PATENT DOCUMENT

Publication Number: US-9681228-B2
Application Number: US-201514679807-A
Country: US
Kind Code: B2

Title: Capacitive position sensing for transducers

Abstract:
A micro speaker having a capacitive sensor to sense a motion of a speaker diaphragm, is disclosed. More particularly, embodiments of the micro speaker include a conductive surface of a diaphragm facing conductive surfaces of several capacitive plate sections across a gap. The diaphragm may be configured to emit sound forward away from a magnet of the micro speaker, and the capacitive plate sections may be supported on the magnet behind the diaphragm. In an embodiment, the gap provides an available travel for the diaphragm, which may be only a few millimeters. A sensing circuit may sense capacitances of the conductive surfaces to limit displacement of the diaphragm to within the available travel.

Claims:
What is claimed is: 
     
       1. A micro speaker, comprising:
 a diaphragm having a conductive surface; 
 a motor assembly coupled with the diaphragm, wherein the motor assembly includes a voicecoil and a plurality of magnetic stacks behind the diaphragm configured to move the diaphragm to emit sound forward away from the magnetic stacks, wherein the magnetic stacks are separated from each other by one or more vertical slots filled by a dielectric, and wherein each magnetic stack includes
 a magnet portion, and 
 a capacitive plate section mounted on the magnet portion, wherein each capacitive plate section includes a respective conductive surface facing the conductive surface of the diaphragm across a gap distance; and 
 
 a sensing circuit electrically connected with the capacitive plate section. 
 
     
     
       2. The micro speaker of  claim 1 , wherein the plurality of magnetic stacks include at least three capacitive plate sections electrically insulated from each other across the one or more vertical slots. 
     
     
       3. The micro speaker of  claim 2 , wherein the one or more vertical slots include a pair of intersecting vertical slots, and wherein the at least three capacitive plate sections includes capacitive plate quadrants separated by the pair of intersecting vertical slots. 
     
     
       4. The micro speaker of  claim 3 , wherein each magnetic stack includes an insulating layer between the capacitive plate section and the magnet portion. 
     
     
       5. The micro speaker of  claim 4 , wherein the dielectric includes an insulating filler. 
     
     
       6. The micro speaker of  claim 4  further comprising an electrical lead extending from a respective capacitive plate section to the sensing circuit, wherein the electrical lead electrically connects the respective capacitive plate section with the sensing circuit. 
     
     
       7. The micro speaker of  claim 6 , wherein the sensing circuit is configured to measure a capacitance of the facing conductive surfaces of the diaphragm and the respective capacitive plate section. 
     
     
       8. The micro speaker of  claim 7 , wherein the sensing circuit is configured to calculate displacement of the diaphragm based on the measured capacitance. 
     
     
       9. The micro speaker of  claim 4  further comprising a housing in front of the diaphragm, the housing including a port configured to pass the sound emitted by the diaphragm. 
     
     
       10. The micro speaker of  claim 4 , wherein the gap distance is less than 3 mm. 
     
     
       11. The micro speaker of  claim 10 , wherein the gap distance is less than 1 mm. 
     
     
       12. A method, comprising:
 sensing one or more electrical signals, each electrical signal corresponding to one or more capacitances of facing conductive surfaces of a diaphragm of a micro speaker and one or more capacitive plate sections of a plurality of magnetic stacks of the micro speaker, wherein the diaphragm is configured to emit sound forward away from the magnetic stacks of the micro speaker, wherein the magnetic stacks are behind the diaphragm, wherein each magnetic stack includes a magnet portion and a capacitive plate section, and wherein the magnetic stacks are separated from each other by one or more vertical slots filled by a dielectric; and 
 determining, based on the electrical signals, a relative spatial orientation between the diaphragm and the one or more capacitive plate sections. 
 
     
     
       13. The method of  claim 12 , wherein the one or more vertical slots include a pair of intersecting vertical slots, and wherein the one or more capacitive plate sections includes at least three capacitive plate sections. 
     
     
       14. The method of  claim 13 , wherein each capacitive plate section is supported on a respective magnet portion, and wherein the capacitive plate sections and magnet portions are electrically insulated from each other. 
     
     
       15. The method of  claim 14 , wherein a distance between the diaphragm and each of the one or more capacitive plate sections is less than 3 mm. 
     
     
       16. The method of  claim 15 , wherein the distance is less than 1 mm. 
     
     
       17. The method of  claim 16 , wherein determining the relative spatial orientation includes detecting respective distances between the diaphragm and one or more pairs of the one or more capacitive plate sections. 
     
     
       18. The method of  claim 17 , wherein determining the relative spatial orientation includes determining, based on the detected distances, whether the diaphragm is rocking relative to the one or more capacitive plate sections. 
     
     
       19. The method of  claim 18  further comprising:
 providing an electrical driving signal to a voicecoil of the micro speaker based on the detected distances to limit a displacement of the diaphragm within an available travel of the diaphragm.

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 62/057,743, filed Sep. 30, 2014, and this application hereby incorporates herein by reference that provisional patent application. 
    
    
     BACKGROUND 
     Field 
     Embodiments related to an audio speaker having a capacitive sensor to sense motion of a speaker diaphragm are disclosed. More particularly, an embodiment related to a micro speaker having a diaphragm that emits sound forward away from a motor assembly, is disclosed. 
     Background Information 
     An audio speaker driver converts an electrical audio input signal into an emitted sound. Audio speaker drivers typically include a diaphragm connected with a motor assembly, e.g., a voicecoil and a magnet. Thus, when the electrical audio input signal is input to the voicecoil, a mechanical force may be generated that moves the diaphragm to generate sound. Loudspeaker drivers may be divided into two broad classes—“direct radiators”, which couple the diaphragm to the air directly, and “compression drivers”, which use a “phase plug” as an impedance matching device to improve electroacoustical conversion efficiency. Micro speakers, also known as microdrivers, are typically considered a subclass of the direct radiator class, generally meaning a miniaturized implementation which is intended to operate over a broad frequency range with significant diaphragm excursion relative to the diaphragm size, as opposed to a tweeter, which is designed to cover primarily the highest audible frequencies, implying extremely small diaphragm excursion requirements relative to its size. Microdrivers may radiate sound in a forward (front firing) or sideways (side firing) configuration, depending on the particular design goals. A driver typically includes an available excursion space for the diaphragm, over which the diaphragm may move without crashing into other driver components. The available travel in micro speakers is typically on the same order of magnitude as compression drivers, which tends to be significantly smaller compared to typical larger direct radiator transducers. 
     SUMMARY 
     Audio speakers having a capacitive sensor to sense motion of a speaker diaphragm, particularly for use in portable consumer electronics device applications, are disclosed. In an embodiment, a micro speaker includes a diaphragm coupled with a motor assembly. The motor assembly may include a voicecoil and a magnet configured to move the diaphragm to emit sound forward and away from the magnet. Furthermore, the diaphragm may include a conductive surface facing the magnet and attached to the diaphragm. Several capacitive plate sections may be supported on the magnet. Thus, several variable capacitors may be formed between the diaphragm and the capacitive plate sections outside of the sound path. 
     In an embodiment, the micro speaker includes at least three capacitive plate sections behind the diaphragm. More particularly, the capacitive plate sections may be separated by one or more slot, which may be partly filled with an insulating filler or another dielectric. For example, four capacitive plate quadrants may be separated and/or electrically insulated from each other by a pair of intersecting slots that are air-filled. The capacitive plate sections may also be insulated from the magnet that supports them, e.g., by a thin insulating layer. In an embodiment, the slots extend through the capacitive plate sections, the insulating layer, and the magnet such that the magnet includes several magnet portions electrically insulated from each other by the pair of intersecting slots. Thus, the magnetic structure behind the diaphragm may be segmented, and each segment may support a different capacitive plate segment, which forms a portion of a variable capacitor. 
     In an embodiment, a sensing circuit may be electrically connected with each variable capacitor, and more particularly, with the capacitive plate sections. That is, electrical leads may extend from respective capacitive plate sections to electrically connect the capacitive plate sections with the sensing circuit. In an embodiment, pairs of the variable capacitors may be electrically in series through the diaphragm. Furthermore, the sensing circuit may connect with multiple groups of the serially connected variable capacitor pairs. Thus, the electrical leads may convey signals for the variable capacitor pairs to the sensing circuit. Those signals may correspond to capacitance of the variable capacitors. Thus, the sensing circuit may be configured to measure the capacitance and to calculate displacement and position of the diaphragm based on the signals. Monitoring diaphragm position in this way may avoid speaker damage or undesirable acoustic distortion, given that the micro speaker may include limited available travel for the diaphragm. For example, the diaphragm may be separated from the capacitive plate sections in a rearward direction by a small gap, e.g., less than 3 mm. 
     In an embodiment, the diaphragm may be controlled based on the monitored position. A relative spatial orientation between the diaphragm and the capacitive plate sections may be determined based on the calculated displacement of the diaphragm. More particularly, respective distances between the diaphragm and pairs of capacitive plate sections may be calculated to determine absolute position of the diaphragm in multiple axes. Based on the absolute position, the sensing circuit may detect whether the diaphragm is rocking relative to the magnetic structure. In an embodiment, an electrical driving signal is provided to the voicecoil of the micro speaker to drive the diaphragm to a desired position. For example, the diaphragm may be driven to the limit of the available travel of the diaphragm (without exceeding the limit) and/or may be driven to reduce or eliminate non-axial rocking motions. 
     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 an electronic device having a micro speaker in accordance with an embodiment. 
         FIG. 2  is a sectional view of a micro speaker in accordance with an embodiment. 
         FIG. 3  is a sectional view of a front-firing micro speaker having a capacitive sensor in accordance with an embodiment. 
         FIG. 4  is a cross-sectional view, taken about line A-A of  FIG. 3 , of serially arranged variable capacitors of a micro speaker in accordance with an embodiment. 
         FIGS. 5A-5C  are cross-sectional views, taken about line B-B of  FIG. 3  viewed in a rearward direction, of capacitive plate sections arranged in accordance with various embodiments. 
         FIG. 6  is a cross-sectional view, taken about line B-B of  FIG. 3  viewed in a forward direction, of conductive face sections of a diaphragm in accordance with an embodiment. 
         FIG. 7  is a sectional view of a side-firing micro speaker having a capacitive sensor in accordance with an embodiment. 
         FIG. 8  is a flowchart of a method to monitor and/or control a spatial orientation of a micro speaker diaphragm in accordance with an embodiment. 
         FIG. 9  is a schematic view of an electronic device having a micro speaker in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe micro speakers having a capacitive sensor to determine a motion of a speaker diaphragm, particularly for use in portable consumer electronics device applications. However, while some embodiments are described with specific regard to integration within mobile electronics devices such as handheld devices, the embodiments are not so limited and certain embodiments may also be applicable to other uses. For example, a micro speaker as described below may be incorporated into headphones. Furthermore, the micro speaker may be incorporated into systems that remain at a fixed location, e.g., an automated teller machine, or used in a relatively stationary application, e.g., as part of a car infotainment system. 
     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, “forward” may indicate a first axial direction away from a reference point. Similarly, “behind” 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 audio speaker to a specific configuration described in the various embodiments below. For example, a micro speaker 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, a micro speaker includes a series of variable capacitors to sense a position of a diaphragm that emits sound forward away from a motor assembly behind the diaphragm. In an embodiment, the variable capacitors include several electrically insulated capacitive plate sections behind the diaphragm, which have respective conductive surfaces facing a conductive surface on the diaphragm. Given that the variable capacitors share the conductive surface of the moving diaphragm, the variable capacitors may be electrically connected in series without requiring a direct electrical connection to the diaphragm. Furthermore, the variable capacitors behind the diaphragm remain out of the path of sound pressure waves. Thus, the serially arranged capacitive sensors may provide a mechanically stable option for sensing position of the diaphragm. 
     In an aspect, a micro speaker includes a series of variable capacitors electrically connected with a sensing circuit. The sensing circuit may be connected to the series of variable capacitors to detect the diaphragm position in real time. More particularly, the diaphragm position may be determined based on real time measurements of capacitances of the variable capacitors. Accordingly, the diaphragm position and/or displacement may be used for active control of the driver behavior. For example, displacement values may be calculated and used to drive the diaphragm within an available travel such that the excursion limits of the diaphragm are approached, but not exceeded. This may optimize acoustic performance and output of the micro speaker. 
     In an aspect, a micro speaker includes at least three variable capacitors electrically connected with a sensing circuit. For example, the variable capacitors may include four capacitive plate sections arranged in quadrants behind the diaphragm. Pairs of the quadrants may be electrically connected through a conductive portion of a speaker diaphragm to create serially arranged variable capacitors. Each quadrant may be supported by a magnet of a speaker motor assembly, and the magnet may be divided into several magnet portions to electrically insulate each capacitive plate section from an adjacent capacitive plate section and/or magnet portion. Accordingly, capacitance between the diaphragm and the capacitive plate quadrants may be sensed to determine diaphragm motion in multiple axes. That is, non-axial motion of the diaphragm, such as rocking modes, may be sensed by the sensing circuit by monitoring multiple pairs of capacitive plate quadrants located on the magnet. Furthermore, the electrical audio input signal may be adjusted to reduce or eliminate non-axial motion of the diaphragm. 
     Referring to  FIG. 1 , a pictorial view of an electronic device having a micro speaker is shown in accordance with an embodiment. Electronic device  100  may be a smartphone device. Alternatively, it could be any other portable or stationary device or apparatus incorporating an audio speaker, e.g., a micro speaker  106 , such as 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, an integrated microphone  102  may pick up the voice of its user during a call, and a micro speaker  106  may deliver a far-end voice to the near-end user during the call. The micro speaker  106  may also emit sounds associated with music files played by a music player application running on electronic device  100 . A display  104  may 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 . Other conventional features are not shown but may of course be included in electronic device  100 . 
     Referring to  FIG. 2 , a sectional view of a micro speaker is shown in accordance with an embodiment. A micro speaker  106  may include a housing  202  surrounding a diaphragm  204  and a motor assembly  206 . Motor assembly  206  may include a voicecoil  210  and a magnet  212 . More particularly, diaphragm  204  may be connected to housing  202  by a speaker surround  208  that allows diaphragm  204  to move axially with pistonic motion, i.e., forward and backward. Furthermore, diaphragm  204  may be connected to voicecoil  210  of motor assembly  206 , which moves relative to magnet  212  of motor assembly  206 . In an embodiment, magnet  212  is attached to a top plate  214  at a front face and to a yoke  216  at a back face. Magnet  212  may include a permanent magnet and both top plate  214  and yoke  216  may be formed from magnetic materials to create a magnetic circuit having a magnetic gap within which voicecoil  210  may oscillate forward and backward. Thus, when an electrical audio input signal is input to the voicecoil  210 , a mechanical force may be generated that moves diaphragm  204  to radiate sound forward through one or more ports  218  in housing  202 . 
     Micro speakers  106  are commonly incorporated in handheld devices, such as electronic device  100 , or other device applications having tight space requirements. Thus, an available travel distance of diaphragm  204  in micro speaker  106  may be limited. For example, diaphragm  204  may be separated from housing  202  on a front side and/or top plate  214  on a rear side by only a few millimeters or in some cases less than 1 mm of available travel. To prevent diaphragm  204  from contacting housing  202  or top plate  214  during use, the driver design may include dimensional tolerances that account for an expected frequency-dependent diaphragm displacement. However, given that frequency response can vary based on operating temperatures, material nonlinearities such as creep, acoustic loading, and/or aging of the driver, the dimensional tolerances may be difficult to predict accurately. This may result in underestimation of the dimensions, and can result in acoustic distortion or damage to diaphragm  204  if it crashes into an opposing surface. Alternatively, overestimation of the dimensions may result in wasted space, since diaphragm  204  may not fully utilize its available travel, which limits the amount of potential maximum acoustic output, the output being directly proportional to the volume displacement of air by diaphragm  204 . Therefore, performance of micro speaker  106  may be improved by incorporating sensors to monitor and control diaphragm displacement such that the available travel is fully utilized without crashing diaphragm  204  into an opposing surface. 
     Referring to  FIG. 3 , a sectional view of a front-firing micro speaker having a capacitive sensor is shown in accordance with an embodiment. Micro speaker  106  may enclose diaphragm  204  and motor assembly  206  such that sound emitted by diaphragm  204 , in response to the electrical audio signal input to voicecoil  210 , travels forward away from motor assembly  206  and/or magnet  212 , and through one or more ports  218  into a surrounding environment. As diaphragm  204  oscillates forward and backward to generate the sound, a back surface of diaphragm  204  may oscillate closer and farther from a front surface of magnet  212 . More particularly, in an embodiment, several capacitive plate sections  302  may be supported on magnet  212  behind diaphragm  204 , and thus, diaphragm  204  may oscillate closer and farther from the capacitive plate sections  302  during sound generation. 
     As discussed below, diaphragm  204  and each capacitive plate section  302  may incorporate a conductive material. For example, diaphragm  204  may include a conductive layer disposed over a front or back side, or embedded within the body of diaphragm  204 . Similarly, capacitive plate sections  302  may be formed wholly or partially from conductive material. For example, one or more capacitive plate section  302  may include a conductive layer disposed over a front side of magnet  212  or top plate  214 . Alternatively, the conductive layer may be embedded within the capacitive plate section  302 . For example, capacitive plate section  302  may include a capacitive plate or disc encapsulated or substantially surrounded by a layer of insulation, e.g., an insulated coating. Thus, each capacitive plate section  302  may include a conductive portion that pairs with a conductive portion of diaphragm  204  to essentially form a parallel-plate capacitor. That is, a capacitance may exist for each capacitive plate section  302  and diaphragm  204  pairing. Furthermore, given that the distance between diaphragm  204  and capacitive plate section  302  may vary with movement of diaphragm  204  during sound generation, the capacitances corresponding to each capacitive plate section  302  and diaphragm  204  pairing may also vary. Thus, each pairing may essentially form a variable capacitor. 
     Capacitance between each pair of conductive surfaces of diaphragm  204  and capacitive plate section  302  will be inversely proportional to the separation distance. Thus, a sensing circuit  304  may be electrically connected with one or more of the capacitive plate sections  302  by one or more electrical leads  306  to receive an electrical signal that may be used to measure capacitance. The measured capacitance may then be used to calculate a corresponding distance between diaphragm  204  and capacitive plate sections  302  based on the known relationship between the capacitance and the separation distance. Similarly, the measured capacitance may be used to determine displacement and motion of diaphragm  204 , as discussed below. 
     Referring to  FIG. 4 , a cross-sectional view, taken about line A-A of  FIG. 3 , of serially arranged variable capacitors of a micro speaker is shown in accordance with an embodiment. In an embodiment, diaphragm  204  is separated from several capacitive plate sections  302  by a gap  402  in an axial direction. The gap distance may be on the order of a few millimeters or less. More particularly, when diaphragm  204  is in a neutral position, such as when no electrical audio input signals are being delivered to voicecoil  210 , gap  402  may have an axial dimension of less than 5 mm, and in some cases less than 3 mm. For example, gap  402  may be an air-filled space between a rear conductive face  404  of diaphragm  204  and a front conductive surface  406  of capacitive plate section  302 , and the space may have an axial dimension of 1 mm or less. The gap distance may vary as diaphragm  204  moves pistonically during sound generation. However, a maximum gap distance may remain on the order of less than 5 mm when diaphragm  204  is at a maximum forward position. This small gap distance may allow for capacitive sensing to be feasible in the context of micro speaker applications, e.g., in the case of micro speaker  106 . 
     Conductive face  404  may be an outer surface of diaphragm  204  facing magnet  212  of motor assembly  206 . More particularly, conductive face  404  may be on outer surface of a lower layer  408  in a laminate structure that forms a portion of diaphragm  204 . Lower layer  408  may, for example, be formed from an electrically conductive material, such as an aluminum or copper film. The film may be deposited or otherwise layered over a core  410 . Core  410  may be a foam body that is lightweight and rigid, and serves as a substrate for lower layer  408 . In an embodiment, diaphragm  204  may also include an upper layer  412 . Upper layer  412  may be an aluminum film formed over core  410 . Thus, core  410  may be sandwiched between upper layer  412  and lower layer  408 , and in an embodiment, core  410  may be less rigid than at least one of lower layer  408  or upper layer  412 . As shown, in an embodiment, diaphragm  204  does not require circuitry such as electrical leads or integrated circuits to implement the capacitive sensing capability described below. Without the need for external connections or moving components on diaphragm  204 , the diaphragm  204  may be less susceptible to fatigue stress during sound generation, and mechanical stress and possible fatigue failure of the physical connection may be avoided, as compared to a case in which a connection is needed. Furthermore, the layers may be thin, e.g., on the order of 1 nanometer to 100 micron. Thus, diaphragm  204  may remain lightweight such that acoustic performance of diaphragm  204  is not degraded. 
     In an embodiment, a magnetic structure behind diaphragm  204  may also include a laminated structure. That is, the magnetic structure may include a stack that includes magnet  212  having one or more magnet portions  414  supporting other layers. Each magnet portion  414  may include a permanent magnet material, such as ceramic, ferrite, neodymium, samarium cobalt, etc. The permanent magnet material may be processed to form magnetic portions  414  having a desired geometry, e.g., cylindrical or cuboid shapes. Each magnet portion  414  may support top plate  214 . Top plate  214  may include a magnetic material, such as a ferritic steel alloy, and may provide a magnetic core to guide a magnetic field in the magnetic structure, creating a magnetic circuit. An insulating layer  418  may cover an upper surface of top plate  214 , to insulate capacitive plate section  302  from other stack layers. For example, insulating layer  418  may be an insulating material that electrically isolates capacitive plate section  302  from top plate  214  and/or magnet portion  414 . Accordingly, insulating layer  418  may include an epoxy, a polymer such as parylene, a foam, or any other suitable dielectric material. Capacitive plate section  302  may be stacked on insulating layer  418  with conductive surface  406  facing diaphragm  204  across gap  402 . 
     Capacitive plate sections  302  may be supported directly on top plate  214  or magnet portions  414 , i.e., the material of capacitive plate sections  302  may be directly in contact with either top plate  214  or magnet portions  414 . Alternatively, capacitive plate sections  302  may be supported directly on insulating layer  418 . More particularly, capacitive plate sections may be supported on an upper surface of the respective top plate  214 , magnet portion  414 , or insulating layer  418 , i.e., on a surface nearest diaphragm  204 . This contrasts, for example, with supporting the capacitive plate sections  302  on a side surface of top plate  214 , magnet portion  414 , or insulating layer  418 , i.e., on a surface parallel to a surface contour of voicecoil  210 . Supporting capacitive plate sections  302  on an upper surface, e.g., on a surface orthogonal to a direction of sound emission by diaphragm  204 , may provide for the surfaces of conductive face  404  and capacitive plate sections  302  to face each other. 
     The conductive surfaces of conductive face  404  and capacitive plate sections  302  may be considered to face each other when the surface contours are substantially parallel to one another. For example, conductive face  404  may be a lower surface of diaphragm  204  having a laminated construction, e.g., may be a lower surface of lower layer  408 . Thus, conductive face may extend along a plane that is substantially orthogonal to a central axis along which diaphragm oscillates during sound reproduction. Capacitive plate sections  302 , which may be supported on upper surfaces of an underlying magnet portion  414 , top plate  214 , or insulating layer  418 , may also represent a layer of a laminated structure, e.g., of a laminated magnetic structure. As such, conductive surfaces  406  of capacitive plate sections  302  may also span or extend along planes that are substantially orthogonal to the central axis. Accordingly, conductive face  404  and conductive surface  406  may be substantially parallel to each other, and thus, may be considered to face each other in an axial direction (along the central axis or the axis of sound propagation). Furthermore, the faces may be parallel even though lower layer  408  and capacitive plate sections  302  may not span flat planes. For example, in an embodiment, diaphragm  204  may include a conical or curved, e.g., parabolic, surface such that portions of diaphragm extend in varying, non-flat, directions. Accordingly, even though the entirety of conductive face  404  and conductive surface  406  may not be flat, the corresponding contours of the surfaces may nonetheless match. For example, at any location laterally offset from the central axis, the distance between conductive face  404  and conductive surface  406  may be the same. Thus, even though the surfaces may not be flat, the surfaces may nonetheless be considered to be parallel and to face each other. 
     The height of each layer in the segmented magnetic structure behind diaphragm  204  may be minimized to increase the available travel, and potentially the sound output, of diaphragm  204 . Given that the segmented magnetic structure remains stationary during use, i.e., the magnetic structure is not subject to flexing during sound generation, the layers may be made thin without degrading sound quality or leading to mechanical failure of micro speaker  106 . Accordingly, in an embodiment, the insulating layer  418  may be formed with a thickness of 5 microns or less, and in some cases less than 3 microns. For example, insulating layer  418  may have a thickness of 1 micron. Similarly, the capacitive plate sections  302  may have thicknesses similar to that of lower layer  408 . For example, capacitive plate section  302  may have a thickness between 1 nanometer to 100 micron. 
     In an embodiment, conductive surface  406  facing conductive face  404  may be a segmented surface. That is, there may be several capacitive plate sections  302 , and each section may have a separate conductive surface  406 . Each conductive surface  406  may be separated from another by a slot  420 . Slot  420  may be sized and configured to electrically isolate a conductive surface  406  of one capacitive plate section  302  from a conductive surface  406  of another capacitive plate section  302 . In an embodiment, slot  420  between capacitive plate sections  302  may be filled by a dielectric, such as air. The dielectric may include insulating filler  422 , which may be an epoxy, a polymer, or another suitable insulating material, to prevent electrical shorting between conductive surfaces of adjacent capacitive plate sections  302 . Thus, slot  420  may be partially filled by a combination of gas, liquid, or solid dielectric materials. 
     In an embodiment, the entire magnetic structure may be segmented to create individual stacks, including capacitive plate sections  302 , supported on respective magnet portions  414 . For example, slot  420  may extend axially through capacitive plate section  302 , insulating layer  418 , top plate  214 , and at least a portion of magnet  212  to create adjacent magnet portions  414 . In an embodiment, slot  420  extends fully through magnet  212  such that the magnet portions  414  are entirely isolated from each other across slot  420 . That is, the magnet portions  414 , as well as the layers supported on each magnet portion  414 , may be electrically insulated from each other by slot  420 . Furthermore, slot  420  may be at least partly filled by insulating filler  422 . For example, insulating filler  422  may fill slot  420  between magnet portions  414 , but not between the stack over magnet portions  414 , i.e., not between top plates  214 , insulating layers  418 , or capacitive plate sections  302 . Alternatively, insulating filler  422  may fill slot  420  such that magnet portions  414  and adjacent stacks of top plates  214 , insulating layers  418 , or capacitive plate sections  302  are separated across slot  420  by insulating filler  422 . 
     Each pairing of capacitive plate section  302  with diaphragm  204  forms an independent capacitive sensor, i.e., a two-plate variable capacitor, which may be sensed by sensing circuit  304 . For example, the pairing of diaphragm  204  with the left capacitive plate section  302  in  FIG. 4  may form a variable capacitor that is separate from a variable capacitor formed by diaphragm  204  and the right capacitive plate section  302  in the same illustration. Furthermore, given that the area of conductive face  404  on diaphragm  204  opposite the left capacitive plate section  302  is electrically connected with the area of conductive face  404  opposite the right capacitive plate section  302 , the two variable capacitors are electrically in series. That is, the electrical connection between conductive face  404  portions of the variable capacitors may be through a continuous sheet of electrically conductive lower layer  408 . In an alternative embodiment, lower layer  408  may be patterned to include multiple distinct conductive face  404  portions opposite the capacitive plate sections  302  and the patterned conductive faces  404  may be connected by electrical leads or traces running over core  410 . Patterning of the conductive face  404  portions and the electrical connections may be performed using known fabrication techniques, e.g., deposition techniques. 
     Electrical leads  306  may be connected to two of the capacitive plate sections  302  to sense a serially arranged pair of variable capacitors. For example, in an embodiment, the segmented capacitive plate includes two capacitive plate sections  302 , e.g., the left capacitive plate section  302  and the right capacitive plate section  302  in  FIG. 4 . Furthermore, the capacitive plate sections are electrically connected in series through the shared conductive face  404  of diaphragm  204 . An electrical lead  306  may be connected to the left capacitive plate section  302  to convey electrical signals between the left capacitive plate section  302  and sensing circuit  304 . Similarly, an electrical lead  306  may be connected to the right capacitive plate section  302  to convey electrical signals between the right capacitive plate section  302  and sensing circuit  304 . Accordingly, the electrical leads  306  may electrically connect the serially arranged variable capacitors with sensing circuit  304 . 
     Electrical leads  306  may extend from capacitive plate sections  302  to sensing circuit  304  in several manners. For example, an electrical lead  306  may extend from a front or side surface of capacitive plate section  302  to sensing circuit  304  through slot  420  formed between capacitive plate sections  302  and magnet portions  414 . Alternatively, an electrical lead  306  may extend from a rear surface of capacitive plate section  302  through a hole  424  formed in insulating layer  418 , top plate  214 , and/or magnet portion  414  to sensing circuit  304 . Slot  420  or hole  424  may be at least partly filled by a dielectric, such as insulating filler  422 , to insulate and/or stabilize the electrical leads  306  relative to the magnet portions  414 . Numerous other electrical lead  306  configurations for connecting capacitive plate sections  302  with sensing circuit  304  may be used. By way of example, vias may extend from capacitive plate sections  302  through magnet portions  414 . Alternatively, traces may run along a side surface of magnet portions  414  from capacitive plate sections  302 . Thus, several electrical connection schemes may be implemented within the scope of this description. Furthermore, the serially arranged variable capacitors may be electrically connected using the same or different connection schemes. 
     Referring to  FIG. 5A , a cross-sectional view, taken about line B-B of  FIG. 3  viewed in a rearward direction, of an arrangement of capacitive plate sections is shown in accordance with an embodiment. The segmented capacitive plate and/or magnet  212  may include more than two sections. For example, a circular capacitive plate may be split into three or more sectors by slot  420 . The sectors may be symmetric about a central point or axis at which several slot segments intersect. For example, as shown in  FIG. 5A , several slot segments may radiate from a central axis of the magnetic structure. Thus, each capacitive plate section  302  may include a circular sector having an angle between slot segments. The angle may be 120 degrees for each capacitive plate section  302 . In alternative embodiments, the circular sectors may not be symmetric, i.e., at least one of the circular sectors may include an arc along an outer edge that subtends an angle of more than, or less than, 120 degrees. 
     Referring to  FIG. 5B , a cross-sectional view, taken about line B-B of  FIG. 3  viewed in a rearward direction, of an arrangement of capacitive plate sections is shown in accordance with an embodiment. In an embodiment, the segmented capacitive plate and/or magnet  212  may include more than three sections. For example, the capacitive plate may be split into four or more sectors by slot  420 . The sectors may be arranged in a grid pattern. For example, slot  420  may include at least one horizontal slot segment and one vertical slot segment that intersect at a central point. Accordingly, the capacitive plate may be split into quadrants, e.g., capacitive plate quadrants  502 ,  504 ,  506 , and  508 . The quadrants may be arranged in a grid pattern. In an embodiment, additional horizontal and/or vertical slot segments may be added to create a grid having more than four capacitive plate sections  302 . 
     Referring to  FIG. 5C , a cross-sectional view, taken about line B-B of  FIG. 3  viewed in a rearward direction, of an arrangement of capacitive plate sections is shown in accordance with an embodiment. In an embodiment, the segmented capacitive plate and/or magnet  212  may include a central capacitive plate section  302  surrounded by two or more capacitive plate sections  302 . Furthermore, each capacitive plate section  302  may be separated from another by a slot  420  segment. For example, a central capacitive plate section  302 , e.g., a square capacitive plate section  302 , may be surrounded by a slot  420  segment to create a capacitive plate island  510 . Furthermore, two or more capacitive plate sections  302 , e.g., four capacitive plate quadrants  502 ,  504 ,  506 , and  508 , may be arranged symmetrically around the capacitive plate island  510  and divided by a horizontal slot  420  segment and a vertical slot  420  segment that radiate from the capacitive plate island  510  (and that would intersect at the center of the capacitive plate if the capacitive plate island  510  were absent from the arrangement). 
     The examples of capacitive plate section arrangements provided above are not intended to be limiting. More particularly, the principles provided may be extrapolated upon to arrive at a variety of embodiments having three or more capacitive plate sections  302  supported on magnet  212 , or segmented magnet portions  414 , behind diaphragm  204 . Accordingly, the capacitive plate section  302  arrangements discussed above are intended to be illustrative, rather than exhaustive. 
       FIG. 6  is a cross-sectional view, taken about line B-B of  FIG. 3  viewed in a forward direction, of conductive face sections of a diaphragm in accordance with an embodiment. In an embodiment, a metallized portion of diaphragm  204 , e.g., conductive face  404  on lower layer  408 , may also be segmented to correspond to pairs of capacitive plate sections  302 . For example, a conductive face section  602  may be sized and arranged to oppose capacitive plate quadrants  502 ,  504  (see  FIG. 5B ) across gap  402 . Similarly, conductive face section  604  may be sized and arranged to oppose capacitive plate quadrants  506 ,  508  (see  FIG. 5B ) across gap  402 . Thus, the pairing of each capacitive face section with respective pairs of capacitive plate quadrants may form separate variable capacitor pairs. That is, in this example, a left and a right grouping of serially arranged variable capacitors may be provided to allow for capacitance of each grouping to be sensed separately. Separate sensing of variable capacitor pairs may allow for diaphragm position to be determined for different diaphragm regions. For example, a position of a left side of diaphragm  204  corresponding to capacitive plate quadrants  502 ,  504  and a position of a right side of diaphragm  204  corresponding to capacitive plate quadrants  506 ,  508  may be independently determined, as described below. 
     Referring to  FIG. 7 , a sectional view of a side-firing micro speaker having a capacitive sensor is shown in accordance with an embodiment. In an embodiment, the segmented capacitive plate may be integrated on a front cover of housing  202  in front of diaphragm  204 . For example, micro speaker  106  may be a side-firing speaker with port  218  located on a side of housing  202 . Several capacitive plate sections  302  may be located on an inner surface of housing  202  opposite from a front conductive surface of diaphragm  204 , e.g., upper layer  412 . In an embodiment, a separate conductive film  702  may be deposited, printed, or otherwise layered over diaphragm  204  to provide a continuous conductive portion that forms a variable capacitor with respective capacitive plate sections  302 . For example, the left capacitive plate section  302  may form a first variable capacitor with a respective region of conductive film  702  and the right capacitive plate section  302  may form a second variable capacitor with a respective region of conductive film  702 . The variable capacitors may be serially arranged, as discussed above. Furthermore, the variable capacitors may be electrically connected with sensing circuit  304  through electrical leads  306 . Accordingly, serially arranged variable capacitors may be incorporated on the front cover of a micro speaker  106  such that a distance between diaphragm  204  and the front cover may be sensed without placing electrical connections or integrated circuits on diaphragm  204 . 
     It will be appreciated that the arrangement incorporating capacitive plate sections  302  in front of diaphragm  204  may include some of the same features described above with respect to embodiments having the capacitive plate sections  302  behind diaphragm  204 . For example, the capacitive plate sections  302  on the front cover of housing  202  may be separated by slot  420  and have any of the patterns described in  FIGS. 5A-5C . Furthermore, the illustration of front-mounted capacitive plate sections  302  in a side-firing micro speaker  106  is not intended to be limiting. For example, capacitive plate sections  302  may be mounted on a front cover in a front-firing speaker as well. In such case, a hole may extend through housing  202  along slot  420  to allow sound generated by diaphragm movement to radiate into the surrounding environment in a forward direction from the micro speaker  106 . Alternatively, capacitive plate sections  302  may be formed from perforated or mesh material, or otherwise fitted with holes, to permit forward sound emission by the micro speaker  106 . 
     In the embodiments described above, a respective capacitance of each variable capacitor in the system may be sensed. That is, sensing circuit  304  may receive feedback signals through electrical leads  306  that correlate with capacitance between one or more conductive surface  406  and an opposing conductive face  404 . More particularly, the capacitance may correlate with a voltage between the conductive surface  406  and the conductive face  404 . Furthermore, the capacitance depends on a distance between conductive surface  406  and conductive face  404 , e.g., across gap  402  distance. Thus, as the conductive surfaces move relative to each other, the capacitance will vary, and accordingly, the voltage will vary. Voltage variations may be sensed by sensing circuit  304  to calculate the distance between gap  402 . Alternatively, the voltage or other feedback signal may be sensed by sensing circuit  304  and used to calculate displacement of the surfaces, and thus, the displacement of diaphragm  204  in real-time. 
     In an embodiment, capacitive plate sections  302  may be sensed together. For example, capacitances associated with all capacitive plate sections  302  may be sensed at once. In an embodiment, this may be done by sensing a voltage at two capacitive plate sections  302  in a series of three or more variable capacitors. In such case, the sensed voltages would correspond to voltage changes in all of the serially arranged variable capacitors. Sensing all of the capacitive plate sections  302  together in this manner may provide for a higher signal to noise ratio. 
     Alternatively, capacitive plate sections  302  may be detected in groups, rather than all together. This may provide for detection of a rocking motion of diaphragm  204 . In an embodiment, sensing circuit  304  may be able to switch between pairs of electrical leads  306 , to allow for sensing of any grouping of variable capacitors at a time. For example, with respect to the embodiment shown in  FIG. 5A , a voltage of the capacitive plate sections  302  at the 2 o&#39;clock and 6 o&#39;clock positions may be sensed by switching to connect to the appropriate electrical leads. Separately, a voltage of the capacitive plate sections  302  at the 6 o&#39;clock and 10 o&#39;clock positions, and a voltage of the capacitive plate sections  302  at the 10 o&#39;clock and 2 o&#39;clock positions may be sensed by indexing to connect to the appropriate electrical leads. Accordingly, voltage measurements for each pair of plate segments may be sensed and used to calculate a displacement of the plate pairs. Such displacements may be used to determine rocking motions of diaphragm  204 . For example, when the calculated displacement for the capacitive plate sections  302  at the 2 o&#39;clock and 6 o&#39;clock positions is greater than the displacement for the capacitive plate sections  302  at the 10 o&#39;clock and 2 o&#39;clock position, it may be inferred that the diaphragm  204  is rocking toward the 4 o&#39;clock radial direction more than toward the 12 o&#39;clock radial direction. Similarly, where displacements calculated from all plate section capacitances are substantially the same, it may be inferred that diaphragm  204  is exhibiting pistonic, i.e., substantially axial, motion. Accordingly, an audio speaker having three or more capacitive plate sections  302  supported behind diaphragm  204  on magnet  212  may be used to sense displacement of diaphragm  204 . Also, non-axial motion, e.g., rocking, bending, or other modes of undesirable operation, may be detected. 
     In another embodiment, separate groups of serially arranged variable capacitors may include a pair of capacitive plate quadrants  502 ,  504 , representing a left side of micro speaker  106  (see, e.g.,  FIG. 5B ) and a pair of capacitive plate quadrants  506 ,  508 , representing a right side of micro speaker  106  (see, e.g.,  FIG. 5B ). As described above, the capacitive plate quadrant pairs corresponding to the serially arranged variable capacitors may be electrically in series through a shared conductive surface of diaphragm. Thus, sensing circuit  304  may sense a first electrical signal, e.g., a voltage, through electrical leads connected to quadrants  502 ,  504 , and may sense a second electrical signal through electrical leads connected to quadrants  506 ,  508 . Accordingly, the left-side variable capacitor output may be sensed and processed separately from the right-side variable capacitor output. Additional pairs of variable capacitors, such as where the capacitive plate section grid has more than two intersecting slots, may be simultaneously sensed. Accordingly, as more and more pairs of variable capacitors are sensed, a more complex model of diaphragm motion may be determined. Alternatively, the shared capacitive plate on the moving diaphragm may also be divided into multiple sections rather than a single larger plate. 
     Referring to  FIG. 8 , a flowchart of a method to monitor and/or control spatial orientation of a micro speaker diaphragm is shown in accordance with an embodiment. In an embodiment, at process  802 , sensing circuit  304  senses electrical signals from one or more electrical leads  306  connected to one or more capacitive plate sections  302 . For example, sensing circuit  304  may detect a voltage of the capacitive plate sections  302 . In an embodiment, a bias voltage may be applied to the capacitive plate sections  302 , e.g., through electrical leads  306 , to create an electrical charge on the plates. The sensed voltage may be equal to, or different than, the applied bias voltage. For example, when diaphragm  204  is in a neutral position, the bias voltage and the sensed voltage may be the same, but as the diaphragm  204  moves, a capacitance between diaphragm  204  and the capacitive plate section  302  may change resulting in a sensed voltage that differs from the bias voltage. Thus, the sensed voltage, or a difference between the sensed voltage and the bias voltage, may correspond to capacitance between conductive face  404  of diaphragm  204  and respective conductive surfaces  406  of capacitive plate sections  302 . 
     At process  804 , the electrical signals sensed by sensing circuit  304  may be used to determine a relative spatial orientation between diaphragm  204  and capacitive plate sections  302 . More particularly, given that the electrical signals correspond to capacitance, sensing circuit  304  may determine the instantaneous capacitances from the sensed electrical signals. More particularly, changes in capacitance relative to a neutral position of diaphragm  204  may be determined. Furthermore, since capacitance relates to displacement, the capacitance values may be used to calculate a displacement of diaphragm  204  and/or a distance between diaphragm  204  and capacitive plate section  302 , i.e., a gap  402  distance. In an embodiment, the gap distance in the neutral position may be known, e.g., gap  402  may be 1 mm. Accordingly, changes in the capacitance may be used to calculate displacement of diaphragm  204 , and in turn, the displacement may be added or subtracted from the known gap distance to determine a new gap distance corresponding to an absolute diaphragm position relative to capacitive plate sections  302 . 
     At process  806 , the absolute diaphragm position, i.e., the distance between diaphragm  204  and capacitive plate sections  302 , may be used to determine in real-time whether diaphragm  204  is rocking relative to capacitive plate sections  302 . For example, respective distances between several serially arranged variable capacitor pairs may be calculated to determine the relative spatial orientation between diaphragm  204  and the arrangement of capacitive plate sections  302 . The respective distances calculated for each variable capacitor pair may be used to determine whether diaphragm  204  motion is pistonic or non-pistonic. For example, if respective distances of variable capacitor groupings at diametrically opposite portions of diaphragm  204  are different, e.g., a distance of a first variable capacitor grouping at one side of diaphragm  204  is more than the neutral position gap  402  while a distance of a second variable capacitor grouping at another side of diaphragm  204  is less than the neutral position gap, then it may be inferred that diaphragm  204  is rocking, tilting, or tipping toward one of the two sides. Additional distances may be sensed to infer more complex motions of diaphragm  204 . For example, the use of at least four capacitive plate sections  302  may be used to detect rocking modes in multiple axes, diaphragm bending modes, etc. 
     At process  808 , the calculated diaphragm position may be used to actively control motion of diaphragm  204 . For example, a feedback loop may be created for open or closed loop control of diaphragm motion. The setpoint in the control loop may be a desired diaphragm position and the feedback signal may be the various displacement and/or distance values that are calculated in real time for diaphragm  204 . The calculated values may be compared to the setpoint to create a control signal for driving the diaphragm  204  to the desired position. In an embodiment, the desired diaphragm position may take into account the excursion limits of the micro speaker  106 . For example, when gap  402  has a known neutral position distance, the desired position may be limited to be within the neutral position distance to prevent diaphragm  204  from crashing into capacitive plate sections  302  supported on magnet  212 , or housing  202 , during sound generation. Accordingly, the electrical driving signal delivered to voicecoil  210  to generate sound may be adjusted to limit diaphragm displacement to within the excursion limits. Similarly, the desired position may not only limit diaphragm motion to within the excursion limits, but may also be used to drive the diaphragm  204  as close to the excursion limits as possible, thereby maximizing output level within the constraints of the system. It will be appreciated that active control and monitoring of diaphragm position may also be used to compensate for nonlinear distortion in the micro speaker  106 . Accordingly, a micro speaker  106  having capacitive position sensing for diaphragm  204  may exhibit desirable sound output and quality, while being less likely to fail mechanically. 
     Referring to  FIG. 9 , a schematic view of an electronic device having a micro speaker 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. Thus, the diagrammed circuitry is provided by way of example and not limitation. Electronic device  100  may include one or more processors  902  that execute instructions to carry out the different functions and capabilities described above. For example, processor  902  may incorporate and/or communicate with sensing circuit  304 , as well as digital signal processors or other electronics connected to sensing circuit  304 , to determine capacitances of micro speaker components and calculate a relative spatial orientation of diaphragm  204  based on such capacitances. Furthermore, processor  902  may directly or indirectly implement control loops and provide drive signals to voicecoil  210  of micro speaker  106  to limit diaphragm motion to within an available travel. Instructions executed by the one or more processors  902  of electronic device  100  may be retrieved from local memory  904 , 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., phone or telephony and/or music play back. Audio output for telephony and music play back functions may be through an audio speaker, such as micro speaker  106 . 
     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: 20150406
Publication Date: 20170613
Grant Date: 20170613
Priority Date: 20140930
Inventors: WILK CHRISTOPHER
SALVATTI ALEXANDER V.
JENSEN THOMAS M.
PORTER SCOTT P.
DAVE RUCHIR M.
BRIGHT ANDREW P.
HOGAN RODERICK B.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04R3/007", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R9/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R3/007", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 55585928