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I need to make shallow (max 2m) underwater wireless sensor network. Data payload is about 10kB/s. I know that VLF band (~3-30kHz) could be the best solution for that, but because of time-to-market I cannot make hardware and software from the ground up.

Maybe someone could share experience in this field.

Is it possible in the 100-900MHz band to send 10kB/s from one device to another - from 2m underwater to over a dozen cm from water surface? Maybe some IC for ultrasonic communication exist? Other ideas?

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  • $\begingroup$ It would be cool to do something like what the weakly electric fish do en.wikipedia.org/wiki/Electrocommunication. They use some sort of electric field underwater, I don't know exactly. Practically, I would bet ultrasonic would be easiest $\endgroup$ – Skyler 440 Apr 7 '15 at 23:34
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For just 2 m range, how about a low frequency magnetic field, not radio waves*?

Have a coil in each device, and drive a current into it at (say) 22 kHz for 0 and 44 kHz for 1.
Receiving would use the same coil, or one with more turns, connected to an audio amplifier, automatic gain control, and some sort of detector. Even straight into your micro, depending on what it has.
The self-resonance of each coil should be high, at least 100 kHz, and the inductance low enough that you can get reasonable current into it without unreasonable voltage. There's no gain from resonance, you don't want a high Q coil here at all.

This principle is used by heart rate monitors, which work (badly) under water. And I can relate some childhood experiments with a coil around the room, connected to an audio amplifier in place of the loudspeaker, and a search coil picking up the music anywhere nearby.

Fresh water will have almost no effect on your magnetic fields. Seawater, I don't know.

Its quite easy to experiment, with a scope and a signal generator or oscillator.

.* In fact all changing magnetic fields create a changing electric field, and hence an electromagnetic wave, but here we are in the near field where the magnetic field of a loop is dominant.

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For very short distance communication in salty water consider conduction. An audio frequency carrier can be transmitted as a current from surface level to sea bed. The propagation is omnidirectional and loss is high, but test and development would be quick.

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Using very low frequency (electro) magnetic fields make it difficult to get a data rate of 10kbps.

So what about using the 500nm band (blue light)? Attenuation of visible light (in clean water) is lowest for blue colored light.
It should be low enough to do data communication at distances of 2m even if the water is not very clean.

As transmitters you can use blue LEDs.

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