Patent Publication Number: US-9907121-B2

Title: Parallel wire conductor for use with a heating blanket

Description:
FIELD 
     The present disclosure relates generally to susceptors for use with heating blankets. More particularly, the present disclosure relates to parallel wire conductors for use with heating blankets wherein the blankets are used to heat a structure to a substantially uniform temperature. 
     BACKGROUND 
     The reworking of composite structures frequently requires the localized application of heat. When installing a patch in a rework area of a composite structure, heat must typically be applied to the adhesive at the bondline between the patch and rework area in order to fully cure the adhesive. When applying heat to the patch, the temperature of the bondline must typically be maintained within a temperature range that must be held for an extended period of time until the adhesive is cured. Overheating or under heating the rework area or structure located adjacent to the rework area is generally undesirable during the rework process. 
     Conventional heating equipment for heating composite structures may include heating blankets comprised of electrically resistive heating elements. Variations in the construction of conventional heating blankets may result in differential heating across the rework area. In addition, conventional heating blankets may lack the ability to compensate for heat sinks located adjacent to the rework area. Such heat sinks may comprise various elements such as stiffeners, stringers, ribs, bulkheads, and other structural members in thermal contact with the structure. Attempts to provide uniform heat distribution using conventional resistive heating blankets include multi-zone blanket systems, feedback loop systems, positive temperature coefficient heating elements, and temperature stabilizing plugs. Additions of such systems to conventional resistive heating blankets are generally ineffective in providing a substantially uniform temperature without substantial variation across the bondline of the rework area. 
     As can be seen, there exists a need for a system and method for heating a structure such as a rework area of a composite structure in a manner which maintains a substantially uniform temperature across the rework area. More specifically, there exists a need for a system and method for uniformly heating a composite structure and which accommodates heat drawn from the rework area by heat sinks and other thermal variations located adjacent to the rework area. Furthermore, there exists a need for a system and method for uniformly heating a composite structure in a manner which prevents overheating or under heating of the composite structure. Ideally, such system and method for uniformly heating the composite structure is low in cost and simple in construction. There is also a need for a system that provides for temperature regulation over a broad range of temperatures typically required for composite processing, for example, from about 150° F. to about 350° F. 
     There is also a need for a system that reduces certain unwanted induction effects that may be generated by high frequency electric currents in nearby conductive material, such as metal tooling and graphite composite structures. 
     SUMMARY 
     According to an exemplary arrangement, a wire conductor for receiving alternating current and generating a magnetic field in response thereto is disclosed. The wire conductor comprises a plurality of wire conductors in a parallel configured circuit extending between a first side of the wire conductor towards a second side of the wire conductor. A first layer of the plurality of wire conductors running in parallel from a first edge of the wire conductor to a second edge of the wire conductor. A second layer of parallel wire conductors residing above the first layer of the plurality of wire conductors, the second layer of parallel wire conductors running in parallel from the first edge of the wire conductor to the second edge of the wire conductor. The first layer of parallel wire conductors make a 180 degree turn along the first edge of the wire conductor. The first layer of parallel wire conductors make the 180 degree turn along the first edge of the wire conductor by first turning 90 degrees towards the second side of the parallel wire conductor. The first layer of parallel wire conductors make the 180 degree turn along the first edge of the wire conductor by first turning 90 degrees towards the second side of the parallel wire conductor, and then by turning 90 degrees towards the second edge of the parallel wire conductor. 
     In one arrangement, a heating blanket comprises a wire conductor for receiving alternating current and generating a magnetic field in response thereto. The wire conductor comprising a plurality of wire conductors in a parallel configured circuit extending between a first side of the wire conductor towards a second side of the wire conductor. A first layer of the plurality of wire conductors running in parallel from a first edge of the wire conductor to a second edge of the wire conductor. A second layer of parallel wire conductors residing above the first layer of the plurality of wire conductors. The second layer of parallel wire conductors may run in parallel from the first edge of the wire conductor to the second edge of the wire conductor. The first layer of parallel wire conductors make a 180 degree turn. The first layer of parallel wire conductors may make the 180 degree turn along the first edge of the wire conductor. 
     The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments in which further details can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, 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 embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective illustration of a composite structure having a rework area formed therein; 
         FIG. 2  is a plan view illustration of the rework area of  FIG. 1  and illustrating a vacuum bag assembly and a heating blanket applied to the rework area and further illustrating a heat sink comprising a stringer extending along a portion of the rework area on a bottom surfaced of the composite structure; 
         FIG. 3  is a cross-sectional illustration of the composite structure taken along line  3 - 3  of  FIG. 2  and illustrating the stringer (i.e., heat sink) which may draw heat from localized portion of the rework area; 
         FIG. 4  is a perspective illustration of a heating blanket in an embodiment as may be used for heating the rework area of the composite structure, the heating blanket comprising a flattened helical wire conductor positioned perpendicular to an array of susceptor wires that are positioned within the flattened helical wire conductor; 
         FIG. 5  is a schematic illustration of the heating blanket illustrated in  FIG. 4  (with the housing and matrix removed) illustrating the helical wire conductor connected to a power supply, a controller, and a sensor, and with an array of susceptor wires contained within the helical wire conductor; 
         FIG. 6  is a cross-sectional illustration of the heating blanket taken along line  4 - 4  of  FIG. 4  and illustrating the array of susceptor wires provided within the helical wire conductor for induction heating thereof in response to magnetic fields generated by an alternating current applied to the helical wire conductor; 
         FIG. 7  an illustration of a plot of heat output measured over temperature for an embodiment of an exemplary array of susceptor wires; 
         FIG. 8  is an illustration of an alternative susceptor and conductor arrangement that may be used in a heating blanket, such as the heating blanket illustrated in  FIGS. 2 and 3 ; 
         FIG. 9  is an illustration of an alternative heating blanket layout of the alternative susceptor and conductor arrangement illustrated in  FIG. 10 ; 
         FIG. 10  is a schematic illustration of an alternative heating blanket connected to a power supply, a controller and a sensor and illustrating the susceptor and conductor arrangement illustrated in  FIG. 9  housed within a housing of the heating blanket; 
         FIG. 11  is a cross-sectional illustration of the heating blanket taken along line  10 - 10  of  FIG. 10  and illustrating the conductor provided with a plurality of susceptor wires spirally surrounding the conductor for induction heating thereof in response to a magnetic field generated by an alternating current applied to the conductor; 
         FIG. 12  is an enlarged sectional illustration of the conductor and susceptor arrangement of  FIG. 11  surrounded by thermally conductive matrix and illustrating a magnetic field encircling the susceptor wires and generating an eddy current in the susceptor wires oriented in a direction opposite the direction of the magnetic field; 
         FIG. 13  is a schematic illustration of a heating blanket, similar to the heating blanket illustrated in  FIG. 4 , with the heating blanket housing and matrix removed; 
         FIG. 14  illustrates a schematic illustration of a bottom or first layer of the parallel wire conductor of the heating blanket illustrated in  FIG. 13 ; 
         FIG. 15  illustrates a schematic illustration of a top or second layer of the parallel wire conductor illustrated in  FIG. 13 ; 
         FIG. 16  illustrates a first plurality of wires in the bottom/first layer and in the top/second layer of the parallel wire conductor illustrated in  FIGS. 14-15 ; and 
         FIG. 17  illustrates a close up view of a plurality of conductor wires approaching a first edge or translation edge of the parallel wire conductor illustrated in  FIGS. 14-15 . 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all of the disclosed embodiments are shown. Indeed, several different embodiments may be provided and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those skilled in the art. 
     Referring now to the drawings wherein the showings are for purposes of illustrating preferred and various embodiments of the disclosure only and not for purposes of limiting the same, shown in  FIG. 1  is a perspective illustration of a composite structure  10  upon which a rework process may be implemented using a heating blanket  54  illustrated in  FIGS. 2-7 . The heating blanket  54  illustrated in  FIGS. 2-7  and as disclosed herein may be installed on a patch  40  which may be received within a rework area  20  as illustrated in  FIG. 1 . The heating blanket  54  as disclosed herein may apply heat to the rework area  20  in order to elevate the temperature of the rework area  20  to a uniform temperature throughout the rework area  20  in order to cure adhesive bonding the patch  40  to the rework area  20  and/or to cure the composite material forming the patch  40 . In various embodiments, the heating blanket  54  as disclosed herein incorporates a combination of a plurality of susceptors comprising magnetic materials and high frequency alternating current in order to attain temperature uniformity to a structure  10  to which the heating blanket  54  is applied. In one preferred arrangement, and as will be described in greater detail below, the plurality of susceptors are positioned within a conductor comprising a Litz wire that is wound in a flattened helix (i.e., a solenoid structure). In another preferred arrangement, and as will be described in greater detail below, the plurality of susceptors comprise spring formed susceptors that are positioned around a conductor, such as a Litz wire. Alternative susceptor configurations are also disclosed. 
     Advantageously, and as will be discussed in greater detail herein, the temperature-dependent magnetic properties such as the Curie temperature of the magnetic materials used in an array of susceptor wires contained within the heating blanket  54  may prevent overheating or under heating of areas to which the heating blanket  54  may be applied. As illustrated herein, an array of susceptor wires comprises an ordered arrangement of at least a first and a second susceptor wire wherein the first and second susceptor wires comprise different magnetic properties, such as the Curie temperature of the magnetic material. 
     In addition, the susceptor array may comprise a first susceptor comprising a first magnetic material and at least second susceptor. The first susceptor comprises a magnetic material that has a different Curie temperature than a second magnetic material of the second susceptor. In this manner, the combined array of the first and second susceptors of the heating blanket  54  facilitates the uniform application of heat to structures such as composite structures  10  ( FIG. 1 ) during a manufacturing or rework process or any other process where uniform application of heat is required over enhanced temperature ranges. Importantly, the heating blanket  54  comprising an array of susceptor wires wherein the susceptor wires comprise a combination of two or more magnetic materials comprising two or more different Curie temperatures so as to provide for a greater temperature regulation over a wider range of temperatures (e.g., from about 150° F. to about 350° F.). 
     In addition, the heating blanket  54  compensates for heat sinks  28  ( FIG. 1 ) that may draw heat away from portions of a structure  10  ( FIG. 1 ) to which the heating blanket  54  is applied. More specifically, the heating blanket  54  continues to provide heat to portions of the structure  10  located near such heat sinks  28  while areas underneath the heating blanket  54  that have reached or attained the Curie temperature cease to provide heat to the rework area  20 . 
     For example,  FIG. 1  illustrates a composite structure  10  which may include a skin  12  formed of plies  14  of composite material and wherein the skin  12  may have upper and lower surfaces  16 ,  18 . The composite structure  10  may include a rework area  20  in the skin  12  formed by the removal of composite material. As can be seen in  FIG. 2 , the rework area  20  may be formed in the upper surface  16  and may extend at least partially through a thickness of the skin  12  although the rework area  20  may be formed in any configuration through the skin  12 . Various structures may be mounted to the lower surface  18  opposite the rework area  20  such as stringers  30  which may act as heat sinks  28  drawing heat away from certain portions of the rework area  20  while the remaining portions continually receive heat from the heating blanket  54  ( FIG. 2 ). Advantageously, the heating blanket  54  ( FIG. 2 ) facilitates the uniform application of heat to the structure  10  by reducing heat input to portions of the rework area  20  that reach approximately the Curie temperature of the magnetic materials in the heating blanket  54  while maintaining a relatively higher level of heat input to portions of the rework area  20  that are below the Curie temperature as will be described in greater detail below. In practice, all areas have some heat losses to the air or surrounding structure and obtain a temperature at which heat losses equal heat input from the blanket. At equilibrium, areas with high heat losses receive more heat from the blanket than areas with low heat losses. This differential heating results in temperature differences across the rework area that is small and that is with typical limits for adhesive bonding. 
     Referring still to  FIGS. 2-3 , the heating blanket  54  is illustrated as being mounted to the composite structure  10  over the patch  40 . A vacuum bag assembly  100  may be installed over the heating blanket  54 . The vacuum bag assembly  100  may include a bagging film  116  covering the heating blanket  54  and which may be sealed to the upper surface  16  of the composite structure  10  by means of sealant  122 . A vacuum probe  118  and vacuum gauge  120  may extend from the bagging film  116  to a vacuum generator to provide a mechanism for drawing a vacuum on the bagging film  116  for application of pressure and to draw out volatiles and other gasses that may be generated as a result of heating uncured composite material of the patch  40 . 
     As can be seen in  FIG. 3 , the vacuum bag assembly  100  may include a caul plate  102  positioned above a porous or non-porous parting film  110 ,  108 . The caul plate  102  may facilitate the application of uniform pressure to the patch  40 . The porous or non-porous parting film  110 ,  108  may prevent contact between the caul plate  102  and the patch  40 . The vacuum bag assembly  100  may include additional layers such as a bleeder layer  112  and/or a breather layer  114 . The patch  40  may be received within the rework area  20  such that a scarf  44  formed on the patch edge  42  substantially matches a scarf  24  formed at the boundary  22  of the rework area  20 . In this regard, the interface between the patch  40  and rework area  20  comprises the bondline  46  wherein adhesive is installed for permanently bonding the patch  40  to the rework area  20  and includes adhesive located at the bottom center  26  portion of the rework area  20 . 
     As shown in  FIG. 2 , thermal sensors  70  such as thermocouples  72  may be strategically located on upper and lower surfaces  16 ,  18  of the composite structure  10  such as adjacent to the rework area  20  in order to monitor the temperature of such areas during the application of heat using the heating blanket  54 . In this regard, thermocouples  72  may be placed on heat sinks  28  such as the stringer  30  body and stringer flanges  32  illustrated in  FIG. 3  in order to monitor the temperature of such heat sinks  28  relative to other areas of the composite structure  10 . 
       FIG. 4  is a perspective illustration of a heating blanket  54  in an embodiment as may be used for heating the rework area of the composite structure. The heating blanket  54  comprising a flattened helical wire conductor  80  and an array of susceptor wires  82 . Preferably, the array of susceptor wires  82  are arranged within alternating conductors of the helical wire conductor  80  of the heating blanket. More preferably, the array of susceptor wires  82  are arranged perpendicular to the plurality of conductor portions making up the helical wire conductor  80 . In one preferred arrangement, the flattened helical wire conductor  80  comprises a Litz wire that is wound in a flattened helical like structure (e.g., a solenoid) so as to define a plurality of alternating conductors. 
     For example,  FIG. 5  is a schematic illustration of the heating blanket  54  illustrated in  FIG. 4  (with the heating blanket housing  58  and matrix  78  removed) so as to illustrate the helical wire conductor  80  connected to a power supply  90 , a controller  92 , and a sensor  94 . As illustrated, the helical wire conductor  80  comprises a unitary wire that winds back and forth between a first side S 1  of the heating blanket  54  and a second side S 2  of the heating blanket in a flattened helical structure, along a length L HB  of the heating blanket  54 . Importantly, in this illustrated arrangement of the heating blanket  54 , the array of susceptor wires  82  are positioned between the alternating conductors or wires making up the helical wire conductor  80  for inductive heating of the array of susceptor wires  82  in the presence of an alternating current provided by the power source  90 . The inductively heated array of susceptor wires  82  thermally conducts heat to a matrix  78  ( FIG. 4 ). The matrix  78  may thermally conduct heat to a structure  10  to which the heating blanket  54  is mounted (See, e.g.,  FIGS. 1-3 ). 
     Referring to  FIGS. 4 and 5 , the heating blanket  54  may include a housing  58  defining an interior  60 . This interior may be formed of a suitable material which is preferably thermally conductive and which may also be flexible and/or resilient such that the heating blanket  54  may conform to curved areas to which it may be applied. In this regard, the housing  58  is preferably formed of a pliable and/or conformable material having a relatively high thermal conductivity and relatively low electrical conductivity. The housing  58  may comprise upper and lower face sheets  62 ,  64  formed of silicone, rubber, polyurethane or other suitable elastomeric or flexible material that provides dimensional stability to the housing  58  while maintaining flexibility for conforming the heating blanket  54  to curved surfaces. Although shown as having a generally hollow interior  60  bounded by the upper and lower face sheets  62 ,  64 , the housing  58  may comprise an arrangement wherein the conductor  80  and the associated magnetic material are integrated or embedded within the housing  58  such that the conductor  80  is encapsulated within the housing  58  to form a unitary structure  50  that is preferably flexible for conforming to curved surfaces. 
       FIG. 5  illustrates a perspective view of certain components of the heating blanket  54  showing the flattened helical structure of the conductor  80  and the array of susceptor wires  82  residing within this helical structure in greater detail. In one preferred arrangement, and as illustrated in  FIG. 5 , the susceptor wires  82  are arranged within the helical conductor  80  such that a longitudinal axis of the array of susceptor wires  82  resides substantially perpendicular to an electrical current flowing through the helical conductor  80 . In this manner, the varying magnetic fields generated by the helical conductor  80  induce eddy currents in the array of susceptor wires  82  as will be discussed in greater detail herein. In one arrangement, the conductor ( 80 ) may be a single conductor. Alternatively, the conductor ( 80 ) may comprise an array of parallel conductors in order to reduce the voltage that the power supply must provide to the blanket. 
     A power supply  90  providing alternating current electric power may be connected to the heating blanket  54  by means of the heating blanket wiring  56  A,B. The power supply  90  may be configured as a portable or fixed power supply  90  which may be connected to a conventional 60 Hz, 110 volt or 220 volt (480 V or higher as necessary to deliver power to very large blankets) outlet. Although the power supply  90  may be connected to a conventional 60 Hz outlet, the frequency of the alternating current that is provided to the conductor  80  may preferably range from approximately 1,000 Hz to approximately 400,000 Hz. In some cases, the frequency of the alternating current that is provided to the conduction  80  may preferably range from approximately 1,000 Hz to approximately 400.00 Hz. In some cases, the frequency of the alternating current provided to the conduction  80  may be as high as 4 MHz. The voltage provided to the conductor  80  may range from approximately 10 volts to approximately 450 volts but is preferably less than approximately 60 volts. Likewise, the alternating current provided to the conductor  80  by the power supply is preferably between approximately 1 amps and approximately 10 amps. In one preferred arrangement, the blanket wire ( 56 ) delivers between 1 A and 10 A for a single conductor and between about 2 and 20 A for two parallel conductors and so on for larger number of parallel circuits. In this manner, such parallel circuits can reduce the required voltage provided to the blanket. 
       FIG. 6  illustrates a cross sectional view of the array of susceptor wires  82  that may be used with the heating blanket  54  illustrated in  FIGS. 2-5  taken along line  5 - 5  of  FIG. 5 . As illustrated, the linear array of susceptor wires  82  comprises a first plurality of susceptor wires  84 ,  86  arranged in at least one row  81 . In an alternative linear array arrangement, the linear array of susceptor wires  82  comprises a second plurality of susceptor wires arranged in a second row. 
     In one preferred arrangement, at least one of the first plurality of susceptor wires within the linear array  82  comprises a magnetic material having a first Curie temperature. In addition, at least one of the plurality of susceptor wires within the linear array  82  comprises a magnetic material having a second Curie temperature, the second Curie temperature being different than the first Curie temperature of the first susceptor wire. 
     As illustrated in  FIG. 6 , in one arrangement, the linear array of susceptor wires  82  comprises a plurality of first susceptor wires  84  and a plurality of second susceptor wires  86  within the linear array of susceptor wires  82 . Preferably, in one arrangement, the first plurality of susceptor wires  84  comprise a first Curie temperature alloy  124  and the second plurality of susceptor wires  86  comprises a second Curie temperature alloy  126  that is different from the first Curie temperature alloy of the first susceptor wire  124 . 
     As those of ordinary skill will recognize, alternative susceptor array  82  may also be utilized. As just one example, the linear susceptor array  88  may comprise a plurality of third susceptor wires comprising a third Curie temperature alloy. In such an arrangement, the third Curie temperature alloy may be different than the first Curie temperature alloy  124  of the first susceptor wire  84  and also different than the second Curie temperature alloy  126  of the second susceptor wire  86 . 
     In addition, in one exemplary linear array arrangement, the linear array  82  may comprise an equal number of the first susceptor wires  84  and the second susceptor wires  86 . In one preferred arrangement, the linear array  82  comprises an unequal number of the first susceptor wires  84  and the second susceptor wires  86 . Alternatively, where the linear array  82  further comprises a plurality of third susceptor wires, the number of these third susceptor wires may be same as, greater than or less than the number of first susceptor wires  84 . Similarly, the number of third susceptor wires may be same as, greater than or less than the number of second susceptor wires  86 . In an alternative arrangement, more of the first or second susceptor wires  84 ,  86  may be provided. In addition, a diameter size of the first susceptor wires  84 , a diameter size of the second susceptor wires  86 , and a diameter size of the third susceptor wires may all be the same or may all be different. However, as those of ordinary skill in the relevant art will recognize, alternative sized susceptor wire arrangements may be provided. As just one example, the first susceptor wires  84  may comprise may comprise a 10 mil diameter, the second susceptor wires  86  may comprise 13 mil diameter, and the third susceptor wires may comprise 15 mil diameter. Of course, alternative linear arrangements comprising different wire sizes may also be used. 
     Increasing the number of different susceptor wire types provided within the linear susceptor array  82  can be beneficial to obtaining an enhanced temperature regulation over an even wider range of operating temperatures. 
     In one preferred arrangement, the first susceptor conductor  84  comprises a first Curie temperature alloy  124  and the second susceptor conductor  86  comprises a second Curie temperature alloy  128  wherein the second Curie temperature of the second susceptor conductor  86  is a lower temperature than the first Curie temperature alloy of the first susceptor conductor  84 . In one preferred arrangement, the first Curie temperature alloy comprises Alloy  34  having 34% Ni and 66% Fe having a Curie temperature point about 450° F. and comprises a negligible magnetic properties above 400° F. In this same arrangement, the second Curie temperature alloy comprises Alloy  32  having 32% Ni and 68% Fe having a Curie temperature of about 392° F. and comprises a negligible magnetic properties above 250° F. 
     The magnetic fields generated by the alternating current flowing through the helical conductor  80  wound in a Litz wire flattened helix (or solenoid) and inducing eddy currents within the array of susceptor wires  82  will now be described with reference to  FIG. 6 . As those of ordinary skill in the art recognize, a Litz wire is typically used to carry alternating current and may consist of many thin wire strands, individually insulated and twisted or woven together. 
     As can be seen as an example in  FIG. 6 , seven susceptor wires  84 ,  86  are illustrated and these wire reside in a row, adjacent one another and between two alternating conductors of a helical conductor  80 , such as the helical conductor  80  illustrated in  FIG. 5 . In one preferred helical conductor arrangement, the helical conductor is of unitary construction and comprises a single conductor that is wound from one end of the heating blanket to the other in a continuous, flattened helix shape. As just one example, if the helical conductor comprises a single conductor such as helical conductor  80  illustrated in  FIG. 5 , this single conductor  80  may make ten (10) turns per inch in the helix. 
     In an alternative helical conductor arrangement, the helical conductor may comprise two or more conductors forming two or more parallel circuits. Utilizing two or more conductors does not materially affect the generated magnetic field as long as each conductor carriers the same amount of current as the single conductor. With such a multiple conductor helical configuration, the controller  92  and sensor  94  may be operated to adjust and maintain this type of desired current control. One advantage of such a multiple conductor helical configuration is that it acts to reduce the voltage need to provide current from one end of the blanket to the other end of the blanket. For example, instead of having one conductor making ten (10) turns per inch in the helix, the multiple conductor configuration may have, for example, ten (10) conductors making one (1) turn per inch. 
     Another advantage of such a multiple conductor helical configuration is that it acts to reduce the voltage needed to provide current from one end of the blanket to the other end of the blanket. For example, a separate conductor helical configuration may be utilized to activate a first susceptor conductor whereas a second separate conductor may be utilized to activate a second susceptor conductor. As such, in one exemplary arrangement, under the operation and control of the controller ( FIG. 5 ), different susceptor wires within the susceptor array may be activated at different times or points within the heating process. 
     Returning to  FIG. 6 , the linear array  82  comprises a plurality of first susceptor wires  84  having a first Curie temperature  124  and a plurality of second susceptor wires  86  having a second Curie temperature  126 . The first Curie temperature being lower than the second Curie temperature. In this illustrated arrangement, the first susceptor wires  84  may be positioned adjacent two of the plurality of second susceptor wires  86 . In addition, the susceptor linear array  82  may be positioned an equal distance from both a first, lower conductor portion  80 A and a second, upper conductor portion  80 B. The susceptor wires are preferably electrically insulated from these conductor portions  80 A,B. 
     Initially, the application of a first alternating current I i    150  by way of a power source ( FIG. 5 ) to the first conductor portion  80 A produces an alternating magnetic field lines  96 A that comprise concentric circles around the cylindrically current carrying conductor  80 A. In  FIG. 6 , these concentric circles  96 A may be illustrated as comprising a first magnetic field  96  which is illustrated as directed perpendicularly out of the paper. Similarly, the application of a second alternating current I i    160  (flowing in an opposite direction as the first alternation current I i    150 ) through the second conductor portion  80 B produces an alternating magnetic field lines  96 B that comprise concentric circles around the cylindrically current carrying conductor  80 B. 
     Because of the orientation of the first and second magnetic fields  96 A,B, these fields  96 A,B will essentially cancel each another out on the outside of the blanket  54 , below the first conductor  80 A as they reside in opposite directions. Similarly, above the second or upper conductor  80 B on the outside of the blanket  54 , the first and second magnetic fields  96 A,B will also essentially cancel one another out. In contrast, within the heating blanket matrix  78  and hence within the susceptor linear array  82 , the first and second magnetic fields  96 A,B will be additive to one another since both fields are oriented substantially parallel to the axis of the susceptor wires linear array  82 . This substantially parallel combined oscillating magnetic field  96 A,B will therefore generate eddy currents that travel circumferentially within the susceptors  84 ,  86  contained within the susceptor array  82 . Therefore, both the susceptors  84 ,  86  will generate heat simultaneously with the application of the magnetic fields  96 A,B. 
     Initially, the concentration of the magnetic fields  96 A,B results in relatively large eddy currents generated in the plurality of first susceptor wires  84  having the lower Curie temperature as well as eddy currents generated in the plurality of second susceptor wires  86  having the higher curie temperature. As illustrated, eddy currents are generated in both the lower and higher Curie temperature materials  84 ,  86  as long as a susceptor has high permeability and is of sufficient diameter so that the skin depth is substantially smaller than the wire radius. In the present disclosure, and in this illustrated arrangement, the second susceptor does not dominate heating at low temperature by having a smaller concentration of the second susceptor than the first. The induced eddy currents in both the first and second materials result in resistive heating of the first and second susceptor wires  84  and  86 . Although most of the heating is provided by way of the lower Curie temperature material, the eddy currents within the higher Curie susceptor  86  will also provide a certain amount of resistive heating at lower temperatures, albeit less than the heat generated by way of lower Curie temperature susceptor  84 . As such, the first susceptor wire  84  and the second susceptor wire  86  both act to conductively heat the matrix  78  and the structure  10  in thermal contact with the heating blanket  54 . ( FIGS. 5-6 ) The heating of the first susceptor wire  84  and second susceptor wire  86  continues during application of the alternating current until the magnetic material of the first susceptor wire  84  approaches its Curie temperature, which again in this illustrated arrangement is lower than the Curie temperature of the second susceptor wire  84 . 
     Upon approaching the temperature where the magnetic properties of the first susceptor wire  84  becomes negligible, the first susceptor wire  84  becomes non-magnetic. At this non-magnetic point, the magnetic fields  96 A,B generated by the first conductor portion and the second conductor portion  80 A,B continue to generate eddy currents in the higher Curie temperature susceptor because it is still electrically conductive due to its higher Curie temperature. As such, once the lower Curie temperature of the first susceptor wire  84  is achieved, temperature regulation by way of both the first susceptor wire  84  and the second susceptor wire  86  continue, albeit at a higher Curie temperature. 
     As the first susceptor wire  84  no longer generates heat, the concentration of the magnetic field  96 B continues to generate large eddy currents in the second susceptor wire  86 . The continued induction of eddy currents within both the first and second susceptor wire  86  result in resistive heating of the second susceptor wire  86 . The first and second susceptor wire  86  therefore continue to conductively heat the matrix  78  and the structure  10  in thermal contact with the heating blanket  54  ( FIG. 3 ). The heating of the susceptor wire  86  continues during application of the alternating current I i    150  and I ii    160  until the magnetic material of the susceptor wire  86  approaches its Curie temperature, which again in this illustrated arrangement comprises a higher Curie temperature than the Curie temperature of the first susceptor wire  84 . Upon reaching the higher Curie temperature of the second susceptor wire  86 , the susceptor wire  86  becomes non-magnetic. At this non-magnetic point, the magnetic fields  96 A,B are no longer concentrated in the susceptor wire  86 . The induced eddy currents and associated resistive heating of the susceptor wire  86  therefore diminishes to a level sufficient to maintain the temperature of the first and second susceptor wire  86  at the higher Curie temperature. 
     As an example of the heating of the magnetic material to the Curie temperature,  FIG. 7  illustrates a plot of heat output  130  measured over temperature  132  for an exemplary heating blanket comprising an array of susceptors as disclosed herein. Specifically, the heating blanket may comprise an array of susceptors mounted within a conductor  80  wherein the conductor  80  comprises a Litz wire formed as a flattened helix as illustrated in  FIG. 5 . To generate the data presented in this graph, the array of susceptors comprise a 2:1 mixture of a first plurality of first susceptor wires comprising Alloy  32  and a second plurality of second susceptor wires Alloy  34 , wherein each of the first and second wires comprised a 10 mil diameter. Both first and second susceptor wires were inductively heated by way of a 300 KHz magnetic field whose amplitude was increased from 5 Oe to 10 Oe as the temperature rises to compensate for increasing heat losses that occur at higher temperature. The first plurality of first susceptor wires comprised a susceptor wire comprising a 10 mil diameter Alloy  32  (32% Ni and 68% Fe). The second plurality of second susceptor wires comprised a susceptor wire comprising a 10 mil diameter Alloy  34  (34% Ni and 66% Fe) wire. In this susceptor wire arrangement, the susceptor array comprises a 12 mil center-to-center spacing. As those of ordinary skill in the art will recognize, alternative diameter sizes and center-to-center spacing configurations may also be utilized. As can be seen in  FIG. 7 , this susceptor arrangement provided an extended useful temperature range for such a susceptor including a controlled temperature range from about 150° F. to about 380° F. It should be noted that typically, in certain applications, more heat is needed to compensate for higher heat losses at higher temperatures as those temperatures illustrated in  FIG. 7 . In order to provide the required increase in heat, the current and therefore the magnetic fields may be increased as necessary by increasing the power supply current. This increase in current will effectively shift the curve in  FIG. 7  upward so as to provide a desired amount of heat while still maintaining the same negative slope curve shape while providing a greater amount of heat to cooler areas, such as those located near heat sinks. (See e.g., heat sink  28  and  FIG. 1 ). 
     The high frequency electric current provided to the helical conductor illustrated in  FIG. 5  may generate certain undesired consequences. For example, high frequency electric current flowing through such a flattened helical conductor may induce unwanted heating in conductive materials that might reside in the near vicinity to the heating blanket  54 . Such undesired heating may occur in metal tooling and graphite composite structures. As just one example, the high frequency electric current flowing through the flattened helical conductor illustrated in  FIGS. 5 and 6  may produce unwanted heating in nearby conductive material. As described herein, this induced unwanted heating is absent above and below the solenoid portion of the heating blanket since the magnetic fields produced from the current traveling in opposite directions (e.g., current traveling within the upper and lower Litz wires in the heating blanket) nearly cancel each other out as discussed herein in greater detail, for example with reference to  FIG. 6 . 
     In addition, if the heating blanket conductor is in the form of a spiral as the conductor arrangement illustrated in  FIGS. 5 and 6  with the income power lead  56 A and outgoing power lead  56 B located at separate ends of the solenoid conductor  80 , then there is also a net current flowing (in this illustrated arrangement) from left to right that is not cancelled. As such, the alternating input current flowing through the first power lead  56 A and the alternating output current flowing through the second power lead  56 B do not cancel one another. Also, the spiral or helical orientation of the various conductor wires making up the helical conductor  80  can also induce unwanted axial currents in the susceptor wires  82  residing within the helical conductor  80 . 
     Consequently, there is a need for an enhanced wire conductor arrangement for use with a heating blanket (such as the heating blanket illustrated in  FIGS. 2-4 ) that avoids or reduces unwanted or undesired induction heating. Such an enhanced wire conductor reduces unwanted heating of composite structures, tends to cancel alternating currents in the first and second power leads of the heating blanket, and tends to reduce unwanted axial currents in susceptor wires positioned between alternating conductors of the wire conductor. 
       FIG. 13  is a schematic illustration of a heating blanket  410 , similar to the heating blanket  54  illustrated in  FIG. 4  (with the heating blanket housing and matrix removed). The heating blanket  410  comprises a parallel wire conductor  400  that is operably connected to a power supply  460 , a controller  470 , and a sensor  480 . As illustrated, the parallel wire conductor  400  comprises a plurality of wires  402  configured in a generally serpentine parallel configured circuit  404 . This generally serpentine parallel configured circuit  404  enters the parallel conductor  400  along the first power lead  420 , extends along a first edge  446  of the first/bottom conductor layer, towards a first side S 1    484  of the parallel wire conductor  400 . 
     The parallel configured circuit  404  serpentines then back and forth first along the bottom conductor layer  406  from the first edge  446  of the parallel wire conductor  480  and the second edge  452  of the parallel wire conductor  400 . In this illustrated arrangement, the parallel wire conductor  400  comprises a plurality of Litz wires (e.g., parallel wire conductor comprises ten (10) Litz wires) forming the parallel configured circuit  404 . Generally, this parallel circuit  404  serpentines between the top and bottom of the parallel wire conductor layers  412 ,  406 , and then exits out of the output power lead  430 . However, as those of ordinary skill in the relevant art will recognize, alternative parallel circuit arrangements may also be utilized. 
     This alternative wire conductor arrangement  400  comprises a parallel wire conductor comprising a first or bottom layer  406  comprising a plurality of parallel conductors  408 . The parallel wire solenoid further comprises a second or top layer  412  comprising a plurality of alternating parallel conductors  414 . Similar to the helical wire conductor arrangement illustrated in  FIG. 5 , the first power lead  420  and the second power lead  430  operatively coupled to a power supply  460 , a controller  470 , and a sensor  480 . Where the parallel wire conductor  400  is used as part of a heating blanket, an array of susceptor wires  440  (as discussed herein) is positioned within the parallel wire conductor  400 , residing between parallel conductors  408  of the first/bottom layer of conductor  406  and the alternating parallel conductors  414  of the second/top layer  412 , similar to the alternating conductor arrangement illustrated in  FIGS. 4-6 . 
       FIG. 14  is a schematic illustration of the first/bottom  406  of the parallel wire conductor  400  illustrated in  FIG. 13 . Specifically,  FIG. 14  illustrates the plurality of bottom layer conductors  408  of the parallel wire conductor  400 . Also illustrated in  FIG. 14  is the direction of the alternating current I 1A    510  flowing through a first plurality of parallel wires  418  in the bottom layer  406  of the parallel wire conductor  400 . 
     Similarly,  FIG. 15  is a schematic illustration of the second/top layer conductors  414  illustrated in  FIG. 13 . Also illustrated in  FIG. 15  is the direction of the alternating current I 1B    520  flowing through a first plurality of parallel wires  416  in the top layer  414  of the parallel wire conductor  400 . 
     Referring now to  FIGS. 13-15 , the incoming alternating current I IN    424  flows within a grouping of (10) ten parallel Litz wires configured to first enter the parallel wire conductor  400  along the first edge or a translation edge  446  of the parallel wire conductor  400 . As will be described in greater detail below, the first edge or the translation edge  446  of the parallel wire conductor  400  is the edge of the parallel wire conductor  400  where the plurality of conductors are translated 180 degrees. This 180 degree translation preferably occurs in two steps. First, the plurality of conductors are translated 90 degrees so that the conductors are re-directed towards the second side  490  of the parallel wire conductor  400 . In a second translation step, the plurality of conductors are translated a second 90 degrees so that they are now directed back towards the second edge  452  of the parallel wire conductor  400 . 
     As may be seen from  FIG. 13 , in this illustrated parallel wire conductor arrangement  400 , the first or the incoming power lead  420  resides immediately adjacent a second power lead or an outgoing power lead  430 . Incoming alternating current I IN    424  is provided by way of the power supply  460  ( FIG. 14 ) to the parallel wire conductor by way of the first or the incoming power lead. Outgoing alternating current designated generally by I OUT    500  (see, e.g.,  FIG. 16 ) exists the parallel wire conductor  400  by way of the outgoing power lead  430 . More preferably, in one conductor arrangement, the first or the incoming power lead  420  resides either immediately above or immediately below the second or the outgoing power lead  430 . 
     As illustrated, incoming alternating current I IN    424  enters the parallel wire conductor  400  by way of the incoming power lead while the outgoing current I OUT    500  exits the parallel wire conductor  400  by way of the outgoing power lead  430 . Incoming alternating current I IN    424  flowing through the first or incoming power lead  420  generates a first magnetic field  426  as illustrated in  FIG. 14 . This first magnetic field  426  is illustrated as entering the page on the left of the first power lead  420  and exiting the page on the right side of the power lead  420 . 
     Referring back to  FIG. 14 , after entering the parallel wire conductor  400 , the plurality of conductor wires extend along the first edge  446  of the parallel conductor  400 . The plurality of parallel wires then turns towards the first side S 1    484  of the parallel conductor  400 . The plurality of conductors then proceeds in a parallel configuration towards the second edge  452  of the parallel conductor  400 . At this second edge  452 , and as illustrated in  FIG. 14 , the ten parallel wires extend along an entire width W PWC    464  of the parallel conductor  400 , starting from a first edge and extending in a parallel fashion towards the a second edge  452 , along the bottom/first layer  406  of the parallel wire conductor  400 . As such, the plurality of wires carry a first alternating current I 1A    510  travels along the entire width W PWC  of the parallel conductor from the first edge  446  and to the second edge  452  along the bottom layer  406  of the parallel wire conductor. 
       FIG. 16  illustrates a close up view of the plurality of wires nearing the second edge  452  of the parallel wire conductor  400 . As illustrated, once at the second edge  452  of the parallel wire conductor  400 , the plurality of parallel wires extend upwards a certain desired distance D PC    476  from the bottom layer  406  of the parallel wire conductor  400  ( FIG. 14 ) towards the top layer  412  of the parallel wire conductor  400  ( FIG. 15 ). Preferably, the plurality of parallel wires extend upwards the certain desired distance D PC    476  from the bottom layer  406  of the parallel wire conductor  480  ( FIG. 14 ) towards the top layer  412  of the parallel wire conductor  480  ( FIG. 15 ). Distance D PC    476  may be chosen based on an overall height of the matrix and the type of susceptor arrangement provided in between the first and second layers  406 ,  412  of the parallel wire conductor  400 . 
     The first collection of parallel wires residing along the top layer  412  of the parallel wire conductor  400  are positioned parallel with and directly above the first collection of parallel wires extending along the bottom layer  406  of the parallel wire conductor  400  back towards the first edge  446  of the parallel wire conductor  400 . As described above with reference to  FIGS. 4 and 5 , a plurality of susceptors  440  provided are within the parallel wire conductor and are preferably positioned in between these collections of parallel wires residing along the top layer  412  and residing along the bottom layer  406  of the parallel wire conductor  400 . One advantage of such a parallel wire configuration is that the first current I 1A    510  flowing through the first collection of wires flows from the first conductor edge  446  to the second conductor edge  452  while this same current designated by I 1B    520  in  FIG. 16  flows through the first collection of wires along the top layer  412 . Currents I 1A  and I 1B  are directly opposite one another. As such, the magnetic field  514  generated by the first current I 1A    510  flowing in the first plurality of conductors along the bottom conductor layer  406  will cancel out the magnetic field  524  generated by the corresponding current I 1B    520  flowing in an opposite direction along the first collection of wires along the top conductor layer  412  of the parallel conductor  400 . 
     Importantly, in this illustrated arrangement of the parallel wire conductor, the plurality of susceptor wires  440  are positioned between the alternating conductors or wires making up the parallel wire conductor  400  for inductive heating of the plurality of susceptor wires  440  in the presence of the incoming alternating current  424  provided by the power supply  460 . The inductively heated plurality of susceptor wires  440  thermally conducts heat to a corresponding heating blanket matrix (see, e.g., matrix  78  in  FIG. 4 ). 
     As the plurality of wires nears the first/translation edge  446  of the parallel wire conductor  400 , the plurality of wires must now be translated 180 degrees so that plurality of wires maintain their parallel orientation but must now be directed back towards the second edge  452  of the conductor  400 . As such, the plurality of wires need to be directed in a parallel and uniform orientation back along the top layer  412  and towards the second edge  452  of the parallel conductor wire  400 . 
       FIG. 18  illustrates a close up view of a plurality of conductor wires  468  approaching the first edge or translation edge  446  of the parallel wire conductor  400  illustrated in  FIGS. 13-15 . Specifically,  FIG. 17  illustrates one conductor wire arrangement for translating or turning the plurality of wires  468  that are originally oriented towards the first conductor edge  446  of the parallel wire conductor  400 , back towards the second edge  452  of the parallel wire conductor  400 . As illustrated in  FIG. 17 , the plurality of conductor wires  468  are initially directed towards the first edge  446  of the parallel wire conductor  400 . As the plurality of wires approach the first edge  446 , the wires initially undergo a first 90 degree turn  530  back towards the second side S 2    490  of the parallel wire conductor  400 . As such, current I FT    520  flowing along this first turn of the plurality of wires  468  will be now be directed in an opposite direction to the input current I IN    424  that is initially flowing along the first edge  446  of the bottom conductor layer  406  of the parallel conductor wire  400  (see, e.g.,  FIG. 14 ). 
     After this first 90 degree turn  530 , and to now allow the first plurality of conductors  468  to run back towards the second edge  452  of the parallel wire conductor  400 , the plurality wires  468  undergo yet a second 90 degree turn  540 . Consequently, after this second turn  540 , the plurality of wires  468  are now directed back towards the second edge  452  of the parallel wire conductor  400 , and oriented parallel to the first parallel collection of wires. 
     This pattern of two 90 degrees turns is repeated along the entire length L PWC    474  of the parallel wire conductor  400  with the plurality of wires  468  traversing between the top and bottom conductor layers  412 ,  406  and back forth between the first and second edges  446 ,  452  of the parallel wire conductor  400 . Once the plurality of conductor wires reach the second side  490  of the parallel wire conductor  400 , the plurality of conductors  468  will run back along the first edge  446  of the parallel wire conductor  400  towards the first conductor side S 1    484  and towards the output power lead  430 . Consequently, the output alternating current I OUT    500  will flow along the top or second layer  412  in the direction as noted in  FIG. 16 : from the second side  490  of the conductor  400  towards the first side  484  of the conductor  400 . The output current I OUT    500  will be flowing in an opposite direction as the current flowing in the fourth turn I 4T  and the current flowing in the fifth turn I 5T  as illustrate in  FIG. 15 . As such, a magnetic field  504  generated by the output current I OUT    500  will cancel the magnetic fields generated by the currents flowing through the fourth turn I 4T  and the current flowing in the fifth turn I 5T . 
     The parallel wire conductor  400  as illustrated in  FIGS. 13-17  offers a number of advantages. For example, the parallel wired conductor  400  when incorporated in to heating blanket as described here tends to reduce unwanted heating of nearby conductive materials, such as metal tooling and graphite composite structures. In addition, the parallel wire conductor  400  also tends to cancel the alternating currents in the first and second power leads  420 ,  430  of the parallel wire conductor  400 . Moreover, the parallel wire conductor further reduces unwanted axial currents in the susceptor wires positioned between the alternating conductor bottom and top layers  406 ,  412 . 
     Returning now to  FIG. 8 ,  FIG. 8  is an illustration of an alternative susceptor and conductor arrangement  200  that may be used in a heating blanket, such as the heating blanket  54  illustrated in  FIGS. 2-4  or the heating blanket  410  illustrated in  FIG. 13 . In this illustrated alternative arrangement  200 , the susceptor  210  comprises a spring shaped susceptor and is wound around a conductor  220 . In one preferred arrangement, the susceptor  210  comprises a first and second susceptor wire arrangement as describe and illustrated herein. In an alternative preferred arrangement, the susceptor  210  comprises a first, a second, and a third susceptor wire arrangement as described and illustrated in  FIG. 6 , however alternative susceptor arrangements may also be utilized. 
       FIG. 9  is an illustration of an alternative layout of the alternative susceptor and conductor arrangement illustrated in  FIG. 8 . And  FIG. 10  illustrates a top view of an alternative heating blanket arrangement  254  showing the meandering pattern of the conductor  220  and the array of susceptor wires  210  within the housing  258 . In one preferred arrangement, the array of susceptor wires  210  comprise spring formed wires as illustrated in  FIG. 8 . Such susceptor wires  210  may be wound around the conductor  220  such that a longitudinal axis of the array of susceptor wires  210  is substantially perpendicular to an electrical current flowing through the conductor  220  and generating a magnetic field parallel to the longitudinal axis of the susceptor wires  210 . In this manner, a varying magnetic field generated by the conductor  220  induces eddy currents in the array of susceptor wires  210  as discussed in greater detail herein. 
     A power supply  290  providing alternating current electric power may be connected to the heating blanket  254  by means of the heating blanket wiring  256 . The power supply  290  may be configured as a portable or fixed power supply  290  which may be connected to a conventional 60 Hz, 110 volt or 220 volt (or 480V for very large blankets) outlet. Although the power supply  290  may be connected to a conventional 60 Hz outlet, the frequency of the alternating current that is provided to the conductor  220  may preferably range from approximately 1000 Hz to approximately 400,000 Hz (or up to 2 MHz as described above). The voltage provided to the conductor  220  may range from approximately 10 volts to approximately 450 as described above volts but is preferably less than approximately 60 volts. Likewise, the frequency of the alternating current provided to the conductor  220  by the power supply is preferably between approximately 1 A and 10 A as described above. In this regard, the power supply  290  may be provided in a constant-current configuration wherein the voltage across the conductor  220  may decrease as the magnetic materials within the heating blanket  254  approach the Curie temperature at which the voltage may cease to increase when the Curie temperature is reached as described in greater detail below. 
     Referring to  FIGS. 11 and 12 , shown is an embodiment of the magnetic blanket  254  having a spring susceptor  210  formed of magnetic material having a Curie temperature and provided around a conductor  220 . The susceptor  210  may be formed as a solid or unitary component in a cylindrical arrangement in a spiral or spring configuration around the conductor  220  in order to enhance the flexibility of the heating blanket  254 . As just one example, the susceptor  210  may comprise a first plurality of first susceptor wires having a first Curie temperature and a second plurality of second susceptor wires having a second Curie temperature, as illustrated in  FIG. 6 . The first Curie temperature being lower than the second Curie temperature. The plurality of first susceptor wires may be bundled or interleaved with a second plurality of second susceptor wires. 
     As can be seen in  FIG. 12 , the susceptor  210  may extend along a length of the conductor  220  within the housing  258 . The application of alternating current to the conductor  220  produces an alternating magnetic field  296 . The magnetic field  296  is absorbed by the magnetic material from which the susceptor  210  is formed causing the susceptor  210  to be inductively heated. 
     More particularly and referring to  FIG. 12 , the flow of alternating current through the conductor  220  results in the generation of the magnetic field  296  surrounding the susceptor  210 . Eddy currents  298  generated within the susceptor  210  as a result of exposure thereof to the magnetic field  296  causes inductive heating of the susceptor  210 . The housing  258  may include a thermally conductive matrix  278  material such as silicone to facilitate thermal conduction of the heat generated by the susceptor  210  to the surface of the heating blanket  254 . The magnetic material from which the susceptor  210  is formed preferably has a high magnetic permeability and a Curie temperature that corresponds to the desired temperature to which a structure is to be heated by the heating blanket  254 . The susceptor  210  and conductor  220  are preferably sized and configured such that at temperatures below the Curie temperature of the magnetic material, the magnetic field  296  is concentrated in the susceptor  210  due to the magnetic permeability of the material. 
     As a result of the close proximity of the susceptor  210  to the conductor  220 , the concentration of the magnetic field  296  results in relatively large eddy currents  298  in the susceptor  210 . The induced eddy currents  298  result in resistive heating of the susceptor  210 . The susceptor  210  conductively heats the matrix  278  and a structure  10  ( FIGS. 1-3 ) in thermal contact with the heating blanket  254 . The heating of the first and second susceptor wires of the susceptor  210  occurs as previously described herein with reference to  FIG. 6 . 
     The magnetic materials of the first susceptor wire and the second susceptor wire may be provided in a variety of compositions including, but not limited to, a metal, an alloy, or any other suitable material having a suitable Curie temperature. For example, the first or second susceptor wire may be formed of an alloy having a composition of 32 wt. % Ni-64 wt. % Fe having a Curie temperature of approximately 390° F. The alloy may also be selected as having a composition of 34 wt. % Ni-66 wt. % Fe having a Curie temperature of approximately 450° F. However, the susceptor wires may be formed of a variety of other magnetic materials such as alloys which have Curie temperatures in the range of the particular application such as the range of the adhesive curing temperature or the curing temperature of the composite material from which the patch may be formed. Metals comprising the magnetic material may include iron, cobalt or nickel. Alloys from which the magnetic material may be formed may comprise a combination of the above-described metals including, but not limited to, iron, cobalt and nickel. 
     Referring to  FIG. 10 , the meandering conductors can be arranged in parallel and close to other segments of the conductor carrying current in the opposite direction to prevent unwanted induction in nearby metal or other conductive objects in similar manner as described in herein. 
     Likewise, the presently disclosed conductor (such as the conductor  80  illustrated in  FIGS. 4-6  and the conductor  220  illustrated in  FIGS. 8-11 ) may be formed of any suitable material having an electrical conductivity. Furthermore, the conductor is preferably formed of flexible material to facilitate the application of the heating blanket to curved surfaces. In this regard, the conductor may be formed of Litz wire or other similar wire configurations having a flexible nature and which are configured for carrying high frequency alternating current with minimal weight. The conductor material preferably possesses a relatively low electrical resistance in order to minimize unwanted and/or uncontrollable resistive heating of the conductor. The conductor may be provided as a single strand of wire of unitary construction or the conductor may be formed of braided material such as braided cable. In addition, the conductor may comprise a plurality of conductors which may be electrically connected in parallel in order to minimize the magnitude of the voltage otherwise required for relative long lengths of the conductor such as may be required for large heating blanket configurations. 
     Referring back to  FIGS. 11 and 12 , the heat blanket housing  258  may be formed of a flexible material to provide thermal conduction of heat generated by the susceptor sleeve to the structure to which the heating blanket is applied. In order to minimize environmental heat losses from the heating blanket  254 , an insulation layer  268  may be included as illustrated in  FIGS. 11 and 12 . The insulation layer  268  may comprise insulation  272  formed of silicone or other suitable material to minimize heat loss by radiation to the environment. In addition, the insulation layer  268  may improve the safety and thermal efficiency of the heating blanket  254 . As was indicated above, the housing  258  of the heating blanket  254  may be formed of any suitable high temperature material such as silicone or any other material having a suitable thermal conductivity and low electrical conductivity. Such material may include, but is not limited to, silicone, rubber and polyurethanes or any other thermally conductive material that is preferably flexible. 
     Referring back to  FIGS. 5, 10 and 13 , the heating blankets  54 ,  254 , and  400  may include thermal sensors such as thermocouples or other suitable temperature sensing devices for monitoring heat at locations along the area of the heating blankets  54 , 254  in contact with the structure  10  ( FIG. 3 ). Alternatively, the heating blankets  54 , 254  may include a voltage sensor  94 , 294  or other sensing devices connected to the power supply  90 , 290  as illustrated in  FIGS. 5 and 10 . 
     Referring still to  FIGS. 5 and 10 , sensors  94 ,  294  may be configured to indicate the voltage level provided by power supplies  90 ,  290 , respectively. For a constant current configuration of heating blankets  54 ,  254 , the voltage may decrease as the magnetic material approaches the Curie temperature. Power supplies  90 ,  290  may also be configured to facilitate adjustment of the frequency of the alternating current in order to alter the heating rate of the magnetic material. In this regard, power supplies  90 ,  290  may be coupled to a respective controller  92 ,  292  in order to facilitate adjustment of the alternating current over a predetermined range in order to facilitate the application of a heating blanket to a wide variety of structures having different heating requirements. 
     The presently disclosed susceptor wire array provides a number of advantages. For example, it provides for a heating blanket that provides uniform, controlled heating of large surface areas. In addition, a proper selection of the metal or alloy in the susceptor arrays&#39; first and second susceptor wires facilitates avoiding excessive heating of the work piece irrespective of the input power. By predetermining the first and second susceptor wire metal alloys, improved control and temperature uniformity in the work piece facilitates consistent production of work pieces. The Curie temperature phenomenon of both the first and second susceptor wires (again, more than two different types of susceptor wire materials may be utilized) is used to control both the temperature ranges as well as the absolute temperature of the work piece. This Curie temperature phenomenon is also utilized to obtain substantial thermal uniformity in the work piece, by matching the Curie temperature of the susceptor to the desired temperature of the induction heating operation being performed. 
     The description of the different advantageous embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous embodiments may provide different advantages as compared to other advantageous embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.