Patent Publication Number: US-8988396-B2

Title: Piezo-based acoustic and capacitive detection

Description:
This application is a continuation of patent application Ser. No. 12/690,907, filed Jan. 20, 2010, which is hereby incorporated by referenced herein in its entirety. This application claims the benefit of and claims priority to patent application Ser. No. 12/690,907, filed Jan. 20, 2010. 
    
    
     TECHNICAL FIELD 
     Embodiments relate generally to computing input devices, and more specifically to one or more piezo-based acoustic and capacitive sensors to detect key taps on an input device. 
     BACKGROUND 
     Many electronic devices have a keyboard or similar input device with which a user interacts to provide an input to an electronic or computing device. Most keyboards consist of an arrangement of buttons that act as mechanical buttons or switches that are pushed by the user to provide input to the computing device. Each key of the keyboard typically has an engraved or printed character on the key that corresponds to the symbol that is input to the computer when the particular key is pressed by the user. In some situations, several keys may be pressed simultaneously or in sequence to produce actions or commands for the computing device. 
     Some keyboards and other computing input devices have done away with mechanical switches and instead employ a touch-sensitive surface input. One example of a touch-sensitive surface input device is a touch screen, such as those found at automatic teller machines (ATMs) or on personal digital assistants (PDAs), mobile phones, tablet computing devices and other mobile computing devices. To provide an input using a touch screen, the user presses or touches a surface with either the user&#39;s finger or a stylus device. The input device senses the touch, determines its location on the touch screen and generates the corresponding input. Thus, the position of the user&#39;s finger is determined by the touch screen and the corresponding command is inputted to the electronic device. Other touch-sensitive surface input devices may employ materials other than glass, such as a metal or plastic. 
     In general, touch-sensitive surface or related input devices may be less reliable in determining a pressed command or intended input when compared with a traditional mechanical keyboard. For example, some touch screens often require that a user tap on the screen several times before detecting the command. Further, touch-sensitive surface input devices often fail to distinguish between when a user is merely resting on the surface of the device or actively selecting a letter or other input. 
     SUMMARY 
     One embodiment may take the form of an input device for a computing system. The input device may comprise a capacitive sensor configured to detect a location of an input to the input device and a piezoelectric sensor configured to detect an acoustic signature created from the input. Further, the acoustic signature may be compared to a database of reference acoustic signatures that indicate the location of the input to the input device. 
     Another embodiment may take the form of a method for detecting an input to an input device of a computing system. The method may comprise the operations of receiving a first acoustic pulse at a first piezoelectric sensor and comparing the first acoustic pulse to a first database comprising a plurality of first reference acoustic signatures to determine the location of the input. In addition, the method may comprise the operations of receiving a second acoustic pulse at a second piezoelectric sensor and comparing the second acoustic pulse to a second database comprising a plurality of second reference acoustic signatures to determine the location of the input. 
     Yet another embodiment may take the form of a computing system. The computing system may comprise an input device including an input surface and configured to receive an input to the computing system from a user and a computer-readable storage device configured to store a database of reference acoustic signatures. The computing system may also include a capacitive sensor configured to detect a location of the input on the input surface and a piezoelectric sensor configured to detect the at least one acoustic signature representing the input, such that the detected at least one acoustic signature is compared to the database to determine the location of the input. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a top view of an input device for a computing device. 
         FIG. 2  is a top view of a flat-surface keyboard input device utilizing acoustic pulse recognition to detect a tap on the surface of the keyboard. 
         FIG. 3  depicts a cross-sectional view of the flat-surface keyboard device utilizing acoustic pulse recognition to detect a tap on the keyboard of  FIG. 2  along the line marked “AA”. 
         FIG. 3A  depicts a cross-sectional top view of the keyboard device of  FIG. 3  along line designated “BB” that utilizes three piezo sensors  310 - 314  to detect an acoustic pulse recognition of a tap on the keyboard surface  302 . 
         FIG. 4  depicts a cross-sectional view similar to that shown in  FIG. 3  of a keyboard device that utilizes a combination of piezoelectric sensors and capacitive sensors to detect a tap on the keyboard surface. 
         FIG. 5  depicts a cross-sectional view similar to that shown in  FIG. 3  of a keyboard device utilizing acoustic pulse recognition to detect a tap on the keyboard, including tuning features to distort or alter the resultant acoustic signature of the tap. 
         FIG. 6  depicts a cross-sectional view similar to that shown in  FIG. 3  of a keyboard device utilizing acoustic pulse recognition to detect a tap on the keyboard, including openings on the surface of the keyboard to distort or alter the resultant acoustic signature of the tap. 
         FIG. 6A  depicts a cross-sectional top view similar to that shown in  FIG. 3A  of the keyboard device utilizing acoustic pulse recognition to detect a tap on the keyboard, including openings in the surface of the keyboard to distort or alter the resultant acoustic signature of the tap. 
         FIG. 7  depicts a cross-sectional view similar to that shown in  FIG. 3  of a keyboard device utilizing a combination of piezoelectric sensors to detect a tap on the keyboard surface and pressure sensors to detect a dampening force applied to the device. 
         FIG. 7A  depicts a bottom view of a keyboard device utilizing a combination of piezoelectric sensors and a pressure sensor to detect a tap on the keyboard surface and a dampening force applied to the device. 
         FIG. 8  depicts a top view of a keyboard device utilizing a microphone to measure ambient noise around the keyboard to aid in detecting a tap on the surface of the keyboard. 
         FIG. 9  depicts a cross-sectional view similar to that shown in  FIG. 3  of a keyboard device utilizing a combination of piezoelectric sensors and proximity sensors to detect and locate a tap on the keyboard surface. 
         FIG. 10  is a block diagram illustrating an exemplary device or docking station which may be used in implementing embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     One embodiment described herein takes the form of an input device for a computing system, such as a keyboard of a computer system or a touch screen for a mobile computing device. The input device includes an input surface on which one or more input characters are shown, such that a user may press or tap on the character to provide an input corresponding to that character to the computing system. The input device may also include one or more sensors to detect which input character is pressed or otherwise selected by the user. In one example, the input device may have one or more acoustic sensors that detect an acoustic pulse created when the user taps on the input surface to indicate a selected key. Each input area on the surface of the input device creates a different acoustic pulse signature when tapped, given the internal geometry and physical characteristics of the device. Thus, upon receipt and detection of the acoustic pulse at the acoustic sensors, the input device (or associated computing device) may compare the received pulse to a database of stored pulse signatures in order to determine what segment of the surface of the input device was tapped by the user. Such detection may be sufficiently precise to map the tap to a particular key of keyboard, for example. 
     Several other features may be incorporated into the input device to further determine which segment of the input device is tapped by the user. For example, one or more tuning features may be situated near or on the input device to alter the acoustic pulse created when a particular segment of the input device is tapped. These tuning features may create a new acoustic signature for one or more segment of the input device to assist the computer system in differentiating between the taps on the segments of the input device. Additional sensors may also be incorporated to assist the computing system or input device in determining which segment of the input device is pressed by the user. For example, a capacitive sensor may be incorporated into the input device to narrow the list of possible intended segments of the input device tapped by the user, as well as to determine when the user is continually pressing on a particular segment or otherwise maintaining an input. One or more pressure switches and/or proximity devices may also be incorporated to further define the segment of the input device pressed by the user. The pressure switches may also be used to detect a dampening force present on the input device that may alter the resultant acoustic signature from a particular tap. Through these and additional sensors, the input surface of the input device can detect and locate an input on the surface of the device and provide a corresponding input to a computing system. 
       FIG. 1  depicts a top view of a mechanical-based keyboard  100  for a computing device. As described above, the keyboard may be utilized to provide an input to a computing system such that a user may interact with the computing system. The keyboard  100  shown includes several keys arranged as buttons that act as mechanical buttons or switches. Each key of the keyboard typically has an engraved or printed character on the key that corresponds to the symbol that is input to the computer when the particular key is pressed by the user. As should be appreciated, for the mechanical buttons of the keyboard  100  to operate, the buttons or keys of the keyboard must move in a vertical manner when pressed by a finger of a user. This movement activates the button or switch below the keys to determine which key is pressed by the user. 
     In some instances, an input device for a computing system made of mechanical buttons or switches may not be feasible. For example, it may be useful to provide an input device that is flat and has few to no moving pieces, as this may yield a more robust product. One such device is a touch-based input device for a computing system. Embodiments of the present disclosure may take the form of such input devices. 
     As discussed herein, one embodiment of the present disclosure may take the form of a flat surface input device with a keyboard interface similar to that shown in  FIG. 1  associated with the flat surface.  FIG. 2  is a top view of a flat-surface keyboard input device  200  utilizing acoustic pulse recognition to detect a tap on the surface of the keyboard. While the embodiments described herein and throughout provide for a keyboard-type input device  200 , it should be appreciated that the embodiments discussed may take any form of a input-surface input device for a computing system. For example, the embodiments discussed herein may apply to a touch-screen of a mobile device or to a tablet computing system. In addition, the functions of the input devices described herein may apply to surfaces of the input device that are not flat. For example, the characteristics and functions described may also be included in a curved surface, such as that of a mouse input device. Generally, the embodiments described may apply to any type of an input device for a computing system, including but not limited to, a touch-screen, a mouse, a flat-surface keyboard, a tablet-type computing screen, and so on. The description of the embodiments below in relation to a flat surface keyboard is for convenience only and should not be considered as limiting to the present disclosure. 
     In addition, the computing systems described herein may be any type of computing or electronic device, such as a desktop computer, handheld computing device, personal digital assistant, mobile telephone, music or audio player (such as an MP3 player), health or medical device, auto/vehicle-mounted device, and so on. Accordingly, a “computing device” or “computing system” as used encompasses all such devices and any other electronic device having a processor for performing mathematical or computational processes. 
     A flat surface keyboard  200  embodiment of the present disclosure may take the form of at least one input surface  202  with some type of indicator on the surface for each of the input characters of the keyboard. The input surface  202  may be constructed from any solid material, such as metal, glass, plastic, and so on. In a metal or plastic embodiment, the keys may be machined, stamped or micro-perforated into the input surface  202  such that a user may press or tap on a key to provide a corresponding input to the computing system. In a glass embodiment, the keys may be painted on the surface  202  or provided as graphics on a display screen located below the glass surface. Generally, the keys may include any indicator that corresponds to an input to the computing system. Further, each character may be associated with a discrete area or segment of the input surface  202  that the user presses or taps to select the character for input. In the examples discussed herein, the input surface keyboard includes an indication of a standard computer keyboard layout, including space bar, enter key, function keys, and so on. 
     In addition to the keyboard layout on the surface  202 , the keyboard  200  may also include one or more surface textures to distinguish the separate keys of the keyboard layout. For example, the characters for each key as well as the outline defining the key edges and other areas may be indented into the keyboard surface  202 . Generally, the keys of the keyboard may be finished with any surface texture that distinguishes them to the touch of a user. Further, the flat surface keyboard  200  may also include a haptic or tactile feedback mechanism that is activated when the user presses or taps on a key of the keyboard. In general, the haptic response may provide a force, vibration and/or motion to the user&#39;s fingers or hands in response to the user pressing on the keyboard surface  202 . For example, each key of the keyboard  200  may move or vibrate slightly when pressed, or when a user&#39;s finger or other object is sensed within a certain proximity. 
     While the keyboard device  200  may provide a haptic response to a user input, the flat surface keyboard typically does not include mechanical switches or buttons to detect the pressing of a key. Instead, the flat surface keyboard  200  may include one or more sensors to detect when and where a user taps the keyboard during operation of the input device. In one embodiment, one or more piezo-electric sensors may be utilized to detect and record an acoustic pulse created when the user taps on the keyboard  200 .  FIG. 3  depicts a cross-sectional view of the flat-surface keyboard device utilizing acoustic pulse recognition to detect a tap on the keyboard of  FIG. 2  along the line marked “AA”. In the example shown, the keyboard  300  takes the form of a box structure with the keyboard layout located on the top surface  302  of the box. The keyboard layout provides an interface to the user and maps out the particular areas of the surface  302  that correspond to the characters of the keyboard. For example, the keyboard layout may display an area defined by a square with a character “H” located within the square. To input the character “H” to the computing device, the user taps or presses on the area defined by the square, similar to a mechanical-based keyboard. In general, the keyboard layout may include any number of defined input areas and any kind of input characters. 
     While the keyboard shown in  FIG. 3  includes a box-like structure, it should be appreciated that the keyboard  300  may take any shape and may not necessarily be an enclosed structure. The keyboard device is shown as a box-like structure merely for convenience herein. For example, the walls of keyboard  300  may be curved or non-linear. In other embodiments, the keyboard device may have an input surface and one or more support structures or legs extending away from the input surface. In yet another embodiment, the keyboard device may be integrated into a computing system, such as a touch screen of a mobile computing device. Generally, the input device may take any shape that includes at least one surface that detects an input provided by a user on that surface. 
     In the example shown in  FIG. 3 , two piezo-electric (“piezo”) sensors  310 ,  312  are arranged within the keyboard structure  300 , one on the left sidewall of the keyboard structure and the other on the right sidewall of the structure. The piezo sensors  310 ,  312  are situated to receive an acoustic pulse created when the user taps a segment or segments of the top surface  302  of the keyboard device  300 . While the example shown includes two piezo sensors  310 ,  312 , other embodiments of an input device may include any number of piezo sensors. For example,  FIG. 3A  depicts a cross-sectional top view of the keyboard device of  FIG. 3  along line “BB” that utilizes three piezo sensors  310 - 314  to detect an acoustic pulse recognition of a tap on the keyboard surface  302 . Further, it is not required that the piezo sensors  310 ,  312  be located on the sidewalls of the keyboard; they may be located anywhere near the keyboard in a manner such that the piezo sensors can receive the acoustic pulse that results from a tap on the surface. 
     While the embodiments described herein and throughout discuss piezo-electric sensors to detect the acoustic pulse resulting from a tap on the input device, it should be appreciated that the embodiments discussed may include any type of sensor that detects an acoustic signal. For example, the input device  200  may incorporate one or more microphones to detect the acoustic signal. In other embodiments, a seismometer or an accelerometer may also be used to detect the acoustic pulse created by a tap on the input device surface  202 . Generally, the embodiments described may utilize any type of acoustic sensors to detect the acoustic pulse. The description of the embodiments below incorporating one or more piezoelectric sensors is for convenience only and should not be considered as limiting to the present disclosure. 
     During operation, a user taps on the surface  302  of the keyboard defined by the keyboard outline. For example, the user may tap on the area of the top surface  302  that includes an indication of the letter “H”. When tapped, one or more acoustic pulses  304 ,  306  propagates away from and along the top surface  302 ; these pulses originate at the point tapped. For simplicity, the acoustic pulses are shown in  FIG. 3  by the arrows  304 ,  306  propagating through the interior of the keyboard. However, it should be appreciated that the acoustic pulses propagate away from the tap in all directions. For example, as shown in  FIG. 3A , the acoustic pulse may also propagate to a third piezo sensor  314  located at the back of the keyboard  300 . In general, the acoustic pulse created by a tap on the surface  302  of the keyboard device  300  is a sound wave, propagating and reflecting off of surfaces as any sound wave typically does. 
     As the acoustic pulses  304 ,  306  propagate through the keyboard  300  and reflect off of the various edges and surfaces of the keyboard, an acoustic signature is created for the separate segments of the keyboard. The acoustic signature for a particular segment is received by the piezo sensors  310 ,  312  and converted into an electrical signal. This electrical signal may than be compared by the keyboard device  300  or an associated computing system to a database of collected reference pulses to determine which character input was tapped. In addition, the internal structure of the keyboard device  300  may affect the acoustic signature of a tap on the surface  302  of the device. The effect of the internal structure of the keyboard  300  on the acoustic signatures is discussed in more detail below with reference to  FIG. 5 . 
     In one example, the user may tap the area of the surface  302  of the keyboard  300  marked as “H” to provide that character as an input to a computing system. The tap creates an acoustic signature that is received at the piezo sensors  310 ,  312 . The keyboard  300  or computing system then compares the received signature to a database of collected acoustic signatures to determine that the received signature indicates that the user has tapped on the keyboard surface  302  to input an “H” character. In this manner, a tap on an input surface  302  of the keyboard  300  is translated into an input to the computing system. 
     The database of acoustic signatures for the keyboard device  300  to which a received acoustic signal is compared may be collected and gathered in several ways. In one example, a plurality of acoustic signatures are gathered during a calibration process for the keyboard device  300 . During calibration, the top surface  302  is tapped at discrete spatial intervals while the acoustic pulse received at the piezo sensors  310 - 314  is stored. In this manner, each individual pulse signature is associated with a particular area or segment of the keyboard device  300 . Because it is known which areas of the surface  302  of the keyboard  300  is associated with which input character, the unique acoustic signatures for each input character can be stored in a database accessible by the keyboard device  300  or computing system for comparison with the received signatures during operation of the input device. 
     In those embodiments that incorporate a plurality of piezo sensors  310 - 314 , the received acoustic signature at each sensor may be stored in the same or separate databases. For example, due to distance traveled and the various surface irregularities of the keyboard, the acoustic pulse received at piezo sensor  314  may be different than the acoustic pulse received at piezo sensor  310  for any given tap on the keyboard surface  302 . Thus, the acoustic signature for an “H” input received at piezo sensor  312  is different from the acoustic signature for the same input at piezo sensor  310 . As such, a separate database may be maintained for the acoustic signatures received at each piezo sensor. Alternatively, a single database may be maintained, and each piezo sensor may include a unique identifier that is used to cross-reference entries in the database. In such an embodiment, the sensor identifier and acoustic signature may both be used to search the database for matching or similar records. 
     During operation, each database may be consulted to determine which area of the surface  302  of the keyboard was tapped  300 . For example, the input device  300  or computing system may compare the received acoustic pulse from a first piezo sensor  310  to a first database. This may narrow the number of possible taps performed by a user. Once narrowed, the input device  300  or computing system may compare the received acoustic pulse from a second piezo sensor  312  to a second database to acquire an accurate determination of the location of the user&#39;s tap to a particular input character. As should be appreciated, several piezo sensors  310 - 314  provide more accuracy in determining of the location of a tap on the surface  302  of the device  300 . 
     The input device  300  or associated computing system may perform the comparison of the received acoustic signal to the acoustic signals maintained in the database in several ways. In one embodiment, the received acoustic signature may be compared directly to the stored acoustic signatures to determine if the received signature exactly matches the stored signature. In another embodiment, a percentage error may be considered such that, if the received signature does not match the stored signature exactly but still falls within the percentage error, the input device  300  or computing system may determine the received signature matches the stored signature. In still another embodiment, the input device  300  or computing system may determine a peak-to-peak value for the received signature and compare that to similar stored peak-to-peak values. Generally, any method for comparing a received acoustic signal to a stored acoustic signal is envisioned and may be performed by the input device  300  or associated computing system. 
     In addition, in those embodiments that include a plurality of piezo sensors, the difference in time between when the plurality of piezo sensors detect the tap may be utilized to determine the location of the tap, similar to a multilateration process. In this embodiment, the input device  300  or associated computing system may use the time difference of arrival of the acoustic pulse emitting from a tap on the surface  302  of the input device. By comparing the time difference of arrival at three or more piezo sensors, the input device  300  or computing system may determine a location on the surface of the device that a tap occurs. Such a determination may also be used in conjunction with the comparison of the received acoustic signatures described above to more accurately determine the location of a tap. 
     While piezo sensors  310 - 314  can detect when a key is pressed or tapped by a user, the piezo-sensors alone may not be able to detect a press-and-hold action. For example, it is occasionally required during operation of a computing device that the user hold down a shift key or other key on the keyboard to achieve a particular input. However, because the piezo sensors  310 - 314  detect a pressed key based on a tap on the surface  302  of the keyboard, holding down a key is typically not measured by the piezo sensors. To acquire such press-and-hold events, the keyboard device  300  may also incorporate a capacitive or other type of sensor to detect the placement and holding of a user&#39;s finger on the surface  302  of the device  300 . 
       FIG. 4  depicts a cross-section view of a keyboard device  400  utilizing a combination of piezoelectric sensors  410 ,  412  and at least one capacitive sensor  418  to detect a tap and press-and-hold movement on the keyboard surface  402 . The keyboard  400  and peizo sensors  410 ,  412  may take the same structure and placement as described above with reference to  FIGS. 3 and 3A . In addition, one or more capacitive sensors  418  may be located along the underside of the top surface  402  of the keyboard device  400  to further detect the position of a finger tap on the device, as well as detect when the user is performing a press-and-hold event on a particular key of the keyboard. 
     The capacitive sensor  418  may form a conductive layer located just beneath the top surface  402  of the keyboard  400 , with a small voltage applied to the layer to create a uniform electrostatic field. Because a human finger may also act as a conductor, placing the finger on the surface  402  of the keyboard  400  above the capacitive sensor  418  may create a distortion in the capacitive field that may be measured by the capacitive sensor. This distortion in the capacitive field may be utilized by the keyboard device  400  to determine the location of the touch on the surface  402 . Further, as long as the user maintains contact with the surface  402 , the distortion in the capacitive field is maintained. 
     In an embodiment of the input device  400  that is composed of a metal, the location of a user&#39;s finger may be detected through a capacitive sensor detecting a distortion in metal surface of the input device surface  402 . In this example, a distortion in the surface of the metal input device can be measured from a capacitive sensor  418  located on the input device  400 . The capacitive sensor  418  may detect a distortion in the surface  402  of the input device  400  from the presence of a user&#39;s input. Thus, as the user presses on the surface of the input device  400 , the capacitive sensor  418  may detect such distortion and locate such distortion similar as described herein. 
     The capacitive sensor  418  may be used in junction with the piezo sensors  410 ,  412  to provide an accurate determination of the location of a tap by the user of the flat keyboard  400  device. For example, the piezo sensors  410 ,  412  may be used as described above with reference to  FIGS. 3 and 3A  to determine which area of the keyboard is tapped. However, in some instances, the exact location of the user&#39;s tap may not be obtained through the piezo sensors  410 ,  412  alone. Rather, due to variation in the acoustic pulse or other unforeseen events, the piezo sensors  410 ,  412  may only be able to determine an approximate location on the surface  402  of the user&#39;s tap. In this circumstance, the keyboard device  400  or associated computing system may employ one or more capacitive sensors  418  in an attempt to narrow the possible area of the user&#39;s tap to a specific area or key. In another embodiment, the keyboard  400  or computing system may utilize the capacitive sensor  418  to obtain a relative area of the surface  402  that is pressed by the user and use the piezo sensors  410 ,  412  to obtain the proper key. Further, a capacitive sensor  418  alone may not distinguish between an accidental touch of the input surface and a deliberate one. However, by employing the piezo sensors (which may not detect an accidental brush against the input surface  402 ), in conjunction with the capacitive sensor  418 , the input device  400  may detect and disregard accidental touches of the input devices. In this manner, the piezo sensors  410 ,  412  and capacitive sensors may be used in conjunction to adequately determine the key that is pressed by the user of the keyboard device  400 . 
     In addition, the capacitive sensor  418  may also be utilized by the keyboard device  400  or computing system to determine when a user is pressing and holding a key down as the change in the capacitive field created by the user&#39;s finger is maintained as long as the user is pressing against the top surface  402 . For example, to input capital letters to the computing system, the user may press and hold the “shift” key of the keyboard device  400  while typing other letters on the keyboard. However, because the piezo sensors  410 ,  412  detect an acoustic pulse created when a user taps on the surface  402  of the input device  400 , the piezo sensors may only detect the first press and may not detect the hold movement performed by the user. Because the user&#39;s finger continues create a change in the capacitive field of the surface  402 , the capacitive sensor  418  may detect the maintained presence of the user. In this manner, the capacitive sensor  418  and piezo sensors  410 ,  412  may be utilized in conjunction to, not only determine the location of a keystroke on the keyboard layout, but to also detect a press-and-hold movement performed by the user. 
     Several other features may also be included in the keyboard device  300  to further refine the determination of a location of the user&#39;s tap on the keyboard surface  302 . For example,  FIG. 5  depicts a cross-sectional view similar to that shown in  FIG. 3  of a keyboard device utilizing acoustic pulse recognition to detect a tap on the keyboard, including tuning features to distort or alter the resultant acoustic signature of the tap. The keyboard depicted in  FIG. 5  is similar to that depicted above in  FIG. 3 . However, in this embodiment, one or more tuning features  520 ,  522  are included in the keyboard  500  to alter the acoustic signal corresponding to a tap on the surface  502 . 
     As described above, a tap on the surface  502  of the keyboard  500  creates an acoustic pulse  504 ,  506  that propagates away from the tapped area. One or more piezo sensors  510 ,  512  located on or near the keyboard receive the acoustic pulse. The acoustic pulse signature received by each sensor is then compared to one or more databases to determine the area on the surface that is tapped. The acoustic signature for any particular tap is created as the acoustic pulse propagates along and reflects off of surfaces of the keyboard or other surfaces near the keyboard before reaching the piezo sensors  510 ,  512 . 
     To further refine or alter the resultant acoustic pulse  504 ,  506  for any particular tap, one or more tuning features may be located between the tapped area on the surface  502  and the piezo sensors  510 ,  512 . These tuning features may alter the propagation and reflection of the acoustic pulse  504 ,  506  before it reaches the piezo sensor  510 ,  512 , essentially altering the characteristics of the acoustic pulse. Such alteration is similar to a phase encoding of sound that occurs naturally when a sound wave enters the human ear. The keyboard  500  of  FIG. 5  includes two tuning features  520 ,  522  that project into the keyboard structure to disrupt and alter the propagation of an acoustic pulse  504 ,  506  resulting from tap on the surface  502 . These features  520 ,  522  may or may not affect the propagation of a particular tap. For example, the propagation of acoustic pulse  506  is altered by tuning feature  522  in such a matter that it does not reach sensor  510 , while acoustic pulse  504  is unaffected by tuning feature  520 . Thus, the combined acoustic signature for the tap shown would be formed of the acoustic pulse  504  received at piezo sensor  512  and no acoustic pulse  506  received at piezo sensor  510 . In reality, however, it is likely that an acoustic pulse from a tap on the surface  502  of the keyboard  500  will be received at each piezo sensor  510 ,  512  after several reflections off of the various surfaces of the keyboard device. 
     In this manner, the acoustic signature for one or more key taps may be tuned or otherwise altered by the addition or subtraction of one or more tuning features of the device. Such tuning may allow a manufacturer of the input device  500  to create truly unique acoustic signatures for one or more taps on the surface  502  of the device. 
     In general, the keyboard device  500  may include any number and type of tuning features that alter the propagation of an acoustic pulse. Some examples of tuning features that may alter an acoustic pulse include rough textures on the interior surface of the input device, projections extending into the propagation path of the pulse, varying dimensions of a propagation pathway, and so on. Further, the keyboard device  500  may include a combination of a plurality of the above tuning features in an attempt to alter the acoustic pulse characteristics. For example, the keyboard  500  may include a projection tuning feature combined with a rough texture on the surface of the projection to alter the acoustic signature of a particular tap on the surface  502  of the keyboard. 
     Another such tuning feature that may alter the acoustic pulse resulting from a tap on the surface of the keyboard device is one or more openings located along the propagation path of the acoustic pulse.  FIG. 6  depicts a cross-sectional view similar to that shown in  FIG. 3  of a keyboard device  600  utilizing acoustic pulse recognition to detect a tap on the keyboard, including openings  640 - 644  on the surface  602  of the keyboard to distort or alter the resultant acoustic signature of the tap.  FIG. 6A  depicts a cross-sectional top view similar to that shown in  FIG. 3A  of the same keyboard device  600  utilizing acoustic pulse recognition to detect a tap on the keyboard. Similar to the other tuning features described above, the openings  640 - 644  may alter the acoustic signature detected by the piezo sensors  610 - 614  created by a tap on the top surface  602  of the keyboard  600  by a user. 
     As described above, a tap on the surface  602  of the keyboard  600  creates an acoustic pulse  604 ,  606  that propagates away from the tapped area. One or more piezo sensors  610 - 614  located on or near the keyboard receive the acoustic pulse which is then compared to one or more databases to determine the area that is tapped. 
     To alter or define the acoustic signature of a tap on the keyboard surface  602 , one or more openings may be located along the surfaces of the keyboard device  600 . In the embodiment shown in  FIG. 6 , a first opening  640  is located along the bottom surface of the keyboard on the left side and a second opening  642  is located along the bottom surface of the keyboard on the right side. A third opening  644 , as shown in  FIG. 6A , is also located along the bottom surface of the keyboard, near the front of the keyboard device  600 . Although three openings  640 - 644  are shown along the bottom surface of the device  600 , the keyboard may include any number of openings on any of the surfaces of the keyboard. Further, while the openings shown are generally circular in shape, the openings may take any shape and size to alter or define the acoustic pulse of a tap on the surface of the keyboard. 
     As mentioned, the openings  640 - 644  may alter the propagation and reflection of the acoustic pulse  604 ,  606  before it reaches the piezo sensors  610 ,  612 , altering the characteristics of the acoustic pulse. For example, the acoustic pulse  606  may split otherwise separate as it encounters the first opening  640  such that some of the pulse passes out of the opening and some of the pulse reaches the piezo sensor  610 . In contrast, acoustic pulse  606  is generally unaffected by the second opening  642  as the acoustic pulse passes over the opening. In this manner, the openings along the surface of the keyboard device  600  may create a phase encoding of the acoustic pulses  604 ,  606  as the pulses propagate and reflect along the surfaces of the keyboard before reaching the piezo sensors  610 - 614 . 
     Upon receipt, the acoustic signatures detected by the piezo sensors  610 - 614  of the keyboard  600  may be compared to a database of signatures by the keyboard or an associated computing system to determine the location of the tap on the surface  602  of the keyboard. In those embodiments that include tuning features  640 - 644  designed to alter the acoustic pulses, a database may be maintained by the input device  600  or computing system that stores such altered acoustic signatures so that the received acoustic signatures are compared to the database of altered acoustic signatures. 
     In addition, other environmental factors may also affect the acoustic signature of the taps along the surface of the keyboard device. For example, the user resting palms or other parts of the hand on the keyboard device while typing may alter the acoustic signature of any particular tap. To account for the effect of the user resting his hands on the keyboard device while typing, one or more pressure sensors may be included to detect pressure applied to the keyboard surface. 
       FIG. 7  depicts a cross-sectional view similar to that shown in  FIG. 3  of a keyboard device  700  utilizing a combination of piezoelectric sensors  710 ,  712  to detect a tap on the keyboard surface and pressure sensors  720 ,  722  to detect a dampening force applied to the keyboard surface  702 .  FIG. 7A  depicts a bottom view of the same keyboard device  700  to detect the presence of pressure on the surface of the keyboard that may dampen or alter the acoustic pulse of a tap on the keyboard surface. The pressure sensors  720 - 728  included may be utilized to detect the presence of a dampening force on the surface of the keyboard, as well as aid in determining the area of the surface  702  that is tapped by the user of the keyboard device  700 . 
     To detect the presence of a dampening force, such as a user resting his palms on the surface  702  of the keyboard  700 , one or more pressure switches  720 ,  722  may be located along the bottom surface of the keyboard. As shown in  FIG. 7A , the pressure switches ( 720 ,  722 ,  726 ,  728 ) may be located at the four corners of the bottom surface of the keyboard device  700 . However, it should be appreciated that the pressure switches may be located anywhere on the keyboard device  700  that may detect the presence of the dampening force. For example, pressure sensor  724  of  FIG. 7  is located just beneath the top surface  702  of the device  700  to detect such a force. In general, the keyboard device  700  may include any number of pressure sensors located in any position on the device to detect the presence of a dampening force on the surface of the keyboard that may alter the acoustic signatures of a tap by the user. 
     In addition, pressure sensors  724  located just beneath the top surface  702  of the keyboard device  700  may aid the device is pinpointing the location of a tap on the surface  702 . This detection may be combined with other sensor detection, such as the detection of the acoustic signature and the capacitive detection described above, to accurately locate a tap on the surface  702  of the keyboard  700  by a user. Further, the pressure sensors  724  located just beneath the surface  702  of the input device  700  may be configured to only detect and transmit a user&#39;s input if the pressure exerted exceeds a set threshold. Thus, if the input provided does not provide enough pressure to the pressure sensor  724 , the input is not processed by the input device. In addition, the pressure sensors  724  may be programmed to detect different pressures applied to different segments of the input surface  702  to account for some users pressing some keys harder than others. 
     The embodiment shown in  FIGS. 7 and 7A  may also utilize a plurality of databases of acoustic signatures to compare a received acoustic signature against during operation of the keyboard  700 . For example, the keyboard  700  or computing system may maintain a first database that stores a plurality of acoustic signatures for the device when no dampening force or pressure is applied to the device, other than the tap provided by the user to indicate a keystroke. However, when a dampening force is detected by one or more of the pressure sensors  720 - 728 , a second database may be utilized that contains the acoustic signatures for the device in a damped configuration. Thus, the pressure sensors  720 - 728  may aid the device in selecting the correct database to compare the received acoustic signatures against to determine the location of a keystroke. Further, the detection of pressure on one pressure sensor but not the other pressure sensors of the device may trigger the accessing of a third database. 
     The database of dampened acoustic signatures may be created in a similar fashion as the undamped database is created. In particular, a damping force may be applied to the device  700  during a calibration phase. Then, the top surface  702  may be tapped at discrete spatial intervals while the acoustic pulse received at the piezo sensors  710 - 714  is stored. In this manner, each dampened individual pulse signature is associated with a particular area of the keyboard device  700 . Because it is known which areas of the surface  702  of the keyboard  700  is associated with which input character, the unique damped acoustic signatures for each input character can be stored in a database accessible by the keyboard device  700  or computing system. This database may be maintained separately and accessed when the device detects a dampening pressure applied to the device  700 . In an alternative embodiment, the dampened acoustic signature and undampened acoustic signature for each key of the keyboard  700  may be maintained in the same database such that the correct signature is accessed based on the environmental condition of the keyboard. 
     Another environmental factor that may affect the acoustic signature of a keystroke on the keyboard device is ambient noise. As should be appreciated, adding noise to the acoustic pulse created by a tap on the surface of the device likely changes the acoustic signature for that tap. Further, because the ambient noise for any particular environment may be difficult to anticipate, a database of the altered acoustic signatures for a device is similarly difficult to create. Therefore, in one embodiment, the input device may include a microphone situated to pick up the ambient noise of the environment in an effort to provide canceling techniques to remove the ambient noise from the received acoustic signatures. 
       FIG. 8  depicts a top view of a keyboard device  800  utilizing a microphone  802  to measure ambient noise around the keyboard to aid in detecting a tap on the surface of the keyboard. The embodiment of the keyboard depicted in  FIG. 8  is similar to the input devices described above, in that a tap performed by a user on the surface of the keyboard creates a unique acoustic signature and detected by one or more piezo sensors. However, ambient noise may alter the acoustic signature for one or more taps such that the keyboard may be unable to determine the correct location of tap on the surface of the device. 
     To combat the altering of the acoustic signature by ambient noise, the microphone  802  may be configured to detect the ambient noise and provide a signal to the device  800  or associated computing system that represents and mirrors the detected ambient noise. This signal may then be subtracted from the acoustic signatures detected by the piezo sensors of the keyboard  800 . Thus, by removing the ambient noise from the detected acoustic signatures, the correct location of the keystroke on the surface of the keyboard device  800  is determined. 
     In the configuration shown, the microphone  802  is located in the upper right-hand corner of the top surface of the keyboard  800 . However, the microphone  802  may be located anywhere on the keyboard that allows the microphone to detect the ambient noise. In an alternate embodiment, the microphone  802  may not located on the device itself, but may be located somewhere near the device that allows the microphone to detect the ambient noise. In general, the location of the microphone  802  does not detract from the described embodiment. Further, while only one microphone  802  is shown in  FIG. 8 , the device  800  may include any number of microphones or sound detecting sensors to collect a sample of the ambient noise and perform noise canceling of the present ambient noise from the resulting acoustic signatures from a tap on the surface of the keyboard device  800 . 
     Yet another sensor may be included in the input keyboard device to further aid in locating the presence of a tap on the surface of the device.  FIG. 9  depicts a cross-sectional view similar to that shown in  FIG. 3  of a keyboard device utilizing a combination of piezoelectric sensors and proximity sensors to detect and locate a tap on the keyboard surface. Similar to the embodiment described above with reference to  FIG. 4 , the proximity sensors  950 ,  952  may be combined with the acoustic signatures detected by the piezo sensors  910 ,  912  to detect a tap on the surface  902  of the keyboard  900 . 
     The proximity sensors  950 ,  952  may include one or more photosensors located along the edge of the keyboard device and corresponding infrared light-emitting diodes (LEDs) oriented to create a grid on the keyboard and such that the photosensors receive the light projected from the LEDs. The presence of a object may be detected by the photosensors when the object interrupts the projected light. In this manner, when a user places a finger on the surface  902  of the device  900 , the proximity sensors may detect the presence of that finger. 
     The proximity sensors  950 ,  952  may be used in junction with the piezo sensors  910 ,  912  to provide an accurate determination of the location of a tap by the user of the input keyboard  900  device. For example, the piezo sensors  910 ,  912  may be used as described above to determine which area of the keyboard is tapped. However, in some instances, the exact location of the user&#39;s tap may not be obtained through the piezo sensors  910 ,  912  alone. In these circumstances, the keyboard device  900  or associated computing system may consult one or more proximity sensors  950 ,  952  in an attempt to narrow the possible area of the user&#39;s tap to a specific area or key. In addition, the proximity sensors  950 ,  952  may be utilized to activate and deactivate the keys or sensors of the keyboard device  900  in response to placement of the user&#39;s finger near a key. For example, when a finger is not detected near a key, such keys may be deactivated in the sense that such keys are removed from the possible keys that may be pressed by the user. However, when a finger is detected, those keys are activated. By removing some keys from the number of possible keys that are tapped by the user at any one time, the keyboard  900  may determine the correct key tap at a faster rate. 
       FIG. 10  is a block diagram illustrating an exemplary computing system that may be used in implementing embodiments of the present disclosure. Further, the input devices described herein may include one or more of the described components to accomplish the described functions. In addition, the computing device and docking station may omit some of the described components. The computer system (system) includes one or more processors  1002 - 1006 . Processors  1002 - 1006  may include one or more internal levels of cache (not shown) and a bus controller or bus interface unit to direct interaction with the processor bus  1012 . Processor bus  1012 , also known as the host bus or the front side bus, may be used to couple the processors  1002 - 1006  with the system interface  1014 . System interface  1014  may be connected to the processor bus  1012  to interface other components of the system  1000  with the processor bus  1012 . For example, system interface  1014  may include a memory controller  1018  for interfacing a main memory  1016  with the processor bus  1012 . The main memory  1016  typically includes one or more memory cards and a control circuit (not shown). System interface  1014  may also include an input/output (I/O) interface  1020  to interface one or more I/O bridges or I/O devices with the processor bus  1012 . One or more I/O controllers and/or I/O devices may be connected with the I/O bus  1026 , such as I/O controller  1028  and I/O device  1030 , as illustrated. 
     I/O device  1030  may also include an input device (not shown), such as an alphanumeric input device, including alphanumeric and other keys for communicating information and/or command selections to the processors  1002 - 1006 . Another type of user input device includes cursor control, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to the processors  1002 - 1006  and for controlling cursor movement on the display device. 
     System  1000  may include a dynamic storage device, referred to as main memory  1016 , or a random access memory (RAM) or other devices coupled to the processor bus  1012  for storing information and instructions to be executed by the processors  1002 - 1006 . Main memory  1016  also may be used for storing temporary variables or other intermediate information during execution of instructions by the processors  1002 - 1006 . System  1000  may include a read only memory (ROM) and/or other static storage device coupled to the processor bus  1012  for storing static information and instructions for the processors  1002 - 1006 . The system set forth in  FIG. 10  is but one possible example of a computer system that may employ or be configured in accordance with aspects of the present disclosure. 
     According to one embodiment, the above techniques may be performed by computer system  1000  in response to processor  1004  executing one or more sequences of one or more instructions contained in main memory  1016 . These instructions may be read into main memory  1016  from another machine-readable medium, such as a storage device. Execution of the sequences of instructions contained in main memory  1016  may cause processors  1002 - 1006  to perform the process steps described herein. In alternative embodiments, circuitry may be used in place of or in combination with the software instructions. Thus, embodiments of the present disclosure may include both hardware and software components. 
     A machine readable medium includes any mechanism for storing information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). Such media may take the form of, but is not limited to, non-volatile media and volatile media. Non-volatile media includes optical or magnetic disks. Volatile media includes dynamic memory, such as main memory  1016 . Common forms of machine-readable medium may include, but is not limited to, magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of medium suitable for storing electronic instructions. 
     The foregoing merely illustrates certain principles and embodiments. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements and methods which, although not explicitly shown or described herein, embody the principles of the embodiments and are thus within the spirit and scope of the present disclosure. From the above description and drawings, it will be understood by those of ordinary skill in the art that the particular embodiments shown and described are for purposes of illustrations only and are not intended to limit the scope of the present disclosure. References to details of particular embodiments are not intended to limit the scope of the disclosure.