Abstract:
A surface acoustic wave (SAW) touch panel with improved touching precision is provided. By forming a matte surface that diffuses a back wave generated by the edge of the SAW touch panel due to discontinuity, the touching precision of the SAW touch panel is improved.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. application Ser. No. 11/819,359, filed on Jun. 27, 2007, which is herein incorporated by reference for all intents and purposes. 
     This application claims the right of priority based on Taiwan Patent Application No. 095123165 entitled “Surface Acoustic Wave Touch Panel with Improved Touching Precision”, filed on Jun. 27, 2006, which is incorporated herein by reference for all intents and purposes and assigned to the assignee herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a touch panel, and more particularly, to a surface acoustic wave (SAW) touch panel capable of reducing a back wave generated from a surface acoustic signal wave therein. 
     2. Description of the Prior Art 
     Electronic devices are generally not inputted by voice or handwriting, which are intuitive to humans, but a keyboard or a mouse. Such inputting through the keyboard or mouse is not made in a direct sense and would possibly form a barrier for those who are not familiar with operations on the electronic devices. In this regard, more intuitively operated inputting devices and methods have been expected to be used on the new electronic devices. Touch panel is one of these promising inputting devices. 
     Touch panel has the simplest user-machine interface among those of the currently available intuitively inputting devices. In operation, an object, normally a stylus or a finger of a user, touches the panel and a position of the touch is determined. Then, when continuous touch positions (in some cases) are obtained, a corresponding input is thus formed. With the provision of the touch panel, it is relatively easier for the user to input to an electronic device by the intuitive sense based inputting method other than the keyboard and mouse lacking of the intuitive basis. 
     In general, a touch panel is a glass substrate constructed by a conductive glass and a conductive film, through which images are displayed on a touch screen thereof with the aid of associated control ICs on a printed circuit board (PCB) provided therebelow. A touch panel has the humanized input interface characteristic and thus requiring the least teaching and learning for man. That is, the user can directly input instructions by a finger or touch pen, etc., through the touch panel according to the function indication shown on the screen. The touch panel may be broadly applied onto, for example, eBook, global positioning system (GPS), personal digital assistant (PDA), WebPhone, notebook, Web Pad, handheld PC, etc. 
     In general, the touch panel are classified into at least four types: resistive, capacitive, IR, and surface acoustic wave (SAW) touch panel. The SAW type touch panel employs acoustic waves propagating in a substrate surface. When an object touches the surface, the propagation of the specific acoustic waves associated therewith will be blocked. By detecting this sudden change, the location on the touch panel touched by the object can be determined. Referring to  FIG. 1A  and  FIG. 1B , which respectively show a vertical view and a 3D diagram of a conventional SAW type touch panel  100 . As shown, the touch panel  100  includes a substrate  104  having a first side  106 , a second side  108 , a third side  110  and a fourth side  112  together defining a surface  104 ; and an X-axis transmitting transducer  114 , an X-axis receiving transducer  116 ; a Y-axis transmitting transducer  124  and a Y-axis receiving transducer  126 . Each of the transducers  114 ,  116 ,  124 ,  126  has a plurality of reflectors formed therein, which are not uniformly arranged in the respective reflecting stripes  114 ,  116 ,  124 ,  126 , exactly, from thinness to thickness when viewed in the propagation direction of the unreflected surface waves, which will be appreciated after the following context is read. The described receiving transducers  116 ,  126  are devices which can transform a mechanical energy to an electrical energy by a piezoelectric material, and vice versa. As generally known to those skilled in the art, each of the transducers  114 ,  116 ,  124 ,  126  may have a wedge or comb form. 
     As shown in  FIG. 2 , it is a case where the wedge formed transducer  230  is used, where a shear wave is transformed into a surface wave. In  FIG. 2 , the reference numeral  232  represents the piezoelectric material, and the arrow indicates the propagation direction of the surface wave. As shown in  FIG. 3 , it is another case where the comb formed transducer  330  is used, where a longitudinal wave is transformed to a surface wave, which is propagated in the direction indicated by the arrow, and the reference numeral  332  represents a piezoelectric material. Referring back to  FIGS. 1A and 1B , the substrate  104  further includes reflecting stripes  190 ,  191 ,  192 , and  193 . The surface wave produced by the X-axis transducer  114  is transmitted along the −x direction and then the +y direction when being reflected by the reflecting strips  193 , where some surface waves are caused to occur. Then, the reflected surface waves proceed along the +x direction when encountering the reflecting strips  191 . Finally, the surface waves are received by the X-axis receiving transducer  116  and transformed into electrical energy thereby. Similarly, the surface wave produced by the Y-axis transducer  124  is transmitted along the −y direction and then the +x direction after being reflected by the reflecting stripes  192 , where some surface waves are caused to present. Then, the reflected surface waves proceed along the +y direction when encounter the reflecting stripes  190 . Finally, the surface waves are received by the Y-axis receiving transducer  126  and transformed into an electrical energy. 
     Take the X-axis as an example, referring to  FIG. 4  and  FIG. 5 ,  FIG. 4  illustrates a voltage wave Vx of the electric energy generated from the X-axis receiving transducer  116  when no any object touches on the surface  104  of the touch panel, and  FIG. 5  illustrates a voltage wave Vx of the electric energy generated from the X-axis receiving transducer  116  when an object touches on the surface  104  of the touch panel. As can be appreciated, the presence of the object leads to an absorption of a large portion of the surface wave energy existing thereunder, and a corresponding voltage drop is thus created on the voltage wave Vx. This voltage drop can be relied upon to deduce the Y-axis position of the object on the substrate  104  of the touch panel based on the fact that different surface waves associated with the X-axis transmitting and receiving transducers  114 ,  116  and different reflectors of the reflecting stripes  191 ,  193  have different times before being received at the receiving transducer  116 . Likewise, a voltage wave Vy in relation to the X-axis position of the object touching on the substrate  104  of the touch panel  100  also exists although not shown in the figures. However, the surface wave does not ideally proceed in a straight direction but somewhat diverges, like that of an optical beam. At this time, when the surface wave is transmitted to an edge of the substrate, a back wave due to discontinuity at the edge is generally generated. The back wave interferes with the propagation of the component of the surface wave still under the corresponding reflecting stripe, and accordingly adversely affects the accuracy of position detection. Therefore, there is a need to provide a touch panel with an improved touch position determining capability. 
     From the above it is clear that prior art still has shortcomings. In order to solve these problems, efforts have long been made in vain, while ordinary products and methods offering no appropriate structures and methods. Thus, there is a need in the industry for a novel technique that solves these problems. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a surface acoustic wave (SAW) type touch panel with an improved touch position determining capability. 
     In one embodiment, disclosed is a touch panel with an improved touch position determining capability is provided. The touch panel includes a substrate having a first side, a second side, a third side, and a fourth side, each having two ends and together defining a surface; an X-axis transmitting transducer located near one end of the first side on the surface; an X-axis receiving transducer located near the other end of the first side on the surface; a Y-axis transmitting transducer located near one end of the second side on the surface; and a Y-axis receiving transducer located near the other end of the second side on the surface. The substrate includes a matte surface between the surface and the third side for diffusing the surface acoustic wave transmitted by the X-axis transmitting transducer. 
     The substrate can also include the matte surface between the surface and the third side for diffusing the surface acoustic wave transmitted by the X-axis transmitting transducer. The matte surface can comprise an inclined surface or a rounded surface. Besides, the substrate can also include the matte surface between the surface and the first side for diffusing a surface acoustic wave transmitted by the X-axis transmitting transducer and the matte surface between the surface and the second side for diffusing a surface acoustic wave transmitted by the Y-axis transmitting transducer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1A  illustrates a top view of a conventional surface acoustic wave (SAW) type touch panel; 
         FIG. 1B  illustrates a three-dimension view of the conventional SAW type touch panel; 
         FIG. 2  illustrates a known wedge type transducer; 
         FIG. 3  illustrates a known comb type transducer; 
         FIG. 4  illustrates a voltage wave generated from a receiving transducer without any object existing on the touch panel; 
         FIG. 5  illustrates a voltage wave generated from a receiving transducer when an object exists on the touch panel; 
         FIG. 6  illustrates a three-dimensional view of a SAW type touch panel with improved touch position determining capability in accordance with an embodiment of the present invention; 
         FIG. 7  illustrates a three-dimensional view of the SAW type touch panel in accordance with another embodiment of the present invention; 
         FIG. 8  illustrates a three-dimensional view of the SAW type touch panel in accordance with yet another embodiment of the present invention; 
         FIG. 9  shows a wedge type transducer incorporated with an inclined surface in accordance with still another embodiment of the present invention; and 
         FIG. 10  illustrates a method for manufacturing a touch panel. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention discloses a touch panel with improved touch position determining capability. For better understanding, one may read the following description in conjunction with the accompanying drawings. 
     In one embodiment,  FIG. 6  illustrates a three-dimensional diagram for a surface acoustic wave (SAW) type touch panel  600  with improved touch position determining capability according to the present invention. The touch panel  600  includes a substrate  602  having a first side  606 , a second side  608 , a third side  610 , and a fourth side  612  together defining a surface  604 , and an X-axis transmitting transducer  614 , an X-axis receiving transducer  616 , a Y-axis transmitting transducer  624  and a Y-axis receiving transducer  626 . Four reflecting stripes  690 ,  691 ,  692 ,  693  are provided on the surface  604  near the first, second, third and fourth sides  606 ,  608 ,  610 ,  612 , respectively. In each of the reflecting stripes  690 ,  691 ,  692 ,  693 , a plurality of reflectors are arranged from thinness to thickness when viewed from the direction a surface wave is emitted from the corresponding transmitting transducers  614 ,  624 . In this manner, the surface wave provided at an upstream part and a downstream part of any of the reflecting stripes  690 ,  691 ,  692 ,  693  can be uniform. That is, the down stream part of any of reflecting stripes  690 ,  691 ,  692 ,  693  can be compensated in an amount of the surface wave. 
     In the touch panel  600 , a third matte surface  650  is provided to the third side  610  for reducing a back wave generated from the surface wave transmitted by the X-axis transmitting transducer  614  is provided. A fourth matte surface  652  is provided to the fourth side  612  to reduce a back wave generated from the surface wave transmitted by the Y-axis transmitting transducer  624 . In an embodiment, the third and fourth matte surfaces  650 ,  652  are each presented rough and uneven in surface, so that a rough feel may be obtained. It is to be noted that the level of the roughness are constructed dependent upon a wavelength of the surface wave. In fact, any rough surface which can diffuse a surface wave can be served as the above mentioned third and fourth matte surfaces  650 ,  652 , even a combination of different matte surfaces. 
     In another embodiment, as shown in  FIG. 7 , the touch panel  700  includes a substrate  702  having a first side  706 , a second side  708 , a third side  710  and a fourth side  712 , together defining a surface  704 , and an X-axis transmitting transducer  714 , an X-axis receiving transducer  716 , a Y-axis transmitting transducer  724  and a Y-axis receiving transducer  726 . In addition, four reflecting stripes  790 ,  791 ,  792 ,  793  are provided on the surface  704  near the first, second, third and fourth sides  706 ,  708 ,  710 ,  712 , respectively. And the details for the touch panel  700  are identical to those of the touch panel  600 , except that the third matte surface  750  and fourth matte surfaces  752 . In this embodiment, the third matte surface  750  and fourth matte surfaces  752  are each designed as an inclined surface. (The inclination of the surface  750  is not shown in  FIG. 7 ) 
     In yet another embodiment, as shown in  FIG. 8 , the touch panel  800  includes a substrate  802  having a first side  806 , a second side  808 , a third side  810  and a fourth side  812 , together defining a surface  804 , and an X-axis transmitting transducer  814 , an X-axis receiving transducer  816 , a Y-axis transmitting transducer  824  and a Y-axis receiving transducer  826 . In addition, four reflecting stripes  890 ,  891 ,  892 ,  893  are provided on the surface  804  near the first, second, third and fourth sides  806 ,  808 ,  810 ,  812 , respectively. And the details for the touch panel  800  are identical to those of the touch panel  600 , except that the third matte surface (not shown) and fourth matte surfaces  852 . In this embodiment, the third matte surface and fourth matte surfaces  852  are each designed as a rounded surface. (The rounded feature of the surface  850  is not shown in  FIG. 8 ) 
     In still another embodiment, in the case of wedge formed transducers for the touch panel schematically depicted in  FIG. 6 ,  FIG. 7  and  FIG. 8 , the first sides  606 ,  706 ,  806  and second sides  608 ,  708 ,  808  may each be provided with an inclined surface. Referring to  FIG. 9 , a piezoelectric material  932  is provided. A transducer  930  is provided on the inclined surface  934 , through which a surface wave generated from the transducer  930  is transmitted to the surface  904 . Certainly, each of the first sides  606 ,  706 ,  806  and second sides  608 ,  708 ,  808  may be provided with the above matte surface or a material capable of absorbing an acoustic wave to avoid interference of a back wave. 
     The above mentioned matte surface can be the glass surface grounded by abrasion or etching to produce a flat but rough (matte) finish. In one of examples of the present invention, referring to  FIG. 6 , the matte surface covers a portion of the surface and a portion of the sides. In another one of examples of the present invention, referring to  FIG. 7  and  FIG. 8 , the matte surface can be provided between the sides and the surface defined by the sides. More particularly, the matte surface can be rounded and without an angle for reflection between the surface and the sides, whereby the surface wave can go through the rounded matte surface to be diffused and none or less of the surface wave is reflected. 
     In further embodiment, a method for manufacturing a touch panel is provided, referring to  FIG. 10 . In step  910 , a substrate having a first side, a second side, a third side, and a fourth side, wherein each of the sides has two ends and the sides define a surface for transmitting the surface acoustic wave. In addition, in step  920  and  930 , the matte surface between the surface and the third sides and the matte surface between the surface and the fourth sides are provided. Furthermore, in step  940 ,  950 ,  960  and  970 , an X-axis transmitting transducer located near one end of the first side, an X-axis receiving transducer located near the other end of the first side on the surface, a Y-axis transmitting transducer located near one end of the second side, and a Y-axis receiving transducer located near the other end of the second side are provide. 
     By means of the detailed descriptions of what is presently considered to be the most practical and preferred embodiments of the subject invention, it is expected that the features and the gist thereof be clearly described. Nevertheless, these embodiments are not intended to be construed in a limiting sense. Instead, it will be well understood that any analogous variations and equivalent arrangements will fall within the spirit and scope of the invention.