Abstract:
Touch user interfaces have been an essential element in the use of smartphones and tablets. An improved touch or near touch sensing structure made of a printed conductive double-wrapped coil is disclosed. A printable substrate is used to provide a base for the double-wrapped coil. On the printable substrate, a double-wrapped coil is printed using at least one flexible conductive material. The double-wrapped coils can be printed sequentially, simultaneously, parts of the two coils are printed and then the rest of the coil parts are printed, or any other useful printing order. The double-wrapped coil provides an increased sensing area and therefore can compute a more efficient capacitance.

Description:
BACKGROUND 
     The present application is related to a touch or near touch sensing device structure, and finds particular application in connection an improved projective capacitive touch and/or near touch-sensing device and will be described with particular reference thereto. It is to be understood, however, that it also finds application in other usage scenarios, and is not necessarily limited to the aforementioned exemplary embodiment. 
     Touch and near touch user interfaces have been an essential element to the popularity of smartphones and tablets as well as other devices. A conventional projective capacitive sensing device is made by a matrix of diamond shaped conductive pads. There is a gap between each row and column pad, which forms a coplanar capacitor that acts as the sending aperture. A drive signal can be applied to one of the pads, on either the row or the column, and, by capacitive coupling, the signal is picked up from the other pad. When a finger touches or nears a panel having these configurations, it distorts the local electrostatic field at that point causing a measurable change in capacitance. 
     As touch and near touch sensing technology has developed, the cost of the sensor device has steadily dropped. As a result, inexpensive touch sensing devices can be used in broad applications, not only for computer or smartphone interfaces, but also for a variety of things that may be connected to the internet cloud services. 
     Projected capacitive sensing is able to sense a finger touch or near touch through a thin interlayer such as a glove. In addition to touch or near touch sensing, the capacitive aperture sensing is sensitive to surface textures and therefore can be used as a texture sensor. However, the effective sensing geometry is at the edges of the diamond pad, which forms the sensing gap with a neighboring pad in the conventional device. 
     INCORPORATION BY REFERENCE 
     The following references, the disclosures of which are incorporated herein by reference in their entireties, are mentioned: 
     U.S. Pub. No. 2006/0097991, published May 11, 2006, entitled Multipoint Touchscreen, by Hotelling, et al. 
     BRIEF DESCRIPTION 
     In one aspect of the presently described embodiments, a touch or near touch sensing device is described. The device includes a printable substrate and a flexible conductive material. The printable conductive material is used to print two conductive double-wrapped coils onto the printable substrate. 
     In another aspect of the presently described embodiments, there is provided a method for printing a touch and/or near touch sensing device. The method prints a pair of coils of flexible conductive material with a printer arrangement onto a substrate. The printed coils are printed such that they form a double-wrapped coil. The double-wrapped coil of flexible conductive material is, in one embodiment, cured using an infrared lamp. The double-wrapped coil is connected to a device, wherein when a finger touches or nears the double-wrapped coil, a signal is sent to the device indicating the capacitance change across the double-wrapped coil. 
     In another aspect of the presently described embodiments, a touch and/or near touch sensing control panel is described. The control panel is comprised of a printable substrate such as a plastic laminated paper holding a plurality of printed double-wrapped coils. In certain embodiments, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), coated paper, and polymide may, among other materials be used as the printable substrate. The double-wrapped coils are arranged on the printable substrate in an array. The touch or near touch sensing control panel further includes an embodiment where the plurality of printed double-wrapped coils are placed in locations corresponding to particular images. A signal readout device is coupled to a Bluetooth device, wherein when the image is touched, a touch signal is transmitted to a device with cloud service applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The exemplary embodiments may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the present exemplary embodiment. 
         FIG. 1A  illustrates a conventional projective capacitive sending device structure; 
         FIG. 1B  illustrates a cross-sectional side view of a co-planar capacitor of panel  100  of  FIG. 1A ; 
         FIG. 2A  illustrates a capacitor formed as a double-wrapped coil; 
         FIG. 2B  illustrates the capacitor of  FIG. 2A  incorporated within a circuit; 
         FIG. 3  illustrates a cross section illustration of a double-wrapped capacitor coil; 
         FIG. 4  illustrates an example of low cost printed capacitive sensing coils such as a printed keyboard and a laminated control panel of a portable device; 
         FIG. 5  illustrates the double-wrapped coil in a keyboard; 
         FIG. 6  describes a method for printing a double-wrapped coil as described by the embodiments; 
         FIG. 7A  illustrates one embodiment with the double-wrapped coil printed between two printed images; 
         FIG. 7B  illustrates one embodiment as shown in  FIG. 7A  where the double-wrapped coil is embedded in a children&#39;s book that is linked to a Bluetooth enabled device; 
         FIG. 8  illustrates an embodiment of a capacitor based capacitive sending device structure formed by a double-wrapped coil; 
         FIG. 9  illustrates a cross section of a double-wrapped coil configuration; 
         FIG. 10A  illustrates a cross section view of the traces of a double-wrapped coil configuration; 
         FIG. 10B  illustrates another embodiment of a cross section view of the traces on a double-wrapped coil configuration. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  describes a conventional projective capacitive sensing device structure (or panel)  100  as used in existing devices. It is made by a matrix of diamond shaped conductive pads  102   a ,  102   b  (only some identified for clarity of the drawing). There is a gap  106  (only some identified for clarity of the drawing) between each of the pads  102   a ,  102   b  for each row R 1 , R 2 , R 3 , R 4  and column C 1 , C 2 , C 3 , C 4 , the pads  102   a ,  102   b  forming a coplanar capacitor. Such a capacitor  104  is shown more clearly in the cross-sectional view (A-A′) of  FIG. 1B , and acts as a sensing aperture. A drive signal is applied to one of the pads  102   a  (row or column) and, by capacitance coupling, a signal is picked up from a neighboring pad  102   b . When a finger touches or is near the panel  100 , it alters a local electrostatic field between the pads  102   a ,  102   b . This is measurable as a change in capacitance. If a finger bridges the gap  106  between two of the pads  102   a ,  102   b  the electric field is further interrupted and detected by a controller (not shown). 
     With attention now to the present embodiments, described is an improved sensing structure (i.e. touch or near touch sensing array) made of a conductive double-wrapped coil. The double-wrapped coil forms a coplanar capacitor with a long gap between two neighboring electrodes, e.g. coils. This geometry provides an efficient sensing aperture and enhances signal/noise (S/N) ratio. The inexpensive touch or near touch sensing device described herein can be used in a multitude of applications from computer or smartphone applications as well as devices connected to the internet cloud services, among others. 
     Turning to  FIG. 2A , illustrated is an embodiment of such an improved touch or near touch sensing structure configured as a conductive double-wrapped coil arrangement  200 . Two coils  202 ,  204  are placed near each other but are physically and electrically isolated. In the described embodiment, the two coils  202 ,  204  are printed by a printer arrangement  208  that is controlled by a controller  210 . The controller  210  contains the necessary instructions to precisely print the double-wrapped coils  202 ,  204  onto a printable substrate  212 . The double-wrapped coils  202 ,  204  terminate at connectors  214 ,  216 . 
     In various embodiments, the printer arrangement  208  can include an inkjet printer, gravure printer, screen-printer, aerosol printer, and/or photolithography arrangement, among others. 
     As will be further described in  FIG. 6 , in one embodiment a first coil  202  is printed on the printable substrate and a second coil  204  is printed on the same printable substrate  202  but without touching the first coil  202 . In alternative embodiments, the printable substrate may be conductive; non-conductive; flexible; or non-flexible. In further alternative embodiments, the first coil  202  and second coil  204  are printed sequentially; simultaneously; parts of the two coils are printed and then the rest of the coil parts are printed; or any other useful printing order. 
     In this embodiment, a gap  206  between the traces (i.e. coils) is about 90 μm. The total diameter of the double-wrapped coil  202 ,  204  is 13.4 mm and the total length of the gap is 426 mm (2 times the length of a coil). In comparison, if the dimension of an edge of a conventional pad is 13.4 mm, the total gap length will be 53.6 mm (4 times the edge). Therefore, the double-wrapped coil  202 ,  204  has a sensing gap about 8 times longer than the conventional pad  106  ( FIGS. 1A and 1B ). This feature provides a larger capacitance change when an object touches or nearly touches the conductive double-wrapped coil arrangement  200  as well as a panel of such conductive double-wrapped arrangement (such as may be used in the device of  FIG. 4 ). The gap dimension between the traces (i.e. coils) ranges from 3 μm to 1 mm depending on the implementation. The diameter of each coil ranges in some embodiments from 50 μm to 10 mm, and in others the overall diameter is between 10 mm to 20 mm. The overall length of the coil depends on the design of the gap, shape, and size of the coil. 
     Turning to  FIG. 2B , depicted is the capacitor of  FIG. 2A  incorporated within a capacitance circuit  220 . The circuit includes coils  202  and  204 , where coil  202  acts as a driving line and coil  204  acts as a sensing line. The coils, as noted previously, are spatially separated thereby forming the gap  206 . The driving line coil  202  is electrically connected to an energy source (e.g., a voltage source)  222 , and the sensing line coil  204  is electrically connected to a capacitive sensor device  224 . The driving line coil  202  is configured to carry a current generated by the energy source  222 , and the sensing line coil  204  is configured to carry a current to the capacitive sensor device  224 . When no object is present at the gap  206 , any capacitive coupling at the gap  206  stays fairly constant. When a finger (or other appropriate object, e.g., a stylus) touches or nearly touches the gap  206 , the previously existing capacitive coupling is altered. The finger shunts a portion of the capacitive field whereby charge across the gap  206  is altered. The variation in the capacitive coupling alters the current being carried in the sensing line coil  202 , which is sensed by the capacitive sensor device  224  and provides this information to a controller  226 . 
     As illustrated in  FIG. 3 , by placing a thin substrate such as, but not limited to paper (˜90 μm thick)  300 , over the double-wrapped coil  306  formed on a substrate  304 , when a finger  302  touches or nearly touches the double-wrapped coil  306  this causes a capacitance of the double-wrapped coil  306  to change. When a finger touches or nearly touches the double-wrapped coil  306  printed on the substrate  304 , it alters the electric field lines and therefore changes the capacitance. In other embodiments, a stylus or other touching device (not shown) is used to touch or nearly touch the double-wrapped coil  306 . The flexible conductive material of the coils may include silver, gold, copper, or conductive carbon, among others. 
     In this embodiment, the double-wrapped coil  306  is printed on a flexible substrate  304 . The following table shows the results of the capacitance measurement with and without a finger touching or nearly touching the double-wrapped coil  306  at different frequencies. Due to dielectric dispersion, the capacitances for both with and without a finger touch are smaller at a larger frequency. The dielectric dispersion caused by the finger seems larger since the change of the capacitance is also larger when the frequency is lower. It is to be understood that nearly touching is understood to mean the ginger is within sufficient proximity to alter the electric fields existing between the two coils. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Capacitance 
                 Capacitance 
                 % of 
               
               
                 Frequency of 
                 without Finger 
                 with Finger 
                 Capacitance 
               
               
                 Measurement 
                 Touch 
                 Touch 
                 Change 
               
               
                   
               
             
             
               
                  1 kHz 
                 41.8 pF  
                 46 pF 
                   10% 
               
               
                 500 Hz 
                  54 pF 
                 62 pF 
                 14.8% 
               
               
                 100 Hz 
                 130 pF 
                 150 pF  
                 15.4% 
               
               
                   
               
             
          
         
       
     
     With a sufficient change in capacitance (as for example the changes shown in Table 1), the S/N ratio requirement for a readout device can be relaxed and therefore the cost of a reading device may be reduced. With this feature, various applications may be enabled. In one example, a paper based instrument control panel may be made by printing a laminated control panel image  400  on one side of a substrate and printing a sensing coil on the other side as shown in  FIG. 4 . The advantages of paper control panel include low cost, customer design, disposable (for sanitation reasons), lightweight, and may be laminated on various surfaces. Additionally, projected capacitive sensing, as disclosed here, is able to sense a finger touch or near finger touch through a thin interlayer such as a glove. 
     In certain embodiments, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), coated paper, and polymide may, among other materials be used as the printable substrate. 
     In another embodiment,  FIG. 5  illustrates a lightweight consumer computer keyboard  500  utilizing a double-wrapped coil arrangement of the present application. Each of the keys of the printed keyboard corresponds to a single double-wrapped coil  502 . As intended to be shown by the breakout portion of  FIG. 5 , each of the individual double-wrapped coils  502  are respectively connected to (and/or used as) one of a driving line  504  or a sensing line  506  (as discussed in connection with  FIG. 2B ). 
     When a finger touches or nearly touches a given key on the surface of the keyboard  500 , the device detects the change in capacitance and sends a signal via connection lines  504 ,  506  to a corresponding output device indicating which letter was pressed. The output device maybe a wired or wireless detector and may be a specific design such as Bluetooth, Wi-Fi, among others. 
       FIG. 6  describes a particular method for printing the described double-wrapped coil. It is to be understood other methods may be employed. The method  600  comprises printing a first and second coil of flexible conductive material, such as silver, onto a flexible substrate  602 . The material is printed by any number of printer arrangements onto, for example, a substrate of paper. The first coil and second coil are then printed around each other forming a double-wrapped coil  602 . Each of the flexible lines (coils) of material are close but do not touch each other. 
     In this embodiment, the gap between the double-wrapped coils is about 90 μm, the diameter of the double-wrapped coil is about 13.4 mm, and the length is about 426 mm. Once the flexible conductive material is printed, it is cured, for example using an infrared lamp  604 . This curing step is optional dependent upon the materials used. Upon curing, the double-wrapped coils are connected to a device  606  wherein, when a finger touches or nearly touches the double-wrapped coils a capacitance change occurs which may be measured  608 . A signal based on the capacitance variation is then sent to a device  610 . 
     The printed double-wrapped coils can be applied to form low cost capacitance sensing devices used in a variety of implementations including but not limited to control panels, keyboards, etc. As illustrated in  FIG. 7A , and  FIG. 7B  a double-wrapped coil  706  is embedded between two pieces of paper  702   a ,  702   b  in a structure  700 . When a finger touches or nearly touches one of the pieces of paper  702   a ,  702   b , a signal is sent to a device (e.g. a Bluetooth device)  704  indicating a change in the capacitance such as by displaying an image or playing a sound. In alternative embodiments, a speaker may be incorporated within the paper  702   a ,  702   b  whereby the signal is output to the embedded speaker. 
     The shape of the double wrapped coil can differ from those that have been shown. For example,  FIG. 8  depicts an embodiment of a sensing structure  800  consisting of a plurality of diamond shaped double wrapped coils  802 , interconnects by lines  804 ,  806 . It is to, be appreciated that double wrapped coils can be configured as pentagons, stars shaped, as well as other geometrics designs. 
     Turning to  FIG. 9 , illustrated is a cross-sectional view of a portion  910  of the structure  800  of  FIG. 8 . In this view, the depicted double wrapped coil portion  900  is designed as a two-layer diamond shape capacitor arrangement. The structure includes a substrate  902  on whose surface is printed a bottom conducting trace  904  which serves as a continuous electrode. As shown in  FIG. 9  and more closely in  FIG. 10A , a top conducting trace  906  is printed above the bottom trace  904 , also acting as a continuous electrode. In an alternative embodiment, the two double-wrapped coils can be printed on the same layer with a crossover structure as shown in  FIG. 10B . In an alternative embodiment, insulating layer  908  can be replaced by a patterned island located at  910 . 
     The traces  904 ,  906  are fixed in close proximity, while nevertheless being physically and electrically isolated from each other. In certain embodiments, the isolation is achieved by use of an insulating layer  908 . Similar to the previous described embodiments, one of the traces  904 ,  906  of the double-wrapped coil portion  900  is used as a capacitor for sensing a capacitance change when an object is near or touching the surface of the capacitive sensor, which passes variations in capacitance between the traces to a capacitance sensing device, such as discussed for example in connection with  FIG. 2B . It is to be understood  FIG. 9  illustrates relevant elements of a two-layer diamond shaped capacitor arrangement and that such a sensor may include additional components or layers such as a front panel to which a finger (or stylus) is touched or nearly touched in order to alter the capacitance between traces  904 ,  906 , as known in the art. 
     It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. All such variations, alternatives, modifications, or improvements therein that may be subsequently made by those skilled in the art are also intended to be encompassed by the following claims.