Acoustic touch sensor
View Patent ↗A touch sensor comprises a substrate capable of propagating acoustic waves and includes a first surface having a touch sensitive region. A first sidewall intersects the first surface along a first edge. The first edge is configured to propagate a first acoustic wave along the first edge. The first acoustic wave may be a one-dimensional edge wave. A wave converter converts the first acoustic wave to a second acoustic wave, and the first surface is configured to propagate the second acoustic wave across the touch sensitive region.
1. A shear-mode transducer for generating or receiving an acoustic edge wave in a touch sensor having a substrate with a first surface having a touch region and a second surface intersecting the first surface along a first edge, the acoustic edge wave propagating along the first edge, the shear-mode transducer mounted on the substrate on the second surface, the shear-mode transducer comprising:
a shear-mode piezoelectric element, the shear-mode piezoelectric element generating shear motion in a direction relative to a plane of the second surface defined by X and Y axes so as to couple to the acoustic edge wave, wherein the shear motion is polarized diagonally in the plane of the second surface defined by the x and y axes; and
a first electrode and a second electrode disposed on the shear-mode piezoelectric element to provide an active region of the shear-mode piezoelectric element, said active region comprising a cross-sectional area of the acoustic edge wave.
2. The shear-mode transducer of claim 1 , wherein the second surface comprises a second sidewall of the substrate, wherein the second sidewall is perpendicular to a propagation direction of the acoustic edge wave.
3. The shear-mode transducer of claim 1 , wherein the shear-mode piezoelectric element has been poled to provide the shear motion in the direction comprising an approximately 45 degree in the plane.
4. The shear-mode transducer of claim 3 , the shear-mode piezoelectric element comprising a front and a back surface, the first electrode covering a portion of the front surface, the second electrode covering a substantial part of the back and front surfaces, the active region corresponding to an area of the shear-mode piezoelectric element where the first and second electrodes overlap.
5. The shear-mode transducer of claim 4 , the first and second electrodes on the front surface of the shear-mode piezoelectric element configured for receiving attachments to first and second electrical connections for exciting the shear-mode piezoelectric element, wherein the front surface is covered by the first and second electrodes which are separate.
6. The shear-mode transducer of claim 4 , the shear-mode piezoelectric element being mounted to the substrate having an overhang portion of the shear-mode piezoelectric element extending beyond at least one of the first surface and the second surface by a distance of less than one wavelength of the acoustic edge wave.
7. The shear-mode transducer of claim 4 , wherein the second electrode wraps around the shear-mode piezoelectric element from the front surface to the back surface.
8. The shear-mode transducer of claim 1 , the shear-mode transducer being bonded to the substrate, the bonding corresponding to a portion of the active region and providing strong acoustic coupling between the substrate.
9. The shear-mode transducer of claim 1 , wherein the active region has a size less than one-wavelength squared of the acoustic edge wave.
10. The shear-mode transducer of claim 1 , the shear-mode piezoelectric element comprising front and back surfaces, a depth, a first side; a second side; the first side and second side not intersecting but being joined by a notched corner, the notched corner also intersecting each of the front and back surfaces, the shear-mode piezoelectric element being poled in a direction perpendicular to the plane; and first and second electrodes formed on first and second edges, the first and second electrodes receiving attachments to first and second electrical contacts for exciting the piezoelectric element.
11. The shear-mode transducer of claim 10 wherein the depth comprises one-half of a bulk shear wave wavelength.
12. The shear-mode transducer of claim 11 , the shear-mode piezoelectric element being mounted to the substrate having an overhang portion of the shear-mode piezoelectric element extending beyond at least one of the first surface and the second surface by a distance of less than one wavelength of the acoustic edge wave.
13. The shear-mode transducer of claim 10 wherein the notched corner has an angle of approximately 45 degrees with respect to the first and second sides.
14. The shear-mode transducer of claim 13 , the shear-mode piezoelectric element being mounted to the substrate having an overhang portion of the shear-mode piezoelectric element extending beyond at least one of the first surface and the second surface by a distance of less than one wavelength of the acoustic edge wave.
15. The shear-mode transducer of claim 10 , the shear-mode piezoelectric element being mounted to the substrate having an overhang portion of the shear-mode piezoelectric element extending beyond at least one of the first surface and the second surface by a distance of less than one wavelength of the acoustic edge wave.
16. The shear-mode transducer of claim 1 , the shear-mode piezoelectric element being mounted to the substrate having an overhang portion of the shear-mode piezoelectric element extending beyond at least one of the first surface and the second surface by a distance of less than one wavelength of the acoustic edge wave.