Materials for transducers

[bob]

Tod has generously offered to order some crystal sheets in bulk, which will save us (me anyway) having to to locate and perhpas pay more for the crystals.


I am planning on building transducers using the metal bar concept that Sure discussed. Here are some other materials I was planning on locating.. If anyone has ideas about where to get them or wants to do a bulk purchase, I would again be interested..


-Conathane EM-9 (I have ordered a data sheet online from Conap)


-Metal for substrate bar. Sture talks about .1mm tolerance, which would not be so easy for me do do. Anyone out there have access to a milling machine? Perhaps we can help each other out!


-Conductive Expoxies. Perhaps Conap can help here..


-Ultrasonic absorbing materials. Hopefully the folks from Conap will once again be helpful, but I would love to hear other ideas.


-Case materials. Maybe there is a rugged material that will also absorb ultrasonics, so there would be one piece that acts as both an absorber and case, but if not, we will need a separate material. I will let you know what I find out.


If anyone knows of good materials in any of the above categories, and/or where to find them, please post!

[Tod]

Re: Materials for transducers

Bob,


I was planing on having the manufacturer cut the ceramic to size. The thickness is important because I think that controls the frequency. I would like to shoot for 500. The ceramic is surrounded by cork on all sides except the output side. Than it is mounted on the steel bar, so the solder can have a relief cut in the cork . The cork lets the ceramic expand and contract to make the wave. I have a full machine shop so I can cut the steel for any one that needs it done. I also think I can find the steel locally. I would like to decide on the dimensions for the ceramic soon so I can order them.


Tod

[Sture Hultqvist]

Re: Materials for transducers

I have tested lot of materials and one of the best


absorber i found is cork mixed with epoxy. I put


cork sheets for gaskets to the car into the kitchen


mixer. From this I have somthing looking like sand wich I mix togheter with epoxy. The cork will float


a little but anyway it works fine.


Conap Conathane EN-9 is little tricky to use. Be very


careful to follow the manufactures instruction. With


Conathane it is not neccesery to tune the aqustic window to a odd number of 1/4 wawelengths thickness.


The acoustic impedance is very close to water. The difference is only a few percent.


In medical equipment there is mixed layer acuostic


windows for higher efficency. Since the crystals have


a impedance of around 30 MRayls and water have 1.5 there are a mismatch. With multilayer windows where each layer have a carefully choosen impedance the


matching can be improved. I have not seen this on any


sidescans .... yet


Sture

[Jan]

Re: Materials for transducers

Tod,


Do you happen to know the Volts/Newton figure these elements will produce ?


I suppose the higher that number the more output we will get from the echo's


I did some checking and found a number of .12 V/N for a 508 kHz element. (it depends on the material used)


regards, Jan

[Patrick]

Re: Materials for transducers

Sture,


Why is "Conap Conathane EN-9" tricky to use?


Patrick

[bob]

Re: Materials for transducers

Tod,


If you want to get your crystals tomorrow, please don't let me hold you up, but I think I will wait a bit. Here is my thinking..




As Sture thinks that 200 - 250KHz might be more ideal, and lower frequencies will have greater tolerance, I would prefer to start working in that range.


Also, Sture uses a width to thickness ratio of 4/3, whereas you appear to be using a ratio of ~2.5 to 1. This seems a bit wide, which will give a narrower vertical beam width.


I called Piezo Kinetics, to see what they had in stock that would be a little thicker, and/or closer to the ratio Sture discussed. I asked about a 3x4mm rod and a 6x8mm rod. (Perhaps you think other dimensions would be better..)


If you can wait until I get a reply, perhaps we can get a better deal by ordering together, but as I said before, if you are excited about moving ahead, I completely understand!


-Bob

[bob]

Re: Materials for transducers

Sture,


How would we use multilayer windows? how much do you think it would increase the sensitivity?


Your absorber idea sounds very easy to use. How thick must your mixture be applied to effectively absorb the ultrasonic energy?


Also, how much cork and epoxy do you use? Is it mostly cork, or mostly epoxy, or is it evenly mixed?


-Bob

[Patrick]

Re: Materials for transducers

In reference to the case ... could you use Delrin? It is very easy to work with and you can buy it in flat stcok and have it machined.


What is the case typically made of?


My two cents worth,


Patrick

[Sture Hultqvist]

Re: Materials for transducers

It hardened quickly and it is difficult to


remove the small air bubbles. The manufacturer


recommend degassing with vacuum.


It should be mixed at 40 degrees celsius.


Sture

[Sture Hultqvist]

Re: Materials for transducers

No


I have not learned how to use this properties.


Sture

[Sture Hultqvist]

Re: Materials for transducers

I have used Delrin myself and it is very nice to work with. I have not tested the acoustic properties but


I guess it behav similar to Polyetene wich was


somewhere between "window" and "absorber".


Sture

[Sture Hultqvist]

Re: Materials for transducers

I have not done any multilayer window myself..yet


The cork and epoxy mix, I filled as much cork as possible into the epoxy.


Sture

[Tod]

Re: Materials for transducers

Bob,


I'll be glad to wait. If someone does electronics for that frequ I'd like to be included. By the way I got the dims from Piezo Kinetics. Thay supply that crystal to someone els that makes sss's.


Tod

[Patrick]

Re: Materials for transducers

Tod and anyone else,


What frequency are you guys interested in?


Patrick

[Tod]

Re: Materials for transducers

Patrick,


I like closer range, finer detail. I work in 30 to 80 feet of water. I like 500 Khz. Bob I think likes 250.