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Connecting a piezoelectric transducer

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Eight

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Hello.

I've been looking at some piezo elements with their driving circuits online, and I'm puzzled by a few things. A piezo element is supposedly a capacitive load, and, according to some forum posts, the polarity doesn't really matter. The manufacturers normally specify their rated peak-to-peak voltage. Now, suppose I have a driving circuit, which generates a 16Vp-p 50% duty cycle square waveform at 1 kHz. Assuming the piezo transducer is rated for this voltage, I'd like to feed the given waveform to the element, but I'm mystified how to correctly connect the device.

Should I connect one end to the driving circuit and the other to ground? Or should I create a low-impedance virtual ground at +8V in place of the normal 0V ground (or rather use a square wave generator i.e. a full-bridge that generates output from -8 to +8V in respect to the ground rather than 0V to 16V range)? See the attached picture. In both cases the element will be driven by a 16Vp-p range, but the mean voltage will shifted by 8V down to ground, allowing negative voltage to appear on the piezo element.

What is the difference in performance when driving a piezoelectric transducer in the two given ways?
 

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  • piezo.gif
    piezo.gif
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There's no difference as long as the applied voltage is considerably below the maximal permitted DC voltage level. Otherwise depolarisation of the piezo can happen.
 

A piezo transducer strongly resonates at a frequency between 3kHz and 6kHz. If you feed it with a 1kHz squarewave then most of its output will be at its odd harmonic number of 3kHz or 5kHz.
 

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  • piezo speaker.PNG
    piezo speaker.PNG
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