Underwater communication

My final project will be (i hope) building two simple identical devices which will be able to communicate underwater. I have never seen (and built) a real device like this from scratch. My local instructor told me that the final project has to be a real challenge for me..and here it is!

Technologies:

• Radio waves: excluded!

  I did a quick search on the web and i found that radio waves are not suitable as medium to communicate underwater. Radio waves do not travel well through good electrical conductors like water. Water becomes a better conductor with more salinity. A better conductor absorbs more energy thereby the communication is worse. I excluded it.
  
  

• Tethering: excluded!

  Another system to communicate underwater is tethering: basically using a cable which connects something on water surface. I want to do a wireless communications then i excluded it.
  
  

• Acoustic waves: the most probable..

  Acoustic waves are more suitable to communicate underwater and they also travel faster in water than air, because water is a stiffer medium. Indeed acoustic waves propagate even faster in solid medium than in air or water. I also read that this kind of waves can annoy big cetaceans. However my project is only a little experiment, I promise I will test it in a little tank or swimming pool, not bothering any cetaceans :) Eventually I could try to do a simple robot-fish with a servo and one LED to test the communication.
  
  

• Light: evaluating ..

  I also read that even light is used to communicate under clean water. Possibly I will consider even this solution. Indeed with light it is possible to communicate faster but only with clean water while with acoustic waves it is possible to communicate even with dirty water and for long distance.
  
  

• Piezo technology: evaluating..

  Usually based around a piezoelectric transducer, hydrophones are used to record underwater sounds.
  
  

  • Underwater communications

  • The instrument used is the hydrophone. With this technology, it looks that one day we will talk with the dolphins. Speaking with the dolphins

  • Nowaday it is not so unusual a swimming pool with underwater music. Buyer’s underwater speakers

  • little experiment (it’s not mine).

  • An interesting instructables page

Fab Academy observations

In this project I think I will use many digital fabrication techniques to make a waterproof shell (or a nice robot fish with a servo as a fin) with all the electronics inside. I thought I can even build a little tank, probably for “Molding and casting” assignment. I think my project will be a good experience to go in depth in various techniques during my Fab academy . I would be happy even if I will transmit even only one bit between two devices.

Some links (section under construction..)

Below some links I read and I am reading to start to understand something more..)

• This website is full of information
• Do you need email underwater? :) sending underwater emails
• Something about using light. The advantage of using light is also that even an aircraft can communicate to something underwater.

So far, it’s been found that blue-green lasers can reach some ten meters beneath the surface, and be used for detection and communication. Not terribly useful for subs (which typically stay farther down than ten meters), although work continues on using this capability to search for bottom mines in shallow waters.

• Commercial products
• I am also reading something on forums and ROV communities. DIY drones community
  
  
  

Scientific papers and technical documents

There are also many scientific papers and technical documents. I have to select and read some of them.