat; however, in other examples, the substrate could be flexible and form a curved surface upon which the various other layers are deposited.

The multilayer stack, similar to the multilayer stack of the device <NUM> shown in <FIG>, could be used in a variety of applications. The multilayer stack is for de-icing of a component (e.g., wing, blade, or any other part) of an aircraft, rotorcraft, wind turbine, etc. The substrate (e.g., the substrate <NUM>) in this example could be a composite structure of the component of the aircraft, rotor craft, wind turbine, etc. The various layers of the multilayer stack could then be printed on the composite structure of the component of the aircraft.

<FIG> illustrates a component <NUM> of an aircraft with a multilayer stack <NUM> deposited on or proximate to a surface <NUM> of the component <NUM>, in accordance to an example implementation. The component <NUM> of the aircraft may, for example, represent a wing, a blade, or any other component of an aircraft. When a power source is connected to the electrical contacts of the conductive polymer layers of the multilayer stack <NUM>, heat is generated for de-icing (i.e., melt any ice or snow accumulated about the component <NUM>) or anti-icing (i.e., prevent ice from forming on the component <NUM>). Distinct layers of the multilayer stacks <NUM> are not shown in <FIG> to reduce visual clutter in the drawing. However, it should be understood that the multilayer stack <NUM> is similar to the multilayer stack of the device <NUM> shown in <FIG>.

In examples, the multilayer stack <NUM> could be deposited on the surface <NUM> of the component <NUM>. In these examples, other protective layers could be deposited on top of the multilayer stack <NUM> for environmental protection and durability. In other examples, the multilayer stack <NUM> may be disposed within the component <NUM> proximate to the surface of the component <NUM>, e.g., within a predetermined distance from the surface <NUM>, so as to heat the surface of the component <NUM> and cause the ice to melt. In an example, the predetermined distance could range between <NUM> millimeter and <NUM> millimeter depending on thermal conductivity of the protective layers that separate the multilayer stack <NUM> from the surface of the component <NUM>. By being proximate to the surface of the component <NUM>, a lesser amount of heat can melt ice or prevent ice from forming, compared to a configuration where the multilayer stack <NUM> is disposed deeper within the component <NUM> away from its surface.

In examples, some portions of the component <NUM> may be more susceptible to icing than others, and in these examples any of the techniques described above could be used to vary the electrical resistance and the amount of heat generated at various locations on the on the component <NUM>. For instance, if ice is melted off a leading edge <NUM> of the component <NUM>, the ice could then move and refreeze at a trailing edge <NUM> of the airfoil (e.g., wing or blade). In this example, it may be desirable to have larger electric resistance at the leading edge <NUM> compared to the trailing edge <NUM>, and thus more heat would be generated at the leading edge <NUM>. As mentioned above, such variation in electrical resistance could be achieved by using a different number of conductive polymer layers, different materials for the conductive polymer layers, different thicknesses for the conductive polymer layers, or using a conductivity enhancer at one location while using no or a different conductivity enhancer at another location. As such, ice can be melted at the leading edge <NUM> rather than being allowed to move to and refreeze at the trailing edge <NUM>.

Additionally, the multilayer stack could be used for dissipating lightning strikes that impact an aircraft. As mentioned above with respect to <FIG>, the substrate (e.g., the substrate <NUM>) could be a composite structure of the aircraft. The various layers of the multilayer stack could then be deposited at particular locations of the aircraft (e.g., at the wing tips, tail, nose, etc.) where a lightning strike can occur.

The electrical contacts of the conductive polymer layers of the multilayer stacks could be coupled to electrodes disposed at the particular locations of the aircraft where a lightning may impact the aircraft (e.g., at the nose, wing tips, tails, etc.). The conductive polymer layers could then form a conductive path that electrically connects a portion of the aircraft where the lightning strike impacts the aircraft to another location of the aircraft where the electrical charge of the lightning strike is discharged. In other words, the electric current generated by the lightning strike could be guided by the conductive polymer layers from one location of the aircraft where the lightning strike impacts the aircraft to another location to be discharged.

The electrical resistance of the conductive polymer layers can cause the electrical charge of the lightning strike to be dissipated as heat generated from the electric current generated by the lightning strike passing through the conductive polymer layers. In examples, if some layers of the multilayer stacks are affected by the heat generated or the electric current of the lightning strike, the multilayer stack can be repaired by depositing new layers to restore expected performance (e.g., the level of electrical conductivity or electrical resistance expected from the multilayer stack).

IThe multilayer stack could also be used for shielding electronic components from electromagnetic interference (EMI). For instance, in some applications, electronic components (e.g., circuit boards) may be disposed within a housing. To shield the electronic components from EMI, the housing could be made of a plastic material configured to be the substrate (e.g., the substrate <NUM>) of the multilayer stack.

Electromagnetic waves surrounding the housing could generate an electric current in the conductive polymer layers, and thus the electromagnetic energy of the electromagnetic waves is dissipated as heat generated by the conductive polymer layers. Further, in this example, the insulating layers of the multilayer stack operate as insulators that preclude electromagnetic waves from penetrating the housing. As such, the conductive polymer layers dissipate the electromagnetic energy, whereas the insulating layers preclude the electromagnetic waves from penetrating the housing, and thus the electronic components within the housing are protected from EMI.

<FIG> is a flowchart of a method <NUM> for forming a multilayer stack of conductive polymer layers and insulating layers, in accordance with an example implementation. The method <NUM> presents an example of a method that could be used to form a multilayer stack of conductive polymer layers interposed between respective insulating layers, such as the multilayers stack of the device <NUM>, for example. The method <NUM> can include one or more operations, functions, or actions as illustrated by one or more of blocks <NUM>-<NUM>. Although the blocks are illustrated in a sequential order, these blocks may also be performed in parallel, and/or in a different order than those described herein. Also, the various blocks can be combined into fewer blocks, divided into additional blocks, and/or removed based upon the desired implementation. It should be understood that for this and other processes and methods disclosed herein, flowcharts show functionality and operation of one possible implementation of present examples. Alternative implementations are included within the scope of the examples of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrent or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art.

At block <NUM>, the method <NUM> includes depositing an insulating layer (e.g., the insulating layer <NUM>) on a substrate (e.g., the substrate <NUM>).

At block <NUM>, the method <NUM> includes forming a conductive polymer layer (e.g., the conductive polymer layer <NUM>) on the insulating layer (e.g., the insulating layer <NUM>).

At block <NUM>, the method <NUM> includes repeating deposition of a respective insulating layer, and formation of a respective conductive polymer layer to form a multilayer stack of respective conductive polymer layers interposed between respective insulating layers (e.g., forming the conductive polymer layers <NUM>, <NUM> interposed between the insulating layers <NUM>, <NUM> and between the insulating layers <NUM>, <NUM> to form the multilayer stack of the device <NUM> shown in <FIG>). Each respective conductive polymer layer has a respective electrical resistance, such that when the respective conductive polymer layers are connected in parallel to a power source (e.g., the power source <NUM>), a resultant electrical resistance of the respective conductive polymer layers is less than each respective electrical resistance.

The operations include forming the conductive polymer layer to include an intrinsic conductive polymer, or a mixture thereof with an extrinsic conductive polymer. The operation of depositing the insulating layer may include depositing a resin layer including polyurethane, epoxy, thermoplastic, phenolic, or silicone material. Further, the operation of forming the conductive polymer layer may include forming a layer of PANI-DNNSA, PEDOT-PSS, PANI-DBSA, or polypyrrole.

<FIG> is a flowchart of additional operations that may be executed and performed with the method <NUM>, in accordance with an example implementation. At block <NUM>, operations include repeating the deposition of the respective insulating layer and the formation of the respective conductive layer until the resultant electrical resistance is substantially equal to a predetermined electrical resistance (e.g., within a percentage such as <NUM>-<NUM>% of a target electrical resistance).

<FIG> is a flowchart of additional operations that may be executed and performed with the method <NUM>, in accordance with an example implementation. At block <NUM>, operations include forming the multilayer stack to include each respective conductive polymer layer interfacing with two insulating layers, one insulating layer on each side of the respective conductive polymer layer (e.g., the conductive polymer layer <NUM> interfacing with the insulating layers <NUM>, <NUM>, the conductive polymer layer <NUM> interfacing with the insulating layers <NUM>, <NUM>, and the conductive polymer layer <NUM> interfacing with the insulating layers <NUM>, <NUM>).

<FIG> is a flowchart of additional operations that may be executed and performed with the method <NUM>, in accordance with an example implementation. At block <NUM>, operations include treating the respective conductive polymer layers with a conductivity enhancer to enhance electrical conductivity of the respective conductive polymer layers. For example, treating the respective conductive polymer layers with the conductivity enhancer comprises treating the respective conductive polymer layers with IPA. In other examples, the respective conductive polymer layers may be treated with a band modifier to enhance electron hole mobility, and thus enhance electrical conductivity of the respective conductive polymer layers.

<FIG> is a flowchart of additional operations that can be executed and performed with the method <NUM>, in accordance with an example implementation. At block <NUM>, operations include forming a first electrical contact (e.g., first electrical contacts <NUM>, <NUM>, <NUM>) on a first edge of each conductive polymer layer, and at block <NUM> operations include forming a second electrical contact (e.g., second electrical contacts <NUM>, <NUM>, <NUM>) on a second edge of each conductive polymer layer. The first electrical contacts and the second electrical contacts of the conductive polymer layers facilitate connecting the conductive polymer layers to the power source.

<FIG> is a flowchart of additional operations that can be executed and performed with the method <NUM>, in accordance with an example implementation. At block <NUM>, operations include curing the insulating layer prior to forming the conductive polymer layer. Curing can be partial or can be full depending on the application and implementation.

Claim 1:
A method (<NUM>) to form a multilayer stack (<NUM>) with enhanced conductivity and stability, wherein the multilayer stack (<NUM>) is for de-icing of a component of an aircraft, rotorcraft or windturbine, the method (<NUM>) comprising:
depositing (<NUM>) an insulating layer (<NUM>) on a substrate (<NUM>);
forming (<NUM>) a conductive polymer layer (<NUM>) on the insulating layer (<NUM>); and
repeating (<NUM>) deposition of a respective insulating layer (<NUM>, <NUM>), and
formation of a respective conductive polymer layer (<NUM>) to form the multilayer stack (<NUM>) of respective conductive polymer layers interposed between respective insulating layers, wherein each respective conductive polymer layer has a respective electrical resistance,
the method further comprising electrically connecting the respective conductive polymer layers in parallel, such that a resultant electrical resistance of the respective conductive polymer layers is less than each respective electrical resi stance,
wherein repeating (<NUM>) deposition of a respective insulating layer, and formation of a respective conductive polymer layer to form a multilayer stack comprises forming (<NUM>) the multilayer stack (<NUM>) to modify electrical resistivity over the substrate (<NUM>) when the conductive polymer layers (<NUM>, <NUM>, <NUM>) are connected in parallel to a power source (<NUM>), wherein forming (<NUM>) the multilayer stack (<NUM>) to modify the electrical resistivity over the substrate (<NUM>) comprises depositing conductive polymer layers having a different conductive polymer at different locations on the substrate (<NUM>), wherein forming (<NUM>) the conductive polymer layer (<NUM>) comprises forming the conductive polymer layer (<NUM>) to include an intrinsic conductive polymer.