Short distance ultrasonic distance meter
First Claim
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1. A transducer assembly for a proximity sensor comprising:
- an elongated polymer piezoelectric film;
a support member for supporting said film;
a first drive circuit connected to said film for applying a first varying electric field of a first phase and a first amplitude across the thickness of said film to cause an ultrasonic acoustic wave to be radiated from said film; and
a second drive circuit connected to said film for applying a second varying electric field of a second phase and a second amplitude across the thickness of said film to cause an ultrasonic acoustic wave to be radiated from said film, whereby the selective application of said first and second varying electric fields reduces the effects of ringing.
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Abstract
A short distance ultrasonic distance meter is disclosed with provisions to reduce the ill-effects of ringing when measurements are of obstacles closer than about ten inches. In one embodiment an opposite phase ultrasonic wave is introduced by a circuit (245) and in another embodiment a strain sensor (232) introduces negative feedback to effect cancellation of ringing (147). Finally, in a third embodiment, both the negative feedback and opposite phase methods are employed for optimal results.
427 Citations
10 Claims
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1. A transducer assembly for a proximity sensor comprising:
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an elongated polymer piezoelectric film; a support member for supporting said film; a first drive circuit connected to said film for applying a first varying electric field of a first phase and a first amplitude across the thickness of said film to cause an ultrasonic acoustic wave to be radiated from said film; and a second drive circuit connected to said film for applying a second varying electric field of a second phase and a second amplitude across the thickness of said film to cause an ultrasonic acoustic wave to be radiated from said film, whereby the selective application of said first and second varying electric fields reduces the effects of ringing. - View Dependent Claims (2, 3, 4, 5)
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6. A transducer assembly for a proximity sensor comprising:
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an elongated polymer piezoelectric film having a first section and a second section, said first section electrically isolated from said second section; a support member for supporting said film; a drive circuit connected to said film for applying a varying electric field across the thickness of said film to cause an ultrasonic acoustic wave to be radiated from said film; and a negative feedback circuit connected between said second section and said drive circuit, whereby the ill-effects of self-vibration in the piezoelectric film are substantially eliminated. - View Dependent Claims (7, 8)
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9. A transducer assembly for a proximity sensor comprising:
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an elongated polymer piezoelectric film, having a first section and a second section, said second section being electrically isolated from said first section; a support member for supporting said film; a first drive circuit connected to said film for applying a first varying electric field of a first phase and a first amplitude across the thickness of said film to cause an ultrasonic acoustic wave to be radiated from said film; a second drive circuit connected to said film for applying a second varying electric field of a second phase and a second amplitude across the thickness of said film to cause an ultrasonic acoustic wave to be radiated from said film, said first and second drive circuits having a common output; and a negative feedback circuit connected between said second section of said film and said common output of said first and second drive circuits, whereby the ill-effects of ringing in the piezoelectric film are substantially eliminated. - View Dependent Claims (10)
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Specification