Acoustic touch signal dispersion response and minimization
View Patent ↗A touch input system includes a substrate configured to support propagation of acoustic signals, a transducer in communication with the substrate and configured to transmit or receive the acoustic signals before or after the propagation, and an array of reflectors disposed on the substrate. Each reflector is oriented on an angle to redirect the acoustic signals along a path toward or away from the transducer. The transducer includes a stepped interface for the redirected acoustic signals. The stepped interface includes a set of interface elements distributed across a width of the acoustic signals and offset from one another along the path to compensate for the angle of the reflectors.
1. A touch input system comprising:
a substrate configured to support propagation of acoustic signals;
a transducer in communication with the substrate and configured to transmit or receive the acoustic signals before or after the propagation; and
an array of reflectors disposed on the substrate, each reflector being oriented on an angle to redirect the acoustic signals along a path toward or away from the transducer;
wherein the transducer comprises a stepped interface for the redirected acoustic signals, the stepped interface comprising a set of interface elements distributed across a width of the acoustic signals and offset from one another along the path to compensate for the angle of the reflectors.
2. The touch input system of claim 1 , wherein the transducer comprises a plurality of piezoelectric elements distributed across the width of the acoustic signals and offset from one another along the path to equalize an arrival time of a respective portion of the redirected acoustic signals captured by the corresponding piezoelectric element.
3. The touch input system of claim 1 , wherein the transducer comprises a mode conversion wedge, the mode conversion wedge comprising a stepped first face and a piezoelectric element disposed at a second face of the mode conversion wedge opposite of the first face.
4. The touch input system of claim 3 , wherein the stepped first face comprises a plurality of reflector steps, and wherein each reflector step comprises a curved surface.
5. The touch input system of claim 3 , wherein the transducer is oriented relative to the array of reflectors to position the stepped first face and the second face such that the acoustic signals travel past the second face before reflection off the stepped first face in the mode conversion wedge.
6. The touch input system of claim 3 , wherein the piezoelectric element may be spaced from a bottom of the mode conversion wedge to avoid affecting the redirected acoustic waves before the reflection off the stepped first face in the mode conversion wedge.
7. The touch input system of claim 3 , wherein the stepped first face includes a plurality of reflector steps.
8. The touch input system of claim 7 , wherein:
the mode conversion wedge comprises an acrylic block having the stepped first face, and
adjacent reflector steps of the plurality of reflector steps are spaced from one another based on a bulk wave speed in the acrylic block.
9. The touch input system of claim 3 , wherein the mode conversion wedge further comprises an undercut bottom in communication with the substrate, the undercut bottom comprising a set of undercut steps that match the stepped first face.
10. The touch input system of claim 9 , wherein:
the stepped first face includes a plurality of reflector steps, and
adjacent reflector steps of the plurality of reflector steps and adjacent undercut steps of the set of undercut steps are spaced from one another to equalize an arrival time of respective portions of the acoustic signals at the piezoelectric element of the transducer.
11. The touch input system of claim 1 , wherein the stepped interface comprises a set of grates to form a grating transducer.
12. The touch input system of claim 11 , wherein each grate is curved.
13. The touch input system of claim 1 , wherein the array of reflectors comprises a plurality of waveguides.
14. The touch input system of claim 1 , wherein the acoustic signals are surface acoustic wave (SAW) signals.
15. A transducer for a touch input system comprising:
a mode conversion wedge comprising a first face and a second face opposite the first face, the mode conversion wedge being configured to convert surface acoustic wave (SAW) signals to bulk pressure waves; and
a piezoelectric element disposed at the second face of the mode conversion wedge opposite of the first face to transmit or receive a reflection of the bulk pressure waves off the second face;
wherein the first face includes a plurality of reflector steps offset from one another to compensate for dispersion of the SAW signals.
16. The transducer of claim 15 , wherein the mode conversion wedge has a bottom between the first and second faces, and wherein the piezoelectric element is spaced from the bottom of the mode conversion wedge to allow the SAW signals to travel past the first face before the reflection of the bulk pressure waves off the second face.
17. The transducer of claim 16 , wherein the bottom of the mode conversion wedge comprises a set of undercut steps that match the plurality of reflector steps.
18. The transducer of claim 15 , wherein the mode conversion wedge comprises an acrylic block.
19. The transducer of claim 15 , wherein each reflector steps comprises a curved surface.
20. The transducer of claim 15 , in combination with a reflector array comprising a plurality of waveguides.