TOUCH SCREEN SENSOR HAVING WAVE ABSORPTION SECTIONS The present invention is related to a touch screen sensor. A touch screen sensor comprises, acoustic reflectors along a length and height, respectively, of the touch screen sensor, an active area having a boundary within a perimeter of the touch screen sensor, acoustic transducers on respective acoustic reflectors, the acoustic transducers emanating acoustic wave forms, and the acoustic reflectors reflecting fractions of the acoustic wave forms to propagate across the active area.

The ultrasonic acoustic waves emanate, and are reflected across the active area of the touch screen sensor, and return to a receiving transducer. Spurious reflections and echoes may be generated. Examples of such spurious reflections and echoes include, second pass reflections, diffraction beam spreading, far corner echo. Unabated, such reflections and echoes can cause distortion and errors in the signals received by the receiving transducer.

The present invention is directed to an improved touch screen sensor that reduces or eliminates some or all of the above-identified problems. According to the invention, a touch screen sensor has sections of wave absorption material on acoustic reflectors, the sections of wave absorption material extending one-third of the length and one-third of the height, respectively, and the sections of wave absorption material intersecting respective projections of the boundaries of an active area to absorb undesired wave forms.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, according to which:

Figure 1 is a front view of a touch screen sensor; Figure 2 is an exploded view of a transducer and shield; Figure 3A is a view of an interface between the wave absorption material and the touch screen sensor; Figure 3B is a view of an alternative interface between the wave absorption material and the touch screen sensor; Figure 3C is a view of an alternate embodiment of the interface between the wave absorption material and the touch screen sensor; Figure 4 is a front view of an alternative touch screen sensor; Figure 5 is a front view of an alternative touch screen sensor; Figure 5A is a front view of an alternative embodiment of a touch screen sensor; and Figure 6 is a front view of an alternative touch screen sensor.

With further reference to Figure 1, a touch screen sensor 10 has a plurality of arrays 18,21 of acoustic reflectors 30, edges 31,32,33 and 34, a perimeter 35, and first, second, third and fourth corners 20,22,24 and 26, respectively. The touch screen sensor 10 further comprises sections 13,15 of a wave absorption material 16 positioned around at least a portion of the perimeter 35 of the touch screen sensor 10. The touch screen sensor 10 further comprises an active area 27 defined by active area boundaries 28.

With reference to Figure 2, a plurality of transducers 17,19 are coupled to the first corner 20 of the touch screen sensor 10. An electromagnetic interference shield 11 is positioned over the

transducers 17,19 to reduce electromagnetic fields produced by the transducers 17,19.

The touch screen sensor 10 may be comprised of a variety of materials, such as glass, metal and plastic.

As shown in Figure 2, two transducers 17,19 are coupled to the touch screen sensor 10. For example, the transducers 17,19 are x-cut Lithium Niobate crystal that operate in a pulse echo mode.

With reference to Figures 1 and 3A-3C, the wave absorption material 16 engage the edges 31-34 of the touch screen sensor 10. For example, the wave absorption material 16 may engage edge 31 of the touch screen sensor 10 at an approximately square interface 40, Figure 3A, a beveled interface 42, Figure 3B, a double beveled interface 44, Figure 3C. The wave absorption material 16 and the illustrative edge 31 are depicted as separated by a space for purposes of clarity.

In one embodiment, as in Figure 3B, the edge 31 of the touch screen sensor 10 is formed at an angle 33 ranging from approximately 20-40 degrees relative to the upper surface 41 of the touch screen sensor. In another embodiment, as in Figure 3C, the edge 31 of the touch screen sensor 10 may have a double bevel in which the included angle 46 of the double bevel may range from approximately 20-80 degrees.

In one embodiment, for example, the wave absorption material 16 has a rectangular cross section and is approximately the same thickness as the thickness of the touch screen sensor 10. For example, the glass touch screen sensor 10 has a thickness range of 0.051cm.- 0.318cm. The width of the wave absorption material, in the direction parallel to the surface of the touch screen sensor, may be varied as a matter of design

choice. For example, the width of the wave absorption material 16 may range between 0.76cm.- 0.61cm.

The width 45 of the absorption material 16 in Figure 3B, is measured across the midpoint 49 of the beveled interface 42. For the embodiment in Figure 3C, the width 45 of the wave absorption material 16 is measured across the midpoint 51 of the double beveled interface 44.

For example, the touch screen sensor 10 is comprised of glass approximately 0.040 inches thick. The transducers 17,19 are 5 MHz piezoelectric transducers.

The double bevel configuration as depicted in Figure 3C has an included angle of 30 degrees, and is approximately 0.10cm. thick and 0.32 cm. wide.

The wave absorption material 16 has an acoustic impedance that matches that of the touch screen sensor 10, and is provided to absorb spurious reflections and echoes. The wave absorption material 16 may be comprised of a polymer-based material, such as an epoxy material, an adhesive material, an elastomeric material, or combinations thereof. Other materials, e. g., metal powders, may be added to comprise the wave absorption material 16. For example, the wave absorption material 16 may be comprised of a biphenol A epoxy, such as Araldite D (trademark of Ciba-Geigy) or Eccosorb CR (trademark of Emerson & Cuming). Alternatively, the wave absorption material 16 may be comprised of an acrylic adhesive, such as UV Adhesive 349 (trademark of Loctite). The wave absorption material 16 may also be comprised of an elastomeric adhesive, such as DP-605 NS (trademark of 3M) urethane or like materials.

Combinations of these materials may also be used. The wave absorption material 16 comprised of an epoxy to

which is added, an elastomer modified epoxy functional adduct material. For example, as available from Royal Dutch Shell Petroleum, and known as, Shell EPON Resin 58005 and 58006.

If desired, filler materials may be added to the polymer-based materials used for the wave absorption material. For example, these additional filler materi- als may be comprised of a metal (e. g., tungsten powder, lead powder, etc.), an inorganic material (e. g., titanium dioxide, graphite, silica, etc.), or an organic material (e. g., the Shell EPON Resin discussed above).

These additional materials may be added for a variety of reasons, e. g., to match the acoustic impedance (density times sound velocity) of the touch screen sensor 10 by increasing the density of the completed wave absorption material 16, and to act as a scatterer of an acoustic wave as it enters the wave absorption material 16. The elastomer, or other like material, is an absorber of the generated waves, and scatters some of the acoustic wave, and withstands thermally induced stresses.

For a touch screen sensor 10 comprised of glass, the wave absorption material 16 may be comprised of Eccosorb CR-124 (trademark of Emerson & Cuming) epoxy combined with 20 weight percent of tungsten powder and 25 weight percent of elastomer EPON Resin 58005 (trademark of Royal Dutch Shell). In this embodiment, the wave absorption material 16 has a density of approximately 4.5 grams/cm3, and may range between 1.0- 7.0 grams/cm3.

The acoustic waves propagate along two different axes, e. g.,"x"and"y"axes. As the generated wave travels, fractions of the generated wave are deflected across an active area of the sensor by the reflector

arrays. Ultimately, the deflected portions of the original wave are returned to, for example, a receiving transducer where they are converted into electrical signals.

An absorber, such as a person's finger in contact with the touch screen sensor, draws energy from the fractions of the ultrasonic waves that are deflected across the active area of the touch screen sensor. The reduction in energy of the transmitted pulse appears as a dip in a wave train of the pulse. The location of the dip in time is proportional to the position of the absorber, i. e., the finger, in a direction, i. e., in the x-direction. This same technique can be used to deter- mine the location of the touch in the y-direction. The x and y coordinates of the absorber, i. e., the finger, is detected. The coordinates correspond to a computer command or response, such as,"START,""COMPLETE," "ENTER." One purpose of the wave absorption material 16 is to absorb spurious echoes and reflections of pulsed waves emanating from the transducers and reflected across the active area 27 of the touch screen sensor 10 and returned to a receiving transducer. Depending on the type of reflections or echoes to be reduced or eliminated, the wave absorption material 16 may be placed in various locations around the perimeter 35 of the touch screen sensor 10.

For example, to reduce what is known as second pass reflections, sections 13 and 15 of the wave absorption material 16 are positioned as indicated in Figure 1. The sections 13 and 15 are adjacent to the transducers 13, 15 and extend along the edges 31 and 34, respectively,

for a distance equal to approximately one third of the width and height, respectively.

As shown in Figure 4, additional sections 53,55 of the wave absorption material 16 are positioned around the second corner 22 and third corner 24, respectively, of the sensor 10 to assist in reducing or eliminating reflected acoustic waves from beam spreading due to diffraction effects in the array. The section 53 extends around the corner 22 for a distance along the edges 31 and 32 of the sensor 10. The section 53 extends along the edges 31 and 32 until it intersects the projection of lines 28 that define the active area 27 of the touch screen sensor 10. The section 55 is positioned around the corner 24 in a similar manner.

As depicted in Figure 5, a further section 57 of the wave absorption material 16 is applied to the fourth corner 26 of the touch screen sensor 10. The section 57 assists in reducing or eliminating far corner echoes.

The section 57 extends for a distance along the edges 32 and 33 until it intersects the projection of the lines 28 that define the active area 27 of the touch screen sensor 10. If desired, the fourth corner 26 of the touch screen sensor 10 may be cut at an angle of approximately 45 degrees, as indicated in Figure 5A, before the section 57 is formed thereon. The section 57 depicted in Figure 5 or 5A may be used on a touch screen sensor 10 by itself, i. e., sections 13,15,53 and 55 may be omitted entirely from the touch screen sensor 10 depicted in Figure 5.

With reference to Figure 6, sections 58 and 59 of the wave absorption material 16 are positioned around a portion of the perimeter 35 of the touch screen sensor 10. The section 58 extends from adjacent the

transducers 12 along the edge 31, around the second corner 22, and along a portion of the edge 32 of the touch screen sensor 10. Similarly, the section 59 extends from adjacent the transducers 12 along the edge 34, around the third corner 24, and along a portion of the edge 34 of the touch screen sensor 10. Positioning the wave absorption material 16 completely behind the arrays 18,21 assists in reducing back edge spurious reflections due to poor edge quality, as well as the other forms of reflections and echoes discussed above.

With reference to Figure 5 and Figure 5A, a section of the wave absorption material 16, similar to section 57 shown in Figure 5 or 5A, is positioned around the fourth corner 26 of the touch screen sensor 10.

The wave absorption material 16 is applied to the edge of the touch screen sensor 10 by a variety of known techniques. For example, in the case where the touch screen sensor is comprised of glass, the epoxy compound described above is applied to the edge of the touch screen by hand, e. g., painting or rolling, and, thereafter, cured by heating to, for example, 75°C for a period of 12 hours.