Author Topic: Piezos for Sidescan Array  (Read 3202 times)

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Offline sonarbear

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Piezos for Sidescan Array
« on: May 01, 2016, 09:53:32 AM »
Hi

I guess there is still no source for Sidescan piezos, correct? Only  broken ducers?
I was thinking about putting 20 each of those in a 1-wavelength array.
https://www.steminc.com/PZT/en/piezoelectric-disc-s-5x04mm-450-khz

What do you think? They seem so thin!

For the receiver I was looking at these guys:

https://www.steminc.com/PZT/en/piezoelectric-disc-5x02-mm-445-khz

I'd be thankful for every tip and comment.


Offline Rickard

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Re: Piezos for Sidescan Array
« Reply #1 on: May 01, 2016, 10:37:38 AM »
Hi,
There are places where you can find piezos, like Steminc. I searched all over the web some yeras ago and found a few manufacturers (some in mainland China), but prices were too high, given the small amounts I needed. It was as expensive, or even cheaper, to buy transducers and then cut them apart to retreive the piezos.

Are you planning for separate transmitter och receiver? The fishfinder transducers use the same piezos in both modes, so they are the same.

I think the circular piezos at Steminc should work. They must operate in radial mode because they are too thin to resonate at that frequency in thickness mode. 20 discs will result in a 100 mm array, plus a few mm for space between the discs (remember the not-more-than-half-wavelenght-between-elements-rule). Thus, it will perform like a standard HB SI or HDSI transducer when it comes to horizontal beamwidth. The vertical beam will be narrower than in the standard transducers.

Soldering on piezos is difficult, they say....

Rickard

Offline sonarbear

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Re: Piezos for Sidescan Array
« Reply #2 on: May 02, 2016, 12:41:44 AM »
So the regular ducers are 10 cm? Do you know how wide? 5 mm? I was also thinking about chaining salvaged downscan piezos.
Is radial mode ok for sonar?

Offline Rickard

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Re: Piezos for Sidescan Array
« Reply #3 on: May 02, 2016, 05:29:19 AM »
The sidescan elements in the SI transducers are 3,2 mm wide. The smaller the width, the wider the beam.

Radial mode is ok. The standard circular 200/50 or 200/83 kHz elements operate in thickness mode at 200 kHz and in radial mode at 50 or 83 kHz, so that mode should be ok. Maybe the Steminc discs will give weak signal, due to their thinness, I'm not sure. I guess the small volume should have some effect on amplitude.

Rickard

Offline sonarbear

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Re: Piezos for Sidescan Array
« Reply #4 on: May 02, 2016, 11:41:56 AM »
Thank you soo much for this information! Now I understand why they always have these two frequencies. I guess the 455 vs 800 kHz for the side imaging is the same idea, correct? I think the Steminc piezos are just described poorly. These are all radial mode frequencies. It kind of fits the diameter. The thickness mode must be very high. It's probably a better idea to buy a thick element and saw/mill it into narrow strips, fitting the desired beam width / frequency.
Do you have any experience about the piezo electric polymers? I've seen a patent on a side scan receiver, that had a circular emitter and a strip receiver from made from PVDF. That would probably be much easier to make. Is PVDF suitable for transmission or does it not work well for transmission? Has anybody tried?

Offline Rickard

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Re: Piezos for Sidescan Array
« Reply #5 on: May 02, 2016, 12:36:17 PM »
Quote
Is PVDF suitable for transmission or does it not work well for transmission? Has anybody tried?

I collected some info on PVDF and found it is not suitable for transmission. The reason is its so thin. One has to stack several layers to get any amplitude. It would be risky to connect a PVDF receiver to a fishfinder unit, because voltage can be extremely high if you just tap on the surface. One would need some kind of "lightning protection". The great advantage with PVDF is that you can cut it in any shape to control beam form. Also, its the ideal chirp material, since it can vibrate in any frequency.

The 455/800 kHz sidescan elements operate in thickness mode att 455 kHz and transversal mode at 800 kHz. Thus, they can vibrate in both frequencies at the same time, but that's not implemented in the units.

Offline sonarbear

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Re: Piezos for Sidescan Array
« Reply #6 on: May 02, 2016, 12:40:18 PM »
Interesting! Do you have a source for PVDF? I'm building my own system anyways, no problem if that burns through one day... But it will take a while until it's finished. Not enough time.

Offline Rickard

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Re: Piezos for Sidescan Array
« Reply #7 on: May 02, 2016, 01:10:43 PM »
I had a good source, but seems I have lost it. That source was filled with practical advice and suggestions. I will try to find it. Anyway, Airmar has their own product: http://www.airmartechnology.com/uploads/airpdf/pvdf_sm.pdf
There are many good academic papers on PVDF based devices. Just Google....

Offline Rickard

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Re: Piezos for Sidescan Array
« Reply #8 on: May 02, 2016, 01:25:47 PM »
Found my old PVDF source! http://emerald.tufts.edu/programs/mma/emid/piezo.pdf
Figures 32 and 33 indicate interesting workarounds to get better amplitude on transmit.
/Rickard
« Last Edit: May 02, 2016, 01:55:22 PM by Rickard »

Offline sonarbear

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Re: Piezos for Sidescan Array
« Reply #9 on: May 03, 2016, 01:18:38 AM »
Do you think there is any chance of getting these babies to emit sound?
http://www.technoplast-onlineshop.de/gruppe,mein_shop,de/Platten,plattenpvdf,42501,PVDF-natur

Too thick?

Offline Rickard

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Re: Piezos for Sidescan Array
« Reply #10 on: May 03, 2016, 11:02:49 AM »
Quote
Do you think there is any chance of getting these babies to emit sound?
I don't know. They seem to lack metal coating, though.

Offline sonarbear

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Re: Piezos for Sidescan Array
« Reply #11 on: May 03, 2016, 03:10:45 PM »
Yes. And I guess they aren't stretched. I'll get a sheet as I need it for work anyways as milling substrate and experiment with it. The coating can be easily done with silver paint. But I fear the stretching might be problematic. I'll then see if it becomes piezo electric and how much. Maybe already a receiving array would be nice. I can then just piggiback on my 898's signal and just receive. Let's see!

Offline sonarbear

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Re: Piezos for Sidescan Array
« Reply #12 on: May 18, 2016, 08:46:36 AM »
The sheet is not piezoelectric whatsoever. I guess one would need to heat and stretch it. Maybe some day...
I did get some of the piezo wire of MeasSpec, though. It does work, surprising. At 10 kHz there is a clear audible noise from the cable if driven at 20 Vpp. It also reacts well to shock. I'd say the effects of mechanical force vs. Voltage at 10 MQ are probably in the range of 1 order of magnitude below what a real 5 mm PZT disc puts out. So I guess I'll try to build a little amplifier and see if I can capture any signals from my HB unit in the water.


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