Patent Publication Number: US-9891723-B2

Title: Active stylus with surface-modification materials

Description:
RELATED APPLICATION 
     This application claims the benefit as a continuation under 35 U.S.C. 120 of U.S. patent application Ser. No. 13/362,921, filed Jan. 31, 2012, which claims the benefit, under 35 U.S.C. § 119(e), of U.S. Provisional Patent Application No. 61/553,114, filed 28 Oct. 2011, both of which is are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure generally relates to active styluses. 
     BACKGROUND 
     A touch sensor may detect the presence and location of a touch or the proximity of an object (such as a user&#39;s finger or a stylus) within a touch-sensitive area of the touch sensor overlaid on a display screen, for example. In a touch-sensitive-display application, the touch sensor may enable a user to interact directly with what is displayed on the screen, rather than indirectly with a mouse or touch pad. A touch sensor may be attached to or provided as part of a desktop computer, laptop computer, tablet computer, personal digital assistant (PDA), smartphone, satellite navigation device, portable media player, portable game console, kiosk computer, point-of-sale device, or other suitable device. A control panel on a household or other appliance may include a touch sensor. 
     There are a number of different types of touch sensors, such as, for example, resistive touch screens, surface acoustic wave touch screens, and capacitive touch screens. Herein, reference to a touch sensor may encompass a touch screen, and vice versa, where appropriate. When an object touches or comes within proximity of the surface of the capacitive touch screen, a change in capacitance may occur within the touch screen at the location of the touch or proximity. A touch-sensor controller may process the change in capacitance to determine its position on the touch screen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example touch sensor with an example touch-sensor controller. 
         FIG. 2  illustrates an example active stylus exterior. 
         FIG. 3  illustrates an example active stylus interior. 
         FIG. 4  illustrates an example active stylus with touch sensor device. 
         FIG. 5  illustrates an example active stylus with surface-modification materials. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
       FIG. 1  illustrates an example touch sensor  10  with an example touch-sensor controller  12 . Touch sensor  10  and touch-sensor controller  12  may detect the presence and location of a touch or the proximity of an object within a touch-sensitive area of touch sensor  10 . Herein, reference to a touch sensor may encompass both the touch sensor and its touch-sensor controller, where appropriate. Similarly, reference to a touch-sensor controller may encompass both the touch-sensor controller and its touch sensor, where appropriate. Touch sensor  10  may include one or more touch-sensitive areas, where appropriate. Touch sensor  10  may include an array of drive and sense electrodes (or an array of electrodes of a single type) disposed on one or more substrates, which may be made of a dielectric material. Herein, reference to a touch sensor may encompass both the electrodes of the touch sensor and the substrate(s) that they are disposed on, where appropriate. Alternatively, where appropriate, reference to a touch sensor may encompass the electrodes of the touch sensor, but not the substrate(s) that they are disposed on 
     An electrode (whether a ground electrode, guard electrode, drive electrode, or sense electrode) may be an area of conductive material forming a shape, such as for example a disc, square, rectangle, thin line, other suitable shape, or suitable combination of these. One or more cuts in one or more layers of conductive material may (at least in part) create the shape of an electrode, and the area of the shape may (at least in part) be bounded by those cuts. In particular embodiments, the conductive material of an electrode may occupy approximately 100% of the area of its shape. As an example and not by way of limitation, an electrode may be made of indium tin oxide (ITO) and the ITO of the electrode may occupy approximately 100% of the area of its shape (sometimes referred to as a 100% fill), where appropriate. In particular embodiments, the conductive material of an electrode may occupy substantially less than 100% of the area of its shape. As an example and not by way of limitation, an electrode may be made of fine lines of metal or other conductive material (FLM), such as for example copper, silver, or a copper- or silver-based material, and the fine lines of conductive material may occupy approximately 5% of the area of its shape in a hatched, mesh, or other suitable pattern. Herein, reference to FLM encompasses such material, where appropriate. Although this disclosure describes or illustrates particular electrodes made of particular conductive material forming particular shapes with particular fill percentages having particular patterns, this disclosure contemplates any suitable electrodes made of any suitable conductive material forming any suitable shapes with any suitable fill percentages having any suitable patterns. 
     Where appropriate, the shapes of the electrodes (or other elements) of a touch sensor may constitute in whole or in part one or more macro-features of the touch sensor. One or more characteristics of the implementation of those shapes (such as, for example, the conductive materials, fills, or patterns within the shapes) may constitute in whole or in part one or more micro-features of the touch sensor. One or more macro-features of a touch sensor may determine one or more characteristics of its functionality, and one or more micro-features of the touch sensor may determine one or more optical features of the touch sensor, such as transmittance, refraction, or reflection. 
     A mechanical stack may contain the substrate (or multiple substrates) and the conductive material forming the drive or sense electrodes of touch sensor  10 . As an example and not by way of limitation, the mechanical stack may include a first layer of optically clear adhesive (OCA) beneath a cover panel. The cover panel may be clear and made of a resilient material suitable for repeated touching, such as for example glass, polycarbonate, or poly(methyl methacrylate) (PMMA). This disclosure contemplates any suitable cover panel made of any suitable material. The first layer of OCA may be disposed between the cover panel and the substrate with the conductive material forming the drive or sense electrodes. The mechanical stack may also include a second layer of OCA and a dielectric layer (which may be made of PET or another suitable material, similar to the substrate with the conductive material forming the drive or sense electrodes). As an alternative, where appropriate, a thin coating of a dielectric material may be applied instead of the second layer of OCA and the dielectric layer. The second layer of OCA may be disposed between the substrate with the conductive material making up the drive or sense electrodes and the dielectric layer, and the dielectric layer may be disposed between the second layer of OCA and an air gap to a display of a device including touch sensor  10  and touch-sensor controller  12 . As an example only and not by way of limitation, the cover panel may have a thickness of approximately 1 mm; the first layer of OCA may have a thickness of approximately 0.05 mm; the substrate with the conductive material forming the drive or sense electrodes may have a thickness of approximately 0.05 mm; the second layer of OCA may have a thickness of approximately 0.05 mm; and the dielectric layer may have a thickness of approximately 0.05 mm. Although this disclosure describes a particular mechanical stack with a particular number of particular layers made of particular materials and having particular thicknesses, this disclosure contemplates any suitable mechanical stack with any suitable number of any suitable layers made of any suitable materials and having any suitable thicknesses. As an example and not by way of limitation, in particular embodiments, a layer of adhesive or dielectric may replace the dielectric layer, second layer of OCA, and air gap described above, with there being no air gap to the display. 
     One or more portions of the substrate of touch sensor  10  may be made of polyethylene terephthalate (PET) or another suitable material. This disclosure contemplates any suitable substrate with any suitable portions made of any suitable material. In particular embodiments, the drive or sense electrodes in touch sensor  10  may be made of ITO in whole or in part. In particular embodiments, the drive or sense electrodes in touch sensor  10  may be made of fine lines of metal or other conductive material. As an example and not by way of limitation, one or more portions of the conductive material may be copper or copper-based and have a thickness of approximately 5 μm or less and a width of approximately 10 μm or less. As another example, one or more portions of the conductive material may be silver or silver-based and similarly have a thickness of approximately 5 μm or less and a width of approximately 10 μM or less. This disclosure contemplates any suitable electrodes made of any suitable material. 
     Touch sensor  10  may implement a capacitive form of touch sensing. In a mutual-capacitance implementation, touch sensor  10  may include an array of drive and sense electrodes forming an array of capacitive nodes. A drive electrode and a sense electrode may form a capacitive node. The drive and sense electrodes forming the capacitive node may come near each other, but not make electrical contact with each other. Instead, the drive and sense electrodes may be capacitively coupled to each other across a space between them. A pulsed or alternating voltage applied to the drive electrode (by touch-sensor controller  12 ) may induce a charge on the sense electrode, and the amount of charge induced may be susceptible to external influence (such as a touch or the proximity of an object). When an object touches or comes within proximity of the capacitive node, a change in capacitance may occur at the capacitive node and touch-sensor controller  12  may measure the change in capacitance. By measuring changes in capacitance throughout the array, touch-sensor controller  12  may determine the position of the touch or proximity within the touch-sensitive area(s) of touch sensor  10 . 
     In a self-capacitance implementation, touch sensor  10  may include an array of electrodes of a single type that may each form a capacitive node. When an object touches or comes within proximity of the capacitive node, a change in self-capacitance may occur at the capacitive node and controller  12  may measure the change in capacitance, for example, as a change in the amount of charge needed to raise the voltage at the ° capacitive node by a pre-determined amount. As with a mutual-capacitance implementation, by measuring changes in capacitance throughout the array, controller  12  may determine the position of the touch or proximity within the touch-sensitive area(s) of touch sensor  10 . This disclosure contemplates any suitable form of capacitive touch sensing, where appropriate. 
     In particular embodiments, one or more drive electrodes may together form a drive line running horizontally or vertically or in any suitable orientation. Similarly, one or more sense electrodes may together form a sense line running horizontally or vertically or in any suitable orientation. In particular embodiments, drive lines may run substantially perpendicular to sense lines. Herein, reference to a drive line may encompass one or more drive electrodes making up the drive line, and vice versa, where appropriate. Similarly, reference to a sense line may encompass one or more sense electrodes making up the sense line, and vice versa, where appropriate. 
     Touch sensor  10  may have drive and sense electrodes disposed in a pattern on one side of a single substrate. In such a configuration, a pair of drive and sense electrodes capacitively coupled to each other across a space between them may form a capacitive node. For a self-capacitance implementation, electrodes of only a single type may be disposed in a pattern on a single substrate. In addition or as an alternative to having drive and sense electrodes disposed in a pattern on one side of a single substrate, touch sensor  10  may have drive electrodes disposed in a pattern on one side of a substrate and sense electrodes disposed in a pattern on another side of the substrate. Moreover, touch sensor  10  may have drive electrodes disposed in a pattern on one side of one substrate and sense electrodes disposed in a pattern on one side of another substrate. In such configurations, an intersection of a drive electrode and a sense electrode may form a capacitive node. Such an intersection may be a location where the drive electrode and the sense electrode “cross” or come nearest each other in their respective planes. The drive and sense electrodes do not make electrical contact with each other—instead they are capacitively coupled to each other across a dielectric at the intersection. Although this disclosure describes particular configurations of particular electrodes forming particular nodes, this disclosure contemplates any suitable configuration of any suitable electrodes forming any suitable nodes. Moreover, this disclosure contemplates any suitable electrodes disposed on any suitable number of any suitable substrates in any suitable patterns. 
     As described above, a change in capacitance at a capacitive node of touch sensor  10  may indicate a touch or proximity input at the position of the capacitive node. Touch-sensor controller  12  may detect and process the change in capacitance to determine the presence and location of the touch or proximity input. Touch-sensor controller  12  may then communicate information about the touch or proximity input to one or more other components (such one or more central processing units (CPUs)) of a device that includes touch sensor  10  and touch-sensor controller  12 , which may respond to the touch or proximity input by initiating a function of the device (or an application running on the device). Although this disclosure describes a particular touch-sensor controller having particular functionality with respect to a particular device and a particular touch sensor, this disclosure contemplates any suitable touch-sensor controller having any suitable functionality with respect to any suitable device and any suitable touch sensor. 
     Touch-sensor controller  12  may be one or more integrated circuits (ICs), such as for example general-purpose microprocessors, microcontrollers, programmable logic devices (PLDs) or programmable logic arrays (PLAs), application-specific ICs (ASICs). In particular embodiments, touch-sensor controller  12  comprises analog circuitry, digital logic, and digital non-volatile memory. In particular embodiments, touch-sensor controller  12  is disposed on a flexible printed circuit (FPC) bonded to the substrate of touch sensor  10 , as described below. The FPC may be active or passive, where appropriate. In particular embodiments multiple touch-sensor controllers  12  are disposed on the FPC. Touch-sensor controller  12  may include a processor unit, a drive unit, a sense unit, and a storage unit. The drive unit may supply drive signals to the drive electrodes of touch sensor  10 . The sense unit may sense charge at the capacitive nodes of touch sensor  10  and provide measurement signals to the processor unit representing capacitances at the capacitive nodes. The processor unit may control the supply of drive signals to the drive electrodes by the drive unit and process measurement signals from the sense unit to detect and process the presence and location of a touch or proximity input within the touch-sensitive area(s) of touch sensor  10 . The processor unit may also track changes in the position of a touch or proximity input within the touch-sensitive area(s) of touch sensor  10 . The storage unit may store programming for execution by the processor unit, including programming for controlling the drive unit to supply drive signals to the drive electrodes, programming for processing measurement signals from the sense unit, and other suitable programming, where appropriate. Although this disclosure describes a particular touch-sensor controller having a particular implementation with particular components, this disclosure contemplates any suitable touch-sensor controller having any suitable implementation with any suitable components. 
     Tracks  14  of conductive material disposed on the substrate of touch sensor  10  may couple the drive or sense electrodes of touch sensor  10  to connection pads  16 , also disposed on the substrate of touch sensor  10 . As described below, connection pads  16  facilitate coupling of tracks  14  to touch-sensor controller  12 . Tracks  14  may extend into or around (e.g. at the edges of) the touch-sensitive area(s) of touch sensor  10 . Particular tracks  14  may provide drive connections for coupling touch-sensor controller  12  to drive electrodes of touch sensor  10 , through which the drive unit of touch-sensor controller  12  may supply drive signals to the drive electrodes. Other tracks  14  may provide sense connections for coupling touch-sensor controller  12  to sense electrodes of touch sensor  10 , through which the sense unit of touch-sensor controller  12  may sense charge at the capacitive nodes of touch sensor  10 . Tracks  14  may be made of fine lines of metal or other conductive material. As an example and not by way of limitation, the conductive material of tracks  14  may be copper or copper-based and have a width of approximately 100 μm or less. As another example, the conductive material of tracks  14  may be silver or silver-based and have a width of approximately 100 μm or less. In particular embodiments, tracks  14  may be made of ITO in whole or in part in addition or as an alternative to fine lines of metal or other conductive material. Although this disclosure describes particular tracks made of particular materials with particular widths, this disclosure contemplates any suitable tracks made of any suitable materials with any suitable widths. In addition to tracks  14 , touch sensor  10  may include one or more ground lines terminating at a ground connector (which may be a connection pad  16 ) at an edge of the substrate of touch sensor  10  (similar to tracks  14 ). 
     Connection pads  16  may be located along one or more edges of the substrate, outside the touch-sensitive area(s) of touch sensor  10 . As described above, touch-sensor controller  12  may be on an FPC. Connection pads  16  may be made of the same material as tracks  14  and may be bonded to the FPC using an anisotropic conductive film (ACF). Connection  18  may include conductive lines on the FPC coupling touch-sensor controller  12  to connection pads  16 , in turn coupling touch-sensor controller  12  to tracks  14  and to the drive or sense electrodes of touch sensor  10 . In another embodiment, connection pads  16  may be connected to an electro-mechanical connector (such as a zero insertion force wire-to-board connector); in this embodiment, connection  18  may not need to include an FPC. This disclosure contemplates any suitable connection  18  between touch-sensor controller  12  and touch sensor  10 . 
       FIG. 2  illustrates an example exterior of an example active stylus  20 . Active stylus  20  may include one or more components, such as buttons  30  or sliders  32  and  34  integrated with an outer body  22 . These external components may provide for interaction between active stylus  20  and a user or between a device and a user. As an example and not by way of limitation, interactions may include communication between active stylus  20  and a device, enabling or altering functionality of active stylus  20  or a device, or providing feedback to or accepting input from one or more users. The device may by any suitable device, such as, for example and without limitation, a desktop computer, laptop computer, tablet computer, personal digital assistant (PDA), smartphone, satellite navigation device, portable media player, portable game console, kiosk computer, point-of-sale device, or other suitable device. Although this disclosure provides specific examples of particular components configured to provide particular interactions, this disclosure contemplates any suitable component configured to provide any suitable interaction. Active stylus  20  may have any suitable dimensions with outer body  22  made of any suitable material or combination of materials, such as, for example and without limitation, plastic or metal. In particular embodiments, exterior components (e.g.  30  or  32 ) of active stylus  20  may interact with internal components or programming of active stylus  20  or may initiate one or more interactions with one or more devices or other active styluses  20 . 
     As described above, actuating one or more particular components may initiate an interaction between active stylus  20  and a user or between the device and the user. Components of active stylus  20  may include one or more buttons  30  or one or more sliders  32  and  34 . As an example and not by way of limitation, buttons  30  or sliders  32  and  34  may be mechanical or capacitive and may function as a roller, trackball, or wheel. As another example, one or more sliders  32  or  34  may function as a vertical slider  34  aligned along a longitudinal axis, while one or more wheel sliders  32  may be aligned along the circumference of active stylus  20 . In particular embodiments, capacitive sliders  32  and  34  or buttons  30  may be implemented using one or more touch-sensitive areas. Touch-sensitive areas may have any suitable shape, dimensions, location, or be made from any suitable material. As an example and not by way of limitation, sliders  32  and  34  or buttons  30  may be implemented using areas of flexible mesh formed using lines of conductive material. As another example, sliders  32  and  34  or buttons  30  may be implemented using a FPC. 
     Active stylus  20  may have one or more components configured to provide feedback to or accepting feedback from a user, such as, for example and without limitation, tactile, visual, or audio feedback. Active stylus  20  may include one or more ridges or grooves  24  on its outer body  22 . Ridges or grooves  24  may have any suitable dimensions, have any suitable spacing between ridges or grooves, or be located at any suitable area on outer body  22  of active stylus  20 . As an example and not by way of limitation, ridges  24  may enhance a user&#39;s grip on outer body  22  of active stylus  20  or provide tactile feedback to or accept tactile input from a user. Active stylus  20  may include one or more audio components  38  capable of transmitting and receiving audio signals. As an example and not by way of limitation, audio component  38  may contain a microphone capable of recording or transmitting one or more users&#39; voices. As another example, audio component  38  may provide an auditory indication of a power status of active stylus  20 . Active stylus  20  may include one or more visual feedback components  36 , such as a light-emitting diode (LED) indicator. As an example and not by way of limitation, visual feedback component  36  may indicate a power status of active stylus  20  to the user. 
     One or more modified surface areas  40  may form one or more components on outer body  22  of active stylus  20 . Properties of modified surface areas  40  may be different than properties of the remaining surface of outer body  22 . As an example and not by way of limitation, modified surface area  40  may be modified to have a different texture, temperature, or electromagnetic characteristic relative to the surface properties of the remainder of outer body  22 . Modified surface area  40  may be capable of dynamically altering its properties, for example by using haptic interfaces or rendering techniques. A user may interact with modified surface area  40  to provide any suitable functionally. For example and not by way of limitation, dragging a finger across modified surface area  40  may initiate an interaction, such as data transfer, between active stylus  20  and a device. 
     One or more components of active stylus  20  may be configured to communicate data between active stylus  20  and the device. For example, active stylus  20  may include one or more tips  26  or nibs. Tip  26  may include one or more electrodes configured to communicate data between active stylus  20  and one or more devices or other active styluses. Tip  26  may be made of any suitable material, such as a conductive material, and have any suitable dimensions, such as, for example, a diameter of 1 mm or less at its terminal end. Active stylus  20  may include one or more ports  28  located at any suitable location on outer body  22  of active stylus  20 . Port  28  may be configured to transfer signals or information between active stylus  20  and one or more devices or power sources. Port  28  may transfer signals or information by any suitable technology, such as, for example, by universal serial bus (USB) or Ethernet connections. Although this disclosure describes and illustrates a particular configuration of particular components with particular locations, dimensions, composition and functionality, this disclosure contemplates any suitable configuration of suitable components with any suitable locations, dimensions, composition, and functionality with respect to active stylus  20 . 
       FIG. 3  illustrates an example internal components of example active stylus  20 . Active stylus  20  may include one or more internal components, such as a controller  50 , sensors  42 , memory  44 , or power source  48 . In particular embodiments, one or more internal components may be configured to provide for interaction between active stylus  20  and a user or between a device and a user. In other particular embodiments, one or more internal components, in conjunction with one or more external components described above, may be configured to provide interaction between active stylus  20  and a user or between a device and a user. As an example and not by way of limitation, interactions may include communication between active stylus  20  and a device, enabling or altering functionality of active stylus  20  or a device, or providing feedback to or accepting input from one or more users. 
     Controller  50  may be a microcontroller or any other type of processor suitable for controlling the operation of active stylus  20 . Controller  50  may be one or more ICs—such as, for example, general-purpose microprocessors, microcontrollers, PLDs, PLAs, or ASICs. Controller  50  may include a processor unit, a drive unit, a sense unit, and a storage unit. The drive unit may supply signals to electrodes of tip  26  through center shaft  41 . The drive unit may also supply signals to control or drive sensors  42  or one or more external components of active stylus  20 . The sense unit may sense signals received by electrodes of tip  26  through center shaft  41  and provide measurement signals to the processor unit representing input from a device. The sense unit may also sense signals generated by sensors  42  or one or more external components and provide measurement signals to the processor unit representing input from a user. The processor unit may control the supply of signals to the electrodes of tip  26  and process measurement signals from the sense unit to detect and process input from the device. The processor unit may also process measurement signals from sensors  42  or one or more external components. The storage unit may store programming for execution by the processor unit, including programming for controlling the drive unit to supply signals to the electrodes of tip  26 , programming for processing measurement signals from the sense unit corresponding to input from the device, programming for processing measurement signals from sensors  42  or external components to initiate a pre-determined function or gesture to be performed by active stylus  20  or the device, and other suitable programming, where appropriate. As an example and not by way of limitation, programming executed by controller  50  may electronically filter signals received from the sense unit. Although this disclosure describes a particular controller  50  having a particular implementation with particular components, this disclosure contemplates any suitable controller having any suitable implementation with any suitable components. 
     In particular embodiments, active stylus  20  may include one or more sensors  42 , such as touch sensors, gyroscopes, accelerometers, contact sensors, or any other type of sensor that detect or measure data about the environment in which active stylus  20  operates. Sensors  42  may detect and measure one or more characteristic of active stylus  20 , such as acceleration or movement, orientation, contact, pressure on outer body  22 , force on tip  26 , vibration, or any other suitable characteristic of active stylus  20 . As an example and not by way of limitation, sensors  42  may be implemented mechanically, electronically, or capcatively. As described above, data detected or measured by sensors  42  communicated to controller  50  may initiate a pre-determined function or gesture to be performed by active stylus  20  or the device. In particular embodiments, data detected or received by sensors  42  may be stored in memory  44 . Memory  44  may be any form of memory suitable for storing data in active stylus  20 . In other particular embodiments, controller  50  may access data stored in memory  44 . As an example and not by way of limitation, memory  44  may store programming for execution by the processor unit of controller  50 . As another example, data measured by sensors  42  may be processed by controller  50  and stored in memory  44 . 
     Power source  48  may be any type of stored-energy source, including electrical or chemical-energy sources, suitable for powering the operation of active stylus  20 . In particular embodiments, power source  48  may be charged by energy from a user or device. As an example and not by way of limitation, power source  48  may be a rechargeable battery that may be charged by motion induced on active stylus  20 . In other particular embodiments, power source  48  of active stylus  20  may provide power to or receive power from the device. As an example and not by way of limitation, power may be inductively transferred between power source  48  and a power source of the device. 
       FIG. 4  illustrates an example active stylus  20  with an example device  52 . Device  52  may have a display (not shown) and a touch sensor with a touch-sensitive area  54 . Device  52  display may be a liquid crystal display (LCD), a LED display, a LED-backlight LCD, or other suitable display and may be visible though a cover panel and substrate (and the drive and sense electrodes of the touch sensor disposed on it) of device  52 . Although this disclosure describes a particular device display and particular display types, this disclosure contemplates any suitable device display and any suitable display types. 
     Device  52  electronics may provide the functionality of device  52 . As example and not by way of limitation, device  52  electronics may include circuitry or other electronics for wireless communication to or from device  52 , execute programming on device  52 , generating graphical or other user interfaces (UN) for device  52  display to display to a user, managing power to device  52  from a battery or other power source, taking still pictures, recording video, other suitable functionality, or any suitable combination of these. Although this disclosure describes particular device electronics providing particular functionality of a particular device, this disclosure contemplates any suitable device electronics providing any suitable functionality of any suitable device. 
     In particular embodiments, active stylus  20  and device  52  may be synchronized prior to communication of data between active stylus  20  and device  52 . As an example and not by way of limitation, active stylus  20  may be synchronized to device through a pre-determined bit sequence transmitted by the touch sensor of device  52 . As another example, active stylus  20  may be synchronized to device by processing the drive signal transmitted by drive electrodes of the touch sensor of device  52 . Active stylus  20  may interact or communicate with device  52  when active stylus  20  is brought in contact with or in proximity to touch-sensitive area  54  of the touch sensor of device  52 . In particular embodiments, interaction between active stylus  20  and device  52  may be capacitive or inductive. As an example and not by way of limitation, when active stylus  20  is brought in contact with or in the proximity of touch-sensitive area  54  of device  52 , signals generated by active stylus  20  may influence capacitive nodes of touch-sensitive area of device  52  or vice versa. As another example, a power source of active stylus  20  may be inductively charged through the touch sensor of device  52 , or vice versa. Although this disclosure describes particular interactions and communications between active stylus  20  and device  52 , this disclosure contemplates any suitable interactions and communications through any suitable means, such as mechanical forces, current, voltage, or electromagnetic fields. 
     In particular embodiments, measurement signal from the sensors of active stylus  20  may initiate, provide for, or terminate interactions between active stylus  20  and one or more devices  52  or one or more users, as described above. Interaction between active stylus  20  and device  52  may occur when active stylus  20  is contacting or in proximity to device  52 . As an example and not by way of limitation, a user may perform a gesture or sequence of gestures, such as shaking or inverting active stylus  20 , whilst active stylus  20  is hovering above touch-sensitive area  54  of device  52 . Active stylus may interact with device  52  based on the gesture performed with active stylus  20  to initiate a pre-determined function, such as authenticating a user associated with active stylus  20  or device  52 . Although this disclosure describes particular movements providing particular types of interactions between active stylus  20  and device  52 , this disclosure contemplates any suitable movement influencing any suitable interaction in any suitable way. 
     In particular embodiments, a stylus may, at least partially, comprise materials on or near the surface of its outer body that are capable of modifying their properties in response to one or more inputs. Such materials on or near the surface of a stylus&#39; outer body may be referred to as “surface-modification materials”. Surface-modification materials may change their size, shape, texture, hardness, effective coefficient of friction, brightness, color, temperature, opacity, viscosity, or other suitable characteristic in response to an electromagnetic field, an electric current, a pH level, a temperature, a radio frequency, or any other suitable input. Surface-modification materials may include shape memory alloys, shape memory polymers, electronic or ionic electroactive polymers (EAPs), magnetocaloric materials, thermoelectric materials, pH-sensitive materials, temperature-responsive materials, piezoelectrics, halochromic materials, chromogenic materials, photomechanical materials, or any other suitable material. The input that induces change in surface-modification materials may originate from a touch-sensitive system, such as a stylus or touch-sensitive device. For example, in response to a signal an electronic circuit in an active stylus may produce the input that induces change in surface-modification materials, for example by generating or initiating the generation of electromagnetic signals, electrical current, or a certain temperature or pH level. The signal received by the electronic circuit may be initiated by a user of the active stylus, for example by the press of a button. The signal received by the electronic circuit may also be initiated by software or settings embodied in non-transitory computer-readable media. These settings may be set by a user of an active stylus, exist as presets on the active stylus, or be set by individual applications or programs associated with the active stylus. Likewise, functionalities associated with altering the properties or characteristics of the surface-modification materials may be set by a user of an active stylus, exist as presets on the active stylus, or be set by individual applications or programs associated with the active stylus.  FIG. 5  illustrates an example active stylus with surface-modification materials. Surface-modification materials may appear on or near the surface of tip  26  of active stylus  20 . In addition or alternatively, surface-modification materials may also appear on or near the outer body  22  of active stylus  20 , and may comprise one or more buttons  30 , sliders  32 , textured surfaces  40 , surface areas  56 , or other suitable components. 
     In particular embodiments, one or more buttons  30  at least partially comprising surface-modification materials may change their properties in order to provide feedback to a user of active stylus  20 . As an example, buttons  30  may comprise an ionic electroactive polymer contained in a suitable enclosure to maintain wetness of the polymer. When subject to an electric current created by an appropriate voltage source (for example, approximately 1 to 10 volts) the ionic polymer may change its viscosity, altering the force required to press the button. This may alert that user that they are in a specific setting or are about to perform a specific function, such as deleting data. In particular embodiments, one or more buttons  30  at least partially comprising surface-modification materials may change their properties to alter or generate input to a touch-sensitive system. Using the example above, buttons  30  may navigate through menus or select menu options when used in normal operation and exit applications when used while exposed to a voltage making button  30  stiffer or changing its size or shape. While the above disclosure provides specific examples of buttons comprising surface-modification materials providing specific functionality, this disclosure contemplates any suitable surface-modification materials on any suitable component of an active stylus providing any suitable functionality. 
     In particular embodiments, one or more sliders  32  at least partially comprising surface-modification materials may change their properties in order to provide feedback to a user of active stylus  20 . As an example, sliders  32  may comprise liquid crystal elastomers that are capable of changing their opacity, and thus their display, when subject to an electric field or change in temperature. By changing the content displayed, sliders  32  may alert the user of information (for example how much battery power remains available to active stylus  20 ). In particular embodiments, one or more sliders  32  at least partially comprising surface-modification materials may change their properties to alter or generate new input to a touch-sensitive system. Using the example above, a user may select a specific mode or function, such as putting active stylus  20  in a secure operating mode, associated with slider  32  by changing the display of the liquid crystal elastomer. While the above disclosure provides specific examples of sliders comprising surface-modification materials providing specific functionality, this disclosure contemplates any suitable surface-modification materials on any suitable component of an active stylus providing any suitable functionality. 
     In particular embodiments, one or more textured surfaces  40  at least partially comprising surface-modification materials may change their properties in order to provide feedback to a user of active stylus  20 . As an example, textured surfaces  40  may comprise at least in part a shape-memory polymer, which changes shape or size in response to a thermal or electrical input. Altering the shape-memory polymer&#39;s size or shape may provide tactile feedback, such as Braille for a visually-impaired user, based on the content displayed on a touch-sensitive device or settings of the device or active stylus  20 . Textured surfaces  40  may be arranged in any suitable configuration, such as an array of posts composed of shape-memory polymers. Individual elements of the configuration, such as individual posts, may have their size or shape modified individually, providing for a wide variety of textures, sizes, and shapes available to textured surfaces  40 . As another example, textured surfaces  40  may change texture in response to output displayed on a device such as roughness of a virtual surface, altitude of particular points in a picture, or changes in any variable embodied by a contour map. The output displayed on the device is communicated to active stylus  20 , which provides the thermal or electrical input necessary to make desired change in textured surfaces  40 . In particular embodiments, one or more textured surfaces  40  at least partially comprising surface-modification materials may change their properties to change or generate input to a touch-sensitive system. As an example, textured surface  40  may be non-operable in its non-actuated configuration and operable in its actuated configuration (for example to prevent accidental activation of an associated function such as deleting files). While the above disclosure provides specific examples of textured surfaces comprising surface-modification materials providing specific functionality, this disclosure contemplates any suitable surface-modification materials on any suitable component of an active stylus providing any suitable functionality. 
     In particular embodiments, one or more surface areas  56  at least partially comprising surface-modification materials may change their properties in order to provide feedback to a user of active stylus  20 . As an example, surface area  56  is an electrochromogenic material that changes brightness, color, or opacity in response to an electrical current. Different colors or degrees of opacity provide feedback such as an indicator of battery level, security settings, success or failure of an operation performed, or any other suitable feedback concerning a touch-sensitive system and associated content. While the above disclosure provides specific examples of surface-modification materials on a particular surface area providing for specific functionality, this disclosure contemplates any suitable surface-modification materials on any suitable component of an active stylus providing any suitable functionality. 
     Herein, reference to a computer-readable non-transitory storage medium encompasses a semiconductor-based or other integrated circuit (IC) (such, as for example, a field-programmable gate array (FPGA) or an application-specific IC (ASIC)), a hard disk (HDD), a hybrid hard drive (HHD), an optical disc, an optical disc drive (ODD), a magneto-optical disc, a magneto-optical drive, a floppy disk, a floppy disk drive (FDD), magnetic tape, a holographic storage medium, a solid-state drive (SSD), a RAM-drive, a SECURE DIGITAL card, a SECURE DIGITAL drive, or another suitable computer-readable non-transitory storage medium or a combination of two or more of these, where appropriate. A computer-readable non-transitory storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile, where appropriate. 
     Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context. 
     This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.