Impedance analysis of piezo/pzt

[antknee]

I have some piezo's and some pzt. I'd like to be able to determine their in built impedance, how would I do that?

Essentially PZT is a mechanical system that has an electrical equivalent. I've attached a pic of their circuit. (Courtesy Unclejed, I believe he is also working on an impedance analyser circuit.)

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A commercial impedance analyser would cost a lot of money I believe, but what they can do is scan through a range of frequencies of the pzt and you find at their resonant frequency the impedance is least. So essentially I'm looking to calculate the impedance of a given piezo/pzt at resonance. It might be useful to determine from that what the resonant frequency of a given piezo is.

Any thoughts?

 

[Vizier87]

I suppose you're building your own sonar system? How about a local college EM lab? they must have all the equipment you need.

 

[Dragon Tamer]

He could also try winging it with calculations. Everything in electronics has a coresponding calculation of some kind.

 

[antknee]

I was offered that kind of help a while back at Leeds Uni, it was difficult to arrange, took months and months, and then I had to leave the area so it fell through anyway.

I am quite good at maths so I was thinking more along the lines of winging it

I'm building an ultrasonic atomiser.

 

[antknee]

I've just been looking to see what is the cheapest impedance analyser I could buy. I can't find any at all...

What would the piece of test equipment be called?

 

[Nigel Goodwin]

Use a frequency generator and a scope, why make life difficult and expensive?.

 

[antknee]

I have both. You are saying put a signal through the piezo with the signal generator and measure the voltage with the scope. In addition to the voltage I'd have to know the current to measure impedance? Piezo's are capacitive and without a drive circuit tend not to have much current. Wouldn't the current be hard/impossible to measure?

I like the idea certainly!

 

[The Electrician]

I've just been looking to see what is the cheapest impedance analyser I could buy. I can't find any at all...

What would the piece of test equipment be called?

They would be called "LCR meter". For example:

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Only US$7000

Or, used, on eBay:

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It would probably work ok to put a 1000 ohm resistor in series with your piezo element and monitor the voltage across the resistor with a scope as you vary the frequency from your signal generator. You should a marked change in voltage across the resistor at resonance. And this would be a lot cheaper than buying an LCR meter.

 

[antknee]

I have an LCR meter, its a handheld device which says not for testing live circuits or similar. It would be handy if I could have used that! I did find an impedance analyser brand new for £100 so I was thinking great! Then I checked the datasheet and it was for audio speakers, soprobably not much use at the 100KHz or so I'd want.

The Agilent LCR meters are more in line with the sort of cost I was expecting. That is the price of quite a decent second hand car/auto!

It would probably work ok to put a 1000 ohm resistor in series with your piezo element and monitor the voltage across the resistor with a scope as you vary the frequency from your signal generator. You should a marked change in voltage across the resistor at resonance. And this would be a lot cheaper than buying an LCR meter.

That is quite a decent suggestion. I will certainly try that.