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Limits on Pizeo buzzers

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Weston

Tue Feb 24 2009, 03:47AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

I am planing on building a VERY loud buzzer by driving a pizeo disk as part of a resonant circuit. What is the limiting factor for pizeo material at high powers, overheating of the disk, or the flexing causing the disk to crack? Also how high a voltage can pizeo material withstand with out breakdown? Thanks

aonomus

Tue Feb 24 2009, 04:02AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

As far as I know, a piezo is electrically equivalent to a small capacitor, so you may get some heating at higher voltages, but at that point you may suffer from the piezo material breaking down (as a dielectric), or the material would just crack apart...

You could always try getting your hands on a few and running it through a function generator with a class D amp on the end, and increase the power.... I myself would like to see how much power one could take.

Weston

Tue Feb 24 2009, 04:22AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

Is my idea feasible though? Running the pizeo in parallel resonance for higher current?

Proud Mary

Tue Feb 24 2009, 04:39AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

You'll never get much out of those things before they fail.

But have you considered magnetostriction? A transformer core hums because the laminations are expanding and contracting with the alternating field.

Hugely powerful magnetostrictive transducers have been built in the past for such work as submarine sonar detection, and in essence are not much more than a ferromagnetic rod with a coil round it - a solenoid.

The real engineering is in the acoustic coupling - the impedance matching between the minute but powerful contractions of the soldenoid and the sea water. Using one in the air would also require an acoustic coupler of your own invention, as well as cooling! It would probably look something like a loudspeaker cone!

TwoSpoons

Tue Feb 24 2009, 04:45AM

Registered Member #1621 Joined: Tue Aug 05 2008, 05:26AM
Location:
Posts: 19

If you are running a single frequency attach the piezo to a helmholtz cavity. I've achieved 100dB at 10cm, 4kHz, driving a 30mm piezo with 10V.

Proud Mary

Tue Feb 24 2009, 04:50AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

See: Magnetostrictive Versus Piezoelectric Transducers For Power Ultrasonic Applications

mikeselectricstuff

Tue Feb 24 2009, 10:16AM

Registered Member #311 Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253

The possible failures are de-bonding of the ceramic from the brass disk, cracking of the ceramic and electrical breakdown which tends to erode the conductive coating on the back of the ceramic.

The way that the disc is mounted and the acoustic cavity makes a huge difference in output - in particular the exact way the edge is supported - clamping force, type of glue etc. For maximum output you want to drive it at resonance with either a square wave from an H-bridge driver.
An open-collector drive with a parallel inductor is a useful cheap way to get high output at lower supplies, but you won't get max output this way.

GeordieBoy

Tue Feb 24 2009, 01:20PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

If I remember correctly, the piezo sounder already behaves like a series resonant RLC tank circuit electrically, that has an additional larger capacitance connected across the terminals. This additional larger capacitance is the DC capacitance of the two conductive layers with the ceramic dielectric between them.

The effective series LCR circuit arises because of the mechanical resonances that Mike mentioned, and is presumably influenced by the surrounding acoustic cavity too.

My limited experience as sounders in electrical products is that when driven at the acoustic resonance they are quite loud, and when driven at any other frequency are very weak.

-Richie,

lhl_henrylui

Tue Feb 24 2009, 02:35PM

Registered Member #1498 Joined: Thu May 22 2008, 07:08AM
Location: Hong Kong
Posts: 72

I tried driving a piezo by a 3V,10kHz signal.When the voltage rised to about 15V ,the loudness droped suddenly.

Marko

Tue Feb 24 2009, 06:13PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I've tried to use one of those toy/postcard piezo speakers to reproduce that cool water mistifying effect by feeding it few tens of W at 1Mhz. The piezo failed in a way that the ceramic overheated and cracked in many places, severing the thin silver layer and causing it to arc until all electrical contact was broken. The piezo was submerged in water with RF silicone coating insulating the back, but despite that it seemed to overheat way too quickly.

Marko

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