How to Communicate Underwater With Robotic Fish.

[amol.gulhane07]

What are different ways to communicate underwater with robotic fish.

I have tried RF, Bluetooth but their range was very less. I am looking for long range modules.

 

[picbits]

How long ? What speed and quantity of data ?

For short to medium range, consider using audio / ultrasonic. You could also consider VLF radio.

 

[Misterbenn]

RF and light are absorbed very quickly by water and the impurites in water.

You will need to use sound ... think of the pinger on flight data recorders, or dolphins, or whales ....

 

[amol.gulhane07]

Thanks for your reply.
I want to be able to communicate with ROBOTIC fish till say at least 300 m Depth.
Speed is 1m/s.

I should be in a position to control the robot from ground station adn also analyse different parameters of water from the data sent by FISH.

Misterbenn: Hey, I know about that. It would be very useful if you could point to exact module which can be used.(name or link for the same)
Thanks again.

 

[JimB]

RF does not work very well in water, lower frequencies 10 to 20kHz (ish) can be used, but the antenna will be VERY large.

As Misterbenn says acoustic is the only way to do this successfully, high frequency RF? no chance!

JimB

 

[Pommie]

A floating aerial would help a lot.

Mike.

 

[amol.gulhane07]

Misterbenn JimB Pommie :Thanks ......But I am not quite sure I am following what you are saying. I googled floating aerial and it came up with bizzare results. Can you suggest some module or device for the same? (name or link for the same)...

 

[Pommie]

I simply meant an aerial that floats on the top of the water and connects to the "fish" via a cable.

Mike.

 

[amol.gulhane07]

Pommie But then it wont be hidden. FiSH can be used for spying as well. (As can be seen in James Bond's Movie: Tomorrow never dies - sea drill)

Also if it is suspended from cable then its movement will be restricted.
any wireless module that works underwater for the longer range?

 

[ClydeCrashKop]

I am thinking fish finder / depth sounder transducer and frequencies.

 

[JimB]

(As can be seen in James Bond's Movie: Tomorrow never dies - sea drill)

That film was FICTION, it was not real.

any wireless module that works underwater for the longer range?

Being quite blunt...
What part of NO do you not understand?

Have a look at this:
https://en.wikipedia.org/wiki/Communication_with_submarines

JimB

 

[Misterbenn]

A module designed for sonar would probably be your best off the shelf solution.

Most remote controlled underwater robots / torpedoes use very thin (and long) fiberoptic.

What kind of communication with FISH do you want? simple up/down left/right, or more complex video comunication? Video could only be achevied via a hardwired link.

 

[amol.gulhane07]

JimB : SO were the touchscreen panels shown in STARTREK series...

want the robot to be able to maneuver in either autonomous mode or maual mode.

SO it should be capable of up/ down/ left / right movement....Also it should be able to send few data parameters to the ground station

 

[ramuna]

Hi,
Is the water environment fresh water or saltwater ?

 

[cowboybob]

The US Navy has considerable experience with robotic subs ("fish").

There are only two types they use (irrespective of the depth and from years of experience); wire tethered or autonomous (as Mristerbenn noted).

No wireless (VLF or acoustic) is ever used for control (as opposed to comms) at that range due to the lack of confidence in the link, primarily because of thermoclines and other density issues associated with water.

 

[amol.gulhane07]

No doubt, All the posts are informative.

ramuna: Right now I will be testing in fresh water. if It works then I will be shifting to saline water.

But I am still wandering in the vast ocean, thinking what should I use..

 

[picbits]

Personally I'd use the audio / ultrasonic for two way communication with a fallback of having a conventional RF signal with an aerial on top of the fish for when it is on the surface. When the fish loses contact with the audio / ultrasonic then it will automatically surface for further instructions.

 

[ramuna]

As several respondents have already mentioned, sound would appear to be your best bet. Imitate nature , see:
**broken link removed**
**broken link removed**
and, how about this: http://news.bbc.co.uk/1/hi/world/americas/2854189.stm

 

[ronsimpson]

I think audio is best.
BUT
There is a very low frequency RF option. (very very low) The antenna does not need to be long. AM radios use ferrite rods with a coil wrapped around as an antennas.

With VLF radio you may have a very low data rate to the point where commands can not be sent fast.

 

[k7elp60]

Audio frequencies are the only reliable for under water communications. Yes the US Navy used to communicate with rf @ 17kc, but they had a long trailing antenna. The transmitters on land were pretty high powered, in excess of 50kw. Some sonar used 17kc. The transmitting and receiving transducer was a high power speaker with a rubber diaphram. I say receiving and transmitting as the sonar was used to detect ships and other objects in the water . When the transmitted pulse bounced off an object the returned echo was received on the same transducer. I was once aboard a ship that had a fathometer that measured the depth of the mariana's trench, about 6000 fathoms, the peak power of the
fathometer was less than 1kw. One of the problems with underwater communications is that temperature layer's can cause the audio waves to bend.