HAIR DRYER HAVING A CERAMIC HEATER

CROSS REFERENCES TO RELATED APPLICATIONS

[0001]This application claims priority to U.S. Provisional Patent Application Ser. No. 63/690,462, filed Sep. 4, 2024, entitled “Hair Dryer Heater Assemblies,” the content of which is hereby incorporated by reference in its entirety.

BACKGROUND

1. Field of the Disclosure

[0002]The present disclosure relates to a hair dryer having a ceramic heater.

2. Description of the Related Art

[0003]Conventional hair dryers most typically apply heated air to the end user. Heating sources in conventional hair dryers are most typically in the form of wire coil heaters, such as nichrome wire or similar. The wire coil is typically mounted in the hair dryer using an insulative board, such as a Mica board, which serves as electrical insulation. The heater coils can reach wire temperatures of 500 degrees Celsius, and higher. Given the tendency in today's market to produce more compact hair dryers, the possibility is increased of further exceeding 500 degrees Celsius, for example using nichrome wire with a heating capability of 1150 degrees Celsius. Typical hair dryers adjust temperature by adjusting voltage to the coil(s).

[0004]In a conventional hair dryer utilizing one or more wire heating coils, the coil itself is not electrically insulated. Such insulation would be impractical, if not impossible, due to finding insulative materials capable of surviving the extremely high surface temperature of the coil during operation. Electrical safety is therefore a concern, achieved only by preventing the user from touching any portion of the wire coil and circuit.

[0005]Furthermore, having a 500+ degrees Celsius heated wire in close proximity to a plastic housing of the hair dryer presents an obvious challenge regarding fire prevention. As with electrical considerations, burn prevention in conventional hair dryers is mostly, if not wholly, dependent upon prevention to touch of the wire coils and associated heating assembly components. Furthermore, any foreign articles/particulates pulled into the airstream are highly subject to burning.

[0006]Conventional hair dryers can produce hot air to temperatures of 40 to 100 degrees Celsius, presenting a burn risk to bare skin of the user. In addition, overheating hair by heating hair that no longer requires moisture removal to be considered “dry” or using a temperature greater than that required to dry the hair puts hair within the air stream of conventional hair dryers at unnecessary risk of hair damage and is energy inefficient.

[0007]Heating module assemblies containing conventional heating coils are also often noisy, primarily due to the creation of turbulent air flow by the heating coil.

[0008]The challenges with conventional hair dryer heating technology include: risk of electrical shock, risk of burns, fire risk, excessive noise, and hair damage.

[0009]Accordingly, a hair dryer having a heater with improved characteristics is desired.

SUMMARY

[0010]A hair dryer according to one embodiment includes an air flow conduit having an entrance and an exit; an air mover configured to induce air flow through the air flow conduit to the exit of the air flow conduit; and a heater comprising a ceramic substrate and an electrically resistive trace on the ceramic substrate. The heater is positioned to supply heat generated by applying an electric current to the electrically resistive trace to air in the air flow conduit.

[0011]Some embodiments include a thermal sensor, and control circuitry of the heater. The thermal sensor is in electrical communication with the control circuitry of the heater for providing feedback regarding a temperature of the heater to the control circuitry of the heater. In some embodiments, the thermal sensor comprises at least one of a flag negative temperature coefficient thermistor or a beam negative temperature coefficient thermistor. In some embodiments, the control circuitry of the heater is configured to control the electric current applied to the electrically resistive trace, based on electrical communication from the thermal sensor, to ensure a surface temperature of the heater does not exceed 300 degrees Celsius.

[0012]Some embodiments include a heater housing within the air flow conduit; the heater being mounted on the heater housing. Embodiments include those wherein the heater housing is composed of a plastic material having a maximum service temperature of at least 200 degrees Celsius. Embodiments include those wherein an entry end of the heater housing is positioned within 50 mm, or within 15 mm of an output of the air mover. Embodiments include those where the entry end of the heater housing is positioned at least 5 mm from the output of the air mover.

[0013]The heater has a length, being a longest dimension of the heater, and, in some embodiments, the heater is positioned with its length aligned with a direction from the entrance to the exit of the air flow conduit.

[0014]Embodiments include those wherein the substrate is an aluminum oxide substrate. In some embodiments, the electrically resistive trace is directly on an exterior surface of the substrate. In some embodiments, the substrate has an electrical resistivity of at least 10¹⁴ Ωcm. In some embodiments, the substrate is a laminated ceramic substrate and/or has fiber laser scribed edges. In some embodiments, the substrate has a thickness of no more than 1.5 mm.

[0015]Some embodiments include one or more further heaters. Each of the further heater(s) comprise a respective further ceramic substrate and a respective further electrically resistive trace on the further ceramic substrate. Each of the further heater(s) are positioned to supply heat generated by applying an electric current to their respective electrically resistive trace to air in the air flow conduit. The heater and the further heater(s) are electrically connected to one another. In some embodiments, the heater and the further heater(s) are positioned with a length of each heater, being a longest dimension of the respective heater, aligned with a direction from the entrance to the exit of the air flow conduit. In some embodiments, the further heater(s) are arranged in a polygon shape around the longitudinal axis of the air flow conduit.

[0016]In some embodiments, a total power consumption of the hair dryer is no greater than 1500 W, preferably no greater than 1050 W or 1200 W. In some embodiments, each of the heater and the further heater(s) has a power of between 200 W and 300 W.

[0017]Embodiments include those wherein the heater includes one or more glass layers on an exterior face of the ceramic substrate that cover the electrically resistive trace for electrically insulating the electrically resistive trace. In some embodiments, the electrically resistive trace comprises silver and palladium.

[0018]A hair dryer according to one embodiment includes an air flow conduit having an entrance and an exit; an air mover configured to induce air flow through the air flow conduit to the exit of the air flow conduit; and a heater. The heater includes a ceramic substrate and an electrical resistor material on the ceramic substrate. The heater is positioned to supply heat generated by applying an electric current to the electrical resistor material to air in the air flow conduit.

[0019]Some embodiments further include a thermal sensor and control circuitry of the heater. The thermal sensor is in electrical communication with the control circuitry of the heater for providing feedback regarding a temperature of the heater to the control circuitry of the heater. Embodiments include those wherein the electrical resistor material comprises silver and/or palladium.

[0020]An air-heating device according to one embodiment includes an air flow conduit having an entrance and an exit; an air mover configured to induce air flow through the air flow conduit to the exit of the air flow conduit; and a heater comprising a ceramic substrate and an electrically resistive trace on the ceramic substrate. The heater is positioned to supply heat generated by applying an electric current to the electrically resistive trace to air in the air flow conduit. Some embodiments include a thermal sensor, and control circuitry of the heater. The thermal sensor is in electrical communication with the control circuitry of the heater for providing feedback regarding a temperature of the heater to the control circuitry of the heater. In some embodiments, the thermal sensor comprises at least one of a flag negative temperature coefficient thermistor or a beam negative temperature coefficient thermistor. In some embodiments, the control circuitry of the heater is configured to control the electric current applied to the electrically resistive trace, based on electrical communication from the thermal sensor, to ensure a surface temperature of the heater does not exceed 300 degrees Celsius.

[0021]Some embodiments include a heater housing within the air flow conduit; the heater being mounted on the heater housing. Embodiments include those wherein the heater housing is composed of a plastic material having a maximum service temperature of at least 200 degrees Celsius. Embodiments include those wherein an entry end of the heater housing is positioned within 50 mm, or within 15 mm of an output of the air mover. Embodiments include those where the entry end of the heater housing is positioned at least 5 mm from the output of the air mover.

[0022]The heater has a length, being a longest dimension of the heater, and, in some embodiments, the heater is positioned with its length aligned with a direction from the entrance to the exit of the air flow conduit.

[0023]Embodiments include those wherein the substrate is an aluminum oxide substrate. In some embodiments, the electrically resistive trace is directly on an exterior surface of the substrate. In some embodiments, the substrate has an electrical resistivity of at least 10¹⁴ Ωcm. In some embodiments, the substrate is a laminated ceramic substrate and/or has fiber laser scribed edges. In some embodiments, the substrate has a thickness of no more than 1.5 mm.

[0024]Some embodiments include one or more further heaters. Each of the further heater(s) comprise a respective further ceramic substrate and a respective further electrically resistive trace on the further ceramic substrate. Each of the further heater(s) are positioned to supply heat generated by applying an electric current to their respective electrically resistive trace to air in the air flow conduit. The heater and the further heater(s) are electrically connected to one another. In some embodiments, the heater and the further heater(s) are positioned with a length of each heater, being a longest dimension of the respective heater, being aligned with a direction from the entrance to the exit of the air flow conduit. In some embodiments, the further heater(s) are arranged in a polygon shape around the longitudinal axis of the air flow conduit.

[0025]In some embodiments, a total power consumption of the hair dryer is no greater than 1500 W, preferably no greater than 1050 W or 1200 W.

[0026]Embodiments include those wherein the heater includes one or more glass layers on an exterior face of the ceramic substrate that cover the electrically resistive trace for electrically insulating the electrically resistive trace. In some embodiments, the electrically resistive trace comprises silver and palladium.

[0027]An air heating device according to one embodiment includes an air flow conduit having an entrance and an exit; an air mover configured to induce air flow through the air flow conduit to the exit of the air flow conduit; and a heater. The heater includes a ceramic substrate and an electrical resistor material on the ceramic substrate. The heater is positioned to supply heat generated by applying an electric current to the electrical resistor material to air in the air flow conduit.

[0028]The air heating device may comprise a hair dryer, a fan heater or any other air heating device.

[0029]Some embodiments further include a thermal sensor and control circuitry of the heater. The thermal sensor is in electrical communication with the control circuitry of the heater for providing feedback regarding a temperature of the heater to the control circuitry of the heater. Embodiments include those wherein the electrical resistor material comprises silver and/or palladium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present disclosure and together with the description serve to explain the principles of the present disclosure.

[0031]FIG. 1 is a perspective cut-through view of a hair dryer according to one example embodiment.

[0032]FIG. 2 is a perspective view of an air flow conduit, heater housing and heaters of the hair dryer of FIG. 1.

[0033]FIG. 3 is a perspective view of the heater housing of the hair dryer shown in FIG. 1.

[0034]FIGS. 4A and 4B are a top plan view and a cross-sectional view, respectively, of a heater of the hair dryer shown in FIG. 1.

[0035]FIG. 5 is a schematic view of a circuit formed by the heaters of the hair dryer shown in FIG. 1.

[0036]FIG. 6 is a schematic cross-sectional view of an air flow conduit of the hair dryer shown in FIG. 1.

[0037]FIG. 7 is a cross-sectional view of a portion of a heater housing and a heater in a second example embodiment.

[0038]FIG. 8 is a schematic perspective view of a fan heater according to one example embodiment of the disclosure.

DETAILED DESCRIPTION

[0039]In the following description, reference is made to the accompanying drawings where like numerals represent like elements. The embodiments are described in sufficient detail to enable those skilled in the art to practice the present disclosure. It is to be understood that other embodiments may be utilized and that process, electrical, and mechanical changes, etc., may be made without departing from the scope of the present disclosure. Examples merely typify possible variations. Portions and features of some embodiments may be included in or substituted for those of others. The following description, therefore, is not to be taken in a limiting sense and the scope of the present disclosure is defined only by the appended claims and their equivalents.

[0040]Referring now to the drawings and particularly to FIG. 1, a hair dryer 100 is shown according to one example embodiment. Hair dryer 100 includes an air flow conduit 101 having an entrance 102 and an exit 103. Air flow conduit 101 may be composed of, for example, a plastic that is thermally insulative and electrically insulative and that possesses relatively high heat resistivity and dimensional stability and low thermal mass.

[0041]Hair dryer 100 includes an air mover 104 configured to induce air flow through air flow conduit 101, such as from the entrance 102 to the exit 103 of air flow conduit 101. In the embodiment illustrated, air mover 104 is a fan/motor, but it will be appreciated that other forms of air mover may be utilized. Hair dryer 100 may further comprise handle 118 which may be integrally formed with air flow conduit 101.

[0042]Hair dryer 100 includes a heater 105 positioned in the air flow conduit. In the embodiment illustrated, hair dryer 100 includes four further heaters 106, 107, 108, 109. Other embodiments may include no further heaters, one further heater, or any plurality of further heaters.

[0043]Hair dryer 100 includes a heater housing 110 within the air flow conduit 101, the heaters 105-109 being mounted on the heater housing 110. The heater housing is shown in more detail in FIG. 2 which shows a perspective view of the air flow conduit 101, heaters 105-109 and heater housing 110 from an entrance end of the air flow conduit 101 of hair dryer 100. FIG. 3 shows a perspective view of the heater housing 110.

[0044]Heater housing 110 may be composed of a plastic material having a maximum service temperature of at least 200 degrees Celsius. Heater housing may be composed of a plastic that is thermally insulative and electrically insulative and that possesses relatively high heat resistivity and dimensional stability and low thermal mass. Due to the proximity to heaters 105-109, heater housing 110 is preferably composed of a plastic capable of resisting thermal degradation and maintaining sufficient strength and stiffness at high temperatures, including plastics having a maximum service temperature of 200 degrees Celsius or more. Example plastics include liquid crystal polymer (LCP) plastics, polyether ether ketone (PEEK) plastics and polyphenylene sulfide (PPS) plastics. Fasteners (not shown), such as screws, mount heater housing 110 to the air flow conduit 101.

[0045]Heater housing 110 may also support thermal sensor 111 (not shown in FIGS. 2 and 3) and/or thermal cutoffs 117 which will be discussed in more detail below.

[0046]Heater housing 110 has a central support 125 from which sets of spokes 126 extend radially outward and end in plastic support structures. Heater mounting grooves 127 may be formed by the plastic support structures. In the embodiment illustrated in FIGS. 2 and 3, in each set of spokes, five spokes 126 extend from central support 125, each spoke ending in a plastic support structure. Each plastic support structure forms two grooves 127, each of the grooves facing a respective adjacent plastic support structure. Heaters 105-109 may be mounted within the heater mounting grooves 127 with each side of each heater being supported by a heater supporting groove 127 as illustrated in FIG. 2. Spokes 126 are equally spaced around the central support 125 and have equal length, resulting in the heaters forming a regular polygonal shape. In the illustrated embodiment, five spokes 126 are present in each set of spokes, and five heaters 105-109 are supported between the grooves 127, resulting in a regular pentagon shape being formed by the heaters, but other numbers of spokes 126 and heaters may be used. The pentagonal shape is schematically illustrated in FIG. 6.

[0047]The heater housing 110 includes two sets of spokes, each set at a respective end of central support. In other embodiments, further sets of spokes may be included.

[0048]Other arrangements of heater housing are envisaged, such as heater housing 110 shown in FIG. 7. In this alternative embodiment, each spoke 1126 provides a plastic support structure with a pair of opposing grooves 1127 which face one another. Heater 105 may be supported in the pair of opposing groves 1127. Other arrangements of support structure are also possible, including those which utilize fasteners to retain the heaters 105-109 on the heater housing 110.

[0049]The heaters 105-109 may be positioned with a length 156 of each heater, being a longest dimension of the respective heater, aligned with a direction from the entrance 102 to the exit 103 of the air flow conduit 101. The heaters 105-109 may be equally spaced around a longitudinal axis A of the air flow conduit 101. The heaters 105-109 may be arranged in a polygon shape around the longitudinal axis A of the air flow conduit. The length of the heaters 105-109 may be substantially parallel to the longitudinal axis A of the air flow conduit. The orientation of the heaters 105-109 enables efficient air flow and reduces turbulence. An end of the heaters 105-109 closest to the entrance 102 of the air flow conduit 101, may be positioned between 5 and 15 mm of an output 128 of the air mover 104.

[0050]Referring to FIGS. 4A and 4B, the construction of heater 105 will be described according to one example embodiment. The construction of further heaters 106, 107, 108 and 109 in the illustrated embodiment is the same and so the description of heater 105 is equally applicable to heaters 106, 107, 108 and 109. It will be appreciated that heaters having different shapes/sizes and/or configurations may be utilized together without departing from the disclosure. FIG. 4A shows a plan view of a top face of the heater 105 and FIG. 4B shows a sectional side view along dashed line B shown in FIG. 4A.

[0051]Heater 105 comprises a ceramic substrate 113 and an electrically resistive trace 114 on the ceramic substrate 113. The heater 105 is positioned, as illustrated in FIGS. 1 and 2, to supply heat generated by applying an electric current to the electrically resistive trace 114 to air in the air flow conduit 101. Ceramic heaters such as heater 105 can be formed with a flat profile and can be readily produced in a high variety of sizes, so that heaters 105 can be adapted to the size/shape of a variety of hair dryer sizes. Further, a fan/motor of the air mover 104 can be aligned to produce air flow across the heaters 105-109 in a way that produces efficient heat transfer without significantly limiting air flow (lower drying performance) or producing unwanted turbulent flow (creating unsatisfactory noise levels).

[0052]In the embodiment illustrated, top face 150 and bottom face 151 are bordered by four sides or edges 152, 153, 154, 155 each having a smaller surface area than top face 150 and bottom face 151. In this embodiment, heater 105 includes a longitudinal dimension 156 that extends from edge 152 to edge 153 and a lateral dimension 157 that extends from edge 154 to edge 155. Heater 105 also includes an overall thickness 158 (FIG. 4B) measured from top face 150 to bottom face 151.

[0053]Heater 105 includes one or more layers of a ceramic substrate 113, such as aluminum oxide (e.g., commercially available 96% aluminum oxide ceramic). Advantageously, there is no need for an insulation layer between an aluminum oxide substrate and the electrically resistive trace, in contrast to a stainless steel substrate. This provides a quicker reaction time of the heater 105 by more quickly providing heat from resistive trace 114 to substrate 113. Further, aluminum oxide is more thermally conductive than other materials such as stainless steel so provides improved spread of heat. The substrate 113 may have an electrical resistivity of at least 10¹⁴ Ωcm, and may have an electrical resistivity not exceeding 10¹⁶ Ωcm. This improves electrical safety of the heater 105.

[0054]The heaters 105-109 have relatively low thermal mass compared with the heating elements of conventional hair dryers. By utilizing a substrate of aluminum oxide, having relatively high electrically resistant properties, heaters 105-109 also have improved electrical safety. Since the heaters 105-109 can be operated at a significantly lower surface temperature than conventional wire coil heaters, the relatively small area electrical connections may be covered with insulative materials, such as glass layer 116, capable of withstanding the operating temperatures of the ceramic heaters 105-109. This is further enhanced by the heaters 105-109 being lower in temperature at the ends than in the center of the heaters.

[0055]Where heater 105 includes a single layer of ceramic substrate 113, a thickness of ceramic substrate 113 may range from, for example, 0.5 mm to 1.5 mm, such as 1.0 mm or 1.27 mm. This provides a low profile in the air flow conduit allowing greater laminar air flow and less turbulence, thereby reducing noise produced by hair dryer 100.

[0056]Where heater 105 includes multiple layers of ceramic substrate 113, each layer may have a thickness ranging from, for example, 0.5 mm to 1.0 mm, such as 0.635 mm. In some embodiments, a length of ceramic substrate along longitudinal dimension 156 may range from, for example, 80 mm to 120 mm. In some embodiments, a width of ceramic substrate 113 along lateral dimension 157 may range from, for example, 10 mm to 20 mm, such as 14 mm. Overall thickness 158 of heater 105 may range from 0.5 mm to 1.6 mm.

[0057]Ceramic substrate 113 includes a top face 162 that is oriented toward top face 150 of heater 105 and a bottom face 163 that is oriented toward bottom face 151 of heater 105. Top face 162 and bottom face 163 of ceramic substrate 113 are positioned on exterior portions of ceramic substrate 113 such that if more than one layer of ceramic substrate 113 is used, top face 162 and bottom face 163 are positioned on opposed external faces of the ceramic substrate 113 rather than on interior or intermediate layers of ceramic substrate 113.

[0058]In the example embodiment illustrated, bottom face 151 of heater 105 is formed by bottom face 163 of ceramic substrate 113 as shown in FIG. 4B.

[0059]In this embodiment, top face 162 of ceramic substrate 113 includes one or more electrically resistive traces 114 and electrically conductive traces 115 positioned directly thereon. One resistive trace 114 is illustrated. Resistive trace 114 includes a suitable electrical resistor material such as, for example, silver palladium (e.g., blended 70/30 silver palladium). Each heater 105-109 may have a resistance of 1.5 to 2.5Ω, for example 2Ω. The sheet resistance of the resistive trace 114 may be 0.3 to 0.4 Ω/sq. The resistivity of the resistive trace 114 may be 2.2 Ωcm.

[0060]Conductive traces 115 include a suitable electrical conductor material such as, for example, silver platinum with 1% platinum.

[0061]In the embodiment illustrated, resistive trace 114 and conductive traces 115 are applied to ceramic substrate 113 by way of thick film printing. For example, resistive trace 114 may have a thickness of 9-12 microns or 18-24 microns. Thicker resistive traces may be formed when more than one, such as two thick film printing cycles are performed. Conductive traces 115 may have a thickness of 9-15 microns. Resistive trace 114 forms the heating element of heater 105 and conductive traces 115 provide electrical connections to resistive trace 114 in order to supply an electrical current to each resistive trace 114 to generate heat.

[0062]In the example embodiment illustrated, heater 105 includes one resistive trace that extends substantially parallel to edges 154, 155 along longitudinal dimension 156 of heater 105, otherwise referred to as the length of the heater 105. The resistive trace 114 may cover a majority of the top face 162 of the substrate 113. Heater 105 also includes a pair of conductive traces 115a, 115b that each form a respective terminal of heater 105. In the embodiment illustrated, heaters 105-109 are positioned with their length aligned with a direction from the entrance 102 to the exit 103 of the air flow conduit 101.

[0063]Portions of resistive trace 114 obscured beneath conductive traces 115a, 115b or glass layer 116 in FIG. 4A are shown in dotted line. Portions of conductive traces 115a, 115b obscured beneath glass layer 116 in FIG. 4A are also shown in dotted line.

[0064]In this embodiment, current input to heater 105 at, for example, conductive trace 115a passes through, in order, resistive trace 114, and conductive trace 115b where it is output from heater 105. Current input to heater 105 at conductive trace 115b travels in reverse along the same path.

[0065]In the embodiment illustrated in FIGS. 4A and 4B, heater 105 includes one or more layers of printed glass 116 on top face 162 of ceramic substrate 113. In the embodiment illustrated, glass 116 covers resistive trace 114 and portions of conductive traces 115a, 115b in order to electrically insulate such features to prevent electric shock or arcing. An overall thickness of glass 116 may range from, for example, 35-45 microns. FIG. 4A shows glass 116 covering resistive trace 114 and adjacent portions of ceramic substrate 113 such that glass 116 forms the majority of top face 150 of heater 105. Bottom face 163 of ceramic substrate 113 is shown forming bottom face 151 of heater 105 as discussed above. In alternative embodiments, glass layer 116 may be omitted and resistive trace 114 may form the majority of top surface 150 of heater 105.

[0066]FIG. 5 shows a heating circuit of hair dryer 100. Hair dryer 100 includes control circuitry 112 configured to control the temperature of the heaters 105-109 by selectively opening or closing a circuit 130 (shown in FIG. 5) supplying electrical current to the heaters 105-109. Where hair dryer 100 includes a plurality of heaters 105-109, control circuitry 112 may be configured to control each heater 105-109 independently or to control all heaters 105-109 jointly. Open loop or, preferably, closed loop control may be utilized as desired. Control circuitry 112 may include a microprocessor, a microcontroller, an application-specific integrated circuit, and/or other form of integrated circuit. In the embodiment illustrated, hair dryer 100 includes a power cord 131 (not shown in FIG. 5) for connecting hair dryer 100 to an external voltage source. In other embodiments, hair dryer 100 may include an internal battery as desired.

[0067]As illustrated in FIG. 5, cables or wires 170 are connected to terminals of heater 105 in order to electrically connect resistive trace 114 and conductive traces 115 to, for example, further heaters 106-109 and control circuitry 112 in order. The control circuitry may be configured to selectively close the circuit formed by resistive traces 114 of heaters 105-109 and conductive traces 115 to generate heat via the resistive traces 114.

[0068]Conductive trace 115a directly contacts resistive trace 114, and conductive trace 115b directly contacts resistive trace 114. Conductive trace 115a is positioned adjacent to edge 153 and conductive trace 115b is positioned adjacent to edge 152 in the example embodiment illustrated, but conductive traces 115a, 115b may be positioned in other suitable locations on ceramic substrate 113 as desired. In the illustrated embodiment, heaters 105-109 are connected in series by cables or wires 170. Heaters 105-109 may alternatively be wired in parallel or hybrid arrangements to achieve a desired power.

[0069]In another embodiment, cables or wires 170 may be formed by busbars which may be directly welded busbars to conductive traces 115. The busbars may be composed of phosphor bronze, copper, and/or brass material(s). The busbars may have a thickness of 0.127 mm. Such busbars advantageously have a low profile within the air flow conduit 101, reducing turbulence in the air flow.

[0070]While the example embodiment illustrated in FIGS. 3-5 includes resistive trace 114 positioned on top face 162 of ceramic substrate 113, in other embodiments, resistive trace 114 may be positioned on bottom face 163 of ceramic substrate 113 along with corresponding conductive traces as needed to establish electrical connections thereto. Glass 116 may cover the resistive traces and conductive traces on top face 162 and/or bottom face 163 of ceramic substrate 113 as desired in order to electrically insulate such features.

[0071]While not illustrated, it will be appreciated that bottom face 163 of ceramic substrate 113 may include one or more glass layers in order to electrically insulate portions of bottom face 151 of heater 105 as desired.

[0072]Hair dryer 100 may include a thermal sensor, such as thermistor 111 positioned in close proximity to, or on a surface of heater 105 in order to provide feedback regarding the temperature of heater 105 to control circuitry 112. The thermistor 111 is in electrical communication with the control circuitry 112 of the heater for providing feedback regarding a temperature of the heater to the control circuitry of the heater and control circuitry 112 may control the current supplied to the heaters 105-109 based on the feedback. Further thermal sensors may also be provided in close proximity to one or more of the further heaters 106-109.

[0073]The thermal sensor 111 may include at least one of a flag negative temperature coefficient thermistor and/or a beam negative temperature coefficient thermistor. The control circuitry of the heater may be configured to control the electric current applied to the heaters 105-109, based on electrical communication from the thermal sensor 111, to ensure a surface temperature of the heaters 105-109 does not exceed 300 degrees Celsius.

[0074]In some embodiments, thermistor 111 is positioned on top face 150 of heater 105. Cables or wires 178a, 178b are connected to terminals of thermistor 111 in order to electrically connect thermistor 111 to, for example, control circuitry 112 in order to provide closed loop control of heater 105. In the embodiment illustrated, thermistor 111 is a chip thermistor welded to a thick film conductor circuit printed on substrate 113 on either side of the resistive trace 114. In this way, the hair dryer 100 is provided with a direct, low thermal mass, temperature sensing and feedback capability.

[0075]However, thermistor 111 may be positioned in other suitable locations near or on heater 105 so long as it does not interfere with the positioning of resistive trace 114 and conductive traces 115. For example, if a contact thermistor is used, it may be positioned on the bottom face 151 of the heater, opposite the resistive trace 114, which may improve the electrical insulation of the heater from the trace 114.

[0076]Thermistor 111 may be positioned so as to not contact the heater(s) 105-109. Where non-contact thermal sensors are used, they may be positioned proximate the top face 150 of the heater 105, so that radiant heat directly from the resistive trace 114 is nearby. In such an embodiment, thermistor 111 may be positioned in close proximity to bottom face 163 of ceramic substrate 113 in order to provide feedback regarding the temperature of heater 105 to control circuitry 112. In this embodiment, thermistor 1111 is not directly attached to ceramic substrate 113 but is instead held against bottom face 163 of ceramic substrate 1113 by a mounting clip (not shown) or other form of fixture or attachment mechanism.

[0077]The thermal sensor may further include a responsive air temperature sensor, such as a bead NTC thermistor (not shown). A combination of the thermal sensor with the use of the ceramic heater(s) 105-109 provides a tightly controlled, responsive hair dryer, regardless of air flow rate, thereby reducing risk of burns and reducing energy consumption while maintaining performance. The power of each of the heaters 105-109 may be 200-300 W. A maximum power consumption of the hair dryer may be no greater than 1500 W, for example 1200-1300 W.

[0078]In the example embodiment illustrated, hair dryer 100 also includes one or more thermal cutoffs 117, which may be bi-metal thermal cutoffs, mounted on heater housing 110 as shown in FIG. 3. Cables or wires 196 are connected to respective terminals of thermal cutoff 117 in order to provide electrical connections to thermal cutoff 117. Thermal cutoff 117 is electrically connected in series with the heating circuit formed by resistive traces 114 and conductive traces 115 permitting thermal cutoff 117 to open the heating circuit formed by resistive traces 114 and conductive traces 115 upon detection by thermal cutoff 117 of a temperature that exceeds a predetermined amount. In this manner, thermal cutoff 117 provides additional safety by preventing overheating of heater 105. Two thermal cutoffs 117 are illustrated in FIGS. 3 and 5, but one or more than two thermal cutoffs may be included in hair dryer 100.

[0079]Heater 105 may be constructed by way of thick film printing. For example, in one embodiment, resistive trace 114 is printed on fired (not green state) ceramic substrate 113, which includes selectively applying a paste containing resistor material to ceramic substrate 113 through a patterned mesh screen with a squeegee or the like. The printed resistor is then allowed to settle on ceramic substrate 113 at room temperature. The ceramic substrate 113 having the printed resistor is then heated at, for example, approximately 140-113 degrees Celsius for a total of approximately 30 minutes, including approximately 10-15 minutes at peak temperature and the remaining time ramping up to and down from the peak temperature, in order to dry the resistor paste and to temporarily fix resistive trace 114 in position. The ceramic substrate 113 having temporary resistive trace 114 is then heated at, for example, approximately 850 degrees Celsius for a total of approximately one hour, including approximately 10 minutes at peak temperature and the remaining time ramping up to and down from the peak temperature, in order to permanently fix resistive trace 114 in position. Conductive traces 115 are then printed on ceramic substrate 113, which includes selectively applying a paste containing conductor material in the same manner as the resistor material. The ceramic substrate 113 having the printed resistor and conductor is then allowed to settle, dried and fired in the same manner as discussed above with respect to resistive trace 114 in order to permanently fix conductive traces 115 in position. Glass layer(s) 116 are then printed in substantially the same manner as the resistors and conductors, including allowing the glass layer(s) 116 to settle as well as drying and firing the glass layer(s) 116. In one embodiment, glass layer(s) 116 are fired at a peak temperature of approximately 810 degrees Celsius, slightly lower than the resistors and conductors. Thermistor 111 is then mounted to ceramic substrate 113 in a finishing operation. Thermistor 111 may be a chip thermistor and a thermistor assembly having a relatively small lead frame may be welded to a thick film conductor circuit printed on substrate 113 on either side of the thick film resistive trace. In this way, the hair dryer 100 is provided with a direct, low thermal mass, temperature sensing and feedback capability.

[0080]Preferably, heaters 105 are produced in an array for cost efficiency. Heaters 105 are separated into individual heaters 105 after the construction of all heaters 105 is completed, including firing of all components and any applicable finishing operations. In some embodiments, individual heaters 105 are separated from the array by way of fiber laser scribing. Fiber laser scribing tends to provide a more uniform singulation surface having fewer microcracks along the separated edge in comparison with conventional carbon dioxide laser scribing. Further, heaters 105-109 are resistive to thermal gradients and thermal shock.

[0081]It will be appreciated that the example embodiments illustrated and discussed above are not exhaustive and that the heaters, air mover, air flow conduit and thermal sensors disclosed above may be applied to any air heating devices which include hair dryers, fan heaters and other air heating devices. Air heating device 2100 may be a fan heater, as illustrated schematically in FIG. 8. Air heating device 2100 includes air flow conduit 2101 with entrance 2102 and exit 2103. Air heating device 2100 includes air mover 2104 which may be a fan, configured to cause air to flow through air flow conduit 2101 from the entrance 2102 to exit 2103. The features of FIG. 8 are labelled with the final three digits corresponding to the features described in relation to the hair dryer of FIG. 1 and this signifies that the features of FIG. 8 have the same characteristics except where specified below. The dimensions of the air flow conduit 2101, air mover 2104 and heaters 2105-2109 (2106-2108 not shown) are increased as desired and the power of the air mover 2104 and heaters 2105-2109 is also increased as desired.

[0082]Further, the heaters of the present disclosure may include resistive and conductive traces in many different geometries, including resistive traces on the top face and/or the bottom face of the heater, as desired. Other components (e.g., a thermistor) may be positioned on either the top face or the bottom face of the heater as desired.

[0083]Further, embodiments of the hair dryer of the present disclosure operate at a more precise and more uniform temperature than conventional hair dryers because of the closed loop temperature control provided by the thermistor in combination with the relatively uniform thick film printed resistive and conductive traces. The capability of the ceramic heater to produce heat at a lower surface temperature than conventional hair dryer heaters and with improved temperature control permits greater energy efficiency in comparison with conventional hair dryers. The improved temperature control and temperature uniformity further increase safety by reducing the occurrence of overheating. The improved temperature control and temperature uniformity also improve the performance of the hair dryer of the present disclosure.

[0084]The foregoing description illustrates various aspects of the present disclosure. It is not intended to be exhaustive. Rather, it is chosen to illustrate the principles of the present disclosure and its practical application to enable one of ordinary skill in the art to utilize the present disclosure, including its various modifications that naturally follow. All modifications and variations are contemplated within the scope of the present disclosure as determined by the appended claims. Relatively apparent modifications include combining one or more features of various embodiments with features of other embodiments.