Transducer bar or no bar?

[bob]

I was initially interested in using a steel bar to align the transducer elements, but then Sture explained that they detached in the transducer he examined.


I guess the reason I didn't want to use a cork backing was the need to keep the elements aligned to .1mm might be hard with a soft material like cork.


Sture said that he was able to get good attachment to a steel bar using a different glue. Perhaps there are newer adhesives out there that will hold up well.


Another idea might be to put a bar in front of the crystals, that could help match the acoustic impedance. If it were an insulator, 2 leads would still need to be soldered on, but if it were a fairly stiff material, we would still get the alignment benefit.


Finally, if we did use a steel bar, a redundant lead could still be connected to the element, so it would still be connected electrically, even if the glue failed.


Just some thoughts.. perhaps others have some ideas..


-Bob

[Sture Hultqvist]

Re: Transducer bar or no bar?

Aligment of the crystals again I have done a


transducer where I used a plastic fixture.


The plastic piece is fixated on a metal piece and


then milled to have a U-shaped pit with tiny corner


on each side to put the crystals on. Then I covered


it with epoxy just from the bottom up to the top


of the crystals. When the epoxy hardened I removed


the array from the plastic. The result was a epoxy


bar with embedded crystals. The epoxy bar is the acoustic window.


This was then embedded in cork and


then filled up with some resin in a U-shaped metal piece.

[bob]

Re: Transducer bar or no bar?

Sture,


This sounds like a great idea, but I am a little confused.. (A picture would be great, but it's ok if you are away from the equipment!)


Does the ultrasound go through the epoxy in normal operation? What kind of epoxy is it.. Aren't you concerned that it will act as an absorber?


Also, about using Conathane EM-9.. I have an artist friend who makes tables that are covered in a thick acrylic. He applies the mixture, and then uses a hair dryer to get the bubbles out. When the hot air hits the acrylic, it becomes like water and the bubbles come to the surface.


Do you think you could do something similar with EM9?


Is it opaque, or can you see the bubbles? also, in your design, how thick is the EM9? (The hair dryer might not work if it is too thick) Does the manufacturer say what the maximum temperature of EM9 is? Perhaps the hair dryer would be too hot!


-Bob

[Patrick]

Re: Transducer bar or no bar?

Bob,


That is an interesting comment on using a hair dryer. Specs state that you have a 70 minute working life with the material, but I would think the dryer would cure it that much quicker.


It certainly is worth a test (without the elements).


Patrick