Reflective mode ultrasonic touch sensitive switch
First Claim
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1. A reflective mode ultrasonic touch sensitive switch comprising:
- a substrate having first and second opposed parallel surfaces, said first surface having a touch region thereon;
a piezoelectric element having first and second generally planar and parallel opposed surfaces and an electrode on each of said piezoelectric element surfaces, said piezoelectric element being secured in parallel relation to said substrate second surface across said substrate from said touch region;
drive means coupled to said electrodes for applying a frequency modulated drive signal to said electrodes, the center frequency of said frequency modulated drive signal being a frequency where the impedance-frequency curve of the assembly of said piezoelectric element together with said substrate exhibits a positive slope;
detection means coupled to said electrodes for providing a demodulated amplitude modulated signal derived from said drive signal; and
discriminating means coupled to receive said demodulated amplitude modulated signal from said detection means for evaluating said demodulated amplitude modulated signal and providing an output signal indicative of a finger touch to said touch region.
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Abstract
A touch sensitive switch is fabricated from a substrate having a touch region on a first surface and a piezoelectric element on a second surface of the substrate. The piezoelectric element is driven by a signal configured so that an ultrasonic wave generated by the element is transmitted into the substrate and is reflected back and forth into the substrate at both surfaces. A touch changes the reflectivity at the first surface, and influences the impedance of the transducer assembly which is comprised of the piezoelectric element and the substrate.
180 Citations
9 Claims
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1. A reflective mode ultrasonic touch sensitive switch comprising:
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a substrate having first and second opposed parallel surfaces, said first surface having a touch region thereon; a piezoelectric element having first and second generally planar and parallel opposed surfaces and an electrode on each of said piezoelectric element surfaces, said piezoelectric element being secured in parallel relation to said substrate second surface across said substrate from said touch region; drive means coupled to said electrodes for applying a frequency modulated drive signal to said electrodes, the center frequency of said frequency modulated drive signal being a frequency where the impedance-frequency curve of the assembly of said piezoelectric element together with said substrate exhibits a positive slope; detection means coupled to said electrodes for providing a demodulated amplitude modulated signal derived from said drive signal; and discriminating means coupled to receive said demodulated amplitude modulated signal from said detection means for evaluating said demodulated amplitude modulated signal and providing an output signal indicative of a finger touch to said touch region. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification