Author Topic: Longer array and narrower beam  (Read 58761 times)

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Offline Rickard

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Longer array and narrower beam
« on: September 08, 2009, 06:37:13 AM »
Hi,
I want to build SI arrays which are longer and have narrower beams than the original HB transducers have (they are about 1.5 degrees at -3dB and 455 kHz). Therefore I need piezos which match 455 kHz. I have tried contacting the technology development people at HB but they are not responsive. Does anyone have any ideas on where I can get hold of suitable piezos? A plan B could be retrieving piezos from broken SI transducers, but my own transducers are all still functioning (does anyone know how many SI elements there are in one array in the SI transducer?), so a plan C could be joining two transducers into one super-ducer twice as long as the original. (This would involve grinding away material from the transducers to bring the piezos close enough together while hoping the transducers have the same internal dimensions. ???)

Why?
SI arrays operated at 455 kHz with about 0.7 degree -3dB main beams would have good range performance and they would extend the area covered at a specific horizontal resolution four times when I do 360 degree scanning under ice. (When moving in a straight path the area is doubled so in normal scanning this improvement is less important). Also, if the 262 kHz channel can be used the image will have better resolution than the original transducers give at 455 kHz. Any comments are welcome, even those which will kill the project instantly!   :)

Rickard


Offline keizerh

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Re: Longer array and narrower beam
« Reply #1 on: September 08, 2009, 10:33:33 AM »
Did you contact airmar already?
They have european headquarters in Birkerod Denmark.

hendrik

Offline Rickard

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Re: Longer array and narrower beam
« Reply #2 on: September 08, 2009, 12:30:45 PM »
Thanks Hendrik,
I have looked through their website but there seems to be no product that fits my needs. They have a custom design page where you can fill in an inquiry, perhaps it could be worthwhile trying that.

Rickard

Offline keizerh

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Re: Longer array and narrower beam
« Reply #3 on: September 08, 2009, 01:14:09 PM »
Not everything they build is on the site.
I know the build sophisticated ones as wel. The fased-array from interphase is also theirs.
You can give it at try at least.

hendrik

Offline Humminbird_Greg

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Re: Longer array and narrower beam
« Reply #4 on: September 14, 2009, 11:38:06 AM »
RadarSonics is also a transducer manufacturer.  Not sure where they are located out of or if they have an overseas (to me at least) facility or not but may be worth checking.
http://www.radarsonics.com/

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline Kimi

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Re: Longer array and narrower beam
« Reply #5 on: December 22, 2010, 12:03:51 PM »
Here is an interesting link about this subject!

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


Kimi..
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Offline Rickard

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Re: Longer array and narrower beam
« Reply #6 on: December 22, 2010, 12:47:33 PM »
Kimi,

Yes, it's interesting and it was the source that made me develop beamform simulations myself. I have built several arrays based on the idea that unequal spacings between elements will suppress sidelobes. However, I couldn't confirm RenÚ's results in my simulations and in the end I contacted Institutt for informatikk in Oslo and they confirmed my suspicions that something was wrong with RenÚ's results. RenÚ put in a comment on this on his homepage in 2007. The sparse array concept is as old as radar and sonar theory and it has been shown that only minor improvements are possible with this method.

Despite that, I built a few experimental arrays with unequal spacings in order to see what happened in reality. These projects have been reported here: http://www.geotech1.com/forums/archive/index.php/t-13311.html
(unfortunately, the images disappeared when the forum moved to a new host)

I knew that full suppression of sidelobes require less than 1/4 of a wavelength spacing between the elements, so I finally made an array with that feature: http://www.xumba.scholleco.com/viewtopic.php?t=778
Thus, it is possible to build a working sidescan array using fishfinder transducer.

Nobody engages in these kinds of projects anymore, the HB SI units have made them unnecessary.

Now, as this thread has become active again, I can't resist disclosing my Christmas project, I will try to join two SI transducers into one long transducer. If that fails, next step is retrieving the piezos and build a long transducer from scratch. The brand new transducers are already in my drawer. :)

Rickard
« Last Edit: December 22, 2010, 12:59:25 PM by Rickard »

Offline Jolly Roger

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Re: Longer array and narrower beam
« Reply #7 on: December 23, 2010, 04:13:30 AM »
Now, as this thread has become active again, I can't resist disclosing my Christmas project, I will try to join two SI transducers into one long transducer. If that fails, next step is retrieving the piezos and build a long transducer from scratch. The brand new transducers are already in my drawer. :)

Rickard

 :o  :o
Allthough this talking about sidelobes and arrays and stuff is way over my head (not only the English), I understand that you're planning to butcher two brandnew transducers, right? Holy smoke!

I'm curious to see your results and wish you all the best and success Rickard. Keep us posted about the outcome  ;).

Best regards and merry Christmas

Harry
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Offline Rickard

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Re: Longer array and narrower beam
« Reply #8 on: December 23, 2010, 06:59:10 AM »
Thanks Harry,

Yes, I will 'butcher' the transducers, but first I will only drill a few holes down to the piezos to verify that the internal positions are similar enough to permit joining the transducers without too much destruction (the magical figure 1/4 of a wavelength (about 1 mm at 455 kHz) comes in here, precision must be better than that). If this is possible the transducers will be possible to fix afterwards if I regret the whole project. If, on the other hand the transducers differ too much the complete butchering is unavoidable.  I will be back with reports on how this develops. Now, there will be a few days with celebrations with relatives so the sonar projects take a rest.

Merry Christmas Harry!

Rickard

Offline sonar2000

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Re: Longer array and narrower beam
« Reply #9 on: December 23, 2010, 07:15:08 AM »
While this takes considerable skill above most of us,  the end product may be something to consider. Should this venture prove successful in all ways then you might want to consider getting the individual components and building from scratch.
You very well may be onto a new innovation.
As Harry said this is way over a lot of us but that is not to say it is not interesting and exciting.
Good holidays and let us know when you are back on the project.
Chuck (sonar2000)
« Last Edit: December 24, 2010, 07:09:21 AM by sonar2000 »

Offline Kimi

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Re: Longer array and narrower beam
« Reply #10 on: December 23, 2010, 02:28:04 PM »
Nobody engages in these kinds of projects anymore, the HB SI units have made them unnecessary.

Thats true, life goes easier that way, but in otherhand.. I give my full respect to these DIY guys who show us how things could be done, and made.

As Harry said this is way over a lot of use but that is not to say it is not interesting and exciting.

Exactly! But knowledge is not "heavy to carry". Ewen If we could know just a little bit moore each day, it helps us to understand how our equipment relly works.

Thanks Rickard.

And Merry Christmas to eweryone!


Kimi..

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Offline abraquelebout

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Re: Longer array and narrower beam
« Reply #11 on: December 23, 2010, 03:38:24 PM »
interresting subject rickard
i have not book or paper who speak about this, my poor inglish don't let me understand technical revue.
if you want 455 khz piezzo why don't you take this transducerila_rendered
it's the SH-B06T
he work in 455 khz but not 800 (i make experience)
262 khz may be a good solution to take larger scaning ??
merry christmas to every one

Offline Rickard

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Re: Longer array and narrower beam
« Reply #12 on: December 24, 2010, 06:00:20 AM »
I will use the older transom mount SI transducers with 262 and 455 kHz. Making a long transducer will not qualify as a new invention really, joining two transducers is just a practical(?) way of getting one. The basics in sonar theory are actually very simple. They are just applications of wave-theory. I learnt these basics by going through the material here: http://www.omg.unb.ca/GGE/SE_3353.html
I can guarantee you will have a number of very interesting hours if you go through the presentations!

Now they are calling me to the Christmas dinner table! Merry Christmas all!

Rickard
« Last Edit: December 31, 2010, 05:27:54 PM by Rickard »

Offline Rickard

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Re: Longer array and narrower beam
« Reply #13 on: December 31, 2010, 05:22:56 PM »
First step

Transducer no 1 has been cut and left and right array of piezos can be seen from the rear. The piezos are 5 mm thick and 6 mm wide, length is unknown. The piezos on left and right side are not positioned with exactly the same distances to the walls of the housing. The error is about 0.5 mm but less than the critical limit 1 mm. As shown in the photo, sound must travel through two types of resin, some kind of flexible epoxy and PVC before water is reached. The dimensions of the piezos are difficult to relate to the resonance frequencies, 455 and 262 kHz. 455 kHz is probably the resonance frequency in the thickness mode and 262 kHz is possible to get as the first overtone in a piezo that is about 26 mm long. This leaves room for a third frequency, about 380 kHz in the transverse mode, but this frequency is not presented as an option in the instruments. I had to sacrifice temp because the wires were impossible to avoid when cutting. The inner walls of the housing and the cork-insulation of the piezos have copper shields. This shield can prevent from some electrical interference, but I think it also provides a radio shield that stops radiation emitted from the piezos.

Next step, cut the other transducer and compare positions of piezos with transducer no 1. This comparison will tell if the transducers can be joined and (hopefully) work as one long transducer

Rickardila_rendered

Offline sonar2000

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Re: Longer array and narrower beam
« Reply #14 on: December 31, 2010, 05:32:21 PM »
Very very interesting. Glad you have the transducers to cut apart.  Too bad that Humminbird would not send you two transducers unassembled for you to play with.  Every one could have benefited from this project. If successful you may have to go into a production mode. Unless HB wants to hire you... ::)
I watched the transducers being assembled in Eufalua at the HB plant.  It would have been very nice to have all the components apart and to start from the beginning to join.
Best of luck on this and please keep us informed on your progress.
Great effort and work on your part..
Chuck

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Re: Longer array and narrower beam
« Reply #15 on: December 31, 2010, 06:07:42 PM »
Chuck,

I tried with the technology development folks but bureaucracy prevented them from sending me parts. HB has tested long transducers, but they didn't help the images enough in regular use so they dropped the idea. Since I have rotation scanning under ice in mind I can expect much better results with a long transducer. This application is not common enough to motivate serial production, I think.

Rickard

Offline Del

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Re: Longer array and narrower beam
« Reply #16 on: January 01, 2011, 02:42:05 AM »
Rickard, i think you smashed your warranty  ;D


No seriously, this is really really interesting and i hope you'll get some positive results! I just started going through the link you provided, and to me its "heavy stuff" but its giving some ideas and even if i don't understand all of it (both, sense and language) it really helps to understand the technology. Thanks a lot for sharing your informations.


Happy new year,
Del

Offline Rickard

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Re: Longer array and narrower beam
« Reply #17 on: January 01, 2011, 01:27:04 PM »
First setback

When exposing the front end of the second transducer a problem appeared, cables are routed in front of the piezo and they seem to be impossible to reroute because of no space between piezo and housing. I have to uncover the rear of the second transducer like I did with the first and join the rear ends instead. One transducer will be oriented backwards in the final long transducer and the sidescan channels must interchange in the backward transducer.

Rickard
ila_rendered

Offline Jolly Roger

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Re: Longer array and narrower beam
« Reply #18 on: January 01, 2011, 03:23:45 PM »
Rickard,

you're unbelievable!

My deepest respect and best wishes for your project. Keep us posted about your progress.

Regards / Harry
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Offline sonar2000

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Re: Longer array and narrower beam
« Reply #19 on: January 01, 2011, 03:24:27 PM »
Sure glad you are in the builder's seat of this project.  I can see some applications for this if successful which are beyond fishing.
Recovery of victims or other submerged items when the surface is ice covered may help the teams with safety if the target can be seen before divers enter the ice hole.
Keep us informed.  And goodluck.  I hope you will get some assistance with the project.
chuck

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Re: Longer array and narrower beam
« Reply #20 on: January 02, 2011, 03:13:18 AM »
hello rickard
interresting thing, why don't you use medical radiography to see the interior of the transducer ??
i contact one of my friend if it's possible...

Offline Rickard

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Re: Longer array and narrower beam
« Reply #21 on: January 02, 2011, 05:10:34 AM »
Hi,

I have thought about x-ray but have no such resources here. Today I cut the rear end of transducer no 2 and found that the internal positions of the sidescan piezos differ from the positions in transducer no 1. The right array, as seen from behind, is mounted too close the housing, it almost touches the wall. This means the left and right arrays are at least one mm farther apart in transducer no 2 compared to transducer no 1. Also, the right array is located about one mm closer the front than the left array. I think I have to conclude that the precision inside the transducers is too low. I'm afraid it's not possible to join these transducers and expect a high quality image. I will think this over now before I go ahead and cut up the transducers to retrieve the piezos.

The photo is from transducer no 2. Note that the right piezo is very close the housing.

I'll be back
Rickard
« Last Edit: January 02, 2011, 05:13:22 AM by Rickard »

Offline Jolly Roger

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Re: Longer array and narrower beam
« Reply #22 on: January 02, 2011, 06:02:07 AM »
Rickard,
check your PM box.

What sort of plastic is in the housing to keep the piezos in place. Can it be disolved by some solution or other chemical stuff?

Regards / Harry
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Offline Rickard

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Re: Longer array and narrower beam
« Reply #23 on: January 02, 2011, 07:56:19 AM »
Harry,

Thanks for the PM. The opaque plastic inside the transducers smells like burnt rubber when I cut it, perhaps that's a clue for what type of compound this is? Acetone will probably dissolve everything, including the insulation of wires. I will try carving in the first place, that will save the wire insulation and it will likely be a quicker method.

Rickard

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Re: Longer array and narrower beam
« Reply #24 on: January 02, 2011, 08:10:01 AM »
Quiet tricky what you are doing Rickard, my deepest respect!

I'm confident that you will take your time to get the "rubber" out. Working with tiny wires needs patience and a long breath  ;).

I'll keep my fingers crossed.

Regards / Harry
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Offline abraquelebout

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Re: Longer array and narrower beam
« Reply #25 on: January 02, 2011, 09:57:45 AM »
i contact my friend who work on hospital, he must make the x-ray picture of the transducer
this week  :D...i'm waiting ;)

Offline Bob B

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Re: Longer array and narrower beam
« Reply #26 on: January 02, 2011, 12:16:38 PM »
Rickard, I don't want to open a "can of worms", but to what extent would the deviation in piezo placement affect the si transducer performance?  :-\
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Re: Longer array and narrower beam
« Reply #27 on: January 02, 2011, 01:41:21 PM »
Bob, here comes the worms :)

It's hard to tell exactly what the practical effect will be. There are at least three separate errors in this case. First, the piezos won't line up in a straight row, at least not on one side. Second, there will be a 1.5 - 2 mm shifting sideways in the middle of one of the arrays. Third, a 2 mm gap will occur between the middle piezos in one array. These errors may be acceptable at 262 kHz but at 455 kHz I believe they will cause ghost images and blurr. It's possible to calculate the precise loss in sidelobe suppression for simple cases like a 2 mm inter-piezo gap, but my simulation program is in a computer 900 km away from here.

But perhaps we will see what these errors really mean because my present idea is to join the transducers after all and line up a perfect(?) array on one side and let the other side take all the errors. Then I will have a good channel and a bad channel and we can inspect the practical difference. The joined transducer can also be run with a long array (right channel) and a normal array (left channel) at the same time and even the practical difference between normal and long good arrays can be observed.

Rickard


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Re: Longer array and narrower beam
« Reply #28 on: January 02, 2011, 01:57:53 PM »
Thanks for the response Rickard.

I studied electronics and communications in my youth, so I have somewhat of an understanding of wavelength interactions, but my knowledge is very old and not used in a long time.  Just started wondering if the accuracy of putting the transducer together might explain why some people are able to achiever better images than others.

I do find your project very interesting, but definitely don't want to kijack your post and put it in a different direction.

I had actually came back to delete my previous post but you had already responded.
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Re: Longer array and narrower beam
« Reply #29 on: January 03, 2011, 01:02:05 AM »
Bob,

Your question does not mean you are hijacking the thread, it is fully justified! I might add that the only really disastrous type of error is displacement of the array halves across the direction of travel. A displacement of half a wavelength, about 1.6 mm at 455 kHz, eliminates the main lobe completely and the instrument can only show echoes from side lobes, that is ghost images! Other positional errors do not kill the main lobe, but the side lobes become unnecessarily strong.

Regards,
Rickard

Offline keizerh

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Re: Longer array and narrower beam
« Reply #30 on: January 03, 2011, 03:01:21 AM »
Rickard,

little off topic, but have you seen this

http://www.drdepth.se/rdthree.php?l=gb

hendrik




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Re: Longer array and narrower beam
« Reply #31 on: January 03, 2011, 04:14:27 AM »
Hendrik,

Yes, I'm aware of Per's 'radar' add-on to DrDepth. It will be a very nice feature I think. I'm curious to see what hardware he will recommend, how hardware and program is synchronized and how it will perform in deep waters. Stable rotation that is controlled from the surface is hard to achieve when distance between surface and transducer is long. You have probably read about Juha's and my solution with a heavy transducer that hangs in the cable and where constant rotation is accomplished by the inertia in a heavy transducer. Radar images can be produced back home with some cutting and image transformation, for free  ;)

But this is another topic and deserves it's own thread, I think.

Regards,
Rickard

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Re: Longer array and narrower beam
« Reply #32 on: January 04, 2011, 09:49:26 AM »
hi
two picture of transducer in x-ray
i don't know if its's help you rickard but i you want, i send you original picture by post officeila_renderedila_rendered

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Re: Longer array and narrower beam
« Reply #33 on: January 04, 2011, 10:07:34 AM »
Thanks a lot Abra!

Very interesting. It's not possible to tell how many elements there are in an array, but it struck me that's what one could expect because the arrays are covered with a copper shield that stops the x-rays. I will analyze the positions and check if they vary like they do in my transducers. Let's hope HB doesn't send the police for you because of espionage!  :)

Thanks again
Rickard

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Re: Longer array and narrower beam
« Reply #34 on: January 04, 2011, 10:09:00 AM »
Wow Abra,

beautiful pictures!!
Are they made from different perspectives (from underneath and above)?

They are really detailed. Excellent work!

Best regards / Harry
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Re: Longer array and narrower beam
« Reply #35 on: January 04, 2011, 10:17:03 AM »
Let's hope HB doesn't send the police for you because of espionage!  :)

Thanks again
Rickard

I don't think so Rickard.
Abra can for sure proof that it was a case of medical emergency to x-ray the transducer. Even I can identify the life threatening cut on the right / left side of the pictures. Abra had to make sure that there are no internal damages caused by the cut.  ;)

Best regards / (Doctor) Harry
YES,......
WE SCAN!

Offline drpelle

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Re: Longer array and narrower beam
« Reply #36 on: January 04, 2011, 02:23:53 PM »
For piezo elements, look here:

http://ferroperm-piezo.com/


Per
www.drdepth.se

Offline abraquelebout

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Re: Longer array and narrower beam
« Reply #37 on: January 04, 2011, 03:57:05 PM »

Offline Humminbird_Greg

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Re: Longer array and narrower beam
« Reply #38 on: January 04, 2011, 05:05:44 PM »
Wow Abra,

beautiful pictures!!
Are they made from different perspectives (from underneath and above)?

They are really detailed. Excellent work!

Best regards / Harry

Harry,
They look like different perspectives to me.  Look at the wires going to the temperature sensor at the bottom of each picture; they are reversed.  Iĺll make a guess that the top image was taken from the bottom of the transducer as it looks like the wires from the Si elements pass between us and the Ĺearsĺ of the top transducer housing.

I just think that he will have a hard time getting his insurance company to pay for the x-rays!

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline Jolly Roger

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Re: Longer array and narrower beam
« Reply #39 on: January 05, 2011, 02:41:44 AM »
Now that you mentioned it Greg, it's actually easy to distinguish which picture was taken from above. The first picture, because it shows the cable is going out from the transducer on the right side. Unless the photo is from transparent nature and turned rearside up when Abra made the photo to post it.....

Regards / Harry

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WE SCAN!

Offline Humminbird_Greg

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Re: Longer array and narrower beam
« Reply #40 on: January 05, 2011, 09:13:59 AM »
Hmmm, didnĺt think about the cable exit hole from the housing location Harry.  Good catch there.  So unless the image got reversed somehow, the top image would be from the top of the transducer and the second from the bottom.  I guess that due to the nature of x-rays and the settings used, that the Ĺearsĺ on the upper housing of the transducer appear more transparent and seem to be behind the wires used to connect the elements in the first picture, instead of in front of the wires where they really are.  I might have to get a transducer and see if they will let me play with our x-ray machine!

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline sonar2000

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Re: Longer array and narrower beam
« Reply #41 on: January 05, 2011, 10:09:20 AM »
Shoot.  you work for them.  they should give you a dozen ducers and color x-ray..... ;D... ;).... :P... >:D

Insurance should pay for the x-ray.  Looks like a classic case of sonaritis to me...
Chuck
« Last Edit: January 05, 2011, 10:32:49 AM by sonar2000 »

Offline abraquelebout

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Re: Longer array and narrower beam
« Reply #42 on: January 05, 2011, 02:35:44 PM »
 :)waiting rickard news
just for fun
how to make an x ray of transducer and escape to police for espionage :Dila_rendered

Offline sonar2000

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Re: Longer array and narrower beam
« Reply #43 on: January 05, 2011, 03:05:00 PM »
Very good.  Looks like a new idea for a towfish....... :P
Chuck

Offline Rickard

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Re: Longer array and narrower beam
« Reply #44 on: January 08, 2011, 08:04:37 AM »
:)waiting rickard news

I have been busy with other things for a few days, so I had to shelve this project for a while  >:(. The sidescan arrays in the X-rayed transducer are parallel and approximately at the same position in the longitudinal direction. But both arrays are pointed at a small angle from that direction. This is easy to see if one inspects the spacings between the ends of the arrays and the closest edges of the housing. I don't think these deviations have any effect at all on the performance of the transducer. In theory, there could be some effect of varying thickness of the matching layer between piezo and water. The 1 mm cork-insulation, plus the copper foil shield makes it difficult to get precise measures of the piezo arrays.

But Abra's transducer confirms what I found in my transducers, internal positions do not parallel with the outer shape of the transducer, thus making it very difficult to join two transducers. I think I have to expose the front ends of all arrays to assess the exact positions before I can line up the arrays on one side to get one good, long array.

Rickard
« Last Edit: January 09, 2011, 01:41:57 AM by Rickard »

Offline Rickard

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The doubleducer is operating.
« Reply #45 on: January 21, 2011, 03:44:45 AM »
At last,

the long transducer is ready and tested. I had to concentrate on right SI channel to secure best possible performance in at least one of the channels. I have no control on the internal configuration in the left channel, but the images in that channel are surprisingly good. To get a perfectly(?) straight right array I had to make the doubleducer slightly bent in the horizontal plane and in the vertical plane. The deviations are rather small, about one mm from what would be at the ends if the doubleducer had been lined up only from the shape of the housings.

A doubleducer operated at 455 kHz will, in theory, have the same beam width as a standard transducer operated at 910 kHz. A doubleducer operated at 262 kHz will perform like a standard transducer at 524 kHz.

I tested the doubleducer by doing ice-scanning with the hanging heavy transducer method the other night. Depth at the location is 6 m and transducer was located 3 m above the seafloor. Targets are two small boats near a rocky shore. The individual transducers were connected with their original cables to a homemade connector box in parallel. A 3 m extention was used between the box and the unit. The radius in the images is 20 m (60 ft). Image properties like brightness and contrast are as they were when the images came out after being processed in SiView with color set to blue. There is no slant range correction because the wrecks are so close the transducer.

It's hard to see any large improvement between a normal transducer and the doubleducer at 455 kHz. The big difference appears at 262 kHz. This means 262 kHz can be used instead of 455 kHz to get much longer range and to compensate for signal loss in a long cable application, like when using a towfish at large depth. Careful examination shows the doubleducer when operated at 262 kHz has better resolution than a standard transducer at 455 kHz.

The uncontrolled left channel performs well which means it's easier than I thought to succeed with a doubleducer.

I must add that ice-scanning in shallow waters is difficult. There will always be interference from secondary reflections from the ice that blurrs the images at exactly twice the depth from the center of the image. In this case all the images are rather fuzzy 12 m from the center, making it more difficult to see the differences between the images.

Regards

Rickard

PS As usual, it's almost impossible to attach multiple images.

The Doubleducer
ila_rendered


The Doubleducer at 262 kHz, right channel.
ila_rendered


Standard transducer at 262 kHz.
ila_rendered


The Doubleducer at 455 kHz, right channel.
ila_rendered



Standard transducer at 455 kHz.
ila_rendered
« Last Edit: January 21, 2011, 02:58:32 PM by Rickard »

Offline abraquelebout

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Re: Longer array and narrower beam
« Reply #46 on: January 21, 2011, 11:49:46 AM »
hello rickard
congratulation
it's nice to publy you result
if i compare the picture, the double may give more contrast and accentuatution of detail
in 262 and 455 khz
you make an opposite mounting transducer, is there a reason ?
as the mounting of two tranducer in a same way on a aluminium barr for sample must give the same result ?
what is the sounder to generate 262 khz. ?
i think to find large contemporain wreek  262 khz it's good solution
i see if it's possible to have 2 transducer and mounting has i said  before (same direction on a bar, connecting 2 side and with luck geting best picture in 455 an 800)


Offline Rickard

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Re: Longer array and narrower beam
« Reply #47 on: January 21, 2011, 12:09:23 PM »
Hi Abra, and thanks!

Yes, there is a reason for joining the rear ends, the piezoelectric elements must be close, not more than a mm. That's why I had to cut away some material and this was not possible to do in the front end because of the wires.

If you arrange two transducers in a row without cutting away some of the transducer housings the piezos will come too far apart which will cause very strong sidelobes and ghost images. I have done such testings in the past with quadrabeam transducers and have seen the impact of ghost images. But please try it, it's very interesting to see the results and it won't cost much work or money (if you already have the transducers).

I have a 981 model and use transducer XHS 9 SI 160 T.
I'm very happy with the good performance at 262 kHz. This can, perhaps, make it possible to use much longer cables than those we use today.

Rickard

Offline RGecy

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Re: Longer array and narrower beam
« Reply #48 on: January 21, 2011, 03:36:47 PM »
Rickard,

Fantastic job.  I know just enough about piezo elements and potting transducers to get me in trouble.  But how hard do you think it would be to build your own elements with longer array.  Basically I was looking to build a custom towfish with 200khz tranducer for depth and and a longer 455khz element for better detail with the increased range the 455khz offers.

Any thoughts?

Robert
Humminbird Guru and Forum Administrator

Offline Rickard

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Re: Longer array and narrower beam
« Reply #49 on: January 21, 2011, 04:20:14 PM »
Robert,

Thanks, after the rather successful doubleducer project I feel it's realistic to make ones own transducer. Late Sture Hultqvist, who presented his methods ten years ago on the Geotech forum, used rather simple methods to build very successful arrays. I remember he used to make "epoxy-bars", which means he mixed as much cork crumbs he could with epoxy and potted the elements in that mixture. It seems as if you don't have to be very precise when building an array, just stay within 1/4 of a wavelength and things will be ok. The problem with making arrays doesn't have to do with the methods, prices for small amounts of elements is the main problem. Another problem is lack of standard elements with correct dimensions. After some research I was adviced to buy transducers and retrieve elements from them, this is the cheapest way they said.

I'm very suspicious about the design of HB:s transducers. They shoot sound through epoxy, a thin copper layer and PVC, and the thickness of those layers varies uncontrolled along the arrays. This must deteriorate the signal because of refraction, attenuation, reflections and standing waves. Sture's arrays had just one layer with calibrated epoxy. The professional arrays have a single layer with urethane. Perhaps I should cut away the outer layer with PVC?  :-\

Added: There is no point in making the arrays extremely long. The nearfield will be wide, but maximum range will not become longer. A too long array will actually have less horizontal resolution than a much shorter array. I decided to not making my transducer longer than two lengths of a standard transducer. Three transducer will result in a more than 10 m wide nearfield with low resolution.

Rickard
« Last Edit: January 24, 2011, 09:09:19 AM by Rickard »


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