PATENT DOCUMENT

Publication Number: US-9942663-B1
Application Number: US-201615389126-A
Country: US
Kind Code: B1

Title: Electromagnetic transducer having paired Halbach arrays

Abstract:
An electromagnetic transducer, such as an audio speaker, having a voicecoil disposed within a magnetic gap between a pair of magnetic arrays, e.g., Halbach arrays, is disclosed. In an example, the paired Halbach arrays include vertically-poled magnets to direct magnetic flux across the magnetic gap orthogonal to electrical current carried by a planar winding of the voicecoil. Accordingly, a Lorentz force may drive an oscillational mass, e.g., a speaker diaphragm, in a longitudinal direction orthogonal to the magnetic flux and the electrical current to generate vibration or sound. Other embodiments are also described and claimed.

Claims:
What is claimed is: 
     
       1. An electromagnetic transducer, comprising:
 a magnetic return structure; 
 a first magnetic Halbach array separated from the magnetic return structure by a magnetic gap, wherein the first magnetic Halbach array includes a first upward-poled magnet and a first downward-poled magnet, wherein the first upward-poled magnet directs magnetic flux upward along a first vertical axis through the magnetic gap, and wherein the first downward-poled magnet directs magnetic flux downward along a second vertical axis through the magnetic gap; and 
 a voicecoil including a planar winding within the magnetic gap, wherein the planar winding includes a first transverse conductor between the first upward-poled magnet and the magnetic return structure to conduct electrical current leftward along a first transverse axis orthogonal to the first vertical axis, and a second transverse conductor between the first downward-poled magnet and the magnetic return structure to conduct electrical current rightward along a second transverse axis orthogonal to the second vertical axis such that the electrical currents intersect the magnetic fluxes to cause a Lorentz force to move the voicecoil axially along a longitudinal axis orthogonal to both vertical axes and both transverse axes. 
 
     
     
       2. The electromagnetic transducer of  claim 1 , wherein the magnetic return structure includes a second magnetic Halbach array including a second upward-poled magnet and a second downward-poled magnet, wherein the upward-poled magnets are aligned along the first vertical axis, and wherein the downward-poled magnets are aligned along the second vertical axis. 
     
     
       3. The electromagnetic transducer of  claim 2  further comprising a speaker diaphragm coupled to the voicecoil, wherein the Lorentz force drives the speaker diaphragm. 
     
     
       4. The electromagnetic transducer of  claim 3  further comprising:
 a piston to couple the voicecoil to the speaker diaphragm; and 
 a constraint mechanism coupled to the piston to constrain the speaker diaphragm to move axially along the longitudinal axis. 
 
     
     
       5. The electromagnetic transducer of  claim 1 , wherein the first transverse conductor includes a plurality of transverse winding segments, and wherein the first transverse conductor includes a conductor width across the transverse winding segments in a longitudinal direction. 
     
     
       6. The electromagnetic transducer of  claim 5 , wherein the planar winding includes a plurality of conformal winding lengths, and wherein each conformal winding length includes one of the plurality of transverse winding segments. 
     
     
       7. The electromagnetic transducer of  claim 5 , wherein the planar winding includes a plurality of coiled winding lengths, and wherein each coiled winding length includes one of the plurality of transverse winding segments. 
     
     
       8. The electromagnetic transducer of  claim 5 , wherein the upward-poled magnets have a magnet width, and wherein the conductor width is greater than the magnet width. 
     
     
       9. The electromagnetic transducer of  claim 1 , wherein each magnetic Halbach array includes a longitudinally-poled magnet between the upward-poled magnet and the downward-poled magnet to direct magnetic flux between the upward-poled magnet and the downward-poled magnet. 
     
     
       10. The electromagnetic transducer of  claim 9 , wherein each magnetic Halbach array includes an end magnet extending in a longitudinal direction between the upward-poled magnet and the downward-poled magnet, wherein the end magnet is poled in a vertical direction, and wherein the planar winding is within the magnetic gap between the end magnets. 
     
     
       11. An electroacoustic transducer, comprising:
 a pair of magnetic Halbach arrays, the pair including an upper magnetic Halbach array separated from a lower magnetic Halbach array by a magnetic gap, wherein each magnetic Halbach array includes an upward-poled magnet and a downward-poled magnet, wherein the upward-poled magnets are aligned along a first vertical axis to direct magnetic flux upward along the first vertical axis through the magnetic gap, and wherein the downward-poled magnets are aligned along a second vertical axis to direct magnetic flux downward along the second vertical axis through the magnetic gap; 
 a voicecoil including a planar winding within the magnetic gap, wherein the planar winding includes a first transverse conductor between the upward-poled magnets to conduct electrical current leftward along a first transverse axis orthogonal to the first vertical axis, and a second transverse conductor between the downward-poled magnets to conduct electrical current rightward along a second transverse axis orthogonal to the second vertical axis such that the electrical currents intersect the magnetic fluxes to cause a Lorentz force to move the voicecoil in a longitudinal direction; and 
 a diaphragm coupled to the voicecoil, wherein the Lorentz force drives the diaphragm to generate sound. 
 
     
     
       12. The electroacoustic transducer of  claim 11 , wherein the Lorentz force drives the diaphragm axially along a longitudinal axis orthogonal to both vertical axes and both transverse axes. 
     
     
       13. The electroacoustic transducer of  claim 12 , wherein the diaphragm is coupled to the voicecoil by a piston, and wherein the piston moves along the longitudinal axis to drive the diaphragm in the longitudinal direction. 
     
     
       14. The electroacoustic transducer of  claim 11 , further comprising a ferrofluid within the magnetic gap between the voicecoil and the pair of magnetic Halbach arrays. 
     
     
       15. The electroacoustic transducer of  claim 11 , further comprising a second diaphragm coupled to the voicecoil, wherein the Lorentz force drives the second diaphragm in the longitudinal direction. 
     
     
       16. The electroacoustic transducer of  claim 11 , further comprising:
 a second voicecoil having a second planar winding within the magnetic gap; and 
 a second diaphragm coupled to the second voicecoil, wherein a second Lorentz force drives the second diaphragm in a second longitudinal direction opposite to the longitudinal direction. 
 
     
     
       17. The electroacoustic transducer of  claim 11 , further comprising:
 a second voicecoil between the voicecoil and the lower magnetic Halbach array, wherein the diaphragm extends between the voicecoil and the second voicecoil; and 
 a second diaphragm extending between the voicecoil and the second voicecoil; 
 wherein an air volume is defined between the voicecoils and the diaphragms, and wherein the air volume changes when the voicecoil is driven in the longitudinal direction to generate sound. 
 
     
     
       18. A mobile electronic device, comprising:
 a housing; 
 a processor; and 
 a micro speaker coupled with the housing and the processor, wherein the micro speaker includes one or more acoustic cells, each acoustic cell including:
 a pair of magnetic Halbach arrays, the pair including an upper magnetic Halbach array separated from a lower magnetic Halbach array by a magnetic gap, wherein each magnetic Halbach array includes an upward-poled magnet and a downward-poled magnet, wherein the upward-poled magnets are aligned along a first vertical axis to direct magnetic flux upward along the first vertical axis through the magnetic gap, and wherein the downward-poled magnets are aligned along a second vertical axis to direct magnetic flux downward along the second vertical axis through the magnetic gap; 
 a voicecoil including a planar winding within the magnetic gap, wherein the planar winding includes a first transverse conductor between the upward-poled magnets to conduct electrical current leftward along a first transverse axis orthogonal to the first vertical axis, and a second transverse conductor between the downward-poled magnets to conduct electrical current rightward along a second transverse axis orthogonal to the second vertical axis such that the electrical currents intersect the magnetic fluxes to cause a Lorentz force to move the voicecoil in a longitudinal direction; and 
 a diaphragm coupled to the voicecoil, wherein the Lorentz force drives the diaphragm to generate sound. 
 
 
     
     
       19. The mobile electronic device of  claim 18 , wherein the diaphragm is coupled to the voicecoil by a piston, wherein the diaphragm is coupled to the housing by a surround, and wherein the piston moves the diaphragm in the longitudinal direction. 
     
     
       20. The mobile electronic device of  claim 18 , wherein the one or more acoustic cells include a plurality of acoustic cells, and wherein the voicecoils of the acoustic cells receive independent electrical audio signals from the processor to generate respective sounds having respective amplitudes and phases.

Description:
BACKGROUND 
     Field 
     Embodiments related to electromagnetic transducers having several Halbach arrays, are disclosed. More particularly, embodiments related to electromagnetic transducers having a voicecoil between a pair of Halbach arrays, are disclosed. 
     Background Information 
     An electromagnetic transducer converts an electrical input signal into a mechanical force. For example, a haptic feedback device may include an electromagnetic transducer to convert an electrical signal into a vibration. Similarly, an audio speaker may include an electroacoustic transducer to convert an electrical audio signal into a sound. An electromagnetic transducer typically includes a motor assembly to generate a force to drive a mass, such as a speaker diaphragm. The motor assembly may include a voicecoil, which typically includes a helical winding disposed in a gap of a magnetic circuit. The magnetic circuit may direct a magnetic field perpendicular to the helical winding such that, when the voicecoil is energized by an electrical input signal, a mechanical force is generated to cause the voicecoil to move back and forth within the gap. 
     SUMMARY 
     Portable consumer electronic devices, such as mobile phones, have continued to become more and more compact. As the form factor of such devices shrinks, system enclosures become smaller and the space available for component integration is reduced. In particular, the trend toward reducing a thickness of these devices (the so-called “z-height”) has generally been a primary challenge for the integration of audio or vibration transducers. In the case of an audio speaker having a voicecoil suspended within a gap of a magnetic circuit, precious space is occupied by a magnetic return structure that is required to direct the magnetic field toward the voicecoil. More particularly, since the voicecoil and the magnetic return structure typically extend along an axis of sound emission, some of the overall z-height required for excursion of the speaker diaphragm is taken up by the motor assembly. Accordingly, the speaker diaphragm may no longer fit within the available z-height, and it may become necessary to separate the motor assembly and the speaker diaphragm. That is, the motor assembly may be coupled to the speaker diaphragm to drive the diaphragm and the generated sound in another direction, e.g., a direction lateral to the z-height. 
     In an embodiment, an electromagnetic transducer includes paired magnetic Halbach arrays forming a magnetic gap, and a voicecoil within the magnetic gap. Electrical current in the voicecoil may interact with magnetic flux in the magnetic gap to generate a Lorentz force that moves the voicecoil axially along a longitudinal axis. An oscillational mass may be coupled to the voicecoil, and thus, the Lorentz force may drive the oscillational mass along the longitudinal axis. In an embodiment, the oscillational mass includes a speaker diaphragm, and thus, the electromagnetic transducer may be an electroacoustic transducer. 
     Paired magnetic Halbach arrays of the electromagnetic transducer and/or electroacoustic transducer may include an upper magnetic Halbach array separated from a lower magnetic Halbach array by the magnetic gap. Each magnetic Halbach array may include an upward-poled magnet and a downward-poled magnet, and the upward-poled magnets and downward-poled magnets of the Halbach arrays may be aligned along respective vertical axes. That is, the upward-poled magnets may be aligned along a first vertical axis to direct magnetic flux upward through the magnetic gap, and the downward-poled magnets may be aligned along a second vertical axis to direct magnetic flux downward through the magnetic gap. A planar winding of the voicecoil may include transverse conductors aligned with the vertical axes. For example, a first transverse conductor may conduct electrical current leftward orthogonal to the first vertical axis, and a second transverse conductor may conduct electrical current rightward orthogonal to the second vertical axis. Accordingly, the interaction between the transverse conductors and the respective pairs of vertically-poled magnets may produce respective Lorentz forces that drive the voicecoil in a same direction, e.g., in the longitudinal direction. 
     The Lorentz force may be controlled by varying structural features of the electromagnetic motor assembly. For example, the planar winding may include several conformal winding lengths or coiled winding lengths having transverse winding segments disposed adjacent to each other. A width across the transverse winding segments may be greater than a width of the vertically-poled magnets such that at least a portion of the transverse conductor remains within the magnetic flux when the voicecoil oscillates to a maximum excursion in the longitudinal direction. In an embodiment, each magnetic Halbach array includes an end magnet extending between vertically-poled magnets of the same array. The end magnets may also be poled in a vertical direction such that longitudinal segments of the planar winding can be disposed between the end magnets of the paired arrays, within the magnetic gap, to generate an additional Lorentz force on the voicecoil. 
     An electroacoustic transducer incorporating the paired magnetic Halbach arrays may include several diaphragms and/or several voicecoils. For example, the electroacoustic transducer may include several diaphragms connected to a same voicecoil and driven in unison by the voicecoil. The electroacoustic transducer may include several independently driven voicecoils, and each voicecoil may be connected to a respective diaphragm such that the diaphragms generate sound independently from each other. In an embodiment, a speaker may include several acoustic cells incorporating respective electroacoustic transducers that are independently driven by different audio channels. The electrical audio signals may be controlled such that the acoustic cells can direct sound in a beam forming application. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial view of a mobile electronic device in accordance with an embodiment of the invention. 
         FIG. 2  is a block diagram of a mobile electronic device in accordance with an embodiment. 
         FIGS. 3A-3B  are pictorial views of an electromagnetic transducer in accordance with an embodiment. 
         FIG. 4  is a sectional view of an electromagnetic transducer in accordance with an embodiment. 
         FIG. 5  is a sectional view of an electromagnetic transducer having an overhung voicecoil in accordance with an embodiment. 
         FIG. 6  is a sectional view of an electromagnetic transducer having an underhung voicecoil in accordance with an embodiment. 
         FIG. 7  is a top view of a voicecoil over a magnetic Halbach array in accordance with an embodiment. 
         FIG. 8  is a top view of a voicecoil over a magnetic Halbach array in accordance with an embodiment. 
         FIG. 9  is a top view of a planar winding of a voicecoil having conformal winding lengths in accordance with an embodiment. 
         FIG. 10  is a top view of a planar winding of a voicecoil having coiled winding lengths in accordance with an embodiment. 
         FIG. 11  is a sectional view of an electromagnetic transducer in accordance with an embodiment. 
         FIG. 12  is a top view of a voicecoil over a magnetic Halbach array in accordance with an embodiment. 
         FIG. 13  is a top view of a voicecoil over a magnetic Halbach array having end magnets in accordance with an embodiment. 
         FIG. 14  is a sectional view of an electroacoustic transducer in accordance with an embodiment. 
         FIG. 15  is a sectional view of an electroacoustic transducer in accordance with an embodiment. 
         FIG. 16  is a sectional view of an electroacoustic transducer in accordance with an embodiment. 
         FIG. 17  is a sectional view of an electroacoustic transducer in accordance with an embodiment. 
         FIG. 18  is a sectional view of an electroacoustic transducer in accordance with an embodiment. 
         FIG. 19A-19B  are detail views of an electroacoustic transducer in accordance with an embodiment. 
         FIG. 20  is a sectional view of an electroacoustic transducer having independently driven acoustic cells in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe an electromagnetic transducer, such as an audio speaker, having a voicecoil disposed within a magnetic gap between a pair of magnetic arrays, e.g., Halbach arrays. While some embodiments are described with specific regard to integration within mobile electronic devices, such as handheld devices, the embodiments are not so limited and certain embodiments may also be applicable to other uses. For example, a haptic feedback mechanism or an audio speaker as described below may be incorporated into other devices and apparatuses, including desktop computers, laptop computers, or tablet computers, to name only a few possible applications. Similarly, although the following description commonly refers to an audio speaker as being a “microspeaker”, this description is not intended to be limiting, and an audio speaker as described below may be scaled to any size and emit any range of frequencies. 
     In various embodiments, description is made with reference to the figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, in order to provide a thorough understanding of the embodiments. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the description. Reference throughout this specification to “one embodiment,” “an embodiment,” or the like, means that a particular feature, structure, configuration, or characteristic described is included in at least one embodiment. Thus, the appearance of the phrase “one embodiment,” “an embodiment,” or the like, in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The use of relative terms throughout the description may denote a relative position or direction. For example, “upward” or “above” may indicate a first axial direction away from a reference point. Similarly, “downward” or “below” may indicate a location in a second direction from the reference point opposite to the first axial direction. However, such terms are not intended to limit the use of an electromagnetic transducer to a specific configuration described in the various embodiments below. For example, a microspeaker may be oriented to radiate sound in any direction with respect to an external environment, including upward toward the sky and downward toward the ground. 
     In an aspect, an electromagnetic transducer and/or an electroacoustic transducer incorporating paired magnetic Halbach arrays are disclosed. The paired magnetic Halbach arrays can drive a voicecoil in a longitudinal direction parallel to a plane along which the Halbach magnets are arranged. More particularly, respective vertically-poled magnets of the paired magnetic Halbach arrays may be aligned along a vertical axis passing through a transverse conductor of the voicecoil to drive the voicecoil in a longitudinal direction orthogonal to both the vertical and transverse directions. By driving the voicecoil in the longitudinal direction, and not the vertical direction, the vertical direction of the transducers may be reduced. Accordingly, the transducer may have a thinner form factor. 
     Referring to  FIG. 1 , a pictorial view of a mobile electronic device is shown in accordance with an embodiment of the invention. An electronic device  100  may be a smartphone device. Alternatively, it could be any other portable or stationary device or apparatus incorporating an electromagnetic or electroacoustic transducer, e.g., a haptic feedback mechanism or a microspeaker. For example, electronic device  100  may be a laptop computer or a tablet computer. Electronic device  100  may include various capabilities to allow the user to access features involving, for example, calls, voicemail, music, e-mail, Internet browsing, scheduling, and photos. Electronic device  100  may also include hardware to facilitate such capabilities. For example, electronic device  100  may include cellular network communications circuitry. An integrated microphone  104  may pick up the voice of its user during a call, and microspeaker may deliver a far-end voice to the near-end user during the call. Microspeaker may also emit sounds associated with music files played by a music player application running on electronic device  100 . A display  106  may be integrated within a housing of electronic device  100  to present the user with a graphical user interface to allow a user to interact with electronic device  100  and applications running on electronic device  100 . The housing may enclose a vibration device (not shown) to provide haptic feedback to a user when the user grips the housing. The housing may be sized to be gripped comfortably by the user. Other conventional features are not shown but may of course be included in electronic device  100 . 
     Electronic device  100  may have a thin profile, and thus, may have limited space, e.g., z-height, available for integration of the electromagnetic or electroacoustic transducer. For example, electronic device  100  may have a z-height that is insufficient to fit an audio speaker having a helically wound voicecoil and magnetic return structure extending away from a diaphragm, as described above. Accordingly, electronic device  100  may benefit from a transducer motor assembly having a topology with a shallow depth and a motor assembly that does not require a helically wound voicecoil or a magnetic return structure. 
     Referring to  FIG. 2 , a block diagram of a mobile electronic device is shown in accordance with an embodiment. As described above, electronic device  100  may be one of several types of portable or stationary devices or apparatuses with circuitry suited to specific functionality. For example, electronic device  100  may be a mobile phone handset, as shown in  FIG. 1 . Accordingly, electronic device  100  may include a housing (not shown) to contain or support various components, such as cellular network communications circuitry, e.g., RF circuitry, menu buttons, or display  106 . Electronic device  100  may contain a haptic feedback mechanism, and more particularly, an electromagnetic transducer  206  to generate vibrations as haptic feedback for a user. Electronic device  100  may contain microspeaker  102 , and more particularly, an electroacoustic transducer  208  to generate sound. 
     The diagrammed circuitry of  FIG. 2  is provided by way of example and not limitation. Electronic device  100  may include one or more processors  202  that execute instructions to carry out the different functions and capabilities described above. For example, processor  202  may incorporate and/or communicate with electronics connected to electromagnetic transducer  206  or electroacoustic transducer  208  to provide electrical signals to drive the transducers. For example, an electrical signal may drive a voicecoil to generate mechanical vibration and/or audio output for electronic device  100 . Instructions executed by the one or more processors  202  of electronic device  100  may be retrieved from a local memory  204 , and may be in the form of an operating system program having device drivers, as well as one or more application programs that run on top of the operating system, to perform the different functions introduced above, e.g., music play back. 
     Referring to  FIGS. 3A-3B , pictorial views of an electromagnetic transducer are shown in accordance with an embodiment. An electromagnetic transducer  206  may convert electrical signals from processor  202  into mechanical movements of a transducer component. 
       FIG. 3A  illustrates electromagnetic transducer  206  incorporating a magnetic Halbach array  302  paired with a magnetic return structure  304 . The structure of electromagnetic transducer  206 , and in particular magnetic Halbach array  302 , is described further beginning with  FIG. 3B . The structure may be referred to as a single-sided Halbach array.  FIG. 3A , however, illustrates that magnetic return structure  304  may provide a return path for flux  305  from magnetic Halbach array  302  on an opposite side of a voicecoil  320 . Magnetic return structure  304  may be a ferromagnetic sheet of material, e.g., a steel plate. Accordingly, magnetic flux directed toward magnetic return structure  304  through voicecoil  320  from an upward-poled magnet  310  of magnetic Halbach array  302  may be returned to a downward-poled magnet  314  of Halbach array  302  through voicecoil  320  from magnetic return structure  304 . 
     Referring to  FIG. 3B , magnetic return structure  304  may be a second magnetic Halbach array  302 . More particularly, electromagnetic transducer  206  may incorporate paired Halbach arrays  302 . The structure may be referred to as a dual- or two-sided Halbach array. That is, a pair of Halbach arrays  302  of electromagnetic transducer  206  may include an upper magnetic Halbach array  304  and a lower magnetic Halbach array  306 . Substantial description of paired Halbach array structures is provided below, but it will be appreciated that the single-sided and dual-sided Halbach array structures of  FIGS. 3A-3B  may both be useful embodiments for certain applications. For example, a dual-sided Halbach array structure having dimensions as described below with respect to  FIG. 5  may have a transduction coefficient (BL) of 1.02 Tesla-meters. Comparatively, a single-sided Halbach array structure having dimensions similar to those described below with respect to  FIG. 5 , with the exception of replacing one Halbach array with a carbon steel plate, may have a transduction coefficient (BL) of 0.84 Tesla-meters. Accordingly, it has been shown that paired Halbach arrays can provide an increase in transduction coefficient of 17%. Nonetheless, a transduction coefficient of both embodiments may be sufficiently high to be useful, and the increase in transduction coefficient for a paired Halbach array structure may be counterbalanced by an increase in design complexity. Thus, either single-sided or dual-sided Halbach array structures may be incorporated in electromagnetic transducer  206  as is otherwise described throughout the following description. 
     Each Halbach array of the pair of Halbach arrays  302  may have a similar structure. For example, a basic cell of the Halbach arrays  302  may include at least three magnets, e.g., bar magnets of any length, sequentially arranged side-by-side along a plane. That is, the Halbach arrays  302  may be planar. Each magnet of the Halbach array  302  may be poled in a respective direction, and the direction of poling for each magnet may be 90° or −90° relative to an adjacent magnet. By way of example, a rightmost magnet of upper Halbach array  304  may be an upward-poled magnet  310 , a middle magnet of upper Halbach array  304  may be a longitudinally-poled magnet  312 , e.g., poled—90° relative to upward-poled magnet  310 , and a leftmost magnet of upper Halbach array  304  may be a downward-poled magnet  314 . Lower Halbach array  306 , like upper Halbach array  304 , may have a respective upward-poled magnet  310  and downward-poled magnet  314 . Furthermore, longitudinally-poled magnet  312  between the vertically-poled magnets of lower Halbach array  306  may be poled 90° relative to upward-poled magnet  310  of lower Halbach array  306 . 
     Although the magnets of Halbach arrays  302  are illustrated having rectangular cross-sections, it will be appreciated that the magnets may have other cross-sectional profiles. For example, the magnets may include triangular, circular, trapezoidal, or other cross-sectional profiles. In an embodiment, the cross-sectional profiles of upward-poled magnets  310 , longitudinally-poled magnets  312 , or downward-poled magnets are complementary. That is, the cross-sectional profiles may mesh to form an overall rectangular profile having a flat upper and lower surface. By way of example, the magnets may have triangular cross-sections, and each sequential magnet may be rotated 180° relative to adjacent magnets such that a magnet having a triangle vertex pointing upward is flanked by magnets having triangle vertices pointing downward. Accordingly, the profiles may mesh together to form an overall rectangular cross-sectional profile of the sequence of magnets. 
     Although the Halbach arrays described herein are depicted as having a direction of magnetization between adjacent elements rotated by 90 degrees, there is no such 90 degree limitation. The magnetic field direction may, however, rotate monotonically through a span of each array. As an example, Halbach array  302  in  FIG. 3A  could be equivalently created by an array of five elements with each field direction vector changing by 45 degrees. That is, the sequence of magnets of Halbach array  302  may have field direction vectors oriented in −90, −45, 0, 45, and 90 degrees directions. This configuration may be compared to the sequence of magnets having three elements with each field direction vector changing by 90 degrees, e.g., vectors oriented in −90, 0, and 90 degrees directions. In fact, the Halbach array  302  could be made with any number of magnetic segments of three or more, depending on a method used to create the array and the degree of resolution practically achievable to create the rotating magnetic field. By way of example, at a limit, Halbach array  302  may be composed of a single monolithic magnet structure having magnetized regions created by imparting a smoothly changing series of magnetic direction vectors without any discernable discrete magnetic direction changes within the length of the array. That is, the field direction vector may change continuously along the length of the array. 
     Upper magnetic Halbach array  304  may be separated from lower magnetic Halbach array  306  by a magnetic gap  308 . In an embodiment, the paired magnetic Halbach arrays  302  are aligned such that magnetic flux is directed across magnetic gap  308  orthogonal to a surface of the Halbach array  302  facing magnetic gap  308 . More particularly, upward-poled magnets  310  of upper Halbach array  304  and lower Halbach array  306  may be aligned along a first vertical axis  316  to direct magnetic flux upward along first vertical axis  316  through magnetic gap  308 . Similarly, the downward-poled magnets  314  may be aligned along a second vertical axis  318  to direct magnetic flux downward along second vertical axis  318  through magnetic gap  308 . Accordingly, the magnetic flux in a basic cell of the paired Halbach arrays  302  may follow a substantially rectangular path having a first side extending through magnetic gap  308  between upward-poled magnets  310 , a second side extending through longitudinally-poled magnet  312  between upward-poled magnet  310  and downward-poled magnet  314  of upper Halbach array  304 , a third side extending through magnetic gap  308  between downward-poled magnets  314 , and a fourth side extending through longitudinally-poled magnet  312  between downward-poled magnet  314  and upward-poled magnet  310  of lower Halbach array  306 . Longitudinally-poled magnet  312  may therefore direct flux between upward-poled magnet  310  and downward-poled magnet  314 . Accordingly, longitudinally-poled magnets  312  may have a shielding effect to contain flux rather than losing that energy to a surrounding environment. 
     Magnetic flux of the pair of Halbach arrays  302  may interact with a voicecoil  320  of electromagnetic transducer  206 . Voicecoil  320  may include a planar winding  322  disposed within magnetic gap  308 . Planar winding  322  may be printed on, or otherwise adhered to, a surface of a substrate  325 . For example, substrate  325  may include a flat polymer film having upper and lower surfaces facing upper Halbach array  304  and lower Halbach array  306 , respectively. Accordingly, magnetic flux passing through magnetic gap  308  may also pass through voicecoil  320  orthogonal to the upper and lower surfaces of substrate  325 . 
     The magnetic flux may pass through planar winding  322  of voicecoil  320 . Planar winding  322  may include a first transverse conductor  324  in magnetic gap  308  between upward-poled magnets  310  of the pair of Halbach arrays  302 . First transverse conductor  324  may conduct electrical current in a first transverse direction, e.g., leftward, along a first transverse axis  326 . First transverse axis  326  may be orthogonal to first vertical axis  316 , and thus, the electrical current in first transverse conductor  324  may pass orthogonally to the magnetic flux crossing magnetic gap  308  between upward-poled magnets  310 . Similarly, planar winding  322  may include a second transverse conductor  327  in magnetic gap  308  between downward-poled magnets  314  of the pair of Halbach arrays  302 . Second transverse conductor  327  may conduct electrical current in a second transverse direction, e.g., rightward, along a second transverse axis  328 . Second transverse axis  328  may be orthogonal to second vertical axis  318 , and thus, the electrical current in second transverse conductor  327  may pass orthogonally to the magnetic flux crossing magnetic gap  308  between downward-poled magnets  314 . Accordingly, the electrical current running through planar winding  322  may intersect the magnetic flux extending between pairs of identically-poled magnets of the pair of Halbach arrays  302 . 
     In an embodiment, the interaction of the electrical current and the magnetic flux causes a Lorentz force ( FIG. 4 ) to act on planar winding  322  in a direction along a longitudinal axis  330 . Longitudinal axis  330  may be orthogonal to both vertical axes, i.e., first vertical axis  316  and second vertical axis  318 , and longitudinal axis  330  may be orthogonal to both transverse axes, i.e., first transverse axis  326  and second transverse axis  328 . The force exerted on planar winding  322  can be transmitted to substrate  325 , and thus, the Lorentz force may act on and move voicecoil  320  axially along longitudinal axis  330 . 
     In an embodiment, voicecoil  320  may be held stationary and a surrounding structure may move relative to voicecoil  320 . For example, Halbach array  302  may move relative to voicecoil  320 . More particularly, voicecoil  320  may be fixed relative to a surrounding environment, and the magnets of Halbach array  302  may be suspended to allow the magnets to vibrate, i.e., oscillate relative to the magnets. In addition to altering which of voicecoil  320  or Halbach array  302  structure is fixed, sizing of the components may also be selected based on an intended application. For example, when electromagnetic transducer  206  is a vibration device, a relative size of Halbach array  302  compared to voicecoil  320  may be different than the relative size when electromagnetic transducer  206  is a speaker. More particularly, when electromagnetic transducer  206  is a vibration device, voicecoil  320  may incorporate a more massive coil and Halbach array  302  may incorporate smaller magnets to reduce a moving mass, as required by design targets of the particular application. 
     Electromagnetic transducer  206  may include an oscillational mass  332  physically connected to voicecoil  320 . For example, a piston  334 , e.g., an elongated rod having a first end connected to substrate  325  and a second end connected to oscillational mass  332 , may couple voicecoil  320  to oscillational mass  332 . When the interaction between the electrical current in planar winding  322  and the magnetic flux of the pair of Halbach arrays  302  drives voicecoil  320  along longitudinal axis  330 , the Lorentz force may also drive oscillational mass  332  in a longitudinal direction along longitudinal axis  330 . Oscillational mass  332  has an inertia, and thus, when oscillational mass  332  is driven back-and-forth along longitudinal axis  330  a vibratory effect may be transmitted to electronic device  100  housing electromagnetic transducer  206 . Accordingly, electromagnetic transducer  206  may be used as a haptic feedback mechanism of electronic device  100  to transmit vibration to a user. 
     Referring to  FIG. 4 , a sectional view of an electromagnetic transducer is shown in accordance with an embodiment. Planar winding  322  between the paired Halbach arrays  302  may include transverse conductors formed from several winding segments. In an embodiment, first transverse conductor  324  includes several transverse winding segments  402 . Transverse winding segments  402  may extend into the page along first transverse axis  326 . Transverse winding segments  402  may carry electrical current orthogonal to both upward magnetic flux and longitudinal axis  330 . Accordingly, a Lorentz force  403  may be generated to move voicecoil  320  in a longitudinal direction  404  along longitudinal axis  330 . 
     The Lorentz force driving voicecoil  320  along longitudinal axis  330  depends on the interaction between the magnetic flux passing vertically through magnetic gap  308  and the electrical current passing transversely through magnetic gap  308 . In an embodiment, when voicecoil  320  is in a non-energized position as shown in  FIG. 4 , transverse winding segments  402  may be vertically aligned with the vertically-poled magnets. Furthermore, transverse winding segments  402  may be sized to continuously interact with the magnetic flux when voicecoil  320  oscillates back-and-forth in longitudinal direction  404 . For example, first transverse conductor  324  may have a conductor width  406  measured across transverse winding segments  402  in longitudinal direction  404 . Similarly, each magnet of Halbach array  302  may have a magnet width measured in longitudinal direction  404 . In an embodiment, magnet width  408  of the vertically-poled magnets aligned with first transverse conductor  324  may be similar to conductor width  406  of transverse winding segments  402  of first transverse conductor  324 . For example, conductor width  406  may be equal to magnet width  408 . 
     Referring to  FIG. 5 , a sectional view of an electromagnetic transducer having an overhung voicecoil is shown in accordance with an embodiment. Voicecoil  320  may be considered as being overhung when conductor width  406  of first transverse conductor  324  is greater than magnet width  408  of the vertically-poled magnets aligned with first transverse conductor  324 . In such case, when voicecoil  320  oscillates along longitudinal axis  330 , at least some transverse winding segments  402  may remain within the path of magnetic flux crossing through magnetic gap  308  when voicecoil  320  reaches a maximum excursion in the longitudinal direction  404  along longitudinal axis  330 . By way of example, the maximum excursion may be 1.4 mm in the longitudinal direction  404  from the at rest, centered location. The motor excursion may be estimated geometrically. For example, the overhang between voicecoil  320  and vertically-poled magnets  310 ,  314  may be calculated, and the calculated dimension may be multiplied by a factor of 1.15 to account for a 15% fringe flux. By way of example, when conductor width  406  is 3.2 mm and vertical magnet width is 0.8 mm, a predicted excursion capability is calculated as: ((3.2 mm−0.8 mm)/2 mm)*1.15=1.4 mm. 
     Referring to  FIG. 6 , a sectional view of an electromagnetic transducer having an underhung voicecoil is shown in accordance with an embodiment. Voicecoil  320  may be considered as being underhung when conductor width  406  of first transverse conductor  324  is less than magnet width  408  of the vertically-poled magnets aligned with first transverse conductor  324 . In such case, when voicecoil  320  oscillates along longitudinal axis  330 , at least some transverse winding segments  402  may remain within the path of magnetic flux crossing through magnetic gap  308  when voicecoil  320  reaches a maximum excursion in the longitudinal direction  404 . 
     Electromagnetic interactions between magnets and conductors of electromagnetic transducer  206  can be controlled by adjusting the widths of the magnets and conductors, as described above. Similarly, electromagnetic interactions may depend on relative lengths of the magnets and conductors in a transverse direction. The concepts of overhung and underhung coils, as well as design rules for calculating the relative lengths of a conductor width and a gap width, apply in a similar fashion to traditional voicecoil motor design. For example, the vertically-poled magnets  310 ,  314  of electromagnetic transducer  206  are analogous to a thickness of a top plate in traditional voicecoil motor design, and conductor width  406  is analogous to a voicecoil winding height in traditional voicecoil motor design. Thus, following the above example, a traditional voicecoil motor design may include a top plate thickness of 0.8 mm, corresponding to a width of vertical magnets  310 ,  314 , and the traditional voicecoil motor design may include a voicecoil winding height of 3.2 mm, corresponding to conductor width  406 . 
     Referring to  FIG. 7 , a top view of a voicecoil over a magnetic Halbach array is shown in accordance with an embodiment. A transverse length of the pair of magnetic Halbach arrays  302  may be greater than a length of transverse winding segments  402 . The ends of upward-poled magnet  310  and downward-poled magnet  314  may extend beyond the ends of planar winding  322 . Accordingly, longitudinal winding segments  702  of planar winding  322  may extend parallel to the magnetic flux in longitudinally-poled magnet  312  within magnetic gap  308 . It will be appreciated that, insofar as longitudinal winding segments  702  carry electrical current parallel to magnetic flux carried by longitudinally-poled magnet  312 , no appreciable Lorentz force is generated within the region of the motor assembly between the vertically-poled magnets. 
     Referring to  FIG. 8 , a top view of a voicecoil over a magnetic Halbach array is shown in accordance with an embodiment. The transverse length of the pair of magnetic Halbach arrays  302  may be less than a length of transverse winding segments  402 . The ends of planar winding  322  may extend beyond the ends of upward-poled magnet  310  and downward-poled magnet  314 . Accordingly, longitudinal winding segments  702  may extend outside of magnetic gap  308 . It will be appreciated that, insofar as the electrical current in longitudinal winding segments  702  is parallel to the magnetic flux in longitudinally-poled magnets, longitudinal winding segments  702  may not contribute significantly to Lorentz force  403 . Thus, electromagnetic transducer  206  may utilize the configuration shown in either of  FIG. 7  or  FIG. 8 , depending upon factors such as space constraints within mobile device, and the configuration may provide a functional transducer. 
     Referring to  FIG. 9 , a top view of a planar winding of a voicecoil having conformal winding lengths is shown in accordance with an embodiment. Planar winding  322  may include several conformal winding lengths  902  traversing curvilinear and/or serpentine paths. Each conformal winding length  902  may be nested with an adjacent conformal winding length  902  such that several winding segments combine to form a conductor. For example, each conformal winding length  902  may include one of the transverse winding segments  402 , and the combined transverse winding segments  402  may form first transverse conductor  324 . Conformal winding lengths  902  may carry electrical current in the same direction, as shown by the arrows in  FIG. 9 , such that the conformal winding lengths  902  interact identically with the magnetic flux in magnetic gap  308 . The electrical current may be delivered to planar winding  322  through a pair of terminals  904 . 
     Referring to  FIG. 10 , a top view of a planar winding of a voicecoil having coiled winding lengths is shown in accordance with an embodiment. Planar winding  322  may include several coiled winding lengths  1002  traversing looped paths. Each coiled winding length  1002  may be nested with an adjacent coiled winding length  1002  such that several winding segments combine to form a conductor. For example, each coiled winding length  1002  may include one of the transverse winding segments  402 , and the combined transverse winding segments  402  may form first transverse conductor  324 . Coiled winding lengths  1002  may carry electrical current in the same direction, as shown by the arrows in  FIG. 10 , such that the coiled winding lengths  1002  interact identically with the magnetic flux in magnetic gap  308 . The electrical current may be delivered to planar winding  322  through terminals  904 . 
     The winding lengths (conformal or coiled) may be disposed adjacent to one another along a transverse plane, as shown in  FIGS. 9-10 . Alternatively, the winding lengths may be stacked upon each other, such that adjacent winding lengths are aligned along vertical planes (not shown). For example, a first conformal winding length  902  may be stacked above a second conformal winding length  902 . The first conformal winding length  902  may be on a top surface of substrate  325 , and the second conformal winding length  902  may be on a bottom surface of substrate  325 . An electrical connection between the vertically stacked conformal winding lengths  902  may be provided by an electrical interconnect, such as a via, extending vertically through substrate  325  from the first conformal winding length  902  to the second conformal winding length  902 . 
     Electrical interconnections between layers of windings may be structures to maximize motor performance. For example, the structure of electrical interconnections may minimize electrical resistance. In an embodiment, electrical resistance may be decreased by reducing an overall quantity of interconnections and/or by increasing a cross-sectional area of each interconnection. Furthermore, winding patterns and layout may be chosen such that a density of conductors in the area of highest magnetic field, e.g., an amount of conductors in the area, is maximized. The density may be increased by using a minimum amount of non-conductive material between each winding segment  402  ( FIG. 5 ). For example, by using winding segments  402  having rectangular cross-sections, rather than circular cross-sections segments as shown throughout the figures, conductive material in the area may be increased. Accordingly, it will be appreciated that circular winding cross-sections are illustrated for simplicity, but the illustrated shapes are not intended to be limiting. 
     The conductor packing factor of vertically-stacked windings may also be maximized by choosing winding layouts to maximize a ratio of a material of active conductors  322 ,  402  to a material of inactive conductor  702  ( FIG. 8 ). The ratio may be maximized, for example, by incorporating an even number of stacked layers, e.g., two or four layers. 
     Conductor material may be selected from materials known to those skilled in the art. For example, conductors may be formed from copper, aluminum, silver, or alloys of these or other materials. Copper is generally chosen when higher motor strength is desired, although the increased motor strength may come at the expense of higher moving mass. An increase in mass, however, may be desirable in some applications, e.g., a wide bandwidth speaker device in a small back volume. Aluminum based alloys may have a higher conductivity to mass ratio, as compared to copper, and thus aluminum may be chosen for having a higher efficiency in some applications. For example, aluminum conductors may be desirable in devices which are intended primarily for high frequency use, such as tweeters. 
     Referring to  FIG. 11 , a sectional view of an electromagnetic transducer is shown in accordance with an embodiment. A basic cell  1102  of the paired Halbach array  302  can be scaled up to form an electromagnetic transducer  206  of any size. More particularly, additional longitudinally-poled magnets and vertically-poled magnets may be sequentially according to the 90° pole shifting scheme, as described above. Furthermore, voicecoil  320  may include additional conductors  1104  adjacent to first transverse conductor  324  and second transverse conductor  327  to grow the motor assembly of electromagnetic transducer  206  in the longitudinal direction  404 . 
     Referring to  FIG. 12 , a top view of a voicecoil over a magnetic Halbach array is shown in accordance with an embodiment. In an embodiment, the scaled up motor assembly shown in  FIG. 11  includes planar winding  322  having conformal winding length  902  traversing a serpentine path between the pair of Halbach arrays  302 . Each transverse winding segment  402  of conformal winding length  902  may extend orthogonally to a direction of magnetic flux in magnetic gap  308 . Adjacent transverse winding segments  402  may carry the electrical current in opposite directions, and adjacent vertically-poled magnets may direct magnetic flux in opposite directions, such that Lorentz force  403  applied to voicecoil  320  is in a same longitudinal direction  404 . In an embodiment, adjacent transverse winding segments  402  are interconnected by longitudinal winding segments  702 . Transverse winding segments  402  may be longer than a transverse length of the magnets, and accordingly, longitudinal winding segments  702  may extend parallel to ends of the pair of Halbach arrays  302  outside of magnetic gap  308 . 
     Referring to  FIG. 13 , a top view of a voicecoil over a magnetic Halbach array having end magnets is shown in accordance with an embodiment. In an embodiment, the scaled up motor assembly shown in  FIG. 11  includes planar winding  322  having coiled winding length  1002  traversing a looped path between the pair of Halbach arrays  302 . Each transverse winding segment  402  of coiled winding length  1002  may extend orthogonally to a direction of magnetic flux in magnetic gap  308 . Adjacent transverse winding segments  402  may carry the electrical current in opposite directions, and adjacent vertically-poled magnets may direct magnetic flux in opposite directions, such that Lorentz force  403  applied to voicecoil  320  is in a same longitudinal direction  404 . In an embodiment, adjacent transverse winding segments  402  are interconnected by longitudinal winding segments  702 . Longitudinal winding segments  702  may carry the electrical current in opposite directions as required by the respective loop structures of coiled winding length  1002 . 
     In an embodiment, the pair of magnetic Halbach arrays  302  incorporate end magnets  1302  to allow all lengths of planar winding  322  to be useful. For example, each magnetic Halbach array  302  may include an end magnet  1302  extending in longitudinal direction  404  between a respective upward-poled magnet  310  and downward-poled magnet  314 . Each end magnet  1302  may be poled in a vertical direction, i.e., upward or downward. Accordingly, the poling of each end magnet  1302  may be in a direction orthogonal to a direction that electrical current is carried through longitudinal winding segments  702 . As such, the electrical current in longitudinal winding segments  702  of planar winding  322  within magnetic gap  308  between end magnets  1302  may interact with the magnetic flux in end magnets  1302  to produce a respective Lorentz force. The Lorentz force generated by end magnets  1302  may be in a transverse direction, e.g., leftward or rightward. Accordingly, the force applied to the voicecoil  320  by end magnets  1302  may be in a different direction than the force applied to voicecoil  320  by the longitudinally extending magnets. Therefore, a net force may be applied to voicecoil  320  in an oblique direction based on a sum of the longitudinal and transverse forces. The oblique forces may nonetheless generate vibration of a haptic feedback mechanism in mobile electronic device  100 . 
     Magnetic Halbach arrays  302  having variously poled regions may be fabricated using different techniques. In an embodiment, vertically-poled magnets of the Halbach array  302  are poled using impulse magnetization. For example, a miniature impulse magnetizer can magnetize a surface of Halbach array  302  to form the various vertically-poled regions, including end magnets  1302 . Impulse magnetization may be incapable of forming longitudinally-poled regions of Halbach array  302 , and thus, those regions may be formed by first removing material from the vertically-poled magnet, and then inserting bar magnets having the longitudinally-poled orientation into the holes. The inserts may be fixed in place, e.g., by an adhesive, to fabricate a sheet of magnetic material having differently poled regions. 
     Halbach arrays  302  may include structures to channel magnetic flux. For example, a backer material, e.g., a thin sheet of steel, may be mounted on one or both of the Halbach arrays  302  opposite of magnetic gap  308 . Accordingly, magnetic flux directed through magnetic gap  308  into a vertically-poled Halbach array  302  may be channeled through both longitudinally-poled magnet and the backer material into an adjacent vertically-poled magnet. Similarly, steel plates may be mounted at the ends of Halbach arrays  302  to direct magnetic flux vertically between leftmost and/or rightmost vertically-poled magnets of Halbach array  302 . That is, the steel plates at the end of the Halbach arrays  302  may act as magnetic flux returns structures to constrain magnetic flux within the paired Halbach arrays  302  rather than losing the magnetic flux to a surrounding environment. Magnetically, the ferromagnetic backer may affect the motor strength insubstantially in certain embodiments, due to a self-shielding nature of Halbach array  302 . It may nonetheless be desirable to use a ferromagnetic backer for structural purposes. For example, a backer plate may facilitate mechanical assembly of electromagnetic transducer  206  by providing an attachment surface to make fixturing, transferring, etc., easier to perform. 
     Although mainly described with respect to incorporation in a haptic feedback mechanism above, electromagnetic transducer  206  may be an electroacoustic transducer  208 . More particularly, voicecoil  320  and paired magnetic Halbach arrays  302  described above may form a motor assembly of an audio speaker, e.g., microspeaker  102 . 
     Referring to  FIG. 14 , a sectional view of an electroacoustic transducer is shown in accordance with an embodiment. Electroacoustic transducer  208  may include a speaker housing  1404  containing speaker components. The speaker components may include a motor assembly having voicecoil  320  and paired Halbach arrays  302 . In an embodiment, oscillational mass  332  includes a speaker diaphragm  1406 . Accordingly, the motor assembly may drive diaphragm  1406  back-and-forth along longitudinal axis  330  to generate sound. 
     It will be appreciated that the motor assembly of electroacoustic transducer  208  may be similar or identical to the motor assembly described above with respect to electromagnetic transducer  206 . More particularly, the motor construction described above with respect to electromagnetic transducer  206  has application in areas beyond haptic feedback mechanisms such as trackpad feedback, and may be applied in areas such as vibration motors and loudspeaker applications. Accordingly, in the interest of brevity, the motor assembly will not be described again here. In the case of electroacoustic transducer  208 , however, a transducer may include additional components related to the generation of sound. For example, piston  334  may connect voicecoil  320  to diaphragm  1406  to drive diaphragm  1406  and generate sound. Electroacoustic transducer  208  may also have one or more constraint mechanism  1400  to constrain diaphragm  1406  along longitudinal axis  330 . More particularly, diaphragm  1406  may be driven axially along longitudinal axis  330  orthogonal to the vertical axes of the pair of Halbach arrays  302  and the transverse axes of the various conductors of voicecoil  320 . Piston  334  may have an elongated section, e.g., a rod-like section, extending through a slot or a hole in a constraint mechanism  1400 . The hole may be sized to receive piston  334  in a sliding relationship, and the constraint mechanism  1400  may acts as a bearing such that piston  334  may move along longitudinal axis  330  to drive diaphragm  1406  in longitudinal direction  404 . Constraint mechanism  1400  may, however, restrict movement of diaphragm  1406  in a vertical or transverse direction orthogonal to longitudinal axis  330 . That is, constraint mechanism  1400  may constrain oscillational mass  332  to move axially along longitudinal axis  330  such that sound is emitted in longitudinal direction  404 . 
     In an embodiment, movement of diaphragm  1406  is constrained by a speaker surround  1408 . For example, surround  1408  may connect the diaphragm  1406  to speaker housing  1404 , and surround  1408  may flex to allow movement along longitudinal axis  330  and to restrict movement in a transverse directions orthogonal to longitudinal axis  330 . Surround  1408  may also provide an acoustic seal separating air on a rear side of diaphragm  1406  from air on a front side of diaphragm  1406 . Accordingly, the motor assembly may generate a Lorentz force to drive piston  334  and diaphragm  1406  back-and-forth in longitudinal direction  404  such that sound is generated and emitted by electroacoustic transducer  208   
     Referring to  FIG. 15 , a sectional view of an electroacoustic transducer is shown in accordance with an embodiment. Electroacoustic transducer  208  may incorporate voicecoil  320  driven parallel to magnetic gap  308  between Halbach arrays  302 . Magnetic gap  308  of electroacoustic transducer  208  having paired Halbach arrays  302  may be less than a magnetic gap required to drive voicecoil  320  in a direction transverse to longitudinal axis  330 . More particularly, since voicecoil  320  need only slide back-and-forth within magnetic gap  308 , and is not required to flex up and down in a direction orthogonal to the Halbach arrays  302 , a vertical width of magnetic gap  308  may be reduced. The vertical width may be a dimension only slightly larger than the vertical thickness of voicecoil  320 . By way of example, an overall thickness of electroacoustic transducer  208 , including the pair of magnetic Halbach arrays  302  and voicecoil  320 , may be less than 0.2 mm. 
     In an embodiment, a ferrofluid  1502  may be disposed within magnetic gap  308  between voicecoil  320  and the pair of magnetic Halbach arrays  302 . Ferrofluid  1502  is a colloidal liquid made of nanoscale ferromagnetic, or ferromagnetic particles, suspended in a carrier fluid such as an organic solvent or water. Ferrofluid  1502  may act as a bearing to reduce friction and facilitate movement of voicecoil  320  in longitudinal direction  404 . Furthermore, ferrofluid  1502  may act as a heat sink material to dissipate heat generated by the movement of voicecoil  320 . Ferrofluid  1502  is drawn to an area of highest magnetic field, and thus, it may be held in place by magnetic forces of Halbach arrays  302 . Accordingly, ferrofluid  1502  may provide a fluid bearing that is resistant to undesirable motion of voicecoil  320 , and may maintain voicecoil  320  in a centered position within magnetic gap  308 . 
     Referring to  FIG. 16 , a sectional view of an electroacoustic transducer is shown in accordance with an embodiment. Electromagnetic transducer  206  and/or electroacoustic transducer  208  may include a second diaphragm  1602  coupled to voicecoil  320  on an opposite side of magnetic Halbach arrays  302  than diaphragm  1406 . For example, diaphragm  1406  may face longitudinal direction  404 , and second diaphragm  1602  may face a second longitudinal direction  1604  opposite of longitudinal direction  404 . Longitudinal direction  404  and second longitudinal direction  1604  may both be along longitudinal axis  330 , and thus, Lorentz force  403  may drive both diaphragm  1406  and second diaphragm  1602  back-and-forth along longitudinal axis  330  in longitudinal direction  404  and second longitudinal direction  1604 . 
     Diaphragm  1406  and second diaphragm  1602  may be supported relative to magnetic Halbach arrays  302  by respective suspensions. The suspensions may constrain movement of the diaphragms  1406  along longitudinal axis  330  such that oscillations of voicecoil  320  within magnetic gap  308  cause the diaphragm to emit sounds in one or more of longitudinal direction  404  or second longitudinal direction  1604 . That is, sound may be emitted from both sides of electroacoustic transducer  208 . 
     In an embodiment, electroacoustic transducer  208  having diaphragm  1406  and second diaphragm  1602  emits sound in a single direction. For example, second diaphragm  1602  may include one or more perforation  1606 . The perforated end of electroacoustic transducer  208 , i.e., the perforated second diaphragm  1602 , may allow sound to pass between the surrounding environment and the magnetic gap  308 . Thus, second diaphragm  1602  may not generate sound. Nonetheless, second diaphragm  1602  and the surround  1408  supporting second diaphragm  1602  may act to constrain movement of voicecoil  320 . Accordingly, sound generated by diaphragm  1406  may be influenced at least in part by the presence of a perforated second diaphragm  1602 . 
     Referring to  FIG. 17 , a sectional view of an electroacoustic transducer is shown in accordance with an embodiment. In an embodiment, electroacoustic transducer  208  includes voicecoil  320  to move diaphragm  1406  in longitudinal direction  404 , as described above. Electroacoustic transducer  208  may also include a second voicecoil  1702  to move second diaphragm  1602  in second longitudinal direction  1604 . More particularly, second voicecoil  1702  may move independently from voicecoil  320  within magnetic gap  308 . Second voicecoil  1702  may include a second planar winding  1704  mounted on a second substrate within magnetic gap  308 . The interaction between second planar winding  1704  and magnetic Halbach arrays  302  may be such that a second Lorentz force is generated to drive second voicecoil  1702  in second longitudinal direction  1604  opposite to longitudinal direction  404 . For example, second planar windings  1704  may carry electrical current in an opposite direction as compared to planar winding  322  of voicecoil  320 . Second voicecoil  1702  may be coupled to second diaphragm  1602 , and thus, the second Lorentz force  403  may drive second diaphragm  1602  and second longitudinal direction  1604 . 
     Referring to  FIG. 18 , a sectional view of an electroacoustic transducer is shown in accordance with an embodiment. Electroacoustic transducer  208  may include several voicecoils occupying a same vertical space within magnetic gap  308 . More particularly, second voicecoil  1702  may be disposed within magnetic gap  308  between voicecoil  320  and lower magnetic Halbach array  306 . Each voicecoil  320  may include respective planar windings  322  carrying an electrical current in opposite directions from one another such that the voicecoils  320  interact with a same magnetic flux differently. That is, the magnetic flux passing through voicecoil  320  along a vertical axis may generate a Lorentz force  403  that drives voicecoil  320  in longitudinal direction  404 , and the same magnetic flux may pass through second voicecoil  1702  along the vertical axis to generate a second Lorentz force that drives second voicecoil  1702  in second longitudinal direction  1604 . Thus, electroacoustic transducer  208  may include independent voicecoils  320  configured to move in opposite directions within the same magnetic field. 
     In an embodiment, the independently moving voicecoils  320  suspended in magnetic gap  308  may support several diaphragms  1406 . For example, diaphragm  1406  may extend between voicecoil  320  and second voicecoil  1702  at a first longitudinal location, and a second diaphragm  1602  may extend between voicecoil  320  and second voicecoil  1702  at a second longitudinal location. Diaphragm  1406  may therefore be longitudinally offset from second diaphragm  1602  such that an air volume  1802  is defined between the voicecoils  320 ,  1702  and the diaphragms  1406 ,  1602 . 
     Referring to  FIG. 19A-19B , detail views of an electroacoustic transducer is shown in accordance with an embodiment. Relative movement between voicecoil  320  and second voicecoil  1702  can actuate the diaphragms to cause a change in air volume  1802 . More particularly, air volume  1802  may change when voicecoils  320 ,  1702  are driven in longitudinal direction  404 . The voicecoils and diaphragms defining air volume  1802  may have a cross-sectional profile resembling a parallelogram. As the voicecoils move relative to each other, an angle of the sides of the parallelogram increases or decreases, causing air volume  1802  to expand or contract, respectively. Furthermore, as the parallelogram changes, air is expelled or drawn into air volume  1802 . Accordingly, the change in air volume  1802  can move air to generate sound. 
     Referring to  FIG. 20 , a sectional view of an electroacoustic transducer having independently driven acoustic cells is shown in accordance with an embodiment. A microspeaker may include one or more acoustic cells  2002 . An acoustic cell  2002  may be defined as one of the electroacoustic transducer units described above, having a motor assembly connected to a diaphragm  1406  to generate sound. Each acoustic cell  2002  may furthermore include the basic cell  1102  of electromagnetic transducer  206  having paired Halbach arrays  302 . In an embodiment, a micro speaker  102  includes several acoustic cells  2002  to independently generate sounds based on electrical audio signals  2004  received from processor(s)  202 . 
     In an embodiment, a micro speaker  102  includes several acoustic cells  2002  arranged sequentially within a housing. Each acoustic cell  2002  may include a respective voicecoil  320  between a respective pair of magnetic Halbach arrays  302 . As shown in  FIG. 20 , the voicecoils  320  may be driven in respective longitudinal directions, which may be into the page in the illustration. More particularly, the voicecoils  320  of the acoustic cells  2002  may receive independent electrical audio signals  2004  from processor  202  to generate respective Lorentz forces that move the voicecoils  320 . That is, the processor  202  may drive each acoustic cell  2002  with a different audio channel. The different audio channels can create phase relationships between the acoustic cells  2002  to control sound emitted by each cell. The respective movements may generate respective sounds having respective amplitudes and phases. For example, during a first time period and a second time period, a leftward and rightward acoustic cell  2002  may be driven with constant electrical audio signals  2004  such that sounds  2006  generated by those acoustic cells  2002  remains the same. By contrast, during the first time period a middle acoustic cell  2002  may be driven by an electrical audio signal  2004  to produce sound  2008  having a first amplitude and phase, and during the second time period the middle acoustic cell  2002  may be driven by a different electrical audio signal  2004  to produce sound  2010  having a second amplitude in phase (represented by a dotted line). The difference in phase relationships may allow for a net sound, i.e., a sum of the individual sounds generated by respective acoustic cells  2002 , to be directed. That is, altering the electrical audio signals  2004  can be used to change a perceived direction of sound emitted by the micro speaker  102 . Accordingly, the microspeaker may be useful in a beam forming application. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Metadata:
Filing Date: 20161222
Publication Date: 20180410
Grant Date: 20180410
Priority Date: 20161222
Inventors: SALVATTI ALEXANDER V.
Ilkorur Onur I.
VIEITES PABLO SEOANE
Assignee: APPLE INC
CPC Classifications: [{"code": "H04R2209/022", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R9/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R9/047", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R9/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R1/403", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/047", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R9/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2209/022", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/047", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R9/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2209/022", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/403", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 61801495