Piezos

[bob]

Sture,


When you say that you tested a bunch of piezos, I was wondering if you have a list of their dimensions and resonant frequencies?


Also, how do you determine the resonant frequency? do you just apply a pulse and see what the output waveform looks like?


Thanks,


-Bob

[Sture Hultqvist]

Re: Piezos

I have tested:


3x5x14 mm around 600KHz


3x4x50 around 500KHZ


6x6x50 220KHZ


2x2x10 don't remember


3x8x40 620 KHz but different embedding.


circular 30x15 (151 KHZ)


The resonant frequency is mainly


the thickness but the crystals have resonances on


all dimensions.


As example the 3x8x40 was ordered to be


a 600KHz but was finally used at the 8 mm


resonances 180 KHz (as a experiment)


The frequency is also depending on wich material


the crystal is made of. I used medium hard wich


is the standard Pz5 or Pz27.


Further more the embedding in epoxy is also


a factor wich is difficult to calculate.


To find out the final resonat frequency I have


done som trial and error.... yeahh lots


of error.... sure...


Right now I use 3 mm thickness and 3 mm epoxy


and this gives me around 500Khz, I can't


measure the exact frequency since the SCR


pulse and the following ringing is difficult


to measure on.


To find the right thickness of epoxy I


put a crystal in epoxy and connected a


transmitter and a oscilloscope.


The Xducer was then put up with a reflector in


100mm distance and adjusted for maximum echo


strenght. Then I grinded off epoxy and looked


at the echo strenght.


The result was that the strenght follow a cos


function (what surprice) and I plotted by hand


thickness versus echo strenght and at 2.9 mm


I did have a good maximum.


Of course this is for my crystals and my epoxy


but probably it is very similar for other kinds


also.


Sture