PATENT DOCUMENT

Publication Number: US-10932062-B2
Application Number: US-201916259211-A
Country: US
Kind Code: B2

Title: Ultrasonic proximity sensors, and related systems and methods

Abstract:
An ultrasonic proximity sensor can determine one or more characteristics of a local environment. For example, the sensor can emit an ultrasonic signal into a local environment and can receive an ultrasonic signal from the local environment. From a measure of correlation between the emitted and the received signals, the sensor can classify the local environment. By way of example, such a sensor can assess whether an in-ear earphone is positioned in a user&#39;s ear. A media device in communication with the sensor can transmit an audio signal to the earphone for audio playback responsive to a determination by the sensor that the earphone is in the user&#39;s ear and can redirect the audio signal to another playback device responsive to a determination by the sensor that the earphone is not in the user&#39;s ear. Related and other aspects also are described.

Claims:
I currently claim: 
     
       1. An audio device, comprising:
 an ultrasonic proximity sensor-comprising an ultrasonic transducer comprising a piezoelectric actuator, the ultrasonic proximity sensor configured to emit an ultrasonic signal from the audio device into its surroundings; and 
 a processor, coupled to the ultrasonic proximity sensor, configured to determine whether a user has donned the audio device responsive to an observed reflection of the ultrasonic signal. 
 
     
     
       2. The audio device according to  claim 1 , further comprising:
 a housing having an interior region, wherein the housing defines an external surface and an internal surface positioned opposite the external surface, wherein the internal surface at least partially surrounds the interior region; and 
 a loudspeaker transducer acoustically coupled with the interior region of the housing, wherein the housing defines a port providing an acoustic pathway from the interior region to an exterior of the housing, wherein the ultrasonic transducer is coupled with the internal surface of the housing. 
 
     
     
       3. The audio device according to  claim 2 , wherein the external surface defines a major medial surface of the housing when the housing rests in a user&#39;s concha cavum between the user&#39;s tragus and anti-tragus. 
     
     
       4. The audio device according to  claim 2 , wherein the piezoelectric actuator is mounted to the internal surface of the housing. 
     
     
       5. The audio device according to  claim 4 , wherein the piezoelectric actuator is a first piezoelectric actuator, wherein the ultrasonic transducer further comprises a second piezoelectric actuator acoustically coupled with the housing. 
     
     
       6. The audio device according to  claim 5 , further comprising an isolation member positioned between the first piezoelectric actuator and the second piezoelectric actuator. 
     
     
       7. The audio device according to  claim 1 , wherein the piezoelectric actuator comprises first and second opposed electrode layers, a layer of piezoelectric material laminated between the first and second opposed electrode layers, and a flexible coating covering at least a portion each of the first and second opposed electrode layers outward of the piezoelectric material. 
     
     
       8. The audio device according to  claim 1 , further comprising a wireless communication connection, wherein the memory contains instructions that, when executed by the processor, cause the audio device to activate the wireless communication connection responsive to a determination by the audio device that the user has donned the audio device. 
     
     
       9. The audio device according to  claim 1 , wherein the ultrasonic transducer is further configured to receive a reflection of the ultrasonic signal from the surroundings. 
     
     
       10. The audio device according to  claim 1 , wherein the ultrasonic transducer is a first ultrasonic transducer, wherein the proximity sensor further comprises a second ultrasonic transducer configured to receive a reflection of the ultrasonic signal from the surroundings. 
     
     
       11. An audio device, comprising:
 a housing comprising a port providing an acoustic pathway from an interior region of the housing to an exterior of the audio device, the housing further defining an external surface and an internal surface, wherein the internal surface at least partially surrounds the interior region; 
 a loudspeaker transducer acoustically coupled with the interior region of the housing; and 
 an ultrasonic transducer coupled with the internal surface of the housing, wherein the ultrasonic transducer comprises:
 an enclosure mounted to the internal surface of the housing and defining an open interior chamber; and 
 a piezoelectric actuator positioned in the enclosure. 
 
 
     
     
       12. The audio device according to  claim 11 , wherein the piezoelectric actuator comprises a first piezoelectric actuator, wherein the ultrasonic transducer comprises a second piezoelectric actuator and an isolation member, wherein the isolation member is positioned between the first piezoelectric actuator and the second piezoelectric actuator. 
     
     
       13. The audio device according to  claim 11 , wherein the ultrasonic transducer comprises a damper positioned between the piezoelectric actuator and the open interior chamber. 
     
     
       14. The audio device according to  claim 13 , wherein the damper defines a sloped face relative to a surface of the enclosure. 
     
     
       15. The audio device according to  claim 11 , wherein the enclosure of the ultrasonic transducer defines a corresponding port providing a corresponding acoustic pathway through the enclosure to the open interior chamber of the ultrasonic transducer, defining a Helmholtz resonator. 
     
     
       16. The audio device according to  claim 11 , further comprising a mechanical coupler physically coupling the piezoelectric actuator with the enclosure of the ultrasonic transducer. 
     
     
       17. The audio device according to  claim 16 , wherein the mechanical coupler clamps the piezoelectric actuator, defining a vibration node of the piezoelectric actuator. 
     
     
       18. The audio device according to  claim 11 , wherein the enclosure mounted to the internal surface of the housing and the piezoelectric actuator define respective boundaries of the open interior chamber of the ultrasonic transducer. 
     
     
       19. An audio device, comprising:
 a housing comprising:
 a port providing an acoustic pathway from an interior region to an exterior of the housing; and 
 a first housing wall and a second housing wall, wherein an internal surface of the first housing wall at least partially surrounds the interior region of the housing; 
 
 a loudspeaker transducer acoustically coupled with the interior region of the housing; 
 a first ultrasonic transducer coupled with the internal surface of the first housing wall, the first ultrasonic transducer comprising a piezoelectric actuator; and 
 a second ultrasonic transducer coupled with an internal surface of the second housing wall. 
 
     
     
       20. The audio device according to  claim 19 , wherein the external surface of the first housing wall defines a corresponding first area and the external surface of the second housing wall defines a corresponding second area, wherein the first area and the second area are spaced apart from each other so that only one of the first area and the second area can contact a flat surface on which the housing rests. 
     
     
       21. A method of detecting whether a user has donned an audio accessory, the method comprising:
 emitting a first ultrasonic signal externally of a housing; 
 receiving a second ultrasonic signal within the housing; 
 determining whether the second ultrasonic signal comprises a reflection of the first ultrasonic signal from a selected anatomical region of the user; and 
 activating a wireless communication connection responsive to a determination that the second ultrasonic signal comprises a reflection of the first ultrasonic signal from the selected anatomical region. 
 
     
     
       22. The method according to  claim 21 , wherein the housing comprises a housing wall, and the act of emitting a first ultrasonic signal externally of the housing comprises emitting the first ultrasonic signal through the housing wall. 
     
     
       23. The method according to  claim 21 , wherein the audio accessory comprises an ultrasonic sensor having a piezoelectric actuator, and wherein the act of emitting the first ultrasonic signal comprises actuating the piezoelectric actuator. 
     
     
       24. The method according to  claim 23 , wherein the piezoelectric actuator is a first piezoelectric actuator, wherein the ultrasonic sensor has a second piezoelectric actuator. 
     
     
       25. The method according to  claim 24 , wherein the second piezoelectric actuator is configured to receive the second ultrasonic signal. 
     
     
       26. The method according to  claim 24 , wherein the second piezoelectric actuator is comparably less stiff than the first piezoelectric actuator. 
     
     
       27. The method according to  claim 24 , wherein the ultrasonic sensor further comprises an isolation member positioned between the first piezoelectric actuator and the second piezoelectric actuator. 
     
     
       28. The method according to  claim 23 , wherein the ultrasonic sensor comprises a monostatic configuration. 
     
     
       29. The method according to  claim 23 , wherein the ultrasonic sensor comprises a bistatic configuration.

Description:
FIELD 
     This application and related subject matter (collectively referred to as the “disclosure”) generally concern ultrasonic proximity sensors, and related systems and methods. More particularly, but not exclusively, this disclosure pertains to proximity sensors having one or more transducers to emit an ultrasonic signal into, and to detect a reflected signal from, a local environment, e.g., of an audio appliance or an associated accessory. 
     BACKGROUND INFORMATION 
     Media devices can communicate an audio signal to one or more audio accessories to playback audio. For example, a media device can communicate audio to one or more in-ear earphones to be worn by a user during playback, or the media device can communicate the audio to another loudspeaker. Perceived sound quality and other measures of performance for an audio accessory can vary in correspondence with a local environment in which the audio accessory is placed. For example, perceived sound quality can deteriorate if an in-ear earphone is not well-seated in a user&#39;s ear. 
     SUMMARY 
     Disclosed ultrasonic proximity sensors, when calibrated, can classify a local environment, in part, based on observations of reflected ultrasonic signals. An audio accessory can incorporate an ultrasonic proximity sensor, and the sensor can be used to automatically determine whether or to what extent the audio accessory may be positioned to provide a desired level of performance. As but one example, an in-ear earphone can include such a sensor to determine whether the earphone is properly or suitably positioned in a user&#39;s ear. Moreover, disclosed sensors can be incorporated in an earphone or other housing having a continuous (e.g., non-perforated or a micro-perforated) external surface. A continuous, non-perforated surface can provide a “clean,” uninterrupted aesthetic, which some may consider to be pleasing. 
     Concepts, systems, methods, and apparatus disclosed herein overcome many problems in the prior art and address one or more of the aforementioned or other needs. 
     According to one aspect, an audio device includes a housing wall defining an external surface to acoustically couple with a local environment. An internal surface is positioned opposite the external surface. A proximity sensor includes an ultrasonic transducer acoustically coupled with the internal surface of the housing wall to emit and/or to receive an ultrasonic signal. 
     The proximity sensor can be configured to determine whether a user is wearing the audio device. In some instances, the ultrasonic transducer includes a piezoelectric actuator to emit and/or to receive the ultrasonic signal. The piezoelectric actuator can be a first piezoelectric actuator to emit the ultrasonic signal. The ultrasonic transducer can include a second piezoelectric actuator to receive ultrasonic energy. 
     In some audio devices, the ultrasonic transducer is a first ultrasonic transducer positioned to define a first sensitive region of the housing wall. Such an audio device can also include a second ultrasonic transducer acoustically coupled with the housing wall. The second ultrasonic transducer can be so positioned relative to the first ultrasonic transducer as to define a second sensitive region of the housing wall. 
     The proximity sensor can be a first proximity sensor, and the audio device can include a second proximity sensor. The second proximity sensor can be an ultrasonic environment sensor or another (e.g., infrared) type of proximity sensor. 
     The ultrasonic transducer can include a piezoelectric actuator mounted to the internal surface of the housing wall. The piezoelectric actuator can be a first piezoelectric actuator, and the ultrasonic transducer can include a second piezoelectric actuator mounted to the internal surface of the housing wall to define a bistatic ultrasonic transducer. 
     The ultrasonic transducer can include an ultrasonic module mounted to the internal surface of the housing wall. The ultrasonic module can include a housing mounted to the internal surface of the housing wall. A piezoelectric actuator can be positioned in the housing. A mechanical coupler can physically couple the piezoelectric actuator with the housing. The mechanical coupler can clamp the piezoelectric actuator along a vibration node or along a periphery of the actuator. 
     The housing mounted to the internal surface of the housing wall and the piezoelectric actuator can define respective boundaries of an acoustic chamber in the ultrasonic module. The housing can define one or more acoustic ports opening to the acoustic chamber to define a Helmholtz resonator. 
     According to another aspect, an audio system is disclosed. The audio system can include a media device having a processor and a memory. An audio accessory can be communicatively coupleable with the media device. An ultrasonic proximity sensor can be configured to determine whether or to what extent a user has donned the audio accessory. The memory can contain instructions that, when executed by the processor, cause the media device to communicatively decouple from the audio accessory responsive to a determination by the ultrasonic proximity sensor that the user has not donned audio accessory. 
     The ultrasonic proximity sensor can include an ultrasonic transducer configured to emit an ultrasonic signal from the audio accessory into a corresponding environment. The ultrasonic transducer can also be configured to receive an ultrasonic signal from the corresponding environment. 
     In some instances, the ultrasonic transducer can be a first ultrasonic transducer. The proximity sensor can also include a second ultrasonic transducer configured to receive an ultrasonic signal from the corresponding environment. 
     The ultrasonic transducer can include a piezoelectric actuator to emit the ultrasonic signal. 
     Also disclosed are associated methods, as well as tangible, non-transitory computer-readable media including computer executable instructions that, when executed, cause a computing environment to implement one or more methods disclosed herein. Digital signal processors embodied in software, firmware, or hardware and being suitable for implementing such instructions also are disclosed. 
     The foregoing and other features and advantages will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings, wherein like numerals refer to like parts throughout the several views and this specification, aspects of presently disclosed principles are illustrated by way of example, and not by way of limitation. 
         FIG. 1  illustrates a media device and an associated audio accessory. 
         FIG. 2  illustrates an isometric view of a housing for an in-ear earphone. 
         FIG. 3  schematically illustrates anatomy of a typical human ear. 
         FIG. 4  schematically illustrates an in-ear earphone positioned in the human ear shown in  FIG. 3 . 
         FIG. 5  illustrates a block diagram of a method to classify a local environment. 
         FIG. 6  schematically illustrates a modular, monostatic, ultrasonic proximity sensor. 
         FIG. 7  schematically illustrates a modular, bistatic, ultrasonic proximity sensor. 
         FIG. 8  schematically illustrates a side elevation of a cross-section of a rectangular, piezoelectric actuator taken along line VIII-VIII in  FIG. 9 . 
         FIG. 9  schematically illustrates plan view from above a rectangular, piezoelectric actuator taken along line IX-IX in  FIG. 8 . 
         FIG. 10  illustrates a plot of deflection for a rectangular piezoelectric actuator of the type shown in  FIGS. 8 and 9 . 
         FIG. 11  illustrates a plot of sound pressure level output for a rectangular piezoelectric actuator of the type shown in  FIGS. 8 and 9 . 
         FIG. 12  schematically illustrates a monostatic piezoelectric actuator mounted to an internal surface of an enclosure for an audio accessory of the type shown in  FIG. 2  to form a monostatic, ultrasonic transducer. 
         FIG. 13  schematically illustrates a bistatic piezoelectric actuator mounted to an internal surface of an enclosure for an audio accessory of the type shown in  FIG. 2  to form a bistatic, ultrasonic transducer. 
         FIGS. 14, 15, 16, and 17  schematically illustrate respective modular piezoelectric actuators mounted to an internal surface of an enclosure for an audio accessory of the type shown in  FIG. 2 . 
         FIG. 18  illustrates a block diagram showing aspects of an audio appliance. 
         FIG. 19  illustrates a block diagram showing aspects of a computing environment. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes various principles related to ultrasonic proximity sensors, and related systems and methods. For example, some disclosed principles pertain to systems, methods, and components to emit an ultrasonic signal into, and to detect a reflected signal from, a local environment, e.g., of an audio appliance. As but one illustrative example, an in-ear earphone has one or more transducers to emit an ultrasonic signal externally of the earphone and to receive an ultrasonic signal, e.g., reflected by a user&#39;s ear, to determine whether and/or how well the earphone may be positioned in a user&#39;s ear. That said, descriptions herein of specific appliance, apparatus or system configurations, and specific combinations of method acts, are but particular examples of contemplated sensors, components, appliances, systems, and methods chosen as being convenient illustrative examples of disclosed principles. One or more of the disclosed principles can be incorporated in various other sensors, components, appliances, systems, and methods to achieve any of a variety of corresponding, desired characteristics. Thus, a person of ordinary skill in the art, following a review of this disclosure, will appreciate that sensors, components, appliances, systems, and methods having attributes that are different from those specific examples discussed herein can embody one or more presently disclosed principles, and can be used in applications not described herein in detail. Such alternative embodiments also fall within the scope of this disclosure. 
     I. Overview 
     An in-ear earphone can automatically detect whether or to what extent it is positioned in a user&#39;s ear and can enable any of a variety of functions in an associated device. For example, the earphone can communicate its status to a media player or other computing environment. When the status indicates the earphone is being worn, the media player or other computing environment can transmit, for example, an audio signal to the earphone and the earphone can decode and playback the audio signal for the user. When the status indicates the earphone is not being worn, the media player can stop transmitting the audio signal to the earphone and, by way of example, instead redirect the audio signal to another playback device, or altogether pause or stop media playback. As well, when an earphone detects that it is not being worn, the earphone can power down or enter a sleep state to preserve battery charge. 
     Because the earbud portion of the earphone sits at least partially within the ear canal of a user during use, an external surface of the earbud generally contacts various portions of the ear to help keep it positioned within the ear of a user. However, perceived sound quality emitted by an in-ear earphone can deteriorate when an earphone is misaligned with a user&#39;s ear. An earphone that can detect whether or to what extent is it aligned with a user&#39;s ear can take one or more remedial steps when misalignment or removal is detected (e.g., by alerting a user of a misaligned earphone, powering down the earphone, communicating the earphone&#39;s status to a media player). 
     A measure of alignment of an earphone relative to a user&#39;s ear can correspond to a measure of contact between one or more regions on the external surface of the housing and one or more corresponding regions of a user&#39;s ear. For instance, an in-ear earphone can be considered to be misaligned if at least one external region, for example, two external regions, of an earphone housing are not seated against, or not well seated against, a corresponding region of a wearer&#39;s ear anatomy. In one example, if an external surface of an earphone housing is not well seated against, e.g., a user&#39;s concha cavum, the earphone may be considered as being misaligned relative to the user&#39;s ear. Alternatively, if a first region of the earphone is not well seated against the user&#39;s tragus and a second region of the earphone is not well seated against the user&#39;s anti-tragus, the earphone may be considered as being misaligned. 
     An proximity sensor, all or a portion of which can be positioned in the earbud, can detect whether or to what extent the earbud is positioned in a user&#39;s ear and is ready to be used for media playback. For example, the proximity sensor can discern differences between being positioned in or near a user&#39;s ear, as compared to being carried in a carrying case or a pocket, or resting on a table. More particularly, but not exclusively, one or more ultrasonic transducers can be positioned in an earphone housing to define one or more corresponding sensitive regions of the housing. Each sensitive region can detect whether the corresponding region of the earphone housing urges against, for example, a user&#39;s ear. 
     II. Media Devices 
       FIG. 1  shows a portable media device  10  suitable for use with a variety of accessory devices. The portable media device  10  can include a touch sensitive display  12  configured to provide a touch sensitive user interface for controlling the portable media device  10  and in some embodiments any accessories to which the portable media device  10  is electrically or wirelessly coupled. For example, the media device  10  can include a mechanical button  14 , a tactile/haptic button, or variations thereof, or any other suitable ways for navigating on the device. The portable media device  10  can also include a communication connection, e.g., one or more hard-wired input/output (I/O) ports that can include a digital I/O port and/or an analog I/O port, or a wireless communication connection. 
     An accessory device can take the form of an audio device that includes two separate earbuds  20   a  and  20   b . Each of the earbuds  20   a  and  20   b  can include wireless receivers, transmitters or transceivers capable of establishing a wireless link  16  with the portable media device  10  and/or with each other. Alternatively and not shown in  FIG. 1 , the accessory device can take the form of a wired or tethered audio device that includes separate earbuds. Such wired earbuds can be electrically coupled to each other and/or to a connector plug by a number of wires. The connector plug can matingly engage with one or more of the I/O ports and establish a communication link over the wire and between the media device and the accessory. In some wired embodiments, power and/or selected communications can be carried by the one or more wires and selected communications can be carried wirelessly. 
     III. In-Ear Earphones 
       FIG. 2  shows an earbud housing  20  configured to operatively engage with common anatomy of a human ear when being worn by a user, and  FIG. 3  illustrates such anatomy  30  schematically.  FIG. 4  shows the earbud housing  20  positioned within an ear  30  of a user during use. As depicted among  FIGS. 2, 3 and 4 , the earbud housing  20  defines a major medial surface  24  that faces the surface of the user&#39;s concha cavum  33  when the housing  20  is properly seated in a user&#39;s ear  30 . 
     For example, when properly positioned in a user&#39;s ear  30 , the earphone housing  20  can rest in the user&#39;s concha cavum  33  between the user&#39;s tragus  36  and anti-tragus  37 , as in  FIG. 4 . An external surface of the housing, e.g., the major medial surface  24 , can be complementarily contoured relative to, for example, the user&#39;s concha cavum  33  (or other anatomy) to provide a contact region  43  ( FIG. 4 ) between the contoured external surface and the user&#39;s skin when the earphone is properly positioned. The contact region  43  can span a major portion of the contoured external surface  24 . Those of ordinary skill in the art will understand and appreciate that, although the complementarily contoured external surface  24  is described in relation to the concha cavum  33 , other external regions of an earphone housing  20  can be complementarily contoured relative to another region of a human ear  30 . For example, the housing  20  defines a major bottom surface  21  that generally rests against the region of the user&#39;s ear between the anti-tragus  37  and the concha cavum  33  to define a contact region  42 . Still other contact regions are possible. 
     The housing  20  also defines a major lateral surface  28  from which a post  22  extends. The post  22  can include a microphone transducer and/or other component(s) such as a battery. Alternatively, in context of a wired earbud, one or more wires can extend from the post  22 . When the earbud is properly donned, as in  FIG. 4 , the post  22  extends generally parallel to a plane defined by the user&#39;s earlobe  39  at a position laterally outward of a gap  38  between the user&#39;s tragus  36  and anti-tragus  37 . 
     Further, the earbud defines an acoustic port  23 . The port  23  provides an acoustic pathway from an interior region of the housing  20  to an exterior  25  of the housing. As shown in  FIG. 4 , the port  23  aligns with and opens to the user&#39;s ear canal  31  when the earbud is properly donned as described above. A mesh, screen, film, or other protective barrier (not shown) can extend across the port  23  to inhibit or prevent intrusion of debris into the interior of the housing. 
     In some earbuds, the housing  20  defines a boss or other protrusion from which the port  23  opens. The boss or other protrusion can extend into the ear canal  31  and can contact the walls of the canal over a contact region  41 . Alternatively, the boss or other protrusion can provide a structure to which a resiliently flexible cover (not shown) such as, for example, a silicone cover, can attach to provide an intermediate structure forming a sealing engagement between the walls of the user&#39;s ear canal  31  and the housing  20  over the contact region  41 . The sealing engagement can enhance perceived sound quality, as by passively attenuating external noise and inhibiting a loss of sound power from the earbud. 
     Although not specifically shown, the housing  20  also can include a compliant member to conform to person-to-person variations in contour among the tragus  36 , anti-tragus  37 , and concha cavum  33 . For example, a compliant member can matingly engage with a region of the housing  20  corresponding to the major surface  24 . Such a compliant member (not shown) can accommodate a certain amount of compression that allows secure seating of housing  20  within the ear  30  of the user, e.g., within the concha cavum  33 . 
     The housing  20  can be formed of any material or combination of materials suitable for earphones. For example, some housings are formed of acrylonitrile butadiene styrene (ABS). Other representative materials include polycarbonates, acrylics, methacrylates, epoxies, and the like. A compliant member can be formed of, for example, polymers of silicone, latex, and the like. 
       FIG. 4  also depicts several regions of contact between the earphone housing  20  and tissue of the user&#39;s ear  30 . Each region  41 ,  42 ,  43  defines an area on the surface of the housing  20 , or surface of an intermediate compliant member, that urges against the user&#39;s tissue. 
     Proximity sensor or portion thereof can be positioned within the housing  20  at a position opposite a selected contact region  41 ,  42 ,  43  relative to the housing wall. For example, a proximity sensor, or a transmitter and/or receiver thereof, can be positioned in the housing  20  opposite a contact region  41 ,  42 ,  43  (or other intended contact region) to define a corresponding sensitive region of the earphone housing. Each respective sensor can assess whether or to what extent the corresponding contact region  41 ,  42 ,  43 , and thus the housing  20 , is aligned in the user&#39;s ear. 
     Further, physical characteristics of a local environment can influence a degree to which an emitted signal may reflect and/or be damped as it passes through the environment. For example, ultrasonic energy may dissipate much more quickly through air or a textile (or other material having a high attenuation coefficient over a frequency range of interest) as compared to water or human tissue. In addition, a reflection of an emitted ultrasonic signal that passes through air or a textile may be much more attenuated when received by the receiver compared to a reflection of an ultrasonic signal that passes through water or human tissue. As well, a reflection of an emitted ultrasonic signal that passes through a dry interface between a given sensor and a given tissue may be much more attenuated when received by the receiver compared to a reflection of an ultrasonic signal that passes through an interface having an acoustic couplant between the sensor and the tissue. If the transducer is positioned to emit the signal into, for example, a user&#39;s tissue or other substance, the tissue or other substance can reflect the signal and the reflected signal can be received by the sensor or a component thereof. Accordingly, reflections received by the sensor can indicate when a user&#39;s tissue (e.g., a user&#39;s ear) is positioned in close proximity to the sensor. Some disclosed proximity sensors can detect characteristics of a local environment through a solid (e.g., non-perforated) housing wall to provide an uninterrupted external surface and an aesthetically pleasing appearance to the housing. Nonetheless, some housing walls may have a plurality of visibly indistinguishable perforations (sometimes referred to as “micro-perforations”). 
     Some earphones define a single sensitive region corresponding to one selected contact region. When the sensitive region is adjacent or immersed in air or a textile, for example, emitted ultrasonic signals may dissipate and reflections might not be received. Accordingly, the underlying proximity sensor can determine that the earbud is not being worn and can emit a corresponding signal to the media device  10 . However, when the sensitive region is adjacent or in contact with, for example, a table or a shelf, the underlying proximity sensor may receive a reflection of an emitted ultrasonic signal and determine (in this example incorrectly) that the earbud is being worn. 
     To avoid a false indication that an earbud is being worn, some earphones incorporate a plurality of proximity sensors or transducers to define a corresponding plurality of sensitive regions on the earbud housing  20 . The plurality of sensitive regions can be spaced apart from each other, for example, so no two sensitive regions can contact a flat surface (e.g., a shelf or a desk) when the earbud housing  20  rests on the flat surface. For example, if transducers are arranged to make the contact regions  41  and  43  sensitive, both contact regions will not simultaneously contact a flat surface on which the earbud housing  20  rests. Thus, both regions will not indicate the earbud is being worn when the earbud housing  20  rests on a flat surface. The underlying sensor can be configured to determine the earbud housing is being worn only when two or more of the sensitive regions receive reflected ultrasonic signals. Otherwise, the sensor can indicate that the earphone is not being worn. 
     IV. Ultrasonic Proximity Sensors: Overview 
       FIG. 5  illustrates a general approach  50  for determining a local environment for an in-ear earphone. At block  52 , a proximity sensor, such as a sensor in an earbud housing, can emit an acoustic signal in an ultrasonic frequency band. The signal can be emitted at a single frequency or over a plurality of frequencies. 
     As shown schematically in  FIGS. 6 and 7 , a sensor can have an ultrasonic transducer  60 ,  70   a  to emit the acoustic signal  2 ,  4  (sometimes referred to as a “transmitter”) into a local medium  61 ,  71  and an ultrasonic transducer  60 ,  70   b  to receive an acoustic signal  2 ,  6  (sometimes referred to as a “receiver”) from the medium. Ultrasonic proximity sensors can have a monostatic configuration  60  ( FIG. 6 ) or a bistatic configuration  70  ( FIG. 7 ). Each transmitter can be activated with an incoming signal over a conductor  68 ,  78   a.    
     With a monostatic transducer  60  as depicted in  FIG. 6 , the transducer acts as a transmitter and a receiver. Stated differently, the same acoustic diaphragm  62  emits and receives acoustic energy  2 . Consequently, the monostatic transducer  60  emits an ultrasonic signal for a selected duration and subsequently awaits reflections of the signal so the sensor can ascertain characteristics of the local environment  61 . A diaphragm suitable to efficiently emit high intensity (e.g., sound-pressure level) acoustic signals may be relatively insensitive to received acoustic energy. Similarly, a diaphragm with high sensitivity to receive even relatively weak acoustic signals may be relatively inefficient and/or incapable of emitting high intensity acoustic signals. Consequently, a diaphragm that is neither an ideal transmitter nor an ideal receiver, but rather a suitable transmitter and a suitable receiver, can be used in monostatic proximity sensor. Nonetheless, by virtue of having a single diaphragm  62 , a monostatic configuration  60  may occupy relatively less space than a bistatic configuration  70 . 
     In contrast, a bistatic configuration  70  ( FIG. 7 ) uses a first electro-acoustic transducer  72   a  to emit acoustic energy  4  (the transmitter) into the local medium  71  and a second electro-acoustic transducer  72   b  to receive acoustic energy  6  (the receiver) from the medium. Consequently, a bistatic configuration  70  lends itself to using a hard or stiff material for the diaphragm  72   a  of the transmitter  70   a  and a soft or flexible material for the diaphragm  72   b  of the receiver  70   b . The transmitter  72   a  and the receiver  72   b  can be acoustically separated from each other, as by an isolation member  79 , to inhibit cross-talk between the transducers  70   a ,  70   b.    
     Regardless of whether a sensor has a monostatic configuration or a bistatic configuration, the corresponding ultrasonic transducer can have a resonant frequency above an upper threshold frequency of human hearing. Often, the upper threshold of human hearing is assumed to be about 20 kHz, though some individuals can hear modestly higher frequencies and the upper threshold frequency often falls with age. Some ultrasonic transducers emit acoustic energy at a frequency well above the assumed threshold of human hearing. For example, some ultrasonic transducers emit acoustic energy at a frequency greater than about 40 kHz, such as, for example, greater than about 42 kHz, or greater than about 45 kHz. The sensor can emit an acoustic signal that includes a resonant frequency of the transducer. 
     At block  54 , the sensor receives one or more ultrasonic signals. Each transducer  60 ,  70  can emit a signal indicative of a received ultrasonic signal over a conductor  68 ,  78   b.    
     More particularly, an acoustic signal received by the receiver  60 ,  70   b  may originate with the transmitter  60 ,  70   a  and be reflected to the receiver by a local medium  61 ,  71 . A reflection of the emitted signal can correlate with the emitted signal, albeit possibly with a shift in phase and/or a lower amplitude due to damping of the emitted signal and the reflected signal by a local environment  61 ,  71 . On the other hand, an acoustic signal received by the receiver may originate from a source other than the transmitter, in which case the received signal would not correlate with a signal emitted by the sensor&#39;s transmitter. Accordingly, correlation between an emitted signal and a received signal can indicate that the received signal constitutes a reflected portion of the emitted signal. At block  56  in  FIG. 5 , a degree of correlation between the emitted signal and the received signal is assessed, so as to determine whether the received signal constitutes a reflection of the emitted signal. 
     Further, reflections of one or more ultrasonic signals can be characterized or calibrated using a variety of measures and across a variety of local environments. For example, variation in magnitude- and/or phase-spectra of reflected ultrasonic signals can be characterized and recorded for each of a variety of parameters. As described more fully below, such parameters include, for example, surrounding material, conditions of an interface between the local surroundings and the sensor or an associated member, configuration of a local surroundings, arrangement of a proximity sensor relative to the local surroundings, and variations thereof. 
     Exemplary surrounding materials include, by way of example, air, textiles, clothing, water, and/or various types of tissue, such as, for example, skin, cartilage, fascia, and bone. Exemplary conditions of an interface between the local surroundings and the sensor or an associated member include, for example, a dry interface between a sensor housing and a user&#39;s skin, a couplant-augmented interface between the sensor housing and the user&#39;s skin, and/or a compressed interface. Exemplary arrangements of a local surroundings include typical arrangements include a supporting flat surface in open air, pants-pockets, typical anatomical arrangements (e.g., concha cavum, tragus, anti-tragus), and variations thereof (e.g., air at various temperatures, clothing of different types and materials). As another example, magnitude and/or phase spectra of reflected ultrasonic signals can be characterized and recorded over a range of coupling conditions between the sensor and one or more local surroundings. Such coupling conditions can include, for example, “good” contact between a sensor housing and a selected region of a user&#39;s ear, “loose” contact between the sensor housing and the selected region of the user&#39;s ear, “good” alignment of an earphone with a selected portion of the user&#39;s ear, “poor” alignment of the earphone with the selected portion of the user&#39;s ear, etc. 
     After being characterized or calibrated across a variety of environments of interest, a proximity sensor can be used in situ to infer information about an unknown local environment (e.g., surrounding material, conditions of an interface between the local surroundings and the sensor or an associated member, configuration of a local surroundings, arrangement of a proximity sensor relative to the local surroundings, and variations thereof). For example, a calibrated proximity sensor can, in situ, emit an acoustic signal over an ultrasonic frequency band to a local environment and observe a magnitude- and/or a phase-spectra of reflections or other received ultrasonic signals. To the extent observed magnitude- and/or phase-spectra of a received ultrasonic signal correlate with the emitted acoustic signal, the sensor can infer that the received ultrasonic signal constitutes a reflection of the emitted signal. Moreover, a match between the observed magnitude- and/or phase-spectra of the unknown environment and a magnitude- and/or phase-spectra of a characterized environment can indicate that the unknown local environment is substantially similar to the characterized environment. Moreover, the sensor can incorporate signals from spaced apart transducers and infer that an earbud is in contact with, for example, a user&#39;s ear only when more than one sensor detects a local surroundings other than air, for example. Thus, as indicated at block  58 , the proximity sensor can determine or classify a local environment in which it rests or is being used. 
     By way of illustration, sensors having piezoelectric transducers suitable to emit and to receive ultrasonic acoustic energy are described in relation to  FIGS. 6 and 7 . As used herein, the term “piezoelectric transducer” generally refers to a device that converts an electrical charge (or current) to mechanical motion or vice-versa using piezoelectric material. In turn, the term “piezoelectric material,” as used herein, refers to a material that exhibits an electromechanical interaction, as by generating an electrical charge (or current or potential) responsive to a mechanical force or deformation applied to the material and/or by exerting a mechanical force or deforming responsive to an electrical charge (or current or potential) applied to the material. By way of example, piezoelectric materials include naturally occurring crystalline materials (e.g., Quartz, Berlinite (AlPO 4 ), Sucrose, Rochelle salt, Topaz, Tourmaline-group minerals, and Lead titanate (PbTiO 3 )), certain biological materials, synthetic crystalline structures (e.g., Langasite (La 3 Ga 5 SiO 14 ), Gallium orthophosphate (GaPO 4 ), Lithium niobate (LiNbO 3 ) Lithium tantalate (LiTaO 3 )), certain ceramic materials (e.g., Barium titanate (BaTiO 3 ), Lead zirconate titanate (Pb[Zr x Ti 1-x ]O 3  with 0≤x≤ 1 , and commonly referred to in the art as “PZT”), Potassium niobate (KNbO 3 ), Sodium tungstate (Na 2 WO 3 ), Ba 2 NaNb 5 O 5 , Pb 2 KNb 5 O 15 , and single-crystal Zinc oxide (ZnO), Sodium potassium niobate ((K,Na)NbO 3 ), Bismuth ferrite (BiFeO 3 ), Sodium niobate (NaNbO 3 ), Bismuth titanate (Bi 4 Ti 3 O1 2 ), Sodium bismuth titanate (NaBi(TiO 3 ) 2 ), Group III-V and Group II-VI semiconductors (e.g., wurtzite structures of GaN, InN, AlN), certain polymers (e.g., Polyvinylidene fluoride (PVDF)), and certain organic nanostructures (e.g., diphenylalanine peptide nanotubes, sometimes referred to as “PNTs”). Hard, stiff ceramics, such as, for example, PZT-4H can provide a correspondingly high drive intensity (sound pressure level) compared to a softer, more flexible ceramic, such as, for example, PZT-5H. Hard, stiff materials can be suitable for transmitters and soft, more flexible materials can provide higher sensitivity and be suited for receivers. 
     Referring again to  FIGS. 6 and 7 , the piezoelectric transducers  60 ,  70  can be coupled with or mounted on an internal surface of the earbud housing. The transducers  60 ,  70  have a respective piezoelectric diaphragm  62 ,  72   a ,  72   b  positioned within a corresponding housing, or enclosure  63 ,  73 , defining respective open interior chambers  64 ,  74   a ,  74   b.    
     A piezoelectric transducer  60 ,  70  can include a piezoelectric diaphragm  62 ,  72   a ,  72   b  laminated between a respective so-called “matching layer”  65 ,  75   a ,  75   b  and a respective damper  66 ,  76   a ,  76   b . As shown in  FIGS. 6 and 7 , the damper (e.g., a damping material)  66 ,  76   a ,  76   b  can be laminated with the diaphragm  62 ,  72   a ,  72   b  on a side opposite the matching layer  65 ,  75   a ,  75   b  relative to the diaphragm. 
     Each damper  66 ,  76   a ,  76   b  can reduce reverberation in the open interior chamber cavity  64 ,  74   a ,  74   b  and improve the sensor&#39;s corresponding spatial resolution. In one aspect, a face  67 ,  77   a ,  77   b  of the damper  66 ,  76   a ,  76   b  can be sloped (e.g., oriented in a non-parallel fashion) relative to an interior surface of the housing  63 ,  73 . Such an orientation can inhibit formation of standing waves and/or other resonance effects that can arise when an acoustic radiator emits waves orthogonally toward a housing wall. 
     Each matching layer  65 ,  75   a ,  75   b  can be formed of one or more materials having a desired combination of characteristics, such as, for example, an acoustic impedance that approximates an acoustic impedance of a housing material and/or a likely or a desired surroundings material. For example, tissue of a user&#39;s ear can have a specific acoustic impedance of about 1.5 MRayls (e.g., between about 1.4 MRayls and about 1.6 MRayls), and ABS can have a specific acoustic impedance of about 2.3 MRayls (e.g., between about 2.2 MRayls and about 2.4 MRayls). Reducing a number and/or a magnitude of discontinuities in acoustic impedance between the diaphragm  62 ,  72   a ,  72   b  and a likely or a desired environment  61 ,  71  into which the ultrasonic signal may be emitted can reduce or eliminate internal reflections arising from an impedance mismatch between the respective transducer  60 ,  70  and the environment. Such internal reflections, if not eliminated or inhibited with a matching layer  65 ,  75   a ,  75   b  or filtered from the output of the receiver  78   b , can introduce errors in the sensor, as by falsely indicating a presence of a desired environment. 
     Acoustic coupling between the transducers  60 ,  70  and a corresponding local environment  61 ,  71  can be enhanced by placing an acoustic couplant  61   a ,  71   a  between a surface of the local environment  61 ,  71  and the respective transducer. For example, the couplant can fill interstitial gaps between a surface of the transducer and a user&#39;s skin. 
     Electro-acoustic transducers having a large lateral dimension, w, relative to an emitted wavelength, λ, (e.g., w&gt;&gt;λ) can provide a high degree of directionality, or a low-degree of divergence. When used as a receiver, such transducers can be highly sensitive to orientation relative to incoming acoustic waves. On the other hand, transducers having a lateral dimension on the order of the wavelength (e.g., w˜λ) tend to be less directional and tend to emit (or receive) acoustic waves over a relatively wider range of angles compared to transducers with a larger lateral dimension. 
     V. Ultrasonic Proximity Sensors: Direct Integration 
     Other configurations for a proximity sensor are possible. For example, a piezoelectric diaphragm (or another actuator) can be mounted to an earbud housing. Deformation of the diaphragm or other actuator can interact with the earbud housing  20  to emit an ultrasonic signal. Similarly, interaction between the earbud housing  20  and a diaphragm responsive to an incoming ultrasonic signal can deform the diaphragm or other actuator and generate an electrical signal. 
     Referring now to  FIGS. 8 and 9 , a piezoelectric actuator  80  suitable for directly coupling to an earbud housing  20  will be described. In  FIG. 8 , a layer of piezoelectric material  81  is laminated between opposed, electrically conductive layers  82   a ,  82   b . A flexible, insulative coating  83 ,  83   a ,  83   b  can encapsulate or otherwise cover at least a portion of one or both electrode layers  82   a ,  82   b  outward of the piezoelectric material. By way of example, the coating  83 ,  83   a ,  83   b  can be formed of polyimide or another flexible, insulative material. One or more regions of the electrically conductive layers (or a region of another electrical conductor electrically coupled with the electrically conductive layers)  82   a ,  82   b  can be exposed to define corresponding electrodes  84   a ,  84   b.    
     A voltage potential  85  applied across the electrodes  84   a ,  84   b , and thus across the piezoelectric material by virtue of the electrically conductive layers  82   a ,  82   b  can cause the piezoelectric material  81  to deform, as indicated by the arrows  86 ,  87 . As the voltage potential  85  varies, e.g., at a selected frequency, the piezoelectric material  81  can deform at a corresponding frequency. 
       FIG. 10  shows a plot of deformation of the piezoelectric actuator  80  relative to the coordinate axes  7 . As shown in  FIG. 10 , a central region  88  of the actuator  80  undergoes a substantially larger deformation along the z-axis (e.g., in a direction orthogonal to the actuator) compared to edge regions  89   a ,  89   b .  FIG. 11  shows a plot of acoustic energy emitted by the actuator  80 . Consistent with the magnitude of deformation shown in  FIG. 10 , the central region  88  emits substantially more acoustic energy than the edge regions  89   a ,  89   b.    
     A piezoelectric actuator can be affixed to an earbud housing in a monostatic ( FIG. 12 ) configuration or in a bistatic ( FIG. 13 ) configuration. 
     In  FIG. 12 , an ultrasonic actuator  90  includes a layer of piezoelectric material  91  positioned between opposed layers  92   a ,  92   b  of electrically conductive material. A flexible coating covers the laminated layers  92   a ,  91 ,  92   b , generally as described above in relation to  FIGS. 8 and 9 . The actuator  90  is mounted to an internal surface of an earbud housing  94 . The internal surface of the housing  94  is positioned opposite an external surface  95  of the housing to be placed in contact with a local material  96 . The external surface  95  defines a sensitive region of the earbud. Couplers  97   a ,  97   b  can include any suitable form of attachment between the actuator  90  and the housing  94 , such as, for example, an adhesive, an epoxy, and a mechanical engagement. The actuator  90  can be deformed in a time-varying manner, as by passing a varying electrical current or a varying electrical potential across the conductive layers  92   a ,  92   b . The mechanical attachment between the actuator  90  and the housing  94  can cause the housing to deform in correspondence with deformations of the actuator  90 . The combined deformations of the housing  94  and the actuator  90  can emit an ultrasonic signal  98  into the local environment  96 . Alternatively, an incoming ultrasonic signal  98  (e.g., a reflection of an emitted ultrasonic signal) can cause the housing  94  and thus the actuator  90  to deform. Deformation of the actuator  90  can induce the piezoelectric material  91  to generate an electrical signal in (e.g., a voltage potential or an electrical current across) the conductive layers  92   a ,  92   b . A processing unit of the sensor (including an analog-to-digital converter) can receive and process the electrical signal to assess whether or to what extent the housing  94  is in sufficient contact with a desired environment. 
     In  FIG. 13 , an ultrasonic actuator  100  includes a first layer of piezoelectric material  101   a  (a transmitter) and a second layer of piezoelectric material  101   b  (a receiver). The first layer of piezoelectric material  101   a  is positioned between corresponding opposed layers  102   a ,  102   b  of electrically conductive material. The second layer of piezoelectric material  101   b  is positioned between corresponding opposed layers  103   a ,  103   b  of electrically conductive material. A flexible coating  104  covers the laminated layers  102   a ,  101   a ,  102   b  and the laminated layers  103   a ,  101   b ,  103   b  generally as described above in relation to  FIGS. 8, 9, and 10 , except that the coating  104  defines an acoustic isolation region  109  positioned between the laminated layers  102   a ,  101   a ,  102   b  and the laminated layers  103   a ,  101   b ,  103   b . The actuator  100  is mounted to an internal surface of an earbud housing  105 . The internal surface of the housing  105  is positioned opposite an external surface  105   a  of the housing in contact with a local material  106 . The external surface  105   a  defines a sensitive region of the earbud. Couplers  107   a ,  107   b ,  107   c  can include any suitable form of attachment between the actuator  100  and the housing  105 , such as, for example, an adhesive, an epoxy, and a mechanical engagement. 
     The transmitter-portion of the actuator  100  can be deformed in a time-varying manner, as by passing a varying electrical current or a varying electrical potential across the conductive layers  102   a ,  102   b  to cause the piezoelectric layer  101   a  to deform. The mechanical attachment between the actuator  100  and the housing  105  can cause the housing to deform in correspondence with deformations of the piezoelectric layer  101   a . The combined deformations of the housing  105  and the piezoelectric layer  101   a  can emit an ultrasonic signal  108   a  into the local environment  106 . An incoming ultrasonic signal  108   b  (e.g., a reflection of an emitted ultrasonic signal  108   a ) can cause the housing  105  and thus the piezoelectric layer  101   b  to deform. Deformation of the piezoelectric layer  101   b  can induce the piezoelectric material  101   b  to generate an electrical signal in (e.g., a voltage potential or an electrical current across) the conductive layers  103   a ,  103   b . A processing unit of the sensor (including an analog-to-digital converter) can receive and process the electrical signal to assess whether or to what extent the housing  105  is in sufficient contact with a desired environment. 
     VI. Modular Ultrasonic Proximity Sensors 
     Modular ultrasonic transducers also are possible and are described in relation to  FIGS. 14, 15, 16, and 17 . The modular ultrasonic transducers can be configured as a monostatic transducer or as a bistatic transducer. Unlike a directly integrated transducer, modular ultrasonic transducers can be assembled and tested prior to being incorporated into an earbud. 
     Rather than directly integrating, e.g., a piezoelectric actuator with the earbud housing as in  FIGS. 12 and 13 , a modular ultrasonic transducer  110   a ,  110   b ,  110   c ,  110   d  can include a housing  111   a ,  111   b ,  111   c ,  111   d  in which a piezoelectric diaphragm  112   a ,  112   b ,  112   c ,  112   d  is mounted. The modular transducer  110   a ,  110   b ,  110   c ,  110   d  can be physically coupled with (e.g., mounted to, adhered to, or affixed on) an interior surface of an earbud housing  116 . An opposed, external surface  117  of the earbud housing  116  can emit and be sensitive to ultrasonic signals, generally as described above. 
     The housing  111   a ,  111   b ,  111   c ,  111   d  and diaphragm  112   a ,  112   b ,  112   c ,  112   d  can define a resonant chamber  113   a ,  113   b ,  113   c ,  113   d . Diaphragm excursions for a primary mode of each transducer  110   a ,  110   b ,  110   c ,  110   d  are shown by the dashed lines  115   a ,  115   b ,  115   c ,  115   d.    
     As in  FIG. 14 , the diaphragm  112   a  can be clamped within the housing, as along a nodal line  114   a  along which the diaphragm does not oscillate. With a configuration as in  FIG. 14 , high amplitude and relatively low energy losses can be attained. Nonetheless, a portion of the diaphragm  112   a  positioned laterally or radially outward of the nodal line  114   a  vibrates out-of-phase relative to a portion positioned laterally or radially inward of the nodal line, giving rise to a potential for interference between the emissions of the inward and the outward portions. 
     Alternatively, as in  FIG. 15 , a circular diaphragm  112   b  can be clamped within the housing  111   b  along a circumference. The circumferentially clamped diaphragm  112   b  can vibrate at a frequency similar to that shown in  FIG. 14 . However, greater interaction between the housing  111   b  and the diaphragm  112   b  can dampen oscillations and result in a relatively larger loss of energy and lower amplitude than the configuration in  FIG. 14 . Additionally, the housing  111   b  may need to be more massive to accommodate increased mechanical loads compared to the arrangement in  FIG. 14 . Nonetheless, the entire diaphragm  112   b  largely vibrates in phase and thus the arrangement in  FIG. 15  can be less susceptible to destructive interference from an anti-phase emission. 
     As another alternative, as in  FIG. 16 , a non-circular, e.g., a rectangular, diaphragm  112   c  can be edge clamped by the housing  111   c . Consequently, angular deformations of the diaphragm  112   c  are possible and the corresponding resonant frequency is expected to be about one-half of that of the configurations in  FIGS. 14 and 15 . 
     As shown in  FIG. 15 , the enclosure wall that contacts the earbud housing wall  116  can be solid, as with the wall  118   a . Alternatively, as shown in  FIG. 17 , the wall  118   b  can define one or more acoustic ports, making the resonant chamber  113   d  a Helmholtz resonator. Where a thickness of the earbud wall  116  is substantially less than a wavelength of an ultrasonic signal, interference by the wall  116  can be relatively small or insignificant. A resonant frequency, fr, of the chamber  113   d  can be approximated using the following relationship: 
     
       
         
           
             
               f 
               r 
             
             = 
             
               
                 c 
                 
                   2 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   π 
                 
               
               ⁢ 
               
                 
                   
                     n 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     π 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       r 
                       2 
                     
                   
                   
                     v 
                     ⁡ 
                     
                       ( 
                       
                         l 
                         + 
                         
                           
                             π 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               r 
                               2 
                             
                           
                           2 
                         
                       
                       ) 
                     
                   
                 
               
             
           
         
       
     
     where f r  is a resonant frequency of the chamber  113   d , visa volume of the chamber  113   d, n  is the number of holes in the wall  118   b, r  is a radius of each hole in the wall  118   b ,  1  is a thickness of the wall (or a length of the holes), and c is the speed of sound in air (e.g., about 343 m/s). When a frequency of vibration of the diaphragm  112   d  equals the resonant frequency, fr, the transducer module  110   d  can emit a maximum sound pressure level. 
     VII. Computing Environments 
       FIG. 18  shows an example of a suitable architecture for an audio appliance (e.g., a media device  10 , in  FIG. 1 ). The audio appliance  180  includes an audio acquisition module  181  and aspects of a computing environment (e.g., described more fully below in connection with  FIG. 19 ) that can cause the appliance to communicate with an audio accessory in a defined manner. For example, the illustrated appliance  180  includes a processing unit  184  and a memory  185  that contains instructions the processing unit can execute to cause the audio appliance to, e.g., carry out one or more aspects of receiving an output from an ultrasonic proximity sensor and/or responding to an indication of an environment in which an audio accessory  20   a ,  20   b  ( FIG. 1 ) is positioned. 
     For example, such instructions can cause the audio appliance  180  to capture ambient sound with the audio acquisition module  181  and to communicate some or all of an acquired audio signal over a communication connection  186  to a remote speech-recognition system (not shown). The captured ambient sound can include a user&#39;s uttered command. By way of further example, the speech-recognition system can extract such an uttered command from the audio signal and communicate a machine-readable command to the audio appliance  180  over the communication connection  186 . The command can invoke an audio codec (not shown) and/or other instructions to cause the audio appliance to selectively play a song over a loudspeaker  187  or one or both audio accessories  20   a ,  20   b.    
     Referring still to  FIG. 18 , an audio appliance typically includes a microphone transducer to convert incident acoustic signals to corresponding electrical output. As used herein, the terms “microphone” and “microphone transducer” are used interchangeably and mean an acoustic-to-electric transducer or sensor that converts an incident acoustic signal, or sound, into a corresponding electrical signal representative of the incident acoustic signal. Typically, the electrical signal output by the microphone is an analog signal. 
     Although a single microphone is depicted in  FIG. 18 , this disclosure contemplates the use of plural microphones. For example, plural microphones can be used to obtain plural distinct acoustic signals emanating from a given acoustic scene, and the plural versions can be processed independently and/or combined with one or more other versions before further processing by the audio appliance  180 . 
     As shown in  FIG. 18 , the audio acquisition module  21  can include a microphone transducer  182  and a signal conditioner  183  to filter or otherwise condition the acquired representation of ambient sound. Some audio appliances have an analog microphone transducer and a pre-amplifier to condition the signal from the microphone. 
     As shown in  FIG. 18 , an audio appliance  180  or other electronic device can include, in its most basic form, a processor  184 , a memory  185 , and a loudspeaker or other electro-acoustic transducer  187 , and associated circuitry (e.g., a signal bus, which is omitted from  FIG. 18  for clarity). 
     The audio appliance  180  schematically illustrated in  FIG. 18  also includes a communication connection  186 , as to establish communication with another computing environment or an audio accessory, such as accessory  20   a ,  20   b  ( FIG. 1 ). The memory  185  can store instructions that, when executed by the processor  184 , cause the circuitry in the audio appliance  180  to drive the electro-acoustic transducer  187  to emit sound over a selected frequency bandwidth or to communicate an audio signal over the communication connection  186  to an audio accessory  20   a ,  20   b  for playback. In addition, the memory  185  can store other instructions that, when executed by the processor, cause the audio appliance  180  to perform any of a variety of tasks akin to a general computing environment as described more fully below in connection with  FIG. 19 . 
       FIG. 19  illustrates a generalized example of a suitable computing environment  190  in which described methods, embodiments, techniques, and technologies relating, for example, to assessing a local environment for the computing environment or an accessory thereto can be implemented. The computing environment  190  is not intended to suggest any limitation as to scope of use or functionality of the technologies disclosed herein, as each technology may be implemented in diverse general-purpose or special-purpose computing environments, including within an audio appliance. For example, each disclosed technology may be implemented with other computer system configurations, including wearable and/or handheld appliances (e.g., a mobile-communications device, such as, for example, IPHONE®/IPAD®/AIRPODS®/HOMEPOD™ devices, available from Apple Inc. of Cupertino, Calif.), multiprocessor systems, microprocessor-based or programmable consumer electronics, embedded platforms, network computers, minicomputers, mainframe computers, smartphones, tablet computers, data centers, audio appliances, and the like. Each disclosed technology may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications connection or network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. 
     The computing environment  190  includes at least one central processing unit  191  and a memory  192 . In  FIG. 19 , this most basic configuration  193  is included within a dashed line. The central processing unit  191  executes computer-executable instructions and may be a real or a virtual processor. In a multi-processing system, or in a multi-core central processing unit, multiple processing units execute computer-executable instructions (e.g., threads) to increase processing speed and as such, multiple processors can run simultaneously, despite the processing unit  191  being represented by a single functional block. 
     A processing unit, or processor, can include an application specific integrated circuit (ASIC), a general-purpose microprocessor, a field-programmable gate array (FPGA), a digital signal controller, or a set of hardware logic structures (e.g., filters, arithmetic logic units, and dedicated state machines) arranged to process instructions. 
     The memory  192  may be volatile memory (e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or some combination of the two. The memory  192  stores instructions for software  198   a  that can, for example, implement one or more of the technologies described herein, when executed by a processor. Disclosed technologies can be embodied in software, firmware or hardware (e.g., an ASIC). 
     A computing environment may have additional features. For example, the computing environment  190  includes storage  194 , one or more input devices  195 , one or more output devices  196 , and one or more communication connections  197 . An interconnection mechanism (not shown) such as a bus, a controller, or a network, can interconnect the components of the computing environment  190 . Typically, operating system software (not shown) provides an operating environment for other software executing in the computing environment  190 , and coordinates activities of the components of the computing environment  190 . 
     The store  194  may be removable or non-removable, and can include selected forms of machine-readable media. In general, machine-readable media includes magnetic disks, magnetic tapes or cassettes, non-volatile solid-state memory, CD-ROMs, CD-RWs, DVDs, magnetic tape, optical data storage devices, and carrier waves, or any other machine-readable medium which can be used to store information, and which can be accessed within the computing environment  190 . The storage  194  can store instructions for the software  98   b  that can, for example, implement technologies described herein, when executed by a processor. 
     The store  194  can also be distributed, e.g., over a network so that software instructions are stored and executed in a distributed fashion. In other embodiments, e.g., in which the store  194 , or a portion thereof, is embodied as an arrangement of hardwired logic structures, some (or all) of these operations can be performed by specific hardware components that contain the hardwired logic structures. The store  194  can further be distributed, as between or among machine-readable media and selected arrangements of hardwired logic structures. Processing operations disclosed herein can be performed by any combination of programmed data processing components and hardwired circuit, or logic, components. 
     The input device(s)  195  may be any one or more of the following: a touch input device, such as a keyboard, keypad, mouse, pen, touchscreen, touch pad, or trackball; a voice input device, such as one or more microphone transducers, speech-recognition technologies and processors, and combinations thereof; a scanning device; or another device, that provides input to the computing environment  190 . For audio, the input device(s)  195  may include a microphone or other transducer (e.g., a sound card or similar device that accepts audio input in analog or digital form), or a computer-readable media reader that provides audio samples and/or machine-readable transcriptions thereof to the computing environment  190 . 
     Speech-recognition technologies that serve as an input device can include any of a variety of signal conditioners and controllers, and can be implemented in software, firmware, or hardware. Further, the speech-recognition technologies can be implemented in a plurality of functional modules. The functional modules, in turn, can be implemented within a single computing environment and/or distributed between or among a plurality of networked computing environments. Each such networked computing environment can be in communication with one or more other computing environments implementing a functional module of the speech-recognition technologies by way of a communication connection. 
     The output device(s)  196  may be any one or more of a display, printer, loudspeaker transducer, DVD-writer, signal transmitter, or another device that provides output from the computing environment  190 , e.g., an audio accessory  20   a ,  20   b  ( FIG. 1 ). An output device can include or be embodied as a communication connection  197 . 
     The communication connection(s)  197  enable communication over or through a communication medium (e.g., a connecting network) to another computing entity or accessory. A communication connection can include a transmitter and a receiver suitable for communicating over a local area network (LAN), a wide area network (WAN) connection, or both. LAN and WAN connections can be facilitated by a wired connection or a wireless connection. If a LAN or a WAN connection is wireless, the communication connection can include one or more antennas or antenna arrays. The communication medium conveys information such as computer-executable instructions, compressed graphics information, processed signal information (including processed audio signals), or other data in a modulated data signal. Examples of communication media for so-called wired connections include fiber-optic cables and copper wires. Communication media for wireless communications can include electromagnetic radiation within one or more selected frequency bands. 
     Machine-readable media are any available media that can be accessed within a computing environment  190 . By way of example, and not limitation, with the computing environment  190 , machine-readable media include memory  192 , storage  194 , communication media (not shown), and combinations of any of the above. Tangible machine-readable (or computer-readable) media exclude transitory signals. 
     As explained above, some disclosed principles can be embodied in a store  194 . Such a store can include tangible, non-transitory machine-readable medium (such as microelectronic memory) having stored thereon or therein instructions. The instructions can program one or more data processing components (generically referred to here as a “processor”) to perform one or more processing operations described herein, including estimating, computing, calculating, measuring, adjusting, sensing, measuring, filtering, correlating, and decision making, as well as, by way of example, addition, subtraction, inversion, and comparison. In some embodiments, some or all of these operations (of a machine process) can be performed by specific electronic hardware components that contain hardwired logic (e.g., dedicated digital filter blocks). Those operations can alternatively be performed by any combination of programmed data processing components and fixed, or hardwired, circuit components. 
     VIII. Other Embodiments 
     The examples described above generally concern ultrasonic proximity sensors, and related systems and methods. The previous description is provided to enable a person skilled in the art to make or use the disclosed principles. Embodiments other than those described above in detail are contemplated based on the principles disclosed herein, together with any attendant changes in configurations of the respective apparatus described herein, without departing from the spirit or scope of this disclosure. Various modifications to the examples described herein will be readily apparent to those skilled in the art. 
     For example, an earbud can also be equipped with various other sensors that can work independently or in concert with the proximity sensor described herein. For example, in some embodiments, the other sensors can take the form of an orientation sensor to help the earbud determine which ear the earbud is positioned within and then adjust operation of the earbud in accordance with that determination. In some embodiments, the orientation sensor can be a traditional inertial-based sensor while in other embodiments, sensor readings from another biometric sensor such as a proximity sensor or a temperature sensor can be used to make an orientation determination. 
     An earbud with the aforementioned sensors can also include additional sensors such as a microphone or array of microphones. In some embodiments, at least two microphones from a microphone array can be arranged along a line pointed towards or at least near the mouth of a user. By using information received by the orientation sensor or sensors, a controller within the earbud can determine which microphones of a microphone array should be activated to obtain this configuration. By activating only those microphones arranged along a vector pointed at or near the mouth, ambient audio signals not originating near the mouth can be ignored by applying a spatial filtering process. 
     Directions and other relative references (e.g., up, down, top, bottom, left, right, rearward, forward, etc.) may be used to facilitate discussion of the drawings and principles herein, but are not intended to be limiting. For example, certain terms may be used such as “up,” “down,”, “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” and the like. Such terms are used, where applicable, to provide some clarity of description when dealing with relative relationships, particularly with respect to the illustrated embodiments. Such terms are not, however, intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an “upper” surface can become a “lower” surface simply by turning the object over. Nevertheless, it is still the same surface and the object remains the same. As used herein, “and/or” means “and” or “or”, as well as “and” and “or.” Moreover, all patent and non-patent literature cited herein is hereby incorporated by reference in its entirety for all purposes. 
     And, those of ordinary skill in the art will appreciate that the exemplary embodiments disclosed herein can be adapted to various configurations and/or uses without departing from the disclosed principles. Applying the principles disclosed herein, it is possible to provide a wide variety of damped acoustic enclosures, and related methods and systems. For example, the principles described above in connection with any particular example can be combined with the principles described in connection with another example described herein. Thus, all structural and functional equivalents to the features and method acts of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the principles described and the features claimed herein. Accordingly, neither the claims nor this detailed description shall be construed in a limiting sense, and following a review of this disclosure, those of ordinary skill in the art will appreciate the wide variety of ultrasonic proximity sensors, and related methods and systems that can be devised under disclosed and claimed concepts. 
     Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim feature is to be construed under the provisions of 35 USC 112(f), unless the feature is expressly recited using the phrase “means for” or “step for”. 
     The appended claims are not intended to be limited to the embodiments shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to a feature in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. Further, in view of the many possible embodiments to which the disclosed principles can be applied, I reserve to the right to claim any and all combinations of features and technologies described herein as understood by a person of ordinary skill in the art, including, for example, all that comes within the scope and spirit of the following claims.

Metadata:
Filing Date: 20190128
Publication Date: 20210223
Grant Date: 20210223
Priority Date: 20180217
Inventors: GREENLEE, CHARLES L.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04R17/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R1/1041", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01H11/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/1041", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2460/15", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2460/03", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/1016", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01H11/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04S7/304", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2460/15", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2420/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/1016", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R5/033", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2460/03", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R5/04", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R17/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01H11/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2460/15", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/1041", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2420/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04S7/304", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R17/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R5/033", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2460/03", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/1016", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 67617121