Piezos

[Patrick]

Bob,


Did you decide on the freq you are shooting for? What size piezo do you think you'll order and from who?


If you are not sure, please post prior to ordering so I can order them at the same time.


Patrick

[Jan]

Re: Piezos

Bob,


And please state price.. or do you know, Patrick ?


Regards, Jan

[bob]

Re: Piezos

BEFORE WE GO ANY FURTHER, I FOUND ANOTHER ERROR IN THE CALCULATIONS FOR THE CHANNEL INDUSTRIES PARTS JAN IS CONSIDERING!


(Sorry, didn't want to sound like that guy Greg, but I wanted you guys to take note!)


I went to the channel industries web, and on page 9 it shows the WIDTH, not the THICKNESS of the element determining resonant frequency. (When using mode 2b) Therefore, the elements that Jan is considering will be resonant at ~150kHz.


Also, this changes the resonance of the 4 inch long in stock elements at Piezo Kinetics to about 300kHz.


This is a reasonable wavelenghth, but then I checked the vertical beamwith.. PROBLEM! (Unless I made a mistake, which would be great because it would make life easier...)


If the element is 4x.25x.082 inches, then the .082 inch (2mm) side would face the water. A 300kHz signal will have a wavelength of 5mm, so we would have a beamwith of 5/2 radians, or about 140 degrees! (see Sture's post under 'Beamwidth')


I poked around with the formulas, and to say it simply: Regardless of using the side firing or direct firing methods (Jan's way or Sture's way) and regardless of the vendor we get the ceramics from, we still come up needing a length to width ratio of about 1:1 to 1.5:1 in order to get vertical beamwiths of 60 to 90 degrees.


If we want to keep the 3:1 ratio, then we will have to live with a beamwith of 140 degrees. This would reduce range, and wierd things may happen at such a wide beamwith. At the least, I would want to get Sture's input before going ahead with a 3:1 ratio.


SO I guess we need to get some more equations that deal with length to width ratios that are less than 3, and are closer to 1.


Perhaps someone could contact Channel Industries and ask them how their equations for modes 2b and 4 change when the l/w ratio is less than 3, and closer to 1. (I would do it, but I am getting busy as I prepare for a trip next week.)


Sorry guys, but I'd hate to have us buy parts we can't use!


-Bob

[Jan]

Re: Piezos

Bob,


I got the sizes using the "EQUATIONS" button on Channel Industries webpage.


Assuming that there is no error in that code (hardly can believe that) the sizes should be correct.


I think I saw on other webpages also that thickness determines the frequency.


I will have a look again.


It would be pretty stupid if I made another mistake.


Will have to ask my mother for an upgrade of my brain... hehe (But she always says there is no garantee on her (un)handywork..)


Regards, Jan

[bob]

Re: Piezos

Please do check my math. As I said, I would prefer a mistake, it would make life easier!


-Bob

[Jan]

Re: Piezos

Bob,


I had a look at the webpage again.


If I use the "EQUATIONS" button I get the data I posted.


It shows also that the Thicknes determines the frequency.


However, the page you mention has a somewhat funny formula.


I find it very difficult to read the text properly


Does it say (1.06 N * n2)/w or (1.D6)/w ?


It does not seem to be a zero since the left side is straight.


Have not found D6 in the pages..


To be quite honest, I cannot make head or tail out of that formula.


I found an older email i have from Sture and there he mentions elements 6mm x 6mm x 50mm working on 220Khz


I tried that with the equations button but the frequency varies wildly when I use different materials. (300-450 kHz)


When you use your equation, do you then get to 220 kHz ?


Regards, Jan

[bob]

Re: Piezos

Jan,


On page 9, for mode 2b, it says (1.06 N)/w (actually N subscript 1 but I can't type that...)


The thing is, if you look at what w is in case 2b on the previous page, it is not the thickness, but the width.


(In the illustration, w is down to the left.. Thickness, t is higher on the right... This is not so easy to see.)


Using the Piezokinetics materials, with an n1 of ~1700 and an n3 of about 2000 give me somewhat higher frequencies.. (280 - 320 kHz, depending on the mode.)


Perhaps Sture is using materials with lower N values. I couldn't find N values for the channel industries materials or on the Ferroperm site. Do you or anyone have a way to calculate N from other constants??


-Bob

[Jan]

Re: Piezos

Bob,


I have no values for N


I have seen they use the width (w) but the N value does not say very much.


And, because its divided by w it would imply that w is the key factor to determine the frequency


Funny that their own calculator shows t (thickness) to be the frequency controling parameter.


Very confusing..


Best thing would be to ask Channel Industries.


But I would like to have some other prices to compare.


I had the idea that Channel Industries is more expensive as others.


I do not mind paying $32.50 per element, but if you can get the same elements for $4 ...


Sture mentioned also prices of about $10 per element and did not notice any difference between brands.


Regards, Jan.

[bob]

Re: Piezos

Jan,


By all means, ask them. They may have confused themselves with their own drawings!!


I would imagine that the width would control the resonant frequency. The way I figure it, the resonant wave will be bouncing back and forth along the width, and then shooting out the side.


I do think that 32.50 an element is a bit pricey.


Be aware though, that most manufacturers are used to dealing with much bigger orders than ours. I got that feeling when talking to Piezo Kinetics. They were polite, but I think they would have called back faster if I had a 1,000 element order! So, I try not to call too often.


Unfortunately, I have to sign off for a while. I will be back in 1 week. If I get acccess to a browser, I may be back sooner, but don't count on it.


In the mean time, remember what they say in woodworking.. Measure twice, cut once!


-Bob

[Sture Hultqvist]

Re: Piezos

Ouch....


I tried in a early stage to calculate my piezos and


nothing was theoretical predictiable unless you


are tech science doctor professor and higher and


can let a student do the work for you.


I simply tested a batch of piezos, around 10,


and just noticed what thickness gives what frequency.


This differ from material to material but the last


one I used is Pz27 from Ferroperm and 3mm gives


a frequency over 500KHz. The 6x6x50 with same


material gives 220KHz. It also differs if the crystal


is free or embedded in epoxy.


Sture

[rick]

Re: Piezos

hi guys--


not to push in but just to let you know--


there is an old text book at some library from


bell labs on ultrasonics..


included is some data on ferrites which can produce


ultrasonic energy (not sure how high of frequency vs


shape/size) but this is the 'ducer typical in


cavitators (ultrasonic mixer/blaster) rather than


a pzt or adp or quartz...thinking about it--


many years ago,they even had pictures/data on big


boat sonar stuff...they used adp xtals on a rubber


membrane etc.....


the ferrite phenomina was "magneto-striction" and


for big out power----this is the ticket...if my


memory is correct this is the place my eyes see


picture of a concave reflector to focus sound on


paper---make smoke/fire--


reg-rick

[help]

Treasure Hunting

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[Jim Kennard]

If there was no metalic content in the tupperware container then I would suggest that you may be able to locate it by using ground penetrating radar. See the Geophysical Survey Systems website for info and application information at: http://www.geophysical.com Regards, Jim