Problem receiving signal from Hydrophone(devices: converts sound into electrical)

[imran kandhro]

hi! i am trying to make 'pc-based underwater acoustic communication system" in which i have two laptops.

laptop 1 is connected to acoustic projector(device that converts electrical pulse into sound wave)

while...

laptop 2 is connected to acoustic hydrophone(device that converts sound wave into electrical pulse)

and these two devices (hydrophone and projector) are laid down into water tup. and i am using matlab to transmit and receive signal through using their sound card. but the problem is i am not receiving signal which is being transmitted??? if any one knows

and the files are attached for design of hydrophone and projector and if any knows if i am making mistake kindly suggests me??

thanks

plz help me!!!

 

[Dan Mills]

What are you using as a preamp on the receve side? Most hydrophones are capacitive devices and require a high Z input with very low current noise if they are to work well.

What frequency are you working at?
How big is your tank?

Be aware that projector/hydrophone systems are seldom linear phase and usually have horrible phase response, what comes out generally bears little superficial resembelence to what you fed the projector, and that is before we get into the linearity or lack therof of a hunk of PZT driven at any reasonable power level.

Further be aware that in shallow water, multipath is a massive issue, there will be massive amounts of reverb to deal with.

Underwater acoustic modems are a fun area to play with.

Regards, Dan.

 

[imran kandhro]

thank you dear! for your response.....

no i am not using any pre-amp circuit..
my frequency of operation for 1's is 1000hz and for 0's 500hz i am using fsk modulation..

and further more my tup is about 1 meter (just for analysing)

and yes there is some sort of signal coming but it is totally deformed so i can't distinguish b/w 0's and 1's. i mean to say received signal is subsequently different when i tries to receive that signal many times. i mean it is changed turn to trun

and did you read that attached files! what do thing are they correct????

 

[Dan Mills]

500Hz? That is very, very low.
Down there the usual designs are either free flooded rings of epic proportions or arrays of 'tonpills' elements, both are huge and power hungry.

Consider that the wavelength of sound in water at 500Hz is of the order of 3m, and that for a projector to be reasonably efficient it needs to be at least of the order of a 1/4 wavelength long.

Most acousic modems work in the 10s of KHz region for relatively deep water at lowish data rates, to several hundred KHz for relatively short links at higher data rates, about the only things working down at 500Hz are some military systems but they do not use hydrophones made from tin cans and thin disks.... Think flooded ring transducers weighing hundreds of kg each.

While that 'hydrophone' will possibly sort of work (For very small values of work), the matching between the piezo and the water will be horribly poor so the Q will likely be very high, and the beam pattern is anybodies guess.

Have you plotted impedance and admittance accros your desired operating frequency range? This together with a plot of hydrohone sensitivity will allow you to calculate the projector sensitivity of the thing, and from there a link budget is a small step.

The paper from ultra is somewhat interesting if a bit light on the details, single crystal is nice, but very, very expensive, so I suspect that ceramic or piezo composite of the standard sort will continue to be used for a while yet. The .rar file seems to be some sort of web page with (looking at the pictures) a very poorly thought out hydrophone design which might sort of work as a receiver, but will not be very good (acoustic impedance matching), and will posess both a really weird beam pattern and rather more Q then is good.

I have to be a little careful as my day job is working for a manufacturer of underwater acoustic transducers, so details get into trade secret issues quickly.

Regards, Dan.

 

[imran kandhro]

thank you Dan,

yes , Dan : i tried at frequencies about 10s Khz, but as usual i am receiving same sort of different signal but still can't distinguish b/w 0's and 1's. and distance b/w rx(hydrophone) and tx(projector) is very very small let say about half of the (half of meter)

no i have not plotted impedance and admittance and furthermore i have used ceramic peizo b/c single crystal is not available in my country



and i am working on this project since 4 months but at the last point i am not getting results. plz plz help me!

plz help me i am in trouble

if you need results i can show to you or you need further information plz ask me.

e-mail : imran_ali201085@yahoo.com
Skype: imran_ali201085

 

[Dan Mills]

Almost nobody uses single crystal for this sort of thing, it is way too expensive, PZT 5A or 5H is common, cheap and good enough for short range acoustic modems, single crystal is expensive to the point that it is still pretty much a research subject with a few military applications.

Here: **broken link removed** are some tutorials on these materials and how to apply them (From the web site of one of our suppliers).

If you must use that existing hydrophone design (Which is awful by the way), I would firstly try running the thing at a few Khz, tune around a bit to find the frequency that gives the maximum tone level in the water, then hook up your hydrophone and make sure you can see the tone on a FFT (Just record it with something like audacity and use the spectrum view).
Make sure you can see both tones clearly.
I would then advocate the use of the overlapped Gortzel algorithm to pick out the two tones, and feed them to whatever decoder makes sense.
Over less then a meter even with fairly awful gear this should be easy to get to work, getting a good data rate might be another story, but you should be able to at least see both tones on an fft or output of a gortzel filter.

However I would really suggest begging or borowing a couple of real transducers from someone, maybe a local university or such, I think you will be much happier with a couple of transducers made for the purpose rather then trying to use gear designed for air under water.
I would offer to sell you some new ones but suspect that money may be an issue.

Still if you want to see the sort of thing used for this stuff professionally, I work here:
https://www.neptune-sonar.co.uk

Regards, Dan.

 

[imran kandhro]

yes! dan!

i can hear only tunes of 1's and 0's but they can't be shown on fft! in matlab. and i think code is 100% right!
if you want to know about code then i can show you??
and furthermore in my university none of other have work on pzt still.
so how much it would be cost in pakistan???? if i want pzt from you!

projector: Model D/60

hydrophone: Model D/60

thank! very much!