Acoustic wave type contact detector

BACKGROUND OF THE INVENTION

Field of the Invention

0001The present invention relates to an acoustic wave contact detecting apparatus that detects a contact position acoustically, such as an ultrasonic touch panel.

Description of the Related Art

0002Ultrasonic acoustic wave contact detecting apparatuses are in widespread use. Examples of their applications include operating screens of personal computers, ticket dispensers at train stations, copiers installed in convenience stores, and ATM's at financial institutions. These acoustic wave contact detecting apparatuses utilize transducers, including piezoelectric vibrators (piezoelectric elements) provided on a substrate (touch panel) formed of glass or the like. These transducers function both as generating means for bulk waves and as sensors for detecting acoustic waves which are scattered by a finger or the like that contacts the touch panel. The surface acoustic waves are scattered by a finger or the like. The scattering of the surface acoustic waves is detected by detection means. The detected signal is referenced against a clock signal of a controller, and the position at which the surface acoustic waves are scattered is determined.

0003Ultrasonic vibrations, which are generated as bulk waves, are converted to surface acoustic waves by acoustic wave generating means, and are propagated along the substrate.

0004When the bulk waves are converted to surface acoustic waves by the acoustic wave generating means, not all of the bulk waves are converted. Spurious waves, including unconverted bulk waves, surface acoustic waves which have passed through a reflection array, and surface acoustic waves which are reflected in directions other than predetermined directions, are generated. If these spurious waves are reflected along the substrate and reach the sensor side converters, they cause these converters to vibrate and generate voltages. These voltages are received as noise, and throw off proper judgment by the controller.

0005For this reason, vibration insulating or vibration absorbing materials are provided on the substrate to absorb the generated spurious waves (disclosed, for example, in Japanese Unexamined Patent Publication Nos. <patcit id="pcit0001" dnum="JP6324792A"><text>6 (1994)-324792</text></patcit> (page 2, <figref idref="f0001">Figure 1</figref>) and <patcit id="pcit0002" dnum="WO611986239322A"><text>61 (1986)-239322</text></patcit> (page 11, <figref idref="f0002">Figure 2</figref>)). These vibration insulating and vibration absorbing materials are normally in the form of resin tape, which is adhesively attached to the substrate. The spurious waves which reach the tape are absorbed and attenuated.

0006In the conventional art, it is necessary to adhesively attach the vibration insulation or vibration absorbing member to the substrate. The adhesive attachment operation is manually performed, therefore increasing the manufacturing steps and reducing productivity. As a result, there is a problem that manufacturing costs are increased.

0007<patcit id="pcit0003" dnum="US5260913A"><text>US 5,260,913</text></patcit> discloses multiple SAW filters formed on a mother substrate. When the individual SAW filters are divided from one another, rough surfaces are formed at the edges of the filters. The rough surfaces can disperse a bulk wave.

0008The present invention has been developed in view of the above points. It is an object of the present invention to provide an acoustic wave contact detecting apparatus, which is capable of effectively scattering and eliminating spurious waves, with increased productivity and reduced manufacturing costs.

DISCLOSURE OF THE INVENTION

0009The acoustic wave contact detecting apparatus of the present invention is defined by the appended claim 1.

0010A construction may be adopted wherein the spurious wave scattering means comprises a reflection array formed of the same material as that of the substrate.

0011The acoustic wave generating means and the spurious wave scattering means may be formed either by printing or etching.

0012Here, the "acoustic waves" include ultrasonic waves that propagate within a thin substrate along the surface thereof, in addition to surface acoustic waves that propagate along the surface of the substrate.

0013The acoustic wave generating means may include a mode converting element and an ultrasonic vibrator.

0014The detector may be a converter. The converter is an element that converts ultrasonic vibrations to electric signals, or an element that converts electric signals to ultrasonic vibrations.

0015The spurious wave scattering means may be a diffusion grating.

0016In the acoustic wave contact detecting apparatus of the present invention, a spurious wave scattering means for diffusing spurious waves, which are generated accompanying the generation of acoustic waves, is formed on the substrate. Therefore, the spurious waves are enabled to be effectively scattered by the spurious wave scattering means.

0017A construction may be adopted wherein the spurious wave scattering means comprises a reflection array formed of the same material as that of the substrate. In this case, the spurious waves are enabled to be scattered effectively.

0018The acoustic wave generating means and the spurious wave scattering means may be formed by printing. In this case, the productivity is increased and the manufacturing costs are reduced, because efficient production is enabled by automated printing, in addition to enabling effective scattering of spurious waves. The acoustic wave generating means and the spurious wave scattering means may alternatively be formed by etching. In this case also, productivity is increased and the manufacturing costs are reduced, because a single method can be used for forming both means, in addition to enabling effective scattering of spurious waves.

BRIEF DESCRIPTION OF THE DRAWINGS

0019<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Figure 1</figref> is a front view of a touch panel, to be utilized in an acoustic wave contact detecting apparatus of the present invention.</li><li><figref idref="f0002">Figure 2</figref> is a front view illustrating an FPC which is attached to a substrate.</li><li><figref idref="f0003">Figure 3</figref> is a schematic plan view showing the entirety of the FPC.</li><li><figref idref="f0004">Figure 4</figref> is a magnified view of the portion of the FPC indicated by B in <figref idref="f0003">Figure 3</figref>.</li><li><figref idref="f0005">Figure 5</figref> is a front view of a reflection array, corresponding to that shown in <figref idref="f0001">Figure 1</figref>.</li><li><figref idref="f0006">Figure 6</figref> is a front view of mode converting elements and a diffusion grating, corresponding to that shown in <figref idref="f0001">Figure 1</figref>.</li><li><figref idref="f0007">Figure 7</figref> is a partial magnified view of the reflection array and the diffusion grating.</li><li><figref idref="f0008">Figure 8</figref> is another partial magnified view of the reflection array and the diffusion grating.</li><li><figref idref="f0009">Figure 9</figref> is a magnified view of an alternate form of the diffusion grating.</li><li><figref idref="f0010">Figure 10</figref> is a front view illustrating the relative positions of the diffusion grating and the reflection array.</li><li><figref idref="f0011">Figure 11</figref> is a schematic partial magnified view of the substrate of <figref idref="f0001">Figure 1</figref>, viewed from the direction of arrow A.</li></ul>

DESCRIPTION OF THE PREFERRED EMBODIMENTS

0020A preferred embodiment of the acoustic wave contact detecting apparatus (hereinafter, simply referred to as "apparatus") will be described with reference to the attached drawings.

0021<figref idref="f0001">Figure 1</figref> is a front view of a touch panel 3, to be utilized in an apparatus 1. As shown in <figref idref="f0001">Figure 1</figref>, the touch panel 3 comprises: a substrate 2 formed by a rectangular glass plate; a Flexible Printed Circuit 4 (FPC) mounted on the substrate 2; and a controller 6, which is electrically linked to the FPC 4.

0022The FPC 4 is branched into an FPC branch 4a and an FPC branch 4b. The FPC branch 4a extends along the horizontal direction of the substrate 2, that is, the X axis direction indicated by the arrow X. The FPC branch 4b extends along the vertical direction of the substrate perpendicular to the X axis, that is, the Y axis direction indicated by the arrow Y. Converters (bulk wave generating means) 8 and 10 for generating ultrasonic waves are mounted on the FPC 4. In addition, converters (detectors) 12 and 14, which function as sensors, are mounted on the FPC 4.

0023A reflection array 18, comprising a great number of inclined lines 16, is formed along the Y axis on the front surface of the substrate 2, in the vicinity of one lateral edge 44 thereof. A reflection array 22, comprising a great number of inclined lines 20, is formed to face the reflection array 18, at the other lateral edge 44 of the substrate. A reflection array 28, comprising a great number of inclined lines 26, is formed along the X axis in the vicinity of the upper edge 24 of the substrate 2. A reflection array 32, comprising a great number of inclined lines 30, is formed to face the reflection array 28, in the vicinity of the lower edge 45 of the substrate. The patterns of these reflection arrays 18, 22, 28, and 32 are those disclosed in Japanese Unexamined Patent Publication Nos.<patcit id="pcit0004" dnum="JP61239322A"><text> 61 (1986)-239322</text></patcit> and <patcit id="pcit0005" dnum="JP2001014094A"><text>2001-14094</text></patcit>. Note that the reflection arrays 18, 22, 28, and 32 will collectively be referred to as a reflection array 33. The reflection array 33 reflects acoustic waves, and causes them to propagate along the front surface of the substrate 2.

0024The converters 8, 10, 12, and 14 are adhesively attached to the rear surface of the substrate 2. Mode converting elements 78, 80, 82, and 84 (gratings) are formed on the front surface of the substrate 2, at positions corresponding to the converters 8, 10, 12, and 14, respectively. This construction will be described with reference to <figref idref="f0011">Figure 11</figref>, taking the mode converting element 80 as an example. <figref idref="f0011">Figure 11</figref> is a schematic partially magnified view of the substrate 2, viewed from the direction of arrow A. The mode converting element 80 of <figref idref="f0011">Figure 11</figref> is formed by sintering glass paste on the substrate 2, and comprises a plurality of parallel ridges 80a. The ridges 80a shown in <figref idref="f0011">Figure 11</figref> extend in the direction perpendicular to the surface of the drawing sheet.

0025The widths of the ridges 80a are set to be 400µm, and the heights are set to be 35µm or greater. The direction in which the bulk waves are reflected is changed by varying the intervals among the ridges 80a. In the present embodiment, the ridges 80a are formed with intervals that cause surface acoustic waves to be generated directly beside the ridges 80a. The converter 10 is adhesively attached on the side of the substrate opposite the mode converting element 80, and is electrically connected to the FPC branch 4b with solder.

0026The other mode converting elements 78, 82, and 84 are of the same construction. Of these, the mode converting elements (acoustic wave generating means) denoted by reference numerals 78 and 80 convert bulk waves generated by the transmission side converters 8 and 10 into surface acoustic waves. The mode converting elements 82 and 84 convert the surface acoustic waves (acoustic waves), which have propagated along the front surface of the substrate 2, back into bulk waves.

0027The converter 10 generates ultrasonic vibrations (bulk waves) at a frequency of approximately 5.5MHz. The ultrasonic vibrations travel through the interior of the substrate 2 from the rear surface thereof, and reach the mode converting element 80. The mode converting element 80 converts the ultrasonic vibrations to surface acoustic waves, which are propagated (reflected) perpendicular to the ridges 80a, toward the reflection array 32. The surface acoustic waves are reflected by the inwardly inclined lines 30 of the reflection array 32 and propagate along the front surface of the substrate 2 toward the reflection array 28 until they reach the inwardly inclined lines 26.

0028Bulk waves which are not converted to surface acoustic waves by the mode converting elements 78 and 80 are not radiated in a specific direction, but propagate in all directions from the mode converting elements 78 and 80. If a portion of the unconverted bulk waves are transmitted to the converters 12 and 14, they become spurious waves that obstruct primary signal detection. In addition, although the mode converting elements 78 and 80 are constructed to generate surface acoustic waves in a direction perpendicular to the ridges thereof, it is known that slight surface acoustic waves are generated in unintended directions. These surface acoustic waves may also become spurious waves that obstruct primary signal detection. If these spurious waves reach the converters 12 and 14, noise signals are generated thereat.

0029The surface acoustic waves that reach the reflection array 28 are reflected thereby to propagate toward the mode converting element 84. The surface acoustic waves that reach the mode converting element 84 are converted to bulk waves thereby. The converted bulk waves are transmitted to the converter 14 on the rear surface of the substrate 2, which senses and converts the vibrations thereof to electrical signals.

0030In a similar manner, the ultrasonic vibrations (bulk waves) generated by the converter 8 are converted to surface acoustic waves by the mode converting element 78. Then, the surface acoustic waves reach the mode converting element 82 via the reflection array 18 and the reflection array 22. The surface acoustic waves are converted to bulk waves by the mode converting element 82 and transmitted to the converter 14, which senses and converts them to electrical signals.

0031In this manner, the surface acoustic waves are propagated across the entire region of the front surface of the substrate 2 covered by the reflection arrays 18, 22, 28, and 32. Therefore, if a finger (object) contacts (touches) the substrate 2 within this region, the surface acoustic waves blocked by the finger disappear or are attenuated. The signal change accompanying the change in the surface acoustic waves is transmitted from the converters 12 and 14, which function as sensors, to a timing circuit (not shown) of the controller 6 connected thereto. The controller 6 determines the geometric coordinates of the position touched by the finger.

0032The surface acoustic waves are reflected by each of the inclined lines 16, 20, 26, and 30 of the reflection array 33. 0.5% to 1% of the surface acoustic waves that reach each of the inclined lines are reflected thereby. The remainder passes through and is transmitted to the adjacent inclined line, so that all of the inclined lines sequentially reflect the surface acoustic waves.

0033Spurious wave scattering means for reducing noise by diffusing spurious waves, that is, diffusion gratings (diffusing portions), are formed on the front surface of the substrate 2 of the apparatus 1. The diffusion gratings include the rectangular portions denoted by reference numerals 34, 36, and 38 in <figref idref="f0001">Figure 1</figref>, a diffusion grating 43 formed by inclined lines 40 and 42 along the upper edge 24, and a diffusion grating 49 formed by inclined lines 46 and 48 along the lateral edge 44. The inclined lines 40, 42, 46, and 48 construct a second reflection array, having a function different from that of the reflection arrays 18, 22, 28, and 32. The second reflection array is also provided within the diffusion gratings 34, 36, and 38 (refer to <figref idref="f0007">Figure 7</figref>). Details of the diffusion gratings 34, 36, 38, 43, and 49 will be described later. Note that the diffusion gratings will collectively be referred to as a diffusion grating 50.

0034Next, the FPC 4, which is adhesively attached to the substrate 2, will be described with reference to <figref idref="f0002">Figure 2</figref>, <figref idref="f0003">Figure 3</figref>, and <figref idref="f0004">Figure 4</figref>. <figref idref="f0002">Figure 2</figref> is a front view illustrating the FPC 4, which is attached to the substrate 2. Although the FPC 4 is adhesively attached to the rear surface of the substrate 2, it is drawn in solid lines for the sake of convenience. Note that the reflection array 33 and the diffusion grating 50 are omitted from <figref idref="f0002">Figure 2</figref>. <figref idref="f0003">Figure 3</figref> is a schematic plan view showing the entirety of the FPC 4. <figref idref="f0004">Figure 4</figref> is a magnified view of the portion of the FPC 4 indicated by B in <figref idref="f0003">Figure 3</figref>. The FPC 4 as shown in <figref idref="f0003">Figure 3</figref> and <figref idref="f0004">Figure 4</figref> correspond to a state in which it is viewed from the rear surface of the substrate 2 of <figref idref="f0002">Figure 2</figref>.

0035Electrodes 52 and 54, corresponding respectively to the converters (sensors) 12 and 14, are provided at one end of the FPC 4, as shown in <figref idref="f0003">Figure 3</figref> and <figref idref="f0004">Figure 4</figref>. The electrodes 52 and 54 are connected to the converters 12 and 14 from above by soldering, a conductive adhesive such as silver paste, or an anisotropic conductive adhesive. That is, the converters 12 and 14 are positioned between the FPC 4 and the rear surface of the substrate 2. The FPC 4 is constructed by the aforementioned FPC branches 4a and 4b, and a connection line 4c for connecting with the controller 6.

0036The connection line 4c and the FPC branch 4a are of the same length, and are formed integrally as a band (refer to <figref idref="f0003">Figure 3</figref>). Perforations 56 are formed between the connection line 4c and the FPC branch 4a, to enable separation of the two. An electrode 58, for connecting with the converter 8, is formed at the end of the FPC branch 4a opposite that at which the electrode 52 is provided. An electrode 60, for connecting with the controller 6, is formed at the end of the connection line 4c near the electrode 58. An electrode 62, for connecting with the converter 10, is formed at the end of the FPC branch 4b opposite that at which the electrode 54 is provided (refer to <figref idref="f0003">Figure 3</figref>).

0037As shown in <figref idref="f0004">Figure 4</figref>, a printed wiring 64 of the connection line 4c comprises ten printed wires 64a, 64b, 64c, 64d, 64e, 64f, 64g, 64h, 64i, and 64j . A signal wire group is constructed by four printed wires (signal reception wires) 64d, 64e, 64f, and 64g, which are connected to the converters (sensors) 12 and 14. What is important here is that grounding wires 64c and 64h are provided at either side of the signal wire group.

0038Signal wires 64b and 64i, which are connected to the transmission converters 8 and 10, are provided adjacent to the grounding wires 64c and 64h, respectively. Further, grounding wires 64a and 64j are provided adjacent to the signal wires 64b and 64i, respectively on the outsides thereof. This construction results in shielding of all of the signal wires, by the signal reception wires 64d, 64e, 64f, and 64g being surrounded by the grounding wires 64c and 64h, and the signal transmission wires 64b and 64i being surrounded by the grounding wires 64c and 64a, and the grounding wires 64h and 64j, respectively. This relationship is maintained in the FPC branches 4a and 4b as well. By this construction, the signal wire group consisting of the printed wires 64b, 64d, 64e, 64f, 64g, and 64i are less likely to be influenced by external electromagnetic waves. At the same time, an effect that electromagnetic waves are less likely to be radiated toward the exterior is also obtained. The above construction is particularly effective in improving anti-EMI properties in the case that the FPC 4 is extended over a long distance along the substrate 2.

0039Note that bending lines of the FPC branch 4b are denoted by reference numerals 66 and 68 in <figref idref="f0004">Figure 4</figref>. The FPC branch 4b is bent along the bending line 66 in the direction toward the surface of the drawing sheet of <figref idref="f0004">Figure 4</figref>. Then, the FPC branch 4b is bent again along the bending line 68 in the direction away from the surface of the drawing sheet of <figref idref="f0004">Figure 4</figref>, so that the electrode 62 (refer to <figref idref="f0003">Figure 3</figref>) faces the converter 10. The bending portion is denoted by reference numeral 69 in <figref idref="f0002">Figure 2</figref>. In this manner, the FPC branch 4b is arranged along the lateral edge 44 of the substrate 2. Note that the FPC 4 is fixed to the substrate 2 by an adhesive (not shown) or the like.

0040Next, the arrangement of the reflection array 33 will be described with reference to <figref idref="f0005">Figure 5. Figure 5</figref> is a front view of the reflection array 33, corresponding to that shown in <figref idref="f0001">Figure 1</figref>. The diffusion gratings 34, 36, 38, and the like for scattering spurious waves are omitted from <figref idref="f0005">Figure 5</figref>. Each of the inclined lines 16, 20, 26, and 30 of the reflection arrays 18, 22, 28, and 32 is inclined at an angle of 45°. The inclined lines 16, 20, 26, and 30 are configured to reflect surface acoustic waves toward the reflection array that faces them across the substrate 2. The reflection array 33 is formed by printing fine particles of lead glass formed into a paste on the front surface of the substrate 2 by screen printing or the like, then sintering at approximately 500°C. Note that the corners of the substrate 2 are partially illustrated in <figref idref="f0005">Figure 5</figref>, denoted by reference numeral 25. Alternatively, a UV curable organic ink, or an organic ink having metal particles added as filler therein to improve the reflective properties thereof, may be utilized as the material of the reflection array.

0041The intervals among the inclined lines 16, 20, 26, and 30 decrease, that is, the inclined lines are arranged at higher densities, the further they are from the transmission side converters 8 and 10. This is because the intensities of the surface acoustic waves become attenuated as they pass through the inclined lines 16, 20, 26, and 30. Therefore, it becomes necessary to adopt the above construction to compensate for the attenuation to propagate the surface acoustic waves evenly along the front surface of the substrate 2. Note that the reflection arrays 22 and 28 are provided slightly inward from the upper edge 24 and the lateral edge 44 (refer to <figref idref="f0001">Figure 1</figref>) of the substrate, respectively. This is so that the inclined lines 40, 42, 46, and 48 of the diffusion grating 50, to be described later, may be provided at the outsides of the reflection arrays 22 and 28.

0042Next, the diffusion grating 50, which functions as a spurious wave scattering means, will be described with reference to <figref idref="f0006">Figure 6. Figure 6</figref> is a front view, corresponding to <figref idref="f0001">Figure 1</figref>, that shows the diffusion grating 50 along with the mode converting elements 78, 80, 82, and 84. The inclined lines 40 and 42, which constitute the second reflection array, are formed at opposite angles with respect to each other in the vicinity of the upper edge 24 of the substrate 2. The angles of the inclined lines are such that they are close to perpendicular toward the central portion of the substrate 2, and gradually decrease toward the edges thereof. In a similar manner, the other inclined lines 46 and 48, which constitute the second reflection array, are formed at opposite angles with respect to each other, with gradually changing angles. This is so that spurious waves are not reflected in the same direction, but rather are diffused.

0043The inclined lines 40, 42, 46, and 48 are positioned at regions where tape and the like are adhered to in conventional touch panels. That is, the inclined lines 40, 42, 46, and 48 are formed to replace the tape of conventional touch panels. The spurious waves that reach these regions are diffusively reflected by the inclined lines 40, 42, 46, and 48, so that they are not propagated to the converters (sensors) 12 and 14. The attenuation rate of ultrasonic vibration energy differs according to the frequency of the ultrasonic waves, the vibration mode, and the type of glass. The intensity of surface acoustic waves at a frequency of 5.5MHz attenuates to 1/10 its original intensity after propagating 40cm along a typical substrate 2 formed of soda lime glass. Accordingly, the diffusively reflected spurious waves attenuate rapidly and disappear as they are reflected across the substrate 2.

0044A plurality of separate ridges, that is, inclined lines, inclined at angles other than 45° or -45°, are formed at the rectangular diffusion gratings 34, 36, and 38. The shapes of the ridges will be described with reference to <figref idref="f0007">Figure 7</figref> and <figref idref="f0008">Figure 8</figref>. <figref idref="f0007">Figure 7</figref> is a partial magnified view of the diffusion grating 36 and the reflection array 33. <figref idref="f0008">Figure 8</figref> is a partial magnified view of the diffusion grating 38 and the reflection array 33. It is clearly shown in <figref idref="f0007">Figure 7</figref> that inclined lines 36a of the diffusion grating 36 are oriented at angles different from those of the reflection arrays 18 and 32. Likewise, <figref idref="f0008">Figure 8</figref> clearly shows the diffusion grating 38, which is constituted by steeply inclined lines 38a.

0045These diffusion gratings 36 and 38 also function to diffusively reflect spurious waves that propagate along the front surface of the substrate 2 toward the exterior, at angles other than 45° or -45°. The diffusion grating 34, although not illustrated in detail, possesses a similar structure and function. The inclined lines 36a and 38a may be parallel or have gradually changing angles within the respective diffusion gratings 36 and 38. The diffusion gratings 34 and 38 also function to block the paths of surface acoustic waves that propagate in directions other than a predetermined direction, so that they do not reach the converters (sensors) 12 and 14.

0046The diffusion grating 50 is printed on the substrate 2 using lead glass particles formed into a paste as ink, in the same manner as the reflection array 33. Accordingly, the diffusion grating 50 maybe printed at the same time that the reflection array 33 is formed. This improves productivity and reduces manufacturing costs.

0047The inclined lines 36a and 38a of the diffusion gratings 36 and 38 are formed as a plurality of ridges. However, the diffusion gratings are not limited to being formed by ridges, and various modifications are possible. An alternate construction of the diffusion grating (diffusing portion) is shown in <figref idref="f0009">Figure 9. Figure 9</figref> is a magnified view of an alternate form of the diffusion grating (diffusing portion). This diffusing portion 51 is constructed by a great number of protrusions 51a, which are diamond shaped in plan view. Spurious waves that reach the diffusing portion 51 are attenuated while being repetitively reflected by the protrusions 51a within the region formed thereby. The shape of the protrusions is not limited to a diamond shape, and may be any desired shape, such as rectangles, triangles, other polygonal shapes, or ovals.

0048<figref idref="f0010">Figure 10</figref> is a front view illustrating the relative positions of the diffusion grating 50 and the reflection array 33, formed on the front surface of the substrate 2. <figref idref="f0010">Figure 10</figref> clearly illustrates that the inclined lines 40 and 42 are positioned outside the reflection array 28, and that the inclined lines 46 and 48 are positioned outside the reflection array 22. The diffusion gratings 34, 36, and 38 are positioned so that acoustic waves (surface acoustic waves), which pass through the reflection array 33 without being reflected, are reflected in directions different from those in which the reflection array 33 reflects them.

0049More specifically, for example, surface acoustic waves generated by the converter 8 and the mode converting element 78 are reflected toward the reflection array 22 by the reflection array 18 while passing therethrough. The surface acoustic waves which are not reflected by the reflection array 18 reach the diffusion grating 36. As shown in <figref idref="f0007">Figure 7</figref>, the diffusion grating 36 functions to reflect surface acoustic waves toward the outside of the substrate 2. That is, the diffusion grating 36 reflects the surface acoustic waves in the opposite direction from the primary direction, so that ultrasonic vibrations that would cause noise do not reach the converter (sensor) 12.

0050The inclined lines 40, 42, 46, and 48 formed along the edges of the substrate 2 are structured to diffusively reflect and attenuate bulk waves that propagate along the front surface of the substrate 2. Normally, bulk waves are converted to surface acoustic waves by the mode converting elements 78 and 80. However, bulk waves which are not 100% converted propagate in directions other than the predetermined directions therefor. Therefore, the inclined lines 40, 42, 46, and 48 are utilized to attenuate these spurious bulk waves.

0051In addition, surface acoustic waves propagate in directions other than the predetermined directions therefor after being converted by the mode converting elements 78 and 80. The inclined lines 40, 42, 46, and 48 also diffusively reflect these stray surface acoustic waves so that they are scattered in various directions. The risk that spurious ultrasonic vibrations reach the converters (sensors) 12 and 14 to cause noise is reduced by this diffusive reflection.

0052Pictures 82 of dolphins are printed between the inclined lines 40 and 42, and also between the inclined lines 46 and 48 in <figref idref="f0010">Figure 10</figref>. The pictures 82 are also effective in reducing noise. The pictures 82 have curved outlines. Bulk waves or stray surface acoustic waves that reach the outlines of the pictures 82 are reflected in various directions and attenuated. Any picture may be employed as long as the outline thereof is formed of curved lines, or are of angles that cause spurious waves to be diffusively reflected in various directions. Alternatively, patterns may be printed on the substrate 2 at these portions.

0053An embodiment of the present invention has been described in detail above. However, the present invention is not limited to the embodiment described above. For example, the diffusion grating 50 may be formed by etching with hydrofluoric acid. The diffusion grating 50 may also be formed by a chemical or physical removal process employing lasers, sandblasting, or cutting. In other words, the diffusion grating 50 may be formed by grooves instead of protrusions.

0054In the present embodiment, the case in which surface acoustic wave generating means of the so-called "grating type", which have mode converting elements 78, 80, 82, and 84, are employed has been described. However, the present invention is not limited to apparatuses that employ this type of surface acoustic wave generating means. For example, the present invention may be applied to an acoustic wave contact detecting apparatus that generates surface acoustic waves by means of a wedge type converter (not shown) that utilizes an acrylic prism (not shown). The present invention may also be applied to an acoustic wave contact detecting apparatus that employs a pair of comb electrodes formed on an ultrasonic vibrator, without a grating nor a wedge.

0055The FPC 4 which is utilized in the present invention may be adhesively attached to the substrate 2 with any desired adhesive. However, it is preferable that piezoelectric vibrators be adhesively attached using ultraviolet cured adhesive. This is to enable adjustment of the positions of the converters 8, 10, 12, and 14 with respect to the mode converting elements 78, 80, 82 and 84 to confirm optimal generation of surface acoustic waves prior to irradiation of ultraviolet rays, which causes adhesion.

0056The spurious wave scattering means may be of the type that causes diffusive reflection and attenuation, as described above. Note that the two converters (sensors) 12 and 14 are provided in close proximity to each other in the embodiments described above. However, the converters (sensors) 12 and 14 may switch places with the transmission converters 8 and 10, so that they are positioned apart from each other. In this case, when surface acoustic waves leak from either the converter 12 or 14, as the other converter 14 or 12 is not in close proximity therewith, the noise picked up by the other converter is suppressed. In addition, the electrical path from the controller 6 to the transmission converters 8 and 10 can be shortened. Therefore, spurious radiation, that is, emission of electromagnetic waves, from the electrical path, can be suppressed.

0057A case in which FPC's are utilized has been described in the above embodiment. However, FFC's, that is, flexible flat cables, may be employed instead of the FPC's. In the case that FFC's are employed, the converters 8, 10, 12, and 14 are electrically connected to conductors of the FFC's. FFC's may be adhesively attached to the substrate 2, in a manner similar to that of the FPC 4.