Transducer arrays?

[tohu]

Hehe, thanks!

After a gluing incident the array looks worse than ever. Some of the PZT(?) has fallen off and some of the remaining have been covered in tin...

However, using a laptop and a microphone I was able to measure the main beam to somewhere between 14 and 28 degrees wide (and sort of 140 degs high), but this was in our living-room so I had to use a low strength signal to reduce the scattered reflections off our furniture...
It is also important to note that I have no idea what the specs of the mic are. It's the mic of a simple Logitech headset and it probably isn't ideal for picking up the 15kHz signal I use...

I spaced the elements a wavelength apart (11mm), if possible I'll try to put them next to each other and see if I get a different result. It is also important to test the characteristics of a single element.

I've ordered a bunch of new elements to make further tests with more than three (and I may even use better tools to cut them, free-hand with the dremel isn't the best way to go about it).

I've been thinking about turning the brass(?)-side outwards (way thicker than 1/4-wl, but what the heck) and adding an inch or so of plaster to the side with the element, any thought on this? Do you have any hints-from-the-pro, GLB?

[Francisco Xavier]

One very important thing to have success assembling SSS transducers is to to isolate the sides and top of each piezo with cork some kind of sintetic foam avoiding the sound pass thru the sides or background making it ringing or interfering.
The piezos just must emit to the sound window faced to the water.
Some years ago Sture e-mail me to answer about if would be advisable to glue all the sound window faces of the piezos on a steel ruler and He advice me to not glue once the reception gain incrase would be minimized by ruler ringing tendence (bell effect).

Good success,

Francisco

[tohu]

Yeah, that is absolutely right. I think that glueing them to an aluminum plate like I did really didn't help at all since the entire aluminum plate is resonating.
The signal was just as clear/high on the backside of the array. I glued some foam to the backside to stop that but from what I've read elsewhere they should ideally be backed by something having the same characteristics as the piezo-element itself, thus my idea of using plaster/cement...

Do you think it would be a good idea to suspend the entire array in some sort of rubber to keep the hull from resonating?

[PerAmpére]

Keep up the good work...

Hi tohu and everyone else.

I've been looking into the same buissness as you for a while but haven't had time to complete my project.

A few months ago I bought 30 Pcs of the Piezo Ceramic Discs 15x0.9mm from STEINER & MARTINS, INC. http://www.steminc.com/
They have a frequency constant of 1950 in thickness mode and 1980 in planar mode.
This gives a resonance at 2,16 Ghz in thickness mode and 132 Khz in planar mode.

But 2,16 Ghz does not sound very interesting for a sonar transducer....
... but that is not a problem. You can use a combined mode where the piezo is working in planar mode and additional mathching layers are working in thickness mode.

So you need to make a sandwich with a matching layer at the front and tha back.
The material in front should have a fequency constant between water and piezo and it should be 1/4 wavelenght thick. Additionally you could add another 1/4 wavelength of epoxy on that as a window.

On the back there should be another layer of a material with a frequency constant preferably higher than that of the piezo, also 1/4 wavelenght thick.
As backning/damping you can use cork as suggested or rubber (NOT syntetic rubber).

I will try to make some experiments later this summer....
Also got some schematics for a sounder/generator and ideas of how collect the data back into a laptop which I can share when I find them...

Good luck.