Dear Viky,

A communication link consists of a transmitter , a receiver and a communication medium. Every medium has the suitable signal energy form to propagate easily in it.

Good electricity conductors such as metals are conveyor of electricity.Therefore transmission lines are made from metallic conductors like copper and aluminium.It is not practical to connect the transmitters and receivers in underwater by transmission line.

Therefore one uses the suitable wireless system for under ware communication.

Basically there are two basic wave types, the acoustic waves and the electromagnetic waves. Sea water is salty and therefore good conducting as Dr Garry mentioned. Consequently it attenuates the electromagnetic waves and this attenuation increase as the frequency increases. Only low frequency electromagnetic waves are capable to propagate an appreciable distance before it gets undetectable.Therefore the radio wave under sea water communication is restricted to very low frequency waves with very small band width and consequently very low data rates. Newly, short distance under water optical communication links are developed operating in the wavelength range from 0.4 to 0.55 micrometers.They can be considered also wireless electromagnetic wave communication.

As a medium the sea water is suitable as a fluid is suitable for acoustic wave propagation. Therefore, the under water communication systems are normally

based on acoustic wave transmission. Here piezo electric transducers are used to convert the electrical signal into acoustic waves and vice verse. The rest of the system remains the same.For more details please go to the link: www.tr.ietejournals.org/article.asp?issn=0256-4602;year=2012

Yes. One may form an Underwater Wireless Sensor Network. I suggest the following reading list

J. Heidermann, M. Stojanovic, M. Zorzi, "Underwater Sensor Networks: Applications, Advances and Challenges, Philosophical Transactions of Royal Society A: Mathematical, Physical and Engineering Sciences, A 2012 370, pp. 158-175, August 2012.

Ash, the paper you linked to predominantly discusses wireless *acoustic* networks.

The original question is about radio links.

The penetration depth of radio waves through a conductor is determined by the skin depth. And in turn the skin depth (wherein the signal is propagated) is small for high frequency signals, and is also small for good conductors.

(the exact dependence escapes me - I dimly recall a square root)

So an excellent conductor, like sea water, can be transmitted through by RF signals only at very very low wavelengths.

Indeed, submarines can communicate by VLF radio in some situations. But the low frequencies (a few tens of Hz) means that bandwidths will be dreadful and any

'high quality' links had better have patient sender/receivers at either end.

Dear Viky,

A communication link consists of a transmitter , a receiver and a communication medium. Every medium has the suitable signal energy form to propagate easily in it.

Good electricity conductors such as metals are conveyor of electricity.Therefore transmission lines are made from metallic conductors like copper and aluminium.It is not practical to connect the transmitters and receivers in underwater by transmission line.

Therefore one uses the suitable wireless system for under ware communication.

Basically there are two basic wave types, the acoustic waves and the electromagnetic waves. Sea water is salty and therefore good conducting as Dr Garry mentioned. Consequently it attenuates the electromagnetic waves and this attenuation increase as the frequency increases. Only low frequency electromagnetic waves are capable to propagate an appreciable distance before it gets undetectable.Therefore the radio wave under sea water communication is restricted to very low frequency waves with very small band width and consequently very low data rates. Newly, short distance under water optical communication links are developed operating in the wavelength range from 0.4 to 0.55 micrometers.They can be considered also wireless electromagnetic wave communication.

As a medium the sea water is suitable as a fluid is suitable for acoustic wave propagation. Therefore, the under water communication systems are normally

based on acoustic wave transmission. Here piezo electric transducers are used to convert the electrical signal into acoustic waves and vice verse. The rest of the system remains the same.For more details please go to the link: www.tr.ietejournals.org/article.asp?issn=0256-4602;year=2012

I'd suggest you to look through following books. The first one is the most important.

Nonsinusoidal Waves for Radar and Radio Communications by Henning F. Harmuth 1981,

Harmuth H.F., Boules R.N., Hussain M.G.M. Electromagnetic signals: reflection, focusing, distortion, and their practical applications. – New York: Kluwer Academic / Plenum Publishers, 1999.

Boules R.N. Synchronous communications in lossy medium using nonsinusoidal waves // IEEE Transactions on Electromagnetic Compatibility. – 1991. – Vol.33, №4. – P.295–303.

Hartmuth H.F. On effect of absorbing materials on electromagnetic waves with large relative bandwidth // IEEE Transactions on Electromagnetic Compatibility. – 1983. – Vol.25, №1. – P. 32–39.

People at MIT WHOI were working for Highspeed Underwater video transmission

What about a pile of potatoes environment.I need to place a radio sensor node in the middle of pIle of potatoes. Can we  assume the pile of potatoes as a water environment? What kind of possible  difficulty will I come across ? I am assuming that the power consumption of the radio node will increase due t effect of the water potatoes contain and the transmission range will decreas.  Any suggestions? 

Yalcin,

The frequency of the radio link will be important. If the wavelength is about the same as the average potato size (I can't believe that I'm writing this), and they are dry, then there will be significant attenuation. So for a 6GHz link, a pile of potatoes will look like a semi-infinite conductive mass.

If the potatoes are dry, and the wavelength is longer than the average potato, then you have a chance - and the attentuation will be lower.

May I ask what bandwidth you need, how large the sensor can be, and your power requirements? Because I think that a plain ol' AM transmitter (say, 100MHz or a repurposed 27MHz transponder) may suffice.

Welcome ,Yalcin and James,

Meeting again after long time because of the question of Yalcin,

As the electromagnetic waves will be attenuated in potatoes, i would propose to work in short wave range using fsk modulation or one can  better introduce plastic tubes through the potatoes to give an easy path to waves and guide them out side the pile.

I thin this solution will work, in ware one can not easily apply this solution.

Best wishes

Hi, thank you for your answers.James ,sensor(radio node) is powered by  a battery and it consumes less then a watt energy.The frequency is 2.4 ghz.It works as transmitter/ receiver and it's a one of the node of the WSN.Potatoes are quite juicy:) Does that  change the situation James?

That plastic tube, can we apply it? If so , could you be a more specific Abdelhalim.?

Yalcin,

>Does that change the situation James?

Yes, I suspect that you will get many tens of dB of loss per metre of potato. The wavelength is comparable to the scale of the average potato - and moisture 'short-circuiting' the potatoes, will make it worse.

Are you totally constrained to use a 2.4GHz link?

I can't imagine that you need HDTV from inside the potato pile - perhaps you are monitoring humidity and temperature - and so you could use a very low frequency transmitter.

https://en.wikipedia.org/wiki/2200-meter_band

Perhaps this is a bit extreme (the antenna would be a rather long dipole!) but you get the idea.

Something in the 27MHz range ought to be both cheap and simple to make:

http://hackaday.com/2012/10/18/27-mhz-transmitterreceiver-pair-made-with-555-timers/

And legal too (probably).

So, I need to reduce to frequency first, on top of this let the  sensor node consume more power and expect to send less data. What if I reduce only that node frequency ? Does that node work with the others in harmony? I mean one of them gonna speak slower than others.Thank you James in deed. 

salaam 

it is important to note that there are environmental affects of these various methods of underwater communication. many underwater organisms use sophisticated acoustic and bio-electric mechanisms  for communication, & navigation. disrupting these should be avoided.

Yalcin,

How many transmitters do you forsee?

If this is a single pile of potatoes that has to be monitored, then a VHF link would be ideal between the potato pile and the base station. Perhaps you have some 'intelligence' in the transmitter to encode a sensor's data (Arduino, etc.)

I would then take the serial data from the VHF receiver and feed it into a standard 418MHz module.

And *that* then can be part of a wifi mesh. Okay, you would then need dedicated crystals for each transmitter. Or you could implement a CANbus style network, and allow collisions.

As long as each sensor broadcast infrequently, and semi-randomly, you ought to be able to support a large number of potato piles.

There's no particular reason why the sensor/transmitter would need more power. What are you trying to measure, and how frequently are you trying to measure it?

(Bluetooth might also be an option - cheap and worth trying) 

Yalcin,

The idea is simple. at 2.4 Ghz you can guide the waves outside the pile  by waveguides that may be plastic tubes coated with metal at its interior walls. The antenna of the sensor node is made directive and coupled to  the waveguide tube. in this way will need low power to send the data rate you  intend. 

The idea is simple and feasible.

Abdelhalim,

An interesting idea, but I wonder about the practicalities - I imagine that Yalcin is attempting to measure some property of the potatoes' environment - perhaps the temperature or humidity.

To add an array (omnidirectional perhaps) of pipes seems to be problematic from the perspective of the driver who has to tip the potatoes into a warehouse bin or holding container. How is this array of pipes fixed? How are they cleaned? If a potato falls into one, and jams (non zero probability) then... And then how are the potatoes removed from the bin, given that an array of pipes is interspersed through the pile?

etc.

I would, as a first step, try a number of different link frequencies to find the attenutation.

Perhaps waveguides might be needed - perhaps they will not.

If we knew the bandwidth requirements, then we could estimate a link budget and a power profile. Even the attenutation coefficient can be estimated with a simple function generator and a signal analyzer.

Some work in the area exists.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4541835/#B22-sensors-15-15363

James, I am measuring humidity and temperature.That node is one of the member of the cloud. Also, that sensor node  will be  slave providing   data.

Abdelhalim, your propose is quite interesting, I am not sure I have deep  antenna knowledge to apply your idea in order to design it. 

salaam Abdelhalim,

how would one determine the ideal length/diameter of the wave guides? what metal would you recommend to coat the tubes with? would you use vacuum vapor deposition? thank you.