Abstract:
An apparatus and system for recognizing touch positions is comprised of multiple acoustically coupled substrates, said coupling functioning also as an environmental seal. At least one secondary substrate, with means to transmit and receive acoustic waves, is coupled to a primary substrate capable of propagating acoustic waves such that an intentional touch on the surface causes a perturbation of the waves passing through a desired region of touch detection. Said perturbation is analyzed by circuitry to determine corresponding physical position of the touch on surface

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0003]     This invention relates, in general, to a touch detection apparatus and touch control systems for use in conjunction with graphic display device or for controlling a remote device or process.  
         [0004]     This invention concerns a touch detection apparatus or touch panel, one use of which is as a selector device for controlling a remotely located device. It is known to use a touch panel in the form of a keypad or keyboard tablet which may be connected to a graphic display or other device and is adapted to be disposed on a desk or work table. Examples of disclosures of such touch control tablets are found in U.S. Pat. No. 3,653,031.  
         [0005]     Graphics display devices, of the type herein considered, generally utilize a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display panel (PDP), or any of several other display technologies which in a given application can be used. However, in some applications an actual standard glass window to a real world view could be the desired touch control region.  
         [0006]     In the prior are there are three major touch detection systems in common use. The least expensive is an electrically resistive membrane placed in front of a display device. This technique is common in point of sale (POS) applications as typically seen in fast-food restaurants such a McDonalds, Wendy&#39;s, etc. The second is infa-red (IR) light beam technology, and the third is acoustic wave technology manufactured for example by ELO and Electro Plasma (licensed under U.S. Pat. No. 4,645,870). This application concerns the third type, utilizing acoustic wave absorbtion technology.  
         [0007]     An acoustic touch detection system has a touch sensitive region on which the occurrence and location of a touch is sensed via the touch&#39;s effect, typically absorbtion of energy, on the transmission of acoustic waves transversing on or near the surface of the desired touch sensitive region. A common type of acoustic touch control apparatus employs Rayleigh waves, a term which, as used herein, subsumes quasi-Rayleigh waves. Acoustic touch control apparatus employing other types of acoustic waves such as Lamb or shear waves, or combinations of different types acoustic waves, including combinations involving Rayleigh waves, are also known.  
         [0008]     Referring now to the drawings, there is illustrated in  FIG. 1 , the operation of a typical acoustic touch control apparatus having substrate  1  with an active, or touch sensitive region  9 , that is defined as being inside the dotted line. A first transmitting transducer  3   a  is disposed upon the substrate  1  and positioned outside of touch sensitive region  9 . The transducer  3   a  is acoustically coupled to the surface of touch control apparatus substrate  1 , and is operable to send an acoustic signal in the form of an acoustic wave  11   a  traveling parallel to the top edge of touch control apparatus substrate  1  and generally in the plane of touch control substrate  1 . Also disposed upon the substrate  1  and aligned in the transmission path of acoustic wave  11   a  is a linear array of partially acoustically reflective elements  4   a , each of which is set an angle to the transmission path and partially reflects, by approximately 90 degrees as shown in  FIG. 1 , and partially transmits the acoustic signals, creating a plurality of acoustic waves, exemplarily  5   a ,  5   b , and  5   c , traveling vertically, or parallel to the Y-axis, across touch sensitive region  9  separated in time. The spacing of reflective elements  4   a  as shown in  FIG. 1  is variable to compensate for the attenuation of the acoustic signals with increasing distance from first transmitter  3   a . Acoustic waves  5   a ,  5   b , and  5   c , upon reaching the lower edge of touch control substrate  1 , are again reflected by approximately 90.degree, as shown by arrow  11   b , by another linear array of similarly partially acoustically reflective elements  4   b  that also are disposed upon substrate  1  towards a first receiving transducer  6   a , where the waves are detected and converted to electrical signals for data processing.  
         [0009]     Along the left and right edges of touch control apparatus substrate  1  are located a similar arrangement. A second transmitting transducer  3   b  generates an acoustic wave  12   a  that propagates along the left edge, with a linear array of partially acoustically reflective elements  4   c  creating a plurality of acoustic waves, exemplarily  7   a ,  7   b , and  7   c , traveling horizontally, or parallel to the X-axis, across touch sensitive region  9 . Acoustic waves  7   a ,  7   b , and  7   c  are redirected, as shown by arrow  12   b , by yet another linear array of partially acoustically reflective elements  4   d  towards a receiving transducer  6   b , where the waves are also detected and converted to electrical signals.  
         [0010]     If touch sensitive region  9  is touched, for example at position  8 , by an object such as a finger or a stylus, some of the energy of the acoustic waves  5   b  and  7   b  is absorbed by the touching object. The resulting attenuation is detected by receiving transducers  6   a  and  6   b  as a perturbation in the acoustic signal. Analysis of the data with the aid of a microprocessor (not shown) allows determination of the coordinates of position  8 , and, if desired, a number relating to the amount of attenuation which may be interpreted as a pressure.  
         [0011]     The touch control apparatus substrate  1  may be either a separate plate that is typically made of glass, or another hard substrate material, mounted over a display panel such as a cathode ray tube (CRT), a liquid crystal display (LCD), plasma display panels (PDP), electroluminescent, or other type of display. Alternatively touch control apparatus  1  may be constructed directly on the face of the display panel (e.g., CRT or plasma) itself or onto an optical or EMI filter, whatever is the first contactable surface of the display device.  
         [0012]     In normal usage a housing (not shown) typically made of a molded polymer, is associated with touch control apparatus  1 . Such a housing usually contains a bezel (not shown) that overlays touch control apparatus  1 , cosmetically concealing the transmitting and receiving transducers, the reflective elements, and other components, but exposing touch sensitive region  9 . Further, this arrangement protects the concealed components from contamination and/or damage, as well as presenting an aesthetically pleasing appearance, while also defining the touch sensitive region for the user.  
         [0013]     The housing bezel may be spaced apart from touch control apparatus substrate  1 . In an abutted configuration bezel attenuates the acoustic signals, reducing the touch control apparatus&#39;s responsiveness. However, a spaced-apart bezel leaves a gap through which contaminants, such as dirt, dust, and, especially, liquids, may enter and damage or interfere with the function of the concealed components. Acoustic touch control apparatus intended for operation in outdoor environments or in facilities such as restaurants or factories, where exposure to rain, fog, spills, sprays, or cleaning solutions is a likelihood, are especially vulnerable in this regard.  
         [0014]     Theoretically, a liquid-impermeable seal can be formed by applying a caulking between the bezel and touch control apparatus substrate  1  around the perimeter of active area  9 , but the caulking will absorb acoustic energy, interfering with touch control apparatus operation. Rayleigh wave touch control apparatus, because of the surface-propagating nature of their acoustic waves, are especially likely to be adversely affected. U.S. Pat. No. 5,332,238 to Borucki, hereinafter referred to as the Borucki patent, and incorporated herein by reference, states that a caulking will not only absorb significant amounts of acoustic energy so as to render the touch control apparatus inoperable, but will also acoustically couple the substrate  1  to the screen and can cause a false touch to be registered around the entire perimeter of the screen.  
         [0015]     The solution to the sealing problems disclosed in the Borucki patent is to employ a foam strip compressed between the bezel/housing and the touch control apparatus. Acoustic attenuation is limited to an acceptable level by placing an open-cell surface of the foam against the touch control apparatus or by restricting contact with the touch control apparatus to a corner of the foam.  
         [0016]     An alternative bezel sealing arrangement is disclosed in U.S. Pat. No. 5,784,054 to Armstrong et al., hereinafter referred to as the Armstrong patent, and incorporated herein by reference, in which a sealing strip made of closed cell foam or, alternatively, expanded polytetrafluoroethylene, is preferably adhesively affixed to the bezel.  
         [0017]     Whatever the sealing system, it is operationally desirable to limit acoustic signal loss attributable to the sealant to less than −6 dB as stated in U.S. Pat. No. 6,254,105.  
         [0018]     Therefore, while SAW technology has proven to be both ergonomically acceptable and reliable, there are several draw-backs. First, while the printing and firing process applied directly onto a display device provides the best cosmetic arrangement, the process can become rather costly due to the attendant lower manufacturing yields. Second, the placement of the reflector arrays on the display faceplate or glass overlay is associated with significant signal loss due to the attenuation of such surface acoustic waves in glass. This limits the size of touch systems which are in practical use. Furthermore, the reflector arrays, although generally covered with a bezel, are not easily sealed and therefore are exposed to the environment, subject to physical and chemical abuse as well as contamination such a condensing water or spilled drinks such as coffee or soda pop.  
         [0019]     Accordingly, it would be desirable to provide an acoustic wave touch control system that could be more easily applied directly to display devices or directly to windows, used over a geometrically larger area, and function under more severe environmental constraints than the prior art systems described above.  
       BRIEF SUMMARY OF THE INVENTION  
       [0020]     It is an object of this invention to provide an acoustic wave touch control system for use in or with a display apparatus, or for controlling a remote device such as an electrical apparatus, wherein such systems can be more easily applied directly to display devices, directly to windows, used over a geometrically larger area, and function under more severe environmental constraints.  
         [0021]     The present invention contemplates a touch detection apparatus that includes a primary substrate having a surface capable of propagating acoustic waves and being so characterized that the surface is touch sensitive such that a touch on the surface causes a perturbation, in the form of at least a partial absorption of energy, of an acoustic wave propagating through a region of desired touch detection. The apparatus also includes at least one transmitter secondary substrate mounted along an edge of the primary substrate and at least one receiver secondary substrate mounted along another edge of the primary substrate opposite from the transmitter secondary substrate. The apparatus further includes at least one input transducer, coupled to a the transmitter secondary substrate, which is operative to launch a burst of acoustic waves onto the transmitter secondary substrate and at least one output acoustic wave transducer coupled to the receiver secondary substrate that detects received acoustic waves. Additionally, the apparatus includes a first coupling means disposed between the transmitter secondary substrate and the primary substrate to transfer the wave components to a first edge defining a first axis of the desired touch sensing area of the primary substrate surface, and a second coupling means disposed between the primary substrate and the receiver secondary substrate to transfer and redirect acoustic waves to the output transducer after propagating across the first surface at least once such that the wave components are caused to traverse the axis along a progression of paths differing in time and associated with different touch positions along the axis.  
         [0022]     The invention further contemplates that the apparatus also may include at least one wave redirecting means disposed upon at least one secondary substrate which derives wave components separated in time from a launched wave, the wave components substantially perpendicular to the launched wave.  
         [0023]     Additionally, the invention contemplates that the apparatus includes circuitry coupled to the input and output transducers which initiates acoustic wave bursts causing derived wave components separated in time across the primary substrate surface and detects touch-induced perturbations of the received waves indicative of the location of a touch along the axis, the circuit means also including means for determining, by an analysis based on the transit time of the detected perturbed wave burst component, which of a plurality of paths was traversed by the touch-perturbed wave burst component and thus determining the location of the touch along the axis of the substrate surface.  
         [0024]     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  illustrates, partially in schematic form, a top view of a touch detection apparatus illustrating the prior art.  
         [0026]      FIG. 2   a  illustrates, partially in schematic form, a top view sketch of a touch detection apparatus embodying the basic novel features of the present invention.  
         [0027]      FIG. 2   b  illustrates a 3-D sketch of the touch detection apparatus shown in  FIG. 2   a.    
         [0028]      FIG. 3   a  illustrates, partially in schematic form, a section view illustrating the novel arrangement and acoustical coupling of secondary substrates to the desired touch sensitive region on the first substrate for the touch detection apparatus shown in  FIG. 2   a.    
         [0029]      FIG. 3   b  illustrates an alternate embodiment of the coupling arrangement shown in  FIG. 3   a.    
         [0030]      FIG. 4   a  illustrates, partially in schematic form, a top view sketch of a touch detection apparatus according to the present invention that has geometry to provide an inherent protective seal as can be assembled in modular sections.  
         [0031]      FIG. 4   b  illustrates a 3-D sketch of the touch detection apparatus shown in  FIG. 4   a.    
         [0032]      FIG. 5  illustrates, with a 3-D sketch, an alternate configuration of the touch detection apparatus shown in  FIG. 2   a  wherein the secondary substrates are combined into one as a bezel.  
         [0033]      FIG. 6   a  illustrates, partially in schematic form, a top view of a touch detection apparatus in accordance with the invention that employs an acoustic reflector causing acoustic waves to transverse the desired touch sensitive region twice per each path.  
         [0034]      FIG. 6   b  illustrates an alternate embodiment of the touch detection apparatus shown in  FIG. 6   a  that utilizes reflections at an edge of the primary substrate  1 .  
         [0035]      FIG. 7  illustrates, with a 3-D sketch, an alternate configuration of the touch detection apparatus in accordance with the invention wherein the transducers for transmitting and receiving are indirectly coupled to the secondary substrates via the primary substrate.  
         [0036]      FIG. 8  illustrates, partially in schematic form, a top view of a touch detection apparatus in accordance with the invention comprising a long transmitting device on the first secondary substrate. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0037]     The inventor has developed a novel configuration for acoustic touch detection systems that consists of multiple substrates. It is built on a primary substrate and utilizes one or multiple secondary substrates for wave generation and propagation that are coupled to the primary substrate and have different properties therefrom.  
         [0038]     This present invention solves or improves three problems historically associated with such systems. The three problems summarized are:  
         [0039]     First, in a typical prior art arrangement wherein the desired touch region is to correspond to a visual display, the only reasonable choice of substrate material is glass, and typically a lead glass, as is utilized in a Cathode Ray Tube (CRT) display, soda lime glass, such as an ordinary window glass, or another float glass, as used in Plasma Display Panels (PDP) and most optical filter substrates. All of these substrate materials significantly attenuate the acoustic wave amplitude as it propagates along the surface, thus limiting the size of practical touch displays because the acoustic waves must travel not only across the desired touch region but also twice along two edge lengths which comprise the wave redirecting arrays.  
         [0040]     Second, as the acoustic wave redirecting arrays constructed on the glass substrate are almost necessarily for economic and compatibility reasons glass frit fired at high temperature, the manufacturing process thereby is caused to have lowered yields. Further, replacement of damaged or defective parts is also correspondingly higher.  
         [0041]     Third, as the acoustic wave redirecting arrays are located on same substrate as the desired touch detection region, and acoustic waves must transverse along the surface, it is difficult to provide a protective seal for the redirecting arrays, coupled transducers, and other associated components because typical sealing materials severely divert and attenuate the acoustic wave. Prior art seal systems have difficulty limiting this attenuation to at least −6 db, as stated in U.S. Pat. No. 6,236,391, and, even worse, to keep it non-varying which, if varying, causes false touch reports.  
         [0042]     Now it is well known that other materials, such as steel, aluminum, or brass transmit sound more efficiently than glass, but are opaque. Indeed, although some glasses are more efficient, they are typically expensive or otherwise unusable with existing display devices. However, if the acoustic wave redirecting arrays could exist on a more efficient surface the first problem listed above would be significantly reduced and larger touch systems could be built. Modifying the glass substrate in the array regions, perhaps laminating a thin layer of a material such as brass or aluminum is out of the question, being very impractical because the thermal expansion coefficients are very different.  
         [0043]     The inventor has determined that just that can be done in a novel arrangement wherein the redirected waves can easily and relatively efficiently be coupled, or transferred, from one substrate of a different material, such as, for example, aluminum to the touch region on a substrate of glass. The inventor has developed an arrangement of two overlapping substrates wherein the acoustic waves are easily transferred between facing surfaces utilizing a coupling material with the property that the wavelength of the longitudinal bulk wavelength is less than the surface wavelength of either substrate. This acoustic coupling means is illustrated in  FIG. 3  and described in the following detailed description section of the present invention.  
         [0044]     The benefits of this coupling means, by allowing the acoustic wave redirecting reflector arrays to be positioned on a secondary substrate with less acoustic energy loss, can now be seen to also provide a sealing method with acceptable and non-varying attenuation. Indeed, such seal means can be extended to surround and isolate the reflector arrays and further to seal the entire periphery of the desired touch region. Moreover, the construction of the reflector arrays can be of more exacting and less expensive manufacturing methods as is commonly available, such as stamping, etching, electro-plating, anodizing, etc. Thermal expansion mismatch can be compensated for by laminating a material, not shown, to the back of the secondary substrates. Therefore, all of the three problems listed above are solved or significantly reduced by this novel configuration  
         [0045]     Referring again to the drawings, there is illustrated, for example most basically in  FIG. 2 , an acoustic touch detection apparatus that includes components  1  through  23  and that is in accordance with the present invention. Components shown in  FIG. 2  that are similar to components shown in  FIG. 1  have the same numerical identifiers. The apparatus may be part of graphics display apparatus, the first contactable surface corresponding to displayed images being integral to said graphic display. Such graphic display typically comprising a graphics controller, not shown, and a display device such as an LCD, CRT, or PDP having a touchable display surface  9 . However, it is to be appreciated that the invention is readily applicable to other display devices, e.g., electroluminescent, LED, or even displays as simple as an elevator number display, any of these can be employed. Moreover, the controlled apparatus need not necessarily be a display device since the touch control system to be described can, as readily, evoke a response from other types of controllable apparatus. In some applications, a separate panel is disposed over the faceplate of the display device or, if desired, such separate panel can be disposed at a location remote from the controlled device or be a window to a real world view.  
         [0046]     In the apparatus illustrated in  FIG. 2 , the apparatus includes a primary substrate  1 , is typically the faceplate, or panel, commonly designated a “touch control panel” or simply “touch panel” since graphics, or other information may be ordered up for display from a controller  24  in response to an operator&#39;s command which can take the form of a touching of a particular area of a menu associated with the touch control panel. In the preferred embodiment, the primary substrate is formed from a transparent material, such as a glass that would be utilizes in one of the devices described in the immediately preceding paragraph and also including soda lime glass, leaded glass and EMI glass. The display surface corresponds to the touch region  9 , whether it is an actual graphic apparatus faceplate, optical or EMI filter, the window of a building or vehicle, or a separate panel, any of these constitutes a primary substrate  1 , the surface of which is capable of propagating surface acoustic waves.  
         [0047]     It is to be appreciated that the touch panel can adopt the format of a tablet, e.g., a sheet of glass or other substrate capable of propagating surface acoustic waves which, in the interests of convenience, or to import flexibility to the system, can be positioned at a location remote from the apparatus to be controlled. More particularly, a touch control tablet which is positioned at a location remote from a controlled image display device can be a video monitor or computer display monitor. A touch control panel can be coupled to the monitor by a cable  13 . However, it is recognized that the control effects instituted by the tablet could readily be applied to the monitor by an infrared (IR) or other wireless means so as to dispense with cabling. Moreover, as noted, the apparatus controlled by the touch control tablet need not be an image display device. It can be, by way of example, a home entertainment center (radio, stereo, TV, etc.), actuated by a remotely located touch control tablet.  
         [0048]     Such a touch panel according to this invention works as follows. The act of touching serves to interrupt or reduce wave energy directed along one or more paths that form a grid overlying the panel. Detection and analysis of such interruption serves to identify the X, Y, or other coordinates of the touched area, and, if desired, a number relating to the amount of wave energy reduction loosely interpreted as a pressure, which information, in turn, is determinative of the graphics to be delivered up for display or other response as intended by a purposefully initiated touch.  
         [0049]     To this end, the touch control system may further include a computer for the controller  24  for rendering an interface circuit  14  operative in a predetermined sequence so that when a perturbation, or interruption of acoustic wave energy is detected, converted to an electrical signal and fed back to the computer, via said interface circuit, such that the location of the interruption is identifiable by the computer. The computer utilized for the controller  24 , appropriately programmed, can then take any predetermined controlled action as necessary with devices controlled by, or in communication with, said system. Such action typically includes the output of appropriate information to a display controller to change the video display to graphics associated with the “touch panel” address intentionally activated by the operator.  
         [0050]     A conventional touch screen interface circuit  14  has input terminals coupled, via a cable  13   a , to receiver transducers  6   a ,  6   b  and output terminals coupled to transmitter transducers  3   a ,  3   b  which are positioned as illustrated in  FIG. 2   a . It is understood that the interface circuit  14  has additional input and output terminals or cable  13   b  that may be coupled to the computer  24  for interacting therewith. Preferably, the interface circuit  14 , often in conjunction with timing signals from a computer, outputs firing signals that stimulate transducers  3   a  and  3   b  in a timed sequence so that the location of a subsequent interruption of a surface wave is identifiable.  
         [0051]     At least one transmitter transducer  3  which may be of the type particularly described in the Adler patent, is coupled to or mounted upon the bottom, or lower, surface of at least one secondary substrate  2  that is carried along an edge of the primary substrate  1 . The transmitter transducer couples acoustic energy to the secondary substrate. For the apparatus shown in  FIG. 2 , there are two secondary substrates  2   a  and  2   b  with transducer  3   a  mounted upon one of the secondary substrates  2   a  and transducer  3   b  mounted upon the other of the secondary substrates  2   b.    
         [0052]     An energy source (not shown) in the interface circuit  14  serves to apply input signals to transmitter, or input, transducers  3   a  and  3   b , as shown in  FIG. 2 , which transducers, in response thereto, individually launch a burst of acoustic surface waves along first and second paths  11   a ,  12   a , respectively on or near the bottom surfaces of substrates  2   a  and  2   c  which carry wave directing arrays  4   a  and  4   c . The arrays  4   a  and  4   c  derive wave components  5   a ,  5   b , and  5   c  and  7   a ,  7   b , and  7   c  directed toward the edge of substrates  2   a  and  2   c  geometrically positioned near and towards the touch sensitive surface  9 , on the upper, or top, surface of substrate  1 . As illustrated in  FIG. 3 , wave components are acoustically coupled via coupling material  10   a  and transferred from the bottom surfaces of the secondary substrates  2   a  and  2   c  to the top surface, or near the top surface, of primary substrate  1  to transverse the touch sensitive region  9 .  
         [0053]     Also as shown in  FIG. 2 , the first and second receiver, or output, transducers  6   a  and  6   b , are disposed upon and acoustically coupled to the bottom surfaces of their own secondary substrates  2   b  and  2   d  which are mounted along edges of the primary substrate  1  opposite from corresponding secondary substrates,  2   a  and  2   c , respectively. The invention contemplates that, in the preferred embodiment, the secondary substrates  2   a  and  2   c  are formed from a metallic material, such as, for example, aluminum, brass, steel, nickel, chrome, copper, or combinations and alloys thereof or from a high efficiency tempered glass. The output transducers  6   a  and  6   b  develop electrical signals in response to acoustic energy received along paths  11   b  and  12   b  along the bottom surfaces of the substrates  2   b  and  2   d . This acoustic energy is collected by the wave component directing arrays  4   b  and  4   d , disposed upon the bottom surfaces of substrates  2   b  and  2   d , from derived wave components  5   a ,  5   b , and  5   c  and  7   a ,  7   b , and  7   c  which are received after propagating across the touch sensitive region  9  on the top surface of the primary substrate  1  and acoustically coupled via coupling material  10   a  and transferred to the bottom surfaces of substrates  2   b  and  2   d . The invention contemplates that, in the preferred embodiment, the secondary substrates  2   b  and  2   d  also are formed from a metallic material, such as, for example, aluminum, brass, steel, nickel, chrome, copper, or combinations and alloys thereof or from a high efficiency tempered glass, while the coupling material is selected as one of the group of an acrylic glass such as Plexiglass, an acrylic glass such as Lucite (Polymethyl methacrylate (PMMA), poly(methyl 2-methylpropenoate), an elastomer, rubber, latex, silicone, a grease, and combinations thereof. The invention also contemplates that, in the preferred embodiment, the wave component directing arrays  4   a ,  4   b ,  4   c  and  4   d  comprise individual reflectors elements created by steps or grooves oriented at an angle in the basic substrate material that are formed by a processes of etching, stamping, molding, plating or screening and firing.  
         [0054]     Receiver transducers  6   a  and  6   b , upon receipt of the surface waves launched by their associated input transducers develop respective output signals which, upon analysis, will exhibit a characteristic of the launched surface wave. Such characteristic, e.g. a change in amplitude, is attributable to a perturbation of a received surface wave component relating to an intentionally touched probe shown at position  8  in  FIG. 2   b , which diverts, or damps, acoustic energy from the wave burst components  5   b  and  7   b  associated with probe position  8  and the time the wave burst components pass through it relative to the time the bursts were initiated.  
         [0055]     While the preferred embodiment of the invention has been illustrated and described as utilizing surface acoustic waves, it will be appreciated that the invention also may be practiced with any acoustic waves that propagate through the primary and secondary substrates, preferably near the surfaces thereof.  
         [0056]     An important difference between the present invention and prior art devices is that prior art, as exemplified by the afore referenced Adler patent, specifically and intentionally claimed and specified a single substrate associated with the touch region and wave component generating arrays. Indeed, the novelty of arrangement of functions in the present invention is due to a coupling means, specifically a proper choice of material and geometry, to acoustically couple and transfer surface or near surface waves between independent substrates which can be of different physical properties.  
         [0057]     The general principal of this coupling means is similar to that of wedge transducers commonly used to initiate surface waves for surface analysis and quality testing. Referring to  FIG. 3   a , an acoustic wave  15   a  traveling toward an edge on or near the surface of the secondary substrate  2  is converted into a longitudinal bulk wave  16   a  at the junction of the coupling material  10   a  just as if it were passing through a wedge transducer. This coupling is quite efficient, having coupling coefficients of typically 60% to 80% wave amplitude reduction, or more, and travels at an angle  18  to the surface determined by arc-cos(longitudinal wavelength in the coupling material  10   a /surface wavelength along surface  2 ). As the bulk wave  16   a  travels through to the other, now facing, surface of the substrate  1  to be intentionally touched, it is again converted into a surface wave  17  which then travels on or near the surface of the substrate  1  to be intentionally touched. The second conversion is most efficient at the angle  19  determined by arc-cos(longitudinal wavelength in the coupling/surface wavelength along surface  1 ).  
         [0058]     This two-step conversion coupling method transfers acoustic waves most efficiently when the two substrates are at a slight angle to each other in the region of coupling as illustrated in  FIG. 3   a . However, coupling materials can be chosen with properties such that the loss is small even when the substrates are parallel, as shown in  FIG. 3   b . Indeed, as long as there is intimate contact, which can be accomplished by physical bonding, along the entire axis the coupling is non-critical to the dimensions of the coupling material. The following example illustrates this relationship in some detail so that both the elegance and novelty of this invention may be fully appreciated.  
       EXAMPLE  
       [0059]     The following example illustrates the calculation of the angles  18  and  19  of  FIG. 3   a  for selected materials. Selecting Lucite as the coupling material  10 , glass for the primary substrate  1  whereupon touches are detected, and aluminum for the secondary substrates  2 , acoustic waves are generated with a frequency of 5.53 MHz, which is common in the industry because of compatibility with communication systems. The velocity of acoustic waves in these materials, and several others, are summarized as follows:  
                                                                     Wave Velocities in cm/usec                MATERIAL   Longitudinal   Shear   Surface                       Aluminum   0.635   0.310   0.290           Brass   x   x   0.148           Glass (float)   0.679   0.343   0.310           Steel   x   x   0.281           Lucite   0.268   x   x           Rubber   0.149   x   x                      
 
         [0060]     Calculating per the relationships given above, the results are:  
         [0061]     For angle  18  (aluminum and Lucite)—22.46 degrees  
         [0062]     For angle  19  (glass and Lucite)—30.17 degrees  
         [0063]     Now, if it is assumed that the coupling material  10  is rubber, the results are:  
         [0064]     For angle  18  (aluminum and rubber)—59.08 degrees  
         [0065]     For angle  19  (glass and rubber)—61.27 degrees  
         [0066]     Now this is a very interesting result. With rubber, there is only about 2 degrees difference between the calculated values for angles  18  and  19 . It is therefore possible to just fill a gap at the edge between two facing parallel substrates, either an ultraviolet or air curing silicone rubber will work well, and a reasonably efficient coupling results, well within the −6 db design goal. Further, the width and thickness of the coupling material  10  are not critical. The bond can be arbitrarily thin. Experience teaches that the width of the coupling material seal, although not critical, should be about 5 wavelengths, that is, about 5×0.022 in (for glass)=0.11 in. or about ⅛ inch. Use of a rubber product, such as RTV silicone is also perfect for forming seals.  
         [0067]     The realization that this coupling material in this geometrical configuration can also be used as a seal has already been mentioned. There are several embodiments of this invention contemplated which utilize this fact. First, the touch apparatus can be built and sealed modularly as illustrated in  FIG. 4 . This is the preferred embodiment for larger size touch systems. Here, each wave component deriving or gathering re-directing reflector array  4   a ,  4   b ,  4   c , and  4   d  on substrates  2   a ,  2   b ,  2   c , and  2   d  can be individually attached and sealed to any touch substrate capable of propagating acoustic waves, without modification of that substrate except simple attachment with a common and inexpensive calking method, e.g. RTV silicone, at room temperature.  
         [0068]     An alternate embodiment of the invention, shown in  FIG. 5 , uses a common secondary substrate formed into a protective bezel. Another alternate embodiment of the invention, shown in  FIG. 6   a  includes reflective secondary substrates that reflect the acoustic waves back to the secondary substrate carrying the transmitter transducer. This embodiment also contemplates that the transducer functions as both transmitting and receiving transducers with the propagation of the acoustic waves illustrated by the arrows shown in  FIG. 6   a . An alternate embodiment of the screen shown in  FIG. 6   a  is illustrated in  FIG. 6   b  that utilizes reflections at an edge of the primary substrate  1  without provision of a secondary substrate.  
         [0069]     Other possible embodiments include, but are not limited to, the acoustic coupling of the transducers external to the secondary arrays as illustrated in  FIG. 7 , the bending of the substrates  2  around the sides of a display device to lessen the edge, or bezel border dimension, and lamination of materials to the fronts of the secondary substrates  2  to compensate for temperature induced stress due to differing expansion coefficients. Yet another embodiment of the invention is illustrated in  FIG. 8 , which includes longer transmitting devices,  3   a  and  3   b , that extend along their respective secondary substrates  2   a  and  2   c  parallel to the edge of the primary substrate  1 . Thus, the transmitting devices  3   a  and  3   b  launch acoustic waves directly across the primary substrate  1 , as illustrated by the arrows labeled  5   a ,  5   b ,  5   c ,  7   a ,  7   b  and  7   c.    
         [0070]     Still other embodiments and implementations of the present invention are contemplated and are within the spirit and scope of this invention. For example, the long transmitters shown in  FIG. 8  may be utilized with the reflective edges of the primary substrate  1  illustrated in  FIG. 6   a , in conjunction with a receiving array on the same secondary substrate.  
         [0071]     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.