PATENT DOCUMENT

Publication Number: US-11347355-B2
Application Number: US-201815989063-A
Country: US
Kind Code: B2

Title: System and method for acoustic touch and force sensing

Abstract:
Acoustic touch and/or force sensing system architectures and methods for acoustic touch and/or force sensing can be used to detect a position of an object touching a surface and an amount of force applied to the surface by the object. The position and/or an applied force can be determined using time-of-flight (TOF) techniques, for example. Acoustic touch sensing can utilize transducers (e.g., piezoelectric) to simultaneously transmit ultrasonic waves along a surface and through a thickness of a deformable material. The location of the object and the applied force can be determined based on the amount of time elapsing between the transmission of the waves and receipt of the reflected waves. In some examples, an acoustic touch sensing system can be insensitive to water contact on the device surface, and thus acoustic touch sensing can be used for touch sensing in devices that may become wet or fully submerged in water.

Claims:
What is claimed is: 
     
       1. A touch and force sensitive device, comprising:
 a surface; 
 a deformable material disposed between the surface and a rigid material, such that force on the surface causes a deformation of the deformable material; 
 one or more transducers coupled between the surface and the deformable material and configured to transmit ultrasonic waves to and receive ultrasonic waves from the surface and the deformable material; and 
 a processor configured to:
 determine a location of a contact by an object on the surface based on ultrasonic waves propagating in the surface; and 
 determine an applied force by the contact on the surface based on ultrasonic waves propagating in the deformable material. 
 
 
     
     
       2. The device of  claim 1 , wherein the surface comprises a glass or sapphire external surface of the device, the rigid material comprises a portion of a metal housing of the device, and the deformable material forms a gasket between the metal housing and the surface. 
     
     
       3. The device of  claim 1 , wherein the one or more transducers comprises at least a first transducer coupled to the deformable material and configured to transmit an ultrasonic wave through a thickness of the deformable material. 
     
     
       4. The device of  claim 3 , wherein the first transducer is also configured to receive one or more ultrasonic reflections from a boundary between the deformable material and the rigid material. 
     
     
       5. The device of  claim 3 , wherein the one or more transducers comprises at least a second transducer coupled between the deformable material and the rigid material and configured to receive the ultrasonic wave transmitted through the thickness of the deformable material. 
     
     
       6. The device of  claim 1 , wherein the one or more transducers comprises at least one transducer configured to simultaneously transmit an ultrasonic wave in the surface and an ultrasonic wave through the deformable material. 
     
     
       7. The device of  claim 1 , wherein the one or more transducers comprises four transducers, wherein each of the four transducers is disposed proximate to a respective edge of the surface. 
     
     
       8. The device of  claim 1 , further comprising an ultrasonic absorbent material coupled to the deformable material, the ultrasonic absorbent material configured to dampen ultrasonic ringing in the deformable material. 
     
     
       9. The device of  claim 1 , wherein determining the location of the contact by the object on the surface comprises:
 determining a first time-of-flight of an ultrasonic wave propagating between a first edge the surface and a first leading edge of the object proximate to the first edge; 
 determining a second time-of-flight of an ultrasonic wave propagating between a second edge the surface and a second leading edge of the object proximate to the second edge; 
 determining a third time-of-flight of an ultrasonic wave propagating between a third edge the surface and a third leading edge of the object proximate to the third edge; and 
 determining a fourth time-of-flight of an ultrasonic wave propagating between a fourth edge the surface and a fourth leading edge of the object proximate to the fourth edge. 
 
     
     
       10. The device of  claim 1 , wherein determining the applied force by the contact on the surface comprises:
 determining a time-of-flight of an ultrasonic wave propagating from a first side of the deformable material and reflecting off of a second side, opposite the first side, of the deformable material. 
 
     
     
       11. A method comprising:
 at a device comprising one or more transducers coupled between a surface and a deformable material:
 transmitting ultrasonic waves in the surface; 
 receiving ultrasonic reflections from the surface; 
 transmitting ultrasonic waves through the deformable material; 
 receiving ultrasonic reflections from the deformable material; 
 determining a position of an object in contact with the surface from the ultrasonic reflections received from the surface; and 
 determining a force applied by the object in contact with the surface from the ultrasonic reflections received from the deformable material. 
 
 
     
     
       12. The method of  claim 11 , wherein at least one of the ultrasonic waves transmitted in the surface and at least one of the ultrasonic waves transmitted in the deformable material are transmitted simultaneously. 
     
     
       13. The method of  claim 12 , wherein the at least one of the ultrasonic waves transmitted in the surface and the at least one of the ultrasonic waves transmitted in the deformable material are transmitted by a common transducer of the one or more transducers. 
     
     
       14. The method of  claim 11 , further comprising:
 determining a time-of-flight through the deformable material based on a time difference between transmitting an ultrasonic wave through the deformable material and receiving an ultrasonic reflection from the deformable material, wherein the force applied by the object is determined based on the time-of-flight through the deformable material. 
 
     
     
       15. The method of  claim 14 , wherein the ultrasonic reflection from the deformable material results from the ultrasonic wave transmitted through the deformable material reaching a boundary between the deformable material and a rigid material. 
     
     
       16. The method of  claim 14 , wherein the ultrasonic reflection from the deformable material is received before the ultrasonic reflection from the surface. 
     
     
       17. The method of  claim 11 , further comprising:
 determining a time-of-flight in the surface based on a time difference between transmitting an ultrasonic wave in the surface and receiving an ultrasonic reflection from the surface corresponding to the object in contact with the surface, wherein determining the position of the object comprises determining a distance from an edge of the surface to a leading edge of the object proximate to the edge of the surface based on the time-of-flight in the surface. 
 
     
     
       18. A non-transitory computer readable storage medium storing instructions, which when executed by a device comprising a surface, a plurality of acoustic transducers coupled between edges of the surface and a deformable material, an acoustic touch and force sensing circuit, and one or more processors, cause the acoustic touch and force sensing circuit and the one or more processors to:
 for each of the plurality of acoustic transducers:
 simultaneously transmit an ultrasonic wave in the surface toward an opposite edge of the surface and transmit an ultrasonic wave through the deformable material; 
 receive an ultrasonic reflection from the deformable material in response to the ultrasonic wave transmitted through the deformable material traversing a thickness of the deformable material; 
 receive an ultrasonic reflection from the surface; 
 determine a first time-of-flight between the ultrasonic wave transmitted through the deformable material and the ultrasonic reflection from the deformable material; and 
 determine a second time-of-flight between the ultrasonic wave transmitted in the surface and the ultrasonic reflection from the surface; 
 
 determine a position of an object on the surface based on respective second time-of-flight measurements corresponding to the plurality of transducers; and 
 determine an amount of applied force by the object on the surface based on respective first time-of-flight measurements corresponding to the plurality of transducers. 
 
     
     
       19. The non-transitory computer readable storage medium of  claim 18 , wherein the ultrasonic wave transmitted in the surface and the ultrasonic wave transmitted through the deformable material comprise shear waves. 
     
     
       20. The non-transitory computer readable storage medium of  claim 18 , wherein the ultrasonic reflection from the deformable material is received before the ultrasonic reflection from the surface. 
     
     
       21. An electronic device, comprising:
 a cover surface; 
 a deformable material disposed between the cover surface and a housing of the electronic device; 
 an acoustic transducer coupled between the cover surface and the deformable material and configured to produce a first acoustic wave in the cover surface and a second acoustic wave in the deformable material. 
 
     
     
       22. The electronic device of  claim 21 , wherein the deformable material and cover surface are further configured such that the first acoustic wave is capable of being propagated in a first direction and the second acoustic wave is capable of being propagated in a second direction, different from the first direction. 
     
     
       23. The electronic device of  claim 22 , wherein the first acoustic wave is incident upon a bezel portion of the cover surface in a third direction and reflected by the bezel portion of the cover surface in the first direction, different from the third direction. 
     
     
       24. The electronic device of  claim 23 , wherein the first and third directions are opposite to one another. 
     
     
       25. The electronic device of  claim 23 , wherein the first and third direction are orthogonal. 
     
     
       26. The electronic device of  claim 21 , wherein the deformable material is included in a gasket positioned between the housing and a first side of the cover surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application Ser. No. 62/510,416, filed May 24, 2017, U.S. Provisional Application Ser. No. 62/510,489, filed May 24, 2017, and U.S. Provisional Application Ser. No. 62/510,460, filed May 24, 2017, the contents of which are hereby incorporated herein by reference in their entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     This relates generally to touch and/or force sensing systems, and more particularly, to integrated acoustic touch and force sensing systems and methods for acoustic touch and force sensing. 
     BACKGROUND OF THE DISCLOSURE 
     Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch and the position of the touch on the touch sensor panel, and the computing system can then interpret the touch in accordance with the display appearing at the time of the touch, and thereafter can perform one or more actions based on the touch. In the case of some touch sensing systems, a physical touch on the display is not needed to detect a touch. For example, in some capacitive-type touch sensing systems, fringing electrical fields used to detect touch can extend beyond the surface of the display, and objects approaching near the surface may be detected near the surface without actually touching the surface. Capacitive-type touch sensing systems, however, can experience reduced performance due to conductive, electrically-floating objects (e.g., water droplets) in contact with the touch-sensitive surface. 
     SUMMARY 
     This relates to acoustic touch and/or force sensing systems and methods for acoustic touch and/or force sensing. The position of an object touching a surface can be determined using time-of-flight (TOF) techniques, for example. Acoustic touch and/or force sensing can utilize transducers, such as piezoelectric transducers, to transmit ultrasonic waves along a surface and/or through the thickness of one or more materials (e.g., a thickness of an electronic device housing). As the wave propagates along the surface and/or through the thickness of the one or more materials, an object (e.g., finger, stylus, etc.) in contact with the surface can interact with the transmitted wave, causing a reflection of at least a portion of the transmitted wave. Portions of the transmitted wave energy after interaction with the object can be measured to determine the touch location of the object on the surface of the device. For example, one or more transducers (e.g., acoustic transducers) coupled to a surface of a device can be configured to transmit an acoustic wave along the surface and/or through the thickness of the one or more materials and can receive a portion of the wave reflected back when the acoustic wave encounters a finger or other object touching the surface. The location of the object can be determined, for example, based on the amount of time elapsing between the transmission of the wave and the detection of the reflected wave. Acoustic touch sensing can be used instead of, or in conjunction with, other touch sensing techniques, such as resistive, optical, and/or capacitive touch sensing. In some examples, the acoustic touch sensing techniques described herein can be used on a metal housing surface of a device, which may be unsuitable for capacitive or resistive touch sensing due to interference (e.g., of the housing with the capacitive or resistive sensors housed in the metal housing). In some examples, the acoustic touch sensing techniques described herein can be used on a glass surface of a display or touch screen. In some examples, an acoustic touch sensing system can be configured to be insensitive to contact on the device surface by water, and thus acoustic touch sensing can be used for touch sensing in devices that may become wet or fully submerged in water. 
     Additionally or alternatively, a force applied by the object on the surface can also be determined using TOF techniques. For example, one or more transducers can transmit ultrasonic waves through the thickness of a deformable material, and reflected waves from the opposite edge of the deformable material can be measured to determine a TOF or a change in TOF. The TOF, or change in TOF (ATOF), can correspond to the thickness of the deformable material (or changes in thickness) due to force applied to the surface. Thus, the TOF or change in TOF (or the thickness or change in thickness) can be used to determine the applied force. In some examples, using acoustic touch and force sensing can reduce the complexity of the touch and force sensing system by reducing the sensing hardware requirements (e.g., transducers, sensing circuitry/controllers, etc. can be integrated/shared). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1G  illustrate exemplary systems with touch screens that can include acoustic sensors for detecting contact between an object and a surface of the system according to examples of the disclosure. 
         FIG. 2  illustrates an exemplary block diagram of an electronic device including an acoustic touch and/or force sensing system according to examples of the disclosure. 
         FIG. 3A  illustrates an exemplary process for acoustic touch and/or force sensing of an object in contact with a touch and/or force sensitive surface according to examples of the disclosure. 
         FIG. 3B  illustrates an exemplary system, which can perform an exemplary process for acoustic touch and/or force sensing of an object in contact with a touch and/or force sensitive surface, according to examples of the disclosure. 
         FIG. 4  illustrates an exemplary configuration of an acoustic touch and/or force sensing circuit according to examples of the disclosure. 
         FIGS. 5A-5C  illustrate exemplary system configurations and timing diagrams for acoustic touch sensing to determine position using time-of-flight measurements according to examples of the disclosure. 
         FIGS. 6A-6D  illustrate exemplary system configurations and timing diagrams for acoustic force sensing to determine an amount of applied force using a time-of-flight measurement according to examples of the disclosure. 
         FIG. 7  illustrates a timing diagram for acoustic touch and force sensing according to examples of the disclosure. 
         FIGS. 8A-C  illustrate exemplary circuits for force detection according to examples of the disclosure. 
         FIG. 9  illustrates an exemplary configuration of an acoustic touch and/or force sensing circuit according to examples of the disclosure. 
         FIGS. 10A-10E  illustrate exemplary integration of an acoustic touch and force sensing circuit and/or one or more processors with transducers mechanically and acoustically coupled to a surface and/or a deformable material according to examples of the disclosure. 
         FIG. 11  illustrates an exemplary configuration of an acoustic touch and force sensing circuit according to examples of the disclosure. 
         FIGS. 12A-12E  illustrate exemplary integration of an acoustic touch and force sensing circuit and/or one or more processors with groups of transducers mechanically and acoustically coupled to a surface and/or a deformable material according to examples of the disclosure. 
         FIG. 13  illustrates a first exemplary configuration for integrating touch sensing and force sensing circuitry with a housing and cover glass of an electronic device. 
         FIG. 14  illustrates a second exemplary configuration for integrating touch sensing and force sensing circuitry with a housing and cover glass of an electronic device. 
         FIG. 15  illustrates a third exemplary configuration for integrating touch sensing and force sensing circuitry with a housing and cover glass of an electronic device. 
         FIG. 16  illustrates a variation of the third configuration of  FIG. 10  with the addition of an encapsulant material. 
         FIG. 17  illustrates a fourth exemplary configuration for integrating touch sensing and force sensing circuitry with a housing and cover glass of an electronic device. 
         FIG. 18  illustrates a fifth exemplary configuration for integrating touch sensing and force sensing circuitry with a housing and cover glass of an electronic device. 
         FIGS. 19A and 19B  illustrate exemplary configurations for integrating touch sensing and force sensing circuitry with shared elements with a housing and cover glass of an electronic device. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of various examples, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the various examples. 
     This relates to acoustic touch and/or force sensing systems and methods for acoustic touch and/or force sensing. The position of an object touching a surface can be determined using time-of-flight (TOF) techniques, for example. Acoustic touch and/or force sensing can utilize transducers, such as piezoelectric transducers, to transmit ultrasonic waves along a surface and/or through the thickness of one or more materials (e.g., a thickness of an electronic device housing). As the wave propagates along the surface and/or through the thickness of the one or more materials, an object (e.g., finger, stylus, etc.) in contact with the surface can interact with the transmitted wave, causing a reflection of at least a portion of the transmitted wave. Portions of the transmitted wave energy after interaction with the object can be measured to determine the touch location of the object on the surface of the device. For example, one or more transducers (e.g., acoustic transducers) coupled to a surface of a device can be configured to transmit an acoustic wave along the surface and/or through the thickness of the one or more materials and can receive a portion of the wave reflected back when the acoustic wave encounters a finger or other object touching the surface. The location of the object can be determined, for example, based on the amount of time elapsing between the transmission of the wave and the detection of the reflected wave. Acoustic touch sensing can be used instead of, or in conjunction with, other touch sensing techniques, such as resistive, optical, and/or capacitive touch sensing. In some examples, the acoustic touch sensing techniques described herein can be used on a metal housing surface of a device, which may be unsuitable for capacitive or resistive touch sensing due to interference (e.g., of the housing with the capacitive or resistive sensors housed in the metal housing). In some examples, the acoustic touch sensing techniques described herein can be used on a glass surface of a display or touch screen. In some examples, an acoustic touch sensing system can be configured to be insensitive to contact on the device surface by water, and thus acoustic touch sensing can be used for touch sensing in devices that may become wet or fully submerged in water. 
     Additionally or alternatively, a force applied by the object on the surface can also be determined using TOF techniques. For example, one or more transducers can transmit ultrasonic waves through the thickness of a deformable material, and reflected waves from the opposite edge of the deformable material can be measured to determine a TOF or a change in TOF. The TOF, or change in TOF (ATOF), can correspond to the thickness of the deformable material (or changes in thickness) due to force applied to the surface. Thus, the TOF or change in TOF (or the thickness or change in thickness) can be used to determine the applied force. In some examples, using acoustic touch and force sensing can reduce the complexity of the touch and force sensing system by reducing the sensing hardware requirements (e.g., transducers, sensing circuitry/controllers, etc. can be integrated/shared). 
       FIGS. 1A-1G  illustrate exemplary systems with touch screens that can include acoustic sensors for detecting contact between an object (e.g., a finger or stylus) and a surface of the system according to examples of the disclosure. Detecting contact can include detecting a location of contact and/or an amount of force applied to a touch-sensitive surface.  FIG. 1A  illustrates an exemplary mobile telephone  136  that includes a touch screen  124  and can include an acoustic touch and/or force sensing system according to examples of the disclosure.  FIG. 1B  illustrates an example digital media player  140  that includes a touch screen  126  and can include an acoustic touch and/or force sensing system according to examples of the disclosure.  FIG. 1C  illustrates an example personal computer  144  that includes a touch screen  128  and a track pad  146 , and can include an acoustic touch and/or force sensing system according to examples of the disclosure.  FIG. 1D  illustrates an example tablet computing device  148  that includes a touch screen  130  and can include an acoustic touch and/or force sensing system according to examples of the disclosure.  FIG. 1E  illustrates an example wearable device  150  (e.g., a watch) that includes a touch screen  152  and can include an acoustic touch and/or force sensing system according to examples of the disclosure. Wearable device  150  can be coupled to a user via strap  154  or any other suitable fastener.  FIG. 1F  illustrates another example wearable device, over-ear headphones  160 , that can include an acoustic touch and/or force sensing system according to examples of the disclosure.  FIG. 1G  illustrates another example wearable device, in-ear headphones  170 , that can include an acoustic touch and/or force sensing system according to examples of the disclosure. It should be understood that the example devices illustrated in  FIGS. 1A-1G  are provided by way of example, and other types of devices can include an acoustic touch and/or force sensing system for detecting contact between an object and a surface of the device. Additionally, although the devices illustrated in  FIGS. 1A-1E  include touch screens, in some examples, the devices may have a non-touch-sensitive display (e.g., the devices illustrated in  FIGS. 1F and 1G ). 
     Acoustic sensors can be incorporated in the above described systems to add acoustic touch and/or force sensing capabilities to a surface of the system. For example, in some examples, a touch screen (e.g., capacitive, resistive, etc.) can be augmented with acoustic sensors to provide a touch and/or force sensing capability for use in wet environments or under conditions where the device may get wet (e.g., exercise, swimming, rain, washing hands) or for use with non-conductive or partially-conductive touch objects (e.g., gloved or bandaged fingers) or poorly grounded touch objects (e.g., objects not in contact with the system ground of the device). In some examples, an otherwise non-touch sensitive display screen can be augmented with acoustic sensors to provide a touch and/or force sensing capability. In such examples, a touch screen can be implemented without the stack-up required for a capacitive touch screen. In some examples, the acoustic sensors can be used to provide touch and/or force sensing capability for a non-display surface. For example, the acoustic sensors can be used to provide touch and/or force sensing capabilities for a track pad (e.g., trackpad  146  of personal computer  144 ), a button, a scroll wheel, part or all of the housing or any other surfaces of the device (e.g., on the front, rear or sides). For example, acoustic sensors can be integrated into over-ear headphones  160  (e.g., in exterior circular region  162 , interior circular region  164 , and/or over-head band  166 ) or in-ear headphones  170  (e.g., in earbud  172  or protrusion  174 ) to provide touch and/or force input (e.g., single-touch or multi-touch gestures including tap, hold and swipe). The acoustic sensing surfaces for acoustic touch and/or force sensing can be made of various materials (e.g., metal, plastic, glass, etc.) or a combination of materials. 
       FIG. 2  illustrates an exemplary block diagram of an electronic device including an acoustic touch and/or force sensing system according to examples of the disclosure. In some examples, housing  202  of device  200  (e.g., corresponding to devices  136 ,  140 ,  144 ,  148 , and  150  above) can be coupled (e.g., mechanically) with one or more acoustic transducers  204 . In some examples, transducers  204  can be piezoelectric transducers, which can be made to vibrate by the application of electrical signals when acting as a transmitter, and generate electrical signals based on detected vibrations when acting as a receiver. In some examples, transducers  204  can be formed from a piezoelectric ceramic material (e.g., PZT or KNN) or a piezoelectric plastic material (e.g., PVDF or PLLA). Similarly, transducers  204  can produce electrical energy as an output when vibrated. In some examples, transducers  204  can be bonded to housing  202  by a bonding agent (e.g., a thin layer of stiff epoxy). In some examples, transducers  204  can be deposited on one or more surfaces (e.g., a cover glass of touch screen  208  and/or a deformable material as described in more detail below) through processes such as deposition, lithography, or the like. In some examples, transducers  204  can be bonded to the one or more surfaces using electrically conductive or non-conductive bonding materials. When electrical energy is applied to transducers  204  it can cause the transducers to vibrate, the one or more surfaces in contact with the transducers can also be caused to vibrate, and the vibrations of the molecules of the surface material can propagate as an acoustic wave through the one or more surfaces/materials. In some examples, vibration of transducers  204  can be used to produce ultrasonic acoustic waves at a selected frequency over a broad frequency range (e.g., 500 kHz-10 MHz) in the medium of the surface of the electronic device which can be metal, plastic, glass, wood, or the like. It should be understood that other frequencies outside of the exemplary range above can be used while remaining within the scope of the present disclosure. 
     In some examples, transducers  204  can be partially or completely disposed on (or coupled to) a portion of a touch screen  208 . For example, touch screen  208  (e.g., capacitive) may include a glass panel (cover glass) or a plastic cover, and a display region of the touch screen may be surrounded by a non-display region (e.g., a black border region surrounding the periphery of the display region of touch screen  208 ). In some examples, transducers  204  can be disposed partially or completely in the black mask region of touch screen  208  (e.g., on the back side of the glass panel behind the black mask) such that the transducers are not visible (or are only partially visible) to a user. In some examples, transducers  204  can be partially or completely disposed on (or coupled to) a portion of a deformable material (not shown). In some examples, the deformable material can be disposed between touch screen  208  and a rigid material (e.g., a portion of housing  202 ). In some examples, the deformable material can be silicone, rubber or polyethylene. In some examples, the deformable material can also be used for water sealing of the device. 
     Device  200  can further include acoustic touch and/or force sensing circuitry  206 , which can include circuitry for driving electrical signals to stimulate vibration of transducers  204  (e.g., transmit circuitry), as well as circuitry for sensing electrical signals output by transducers  204  when the transducer is stimulated by received acoustic energy (e.g., receive circuitry). In some examples, timing operations for acoustic touch and/or force sensing circuitry  206  can optionally be provided by a separate acoustic touch and/or force sensing controller  210  that can control timing of and other operations by acoustic touch and/or force sensing circuitry  206 . In some examples, touch and/or force sensing controller  210  can be coupled between acoustic touch and/or force sensing circuitry  206  and host processor  214 . In some examples, controller functions can be integrated with acoustic touch and/or force sensing circuitry  206  (e.g., on a single integrated circuit). In particular, examples integrating touch and force sensing circuitry and controller functionality into a single integrated circuit can reduce the number of transducers (sensor elements) and electronic chipsets for a touch and force sensing device. Output data from acoustic touch and/or force sensing circuitry  206  can be output to a host processor  214  for further processing to determine a location of and a force applied by an object contacting the device as will be described in more detail below. In some examples, the processing for determining the location of and a force applied by the contacting object can be performed by acoustic touch and/or force sensing circuitry  206 , acoustic touch and/or force sensing controller  210  or a separate sub-processor of device  200  (not shown). 
     In addition to acoustic touch and/or force sensing, device  200  can include additional touch circuitry  212  and optionally a touch controller (not shown) that can be coupled to the touch screen  208 . In examples including a touch controller, the touch controller can be disposed between touch circuitry  212  and host processor  214 . Touch circuitry  212  can, for example, be capacitive or resistive touch sensing circuitry, and can be used to detect contact and/or hovering of objects (e.g., fingers, styli) in contact with and/or in proximity to touch screen  208 , particularly in the display region of the touch screen. Thus, device  200  can include multiple types of sensing circuitry (e.g., touch circuitry  212  and acoustic touch and/or force sensing circuitry  206 ) for detecting objects (and their positions and/or applied force) in different regions of the device and/or for different purposes, as will be described in more detail below. Although described herein as including a touch screen, it should be understood that touch circuitry  212  can be omitted, and in some examples, touch screen  208  can be replaced by an otherwise non-touch-sensitive display (e.g., but-for the acoustic sensors). 
     Host processor  214  can receive acoustic or other touch outputs (e.g., capacitive) and/or force outputs and perform actions based on the touch outputs and/or force outputs. Host processor  214  can also be connected to program storage  216  and touch screen  208 . Host processor  214  can, for example, communicate with touch screen  208  to generate an image on touch screen  208 , such as an image of a user interface (UI), and can use touch sensing circuitry  212  and/or acoustic touch and/or force sensing circuitry  206  (and, in some examples, their respective controllers) to detect a touch on or near touch screen  208  and/or an applied force, such as a touch input and/or force input to the displayed UI. The touch input and/or force input can be used by computer programs stored in program storage  216  to perform actions that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. Host processor  214  can also perform additional functions that may not be related to touch and/or force processing. 
     Note that one or more of the functions described herein can be performed by firmware stored in memory and executed by touch circuitry  212  and/or acoustic touch and/or force sensing circuitry  206  (or their respective controllers), or stored in program storage  216  and executed by host processor  214 . The firmware can also be stored and/or transported within any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “non-transitory computer-readable storage medium” can be any medium (excluding a signal) that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The non-transitory computer readable medium storage can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks, and the like. 
     The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. 
     It is to be understood that device  200  is not limited to the components and configuration of  FIG. 2 , but can include other or additional components in multiple configurations according to various examples. Additionally, the components of device  200  can be included within a single device, or can be distributed between multiple devices. Additionally, it should be understood that the connections between the components is exemplary and different unidirectional or bidirectional connections can be included between the components depending on the implementation, irrespective of the arrows shown in the configuration of  FIG. 2 . 
       FIG. 3A  illustrates an exemplary process  300  for acoustic touch and/or force sensing of an object in contact with a touch and/or force sensitive surface according to examples of the disclosure.  FIG. 3B  illustrates an exemplary system  310 , which can perform an exemplary process  300  for acoustic touch and/or force sensing of an object in contact with a touch and/or force sensitive surface, according to examples of the disclosure. At  302 , acoustic energy can be transmitted (e.g., by one or more transducers  204 ) along a surface and/or through the thickness of a material in the form of an ultrasonic wave, for example. For example, as illustrated in  FIG. 3B , transducer  314  can generate a transmit ultrasonic wave  322  in cover glass  312  (or other material capable of propagating an ultrasonic wave). In some examples, the wave can propagate as a compressive wave, a guided wave such as a shear horizontal wave, a Rayleigh wave, a Lamb wave, a Love wave, a Stoneley wave, or a surface acoustic wave. Other propagation modes for the transmitted acoustic energy can also exist based on the properties of the surface material, geometry and the manner of energy transmission from the transducers to the surface of the device. In some examples, the surface can be formed from glass, plastic, or sapphire crystal (e.g., touch screen  208 , cover glass  312 ) or the surface can be formed from metal, ceramics, plastic, or wood (e.g., housing  202 ). Transmitted energy can propagate along the surface (e.g., cover glass  312 ) and/or through the thickness until a discontinuity in the surface is reached (e.g., an object, such as a finger  320 , in contact with the surface), which can cause a portion of the energy to reflect. In some examples, a discontinuity can occur at edges (e.g., edge  330 ) of the surface material (e.g., when the ultrasonic wave propagates to the edge of the surface opposite the transducer). When the transmitted energy reaches one of the discontinuities described above, some of the energy can be reflected, and a portion of the reflected energy (e.g., object-reflected wave  326 , edge-reflected wave  328 ) can be directed to one or more transducers (e.g., transducers  204 ,  314 ). In some examples, water or other fluids in contact with the surface of the device (e.g., device  200 ) will not act as a discontinuity to the acoustic waves, and thus the acoustic touch sensing process can be effective for detecting the presence of an object (e.g., a user&#39;s finger) even in the presence of water drops (or other low-viscosity fluids) on the surface of the device or even while the device is fully submerged. 
     At  304 , returning acoustic energy can be received, and the acoustic energy can be converted to an electrical signal by one or more transducers (e.g., transducers  204 ). For example, as illustrated in  FIG. 3B , object-reflected wave  326  and edge-reflected wave  328  can be received by transducer  314  and converted into an electrical signal. 
     At  306 , the acoustic sensing system can determine whether one or more objects is contacting the surface of the device, and can further detect the position of one or more objects based on the received acoustic energy. In some examples, a distance of the object from the transmission source (e.g., transducers  204 ) can be determined from a time-of-flight between transmission and reception of reflected energy, and a propagation rate of the ultrasonic wave through the material. In some examples, baseline reflected energy from one or more intentionally included discontinuities (e.g., edges) can be compared to a measured value of reflected energy corresponding to the one or more discontinuities. The baseline reflected energy can be determined during a measurement when no object (e.g., finger) is in contact with the surface. Deviations of the reflected energy from the baseline can be correlated with a presence of an object touching the surface. 
     Although process  300 , as described above, generally refers to reflected waves received by the same transducer(s) that transmitted the waves, in some examples, the transmitter and receiver functions can be separated such that the transmission of acoustic energy at  302  and receiving acoustic energy at  304  may occur at different co-located transducers (e.g., one transducer in a transmit configuration and one transducer in a receive configuration). In some examples, the acoustic energy can be transmitted along and/or through the surface (e.g., cover glass  312 ) by one or more transducers (e.g., transducer  314 ) and received on an opposite edge (e.g., edge  330 ) of the surface by one or more additional transducers (not shown). The attenuation of the received acoustic energy can be used to detect the presence of and/or identify the position of one or more objects (e.g., finger  320 ) on the surface (e.g., cover glass  312 ). Exemplary device configurations and measurement timing examples that can be used to implement process  300  will be described in further detail below. In some examples, the transmitted acoustic energy from transducer  314  can be received at the transmitting transducer and also received at one or more other non-transmitting transducers located in different positions (e.g., at different edges of the surface (e.g., cover glass  312 ). Energy can reflect from one or more objects at multiple angles, and the energy received at all of the receiving transducers can be used to determine the position of the one or more objects. In some examples, the non-transmitting transducers can be free of artifacts that can be associated with transmitting acoustic energy (e.g., ringing). In some examples, the energy can be received at two transducers perpendicular to the transmitting transistor. 
     In some examples, the acoustic energy transmitted and received through a deformable material can be used to determine changes in the thickness of the deformable material and/or an applied force. For example, at  302 , acoustic energy can be transmitted (e.g., by transducer  314 ) through the thickness of deformable material  316  in the form of a transmit ultrasonic wave  324 . Transmitted energy can propagate through the deformable material  316  until it reaches a discontinuity at the rigid material  318  (e.g., at the opposite edge of the deformable material  316 ). When the transmitted energy reaches the discontinuity, some of the energy can be reflected, and a portion of the reflected energy can be directed back to transducer  314 . At  304 , returning acoustic energy can be received, and the acoustic energy can be converted to an electrical signal by transducers  314 . At  306 , the acoustic sensing system can determine an amount of force applied by one or more objects contacting the surface (e.g., cover glass  312 ) based on the received acoustic energy. In some examples, a thickness of deformable material  316  can be determined from a time-of-flight between transmission and reception of reflected energy, and a propagation rate of the ultrasonic wave through the material. Changes in the thickness of the deformable material (or the time-of-flight through the deformable material) can be used to determine an amount of applied force, as described in more detail below. 
       FIG. 4  illustrates an exemplary configuration of an acoustic touch and/or force sensing circuit  400  according to examples of the disclosure. Acoustic touch and/or force sensing circuit  400  can include transmit circuitry (also referred to herein as Tx circuitry or transmitter)  402 , switching circuitry  404 , receive circuitry (also referred to herein as Rx circuitry or receiver)  408  and input/output (I/O) circuit  420  (which together can correspond to acoustic touch and/or force sensing circuitry  206 ) and acoustic scan control logic  422  (which can correspond to acoustic touch and/or force sensing controller  210 ). Transmitter  402 , switching circuitry  404 , receiver  408 , I/O circuit  420  and/or acoustic scan control logic  422  can be implemented in an application specific integrated circuit (ASIC) in some examples. In some examples, acoustic touch and/or force sensing circuit  400  can also optionally include transducers  406  (which can correspond to transducers  204 ). 
     In some examples, a transmitter  402  can generate an electrical signal for stimulating movement of one or more of a plurality of transducers  406 . In some examples, the transmitted signal can be a differential signal, and in some examples, the transmitted signal can be a single-ended signal. In some examples, transmitter  402  can be a simple buffer, and the transmitted signal can be a pulse (or burst of pulses at a particular frequency). In some examples, transmitter  402  can include a digital-to-analog converter (DAC)  402 A and an optional filter  402 B that can be optionally used to smooth a quantized output of DAC  402 A. In some examples, characteristics of the transducer itself can provide a filtering property and filter  402 B can be omitted. DAC  402 A can be used to generate transmit waveform (e.g., any transmit waveform suitable for the touch and/or force sensing operations discussed herein). In some examples, the transmit waveform output can be pre-distorted to equalize the channel. In some examples, the characteristics of each channel, such as the properties of the surface material (and/or deformable material) coupled to transducers  406 , the discontinuities in the surface material and/or deformable material, and the reflection characteristics of an edge of the device or deformable material can be measured and stored. In some examples, the channel characteristics can be measured as a manufacturing step (or factory calibration step), and in other examples the characteristics can be measured as a periodic calibration step (i.e., once a month, once a year, etc. depending on how quickly the channel characteristics are expected to change). In some examples, the channel characteristics can be converted to a transfer function of the channel, and the transmit waveform can be configured using the inverse of the channel transfer function such that the returning signal is equalized (e.g., returning signal can be detected as a pulse or a burst of pulses despite the transmitted waveform having a seemingly arbitrary waveform). In some examples, a single differential pulse can be used as a transmit waveform. For example, a bipolar square pulse (where the voltage applied to the transducer can be both positive and negative) can be used as the transmit waveform, and the bipolar square pulse can be implemented using a single-ended or differential implementation. In some examples, an energy recovery architecture can be used to recover some of the energy required for charging and discharging the transducer. 
     Switching circuitry  404  can include multiplexers (MUXs) and/or demultiplexers (DEMUXs) that can be used to selectively couple transmitter  402  and/or receiver  408  to one of transducers  406  that can be the active transducer for a particular measurement step in a measurement cycle. In a differential implementation, switching circuitry  404  can include two MUXs and two DEMUXs. In some examples, a DEMUX can have a ground connection, and the non-selected DEMUX outputs can be shorted, open, or grounded. In some examples, the same transducer  406  can be coupled to transmitter  402  by switching circuitry  404  (e.g., DEMUXs) during the drive mode and coupled to receiver  408  by switching circuitry  404  (e.g., MUXs) during the receive mode. Thus, in some examples, a single transducer  406  can be used both for transmitting and receiving acoustic energy. In some examples, a first transducer can be coupled to transmitter  402  by switching circuitry  404  (e.g. DEMUXs) and a second transducer can be coupled by switching circuitry  404  (e.g., MUXs) to receiver  408 . For example, the transmitting transducer and the receiving transducer can be discrete piezoelectric elements, where the transmitting transducer can be designed for being driven by higher voltages (or currents) to produce sufficient motion in transducer  406  to generate an acoustic wave in the surface of a device (e.g., device  200  above), and the receiving transducer can be designed for receiving smaller amplitude reflected energy. In such a configuration, the transmit-side circuitry (e.g., transmitter  402  and DEMUXs of switching circuitry  404 ) can be optionally implemented on a high voltage circuit, and the receive-side circuitry (e.g., receiver  408  and MUXs of switching circuitry  404 ) can be optionally implemented on a separate low voltage circuit. In some examples, switching circuitry  404  (MUXs and DEMUXs) can also be implemented on the high voltage circuit to properly isolate the remaining receive-side circuitry (e.g., receiver  408 ) during transmission operations by transmit side circuitry. Additionally or alternatively, in some examples, the transmit circuit can include an energy recovery architecture that can be used to recover some of the energy required for charging and discharging the transducer. It should be understood that for a single-ended implementation, switching circuitry  404  can include a single DEMUX and MUX. In such a configuration, transmitter  402  and receiver  408  can be single-ended as well. Differential implementations, however, can provide improved noise suppression over a single-ended implementation. 
     Receiver  408  can include an amplifier  410  such as a low-noise amplifier (LNA) configured to sense the transducer. Receiver  408  can also include a gain and offset correction circuit  412 . The gain and offset correction circuit can include a programmable gain amplifier (PGA) configured to apply gain to increase (or in some cases decrease) the amplitude of the signals received from LNA. The PGA can also be configured to filter (e.g., low pass) the signals received from the LNA to remove high frequency components. Additionally, the PGA circuit can also be configured to perform baselining (offset correction). 
     In some examples, the output of gain and offset correction circuit  412  can optionally be coupled to one or more analog processing circuits. In some examples, the output of gain and offset correction circuit  412  can be coupled to a demodulation circuit  414  configured to demodulate the received signals (e.g., by I/Q demodulation). In some examples, the output of the gain and offset correction circuit  412  can be coupled to an envelope detection circuit  415  configured to perform envelope detection on the received signals. In some examples, the output of gain and offset correction circuit  412  can be filtered at filter  416 . In some examples, these blocks/circuits can be placed in a different order. In some examples, the processing of one or more of these analog processing circuits can be performed in the digital domain. 
     The received signals, whether raw or processed by one or more of demodulation circuit  414 , envelope detection circuit  415  or filter  416 , can be passed to an analog-to-digital converter (ADC)  418  for conversion to a digital signal. In some examples, an input/output (I/O) circuit  420  can be used to transmit received data for processing. In some examples, the output of I/O circuit  420  can be transferred to a host processor of the device, or to an auxiliary processor (sub-processor) separate from the host processor. For example, as illustrated, the output of I/O circuit  420  can be coupled to a processor system-on-chip (SoC)  430 , which can include one or more processors. In some examples, processor SoC  430  can include a host processor  432  (e.g., an active mode processor) and an auxiliary processor  434  (e.g., a low power processor). In some examples, some digital signal processing can be performed (e.g., by acoustic touch and/or force sensing circuit  400 ) before transmitting the data to other processors in the system (e.g., processor SoC  430 ). In some examples, the I/O circuit  420  is not only used for data transfer to processor SoC  430  (e.g., host processor  432 ), but also is used for writing the control registers and/or firmware download from processor SoC  430 . 
     The components of receiver circuitry  408  described above can be implemented to detect touch (e.g., presence and location of a touch on a surface). In some examples, receiver  408  can also include a force detection circuit  424  to detect applied force (e.g., of the touch on the surface). In some examples, the force detection circuit  424  can include the same or similar components as described above (e.g., amplifier, gain and offset correction, etc.). In some examples, the function of force detection circuit  424  can be performed using the same components described above that are used to determine time-of-flight for touch detection. In some examples, a low-power time gating circuit can be used to determine time-of-flight for force detection. Data from force sensing circuit  424  can be transferred to I/O circuit  420  and/or processor SoC  430  for further processing of force data in a similar manner as described above for touch data. In some examples the same circuitry for touch detection can be used to detect force. 
     A control circuit, acoustic scan control circuit  422 , can be used to control timing and operations of the circuitry of acoustic touch and/or force sensing circuit  400 . Acoustic scan control circuit  422  can be implemented in hardware, firmware, software or a combination thereof. In some examples, acoustic scan control circuit  422  can include digital logic and timing control. Digital logic can provide the various components of acoustic touch and/or sensing circuit  400  with control signals. A timing control circuit can generate timing signals for acoustic touch and/or sensing circuit  400  and generally sequence the operations of acoustic touch and/or force sensing circuit  400 . In some examples, the acoustic touch and/or force sensing circuit  400  can receive a master clock signal from an external source (e.g., clock from the host processor, crystal oscillator, ring oscillator, RC oscillator, or other high-performance oscillator). In some examples, an on-chip oscillator can be used to generate the clock. In some examples, a master clock signal can be generated by an on-chip phase locked loop (PLL), included as part of acoustic touch and/or force sensing circuit  400 , using an external clock as the input. In some examples, a master clock signal can be routed to the acoustic touch sensing circuit from processor SoC  430 . The appropriate master clock source can be determined based on a tradeoff between area, thickness of the stack-up, power and electromagnetic interference. 
     It is to be understood that the configuration of  FIG. 4  is not limited to the components and configuration of  FIG. 4 , but can include other or additional components (e.g., memory, signal processor, etc.) in multiple configurations according to various examples. Additionally, some or all of the components illustrated in  FIG. 4  can be included in a single circuit, or can be divided among multiple circuits while remaining within the scope of the examples of the disclosure. 
     As described herein, various acoustic sensing techniques can be used to determine the position of an object touching a surface and/or its applied force on the surface. In some examples, one or more time-of-flight measurements can be performed using one or more acoustic transducers to determine boundaries of the position of the contacting object.  FIGS. 5A-5C  illustrate exemplary system configurations and timing diagrams for acoustic touch sensing to determine position using time-of-flight measurements according to examples of the disclosure.  FIG. 5A  illustrates an exemplary acoustic touch sensing system configuration using four acoustic transducers  502 A-D mounted along (or otherwise coupled to) four edges of a surface  500  (e.g., corresponding to cover glass  312 ). Transducers  502 A-D can be configured to generate acoustic waves (e.g., shear horizontal waves) and to receive the reflected acoustic waves. Propagation of shear horizontal waves can be unaffected by water on surface  500  because low viscosity fluids and gases (such as water and air) have a very low shear modulus, and therefore do not perturb the boundary conditions that affect wave propagation. Shear horizontal waves can be highly directional waves such that the active detection region (or active area)  504  can be effectively defined based on the position and dimensions of the acoustic transducers  502 A-D. It should be understood, however, that active area can change based on the directionality property of the acoustic waves and the size and placement of acoustic transducers  502 A-D. Additionally, it should be understood that although illustrated as transmit and receive transducers (i.e., transceivers), in some examples, the transmit and receive functions can be divided (e.g., between two transducers in proximity to one another, rather than one transmit and receive transducer). 
     The position of a touch  506  from an object in contact with surface  500  can be determined by calculating TOF measurements in a measurement cycle using each of acoustic transducers  502 A-D. For example, in a first measurement step of the measurement cycle, acoustic transducer  502 A can transmit an acoustic wave and receive reflections from the acoustic wave. When no object is present, the received reflection can be the reflection from the acoustic wave reaching the opposite edge of surface  500 . However, when an object is touching surface  500  (e.g., corresponding to touch  506 ), a reflection corresponding to the object can be received before receiving the reflection from the opposite edge. Based on the received reflection corresponding to the object received at transducer  502 A, the system can determine a distance to the edge (e.g., leading edge) of touch  506 , marked by boundary line  510 A. Similar measurements can be performed by transducers  502 B,  502 C and  502 D to determine a distance to the remaining edges of touch  506 , indicated by boundary lines  510 B,  510 C and  510 D. Taken together, the measured distances as represented by boundary lines  510 A- 510 D can form a bounding box  508 . In some examples, based on the bounding box, the acoustic touch sensing system can determine the area of the touch (e.g., the area of the bounding box). Based on the bounding box, the acoustic touch sensing system can determine position of touch  506  (e.g., based on a centroid and/or area of the bounding box). 
     The acoustic touch sensing scan described with reference to  FIG. 5A  can correspond to the acoustic touch detection described above with reference to  FIGS. 3A and 3B . Acoustic waves transmitted and received along or through cover glass  312  can be used to determine the position/location of an object touching the surface of cover glass  312 . 
       FIG. 5B  illustrates an exemplary timing diagram  560  for an acoustic touch sensing scan described in  FIG. 5A  according to examples of the disclosure. As illustrated in  FIG. 5B , each of the transducers can transmit acoustic waves and then receive reflected waves in a series of measurement steps. For example, from t 0  to t 1  a first transducer (e.g., acoustic transducer  502 A) can be stimulated, and reflections at the first transducer can be received from t 1  to t 2 . From t 2  to t 3  a second transducer (e.g., acoustic transducer  502 B) can be stimulated, and reflections at the second transducer can be received from t 3  to t 4 . From t 4  to t 5  a third transducer (e.g., acoustic transducer  502 C) can be stimulated, and reflections at the third transducer can be received from t 5  to t 6 . From t 6  to t 7  a fourth transducer (e.g., acoustic transducer  502 D) can be stimulated, and reflections at the fourth transducer can be received from t 7  to t 8 . Although the transmit (Tx) and receive (Rx) functions are shown back-to-back in  FIG. 5B  for each transducer, in some examples, gaps can be included between Tx and Rx functions for a transducer (e.g., to minimize capturing portions of the transmitted wave at the receiver), and or between the Tx/Rx functions of two different transducers (such that acoustic energy and the transients caused by multiple reflections from a scan by one transducer does not impact a scan by a second transducer). In some examples, unused transducers can be grounded (e.g., by multiplexers/demultiplexers in switching circuitry  404 ). 
     The distance between an object touching the surface and a transducer can be calculated based on TOF principles. The acoustic energy received by transducers can be used to determine a timing parameter indicative of a leading edge of a touch. The propagation rate of the acoustic wave through the material forming the surface can be a known relationship between distance and time. Taken together, the known relationship between distance and time and the timing parameter can be used to determine distance.  FIG. 5C  illustrates an exemplary timing diagram according to examples of the disclosure.  FIG. 5C  illustrates the transducer energy output versus time. Signal  550  can correspond to the acoustic energy at the transducer from the generation of the acoustic wave at a first edge of the surface. Signal  552  can correspond to the acoustic energy at the transducer received from the wave reflected off of a second edge opposite the first edge of the surface. Due to the known distance across the surface from the first edge to the opposite second edge and the known or measured propagation rate of the acoustic signal, the reflection off of the opposite edge of the surface occurs at a known time. Additionally, one or more objects (e.g., fingers) touching the surface can cause reflections of energy in the time between the generation of the wave and the edge reflection (i.e., between signals  550  and  552 ). For example, signals  554  and  556  can correspond to reflections of two objects touching the surface (or a leading and trailing edge of one object). It should be understood that signals  550 - 556  are exemplary and the actual shape of the energy received can be different in practice. 
     In some examples, the timing parameter can be a moment in time that can be derived from the reflected energy. For example, the time can refer to that time at which a threshold amplitude of a packet of the reflected energy is detected. In some examples, rather than a threshold amplitude, a threshold energy of the packet of reflected energy can be detected, and the time can refer to that time at which a threshold energy of the packet is detected. The threshold amplitude or threshold energy can indicate the leading edge of the object in contact with the surface. In some examples, the timing parameter can be a time range rather than a point in time. To improve the resolution of a TOF-based sensing scheme, the frequency of the ultrasonic wave and sampling rate of the receivers can be increased (e.g., so that receipt of the reflected wave can be localized to a narrower peak that can be more accurately correlated with a moment in time). 
     In some examples (e.g., as illustrated in  FIG. 5B ), transducers  502 A-D can operate in a time multiplexed manner, such that each transducer transmits and receives an acoustic wave at a different time during a measurement cycle so that the waves from one transducer do not interfere with waves from another transducer. In other examples, the transducers can operate in parallel or partially in parallel in time. The signals from the respective transducers can then be distinguished based on different characteristics of the signals (e.g., different frequencies, phases and/or amplitudes). 
     Although four transducers are illustrated in  FIG. 5A , in some examples, fewer transducers can be used. For example, when using an input object with known dimensions (e.g., stylus or a size-characterized finger), as few as two transducers mounted along two perpendicular edges can be used. Based on the known dimensions of an object, a bounding box  518  can be formed by adding the known dimensions of the object to the first and second distances, for example. Additionally, although  FIG. 5A  illustrates detection of a single object (e.g., single touch), in some examples, the acoustic touch sensing system can use more transducers and be configured to detect multiple touches (e.g., by replacing each of transducers  502 A-D with multiple smaller transducers). 
     TOF schemes described with reference to  FIGS. 5A-5C  can provide for touch sensing capability using a limited number of transducers (e.g., as compared with a number of electrodes/touch nodes of a capacitive touch sensing system) which can simplify the transmitting and receiving electronics, and can reduce time and memory requirements for processing. Although  FIGS. 5A-5C  discuss using a bounding box based on TOF measurements to determine position of an object, in other examples, different methods can be used, including applying matched filtering to a known transmitted ultrasonic pulse shape, and using a center of mass calculation on the filtered output (e.g., instead of a centroid). 
     In some examples, a time-of-flight measurement can be performed using one or more acoustic transducers to determine an amount of force applied by an object touching a surface.  FIGS. 6A-6D  illustrate exemplary system configurations and timing diagrams for acoustic force sensing to determine an amount of applied force using a time-of-flight measurement according to examples of the disclosure.  FIG. 6A  illustrates an exemplary acoustic force sensing system stack-up  600  including a deformable material  604  in between two rigid surfaces. One of the rigid surfaces can be a cover glass  601  (e.g., corresponding to cover glass  312 ). The second of the rigid surfaces can be a portion of a device housing, for example (e.g., corresponding to housing  202 ). An acoustic transducer  602  (e.g., corresponding to transducer  314 ) can mounted to (or otherwise coupled to) the deformable material  604 . For example, as illustrated in  FIG. 6A , transducer  602  can be disposed between cover glass  601  and deformable material  604 . Transducer  602  can be configured to generate acoustic waves (e.g., shear horizontal waves) and to receive the reflected acoustic waves from the discontinuity at the edge between deformable material  604  and rigid material  606 . It should be understood that although illustrated as transmit and receive transducers (i.e., transceivers), in some examples, the transmit and receive functions can be divided (e.g., between two transducers in proximity to one another, rather than one transmit and receive transducer). Shear horizontal waves can be highly directional waves such that the time of flight can be effectively measure the thickness of the deformable material. A baseline thickness (or time-of-flight) can be determined for a no-force condition, such that changes in thickness (Ad) (or time-of-flight) can be measured. Changes in thickness or time-of-flight can correspond to amount of applied force. 
     For example, plot  630  of  FIG. 6D  illustrates an exemplary relationship between time-of-flight (or thickness) and applied force according to examples of the disclosure. For example, in a steady state condition, where there is no change in time-of-flight across the deformable material  604 , the applied force can be zero. As the time-of flight varies (e.g., decreases), the applied force can vary as well (e.g., increase). Plot  630  illustrates a linear relationship between TOF and force, but in some examples, the relationship can be non-linear. The relationship between TOF and applied force can be empirically determined (e.g., at calibration) using a correlation. In some examples, the calibration can include linearizing the inferred applied force and normalizing the measurements (e.g., removing gain and offset errors). In some examples, the Young&#39;s modulus of the deformable material can be selected below a threshold to allow a small applied force to introduce a detectable normal deformation. 
       FIG. 6B  illustrates another exemplary acoustic force sensing system stack-up  610  including a deformable material  614  in between two rigid surfaces (e.g., between cover glass  611  and rigid material  618 ). An acoustic transducer  612  can mounted to (or otherwise coupled to) one side of deformable material  614 , and a second acoustic transducer  616  can be mounted to (or otherwise coupled to) a second side (opposite the first side) of deformable material  614 . For example, as illustrated in  FIG. 6B , transducer  612  can be disposed between cover glass  611  and deformable material  614  and transducer  616  can be disposed between rigid material  618  and deformable material  614 . Transducer  612  can be configured to generate acoustic waves (e.g., shear horizontal waves) and transducer  616  can be configured to receive the acoustic waves. The configuration of transducers in stack-up  610  can be referred to as a “pitch-catch” configuration in which one transducer on one side of a material transmits acoustic waves to a second transducer on an opposite side, rather than relying on a reflected acoustic wave. The time-of-flight between the time of transmission and the time of receipt of the acoustic wave can be measured to determine the amount of applied force in a similar manner as discussed above with respect to  FIG. 6D . 
       FIG. 6C  illustrates an exemplary timing diagram  640  according to examples of the disclosure.  FIG. 6C  illustrates the transducer energy output versus time. Signal  620  can correspond to the acoustic energy at transducer  602  from the generation of the acoustic wave at a first edge of the deformable material  604 . Signal  622  can correspond to the acoustic energy at transducer  602  received from a first wave reflected off of a second edge, opposite the first edge, of the deformable material  604 . Due to the known distance across the surface from the first edge to the opposite, second edge (under steady-state) and the known or measured propagation rate of the acoustic signal, the reflection off of the opposite edge of the surface occurs at a known time. In some examples, rather than using the first reflection, a different reflection of the acoustic energy can be used to determine time of flight. For example, signal  624  can refer to the acoustic energy at transducer  602  received from a second wave reflected off of the second edge of deformable material  604  (e.g., signal  622  can reflect off of the first side of  604  deformable material and reflect a second time off of the second edge of deformable material  604 ). In some examples, signal  556  can correspond to an integer number reflection after repeated reflections between the two edges of deformable material  604 . It should be understood that signals  620 - 626  are exemplary and the actual shape of the energy received can be different in practice. In some examples, the choice of which reflection to use for the time-of-flight calculation for force sensing can be a function of the thickness of the material and the frequency of the transmitted wave. 
     In some examples, rather than using time-of-flight measurements to determine thickness of the deformable material, other methods can be used. For example, transducer  602  can stimulate the deformable material  604  with ultrasonic waves at a resonant frequency. As the deformable material  604  changes in thickness due to applied force, the resonant frequency can shift. The change in resonant frequency can be measured to determine the applied force. Using a resonant frequency can result in better signal-to-noise ratio (SNR) performance and better accuracy as compared with the time-of-flight method. 
     As described above with reference to  FIGS. 3A-3B , in some examples acoustic touch and force sensing can both be performed. In some examples, the two operations can be time-multiplexed. Transducers  502 A-D (e.g., one of which can correspond to transducer  314 ) can generate transmit waveforms and receive reflections to determine a location/position of touch on a surface (e.g., cover glass  312 ) as described with reference to timing diagram  560  during an acoustic touch sensing phase. Transducer  602  (e.g., corresponding to transducer  314 ) can generate a transmit waveform and receive a reflection to determine an amount of force applied to the surface (e.g., cover glass  312 ) as described with reference to timing diagram  640  during an acoustic force sensing phase. 
     In some examples, the acoustic touch and force sensing can be performed using transmit waveforms generated at the same time.  FIG. 7  illustrates a timing diagram  700  for acoustic touch and force sensing according to examples of the disclosure. Signal  702  can correspond to a transmit waveform generated by a transducer (e.g., transducer  314 ) to simultaneously propagate in deformable material  316  and in cover glass  312 . Signal  704  can correspond to a reflection (e.g., a first reflection) from the boundary between deformable material  316  and rigid material  318 . Signal  706  can correspond to a reflection from an object (e.g., a finger) on the surface of cover glass  312 . Signal  708  can correspond to a reflection from the opposite edge of cover glass  312 . Based on the timing of signal  704 , the acoustic touch and force sensing circuitry can measure a time-of-flight across the deformable material. Based on the timing of signals  706  and/or  708 , the acoustic touch and force sensing circuitry can measure the time-of-flight along the surface of cover glass  312  to an object (or an edge when no object is contacting the cover glass). The time-of-flight measurements for touch can be repeated for each transducer  502 A-D (e.g., four times) to determine the location/position of the object. The time-of-flight measurements can optionally be repeated (e.g., for each of transducers  502 A-D) to measure force applied to the cover glass  312 . In some examples, an average force measurement can be determined from repeated force measurements. In some examples, the repeated measurements can indicate relative force applied to different edges of the cover glass. In some examples, the measurements and different edges of the cover glass can be combined to determine an applied force. 
     Performing acoustic touch and force sensing using one or more shared transducers can provide for both touch and force information with one set of ultrasonic transducers (e.g.,  502 A-D) and one sensing circuit (e.g., acoustic touch and/or force sensing circuit  400 ). As a result, the touch and force sensing systems can potentially be reduced in size, in complexity and in power consumption. 
     Performance of ultrasonic touch and force sensing using ultrasonic waves transmitted into deformable material  316  and cover glass  312  at the same time can depend, in some examples, on the separation between the transmitted ultrasonic waves for touch and for force. For example,  FIG. 7  illustrates signals  704  and  706  corresponding to force and touch reflections, respectively, that can be well separated in time (e.g., such that the force reflections arrive in a dead zone for touch reflections). In practice, an integration of acoustic touch and force sensing can subject each measurement (touch/force) to noise/interference from the other measurement (force/touch). 
     In some examples, interference between ultrasonic waves in the deformable material and the cover glass can be reduced or eliminated based on the design of the deformable material. For example, the deformable material can be selected to have an ultrasonic attenuation property above a threshold, such that the signal in the deformable material can be damped before reflections in the cover glass are received. In some examples, the thickness of the deformable material can be selected to allow for one or more reflections through the deformable material to be received before reflections from the cover glass. In some examples, the reflection (e.g., first, second, nth) through the deformable material can be selected such that the reflection of interest occurs between reflections from the cover glass can be received. In some examples, an absorbent material can be coupled to the deformable material to further dampen ringing of ultrasonic signals in the deformable material. In some examples (e.g., when force and touch ultrasonic waves do not overlap in time), more than one of the transducers (and in some cases all of the transducers) can transmit a wave and receive the reflections at the same time to measure the force applied. Then, individual transducers can transmit waves and receive reflected waves sequentially for touch detection. 
     Processing data from acoustic touch and/or force detection scans can be performed by different processing circuits of an acoustic touch and/or force sensing system. For example, as described above with respect to  FIG. 4 , an electronic device can include an acoustic touch and force sensing circuit  400  and a processor SoC  430  (e.g., including a host processor  432  and an auxiliary processor/sub-processor  434 ). As described in detail below, processing of touch and/or force data can be performed by one or more of these processors/circuits, according to various examples. For example, according to the various examples, the processing of touch and/or force data can be performed by the acoustic touch and force sensing circuit, by the processor SoC, or partially by the acoustic touch and force sensing circuit and partially by the processor SoC. The description of the data processing below first addresses touch data processing and then addresses force data processing. 
     As described below in more detail, in some examples, raw touch sensing data can be transmitted to a processor SoC to be processed by one or more processors of processor SoC (e.g., host processor  432  and an auxiliary processor/sub-processor  434 ). In some examples, the touch sensing data can be processed in part by analog processing circuits (e.g., as described above with reference to  FIG. 4 ) and/or digital processing circuits (e.g., averaging of ADC outputs) of an acoustic touch (and/or force) sensing circuit. The partially processed touch sensing data can be transmitted to the processor SoC for further processing. In some examples, an acoustic touch (and/or force) sensing circuit can process the touch sensing data and supply the processor SoC with high level touch information (e.g., the centroid of the touch). The acoustic touch and force sensing circuit can be referred to as an acoustic touch sensing circuit to simplify the description of touch data processing among the various processors and circuits below. 
     In some examples, an auxiliary processor (e.g., auxiliary processor  434 ) can be a low power processor that can remain active even when a host processor (e.g., host processor  432 ) can be idle and/or powered down. An acoustic touch sensing circuit (e.g., corresponding to acoustic touch and force sensing circuit  400 ) can perform acoustic touch sensing scans and generate acoustic touch data. The acoustic touch data can be transferred to the auxiliary processor for processing according one or more touch sensing algorithms. For example, in a low-power mode, the acoustic touch sensing circuit can perform a low power touch detection scan. The low power touch detection scan can include receiving reflections from a barrier (e.g., surface edge) opposite a transducer for one or more transducers (e.g., from one transducer rather than the four illustrated in  FIG. 5A ). The acoustic touch data corresponding to the received reflections from the barrier(s) can be transmitted to the auxiliary processor via a communication channel and processed by the auxiliary processor to determine the presence or absence of an object touching the sensing surface. Once an object is detected touching the sensing surface, the system can transition from the low-power mode to an active mode, and the acoustic touch sensing circuit can perform an active mode touch detection scan. Additionally or alternatively, in some examples, a low power force detection scheme (e.g., performed using one transducer) can be used in the low-power mode. The active mode touch detection scan can include, for example, scanning the sensing surface as described above with respect to  FIG. 5A . The acoustic touch data corresponding to the active mode touch detection scan can be transmitted to the auxiliary processor via a communication channel and processed by the auxiliary processor to determine the location of the object. In some examples, determining the location of the object can include determining the area and/or centroid of the object. The host processor can receive the location of the object touching the surface from the auxiliary processor and perform an action based thereon. 
     In some examples, the acoustic touch sensing circuit can perform some processing before sending acoustic touch data to the auxiliary processor. For example, to reduce the requirements for the data communication channel between the acoustic touch sensing circuit and the auxiliary processor, the acoustic touch sensing circuit can include a digital signal processor which can average samples from the ADC output. Averaging the samples can compress the amount of acoustic touch data to be communicated to the auxiliary processor. The averaging performed by the digital signal processor can be controlled by control circuitry (e.g., acoustic scan control logic  422 ) in the acoustic touch sensing circuit. In some examples, the transmit signal can be coded to allow for averaging without a time penalty. Although averaging is described, in other examples, other forms of processing can be applied to the acoustic touch data before transferring the acoustic touch data. 
     In some examples, the data communication channel between the acoustic touch sensing circuit and the auxiliary processor can be a serial bus, such as a serial peripheral interface (SPI) bus. In addition, the communication channel can be bidirectional so information can also be transmitted from the auxiliary processor to the acoustic touch sensing circuit (e.g., register information used for programming acoustic touch sensing circuit). Additionally, the acoustic touch sensing circuit can receive one or more synchronization signals from the auxiliary processor configured to synchronize acoustic touch sensing scanning operations by the acoustic touch sensing circuit. Additionally, the acoustic touch sensing circuit can generate an interrupt signal configured to provide for proper acoustic data transfer from the acoustic touch sensing circuit to the auxiliary processor. In some examples, the detection and the processing for the low power touch detection mode can be done on-chip (e.g., by the acoustic touch sensing circuit). In these examples, interrupt signals can be used to indicate (e.g., to the auxiliary processor) when a finger is detected on the surface of the device. 
     In some examples, the acoustic touch sensing circuit can perform acoustic touch sensing scans and generate acoustic touch data. The acoustic touch data can be transferred to the auxiliary processor and/or the host processor for processing according one or more touch sensing algorithms. For example, in a low-power mode, the acoustic touch sensing circuit can perform a low power detection scan as described herein. The acoustic touch data can be transmitted to the auxiliary processor via a communication channel and processed by the auxiliary processor to determine the presence or absence of an object touching the sensing surface. Once an object is detected touching the sensing surface, the system can transition from the low-power mode to an active mode, and the acoustic touch sensing circuit can perform an active mode detection scan as described herein. The acoustic touch data corresponding to the active mode detection scan can be transmitted to the host processor via a high-speed communication channel and processed by the host processor to determine the location of the object. In some examples, the data transfer via the high-speed communication channel can be done in a burst mode. In some examples, determining the location of the object can include determining the area and/or centroid of the object. The host processor can perform an action based on the location. 
     In some examples, the high-speed communication channel can provide sufficient bandwidth to transfer raw acoustic touch data to the host processor, without requiring processing by the acoustic touch sensing circuit. In some examples, the high-speed communication channel can include circuitry to serialize the acoustic touch data (e.g., a serializer) and transfer the serialized acoustic touch data using a low-voltage differential signal (LVDS) communication circuit. In some examples, other I/O blocks can be utilized for the data transfer. In some examples, the acoustic touch sensing circuit can perform some processing (e.g., averaging) before sending acoustic touch data to the host processor. In some examples, the amount of data resulting from a low power detection scan can be relatively small (compared with an active mode detection scan) such that the raw acoustic touch data can be transferred to the auxiliary processor without requiring processing by the acoustic touch sensing circuit. In some examples, the acoustic touch sensing circuit can perform some processing (e.g., averaging) before sending acoustic touch data to the host processor. The other aspects of operation (e.g., data transfer from the auxiliary processor to acoustic touch sensing circuit, synchronization signals and interrupt signals, etc.) can be the same as or similar to the description above. Although described above as processing acoustic touch data from low power detection scans in the auxiliary processor and acoustic touch data from active mode detection scans in the host processor, it should be understood that in some examples, the host processor can perform processing for both low power detection scans and active mode detection scans. 
     In some examples, the acoustic touch sensing circuit can include an acoustic touch digital signal processor (DSP). In some examples, the acoustic touch DSP can be a separate chip coupled between the acoustic touch sensing circuit and the processor SoC. The acoustic touch sensing circuit can perform acoustic touch sensing scans and generate acoustic touch data. The acoustic touch data can be transferred to the acoustic touch DSP for processing according one or more touch sensing algorithms. For example, in a low-power mode, the acoustic touch sensing circuit can perform a low power detection scan as described herein. The acoustic touch data can be transmitted to the acoustic touch DSP via a communication channel and processed by the acoustic touch DSP to determine the presence or absence of an object touching the sensing surface. In some examples, the acoustic touch sensing circuit can process the acoustic touch data to determine the presence or absence of the object touching the surface. Once an object is detected touching the sensing surface, the system can transition from the low-power mode to an active mode, and the acoustic touch sensing circuit can perform an active mode detection scan as described herein. The acoustic touch data corresponding to the active mode detection scan can be transmitted to the acoustic touch DSP via a high-speed communication channel and processed by the acoustic touch DSP to determine the location of the object. In some examples, determining the location of the object can include determining the area and/or centroid of the object. The location can be passed to the auxiliary processor and/or the host processor, and the auxiliary processor and/or the host processor can perform an action based on the location. 
     In some examples, the high-speed communication channel can provide sufficient bandwidth to transfer raw acoustic touch data to the acoustic touch DSP, without requiring processing by the acoustic touch sensing circuit. In some examples, the high-speed communication channel can include circuity to serialize the acoustic touch data (e.g., CMOS serializer) and transfer the serialized acoustic touch data using a low-voltage differential signal (LVDS) communication circuit. In some examples, the acoustic touch sensing circuit can perform some processing (e.g., averaging) before sending acoustic touch data to the acoustic touch DSP. In some examples, the amount of data resulting from a low power detection scan can be relatively small (compared with an active mode detection scan) such that the raw acoustic touch data can be transferred to the acoustic touch DSP without requiring processing by the acoustic touch sensing circuit. In some examples, the data from low power detection scans can also be transferred to the acoustic touch DSP via the high-speed communication channel. 
     Data transfer from the auxiliary processor to the acoustic touch sensing circuit, synchronization signals and interrupt signals can be the same as or similar to the description above, except that, in some examples, the various signals and data can pass through the acoustic touch DSP. 
     In some examples, the acoustic touch sensing circuit can perform acoustic touch sensing scans and generate acoustic touch data. The acoustic touch data (e.g., for a low-power detection scan) can be processed by the acoustic touch sensing circuit to determine the presence or absence of the object touching the surface. Once an object is detected touching the sensing surface, the system can transition from the low-power mode to an active mode, and the acoustic touch sensing circuit can perform an active mode detection scan as described herein. The acoustic touch data corresponding to the active mode detection scan can be processed by the acoustic touch sensing circuit to determine the location of the object. In some examples, determining the location of the object can include determining the area and/or centroid of the object. The presence and/or location of the object can be passed to the auxiliary processor and/or the host processor, and the auxiliary processor and/or the host processor can perform an action based on the presence and/or location of the object. 
     In some examples, the amount of post-processing information (e.g., centroid) can be relatively small (compared with raw acoustic touch data) such that the information can be transferred to the auxiliary processor and/or the host processor via a serial communication bus (e.g., SPI), without a high-speed data channel. 
     Data transfer from the auxiliary processor to acoustic touch sensing circuit, synchronization signals and interrupt signals can be the same as or similar to the description above. In some examples, separate data communication channels can be provided between the acoustic touch sensing circuit and each of the auxiliary processor and the host processor. In some examples, the data communication channel can be a shared bus (e.g., shared SPI bus) between the acoustic touch sensing circuit and each of the auxiliary processor and the host processor. 
     The acoustic touch sensing circuit, as described herein, can be powered down or put in a low power state when not in use. In some examples, the acoustic touch sensing circuit can be on only during acoustic touch detection scans (e.g., during Tx and Rx operations). In some examples, the acoustic touch sensing circuit can be on in a low power state at all time (e.g., running at a low frame rate, performing a low power detection scan), and can transition into an active mode state when an object is detected. 
     In a similar manner, processing force data can be performed by different processing circuits of an acoustic touch and/or force sensing system. For example, as described above with respect to  FIG. 4 , an electronic device can include an acoustic touch and force sensing circuit  400  and a processor SoC  430  (e.g., including a host processor  432  and an auxiliary processor/sub-processor  434 ). In some examples, force detection circuit  424  can duplicate (or reuse) the touch sensing circuitry of  FIG. 4  to collect and/or processes force data. In some examples, raw force sensing data can be transmitted by a force detection circuit  424  to a processor SoC to be processed by one or more processors of processor SoC (e.g., host processor  432  and an auxiliary processor/sub-processor  434 ). In some examples, the force sensing data can be processed in part by analog processing circuits and/or digital processing circuits of an acoustic force (and/or touch) sensing circuit. The partially processed force sensing data can be transmitted to the processor SoC for further processing. In some examples, an acoustic force (and/or touch) sensing circuit can process the force sensing data and supply the processor SoC with force information (e.g., an amount of applied force). Additionally, a low power force detection scan can be used in addition to or in place of a low power touch detection scan described above (e.g., to cause the device to exit a low power or idle mode). The low power force detection scan can include, for example, determining force applied to the surface using fewer than all transducers (e.g., one transducer). 
     In some examples, force detection circuit  424  can be simplified with respect to touch detection circuitry to reduce power and hardware requirements.  FIGS. 8A-C  illustrate exemplary circuits for force detection according to examples of the disclosure. It should be understood that the circuits of  FIGS. 8A-C  are exemplary, and other circuits can be used for force sensing. Additionally, although the circuits of  FIGS. 8A-C  can be single-ended circuits, partially or fully differential circuits can also be used.  FIG. 8A  illustrates an exemplary force detection circuit  800  according to examples of the disclosure. Force detection circuit  800  can include a gate (or switch)  801 , a programmable gain amplifier (PGA)  802 , an analog comparator  804 , a time-to-digital signal converter  806  and, optionally, a digital comparator  808 . A gate timing signal can be used to activate gate  801  (e.g., close a switch) between the input from the transducer used to measure force and the PGA  802 . The gate timing signal can also be used to start timing by time-to-digital signal converter  806 . The output of PGA  802  can be input into comparator  804 , which can be used for finding a reliable transition edge of the receive signal. When the comparator transitions, the timing by the time-to-digital signal converter  806  stops. The digital output (e.g., a digitized number) of the time-to-digital signal converter  806 , which can be proportional to the applied force, can be sent from the acoustic force (and/or touch) sensing circuit to a processor. In some examples, an optional digital comparator  808  can be used to transmit force reading exceeding a threshold amount of force. In some examples, a time window can be selected and all or some of the threshold crossing time stamps can be sent from the acoustic force (and/or touch) sensing circuit to the processor SoC, and the time stamps can be used to detect the time-of-flight change (and therefore the force applied). In some examples, the digitized data for a given time window can be sampled at two different times (one time without and one time with the force applied) and the correlation between the two time-of-flight measurements can be used to determine the change in time-of-flight (and therefore applied force). 
       FIG. 8B  illustrates an exemplary force detection circuit  810  according to examples of the disclosure. Force detection circuit  810  can include a gate (or switch)  811 , a PGA  812 , a differential-to-single-ended converter circuit  812 , an analog comparator  814 , a logical AND gate  816 , a digital counter  818  and a clock  820 . A gate timing signal can be used to activate gate  811  (e.g., close a switch) between the input from the transducer used to measure force and the differential-to-single-ended converter circuit  812 . The single-ended output of the differential-to-single-ended converter circuit  812  can be provided to PGA  812 . The gate timing signal can also be output to logical AND gate  816 . When the gate timing signal and the output of analog comparator  814  can both be high, counter  818  can start timing based on a clock signal from clock  820 . The output of PGA  812  can be input into comparator  814 , which can be used for finding a reliable transition edge of the receive signal. When the comparator transitions, the timing by the counter  818  can be stopped. The digital output (e.g., a digitized number) from counter  818 , which can be proportional to the applied force, can be sent from the acoustic force (and/or touch) sensing circuit to a processor. 
     It should be understood exemplary force detection circuits  800  and  810  can be reconfigured to output the threshold crossing on a rising edge, a falling edge or both edges of the received signal. Force detection circuits  800  and  810  as illustrated in  FIGS. 8A and 8B  output the rising edge threshold crossings after each rising edge of the time gating signal. In some examples, threshold crossings can be detected on both rising and falling edges of the input signal.  FIG. 8C  illustrates an exemplary force detection circuit  830  according to examples of the disclosure. Force detection circuit  830  can include a gate (or switch)  831 , a PGA  832 , an analog comparator  834 , a logical inverter  836 , n-bit D-Flip Flops  838  and  840 , a clock  842  and a digital counter  844 . A reset signal can be used to reset D-Flip Flops  838  and  840 . A time window signal can be used to activate gate  831  between the input from the transducer used to measure force and PGA  832 . The time window signal can also enable counter  844  to start timing based on a clock signal from clock  842 . The output of PGA  832  can be input into comparator  834 , which can be used for finding reliable transition edges of the receive signal. The output of comparator  834  can be used to clock D-Flip Flops  838  and  840 . D-Flip Flop  838  can be clocked with an inverted version of the comparator output to detect the opposite edge. D-Flip Flops  838  and  840  can receive the output of counter  844  as data inputs, and output the count of counter  844  for a rising and falling edge transition, respectively. The digital outputs (e.g., digitized numbers) of D-Flip Flops  838  and  840 , which can be proportional to the applied force, can be sent from the acoustic force (and/or touch) sensing circuit to a processor. 
     As discussed above, in some examples, the force data can be sampled at two different times (one time without and one time with the force applied) and the correlation between the two time-of-flight measurements can be used to determine the change in time-of-flight (and therefore applied force).  FIG. 9  illustrates an exemplary configuration of an acoustic touch and/or force sensing circuit according to examples of the disclosure. The circuitry illustrated in  FIG. 9  can correspond to the corresponding circuitry illustrated in  FIG. 4 , implemented to detect force, for example. Unlike  FIG. 4 , the acoustic touch and/or force sensing circuitry of  FIG. 9  can include a correlator  950 . Correlator  950  can be a digital correlator configured to correlate force data for a no-applied force case (e.g., baseline) with measured force data that may include an applied force. The correlation can indicate a change in the time of flight (or resonance) in the deformable material, and thereby indicate an applied force. 
     As described above, acoustic touch and force sensing scans performed by an acoustic touch and force sensing circuit can involve stimulating and sensing one or more transducers.  FIGS. 10A-10E  illustrate exemplary integration of an acoustic touch and force sensing circuit and/or one or more processors (e.g., processor SoC) with transducers mechanically and acoustically coupled to a surface (e.g., glass, plastic, metal, etc.) and/or a deformable material (e.g., silicone, rubber, etc.) according to examples of the disclosure.  FIG. 10A  illustrates an exemplary acoustic touch and force sensing system configuration  1000  using four acoustic transducers  1004 A-D mounted along (or otherwise coupled to) four edges of a surface  1002  (e.g., underside of a cover glass). Transducers  1004 A-D can be configured to generate acoustic waves (e.g., shear horizontal waves) and to receive the reflected acoustic waves. Additionally, the acoustic transducers  1004 A-D can also be mounted over (or otherwise coupled to) a deformable material (e.g., gasket) disposed between the surface  1002  and a rigid material (e.g., a portion of the housing). One or more acoustic touch and force sensing circuits can be included. For example,  FIG. 10A  illustrates a first acoustic touch and force sensing circuit  1006  positioned proximate to neighboring edges of transducers  1004 C and  1004 D. Likewise, a second acoustic touch and force sensing circuit  1006 ′ can be positioned proximate to neighboring edges of transducers  1004 A and  1004 B. Placement of acoustic touch and force sensing circuits as illustrated can reduce routing between transducers  1004 A-D and the respective acoustic touch and force sensing circuits. Processor SoC  1008  can be coupled to the one or more acoustic touch and force sensing circuits to perform various processing as described herein. In some examples, some or all of the drive circuitry (Tx circuitry) and/or some or all of the receive circuitry (Rx circuitry) of the touch and force sensing circuit can be implemented on different silicon chips. 
     In some examples, transducers  1004 A-D can be coupled to one or more acoustic touch and force sensing circuits via a flex circuit (e.g., flexible printed circuit board).  FIG. 10B  illustrates a view  1010  of exemplary acoustic touch and force sensing system configuration  1000  along view AA of  FIG. 10A . As illustrated in  FIG. 10B , transducer  1004 D can be coupled to surface  1002  by a bonding between a bonding material layer  1014  on an underside of surface  1002  and a first signal metal layer  1012 A on one side of transducer  1004 D. In some examples, the bonding material layer  1014  can be electrically conductive (e.g., a metal layer). In some examples, the bonding material layer  1014  can be electrically non-conductive. The first signal metal layer  1012 A on one side of transducer  1004 D and a second signal metal layer  1012 B on a second side of transducer  1004 D can provide two terminals of transducer  1004 D to which stimulation signals can be applied and reflections can be received. The first signal metal layer  1012 A can wrap around from one side of transducer  1004 D to an opposite side to enable bonding of both signal metal layers of the transducer  1004 D on one side of transducer  1004 D. In  FIG. 10B , acoustic touch and force sensing circuit  1006  can be coupled to a flex circuit  1016  and the flex circuit can be respectively bonded to signal metal layers  1012 A and  1012 B of transducer  1004 D (e.g., via bonds  1018 ). Likewise, transducer  1004 C can be coupled to surface  1002  (e.g., via bond metal layer/first signal metal layer bonding) and to acoustic touch and force sensing circuit  1006  by bonding a flex circuit to signal metal layers on the transducer side opposite the surface. Similarly, transducers  1004 A and  1004 B can be coupled to surface  1002  and second acoustic touch and force sensing circuit  1006 ′. 
     Transducers  1004 A-D can also be coupled to deformable material  1003 . For example, deformable material  1003  can be a gasket disposed between the surface  1002  and a rigid material  1007 . When assembled, deformable material  1003  (e.g., gasket) can form a water-tight seal between surface  1002  (e.g., cover glass) and a rigid material  1007  (e.g., housing). Transducers  1004 A-D in contact with deformable material  1003  can apply stimulation signals to and receive reflections from the deformable material  1007 . In a similar manner, transducers  1004 A-D can also be coupled to deformable material  1003  as illustrated in  FIGS. 10C-E . 
     In some examples, transducers  1004 A-D can be coupled to acoustic touch and force sensing circuits via an interposer (e.g., rigid printed circuit board).  FIG. 10C  illustrates a view  1020  of exemplary acoustic touch and force sensing system configuration  1000  along view AA. Transducers  1004 C and  1004 D can be coupled to surface  1002  as illustrated in and described with respect to  FIG. 10B . Rather than coupling acoustic touch and force sensing circuit  1006  to a flex circuit  1016  and bonding the flex circuit to signal metal layers  1012 A and  1012 B of transducer  1004 D, however, in  FIG. 10C , an interposer  1022  can be bonded to signal metal layers  1012 A and  1012 B of transducer  1004 D (e.g., via bonds  1024 ). Acoustic touch and force sensing circuit  1006  can be bonded or otherwise coupled to interposer  1022 . Similarly, transducers  1004 A and  1004 B can be coupled to surface  1002  and second acoustic touch and force sensing circuit  1006 ′. In some examples, transducers  1004 A-D can be directly bonded to acoustic touch and force sensing circuits.  FIG. 10D  illustrates a view  1030  of exemplary acoustic touch and force sensing system configuration  1000  along view AA. Transducers  1004 C and  1004 D can be coupled to surface  1002  as illustrated in and described with respect to  FIG. 10B . Rather than coupling acoustic touch and force sensing circuit  1006  to a flex circuit or interposer and bonding the flex circuit/interposer to signal metal layers  1012 A and  1012 B of transducer  1004 D, however, in  FIG. 10D , an acoustic touch and force sensing circuit  1006  can be bonded to signal metal layers  1012 A and  1012 B of transducer  1004 D (e.g., via bonds  1032 ). Similarly, transducers  1004 A and B can be coupled to surface  1002  and second acoustic touch and force sensing circuit  1006 ′. 
     In  FIGS. 10B-D , signal metal layer  1012 A was routed away from surface  1002  and both signal metal layers  1012 A and  1012 A were bonded to an acoustic touch and force sensing circuit via bonding on a side of transducer  1004 D separate from surface  1002  (e.g., via flex circuit, interposer or direct bond). In some examples, the acoustic touch and force sensing circuits can be bonded to routing on surface  1002 .  FIG. 10E  illustrates a view  1040  of exemplary acoustic touch and force sensing system configuration  1000  along view AA. Unlike in  FIG. 10A , for example, transducer  1004 D can be coupled to surface  1002  via two separate portions of metal bond layer. A first portion of the metal bond layer  1042 A can be bonded to a first signal metal layer  1044 A (using a metal to metal conductive bonding), and a second portion of the metal bond layer  1042 B can be bonded to a second signal metal layer  1044 B (which can optionally be wrapped around transducer  1004 D). Although not shown, the first and second portions of the metal bond layer  1042 A and  1042 B can be routed along the underside of surface  1002  and bond connections can be made with a flex circuit or interposer including an acoustic touch and force sensing circuit, or directly to the acoustic touch and force sensing circuit. Likewise, transducer  1004 C can be coupled to surface  1002  and acoustic touch and force sensing circuit  1006  via routing on the surface. Similarly, transducers  1004 A and  1004 B can be coupled to surface  1002  and coupled to second acoustic touch and force sensing circuit  1006 ′ via routing on the surface. It should be noted, that one advantage of the integration illustrated in  FIG. 10E  over the integrations of  FIGS. 10B-D , can be that the deformable material  1003  can have a more uniform shape around the perimeter of the device. In contrast, as illustrated in  FIGS. 10B-D , the deformable material may include a cutout or notch or have different properties (e.g., different thickness) where the acoustic touch and force sensing circuit (and/or flex circuit or interposer) is located. Alternatively, the transducer can be made thinner in the electrical connection area to accommodate for the electrical connection in  FIGS. 10B-D  without a notch or cutout. In some examples, pitch-catch force sensing can be used. In such examples, a receive transducer can be added between the deformable material  1003  and rigid material  1007  (e.g., as illustrated in  FIG. 6B .) 
     It should be understood that the exemplary integration of an acoustic touch and force sensing circuit, transducers and a surface described herein are exemplary and many other techniques can be used. Transducers can be attached to the edge of the cover glass (e.g., on a side of the cover glass) or underneath the cover glass. In some examples, the transducers can be integrated in a notch in the cover glass. In all of the integrations of the transducers and the cover glass, the attachment and the bonding should be done in a way that can allow for the desired acoustic wave to be generated and propagated in the cover glass (or on top of the cover glass). In some examples, matching or backing materials can be added to the transducers to increase their performance as well as the matching to the target surface medium (e.g., cover glass). Likewise, matching or backing materials can be added to the transducers interfacing with deformable material  1003  to increase performance of force detection as well as the matching to the deformable material medium. In some examples, transducers for touch detection can be implemented on the edges of the cover glass and the transducers for force detection can be implemented on the corners of the cover glass. 
     As described above, in some examples, the transmitter and receiver functions can be separated such that the transmission of acoustic energy at  302  and the receiving of acoustic energy at  304  may not occur at the same transducer. In some examples, the transmit transducer and the receive transducer can be made of different materials to maximize the transmit and receive efficiencies, respectively. In some examples, having separate transmit and receive transducers can allow for high voltage transmit circuitry and low voltage receive circuitry to be separated (for touch and/or force sensing circuits).  FIG. 11  illustrates an exemplary configuration of an acoustic touch and force sensing circuit  1100  according to examples of the disclosure. The configuration of  FIG. 11 , like the configuration of  FIG. 4 , can include an acoustic touch and force sensing circuit  1100  and a processor SoC  1130 . As described above, processor SoC  1130  can include a host processor  1132  (e.g., corresponding to processor  432 ) and an auxiliary processor  1134  (corresponding to auxiliary processor  434 ). Likewise, acoustic touch and force sensing circuit  1100  can include transmitter  1102  (corresponding to transmitter  402 ), transmit switching circuitry  1104 A (corresponding to demultiplexers of switching circuitry  404 ), receive switching circuitry  1104 B (e.g., corresponding to multiplexers of switching circuitry  404 ), an amplifier  1110  (e.g., corresponding to amplifier  410 ), gain and offset correction circuit  1112  (e.g., corresponding to gain and offset correction circuit  412 ), demodulation circuit, envelope detection circuit, and/or filter  1114 - 1116  (e.g., corresponding to demodulation circuit  414 , envelope detection circuit  415 , and/or filter  416 ), ADC  1118  (e.g., corresponding to ADC  418 ) and I/O circuit  1120  (e.g., corresponding to I/O circuit  420 ). Acoustic touch and force sensing circuit  1100  can also include a force detection circuit  1124  (e.g., corresponding to force detection circuit  424 ). The operation of these components can be similar to that described above with respect to  FIG. 4 , and is omitted here for brevity. Unlike  FIG. 4 , which includes transducers  406  performing both transmit and receive operations, the configuration illustrated in  FIG. 11  can include transducers  1106 A operating as transmitters and separate transducers  1106 B operating as receivers. Transducers  1106 A and  1106 B can co-located at locations where transmit and receive transducers are previously described. For example, transducer  502 A can be replaced by a first transducer configured to transmit and a second transducer configured to receive. 
     It is to be understood that the configuration of  FIG. 11  is not limited to the components and configuration of  FIG. 11 , but can include other or additional components in multiple configurations according to various examples. Additionally, some or all of the components illustrated in  FIG. 11  can be included in a single circuit, or can be divided among multiple circuits while remaining within the scope of the examples of the disclosure. In some examples, some or all of the transmit circuitry  1102  and transmit switching circuitry  1104 A can be implemented in one chip and some or all of the receive circuitry  408  and receive switching circuitry  404 B can be implemented in a second chip. The first chip including transmit circuitry can receive and/or generate via a voltage boosting circuit a high voltage supply for stimulating the surface. The second chip including the receive circuitry can operate without receiving or generating a high voltage supply. In some examples, more than two chips can be used, and each chip can accommodate a portion of the transmit circuitry and/or receive circuitry. 
       FIGS. 12A-12E  illustrate exemplary integration of an acoustic touch and force sensing circuit and/or one or more processors (e.g., processor SoC) with groups of transducers (e.g., one transmitting and one receiving) mechanically and acoustically coupled to a surface (e.g., glass, plastic, metal, etc.) and/or a deformable material (e.g., silicone, rubber, etc.) according to examples of the disclosure.  FIG. 12A  illustrates an exemplary acoustic touch and force sensing system configuration  1200  using eight acoustic transducers, including four transmit transducers  1204 A-D and four receive transducers  1205 A-D mounted along (or otherwise coupled to) four edges of a surface  1202  (e.g., cover glass). Transmit transducers  1204 A-D can be configured to generate acoustic waves (e.g., shear horizontal waves) and receive transducers  1205 A-D can be configured to receive the reflected acoustic waves. Additionally, the acoustic transducers  1204 A-D and  1205 A-D can also be mounted over (or otherwise coupled to) a deformable material (e.g., gasket) disposed between the surface  1002  and a rigid material (e.g., a portion of the housing). One or more acoustic touch and force sensing circuits can be included. For example,  FIG. 12A  illustrates a first acoustic touch and force sensing circuit  1206  positioned proximate to neighboring edges of transmit transducers  1204 C-D and receive transducers  1205 C-D. Likewise, a second acoustic touch and force sensing circuit  1206 ′ can be positioned proximate to neighboring edges of transmit transducers  1204 A-B and receive transducers  1205 A-B. Placement of acoustic touch and force sensing circuits as illustrated can reduce routing between transducers and corresponding acoustic touch and force sensing circuits. Processor SoC  1208  can be coupled to the one or more acoustic touch and force sensing circuits. 
     In some examples, transducers  1204 A-D/ 1205 A-D can be coupled to acoustic touch and force sensing circuits via a flex circuit (e.g., flexible printed circuit board).  FIG. 12B  illustrates a view  1210  of exemplary acoustic touch and force sensing system configuration  1200  along view AA of  FIG. 12A . As illustrated in  FIG. 12B , receiver transducer  1205 D can be coupled to surface  1202  by a bonding between a bond material layer  1214  on an underside of surface  1202  and a first signal metal layer  1212 A on one side of receive transducer  1205 D. In some examples, the bonding material layer  1214  can be electrically conductive (e.g., a metal layer). In some examples, the bonding material layer  1214  can be electrically non-conductive. The first signal metal layer  1212 A on one side of receive transducer  1205 D and a second signal metal layer  1212 B on a second side of receive transducer  1205 D can provide two terminals of receive transducer  1205 D from which reflections can be received. The first signal metal layer  1212 A can wrap around from one side of receive transducer  1205 D to an opposite side to enable bonding of both signal metal layers of receive transducer  1205 D on one side of receive transducer  1205 D. In  FIG. 12B , acoustic touch and force sensing circuit  1206  can be coupled to a flex circuit  1216  and the flex circuit can be respectively bonded to signal metal layers  1212 A and  1212 B of receive transducer  1205 D (e.g., via bonds  1218 ). Similarly transmit circuit  1204 D (not shown) can be coupled to surface  1202  and can provide two terminals to which stimulation signals can be applied. The flex circuit can be bonded to respective signal metal layers of transmit transducer  1204 D. Likewise, transmit transducer  1204 C and receive transducer  1204 D can be coupled to surface  1202  (e.g., via bond metal layer/first signal mental layer bonding) and to acoustic touch and force sensing circuit  1206  by bonding the flex circuit to signal metal layers on the side of the transducer opposite the surface. Similarly, transmit transducers  1204 A-B and receive transducers  1205 A-B can be coupled to surface  1202  and second acoustic touch and force sensing circuit  1206 ′. 
     Transducers  1204 A-D and  1205 A-D can also be coupled to deformable material  1203 . For example, deformable material  1203  can be a gasket disposed between the surface  1202  and a rigid material  1207 . When assembled, deformable material  1203  (e.g., gasket) can form a water-tight seal between surface  1202  (e.g., cover glass) and a rigid material  1207  (e.g., housing). Transducers  1204 A-D and  1205 A-D in contact with deformable material  1203  can apply stimulation signals to and receive reflections from the deformable material  1207 . In a similar manner, transducers  1204 A-D and/or  1205 A-D can also be coupled to deformable material  1203  as illustrated in  FIGS. 12C-E . 
     In some examples, transmit transducers  1204 A-D and receive transducers  1205 A-D can be coupled to acoustic touch and force sensing circuits via an interposer (e.g., rigid printed circuit board).  FIG. 12C  illustrates a view  1220  of exemplary acoustic touch and force sensing system configuration  1200  along view AA. Transmit transducers  1204 C-D and receive transducers  1205 C-D can be coupled to surface  1202  as illustrated in and described with respect to  FIG. 12B . Rather than coupling acoustic touch and force sensing circuit  1206  to a flex circuit  1216  and bonding the flex circuit to signal metal layers  1212 A and  1212 B of receive transducer  1205 D, however, in  FIG. 12C , an interposer  1222  can be bonded to signal metal layers  1212 A and  1212 B of receive transducer  1205 D (e.g., via bonds  1224 ). Acoustic touch and force sensing circuit  1206  can be bonded or otherwise coupled to interposer  1222 . Similarly, the remaining transducers (transmit and receive) can be coupled to surface  1202  and the first or second acoustic touch and force sensing circuits  1206  and  1206 ′. 
     In some examples, transmit transducers  1204 A-D and receive transducers  1205 A-D can be directly bonded to acoustic touch and force sensing circuits.  FIG. 12D  illustrates a view  1230  of exemplary acoustic touch and force sensing system configuration  1200  along view AA. Transmit transducers  1204 C-D and receive transducers  1205 C-D can be coupled to surface  1202  as illustrated in and described with respect to  FIG. 12B . Rather than coupling acoustic touch and force sensing circuit  1206  to a flex circuit or interposer and bonding the flex circuit/interposer to signal metal layers  1212 A and  1212 B of receive transducer  1205 D, however, in  FIG. 12D , an acoustic touch and force sensing circuit  1206  can be bonded to signal metal layers  1212 A and  1212 B of receive transducer  1205 D (e.g., via bonds  1232 ). Similarly, the remaining transducers (transmit and receive) can be coupled to surface  1202  and the first or second acoustic touch and force sensing circuits  1206  and  1206 ′. 
     In  FIGS. 12B-D , signal metal layer  1212 A was routed away from surface  1202  and both signal metal layers  1212 A and  1212 B were bonded to an acoustic touch and force sensing circuit via bonding on a side of receive transducer  1205 D separate from surface  1202  (e.g., via flex circuit, interposer or direct bond). In some examples, the acoustic touch and force sensing circuits can be bonded to routing on surface  1202  instead, similar to the description above with respect to  FIG. 10E , for example. 
     Although  FIG. 12A  illustrates transmit transducers  1204 A-D as being side-by-side with receive transducers  1205 A-D, in some examples, transmit transducers  1204 A-D and receiver transducers  1205 A-D can be stacked on one another.  FIG. 12E  illustrates a view  1240  of exemplary acoustic touch and force sensing system configuration  1200  along view AA. As illustrated in  FIG. 12E , receiver transducer  1205 D can be coupled to surface  1202  by a bonding between a bond metal layer  1242  on an underside of surface  1202  and a first signal metal layer  1246 A on one side of receive transducer  1205 D. Transmit transducer  1204 D can be coupled to receive transducer  1205 D via a common second signal metal layer  1244  on a second side of receive transducer  1205 D. A first metal layer  1246 B can be deposited on the second side of transmit transducer  1204 D. First signal metal layer  1246 A and common second signal metal layer  1244  can provide two terminals of receive transducer  1205 D from which reflections can be received. First signal metal layer  1246 B and common second signal metal layer  1244  can provide two terminals of transmit transducer  1204 D to which transmit waves can be applied. In some examples, the common signal metal layer can be a common ground for the transmit and receive transducers. In some examples, the metal connections for the transmit and receive transducers can be separated from each other and differential or single ended transmit and receive circuitry can be used. Although not shown, routing of signal metal layers  1244 ,  1246 A and  1246 B can be placed so that acoustic touch and force sensing circuit  1206  can be coupled to routing on surface  1202  or exposed surfaces of transmit transducer  1204 D and/or receive transducer  1205 D to enable direct or indirect bonding of the acoustic touch and force sensing circuit to routing on surface  1202  or on transducers  1204 D/ 1205 D. In some examples, bond metal  1242  can be bonded to  1246 A signal metal (using a metal to metal conductive bonding). It should be noted, that one advantage of the integration illustrated in  FIG. 12E  over the integrations of  FIGS. 12B-D , can be that the deformable material  1003  can have a more uniform shape around the perimeter of the device. In contrast, as illustrated in  FIGS. 12B-D , the deformable material may include a cutout or have different properties (e.g., different thickness) where the acoustic touch and force sensing circuit (and/or flex circuit or interposer) is located. 
       FIGS. 13-19  illustrate various configurations for integrating touch and force sensing functionality within an electronic device. Each of the  FIGS. 13-19  includes a cover glass that can correspond to cover glass  312  above, a display stackup, a housing that can correspond to rigid material  318  above, a transducer that can correspond to transducer  314  above, and a deformable material (e.g., that can be included in a force sensing stackup) that can correspond to deformable material  316  above. In some examples, the display stackup can include a stackup for touch sensing circuitry (e.g., capacitive touch sensing). Each of the different configurations can be used to create a device that has both touch sensing and force sensing capability, as will be described in more detail below. 
       FIG. 13  illustrates a first exemplary configuration for integrating touch sensing and force sensing circuitry with housing  1304  and cover glass  1302  of an electronic device. In some examples, transducer  1308  can be coupled to a side of the cover glass  1302 . In some examples, cover glass  1302  can be disposed over a display stackup  1306 . In some examples, the display stackup  1306  can include a touch sensor stackup, e.g., a capacitive touch sensor stackup. In some examples, the transducer  1308  can have a height in the y-axis dimension that can be close to the thickness in the y-axis dimension of the cover glass  1302 . In some examples, this can allow the transducer  1308  to produce a uniform acoustic wave throughout the thickness of the cover glass  1302 . In some examples, by placing the transducer  1308  on the side of the cover glass, stimulating the transducer with a voltage or current can produce a horizontal shear wave, Rayleigh wave, Lamb wave, Love wave, Stoneley wave, or surface acoustic wave in the cover glass  1302  travelling along the x-axis direction. In some examples, more than one transducer  1304  can be disposed around the perimeter of the cover glass  1302  to provide touch measurements having two-dimensional coordinates on the cover glass surface (e.g., as described with respect to transducers  502 A- 502 D above). The transducer  1308  can be disposed on a backing material  1310  that can in turn provide mechanical coupling between the transducer and the housing  1304 . In some examples, an encapsulant  1316  can be provided to hide the transducer  1308  and backing material  1310  from being visible to a user as well as providing additional mechanical stability. In some examples, the encapsulant  1316  can be a part of the housing  1304  and in some examples the encapsulant can be a separate material from the housing (e.g., glass, zircon, titanium, sapphire, etc.). In some examples, a force sensor stackup  1312  can be positioned behind the cover glass  1302 , and can operate to detect force as described in at least  FIGS. 3 and 6-7  above. 
       FIG. 14  illustrates a second exemplary configuration for integrating touch sensing and force sensing circuitry with housing  1404  and cover glass  1402  of an electronic device.  FIG. 14  illustrates a similar configuration to  FIG. 13  showing the transducer  1408  coupled to a side of the cover glass  1402 . In some examples, the transducer  1408  can have a height in the y-axis dimension that can be close to the thickness in the y-axis dimension of the cover glass  1402 . In some examples, by placing the transducer  1408  on the side of the cover glass, stimulating the transducer with a voltage or current can produce a horizontal shear wave in the cover glass  1402  travelling along the x-axis direction. In some examples, more than one transducer  1404  can be disposed around the perimeter of the cover glass  1402  to provide touch measurements having two-dimensional coordinates on the cover glass surface (e.g., as described with respect to transducers  502 A- 502 D above). In some examples, each transducer  1408  can produce a shear wave oriented in a different direction. In addition to the encapsulant  1416  (which can correspond to the encapsulant  1316  above) a second encapsulant can be used to provide a mechanical base for the cover glass  1402 , transducer  1408  and backing material  1410 . Inclusion of the second encapsulant  1418  can simplify the structure of the housing  1404  by requiring one less notch in the housing. In some examples, the force sensor stackup  1412  can be supported directly by the housing  1404 , and can operate to detect force as described in at least  FIGS. 3 and 6-7  above. 
       FIG. 15  illustrates a third exemplary configuration for integrating touch sensing and force sensing circuitry with housing  1504  and curved cover glass  1502  of an electronic device. Unlike the configurations of  FIGS. 13 and 14  above, the orientation of the transducer  1508  does not necessarily need to match with the direction of acoustic wave propagation (e.g., along the x-axis). In the illustrated configuration, the transducer  1508  can be attached to an edge of the curved cover glass  1502  and backing material  1510  can be disposed between the transducer  1580  and the housing  1504 . In some examples, the transducer  1508  and backing material  1510  can be positioned within a notch or groove in the housing  1504  as illustrated in  FIG. 15 . In some examples, the acoustic energy produced by the transducer  1508  can be guided along the curved edge  1502 ′ of the cover glass and can continue to propagate along the surface to perform touch detection as described above with regards to  FIGS. 2-5 . In some examples, a gradual curvature of the cover glass  1502  can be used to guide the wave along the curved edge  1502 ′ of the cover glass toward the flat surface. Force sensor stackup  1512  can be supported by the housing  1504 , and a standoff  1514  can be coupled to the cover glass  1502  to transfer a force applied to the cover glass into the force sensor stackup as described in at least  FIGS. 3 and 6-7  above. In particular, because the force sensor stackup  1512  can be located beneath the curved edge  1502 ′ of the cover glass  1502 , the standoff  1514  can be included to translate the force onto a flat force sensor stackup. 
       FIG. 16  illustrates a variation of the third configuration of  FIG. 15  with the addition of an encapsulant material  1616  (which can correspond to encapsulant materials  1316 ,  1416 , and  1418  above) that can be used to mechanically secure the transducer  1608  and backing  1610  to the housing  1604  as well as visually obscure the transducer assembly from a user of the electronic device. Similar to  FIG. 10 , force sensor stackup  1612  can be located beneath the curved edge  1602 ′ of cover glass  1602  and a standoff  1614  can be coupled to the cover glass  1602  to transfer a force applied to the cover glass into the force sensor stackup. 
       FIG. 17  illustrates a fourth exemplary configuration for integrating touch sensing and force sensing circuitry with housing  1704  and cover glass  1702 . Transducer  1708  can be disposed on a backing material  1710  within a cavity formed behind the cover glass  1702 . An acoustic wave generated by stimulating the transducer  1708  can approximate the stimulation directly at the side of the cover glass  1702  as illustrated in  FIGS. 13 and 14  while maintaining a curved edge  1702 ′ of cover glass surface as illustrated in  FIGS. 15 and 16 . In other words, the transducer  1708  can be used to generate a wave that travels along the flat surface of the cover glass  1702  in the x-axis direction directly, without relying on guiding the wave through the curved edge  1702 ′ of the cover glass. Reflection of the transmitted acoustic energy can be used for touch detection as described above (e.g., with respect to  FIGS. 2-5 ). Force sensing stackup  1712  can be disposed between the cover glass  1702  and the housing  1704  to perform force sensing as described in at least  FIGS. 3 and 6-7  above. 
       FIG. 18  illustrates a fifth exemplary configuration for integrating touch sensing and force sensing circuitry with housing  1804  and cover glass  1802 . In some examples, transducer  1808  and backing material  1810  can be disposed on a back side of the cover glass  1802 . In some examples, acoustic energy from the transducer  1808  can begin propagating along the y-axis direction, can reflect from the curved edge  1802 ′ of the cover glass  1802 , and can travel along the x-axis direction as in the examples described above. In some examples, the amount of curvature of the curved edge  1802 ′ can determine the dispersion of the reflected acoustic energy. In some examples, this dispersion can lead to dispersion in the measured time of flight for reflected acoustic energy and can have an effect on touch detection as described in  FIGS. 2-5  above. Force sensor stackup  1812  can be coupled to the housing  1804  to perform force sensing as described in  FIGS. 6-7  above. 
       FIGS. 19A and 19B  illustrate exemplary configurations for integrating touch sensing and force sensing circuitry with shared elements with housing  1904  and cover glass  1902  of an electronic device. In some examples, the illustrations of  FIGS. 19A and 19B  can be implementations for integrating the touch sensing and force sensing as described in  FIGS. 2-7  above, with particular reference to  FIGS. 3B, 5A, 6A, and 6B .  FIGS. 19A and 19B  differ in the shape of the cover glass  1902 . In  FIG. 19A , the illustrated cover glass  1902  can have a flat back side, and the transducer  1908  can be disposed directly to the back side of the cover glass. In  FIG. 19B , the illustrated cover glass  1902  can have a downwardly extending portion at edges of the cover glass, and the transducer  1908  can be disposed on the downwardly extending portion of the cover glass. In other examples, the transducer  1908  can be attached to a curved cover glass  1902  such as those illustrated in  FIGS. 15-17  above. Similar to the configuration described for  FIG. 18 , acoustic energy from the transducer  1808  can begin propagating along the y-axis direction, can reflect from the bezel portion  1902 ′ of the cover glass  1902 , and can travel along the x-axis direction. In the illustrated examples of  FIGS. 19A and 19B , the bezel  1902 ′ is drawn as a perfectly formed 45 degree angle, which can produce a 90 degree change in orientation of the acoustic energy from the reflection at the bezel. It should be understood that the same principles apply to the curved cover glass  1802  of  FIG. 18 , and that acceptable performance can be obtained in the presence of a non-flat bezel  1902 ′, such as a curved edge  1802 ′ above. The illustrated flat bezel  1902 ′ could be used to provide a desirable reflection, but can result in a sharp edge that could be unpleasant for a user to touch. In some examples, a portion of the bezel  1902 ′ can be flat, while sharp edges of the bezel can be avoided by rounding of the edges. In some examples, the length (e.g., x-axis dimension) of the transducer  1908  can be made equal to or nearly equal to the thickness (e.g., y-axis dimension) of the cover glass  1902  so that a uniform acoustic wave  1920  can be transmitted throughout the thickness of the cover glass material. Using the principles described above in  FIGS. 2-5 , the transducer  1908  can be used to detect the touch position of object  1922  on the cover glass. As should be understood,  FIGS. 19A and 19B  illustrate how the configuration of  FIG. 3B  can be integrated into an electronic device cover glass for performing touch sensing. In addition, by placing a deformable material  1910  behind the transducer (e.g., as a backing material), the force sensing described in  FIGS. 3-7  above can simultaneously be performed using the same transducer  1908 . For example, as compared to  FIG. 6A , the cover glass  1902 , transducer  1908 , deformable material  1910 , and housing  1904  can correspond to cover glass  601 , transducer  602 , deformable material  604 , and rigid material  606  respectively. Also, although not shown, a second transducer can be included between the deformable material  1910  and the housing  1904  to match the configuration illustrated in  FIG. 6B . 
     Therefore, according to the above, some examples of the disclosure are directed to An electronic device, comprising: a cover surface; a deformable material disposed between the cover surface and a housing of the electronic device; an acoustic transducer coupled to the cover surface and the deformable material and configured to produce a first acoustic wave in the cover surface and a second acoustic wave in the deformable material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the deformable material and cover surface are further configured such that the first acoustic wave is capable of being propagated in a first direction and the second acoustic wave is capable of being propagated in a second direction, different from the first direction. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first acoustic wave is incident upon a bezel portion of the cover glass in a third direction and reflected by the bezel portion of the cover glass in the first direction, different from the third direction. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first and third directions are opposite to one another. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first and third direction are orthogonal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the deformable material is included in a gasket positioned between the housing and a first side of the cover surface. 
     Some examples of the disclosure are directed to a touch and force sensitive device. The device can comprise: a surface, a deformable material disposed between the surface and a rigid material, such that force on the surface causes a deformation of the deformable material, a plurality of transducers coupled to the surface and the deformable material, and processing circuitry coupled to the plurality of transducers. The processing circuitry can be capable of: stimulating the plurality of transducers to transmit ultrasonic waves to the surface and the deformable material, receiving, from the plurality of transducers, reflected ultrasonic waves from the surface and the deformable material, determining a location of a contact by an object on the surface based the reflected ultrasonic waves propagating in the surface received at the plurality of transducers, and determining an applied force by the contact on the surface based on one or more reflected ultrasonic waves propagating in the deformable material received from one or more of the plurality of transducers. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the surface can comprise an external surface of the device. Additionally or alternatively to one or more of the examples disclosed above, in some examples,the rigid material can comprise a portion of a housing of the device. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the deformable material can form a gasket between the portion of the housing and the external surface of the device. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the plurality of transducers can comprise at least four transducers bonded to the surface. Each of the four transducers can be disposed proximate to a different one of four respective edges of the surface and can be disposed over a portion of the gasket proximate to a respective edge of the housing of the device. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the processing circuitry can comprise one or more acoustic touch and force sensing circuits. The acoustic touch and force sensing circuit can be coupled to the plurality of transducers via direct bonding between the plurality of transducers and the one or more acoustic touch and force sensing circuits, via bonding between the plurality of transducers and a flexible circuit board coupled to the one or more acoustic touch and force sensing circuits, or via bonding between the plurality of transducers and a rigid circuit board coupled to the one or more acoustic touch and force sensing circuits. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the device can further comprise routing deposited the surface proximate to the plurality of transducers. The processing circuitry can comprise one or more acoustic touch and force sensing circuits. The one or more acoustic touch and force sensing circuits can be coupled to the plurality of transducers via coupling of the one or more acoustic touch and force sensing circuits to the routing deposited on the surface. Additionally or alternatively to one or more of the examples disclosed above, in some examples, stimulating the plurality of transducers to transmit ultrasonic waves to the surface and the deformable material and receiving, from the plurality of transducers, reflected ultrasonic waves from the surface and the deformable material can comprise: stimulating a first transducer of the plurality of transducers to transmit a first ultrasonic wave to the surface and receiving a first reflected ultrasonic wave from the first transducer from the surface in response to the transmitted first ultrasonic wave; stimulating a second transducer of the plurality of transducers to transmit a second ultrasonic wave to the surface and receiving a second reflected ultrasonic wave from the second transducer from the surface in response to the transmitted second ultrasonic wave; stimulating a third transducer of the plurality of transducers to transmit a third ultrasonic wave to the surface and receiving a third reflected ultrasonic wave from the third transducer from the surface in response to the transmitted third ultrasonic wave; and stimulating a fourth transducer of the plurality of transducers to transmit a fourth ultrasonic wave to the surface and receiving a fourth reflected ultrasonic wave from the fourth transducer from the surface in response to the transmitted fourth ultrasonic wave. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first ultrasonic wave, second ultrasonic wave, third ultrasonic wave and fourth ultrasonic wave can be transmitted in series to reduce interference between the plurality of transducers. Additionally or alternatively to one or more of the examples disclosed above, in some examples, determining the location of the contact by the object on the surface can be based the first reflected ultrasonic wave, the second reflected ultrasonic wave, the third reflected ultrasonic wave and the fourth reflected ultrasonic wave. Additionally or alternatively to one or more of the examples disclosed above, in some examples, stimulating the plurality of transducers to transmit ultrasonic waves to the surface and the deformable material and receiving, from the plurality of transducers, reflected ultrasonic waves from the surface and the deformable material can further comprise: stimulating the first transducer of the plurality of transducers to transmit a fifth ultrasonic wave to the deformable material and receiving a fifth reflected ultrasonic wave from the first transducer from the deformable material in response to the transmitted fifth ultrasonic wave; stimulating the second transducer of the plurality of transducers to transmit a sixth ultrasonic wave to the deformable material and receiving a sixth reflected ultrasonic wave from the second transducer from the deformable material in response to the transmitted sixth ultrasonic wave; stimulating the third transducer of the plurality of transducers to transmit a seventh ultrasonic wave to the deformable material and receiving a seventh reflected ultrasonic wave from the third transducer from the deformable material in response to the transmitted seventh ultrasonic wave; and stimulating the fourth transducer of the plurality of transducers to transmit an eighth ultrasonic wave to the deformable material and receiving an eighth reflected ultrasonic wave from the fourth transducer from the deformable material in response to the transmitted eighth ultrasonic wave. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the fifth ultrasonic wave, the sixth ultrasonic wave, the seventh ultrasonic wave and the eighth ultrasonic wave can be transmitted in series to reduce interference between the plurality of transducers. Additionally or alternatively to one or more of the examples disclosed above, in some examples, determining the applied force by the contact on the surface can be based the fifth reflected ultrasonic wave, the sixth reflected ultrasonic wave, the seventh reflected ultrasonic wave and the eighth reflected ultrasonic wave. Additionally or alternatively to one or more of the examples disclosed above, in some examples, determining the applied force by the contact on the surface can comprise averaging time of flight measurements corresponding to the the fifth reflected ultrasonic wave, sixth reflected ultrasonic wave, seventh reflected ultrasonic wave and eighth reflected ultrasonic wave. Additionally or alternatively to one or more of the examples disclosed above, in some examples, stimulating the plurality of transducers to transmit ultrasonic waves to the surface and the deformable material and receiving, from the plurality of transducers, reflected ultrasonic waves from the surface and the deformable material can comprise: stimulating a first transducer of the plurality of transducers to simultaneously transmit a first ultrasonic wave to the surface and to the deformable material; receiving a first reflected ultrasonic wave from the surface from the first transducer in response to the first ultrasonic wave transmitted to the surface and a first reflected ultrasonic wave from the deformable material from the first transducer in response to the first ultrasonic wave transmitted to the deformable material; stimulating a second transducer of the plurality of transducers to simultaneously transmit a second ultrasonic wave to the surface and to the deformable material; receiving a second reflected ultrasonic wave from the surface from the second transducer in response to the second ultrasonic wave transmitted to the surface and a second reflected ultrasonic wave from the deformable material from the second transducer in response to the second ultrasonic wave transmitted to the deformable material; stimulating a third transducer of the plurality of transducers to simultaneously transmit a third ultrasonic wave to the surface and to the deformable material; receiving a third reflected ultrasonic wave from the surface from the third transducer in response to the third ultrasonic wave transmitted to the surface and a third reflected ultrasonic wave from the deformable material from the third transducer in response to the third ultrasonic wave transmitted to the deformable material; and stimulating a fourth transducer of the plurality of transducers to simultaneously transmit a fourth ultrasonic wave to the surface and to the deformable material; receiving a fourth reflected ultrasonic wave from the surface from the fourth transducer in response to the fourth ultrasonic wave transmitted to the surface and a fourth reflected ultrasonic wave from the deformable material from the fourth transducer in response to the fourth ultrasonic wave transmitted to the deformable material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first ultrasonic wave, the second ultrasonic wave, the third ultrasonic wave and the fourth ultrasonic wave can be transmitted in series to reduce interference between the plurality of transducers. Additionally or alternatively to one or more of the examples disclosed above, in some examples, determining the location of the contact by the object on the surface can be based the first reflected ultrasonic wave from the surface, the second reflected ultrasonic wave from the surface, the third reflected ultrasonic wave from the surface and the fourth reflected ultrasonic wave from the surface. Additionally or alternatively to one or more of the examples disclosed above, in some examples, determining the applied force by the contact on the surface can be based the first reflected ultrasonic wave from the deformable material, the second reflected ultrasonic wave from the deformable material, the third reflected ultrasonic wave from the deformable material and the fourth reflected ultrasonic wave from the deformable material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the processing circuitry can comprise a force detection circuit. The force detection circuit can be configured to use time gating to detect one or more transitions in a reflected ultrasonic wave to determine a time of arrival of the reflected ultrasonic wave. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the processing circuitry can comprise one or more acoustic touch and force sensing circuits. Each of the one or more acoustic touch and force sensing circuits can comprise an acoustic touch sensing circuit implemented on a first integrated circuit and an acoustic force sensing circuit implemented on a second integrated circuit, separate from the first integrated circuit. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the processing circuitry can comprise one or more acoustic touch and force sensing circuits. Each of the one or more acoustic touch and force sensing circuits can comprise an acoustic transmit circuit and an acoustic receive circuit. The acoustic transmit circuit can be implemented on a first integrated circuit and the acoustic receive circuit can be implemented on a second integrated circuit, separate from the first integrated circuit. 
     Some examples of the disclosure are directed to a non-transitory computer readable storage medium. The non-transitory computer readable storage medium can store instructions, which when executed by a device comprising a surface, a deformable material, a plurality of acoustic transducers coupled to the surface and the deformable material, and processing circuitry, cause the processing circuitry to: for each of the plurality of acoustic transducers: simultaneously transmit an ultrasonic wave in the surface toward an opposite edge of the surface and transmit an ultrasonic wave through the deformable material; receive an ultrasonic reflection from the deformable material in response to the ultrasonic wave transmitted through the deformable material traversing the thickness of the deformable material; receive an ultrasonic reflection from the surface; determine a first time-of-flight between the ultrasonic wave transmitted through the deformable material and the ultrasonic reflection from the deformable material; and determine a second time-of-flight between the ultrasonic wave transmitted in the surface and the ultrasonic reflection from the surface. The instructions can further cause the processing circuitry to determine a position of an object on the surface based on respective second time-of-flight measurements corresponding to the plurality of transducers; and determine an amount of applied force by the object on the surface based on respective first time-of-flight measurements corresponding to the plurality of transducers. 
     Some examples of the disclosure are directed to a method for determining a position of an object on a surface and an amount of applied force by the object on the surface. The method can comprise: for each of a plurality of acoustic transducers: transmitting an first ultrasonic wave in the surface toward an opposite edge of the surface; receiving a first ultrasonic reflection from the surface; and determining a first time-of-flight between the first ultrasonic wave transmitted in the surface and the first ultrasonic reflection from the surface; determining the position of the object on the surface based on respective first time-of-flight measurements corresponding to the plurality of transducers. The method can further comprise: for each of a plurality of acoustic transducers: transmitting a second ultrasonic wave through the deformable material; receiving a second ultrasonic reflection from the deformable material in response to the second ultrasonic wave transmitted through the deformable material traversing the thickness of the deformable material; and determining a second time-of-flight between the second ultrasonic wave transmitted through the deformable material and the second ultrasonic reflection from the deformable material. The method can further comprise determining the amount of applied force by the object on the surface based on respective second time-of-flight measurements corresponding to the plurality of transducers. 
     Some examples of the disclosure are directed to a touch and force sensitive device. The device can comprise: a surface, a deformable material disposed between the surface and a rigid material, such that force on the surface causes a deformation of the deformable material, one or more transducers coupled to the surface and the deformable material and configured to transmit ultrasonic waves to and receive ultrasonic waves from the surface and the deformable material, and a processor. The processor can be capable of determining a location of a contact by an object on the surface based on ultrasonic waves propagating in the surface and determining an applied force by the contact on the surface based on ultrasonic waves propagating in the deformable material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the surface can comprise a glass or sapphire external surface of the device, the rigid material can comprise a portion of a metal housing of the device, and the deformable material can form a gasket between the metal housing and the surface. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the one or more transducers can comprise at least a first transducer coupled to the deformable material. The first transducer can be configured to transmit an ultrasonic wave through the thickness of the deformable material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first transducer can also be configured to receive one or more ultrasonic reflections from a boundary between the deformable material and the rigid material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the one or more transducers can comprise at least a second transducer coupled between the deformable material and the rigid material. The second transducer can be configured to receive the ultrasonic wave transmitted through the thickness of the deformable material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the one or more transducers can comprise at least one transducer configured to simultaneously transmit an ultrasonic wave in the surface and an ultrasonic wave through the deformable material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the one or more transducers can comprise four transducers. Each of the four transducers can be disposed proximate to a respective edge of the surface. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the device can further comprise an ultrasonic absorbent material coupled to the deformable material. The ultrasonic absorbent material can be configured to dampen ultrasonic ringing in the deformable material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, determining the location of the contact by the object on the surface can comprise: determining a first time-of-flight of an ultrasonic wave propagating between a first edge the surface and a first leading edge of the object proximate to the first edge, determining a second time-of-flight of an ultrasonic wave propagating between a second edge the surface and a second leading edge of the object proximate to the second edge, determining a third time-of-flight of an ultrasonic wave propagating between a third edge the surface and a third leading edge of the object proximate to the third edge, and determining a fourth time-of-flight of an ultrasonic wave propagating between a fourth edge the surface and a fourth leading edge of the object proximate to the fourth edge. Additionally or alternatively to one or more of the examples disclosed above, in some examples, determining the applied force by the contact on the surface can comprise determining a time-of-flight of an ultrasonic wave propagating from a first side of the deformable material and reflecting off of a second side, opposite the first side, of the deformable material. 
     Some examples of the disclosure are directed to a method. The method can comprise transmitting ultrasonic waves in a surface, receiving ultrasonic reflections from the surface, transmitting ultrasonic waves through a deformable material, receiving ultrasonic reflections from the deformable material, determining a position of an object in contact with the surface from the ultrasonic reflections received from the surface, and determining a force applied by the object in contact with the surface from the ultrasonic reflections received from the deformable material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, at least one of the ultrasonic waves transmitted in the surface and at least one of the ultrasonic waves transmitted in the deformable material are transmitted simultaneously. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the at least one of the ultrasonic waves transmitted in the surface and the at least one of the ultrasonic waves transmitted in the deformable material are transmitted by a common transducer. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise determining a time-of-flight through the deformable material based on a time difference between transmitting an ultrasonic wave through the deformable material and receiving an ultrasonic reflection from the deformable material. The force applied by the object can be determined based on the time-of-flight through the deformable material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the ultrasonic reflection from the deformable material can result from the ultrasonic wave transmitted through the deformable material reaching a boundary between the deformable material and a rigid material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the ultrasonic reflection from the deformable material can be received before the ultrasonic reflection from the surface. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise determining a time-of-flight in the surface based on a time difference between transmitting an ultrasonic wave in the surface and receiving an ultrasonic reflection from the surface corresponding to the object in contact with the surface. Determining the position of the object comprises determining a distance from an edge of the surface to a leading edge of the object proximate to the edge of the surface can be based on the time-of-flight in the surface. 
     Some examples of the disclosure are directed to a non-transitory computer readable storage medium. The non-transitory computer readable storage medium can store instructions, which when executed by a device comprising a surface, a plurality of acoustic transducers coupled to edges of the surface, an acoustic touch and force sensing circuit, and one or more processors, cause the acoustic touch and force sensing circuit and the one or more processors to: for each of the plurality of acoustic transducers: simultaneously transmit an ultrasonic wave in the surface toward an opposite edge of the surface and transmit an ultrasonic wave through a deformable material; receive an ultrasonic reflection from the deformable material in response to the ultrasonic wave transmitted through the deformable material traversing the thickness of the deformable material; receive an ultrasonic reflection from the surface; determine a first time-of-flight between the ultrasonic wave transmitted through the deformable material and the ultrasonic reflection from the deformable material; and determine a second time-of-flight between the ultrasonic wave transmitted in the surface and the ultrasonic reflection from the surface. The instructions can further cause the acoustic touch and force sensing circuit and the one or more processors to determine a position of an object on the surface based on respective second time-of-flight measurements corresponding to the plurality of transducers and determine an amount of applied force by the object on the surface based on respective first time-of-flight measurements corresponding to the plurality of transducers. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the ultrasonic wave transmitted in the surface and the ultrasonic wave transmitted through the deformable material can comprise shear waves. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the ultrasonic reflection from the deformable material can be received before the ultrasonic reflection from the surface. 
     Although examples of this disclosure have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of examples of this disclosure as defined by the appended claims.

Metadata:
Filing Date: 20180524
Publication Date: 20220531
Grant Date: 20220531
Priority Date: 20170524
Inventors: KHAJEH, EHSAN
KING, BRIAN MICHAEL
YEKE YAZDANDOOST, MOHAMMAD
YIP, Marcus
TUCKER, AARON SCOTT
YOUSEFPOR, MARDUKE
KARDASSAKIS, Peter Jon
GOZZINI, GIOVANNI
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/0433", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/043", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04105", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0436", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F1/1605", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0436", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04105", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1656", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1656", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0436", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1605", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04105", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 62598070