Advice on building first sidescan sonar

[Dave S.]

Hi, I’m looking for some advice on my first Sidescan Sonar project. I’ve been reading this forum and other information on home grown sidescan units I found on the internet. I probably have enough knowledge now to be dangerous!
My plan is quite simple, build a sonar tow fish and attach it to my existing Zercom LPG 2000. The towfish will be a simple transducer array with no electronics, and I plan to keep the cable short at about 25 ft. It will be connected directly to my existing LPG 2000 unit.
I have a line on some Piezoelectric transducer elements from a company in China (Annon Piezoelectric Co.). They are tuned for 200Khz and designed for sonar. Each is 25mm in diameter and approx 10mm thick. Has anyone had any dealings with this company? They are offering me these elements for $35.00 each, their apparent sample price. I thought this expensive but really have no idea if it’s a lot of money or not.
I plan to use 10 of these in a row, almost touching, for my array. The small 25mm width should give me a pretty wide fan and the 10 inch length should provide a pretty narrow beam at 200kHz. I think with the elements being really close together the side lobes should also be minimal?
I plan on wrapping a thin layer of cork around the circumference of each element and backing the entire array in cork. The whole thing will then be cast in epoxy resin to protect the elements.
Well that’s my plan! I’m looking for you guys to poke holes in it and guide me down the proper path. Don’t feel bad about being critical, I don’t know much about this stuff but am really keen and willing to learn!!

Thanks in advance for everyone's help.

[ApBerg]

Piezo elements

Hello Dave

Look at http://stores.ebay.com/PIEZO-LASERS-MEDICAL-AND-MORE

I have bought some, no problems.

regards

Ap

[ApBerg]

Sonar array

Look at http://www.beugungsbild.de/sidescan/sonar_index.html

Regards.

Ap

[Dave S.]

Thanks for your responses. I was wondering which Piezo elements you purchased from the STEMiNC ebay store. I looked at the 45Khz 50mm items and thought they might work. Will they work OK at 200 kHz.

I will also take a careful look at the website you directed me to. Looks like it has lots of good info on array design.

Thanks again.

[ApBerg]

Piezo elements

Hello Dave.

Well I think you are right, the elements I have bought from them are now not on there website, you need 200khz elements (look at the foto). You can mail them ....
I have also bought some 45 khz elements, with those I like to make a sounder/receiver that works only with audio detection. The receive signal into a sort bat detector system so you can hear the back coming signal. This way large Iron wracks can be detected at long rance. Working with a wesmar sonar you can hear wrecks on the audio output at the same time you see them at the display. Well the batdetector is working ok; summer evening, lazy chair, cold drink, listening to bats.....

Regards.

Ap

[Fred]

Hi Ap !,

Nice links!,
On the ebay store i see no mention to power that the piezos can handle, do you think they will be OK ?
I have made experiments with a 3kw pep sounder,and a defective sensor, there was arcing between leads.
Best regards,
Fred.

[Dave S.]

Hi AP, Thanks for your reply. I think I have found elements that you have on the STEMiNC website. They are tuned for 200 kHz through the thickness and are 44mm in diameter and 10 mm thick. I emailed the company and they don't have any available right now but expect a production run in the next few weeks. $27.00 each, not too bad a price.
Thanks again.

[Rickard]

Link to sonar theory

Hi,

If you need some theoretical background for designing arrays this is an excellent source:

http://www.omg.unb.ca/GGE/JHC_courses.html

After some searching one can find PP-presentations used in courses on oceanography. The presentations are zipped and you have to unzip each slide individually. I can guarantee it's worth the effort! This was the main source in my own project on simulations of beam patterns.

Arcing can be a problem since the output voltage can be higher than 1000 V on some instruments (e.g. Humminbird). I think you should consider the method used by Sture Hultqvist for fixating the piezos. He mixed epoxy and cork to obtain a material that could both insulate and fix the piezos. Stures methods can be found in the forum archive.

Perhaps I should mention that Sture passed away in august last year. He was probably the most skilled amatuer sonar constructor known to this community.

Regards
Rickard

[Fred]

hi,
Commercial sensors for echo sounders have a piece of foam on the back of the element,same size of the element, around 2-3mm thick,(to allow oscillation i suppose), and epoxy all over.
Regards,
Fred.

[Dave S.]

Thanks for the link Rickard. I'll search through and see if I can find the info you reference. The main campus of UNB is about 30 miles from where I live and my son is enrolled in engineering there! I have dismantled a few old commercial transducers and noted the cork behind and around the circumference of the elements. It looks like it plays an important role in the functioning of a transducer.
I'll also try to find Sture's method in the archives.

[Dave S.]

Thanks for the tip Fred. I getting anxious to get my elements and start building.

[ApBerg]

Hello Dave.

Have you some photo's from the transducers you have dismantled.

Regards.

Ap

[Dave S.]

Hi Ap. The transducers wern't sidescan arrays, just through hull transducers for fish finders. I have the parts of one of them if you are still interested I can take a few pictures and post them.

[Dave S.]

transducer pictures

Here are a few pictures of one of the transducers I took apart. It was old in the mid 80's when it was given to me but they haven't changed much. The cork is about 2mm thick and the Piezo is 51mm diameter and 10mm thick. The window was some sort of black plastic 2m thick (not pictured). The window didn't appear to be glued to the Piezo?

[ApBerg]

Thanks Dave for the foto's, it is looks not so hard to make, the transducer looks mutch at the one's I had bought from STEMiNC.

regards.

Ap