undewater piezo electric transducers

What study was that? Isn't it true that WiFi, cell phones, etc., spend far more RF-stage power for transmitting than receiving an identical amount of data? Anyway, as for underwater acoustics, in all the work I did, the power was spent disproportionately in transmitting rather than receiving. Remember that relatively low frequencies are used for underwater communication.

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 Thanks,
    - Win

Hello Intiha, Hello Win,

This was one of those posts that my server swallowed so I couldn't answer before someone else did.

Win, I agree. My background is medical ultrasound and it's the same there. You blast out whatever power the transducer or the T/R switches can take, or the maximum the FDA allows. The receiver consumes next to nothing, unless you count all that digital post-processing.

Intiha, it depends on the distance. A hobbyist's fish spotter, for example, needs very little energy for transmitting (but still more than for the receiver, usually). Now if you want to insonicate the ocean bottom to find oil fields a mile below you need incredible power levels.

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Regards, Joerg

http://www.analogconsultants.com

Not really about your question, but I once designed an underwater communication system using pieso's. The usual way is to do AM type signals and avoid the resonance peak. Instead I operated inside the resonance using narrow-band fm - around 40khz as I recall.

We got over a mile range in the ocean off Santa Barbara running the the units on a nine volt battery. Great for divers.

Luhan

Considering that you can build a simple single-channel receiver that consumes 25 mW, I would say that the transmitter would take more power for useful distances. If your using a complex coding scheme, you'll need to add in power consumption for the receiver system for some sort of processor. The processor could be a significant power hog. If your talking about multi-channel receivers (256+ channels), then the power consumption can be equivalent.

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Mark

I am (at least my group partner is) doing FM at 16 and 18Khz. Regarding the study here is a link

Here the ratio is not more than 4:1 for tx. and receive. It is accepted practice in sensor networks community (research!) that you give receiving as much importance as transmission (when saving energy).

Underwater, if using piezo's it appears we will have to throw this out the window :)

Thanks Affan.

Coooool! what transducers did you use?

Hello Affan,

If power consumption is of utmost importance I'd look for a better CPU.

3.2mA for idling is a lot. You need one that can go into very low power every time it has nothing to do, even for a few milliseconds. IOW a CPU that doesn't need to idle but can turn itself on and off rapidly. Check out the TI MSP430 series. These are 16-bit micro controllers.

LEDs: Consider flashing. I found that strobes as short as 30msec can be seen quite well, often better than a constantly lit LED.

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Regards, Joerg

http://www.analogconsultants.com

How did the whales and dolphins like it?

Thanks, Rich

Just to add, the reason transmit and receive are nearly similar is b/c we are looking at very short range radios where oscillators and mixers domintae the power consumption and thus sensing and transmitting a bit are about the same energy wise

thanks

actually the one in the link (mica2) is was one of the initial research platofrms that was used. The current best choice is telos

that has exactly the TI MSP430. However, the radio has similar characteristics still.

Thanks Affan.,

--- That's crap. The amount of care given to the receiver _always_ needs to be more than the amount of care given to the transmitter.

Transmission, without reciprocity, into a noisy medium is always dumb, and the goal must then be to always provide as much power as needed in order to transmit the data through the medium so that it'll override the noise at the receiver's input and yield reliable data from the receiver's output.

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--- It appears to me that you don't know what you're talking about.

-- John Fields Professional Circuit Designer

If you run a google search on "low power distributed wireless networks" you will find a great deal of research literature on the subject, and much of it can be applied to your work in that the same general considerations apply. The starting point is with the key performance parameters of range, bandwidth, reliability, and the transmit channel characteristics. The transmission channel, more than anything else, influences the requirements on frequency, choice of modulation, power levels, and probably most importantly immunity to interference. You then solidify the actual hardware specifications around that. Frequency obviously comes into play with things like absorption characteristics of the channel, directivity requirements if any, receiver selectivity, component size, antenna apertures and size, component availability and power/efficiency/performance as a function of frequency and type of modulation. The interpretation of these characteristics is constrained by the ultimate performance and reliability which drive the selection of modulation type and a minimum S/N at the receiver, and these in turn set the output power levels. In summary then you first have to work through the basic physics of the environment and the candidate engineering solutions, only then have you earned the privilege of fussing with the digital minutia.

I dont want to get into a useless slanging match; but i think you might have totally misunderstood what i was saying.

to *design* receivers very carefully. I will take your word for it (and also b/c your arguments are convincing) since I am not into designing these stuff. However, what I was refering to when I said "we will have to throw this out the window :)" was the notion/assumption that underwater transmit and receive will take the same amount of power.

If you read my oringnal para it said "you give receiving as much importance as transmission (when saving energy)." Note the (when saving energy) part! i might have been a little unclear on my part for which i apologize, but i didnt mean that receivers are less important from their design point of view point ; but that if you are going to sleep schedule you would have to design a mechanism knowing that when a radio is up for receiving it still takes a lot of energy (as opposed to negligible).

I hope this is more clear now.