Patent Publication Number: US-11042221-B2

Title: Methods, devices, and systems for displaying a user interface on a user and detecting touch gestures

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/241,893, filed Jan. 7, 2019, entitled “Methods, Devices, and Systems for Displaying a User Interface on a User and Detecting Touch Gestures,” which claims priority to U.S. Provisional Application No. 62/647,559, filed Mar. 23, 2018, entitled “Methods, Devices, and Systems for Determining Contact On a User of a Virtual Reality and/or Augmented Reality Device” and U.S. Provisional Application No. 62/647,560, filed Mar. 23, 2018, entitled “Methods, Devices, and Systems for Projecting an Image Onto a User and Detecting Touch Gestures”, each of which is incorporated by reference herein in its entirety. 
    
    
     This application is related to U.S. Utility patent application Ser. No. 16/241,871, filed Jan. 7, 2019, entitled “Methods, Devices, and Systems for Creating Haptic Stimulations and Tracking Motion of a User,” U.S. Utility patent application Ser. No. 16/241,890, filed Jan. 7, 2019, entitled “Methods, Devices, and Systems for Determining Contact On a User of a Virtual Reality and/or Augmented Reality Device,” and U.S. Utility patent application Ser. No. 16/241,900, filed Jan. 7, 2019, entitled “Methods, Devices, and Systems for Creating Localized Haptic Stimulations on a User,” each of which is incorporated by reference herein in its entirety. 
     TECHNICAL FIELD 
     This relates generally to virtual reality/augmented reality, including but not limited to projecting images onto a user and detecting gestures on the user relating to the projection. 
     BACKGROUND 
     Virtual reality (VR) and/or augmented reality (AR) technologies allow users to interact with technologies in different ways. VR and/or AR allows a user to tactilely interact with the digital world. Users may experience haptic responses from electronic devices, allowing users a rich experience. Wearable devices for VR and/or AR may allow users to interact with the digital world through a medium distinct from an electronic device&#39;s screen (e.g., a wearable device projects an image onto a user&#39;s forearm using, e.g., augmented reality). However, determining a location of a gesture on the projected image with sufficient precision presents a challenge. 
     SUMMARY 
     Accordingly, there is a need for methods, devices, and systems for projecting virtual images onto a user with sufficient fidelity in determining whether a contact or gesture has occurred. One solution is to combine computer vision (e.g., a camera on a wearable device) and a separate modality (e.g., a wearable wristband having one or more transducers) for increased fidelity in determining a location and/or pressure of a gesture (e.g., contact). 
     In some embodiments, the solution explained above can be implemented on a wearable device that includes a plurality of transducers (e.g., actuators). The wearable device in some instances is worn on the user&#39;s wrist (or various other body parts) and is used to project an image onto a portion of the user&#39;s body, essentially creating a virtual or augmented reality display on the user&#39;s body. In some embodiments, the wearable device may virtualize an image to be seen through a lens of the wearable device as though the image were projected onto the user. Moreover, the wearable device can be in communication with a host system (e.g., a virtual reality device and/or an augmented reality device, among others), and the wearable device can display images based on instructions from the host system. As an example, the host system may display video data to a user (e.g., may instruct a head-mounted display to display the video data), and the host system may also instruct the wearable device to project images from the video onto the user&#39;s body. 
     The devices, systems, and methods described herein provide benefits including but not limited to: (i) detecting a touch gesture on a projected and/or virtual image by an appendage of a user, (ii) determining a location of a touch gesture on a projected image on a user&#39;s body, (iii) the wearable device does not encumber free motion of a user&#39;s hand and/or wrist (or other body parts), and (iv) multiple wearable devices can be used simultaneously. 
     (A1) In accordance with some embodiments, a method is performed at a first wearable device that includes a projector and a plurality of transducers. The method includes projecting an image onto a portion of a first appendage of a user of the first wearable device and detecting a touch gesture on the image by a second appendage of the user distinct from the first appendage. The method further includes at a second wearable device having a camera and a processor, determining a location of the touch gesture on the image where a computer system is instructed to perform an operation in accordance with the detecting and the location. In some embodiments, the first wearable device is attached to an appendage (e.g., wrist, forearm, bicep, thigh, ankle, etc.) of the user and the second wearable device is worn on the head of the user (e.g., head-mounted display). 
     (A2) In some embodiments of the method of A1, further including, at the second wearable device, confirming, via the camera and the processor, that the detected touch gesture has occurred on the image by the second appendage of the user. The computer system is instructed to perform the operation in further accordance with the confirming. 
     (A3) In some embodiments of the method of any of A1-A2, the plurality of transducers is a first plurality of transducers that can each generate one or more signals and the first wearable device further comprises a first control circuit coupled to the first plurality of transducers. Moreover, the method further includes generating, via the first plurality of transducers, signals that couple/vibrate into at least a portion of the first appendage of the user of the first wearable device. 
     (A4) In some embodiments of the method of A3, further including receiving, via a second plurality of transducers of a third wearable device, at least a portion of the signals generated by the first plurality of transducers when the first appendage of the user is within a threshold distance from the third wearable device, wherein the user is wearing the third wearable device on a second appendage. The method also includes in response to the receiving, determining, via a second control circuit of the third wearable device, a position of a portion of the first appendage with respect to a position of the third wearable device. The computer system is instructed to perform an operation in accordance with the detecting, the position, and the location. 
     (A5) In some embodiments of the method of any of A1-A4, the touch gesture is a swipe gesture. 
     (A6) In some embodiments of the method of any of A1-A4, the touch gesture is a tap gesture. 
     (A7) In some embodiments of the method of any of A1-A4, the touch gesture is a pinch gesture. 
     (A8) In some embodiments of the method of any of A1-A7, the image is a video stream. 
     (A9) In some embodiments of the method of any of A1-A8, the first appendage is a first arm of the user and the second appendage is a second arm of the user. 
     (A10) In another aspect, a system is provided that includes a first wearable device, a second wearable device, a third wearable device, and a computer system, and the system is configured to perform the method steps described above in any of A1-A9. 
     (A11) In yet another aspect, one or more wearable devices are provided and the one or more wearable devices include means for performing the method described in any one of A1-A9. 
     (A12) In still another aspect, a non-transitory computer-readable storage medium is provided (e.g., as a memory device, such as external or internal storage, that is in communication with a wearable device). The non-transitory computer-readable storage medium stores executable instructions that, when executed by a wearable device with one or more processors/cores, cause the wearable device to perform the method described in any one of A1-A9. 
     (B1) In accordance with some embodiments, another method is performed at a first wearable device, attached to a first appendage of a user, that includes one or more transducers. The method includes receiving, by the one or more transducers, a set of signals transmitted by a second wearable device attached to the user, wherein (i) receiving the set of signals creates a signal pathway between the first and second wearable devices, and (ii) signals in the set of signals propagate through at least the user&#39;s first appendage. The method also includes determining baseline characteristics for the signal pathway created between the first wearable device and the second wearable device and sensing a change in the baseline characteristics while receiving the set of signals. The method also includes, in accordance with a determination that the sensed change in the baseline characteristics for the signal pathway satisfies a contact criterion, reporting a candidate touch event on the user&#39;s first appendage. In some embodiments, the contact criterion includes a touch criterion and a hover criterion. In such embodiments, a sensed change in the baseline characteristics caused by finger hovering event may satisfy the hover criterion but will not satisfy the touch criterion. 
     (B2) In some embodiments of the method of B1, reporting the candidate touch event comprises sending transducer data corresponding to the sensed change in the baseline characteristics to a computer system. In some embodiments, the transducer data also includes a time stamp of when the sensed change in the baseline characteristics occurred. In some embodiments, reporting the candidate touch event includes sending, to the computer system, a message reporting the candidate touch event. 
     (B3) In some embodiments of the method of B2, the computer system displays, on the user&#39;s first appendage, a user interface that includes one or more affordances, and the candidate touch event reported by the first wearable device is associated with a first affordance of the one or more affordances included in the user interface. 
     (B4) In some embodiments of the method of any of B2-B3, further including determining an approximate location of the candidate touch event on the user&#39;s first appendage based, at least in part, on the sensed change in the baseline characteristics. The transducer data sent to the computer system further comprises information indicating the approximate location of the candidate touch event. 
     (B5) In some embodiments of the method of B2, the transducer data sent to the computer system also indicates an approximate location of the candidate touch event on the user&#39;s first appendage. 
     (B6) In some embodiments of the method of any of B3-B5, the computer system: (i) captures, via one or more cameras, the candidate touch event, (ii) generates image data according to the capturing of the candidate touch event, and (iii) executes a function associated with the first affordance of the user interface after processing the transducer data and the image data. 
     (B7) In some embodiments of the method of any of B1-B6, the baseline characteristics include a baseline phase value. Furthermore, sensing the change in the baseline characteristics for the signal pathway comprises detecting a phase value of the signal pathway that differs from the baseline phase value. 
     (B8) In some embodiments of the method of B7, the contact criterion includes a phase difference threshold. Furthermore, reporting the candidate touch event is performed in accordance with a determination that a difference between the phase value and the baseline phase value satisfies the phase difference threshold. 
     (B9) In some embodiments of the method of any of B1-B8, the baseline characteristics include a baseline amplitude value. Furthermore, sensing the change in the baseline characteristics for the signal pathway comprises detecting an amplitude value of the signal pathway that differs from the baseline amplitude value. 
     (B10) In some embodiments of the method of B9, the contact criterion includes an amplitude difference threshold. Furthermore, reporting the candidate touch event is performed in accordance with a determination that a difference between the amplitude value and the baseline amplitude value satisfies the amplitude difference threshold. 
     (B11) In some embodiments of the method of any of B1-B10, the baseline characteristics include a baseline amplitude value and a baseline phase value. Furthermore, sensing the change in the baseline characteristics for the signal pathway comprises detecting (i) an amplitude value of the signal pathway that differs from the baseline amplitude value, and (ii) a phase value of the signal pathway that differs from the baseline phase value. 
     (B12) In some embodiments of the method of B11, the contact criterion includes an amplitude difference threshold and a phase difference threshold. Furthermore, reporting the candidate touch event is performed in accordance with a determination that: (i) a difference between the amplitude value and the baseline amplitude value satisfies the amplitude difference threshold, and (ii) a difference between the phase value and the baseline phase value satisfies the phase difference threshold. 
     (B13) In some embodiments of the method of any of B1-B12, the contact criterion includes a time threshold. Furthermore, sensing the change in the baseline characteristics comprises sensing the change for a period of time and reporting the candidate touch event is performed in accordance with a determination that the period of time satisfies the time threshold. Alternatively, in some embodiments, the first wearable device continually sends transducer data to the computer device. 
     (B14) In some embodiments of the method of any of B1-B13, further including, before receiving the set of signals, receiving a plurality predetermined values for signals characteristics. Each of the predetermined values for the signals characteristics corresponds to a specific location of the first appendage of the user. In some embodiments, the transducer data of (B2) includes signals characteristics (e.g., values of phase, amplitude, etc.) that substantially match one of the plurality predetermined values for signals characteristics. 
     (B15) In some embodiments of the method of any of B1-B14, the candidate touch event is selected from the group consisting of a tap gesture, press-and-holder gesture, a swipe gesture, a drag gesture, a multi-tap gesture, a pinch gesture, a pull gesture, and a twist gesture. 
     (B16) In some embodiments of the method of any of B1-B15, reporting the candidate touch event comprises sending, to a computer system, data associated with the sensed change in the signal pathway, and the computer system determines whether the user intended to interact with an affordance of a user interface displayed on the user&#39;s first appendage based, at least in part, on the data associated with the sensed change in the signal pathway. For example, the computer system displays the user interface on the user&#39;s first appendage, and the candidate touch event reported by the first wearable device is associated with one of the affordances included in the user interface. 
     (B17) In some embodiments of the method of B16, the computer system (i) captures, via one or more cameras, an approximate location of the candidate touch event, the approximate location of the candidate touch event corresponding to a location of the affordance in the user interface displayed on the user&#39;s first appendage, and (ii) executes a function associated with the affordance in response to determining that the user intended to interact with the first affordance and in accordance with the approximate location of the candidate touch event. 
     (B18) In some embodiments of the method of any of B1-B17, the computer system is an artificial-reality system selected from the group consisting of an augmented-reality system, a virtual-reality system, and a mixed-reality system. 
     (B19) In yet another aspect, a wearable device is provided and the wearable device includes means for performing the method described in any one of B1-B18 and F1-F2. 
     (B20) In another aspect, a wearable device that includes one or more transducers is provided. In some embodiments, the wearable device is in communication with one or more processors and memory storing one or more programs which, when executed by the one or more processors, cause the wearable device to perform the method described in any one of B1-B18 and F1-F2. 
     (B21) In still another aspect, a non-transitory computer-readable storage medium is provided (e.g., as a memory device, such as external or internal storage, that is in communication with a wearable device). The non-transitory computer-readable storage medium stores executable instructions that, when executed by a wearable device with one or more processors/cores, cause the wearable device to perform the method described in any one of B1-B18 and F1-F2. 
     (B22) In still another aspect, a system is provided. The system includes a first wearable device, a second wearable device, and a computer system that are configured to perform the method described in any one of B1-B18 and F1-F2. In some embodiments, the second wearable device and the computer system are part of the same device while in other embodiments they are separate devices. 
     (C1) In accordance with some embodiments, another method is performed at an artificial-reality system (e.g., AR system  1200 ,  FIG. 12 ; VR system  1300 ,  FIG. 13 ), worn by a user, that includes a head-mounted display, one or more cameras, and at least one processor. The method includes (i) providing first instructions to the head-mounted display to display a user interface on a first appendage of the user, wherein the user is also wearing, on a first appendage, a first wearable device that is in communication with the artificial-reality system, and (ii) providing second instructions to a second wearable device to emit one or more signals, wherein the one or more signals propagate through at least the first appendage of the user and are received by the first wearable device, thereby creating a signal pathway between the first wearable device and the second wearable device. The method also includes (i) receiving, from the first wearable device, data associated with the signal pathway created between the first wearable device and the second wearable device, and (ii) capturing, by the one or more cameras, a candidate touch event at a location on the user&#39;s first appendage, wherein the location is associated with an affordance of the user interface. Thereafter, the method includes determining whether the user intended to interact with the affordance of the user interface based, at least in part, on the data associated with the signal pathway, and in response to determining that the user intended to interact with the affordance and in accordance with the captured location of the candidate touch event, executing a function associated with the affordance. 
     (C2) In some embodiments of the method of C1, displaying the user interface on the first appendage of the user includes: (i) projecting the user interface on the user&#39;s first appendage, or (ii) presenting, using augmented reality, the user interface on the head-mounted display so that the user perceives the user interface on the first appendage. 
     (D1) In accordance with some embodiments, another method is performed at an artificial-reality system (e.g., AR system  1200 ,  FIG. 12 ; VR system  1300 ,  FIG. 13 ), worn by a user, that includes a head-mounted display, one or more cameras, and at least one processor. The method includes, while displaying a user interface on a first appendage of the user: (i) capturing, via the one or more cameras, a candidate touch event at a location on a user&#39;s first appendage, wherein the location is associated with an affordance of the user interface, and (ii) receiving, from a first wearable device worn by the user, data associated with the candidate touch event, wherein the first wearable device is attached to the user&#39;s first appendage. The method also includes determining whether the user&#39;s first appendage was touched based at least in part on the received data, and in accordance with a determination that the user&#39;s first appendage was touched and based on the captured location of the candidate touch event, executing a function associated with the affordance of the user interface. 
     (D2) In some embodiments of the method of D1, the user interface is displayed on the first appendage of the user by: (i) projecting the user interface on the user&#39;s first appendage, or (ii) presenting, using augmented reality, the user interface on the head-mounted display so that the user perceives the user interface on the first appendage. 
     (D3) In some embodiments of the method of any of D1-D2, the first wearable device performs the method described in any one of B1-B15 to generate the data received by the artificial-reality system. 
     (E1) In yet another aspect, an artificial-reality system is provided and the artificial-reality system includes means for performing the method described in any one of C1-C2 and D1-D2. 
     (E2) In another aspect, an artificial-reality system that includes a head-mounted display and one or more cameras is provided. In some embodiments, the artificial-reality system is in communication with one or more processors and memory storing one or more programs which, when executed by the one or more processors, cause the artificial-reality system to perform the method described in any one of C1-C2 and D1-D2. 
     (E3) In still another aspect, a non-transitory computer-readable storage medium is provided (e.g., as a memory device, such as external or internal storage, that is in communication with an artificial-reality system). The non-transitory computer-readable storage medium stores executable instructions that, when executed by an artificial-reality system with one or more processors/cores, cause the artificial-reality system to perform the method described in any one of C1-C2 and D1-D2. 
     (F1) In accordance with some embodiments, another method is performed at a first wearable device, attached to a first appendage of a user, that includes one or more transducers. The method includes (i) receiving, by the one or more transducers, a set of waves (e.g., signals) transmitted by a second wearable device attached to the user, wherein waves in the set of waves travel from the second wearable device to the first wearable device through the first appendage of the user, (ii) after receiving the set of waves, determining first values for one or more waveform characteristics of the set of waves, and (iii) identifying a location of a touch gesture on the first appendage of the user based on the first values for the one or more waveform characteristics of the set of waves. In some embodiments, the one or more waveform characteristics includes at least values for phase and amplitude. 
     (F2) In some embodiments of the method of F1, further including reporting the location of the touch gesture to a computer system (e.g., computer system  130 ,  FIG. 1A ). 
     (F3) In some embodiments of the method of any of F1-F2, the first wearable device performs the method described in any one of B2-B15. 
     In accordance with some embodiments, a plurality of wearable device each includes one or more processors/cores and memory storing one or more programs configured to be executed by the one or more processors/cores. The one or more programs in each wearable devices includes instructions for performing one or more of the operations of the method described above. In accordance with some embodiments, a non-transitory computer-readable storage medium has stored therein instructions that, when executed by one or more processors/cores of a wearable device, cause the wearable device to perform some of the operations of the method described above (e.g., operations of the first wearable device or the second wearable device). In accordance with some embodiments, a system includes a wearable device (or multiple wearable devices), a head-mounted display (HMD), and a computer system to provide video/audio feed to the HMD and instructions to the wearable device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the various described embodiments, reference should be made to the Description of Embodiments below, in conjunction with the following drawings in which like reference numerals refer to corresponding parts throughout the figures and specification. 
         FIG. 1A  is a block diagram illustrating an exemplary projection system, in accordance with various embodiments. 
         FIG. 1B  is a block diagram illustrating an exemplary projection system, in accordance with various embodiments. 
         FIG. 2  is a block diagram illustrating an exemplary wearable device in accordance with some embodiments. 
         FIG. 3  is a block diagram illustrating an exemplary computer system in accordance with some embodiments. 
         FIG. 4A  is an exemplary view of a wearable device on a user&#39;s wrist, in accordance with some embodiments. 
         FIG. 4B  is an exemplary cross-sectional view of a wearable device on a user&#39;s wrist, in accordance with some embodiments. 
         FIG. 5  is an exemplary cross-sectional view of a wearable device in accordance with some embodiments. 
         FIG. 6A  is an exemplary view of a wearable device on a user&#39;s wrist and on the user&#39;s head, in accordance with some embodiments. 
         FIG. 6B  is an exemplary view of a wearable device on a user&#39;s wrist and on the user&#39;s finger, in accordance with some embodiments. 
         FIG. 6C  is an exemplary view of a wearable device on a user&#39;s first wrist and on the user&#39;s second wrist, in accordance with some embodiments. 
         FIG. 6D  is an exemplary signal pathway between two wearable devices, in accordance with some embodiments. 
         FIG. 7  is a flow diagram illustrating a method of projecting images onto a user&#39;s body in accordance with some embodiments. 
         FIG. 8  is a flow diagram illustrating a method of confirming a touch on a user&#39;s body in accordance with some embodiments. 
         FIG. 9  is a high level flow diagram illustrating a method of detecting a touch on a user&#39;s body in accordance with some embodiments. 
         FIG. 10  is a flow diagram illustrating a method of confirming a touch on a user&#39;s body in accordance with some embodiments. 
         FIG. 11  illustrates an embodiment of an artificial reality device. 
         FIG. 12  illustrates an embodiment of an augmented reality headset and a corresponding neckband. 
         FIG. 13  illustrates an embodiment of a virtual reality headset. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Reference will now be made to embodiments, examples of which are illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide an understanding of the various described embodiments. However, it will be apparent to one of ordinary skill in the art that the various described embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments. 
     It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first wearable device could be termed a second wearable device, and, similarly, a second wearable device could be termed a first wearable device, without departing from the scope of the various described embodiments. The first wearable device and the second wearable device are both wearable devices, but they are not the same wearable devices, unless specified otherwise. 
     The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various described embodiments and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     As used herein, the term “if” is, optionally, construed to mean “when” or “upon” or “in response to determining” or “in response to detecting” or “in accordance with a determination that,” depending on the context. Similarly, the phrase “if it is determined” or “if [a stated condition or event] is detected” is, optionally, construed to mean “upon determining” or “in response to determining” or “upon detecting [the stated condition or event]” or “in response to detecting [the stated condition or event]” or “in accordance with a determination that [a stated condition or event] is detected,” depending on the context. 
     As used herein, the term “exemplary” is used in the sense of “serving as an example, instance, or illustration” and not in the sense of “representing the best of its kind.” 
       FIG. 1  is a block diagram illustrating a system  100 , in accordance with various embodiments. While some example features are illustrated, various other features have not been illustrated for the sake of brevity and so as not to obscure pertinent aspects of the example embodiments disclosed herein. To that end, as anon-limiting example, the system  100  includes wearable devices  102   a ,  102   b , which are used in conjunction with a computer system  130  (e.g., a host system or a host computer). In some embodiments, the system  100  provides the functionality of a virtual reality device with image projection, an augmented reality device with image projection, a combination thereof, or provides some other functionality. The system  100  is described in greater detail below with reference  FIGS. 11-13 . 
     An example wearable device  102  (e.g., wearable device  102   a ) includes, for example, one or more processors/cores  104  (referred to henceforth as “processors”), a memory  106 , one or more transducer arrays  110 , one or more communications components  112 , projector(s)  115 , and/or one or more sensors  114 . In some embodiments, these components are interconnected by way of a communications bus  108 . References to these components of the wearable device  102  cover embodiments in which one or more of these components (and combinations thereof) are included. In some embodiments, the one or more sensors  114  are part of the one or more transducer arrays  110  (e.g., transducers in the transducer arrays  110  also perform the functions of the one or more sensors  114 , discussed in further detail below). For example, one or more transducers in the transducer array  110  may be electroacoustic transducers configured to detect acoustic waves (e.g., ultrasonic waves). 
     Another example wearable device  102  (e.g., wearable device  102   b ) includes, for example, one or more processors/cores  104  (referred to henceforth as “processors”), a memory  106 , one or more transducer arrays  110 , one or more communications components  112 , camera(s)  118 , and/or one or more sensors  114 . In some embodiments, these components are interconnected by way of a communications bus  108 . References to these components of the wearable device  102  cover embodiments in which one or more of these components (and combinations thereof) are included. In some embodiments, the one or more sensors  114  are part of the one or more transducer arrays  110  (e.g., transducers in the transducer arrays  110  also perform the functions of the one or more sensors  114 , discussed in further detail below). For example, one or more transducers in the transducer array  110  may be electroacoustic transducers configured to detect acoustic waves (e.g., ultrasonic waves). 
     In some embodiments, a single processor  104  (e.g., processor  104  of the wearable device  102   a ) executes software modules for controlling multiple wearable devices  102  (e.g., wearable devices  102   b  . . .  102   n ). In some embodiments, a single wearable device  102  (e.g., wearable device  102   a ) includes multiple processors  104 , such as one or more wearable device processors (configured to, e.g., generate an image for projection), one or more communications component processors (configured to, e.g., control communications transmitted by communications component  112  and/or receive communications by way of communications component  112 ) and/or one or more sensor processors (configured to, e.g., control operation of sensor  114  and/or receive output from sensor  114 ). 
     In some embodiments, the wearable device  102  is configured to project image(s)  602  (as shown in  FIG. 6A ) via the projector(s)  115  within projection unit  412  (shown in  FIG. 4A ). In such embodiments, the wearable device  102  is configured to generate and project images (e.g., a keyboard or the like) onto the user&#39;s own appendage using, e.g., one or more of the one or more projectors  115 . The AR system  1100  ( FIG. 11 ) shows an example wearable device that can project images (at least in some embodiments). 
     In some other embodiments, the wearable device  102  does not project images and instead the computer system  130  (and the head-mounted display  140 ) is (are) responsible for projecting images onto the user&#39;s own appendage. Alternatively, in some embodiments, the computer system  130  (and the head-mounted display  140 ) uses augmented reality so that the user perceives images on his or her own appendage, but nothing is actually projected. AR system  1200  ( FIG. 12 ) and VR system  1300  ( FIG. 13 ) can be used to project/display images onto the user or areas around the user. 
     In some embodiments, the transducers in a respective transducer array  110  are miniature piezoelectric actuators/devices, vibrotactile actuators, or the like. In some embodiments, the transducers in a respective transducer array  110  are single or multipole voice coil motors, or the like. Each transducer array  110  is configured to generate and transmit signals  116  in response to being activated by the wearable device (e.g., via processors  104  or some other controller included in the wearable device  102 ). In some embodiments, the signals  116  are mechanical waves (e.g., sound waves, ultrasonic waves, or various other mechanical waves). A mechanical wave is an oscillation of matter that transfers energy through a medium. As discussed herein, the “medium” is the wearer&#39;s skin, flesh, bone, blood vessels, etc. It is noted that any device capable of producing mechanical waves (or alternating current signals) can be used as a transducer in the disclosed wearable device  102 . It is also noted that signals (e.g., waves) that propagate through the medium (e.g., the user&#39;s flesh) are said herein to “couple” to the medium or “couple into” the medium. 
     In some embodiments, the wearable device  102  (e.g., wearable device  102   a ,  102   b ) is a receiver and transmitter of one or more signals. For example, in addition to transmitting signals (e.g., mechanical waves), as described above, the wearable device  102  is also configured to receive (e.g., detect, sense) signals transmitted by itself or by another wearable device  102 . To illustrate, a first wearable device  102   a  may transmit a plurality of signals through a medium, such as the wearer&#39;s body, and a second wearable device  102   b  (attached to the same wearer) may receive at least some of the signals transmitted by the first wearable device  102   a  through the medium. Furthermore, a wearable device  102  receiving transmitted signals may use the received signals to determine that a user contacted a particular part of his or her body. To illustrate, the second wearable device  102   b  may initially receive signals transmitted by the first wearable device  102   a  through the medium that have a first set of parameters (e.g., values of phase, amplitude, frequency, etc.). The second wearable device  102   b  may use these initial signals to form a normalized baseline. Thereafter, the wearer of the first and second wearable devices  102  may contact (e.g., touch) a region of her body (e.g., forearm) through which the transmitted signals are travelling. By touching her forearm for example, the wearer alters the signals travelling through her forearm, and in turn the first set of parameters associated with the signals (e.g., values of one or more of phase, amplitude, frequency, etc. may change). Importantly, the second wearable device  102   b  then receives (e.g., detects, senses) these altered signals and can subsequently determine that the user contacted a particular part of her body, e.g., her forearm. The second wearable device  102   b  may further determine that the user contacted a specific part of her forearm (e.g., a change in the phase value by a certain amount from the normalized baseline may indicate that a specific part of her forearm was touched). 
     The computer system  130  is a computing device that executes virtual reality applications and/or augmented reality applications to process input data from the sensors  145  on the head-mounted display  140  and the sensors  114  on the wearable device  102 . The computer system  130  provides output data to at least (i) the electronic display  144  on the head-mounted display  140  and (ii) the wearable device  102  (e.g., processors  104  of the haptic device  102 ,  FIG. 2A ). An exemplary computer system  130 , for example, includes one or more processor(s)/core(s)  132 , memory  134 , one or more communications components  136 , and/or one or more cameras  139 . In some embodiments, these components are interconnected by way of a communications bus  138 . References to these components of the computer system  130  cover embodiments in which one or more of these components (and combinations thereof) are included. 
     In some embodiments, the computer system  130  is a standalone device that is coupled to a head-mounted display  140 . For example, the computer system  130  has processor(s)/core(s)  132  for controlling one or more functions of the computer system  130  and the head-mounted display  140  has processor(s)/core(s)  141  for controlling one or more functions of the head-mounted display  140 . Alternatively, in some embodiments, the head-mounted display  140  is a component of computer system  130 . For example, the processor(s)  132  controls functions of the computer system  130  and the head-mounted display  140 . In addition, in some embodiments, the head-mounted display  140  includes the processor(s)  141  that communicate with the processor(s)  132  of the computer system  130 . In some embodiments, communications between the computer system  130  and the head-mounted display  140  occur via a wired (or wireless) connection between communications bus  138  and communications bus  146 . In some embodiments, the computer system  130  and the head-mounted display  140  share a single communications bus. It is noted that in some instances the head-mounted display  140  is separate from the computer system  130  (as shown in  FIG. 11 ). 
     The computer system  130  may be any suitable computer device, such as a laptop computer, a tablet device, a netbook, a personal digital assistant, a mobile phone, a smart phone, a virtual reality device (e.g., a virtual reality (VR) device, an augmented reality (AR) device, or the like), a gaming device, a computer server, or any other computing device. The computer system  130  is sometimes called a host or a host system. In some embodiments, the computer system  130  includes other user interface components such as a keyboard, a touch-screen display, a mouse, a track-pad, and/or any number of supplemental I/O devices to add functionality to computer system  130 . 
     In some embodiments, one or more cameras  139  of the computer system  130  are used to facilitate virtual reality and/or augmented reality. Moreover, in some embodiments, the one or more cameras  139  also act as projectors to display the virtual and/or augmented images (or in some embodiments the computer system includes one or more distinct projectors). In some embodiments, the computer system  130  provides images captured by the one or more cameras  139  to the display  144  of the head-mounted display  140 , and the display  144  in turn displays the provided images. In some embodiments, the processors  141  of the head-mounted display  140  process the provided images. It is noted that in some embodiments, one or more of the cameras  139  are part of the head-mounted display  140 . 
     The head-mounted display  140  presents media to a user. Examples of media presented by the head-mounted display  140  include images, video, audio, or some combination thereof. In some embodiments, audio is presented via an external device (e.g., speakers and/or headphones) that receives audio information from the head-mounted display  140 , the computer system  130 , or both, and presents audio data based on the audio information. The displayed images may be in virtual reality, augmented reality, or mixed reality. An exemplary head-mounted display  140 , for example, includes one or more processor(s)/core(s)  141 , a memory  142 , and/or one or more displays  144 . In some embodiments, these components are interconnected by way of a communications bus  146 . References to these components of the head-mounted display  140  cover embodiments in which one or more of these components (and combinations thereof) are included. It is noted that in some embodiments, the head-mounted display  140  includes one or more sensors  145 . Alternatively, in some embodiments, the one or more sensors  145  are part of the computer system  130 .  FIGS. 12 and 13  illustrate additional examples (e.g., AR system  1200  and VR system  1300 ) of the head-mounted display  140 . 
     The electronic display  144  displays images to the user in accordance with data received from the computer system  130 . In various embodiments, the electronic display  144  may comprise a single electronic display or multiple electronic displays (e.g., one display for each eye of a user). 
     The sensors  145  include one or more hardware devices that detect spatial and motion information about the head-mounted display  140 . Spatial and motion information can include information about the position, orientation, velocity, rotation, and acceleration of the head-mounted display  140 . For example, the sensors  145  may include one or more inertial measurement units (IMUs) that detect rotation of the user&#39;s head while the user is wearing the head-mounted display  140 . This rotation information can then be used (e.g., by the computer system  130 ) to adjust the images displayed on the electronic display  144 . In some embodiments, each IMU includes one or more gyroscopes, accelerometers, and/or magnetometers to collect the spatial and motion information. In some embodiments, the sensors  145  include one or more cameras positioned on the head-mounted display  140 . 
     In some embodiments, the transducer array  110  of the wearable device  102  may include one or more transducers configured to generate and/or receive signals. Integrated circuits (not shown) of the wearable device  102 , such as a controller circuit and/or signal generator (e.g., waveform generator), may control the behavior of the transducers (e.g., controller  412 ,  FIG. 4A ). 
     The communications component  112  of the wearable device  102  may include a communications component antenna for communicating with the computer system  130 . Moreover, the communications component  136  may include a complementary communications component antenna that communicates with the communications component  112 . The respective communication components are discussed in further detail below with reference to  FIGS. 2 and 3 . 
     In some embodiments, data contained within communication signals is used by the wearable device  102  for selecting and/or generating projection images. In some embodiments, the data contained within the communication signals alerts the computer system  130  that the wearable device  102  is ready for use. As will be described in more detail below, the computer system  130  sends instructions to the wearable device  102 , and in response to receiving the instructions, the wearable device generates projection images  602  that are displayed on an appendage of the user of the wearable device  102 . Alternatively or in addition, in some embodiments, the wearable device  102  sends signals to the computer device  130  that include information indicating a location of a touch on the user&#39;s body (or a position of an appendage with respect to a position of the wearable device). As explained above, a wearable device receiving signals transmitted by another wearable device is able to determine, based on changes of signal parameters caused by the touch, a location of the touch on the wearer&#39;s body. As one example, a keyboard (or some other user interface) may be projected or perceived to be projected onto the user&#39;s forearm, and the wearable device may determine, based on changes of signal parameters caused by the touch, that the user is intending to interact with a first affordance of the keyboard. In this way, the system  100  provides a novel way of determining where (and/or whether) a person contacts his or her skin (e.g., in combination with or separate from other video-based means for making this determination). This is particularly useful when augmented reality is being used, and actual images are not in fact projected onto the user&#39;s body. In another example, the wearable device may determine, based on changes of signal parameters, that the user touched her forearm. Information related to the touch may then be sent to the computer device  130 , and used by the computer device  130  to confirm that a touch occurred on the forearm. 
     Non-limiting examples of sensors  114  and/or sensors  145  include, e.g., infrared, pyroelectric, ultrasonic, microphone, laser, optical, Doppler, gyro, accelerometer, resonant LC sensors, capacitive sensors, acoustic sensors, and/or inductive sensors. In some embodiments, sensors  114  and/or sensors  145  are configured to gather data that is used to determine a hand posture of a user of the wearable device and/or an impedance of the medium. Examples of sensor data output by these sensors include: body temperature data, infrared range-finder data, motion data, activity recognition data, silhouette detection and recognition data, gesture data, heart rate data, and other wearable device data (e.g., biometric readings and output, accelerometer data). In some embodiments, the transducers themselves serve as sensors. 
       FIG. 1B  is a block diagram illustrating an embodiment of the system  100 , in accordance with various embodiments. The system  100  includes wearable devices  102   a ,  102   b , and  102   c  which are used in conjunction with a computer system  130  (e.g., a host system or a host computer). Wearable device  102   c  may be an additional device worn by the user to be used in conjunction with wearable devices  102   a  and  102   b . For example, the wearable device  102   c  may be a ring which may be used to determine a location of a touch gesture. In another example, the wearable device  102   a  and wearable device  102   c  may be distinct wristbands to be worn on each wrist of the user. In some embodiments, the system  100  provides the functionality of a virtual-reality device with image projection, an augmented reality device with image projection, a combination thereof, or provides some other functionality. In some embodiments, the wearable device  102   c  may include all or some of the features embodied in the wearable devices  102   a ,  102   b.    
       FIG. 2  is a block diagram illustrating a representative wearable device  102  in accordance with some embodiments. In some embodiments, the wearable device  102  includes one or more processing units (e.g., CPUs, microprocessors, and the like)  104 , one or more communication components  112 , memory  106 , one or more transducer arrays  110 , one or more projectors  115 , one or more cameras  118 , and one or more communication buses  108  for interconnecting these components (sometimes called a chipset). In some embodiments, the wearable device  102  includes one or more sensors  114  as described above with reference to  FIG. 1 . In some embodiments (not shown), the wearable device  102  includes one or more output devices such as one or more indicator lights, sound cards, speakers, displays for displaying textual information and error codes, etc. 
     Transducers in a respective transducer array  110  generate signals  116  ( FIG. 1 ). In some embodiments, the transducers may include, e.g., hardware capable of generating the signals  116  (e.g., electromagnetic waves, soundwaves, ultrasound waves, etc.). For example, each transducer can convert electrical signals into ultrasound waves. The transducers may be miniature piezoelectric transducers, capacitive transducers, single or multipole voice coil motors, and/or any other suitable device for creation of signals. Additionally, in some embodiments, the transducers can also receive signals (e.g., if the transducer can generate sound waves, it can also receive sound waves). Continuing, in some embodiments, the transducers may also be any of the sensors  114  described above with reference to  FIG. 1 . In some embodiments, a first wearable device  102   a  includes first transducers (e.g., transducers for receiving, sensing, detecting, etc.) while a second wearable  102   b  includes second transducers (e.g., transducers for generates signals to be sensed by the first transducers) distinct from the first transducers. 
     The communication component(s)  112  enable communication between the wearable device  102  and one or more communication networks. In some embodiments, the communication component(s)  112  include, e.g., hardware capable of data communications using any of a variety of wireless protocols (e.g., IEEE 802.15.4, Wi-Fi, ZigBee, 6LoWPAN, Thread, Z-Wave, Bluetooth Smart, ISA100.11a, WirelessHART, MiWi, etc.), wired protocols (e.g., Ethernet, HomePlug, etc.), and/or any other suitable communication protocol, including communication protocols not yet developed as of the filing date of this document. 
     The memory  106  includes high-speed random access memory, such as DRAM, SRAM, DDR SRAM, or other random access solid state memory devices; and, optionally, includes non-volatile memory, such as one or more magnetic disk storage devices, one or more optical disk storage devices, one or more flash memory devices, or one or more other non-volatile solid state storage devices. The memory  106 , or alternatively the non-volatile memory within memory  106 , includes a non-transitory computer-readable storage medium. In some embodiments, the memory  106 , or the non-transitory computer-readable storage medium of the memory  106 , stores the following programs, modules, and data structures, or a subset or superset thereof:
         operating logic  216  including procedures for handling various basic system services and for performing hardware dependent tasks;   communication module  218  for coupling to and/or communicating with remote devices (e.g., computer system  130 , other wearable devices, etc.) in conjunction with communication component(s)  112 ;   sensor module  220  for obtaining and processing sensor data (e.g., in conjunction with sensor(s)  114  and/or transducer arrays  110 ) to, for example, determine an orientation of the wearable device  102  and sensing signals generated by one or more transducers (among other purposes such as determining hand pose of the user of the wearable device);   signal generating module  222  for generating and transmitting (e.g., in conjunction with transducers(s)  110 ) signals. In some embodiments, the module  222  also includes or is associated with a data generation module  223  that is used to generate data corresponding to the received portion of the transmitted signals (e.g., data for a candidate touch event);   database  224 , including but not limited to:
           sensor information  226  for storing and managing data received, detected, and/or transmitted by one or more sensors (e.g., sensors  114 , one or more remote sensors, and/or transducer arrays  110 );   device settings  228  for storing operational settings for the wearable device  102  and/or one or more remote devices (e.g., selected characteristics/parameters values for the signals); and   communication protocol information  230  for storing and managing protocol information for one or more protocols (e.g., custom or standard wireless protocols, such as ZigBee, Z-Wave, etc., and/or custom or standard wired protocols, such as Ethernet);   
           projection module  232  for projecting one or more images onto an appendage of the wearer or user of the wearable device;   tactile gesture detection module  234  for detecting a touch gesture on the one or more projected images projected via projector  115 , including but not limited to:
           tactile location information  236  for detecting a location of the touch gesture on the one or more projected images; and   
           computer vision gesture detection module for detecting a touch gesture on the one or more projected images detected via camera  118 , including but not limited to:
           computer vision location information  240  for detecting a location of the touch gesture on the one or more projected images using computer vision analysis.   
               

     In some embodiments, the tactile gesture detection module  234  uses a known impedance map of the user&#39;s body, capacitive coupling technologies, signal processing techniques, and/or acoustic wave coupling (e.g., ultrasound waves) when determining a location of the touch gesture. In some embodiments, the tactile gesture detection module  234  communicates with the sensor module  220  to determine a location of the touch gesture on the user&#39;s body (e.g., based on the sensor data obtained by the sensor module  220 , the tactile gesture detection module  234  can determine a location of the touch gesture). In some embodiments, the tactile gesture detection module  234  and/or the computer vision gesture detection module  238  is (are) located at the computer system  130 . 
     In some embodiments, the location information  236 ,  240  is determined using computer vision technologies and/or non-optical imaging techniques using capacitance, magnetism, and millimeter wave technologies and/or acoustic wave coupling (e.g., ultrasound waves). 
     In some embodiments (not shown), the wearable device  102  includes a location detection device, such as a GNSS (e.g., GPS, GLONASS, etc.) or other geo-location receiver, for determining the location of the wearable device  102 . Further, in some embodiments, the wearable device  102  includes location detection module (e.g., a GPS, Wi-Fi, magnetic, or hybrid positioning module) for determining the location of the wearable device  102  (e.g., using the location detection device) and providing this location information to the host system  130 . 
     In some embodiments (not shown), the wearable device  102  includes a unique identifier stored in database  224 . In some embodiments, the wearable device  102  sends the unique identifier to the host system  130  to identify itself to the host system  130 . This is particularly useful when multiple wearable devices are being concurrently used. 
     Each of the above-identified elements (e.g., modules stored in memory  106  of the wearable device  102 ) is optionally stored in one or more of the previously mentioned memory devices, and corresponds to a set of instructions for performing the function(s) described above. The above identified modules or programs (e.g., sets of instructions) need not be implemented as separate software programs, procedures, or modules, and thus various subsets of these modules are optionally combined or otherwise rearranged in various embodiments. In some embodiments, the memory  106 , optionally, stores a subset of the modules and data structures identified above. Furthermore, the memory  106 , optionally, stores additional modules and data structures not described above. 
       FIG. 3  is a block diagram illustrating a representative computer system  130  in accordance with some embodiments. In some embodiments, the computer system  130  includes one or more processing units/cores (e.g., CPUs, GPUs, microprocessors, and the like)  132 , one or more communication components  136 , memory  134 , one or more cameras  139 , and one or more communication buses  308  for interconnecting these components (sometimes called a chipset). In some embodiments, the computer system  130  includes a head-mounted display interface  305  for connecting the computer system  130  with the head-mounted display  140 . As discussed above in  FIG. 1 , in some embodiments, the computer system  130  and the head-mounted display  140  are together in a single device, whereas in other embodiments the computer system  130  and the head-mounted display  140  are separate from one another. 
     Although not shown, in some embodiments, the computer system (and/or the head-mounted display  140 ) includes one or more sensors  145  (as discussed above with reference to  FIG. 1 ) and/or one or more instances of the transducer arrays  110 . 
     The communication component(s)  136  enable communication between the computer system  130  and one or more communication networks. In some embodiments, the communication component(s)  136  include, e.g., hardware capable of data communications using any of a variety of custom or standard wireless protocols (e.g., IEEE 802.15.4, Wi-Fi, ZigBee, 6LoWPAN, Thread, Z-Wave, Bluetooth Smart, ISA100.11a, WirelessHART, MiWi, etc.), custom or standard wired protocols (e.g., Ethernet, HomePlug, etc.), and/or any other suitable communication protocol, including communication protocols not yet developed as of the filing date of this document. 
     The memory  134  includes high-speed random access memory, such as DRAM, SRAM, DDR SRAM, or other random access solid state memory devices; and, optionally, includes non-volatile memory, such as one or more magnetic disk storage devices, one or more optical disk storage devices, one or more flash memory devices, or one or more other non-volatile solid state storage devices. The memory  134 , or alternatively the non-volatile memory within memory  134 , includes a non-transitory computer-readable storage medium. In some embodiments, the memory  134 , or the non-transitory computer-readable storage medium of the memory  134 , stores the following programs, modules, and data structures, or a subset or superset thereof:
         operating logic  316  including procedures for handling various basic system services and for performing hardware dependent tasks;   communication module  318  for coupling to and/or communicating with remote devices (e.g., wearable devices  102   a - 102 - n , a remote server (not shown), etc.) in conjunction with communication component(s)  136 ;   virtual-reality generation module  320  that is used for generating virtual-reality images and sending corresponding video and audio data to the HMD  140  (in some embodiments, the virtual-reality generation module  320  is an augmented-reality generation module  320  (or the memory  134  includes a distinct augmented-reality generation module) that is used for generating augmented-reality images and projecting those images in conjunction with the camera(s)  139  and the HMD  140 );   instruction module  322  that is used for generating an instruction that, when sent to the wearable device  102  (e.g., using the communications component  136 ), causes the wearable device  102  to activate two or more transducers;   display module  324  that is used for displaying virtual-reality images and/or augmented-reality images in conjunction with the head-mounted display  140  and/or the camera(s)  139 ;   computer vision gesture detection module  338  for detecting a touch gesture detected via camera  139 , including but not limited to:
           computer vision location information  340  for detecting a location of the touch gesture using computer vision analysis.   
           database  326 , including but not limited to:
           display information  328  for storing (and generating) virtual-reality images and/or augmented-reality images (e.g., visual data);   haptics information  330  for storing (and generating) haptics information that corresponds to displayed virtual-reality images and environments and/or augmented-reality images and environments;   communication protocol information  332  for storing and managing protocol information for one or more protocols (e.g., custom or standard wireless protocols, such as ZigBee, Z-Wave, etc., and/or custom or standard wired protocols, such as Ethernet); and   mapping data  334  for storing and managing mapping data (e.g., mapping one or more wearable devices  102  on a user).   
               

     In the example shown in  FIG. 3 , the computer system  130  further includes virtual-reality (and/or augmented-reality) applications  336 . In some embodiments, the virtual-reality applications  336  are implemented as software modules that are stored on the storage device and executed by the processor. Each virtual-reality application  336  is a group of instructions that, when executed by a processor, generates virtual or augmented reality content for presentation to the user. A virtual-reality application  336  may generate virtual/augmented-reality content in response to inputs received from the user via movement of the head-mounted display  140  or the wearable device  102 . Examples of virtual-reality applications  336  include gaming applications, conferencing applications, and video playback applications. 
     The virtual-reality generation module  320  is a software module that allows virtual-reality applications  336  to operate in conjunction with the head-mounted display  140  and the wearable device  102 . The virtual-reality generation module  320  may receive information from the sensors  145  on the head-mounted display  140  and may, in turn provide the information to a virtual-reality application  336 . Based on the received information, the virtual-reality generation module  320  determines media content to provide to the head-mounted display  140  for presentation to the user via the electronic display  144 . For example, if the virtual-reality generation module  320  receives information from the sensors  145  on the head-mounted display  140  indicating that the user has looked to the left, the virtual-reality generation module  320  generates content for the head-mounted display  140  that mirrors the user&#39;s movement in a virtual/augmented environment. An example VR system  1300  is provided in  FIG. 13 . 
     Similarly, in some embodiments, the virtual-reality generation module  320  receives information from the sensors  114  on the wearable device  102  and provides the information to a virtual-reality application  336 . The application  336  can use the information to perform an action within the virtual/augmented world of the application  336 . For example, if the virtual-reality generation module  320  receives information from the sensors  114  that the user has raised his hand, a simulated hand (e.g., the user&#39;s avatar) in the virtual-reality application  336  lifts to a corresponding height. As noted above, the information received by the virtual-reality generation module  320  can also include information from the head-mounted display  140 . For example, cameras  139  on the head-mounted display  140  may capture movements of the user (e.g., movement of the user&#39;s arm), and the application  336  can use this additional information to perform the action within the virtual/augmented world of the application  336 . 
     To further illustrate with an augmented reality example, if the augment-reality generation module  320  receives information from the sensors  114  that the user has rotated his forearm while, in augmented reality, a user interface (e.g., a keypad) is displayed on the user&#39;s forearm, the augmented-reality generation module  320  generates content for the head-mounted display  140  that mirrors the user&#39;s movement in the augmented environment (e.g., the user interface rotates in accordance with the rotation of the user&#39;s forearm). An example AR system  1200  is provided in  FIG. 12 . 
     In some embodiments, the computer system  130  receives sensor data from the wearable device  102  and the computer system  130  includes a module to determine a touch location associated with the sensor data. In some embodiments, the computer system  130  determines a touch location (e.g., using the computer vision gesture detection module  338 ) based on sensor data from the wearable device  102  and image data captured by the one or more camera  139 . In this way, a majority of the processing is offloaded from the wearable device  102  to the computer system  130 , which may have increased processing abilities. 
     Each of the above identified elements (e.g., modules stored in memory  134  of the computer system  130 ) is optionally stored in one or more of the previously mentioned memory devices, and corresponds to a set of instructions for performing the function(s) described above. The above identified modules or programs (e.g., sets of instructions) need not be implemented as separate software programs, procedures, or modules, and thus various subsets of these modules are optionally combined or otherwise rearranged in various embodiments. In some embodiments, the memory  134 , optionally, stores a subset of the modules and data structures identified above. 
       FIG. 4A  is an example view of the wearable device  102  in accordance with some embodiments. The example view shows the user&#39;s hand  408 , user&#39;s wrist  404 , user&#39;s arm  406 , and the wearable device  102  on the user&#39;s arm  406 . Such an arrangement is merely one possible arrangement, and one skilled in the art will appreciate that the discussion herein is not limited to the arrangement shown in  FIG. 4A . Additionally, the wearable device  102  shown in  FIG. 4A  is shown oversized for ease of illustration. In practice, a size of the wearable device  102  can be reduced, if desired, so that the wearable device  102  has a size similar to a smart watch or fitness tracker. 
     The wearable device  102  includes a wearable structure  402  that may be a flexible mechanical substrate such as a plastic (e.g., polyethylene or polypropylene), rubber, nylon, synthetic, polymer, etc. In some embodiments, the wearable structure  402  is configured to be worn around at least a portion of a user&#39;s wrist or arm  404 / 406  (and various other body parts). The wearable device  102  includes a transducer array  110 , including a plurality of transducers  410  arranged at different locations on the wearable structure  402 . The transducers  410  can be arranged in a pattern along an inner surface of the wearable structure  402  facing the arm  406  such that the transducers  410  contact the user&#39;s skin. In another example, the transducers can be arranged in a radial pattern along an inner perimeter of the wearable structure  502  ( FIG. 5 ). 
     In some embodiments, a respective transducer  410  is configured to generate signals (e.g., waves  116 ,  FIG. 1 ) in response to receiving one or more control signals from a controller (not shown). The one or more control signals instruct one or more transducers  410  in the transducer array  110  to send signals (e.g., ultrasonic waves) into/through the user&#39;s body (e.g., wrist or arm). The signals transmitted by the one or more transducers  410  are to travel (e.g., propagate, radiate) away from the wearable structure  402  through the user&#39;s body. For example, the signals may travel from the user&#39;s arm  406 , through the user&#39;s wrist  404 , to the user&#39;s hand  408  and fingers. In addition, the signals may travel up the user&#39;s arm and eventually travel throughout the user&#39;s body. 
     In some embodiments, the wearable structure  402  includes a projection unit  412  (e.g., projector  115 ,  FIG. 1A ) that projects images onto an appendage of a user. In some embodiments, the wearable structure  402  includes a memory (e.g., memory  106 ,  FIG. 1 ) that stores images to be displayed. For example, the stored images may represent a user interface having keyboard with multiple affordances (various other “touch” interfaces could also be projected onto the user&#39;s appendage). In some embodiments, the controller  412  generates a control signal (or multiple signals) based on an instruction from a host system (e.g., computer system  130 ,  FIG. 1 ). In such embodiments, the wearable device  102  is placed on a user&#39;s arm  406  (or various other locations) to project images onto the forearm  406  of the user. 
     Alternatively, in some embodiments, the wearable device  102  does not project images but instead, through the computer system  130  and the head-mounted display  140 , images are perceived on the user&#39;s arm (or other body part) through augmented reality. In such embodiments, the wearable device  102  is configured to sense interaction with the user&#39;s body. Put another way, the wearable device  102  is used to track a virtual image virtualized by another device (e.g., head-mounted display  140 ), as if the image were projected onto the user&#39;s arm. For example, a camera and/or projector of the other device (e.g., headset, glasses, head-mounted display  140 ) may project an image onto its own lens (e.g., display  144 ,  FIG. 1 ). Augmented reality technologies (e.g., AR system  1200 ,  FIG. 12 ) may implement such an embodiment. 
     In some embodiments, the other device tracks the user&#39;s arm  406  and adjusts the image (e.g., in augmented reality) in accordance with movements of the user&#39;s arm  406 . For example, cameras  139  may be used to track the user&#39;s arm  406 . 
     In some embodiments, the wearable devices  102  are worn in conjunction with one another. In some embodiments, the user may wear a single wearable device. 
     In some embodiments, the wearable devices  102  may be configured to interact with a computer system (e.g., computer system  130 ) that does not include a visual output. For example, wearable device  102  may be used to control settings on a phone while the user is on a call and unable to access the screen. 
     In some embodiments, the transducer array  110  includes transducers  410  designed to make contact with human skin. A contact area having a conductive agent  462  and padding may be used on the wearable device  102  behind each transducer to improve subject comfort and reduce contact impedances (e.g., as shown in  FIG. 5 ). The conductive agent between the transducer and skin may be a “wet” connection using a conductive gel, which may consist of propylene glycol and NaCl, or a “dry” connection, such as a thin layer of conductive polymer (e.g., carbon-doped PDMS). 
       FIG. 4B  is an example cross sectional view of the wearable device  120  taken along the X-Y line shown in  FIG. 4A , in accordance with some embodiments. The cross sectional view shows the user&#39;s arm  406  and a tendon  455  within the user&#39;s arm  406 . In this particular example, the transducers  410  do not fully wrap around the wrist (e.g., transducers  410 -A- 410 -D are disposed on one side of the user&#39;s arm  406 ). 
     One or more of the transducers  410 -A- 410 -D can generate signals (e.g., waves  454 -A and  454 -B) in the user&#39;s arm  406 . The generated signals  454 -A and  454 -B may extend into the user&#39;s body (e.g., extend into the epidermis, the dermis, the muscles, the tendons, the ligaments, the bones, etc.). In some embodiments, each transducer  410  varies one or more of a time period of the signal, an amplitude of the signal, and a phase of the signal when generating the signals. 
     To provide some content, the generated signals  454 -A,  454 -B, or a portion of the signals  454 -A,  454 -B, are reflected by the tendon  455  and/or a portion of the wearable structure  402 . As a result, the reflected signals  456 -A,  456 -B are received by the transducers  410 -A and  410 -D. In some instances, the same transducers that generate the signals do not receive the signals. While not shown in  FIG. 4B , one or more signals transmitted by the wearable device  400  may travel through the user&#39;s appendage and may be received (e.g., sensed) by a different wearable device attached to the user. 
     In some embodiments, the transducers  410  transmit signals into the user&#39;s body in a staggered manner, where different subsets of the transducers transmit signals at different times. In some embodiments, the remaining transducers may be used to measure the altered signals that they receive. This procedure may then be repeated for multiple stimulation patterns defining an order of transducers (e.g., pairs of transducers) selected to emit the signals. 
       FIG. 5  is an exemplary cross-sectional view of a wearable device in accordance with some embodiments. The wearable device  500  (e.g., wearable device  102 ,  FIG. 1A, 1B ) includes a wearable structure  502 . The wearable structure  502  wraps around the part of the user&#39;s body. The wearable device  500  further includes a transducer array  110  having a plurality of transducers  410  positioned along an inner perimeter of the wearable structure  502 . The transducers  410  in this example are radially spaced, such that the transducers  410  wrap around the wearable structure  502  and form a substantially contiguous circle of transducers. In such an arrangement, the wearable device  500  is able to produce signals  116  in a 360-degree fashion. In some embodiments, the wearable structure  502  separates the transducers  410  from the user&#39;s skin. Alternatively, in some embodiments (not shown), the transducers  410  are in direct contact with the user&#39;s skin (a conductive agent may also be included). In some embodiments, the wearable structure  502  includes one or more projectors  506  (e.g., projector  115 ,  FIG. 1A-1B ). 
     The wearable device  500  is configured to be attached to a part of a user&#39;s body. For example, the wearable device  500  is configured to be attached to a wrist, forearm, ankle, bicep, calf, thigh, scalp, and/or various other parts of the user&#39;s body. In some embodiments, the wearable device  500  is a rigid or semi-rigid structure. Alternatively, in some embodiments, the wearable device  500  is a flexible structure. Although the wearable device  500  is shown as a continuous circle, the wearable device  500  may break apart to be attached to the user&#39;s body (e.g., in a similar fashion to a watch). 
       FIG. 6A  is an exemplary view of a wearable device on a user&#39;s wrist and on the user&#39;s head in accordance with some embodiments. In some embodiments, the wearable device  102   a  is worn on the wrist of the user&#39;s arm and the wearable device  102   b  is worn on the head of the user. In some embodiments, the wearable device  102   a  uses one or more projectors  115  to project an image  602  onto the arm of the user. In some embodiments, the wearable device  102   b  includes a camera  118  used for computer vision. In some embodiments, computer vision is used to detect a general position of the wearable device  102   a  and/or the general position of the user&#39;s limb (e.g., hand, arm, fingers). In some embodiments, transducers  410  of the wearable device  102   a  may determine the magnitude and duration of a touch gesture (e.g., determine whether a user&#39;s finger is hovering over the skin, the user&#39;s finger is making direct contact with the skin). 
     In some embodiments, the wearable device  102   a  does not project images and instead the wearable device  102   b  is responsible for projecting image  602  (e.g., a user interface) onto the arm of the user. Alternatively, in some embodiments, the wearable device  102   b  uses augmented reality so that the user perceives the image  602  on his or her arm, but nothing is actually projected. It is noted that the wearable device  102   b  may be replaced with the computer system  130  (and the head-mounted display  140 ). Examples of the computer system  130  and the head-mounted display  140  are provided in  FIGS. 12 and 13 . AR system  1200  ( FIG. 12 ) and VR system  1300  ( FIG. 13 ) can be used to project/display images onto the user or areas around the user. 
       FIG. 6B  is an exemplary view of wearable devices on a user&#39;s wrist and on the user&#39;s finger, in accordance with some embodiments. In some embodiments, a first wearable device  102   a  is worn on the wrist of the user&#39;s arm and a second wearable device  102   c  is worn on a finger on the other arm of the user. In some embodiments, the first wearable device  102   a  uses one or more projectors  115  to project the image  602  onto the user&#39;s arm. Furthermore, the first wearable device  102   a  may use the one or more projectors  115  or one or more cameras  118  to detect touch gesture with respect to the projected image  602 . The touch gesture  804  may be one or more of a tap gesture, a swipe gesture, a pinch gesture, a pull gesture, a twist gesture, etc. on the user&#39;s body. In some embodiments, as noted above, the image  602  is not projected onto the use&#39;s arm by the wearable device  102   a . Instead, the image  602  is perceived in augmented reality. For example, a wearable device (e.g., head-mounted display  140 ) may display the image  602  onto one or more of the displays  144 . Furthermore, the computer system  130  is configured to adjust the display of the image  602  based on detected movement of the user&#39;s arm (discussed above with reference to  FIG. 3 ). 
       FIG. 6C  is an exemplary view of wearable devices on a user&#39;s first wrist and second wrist, in accordance with some embodiments. The arrangement of wearable devices  102  shown in  FIG. 6C  is used to detect a touch location  604  on the user&#39;s body. In some embodiments, a camera is used to detect the touch location  604 . Alternatively or in addition, in some embodiments, detected changes in signal parameters are used to detect the touch location  604  or, more broadly, that a touch occurred. 
     As shown, a first wearable device  102   a  is worn on the left wrist of the user&#39;s left arm and a second wearable device  102   c  is worn on the right wrist of the user&#39;s right arm. In some embodiments, the first and second wearable devices  102  are identical. For example, the first and second wearable devices  102  include the same arrangement and types of transducers  410 . Alternatively, in some embodiments, the first and second wearable devices  102  differ in some way. For example, transducers of the first wearable device  102   a  may differ from the transducers of the second wearable device  102   c . The first wearable device  102   a  may also include one or more sensors  114  that are not included in the second wearable device  102   c . Whether or not the first and second wearable device are identical, in some embodiments, the first wearable device  102   a  may be configured as a receiver and the second wearable device  102   c  may be configured as a transmitter (or vice versa). 
     It is noted that  FIG. 6C  may represent the user touching his left forearm or  FIG. 6C  may represent the user hovering his finger above his left forearm. It is also noted that signals generated by the second wearable device  102   c , at least in some instances, travel up the user&#39;s right arm, across the user&#39;s body, and down the user&#39;s left arm to be received by the first wearable device  102   a . Thus, even if the user is not touching his left forearm, the first wearable device  102   a  is still able to detect signals generated by the second wearable device  102   c . Importantly, by contacting his left forearm (or merely bringing his finger close to the left forearm), the user interferes with the signals traveling across his or her body (e.g., the signals that travel up the right arm and eventually down the left arm). In some instances, the first wearable device  102   a  is able to detect this interference and determine whether the detected interference satisfies contact criterion. Moreover, a magnitude of the detected interference may correspond to a particular event. For example, a large magnitude difference (i.e., a large interference) indicates that a touch occurred on the left forearm while a smaller magnitude difference (relative to the large magnitude different) (i.e., a small interference) may indicate that a hover event occurred. It is noted that hover events can be detected in a variety other ways as well. For example, in addition to the signals that travel up the user&#39;s right arm, across the user&#39;s body, and down the user&#39;s left arm to be received by the first wearable device  102   a , other signals generated by the second wearable device  102   b  can become capacitively coupled through the air when hand hovering occurs (e.g., right hand hovers above left arm). The capacitive coupling is detectable and can be classified as a “hover.” The capacitive coupling reading can have significant noise, which can contribute to the hover classification (e.g., noise is a factor considered when classifying an event as a hover event). Once the touch is made, the strength of the signal increases (e.g., significant jump detected) and can be classified as a “touch.” Additionally, the amount of noise decreases. 
       FIG. 6D  shows one example signal pathway  640  established between two wearable devices. In this example, the second wearable device  102   c  is transmitting one or more signals that couple into the wrist of the user and propagate (e.g., radiate) throughout the user&#39;s body. The first wearable device  102   a  receives at least some of the one or more signals transmitted by the second wearable device  102   c , and in doing so, establishes the signal pathway  640  between the first wearable device  102   a  and the second wearable device  102   c . It is noted that in other embodiments, the first wearable device  102   a  is the transmitter and the second wearable device  102   c  is the receiver. In such embodiments, the signal pathway  640  would be reversed (e.g., signals travel from left to right). The signal pathway  640  is discussed in further detail below with reference to  FIGS. 9 and 10 . 
       FIG. 7  is a flow diagram illustrating a method of projecting images onto a user&#39;s body in accordance with some embodiments. The steps of the method  700  may be performed by a first wearable device (e.g., a wearable device  102   a ,  FIGS. 1A-1B ), a second wearable device (e.g., wearable device  102   b ,  FIGS. 1A-1B ), and a computer system (e.g., computer system  130 ,  FIGS. 1A-1B ).  FIG. 7  corresponds to instructions stored in a computer memory or computer readable storage medium (e.g., memory  106  of the wearable device  102 ). For example, the operations of method  700  are performed, at least in part, by a communication module (e.g., communication module  218 ,  FIG. 2 ), a projection generation module (e.g., projection module  232 ,  FIG. 2 ), gesture detection modules (e.g., tactile gesture detection module  234 , computer vision gesture detection module  238 ,  FIG. 2 ), and/or location information modules (e.g., location information  236 ,  240 ,  FIG. 2 ). 
     At a first wearable device (e.g., wearable device  102   a ) having a projector (e.g., projector  115 ,  FIG. 2 ) and a plurality of transducers (e.g., transducers  410 ,  FIG. 4 ) the first wearable device projects  702  (e.g., using projection module  232 ,  FIG. 2 ), an image onto a portion of a first appendage (e.g., forearm) of a user of the first wearable device. The method further includes detecting  704  (e.g., via tactile gesture detection module  234 ) a touch gesture on the image by a second appendage of the user (e.g., a finger) distinct from the first appendage. 
     The method further comprises at a second wearable device (e.g., wearable device  102   b ) having a camera and a processor, determining  706  (e.g., via computer vision gesture detection module  238 ,  FIG. 2 ) a location (e.g., via location information  240 ,  FIG. 2 ) of the touch gesture on the image. In some embodiments, the second wearable device is an example the head-mounted device  140 , the computer system  130 , or a combination thereof. In some embodiments, the second wearable device (e.g., wearable device  102   b ) is integrated with one or more of the head-mounted device  140  and the computer system  130 . In some other embodiments, the second wearable device (e.g., wearable device  102   b ) is distinct from the head-mounted device  140  and the computer system  130 . In one example, the second wearable device is the AR system  1100  or the VR system  1200 . 
     In some embodiments, the second wearable device confirms  708  that the detected touch gesture has occurred on the image by the second appendage of the user. 
     The method further comprises a computer system (e.g., computer system  130 ,  FIGS. 1A-1B ) is instructed to perform  710  an operation in accordance with the detecting and the location. In some embodiments, the computer system performs  712  the operation in accordance with the confirming that the detected touch gesture has occurred on the image by the second appendage of the user. For example, with reference to  FIG. 6A , the first wearable device  102   a  projects the image  602  (e.g., user interface) onto the user&#39;s left forearm, and a second wearable device  102   b  worn on the user&#39;s head captures, via the camera  118 , the user&#39;s right index finger interacting with the projected image  602 . In this way, the second wearable device  102   b  determines a location of the touch gesture on the image (e.g., touch location  604  in  FIG. 6B ). Additionally, the first wearable device  102   a  is able to detect (sense) the right index finger interacting with the projected image  602  (e.g., sense the touch on the left forearm). Thus, the first and second wearable devices work together to detect the touch gesture on the image. Furthermore, the location of the touch gesture on the image may correspond to an affordance (or some other interface input), and the operation is associated with the affordance. 
       FIG. 8  is a flow diagram illustrating a method of projecting images onto a user&#39;s body in accordance with some embodiments. The steps of the method  800  may be performed by a first wearable device (e.g., a wearable device  102   a ,  FIGS. 1A-1B ), a second wearable device (e.g., wearable device  102   b ,  FIGS. 1A-1B ), a third wearable device (e.g., wearable device  102   c ,  FIG. 1B ) and a computer system (e.g., computer system  130 ,  FIGS. 1A-1B ).  FIG. 8  corresponds to instructions stored in a computer memory or computer readable storage medium (e.g., memory  106  of the wearable device  102 ). For example, the operations of method  800  are performed, at least in part, by a communication module (e.g., communication module  218 ,  FIG. 2 ), a projection generation module (e.g., projection module  232 ,  FIG. 2 ), gesture detection modules (e.g., tactile gesture detection module  234 , computer vision gesture detection module  238 ,  FIG. 2 ), and/or location information modules (e.g., location information  236 ,  240 ,  FIG. 2 ). It is noted that the steps of the method  800  can be performed in conjunction with the steps in method  700 . 
     In some embodiments, a first wearable device (e.g., wearable device  102   a ) projects  802  an image onto a portion of a first appendage of a user of the first wearable device. In some embodiments, the first wearable device generates  804  signals that couple/vibrate into at least a portion of the first appendage of the user of the first wearable device. For example,  FIG. 6C  shows a first wearable device on the left wrist of the user which may generate signals that vibrate through the user&#39;s left arm/wrist/hand/fingers. 
     In some embodiments, a third wearable device (e.g., wearable device  102   c ) receives  812  at least a portion of the signals generated by the first plurality of transducers when the first appendage is within a threshold distance from the third wearable device. For example,  FIG. 6C  shows a user having a first wearable device on the left wrist, and a second wearable device on the right wrist. The first wearable device generates signals through the left wrist which the second wearable device on the right wrist receives when the first and second wearable devices are proximate to each other. 
     In some embodiments, the third wearable device determines  814  a position of a portion of the first appendage with respect to a portion of the third wearable device. For example, the third wearable device may have transducers that receives signals from the first wearable device at specific locations of the third wearable device. The received signal information may be analyzed by the control circuit of the wearable device to determine a position of a portion of the left arm with respect to the right arm. 
     In some embodiments, a second wearable device determines  808  a location of the touch gesture on the image. In some embodiments, the second wearable device confirms  810  that the detected touch gesture has occurred on the image by the second appendage of the user. 
     In some embodiments, a computer system (e.g., computer system  130 ,  FIGS. 1A-1B ) is instructed to perform  816  an operation in accordance with the detecting, the position, and the location. In some embodiments, the computer system performs  818  the operation in accordance with the confirming that the detected touch gesture has occurred on the image by the second appendage of the user. 
       FIG. 9  is a high level flow diagram illustrating a method  900  of detecting a touch on a user&#39;s body in accordance with some embodiments. The steps of the method  900  may be performed by a first wearable device (e.g., instance of wearable device  102 ), a second wearable device (e.g., instance of wearable device  102 ), and a computer system (e.g., computer system  130 ).  FIG. 9  corresponds to instructions stored in a computer memory or computer readable storage medium. For ease of discussion, the first wearable device is attached to a first appendage of the user, such as the user&#39;s wrist. In some embodiments, the second wearable device is also attached to the first appendage, while in other embodiments the second wearable device is attached elsewhere on the user&#39;s body (e.g., the user&#39;s other wrist, on the user&#39;s head, or various other places on the user&#39;s body). It is also noted that, in some embodiments, the computer system and the second wearable device may be part of the same device, while in other embodiments the computer system and the second wearable device are separate from each other. 
     In some embodiments, the method  900  begins with the computer system initiating ( 902 ) a signal transmission from the second wearable device. For example, the computer system may provide instructions to the second wearable device to emit one or more signals (e.g., acoustic waves). In some embodiments, the computer system initiates the signal transmission when the computer system is powered up. The computer system may also initiate the signal transmission when a trigger event occurs in a VR/AR application being run by the computer system. For example, when a user reaches a particular stage in a video game, the computer system may initiate the signal transmission. 
     The method  900  may also include the computer system providing instructions to a head-mounted display (e.g., head-mounted display  140 ,  FIG. 1A ) to display a user interface or other graphics/image(s) (e.g., interface  602 ,  FIG. 6A ) on the first appendage of the user. As discussed above, the user interface may be projected onto the first appendage or presented, using augmented reality, via the head-mounted display so that the user perceives the user interface on the first appendage. In some embodiments, the user may perform an action that triggers display of the user interface (and initiation of the signal transmission). For example, with reference to  FIG. 6A , the user may move his arm and head to display positions (e.g., eyes pointed/aimed towards forearm while forearm is positioned in a viewing position). 
     Additionally, the computer system may receive motion information from sensors  114  of the first wearable device indicating that the user has moved (e.g., rotated) the first appendage while, in augmented reality (or virtual reality), a user interface (or some other augmented object) is being displayed on the user&#39;s first appendage. In such instances, the computer system generates content for the head-mounted display that mirrors and/or otherwise accounts for the user&#39;s movement in the augmented environment (e.g., the user interface in  FIG. 6A  rotates in accordance with the rotation of the user&#39;s forearm). In this way, the displayed user interface appears fixed to the first appendage. Moreover, the computer system may receive motion information from sensors  145  of the head-mounted display indicating that the user has moved his head while, in augmented reality (or virtual reality), the user interface is being displayed on the user&#39;s first appendage. In such instances, the computer system generates content for the head-mounted display that mirrors the user&#39;s movement in the augmented environment. 
     In some embodiments, the first and second wearable devices are transmitters and receivers. For example, when the first wearable device is attached to the user&#39;s left wrist and the second wearable device is attached to the user&#39;s right wrist, the first wearable device may act as a receiver and the second wearable device may act as a transmitter in first circumstances (e.g., when the user has his left arm and head in first display positions), while the first wearable device may act as a transmitter and the second wearable device may act as a receiver in second circumstances (e.g., when the user has his right arm and head in second display positions). In this way, the user can intuitively display a user interface (e.g., interface  602 ) on his left arm when desired, and leverage the first wearable device to confirm touches on the left arm, and also display another interface (or the same interface) on his right arm when desired, and leverage the second wearable device to confirm touches on the right arm. Accordingly, in some embodiments, the computer system determines that a respective appendage is in a predetermined display position (e.g., using at least the cameras  139 ) and that the user&#39;s head is aimed towards the respective appendage (e.g., using at least the cameras  139  or other sensors), and in response to making these determinations, the computer system instructs the head-mounted display to display a user interface on the respective appendage (e.g., as shown in  FIG. 6A ) and also instructs (step  902 ) at least one wearable device to emit signals, as described below. 
     The method  900  includes the second wearable device emitting ( 904 ) the one or more signals that propagate through at least the first appendage of the user (e.g., in response to receiving the instructions from the computer system). The method  900  also includes the first wearable device receiving ( 906 ) at least some of the one or more signals emitted by the second wearable device. In some embodiments, reception of the signals by the first wearable device establishes ( 908 ) a signal pathway between the first wearable device and the second wearable device. Furthermore, after establishing the signal path and while the second wearable device continues to emit the one or more signals, the method  900  further includes the first wearable device sensing ( 910 ) a change in the signal pathway (e.g., values of the set of signals received by the one or more transducers change). The sensed change in the signal pathway may be attributed to a touch event on the user&#39;s first appendage (e.g., user touches left forearm with right index finger) that interferes with the established signal pathway. In such a case, the first wearable device reports ( 912 ) a candidate touch event to the computer system. Alternatively, the sensed change in the signal pathway may be attributed to noise or some other non-touch event. In such a case, the first wearable device forgoes reporting a candidate touch event and continues to monitor the signal pathway. Method  1000 , discussed below, describes the operations of method  900  performed by the first wearable device in more detail. 
     The method  900  further includes the computer system capturing ( 914 ) the candidate touch event. For example, one or more of the cameras  139  of the computer system  130  may capture the user&#39;s right index finger movement towards the user&#39;s left forearm, as illustrated in  FIG. 6A . In some instances, capturing the touch candidate event includes capturing a location of the touch with respect to the displayed user interface. 
     In response to capturing the candidate touch event and receiving ( 916 ) the report of the candidate touch event from the first wearable device, the method  900  includes the computer system executing ( 918 ) a function associated with the candidate touch event. The computer system executes the function if it determines that the capturing of the candidate touch event and the report of the candidate touch event align (e.g., align in time and space). In other words, the report of the candidate touch event from the first wearable device is used by the computer system to confirm what the one or more cameras  139  captured (e.g., the cameras  139  may capture the touch location  604  ( FIG. 6C ) and the report of the candidate touch event from the first wearable device confirms contact with the left appendage). In this way, the computer system is able to distinguish a finger hovering above the user interface and a finger attempting to interact with the user interface (e.g., when a user merely hovers his finger above the interface, the cameras  139  alone struggle to distinguish the hovering from an actual touch event). In some embodiments, the displayed user interface includes one or more affordances, and the capturing of the candidate touch event indicates that the user intended to interact with a first affordance of the one or more affordances (e.g., interface  602  in  FIG. 6A  includes multiple affordances). In such embodiments, executing the function associated with the candidate touch event includes executing a function associated with the first affordance. 
       FIG. 10  is a flow diagram illustrating a method  1000  of confirming a touch on a user&#39;s body in accordance with some embodiments. The steps of the method  1000  may be performed by a first wearable device (e.g., instance of wearable device  102 ) that includes one or more transducers (e.g., transducers  410 ,  FIG. 4 ) ( 1001 ).  FIG. 10  corresponds to instructions stored in a computer memory or computer readable storage medium. For ease of discussion, the first wearable device is attached to a first appendage of the user, such as the user&#39;s wrist. It is noted that the steps of the method  1000  can be performed in conjunction with the steps in methods  700 ,  800 , and  900 . 
     In some embodiments, the method  1000  includes receiving ( 1002 ), by the one or more transducers of the first wearable device, a set of signals transmitted by a second wearable device attached to the user, where (i) receiving the set of signals creates a signal pathway between the first and second wearable devices, and (ii) signals in the set of signals propagate through at least the user&#39;s first appendage. In some embodiments, the second wearable device is also attached to the first appendage, while in other embodiments the second wearable device is attached elsewhere on the user&#39;s body (e.g., on another appendage or the user&#39;s head). To illustrate the signal pathway, with reference to  FIG. 6C , signals generated by the second wearable device  102   c , at least in some instances, travel (e.g., propagate, radiate) up the user&#39;s right arm, across the user&#39;s body, and down the user&#39;s left arm to be received by the first wearable device  102   a  (the generated signals at radiate towards the user&#39;s right-hand fingers). Thus, even if the user is not touching his left forearm with his right hand, the first wearable device  102   a  is still able to detect signals generated by the second wearable device  102   c . It is noted that the signals generated by the second wearable device  102   c  may propagate (radiate) throughout the user&#39;s entire body. 
     In some embodiments, the method  1000  includes determining ( 1004 ) baseline characteristics for the signal pathway created between the first wearable device and the second wearable device. The baseline characteristics may include values for phase, amplitude, frequency, etc. associated with the signals received by the first wearable device. Accordingly, in some embodiments, the baseline characteristics include a baseline phase value ( 1006 ), a baseline amplitude phase ( 1008 ), and/or a baseline frequency value (among other waveform characteristics). In some embodiments, the baseline characteristics are determined during a calibration process of the user, and it is noted that baseline characteristics may vary from user to user based on bodily differences between users (e.g., bodily tissue and bone structure will vary from user to user, creating different impedances to the signals radiating through the body). 
     In some embodiments, the method  1000  includes sensing (detecting, measuring) ( 1010 ) a change in the baseline characteristics while receiving the set of signals. For example, when the baseline characteristics include the baseline phase value, sensing the change in the baseline characteristics for the signal pathway includes detecting a phase value of the signal pathway that differs from the baseline phase value. In another example (or in addition to the previous example), when the baseline characteristics include the baseline amplitude value, sensing the change in the baseline characteristics for the signal pathway includes detecting an amplitude value of the signal pathway that differs from the baseline amplitude value. 
     In some embodiments, the method  1000  includes determining ( 1012 ) whether the sensed change in the baseline characteristics satisfies a contact criterion (or in some embodiments, contact criteria). To provide some context, in some instances, the sensed change in the baseline characteristics is attributable to a touch on the first appendage by the user that interferes with the established signal pathway (e.g., the touch impedes the signal pathway). Additionally, using the wearable device arrangement in  FIG. 6C  as an example, it is noted that when the user touches his left forearm with his right index finger, additional signals may propagate from the right index finger into the left forearm at the touch location, thereby causing (or at minimum contributing to) the interference of the signal pathway. However, in some other instances, the sensed change in the baseline characteristics is attributable to noise, or the user hovering his finger above the first appendage. Accordingly, the first wearable device compares the sensed change with contact criterion to distinguish intended touches from other events. 
     In some embodiments, in accordance with a determination that the sensed change in the baseline characteristics for the signal pathway does not satisfy the contact criterion ( 1012 —No), the method  1000  includes continuing to sense for changes in the baseline characteristics that may satisfy the contact criterion. Sensed changes in the baseline characteristics that do not satisfy the contact criterion may be attributable to noise or quick contacts (e.g., brushes) between appendages. In some embodiments, the contact criterion includes: (i) a touch criterion that is set to be satisfied by touches but not hovering events, and (ii) a hovering criterion that is set to be satisfied by hovering events but not touches. Various examples of the contact criterion are provided below. 
     In some embodiments, in accordance with a determination that the sensed change in the baseline characteristics for the signal pathway satisfies the contact criterion ( 1012 —Yes), the method  1000  includes reporting ( 1016 ) a candidate touch event on the user&#39;s first appendage. In some embodiments, reporting the candidate touch event includes sending a message (e.g., a report) to a computer system (e.g., computer system  130 ) that a candidate touch event was sensed and confirmed (i.e., a touch confirmed flag is sent). The message may also include a timestamp of when the change in the baseline characteristics were sensed (and/or a duration of the sensed change). The candidate touch event may be any one of a tap gesture, a swipe gesture, a pinch gesture, a pull gesture, or a twist gesture. It is also noted that, in some embodiments, the computer system and the second wearable device may be part of the same device, while in other embodiments the computer system and the second wearable device are separate from each other. 
     In some embodiments, the contact criterion includes a phase difference threshold. In such embodiments, reporting the candidate touch event is performed in accordance with a determination that a difference between the detected phase value (from step  1010 ) and the baseline phase value satisfies the phase difference threshold. In some embodiments, the contact criterion includes an amplitude difference threshold. In such embodiments, reporting the candidate touch event is performed in accordance with a determination that a difference between the detected amplitude value (from step  1010 ) and the baseline amplitude value satisfies the amplitude difference threshold. In another embodiment, the contact criteria include an amplitude difference threshold and a phase difference threshold. In such embodiments, reporting the candidate touch event is performed in accordance with a determination that: (i) a difference between the detected amplitude value and the baseline amplitude value satisfies the amplitude difference threshold, and (ii) a difference between the detected phase value and the baseline phase value satisfies the phase difference threshold. In addition to or separately from the embodiments above, the contact criterion may also include a time threshold. In such embodiments, sensing ( 1010 ) the change in the baseline characteristics includes sensing the change for a period of time (i.e., a duration of the sensed change is determined) and reporting the candidate touch event is performed in accordance with a determination that the period of time satisfies the time threshold. The time threshold can be used to filter out noise, as well as accidental/unintentional touching of the first appendage (e.g., a quick brushing of the first appendage with the second appendage can be filtered out). 
     As noted above, the contact criterion may include a touch criterion and a hovering criterion. In some embodiments, the contact criterion includes a first phase difference threshold for the touch criterion and a second phase difference threshold for the hovering criterion. The first phase difference threshold differs (e.g., is larger than) from that of the second phase difference threshold. Accordingly, in some embodiments, the method  1000  includes reporting a candidate hovering event in accordance with a determination that a difference between the detected phase value (from step  1010 ) and the baseline phase value satisfies the second phase difference threshold but does not satisfy the first phase threshold. The contact criterion can also include a first amplitude difference threshold for the touch criterion and a second amplitude difference threshold for the hovering criterion. The first amplitude difference threshold differs (e.g., is larger than) from that of the second amplitude difference threshold. The steps below discuss how the “candidate touch event” can similarly be performed in circumstances when the first wearable device reports a candidate hovering event instead of the candidate touch event. 
     In some embodiments, reporting the candidate touch event includes sending transducer (and/or sensor) data corresponding to the sensed change in the baseline characteristics to the computer system (e.g., computer system  130 ) ( 1018 ). In some embodiments, the transducer (and/or sensor) data includes a time stamp (and/or a duration) associated with sensing the change in the baseline characteristics. Additionally, in some embodiments, the transducer (and/or sensor) data includes the sensed change in the baseline characteristics (e.g., values for phase, amplitude, etc.). In some embodiments, the computer system uses the transducer (and/or sensor) data to confirm that a touch event occurred. Furthermore, in some embodiments, the computer system uses the transducer (and/or sensor) data to determine an approximate location of the candidate touch event on the user&#39;s first appendage. For example, the values for phase, amplitude, etc. may indicate the approximate location of the candidate touch event on the user&#39;s first appendage. 
     As discussed above with reference to the method  900 , the computer system may display, on the user&#39;s first appendage, a user interface that includes one or more affordances, and the candidate touch event may be associated with a first affordance of the one or more affordances included in the user interface. The computer system may use the data/information/report associated with the sensed change in the baseline characteristics to confirm whether a touch event with the displayed user interface occurred. Put another way, the computer system determines whether the user intended to interact with an affordance of the user interface displayed on the user&#39;s first appendage based, at least in part, on the data/information/report associated with the sensed change in the signal pathway received from the first wearable device. 
     In addition, the computer system may capture, via one or more cameras (e.g., cameras  139 ,  FIG. 1A ), the candidate touch event, and generate image data according to the capturing of the candidate touch event. In this way, the computer system may determine an approximate location of the candidate touch event on the user&#39;s first appendage based on the image data. Additionally, the computer system may determine whether the captured movements of the user amount to a candidate touch event (e.g., the second appendage comes within a threshold distance from the first appendage, or the second appendage visually obstructs a portion of the first appendage where the user interface is displayed). The computer system may then use data/information/report received from the first wearable device (step  1012 —Yes) to confirm that the candidate touch event is an actual touch event. The computer system then executes a function associated with the first affordance of the user interface (i) if the data/information/report associated with the sensed change in the signal pathway received from the first wearable device confirms that the user intended to interact with the first affordance and (ii) if the image data confirms that the user intended to interact with the first affordance. This dual confirmation process creates a robust approach to detecting touch events (and hovering events) with artificial user interfaces. 
     In some embodiments, if the computer system receives the reporting of the candidate touch event from the first wearable device within a time window of capturing the candidate touch event, the computer system executes the function. The time window may be a predefined time window. In some embodiments, the computer system tracks a time frame of when the candidate touch event could have occurred, based on the image data (i.e., generates a time frame of when the touch event could have occurred). In such embodiments, if the time stamp included in the data/information/report received from the first wearable device falls within the time frame, the computer system executes the function. It is noted that each of the one or more affordances of the displayed user interface may have a unique function. 
     In some embodiments, the transducer data sent to the computer system further includes information indicating an approximate location of the candidate touch event ( 1020 ). For example, the first wearable device may determine ( 1014 ) the approximate location of the candidate touch event on the user&#39;s first appendage based, at least in part, on the sensed change in the baseline characteristics. This can be accomplished by evaluating a phase value (and/or an amplitude value) of the signal pathway. For example, one or more first phase values (and/or one or more first amplitude values) may indicate that the user touched close to his wrist, whereas one or more second phase values (and/or one or more second amplitude values) different from the one or more first phase values (or the one or more first amplitude values) may indicate that the user touched close to his elbow. Additionally, in some embodiments, the first wearable device may include one or more cameras  118  that capture the candidate touch event. 
     In some embodiments, instead of the first wearable device monitoring changes in an established signal path, the first wearable device determines that a candidate touch event has occurred based on the baseline characteristics of the signal pathway. In other words, values of phase, amplitude, etc. of the set of signals received by the one or more transducers themselves may indicate that a candidate touch event has occurred. 
     Embodiments of the instant disclosure may include or be implemented in conjunction with various types of artificial reality systems. Artificial reality may constitute a form of reality that has been altered by virtual objects for presentation to a user. Such artificial reality may include and/or represent VR, AR, MR, hybrid reality, or some combination and/or variation of one or more of the same. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to a viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., to perform activities in) an artificial reality. 
     Artificial reality systems may be implemented in a variety of different form factors and configurations. Some artificial reality systems may be designed to work without near-eye displays (NEDs), an example of which is AR system  1100  in  FIG. 11 . Other artificial reality systems may include an NED that also provides visibility into the real world (e.g., AR system  1200  in  FIG. 12 ) or that visually immerses a user in an artificial reality (e.g., VR system  1300  in  FIG. 13 ). While some artificial reality devices may be self-contained systems, other artificial reality devices may communicate and/or coordinate with external devices to provide an artificial reality experience to a user. Examples of such external devices include handheld controllers, mobile devices, desktop computers, devices worn by a user (e.g., wearable device  102   a , wearable device  102   b , . . . wearable device  102   n ), devices worn by one or more other users, and/or any other suitable external system. 
       FIGS. 11-13  provide additional examples of the devices used in the system  100 . AR system  1100  in  FIG. 11  generally represents a wearable device dimensioned to fit about a body part (e.g., ahead) of a user. The AR system  1100  may include the functionality of the wearable device  102 , and may include additional functions. As shown, the AR system  1100  includes a frame  1102  (e.g., band) and a camera assembly  1104  that is coupled to frame  1102  and configured to gather information about a local environment by observing the local environment. The AR system  1100  may also include one or more transducers (e.g., instances of the transducers  410 ,  FIG. 4 ). In one example, the AR system  1100  includes output transducers  1108 (A) and  1108 (B) and input transducers  1110 . Output transducers  1108 (A) and  1108 (B) may provide audio feedback, haptic feedback, and/or content to a user, and input audio transducers may capture audio (or other signals/waves) in a user&#39;s environment. In some embodiments, the camera assembly  1104  includes one or more projectors (e.g., projectors  115 ) that allows the AR system  1100  to project images (e.g., if the AR system  1100  is worn on the user&#39;s wrist, then the camera assembly  1104  can project images onto the user&#39;s wrist and forearm). 
     Thus, the AR system  1100  does not include a near-eye display (NED) positioned in front of a user&#39;s eyes. AR systems without NEDs may take a variety of forms, such as head bands, hats, hair bands, belts, watches, wrist bands, ankle bands, rings, neckbands, necklaces, chest bands, eyewear frames, and/or any other suitable type or form of apparatus. While the AR system  1100  may not include an NED, the AR system  1100  may include other types of screens or visual feedback devices (e.g., a display screen integrated into a side of frame  1102 ). 
     The embodiments discussed in this disclosure may also be implemented in AR systems that include one or more NEDs. For example, as shown in  FIG. 12 , the AR system  1200  may include an eyewear device  1202  with a frame  1210  configured to hold a left display device  1215 (A) and a right display device  1215 (B) in front of a user&#39;s eyes. Display devices  1215 (A) and  1215 (B) may act together or independently to present an image or series of images to a user. While the AR system  1200  includes two displays, embodiments of this disclosure may be implemented in AR systems with a single NED or more than two NEDs. 
     In some embodiments, the AR system  1200  may include one or more sensors, such as sensor  1240 . Sensor  1240  may generate measurement signals in response to motion of AR system  1200  and may be located on substantially any portion of frame  1210 . Sensor  1240  may include a position sensor, an inertial measurement unit (IMU), a depth camera assembly, or any combination thereof. In some embodiments, the AR system  1200  may or may not include sensor  1240  or may include more than one sensor. In embodiments in which sensor  1240  includes an IMU, the IMU may generate calibration data based on measurement signals from sensor  1240 . Examples of sensor  1240  may include, without limitation, accelerometers, gyroscopes, magnetometers, other suitable types of sensors that detect motion, sensors used for error correction of the IMU, or some combination thereof. Sensors are also discussed above with reference to  FIG. 1  (e.g., sensors  145  of the head-mounted display  140 ). 
     The AR system  1200  may also include a microphone array with a plurality of acoustic sensors  1220 (A)- 1220 (J), referred to collectively as acoustic sensors  1220 . Acoustic sensors  1220  may be transducers that detect air pressure variations induced by sound waves. Each acoustic sensor  1220  may be configured to detect sound and convert the detected sound into an electronic format (e.g., an analog or digital format). The microphone array in  FIG. 12  may include, for example, ten acoustic sensors:  1220 (A) and  1220 (B), which may be designed to be placed inside a corresponding ear of the user, acoustic sensors  1220 (C),  1220 (D),  1220 (E),  1220 (F),  1220 (G), and  1220 (H), which may be positioned at various locations on frame  1210 , and/or acoustic sensors  1220 (I) and  1220 (J), which may be positioned on a corresponding neckband  1205 . In some embodiments, the neckband  1205  is an example of the computer system  130 . 
     The configuration of acoustic sensors  1220  of the microphone array may vary. While the AR system  1200  is shown in  FIG. 12  as having ten acoustic sensors  1220 , the number of acoustic sensors  1220  may be greater or less than ten. In some embodiments, using higher numbers of acoustic sensors  1220  may increase the amount of audio information collected and/or the sensitivity and accuracy of the audio information. In contrast, using a lower number of acoustic sensors  1220  may decrease the computing power required by a controller  1250  to process the collected audio information. In addition, the position of each acoustic sensor  1220  of the microphone array may vary. For example, the position of an acoustic sensor  1220  may include a defined position on the user, a defined coordinate on the frame  1210 , an orientation associated with each acoustic sensor, or some combination thereof. 
     Acoustic sensors  1220 (A) and  1220 (B) may be positioned on different parts of the user&#39;s ear, such as behind the pinna or within the auricle or fossa. Or, there may be additional acoustic sensors on or surrounding the ear in addition to acoustic sensors  1220  inside the ear canal. Having an acoustic sensor positioned next to an ear canal of a user may enable the microphone array to collect information on how sounds arrive at the ear canal. By positioning at least two of acoustic sensors  1220  on either side of a user&#39;s head (e.g., as binaural microphones), the AR device  1200  may simulate binaural hearing and capture a 3D stereo sound field around about a user&#39;s head. In some embodiments, the acoustic sensors  1220 (A) and  1220 (B) may be connected to the AR system  1200  via a wired connection, and in other embodiments, the acoustic sensors  1220 (A) and  1220 (B) may be connected to the AR system  1200  via a wireless connection (e.g., a Bluetooth connection). In still other embodiments, acoustic sensors  1220 (A) and  1220 (B) may not be used at all in conjunction with the AR system  1200 . 
     Acoustic sensors  1220  on frame  1210  may be positioned along the length of the temples, across the bridge, above or below display devices  1215 (A) and  1215 (B), or some combination thereof. Acoustic sensors  1220  may be oriented such that the microphone array is able to detect sounds in a wide range of directions surrounding the user wearing AR system  1200 . In some embodiments, an optimization process may be performed during manufacturing of AR system  1200  to determine relative positioning of each acoustic sensor  1220  in the microphone array. 
     The AR system  1200  may further include or be connected to an external device (e.g., a paired device), such as neckband  1205 . As shown, neckband  1205  may be coupled to eyewear device  1202  via one or more connectors  1230 . Connectors  1230  may be wired or wireless connectors and may include electrical and/or non-electrical (e.g., structural) components. In some cases, eyewear device  1202  and neckband  1205  may operate independently without any wired or wireless connection between them. While  FIG. 12  illustrates the components of eyewear device  1202  and neckband  1205  in example locations on eyewear device  1202  and neckband  1205 , the components may be located elsewhere and/or distributed differently on eyewear device  1202  and/or neckband  1205 . In some embodiments, the components of eyewear device  1202  and neckband  1205  may be located on one or more additional peripheral devices paired with eyewear device  1202 , neckband  1205 , or some combination thereof. Furthermore, neckband  1205  generally represents any type or form of paired device. Thus, the following discussion of neckband  1205  may also apply to various other paired devices, such as smart watches, smart phones, wrist bands, other wearable devices, hand-held controllers, tablet computers, laptop computers, etc. 
     Pairing external devices, such as neckband  1205 , with AR eyewear devices may enable the eyewear devices to achieve the form factor of a pair of glasses while still providing sufficient battery and computation power for expanded capabilities. Some or all of the battery power, computational resources, and/or additional features of the AR system  1200  may be provided by a paired device or shared between a paired device and an eyewear device, thus reducing the weight, heat profile, and form factor of the eyewear device overall while still retaining desired functionality. For example, neckband  1205  may allow components that would otherwise be included on an eyewear device to be included in neckband  1205  since users may tolerate a heavier weight load on their shoulders than they would tolerate on their heads. Neckband  1205  may also have a larger surface area over which to diffuse and disperse heat to the ambient environment. Thus, neckband  1205  may allow for greater battery and computation capacity than might otherwise have been possible on a stand-alone eyewear device. Since weight carried in neckband  1205  may be less invasive to a user than weight carried in eyewear device  1202 , a user may tolerate wearing a lighter eyewear device and carrying or wearing the paired device for greater lengths of time than the user would tolerate wearing a heavy standalone eyewear device, thereby enabling an artificial reality environment to be incorporated more fully into a user&#39;s day-to-day activities. 
     Neckband  1205  may be communicatively coupled with eyewear device  1202  and/or to other devices. The other devices may provide certain functions (e.g., tracking, localizing, depth mapping, processing, storage, etc.) to the AR system  1200 . In the embodiment of  FIG. 12 , neckband  1205  may include two acoustic sensors (e.g.,  1220 (I) and  1220 (J)) that are part of the microphone array (or potentially form their own microphone subarray). Neckband  1205  may also include a controller  1225  and a power source  1235 . 
     Acoustic sensors  1220 (I) and  1220 (J) of neckband  1205  may be configured to detect sound and convert the detected sound into an electronic format (analog or digital). In the embodiment of  FIG. 12 , acoustic sensors  1220 (I) and  1220 (J) may be positioned on neckband  1205 , thereby increasing the distance between neckband acoustic sensors  1220 (I) and  1220 (J) and other acoustic sensors  1220  positioned on eyewear device  1202 . In some cases, increasing the distance between acoustic sensors  1220  of the microphone array may improve the accuracy of beamforming performed via the microphone array. For example, if a sound is detected by acoustic sensors  1220 (C) and  1220 (D) and the distance between acoustic sensors  1220 (C) and  1220 (D) is greater than, e.g., the distance between acoustic sensors  1220 (D) and  1220 (E), the determined source location of the detected sound may be more accurate than if the sound had been detected by acoustic sensors  1220 (D) and  1220 (E). 
     Controller  1225  of neckband  1205  may process information generated by the sensors on neckband  1205  and/or AR system  1200 . For example, controller  1225  may process information from the microphone array that describes sounds detected by the microphone array. For each detected sound, controller  1225  may perform a direction of arrival (DOA) estimation to estimate a direction from which the detected sound arrived at the microphone array. As the microphone array detects sounds, controller  1225  may populate an audio data set with the information. In embodiments in which AR system  1200  includes an IMU, controller  1225  may compute all inertial and spatial calculations from the IMU located on eyewear device  1202 . Connector  1230  may convey information between AR system  1200  and neckband  1205  and between AR system  1200  and controller  1225 . The information may be in the form of optical data, electrical data, wireless data, or any other transmittable data form. Moving the processing of information generated by AR system  1200  to neckband  1205  may reduce weight and heat in eyewear device  1202 , making it more comfortable to a user. 
     Power source  1235  in neckband  1205  may provide power to eyewear device  1202  and/or to neckband  1205 . Power source  1235  may include, without limitation, lithium-ion batteries, lithium-polymer batteries, primary lithium batteries, alkaline batteries, or any other form of power storage. In some cases, power source  1235  may be a wired power source. Including power source  1235  on neckband  1205  instead of on eyewear device  1202  may help better distribute the weight and heat generated by power source  1235 . 
     As noted, some artificial reality systems may, instead of blending an artificial reality with actual reality, substantially replace one or more of a user&#39;s sensory perceptions of the real world with a virtual experience. One example of this type of system is a head-worn display system, such as VR system  1300  in  FIG. 13 , that mostly or completely covers a user&#39;s field of view. VR system  1300  may include a front rigid body  1302  and a band  1304  shaped to fit around a user&#39;s head. VR system  1300  may also include output audio transducers  1306 (A) and  1306 (B). Furthermore, while not shown in  FIG. 13 , front rigid body  1302  may include one or more electronic elements, including one or more electronic displays, one or more IMUs, one or more tracking emitters or detectors, and/or any other suitable device or system for creating an artificial reality experience. Although not shown, the VR system  1300  may include the computer system  130 . 
     Artificial reality systems may include a variety of types of visual feedback mechanisms. For example, display devices in AR system  1200  and/or VR system  1300  may include one or more liquid-crystal displays (LCDs), light emitting diode (LED) displays, organic LED (OLED) displays, and/or any other suitable type of display screen. Artificial reality systems may include a single display screen for both eyes or may provide a display screen for each eye, which may allow for additional flexibility for varifocal adjustments or for correcting a user&#39;s refractive error. Some artificial reality systems may also include optical subsystems having one or more lenses (e.g., conventional concave or convex lenses, Fresnel lenses, adjustable liquid lenses, etc.) through which a user may view a display screen. 
     In addition to or instead of using display screens, some artificial reality systems may include one or more projection systems. For example, display devices in AR system  1200  and/or VR system  1300  may include micro-LED projectors that project light (using, e.g., a waveguide) into display devices, such as clear combiner lenses that allow ambient light to pass through. The display devices may refract the projected light toward a user&#39;s pupil and may enable a user to simultaneously view both artificial reality content and the real world. Artificial reality systems may also be configured with any other suitable type or form of image projection system. 
     Artificial reality systems may also include various types of computer vision components and subsystems. For example, AR system  1100 , AR system  1200 , and/or VR system  1300  may include one or more optical sensors such as two-dimensional (2D) or three-dimensional (3D) cameras, time-of-flight depth sensors, single-beam or sweeping laser rangefinders, 3D LiDAR sensors, and/or any other suitable type or form of optical sensor. An artificial reality system may process data from one or more of these sensors to identify a location of a user, to map the real world, to provide a user with context about real-world surroundings, and/or to perform a variety of other functions. 
     Artificial reality systems may also include one or more input and/or output audio transducers. In the examples shown in  FIGS. 11 and 13 , output audio transducers  1108 (A),  1108 (B),  1106 (A), and  1306 (B) may include voice coil speakers, ribbon speakers, electrostatic speakers, piezoelectric speakers, bone conduction transducers, cartilage conduction transducers, and/or any other suitable type or form of audio transducer. Similarly, input audio transducers  1110  may include condenser microphones, dynamic microphones, ribbon microphones, and/or any other type or form of input transducer. In some embodiments, a single transducer may be used for both audio input and audio output. 
     The artificial reality systems shown in  FIGS. 11-13  may include tactile (i.e., haptic) feedback systems, which may be incorporated into headwear, gloves, body suits, handheld controllers, environmental devices (e.g., chairs, floormats, etc.), and/or any other type of device or system, such as the wearable devices  102  discussed herein. Additionally, in some embodiments, the haptic feedback systems may be incorporated with the artificial reality systems (e.g., the AR system  1100  may include the wearable device  102  ( FIG. 1 ). Haptic feedback systems may provide various types of cutaneous feedback, including vibration, force, traction, texture, and/or temperature. Haptic feedback systems may also provide various types of kinesthetic feedback, such as motion and compliance. Haptic feedback may be implemented using motors, piezoelectric actuators, fluidic systems, and/or a variety of other types of feedback mechanisms. Haptic feedback systems may be implemented independent of other artificial reality devices, within other artificial reality devices, and/or in conjunction with other artificial reality devices. 
     By providing haptic sensations, audible content, and/or visual content, artificial reality systems may create an entire virtual experience or enhance a user&#39;s real-world experience in a variety of contexts and environments. For instance, artificial reality systems may assist or extend a user&#39;s perception, memory, or cognition within a particular environment. Some systems may enhance a user&#39;s interactions with other people in the real world or may enable more immersive interactions with other people in a virtual world. Artificial reality systems may also be used for educational purposes (e.g., for teaching or training in schools, hospitals, government organizations, military organizations, business enterprises, etc.), entertainment purposes (e.g., for playing video games, listening to music, watching video content, etc.), and/or for accessibility purposes (e.g., as hearing aids, vision aids, etc.). The embodiments disclosed herein may enable or enhance a user&#39;s artificial reality experience in one or more of these contexts and environments and/or in other contexts and environments. 
     Some AR systems may map a user&#39;s environment using techniques referred to as “simultaneous location and mapping” (SLAM). SLAM mapping and location identifying techniques may involve a variety of hardware and software tools that can create or update a map of an environment while simultaneously keeping track of a device&#39;s or a user&#39;s location and/or orientation within the mapped environment. SLAM may use many different types of sensors to create a map and determine a device&#39;s or a user&#39;s position within the map. 
     SLAM techniques may, for example, implement optical sensors to determine a device&#39;s or a user&#39;s location, position, or orientation. Radios including WiFi, Bluetooth, global positioning system (GPS), cellular or other communication devices may also be used to determine a user&#39;s location relative to a radio transceiver or group of transceivers (e.g., a WiFi router or group of GPS satellites). Acoustic sensors such as microphone arrays or 2D or 3D sonar sensors may also be used to determine a user&#39;s location within an environment. AR and VR devices (such as systems  1100 ,  1200 , and  1300 ) may incorporate any or all of these types of sensors to perform SLAM operations such as creating and continually updating maps of a device&#39;s or a user&#39;s current environment. In at least some of the embodiments described herein, SLAM data generated by these sensors may be referred to as “environmental data” and may indicate a device&#39;s or a user&#39;s current environment. This data may be stored in a local or remote data store (e.g., a cloud data store) and may be provided to a user&#39;s AR/VR device on demand. 
     When the user is wearing an AR headset or VR headset in a given environment, the user may be interacting with other users or other electronic devices that serve as audio sources. In some cases, it may be desirable to determine where the audio sources are located relative to the user and then present the audio sources to the user as if they were coming from the location of the audio source. The process of determining where the audio sources are located relative to the user may be referred to herein as “localization,” and the process of rendering playback of the audio source signal to appear as if it is coming from a specific direction may be referred to herein as “spatialization.” 
     Localizing an audio source may be performed in a variety of different ways. In some cases, an AR or VR headset may initiate a DOA analysis to determine the location of a sound source. The DOA analysis may include analyzing the intensity, spectra, and/or arrival time of each sound at the AR/VR device to determine the direction from which the sound originated. In some cases, the DOA analysis may include any suitable algorithm for analyzing the surrounding acoustic environment in which the artificial reality device is located. 
     For example, the DOA analysis may be designed to receive input signals from a microphone and apply digital signal processing algorithms to the input signals to estimate the direction of arrival. These algorithms may include, for example, delay and sum algorithms where the input signal is sampled, and the resulting weighted and delayed versions of the sampled signal are averaged together to determine a direction of arrival. A least mean squared (LMS) algorithm may also be implemented to create an adaptive filter. This adaptive filter may then be used to identify differences in signal intensity, for example, or differences in time of arrival. These differences may then be used to estimate the direction of arrival. In another embodiment, the DOA may be determined by converting the input signals into the frequency domain and selecting specific bins within the time-frequency (TF) domain to process. Each selected TF bin may be processed to determine whether that bin includes a portion of the audio spectrum with a direct-path audio signal. Those bins having a portion of the direct-path signal may then be analyzed to identify the angle at which a microphone array received the direct-path audio signal. The determined angle may then be used to identify the direction of arrival for the received input signal. Other algorithms not listed above may also be used alone or in combination with the above algorithms to determine DOA. 
     In some embodiments, different users may perceive the source of a sound as coming from slightly different locations. This may be the result of each user having a unique head-related transfer function (HRTF), which may be dictated by a user&#39;s anatomy including ear canal length and the positioning of the ear drum. The artificial reality device may provide an alignment and orientation guide, which the user may follow to customize the sound signal presented to the user based on their unique HRTF. In some embodiments, an AR or VR device may implement one or more microphones to listen to sounds within the user&#39;s environment. The AR or VR device may use a variety of different array transfer functions (ATFs) (e.g., any of the DOA algorithms identified above) to estimate the direction of arrival for the sounds. Once the direction of arrival has been determined, the artificial reality device may play back sounds to the user according to the user&#39;s unique HRTF. Accordingly, the DOA estimation generated using an ATF may be used to determine the direction from which the sounds are to be played from. The playback sounds may be further refined based on how that specific user hears sounds according to the HRTF. 
     In addition to or as an alternative to performing a DOA estimation, an artificial reality device may perform localization based on information received from other types of sensors. These sensors may include cameras, infrared radiation (IR) sensors, heat sensors, motion sensors, global positioning system (GPS) receivers, or in some cases, sensor that detect a user&#39;s eye movements. For example, an artificial reality device may include an eye tracker or gaze detector that determines where a user is looking. Often, a user&#39;s eyes will look at the source of a sound, if only briefly. Such clues provided by the user&#39;s eyes may further aid in determining the location of a sound source. Other sensors such as cameras, heat sensors, and IR sensors may also indicate the location of a user, the location of an electronic device, or the location of another sound source. Any or all of the above methods may be used individually or in combination to determine the location of a sound source and may further be used to update the location of a sound source over time. 
     Some embodiments may implement the determined DOA to generate a more customized output audio signal for the user. For instance, an acoustic transfer function may characterize or define how a sound is received from a given location. More specifically, an acoustic transfer function may define the relationship between parameters of a sound at its source location and the parameters by which the sound signal is detected (e.g., detected by a microphone array or detected by a user&#39;s ear). An artificial reality device may include one or more acoustic sensors that detect sounds within range of the device. A controller of the artificial reality device may estimate a DOA for the detected sounds (using, e.g., any of the methods identified above) and, based on the parameters of the detected sounds, may generate an acoustic transfer function that is specific to the location of the device. This customized acoustic transfer function may thus be used to generate a spatialized output audio signal where the sound is perceived as coming from a specific location. 
     Indeed, once the location of the sound source or sources is known, the artificial reality device may re-render (i.e., spatialize) the sound signals to sound as if coming from the direction of that sound source. The artificial reality device may apply filters or other digital signal processing that alter the intensity, spectra, or arrival time of the sound signal. The digital signal processing may be applied in such a way that the sound signal is perceived as originating from the determined location. The artificial reality device may amplify or subdue certain frequencies or change the time that the signal arrives at each ear. In some cases, the artificial reality device may create an acoustic transfer function that is specific to the location of the device and the detected direction of arrival of the sound signal. In some embodiments, the artificial reality device may re-render the source signal in a stereo device or multi-speaker device (e.g., a surround sound device). In such cases, separate and distinct audio signals may be sent to each speaker. Each of these audio signals may be altered according to a user&#39;s HRTF and according to measurements of the user&#39;s location and the location of the sound source to sound as if they are coming from the determined location of the sound source. Accordingly, in this manner, the artificial reality device (or speakers associated with the device) may re-render an audio signal to sound as if originating from a specific location. 
     Although some of various drawings illustrate a number of logical stages in a particular order, stages which are not order dependent may be reordered and other stages may be combined or broken out. While some reordering or other groupings are specifically mentioned, others will be obvious to those of ordinary skill in the art, so the ordering and groupings presented herein are not an exhaustive list of alternatives. Moreover, it should be recognized that the stages could be implemented in hardware, firmware, software or any combination thereof. 
     The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the scope of the claims to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen in order to best explain the principles underlying the claims and their practical applications, to thereby enable others skilled in the art to best use the embodiments with various modifications as are suited to the particular uses contemplated. 
     It is noted that the embodiments disclosed herein can also be combined with any of the embodiments described in U.S. Provisional Application No. 62/647,559, filed Mar. 23, 2018, entitled “Methods, Devices, and Systems for Determining Contact On a User of a Virtual Reality and/or Augmented Reality Device;” U.S. Provisional Application No. 62/636,699, filed Feb. 28, 2018, entitled “Methods, Devices, and Systems for Creating Haptic Stimulations and Tracking Motion of a User;” and U.S. Provisional Application No. 62/614,790, filed Jan. 8, 2018, entitled “Methods, Devices, and Systems for Creating Localized Haptic Sensations on a User.” 
     It also is noted that the embodiments disclosed herein can also be combined with any of the embodiments described in U.S. Utility patent application Ser. No. 15/241,871, entitled “Methods, Devices, and Systems for Creating Haptic Stimulations and Tracking Motion of a User,” filed Jan. 7, 2019, U.S. Utility patent application Ser. No. 16/241,890, entitled “Methods, Devices, and Systems for Determining Contact On a User of a Virtual Reality and/or Augmented Reality Device,” filed Jan. 7, 2019, and U.S. Utility patent application Ser. No. 16/241,900, entitled “Methods, Devices, and Systems for Creating Localized Haptic Sensations on a User,” filed Jan. 7, 2019.