undewater piezo electric transducers

[Intiha]

Generally, low cost RF transducers are such that emperical studies, viz
a viz, sensor networks/motes take nearly the same ballpark amount of
power for transmitting and receiving a symbol.
Now if we are to use piezo-electric oscillators of underwater acoustic
communications, will this still hold or is the transmitter going to to
take up much more energy than the receiver?

I would appreciate any input at all.

Thankyou.

 

[Winfield Hill]

Intiha wrote...

Generally, low cost RF transducers are such that emperical studies,
viz a viz, sensor networks/motes take nearly the same ballpark amount
of power for transmitting and receiving a symbol.
Now if we are to use piezo-electric oscillators of underwater acoustic
communications, will this still hold or is the transmitter going to to
take up much more energy than the receiver?

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.

 

[Joerg]

Hello Intiha, Hello Win,

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

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.

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.

 

[Luhan]

Generally, low cost RF transducers are such that emperical studies, viz
a viz, sensor networks/motes take nearly the same ballpark amount of
power for transmitting and receiving a symbol.
Now if we are to use piezo-electric oscillators of underwater acoustic
communications, will this still hold or is the transmitter going to to
take up much more energy than the receiver?

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

 

[qrk]

Generally, low cost RF transducers are such that emperical studies, viz
a viz, sensor networks/motes take nearly the same ballpark amount of
power for transmitting and receiving a symbol.
Now if we are to use piezo-electric oscillators of underwater acoustic
communications, will this still hold or is the transmitter going to to
take up much more energy than the receiver?

I would appreciate any input at all.

Thankyou.

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.

 

[Intiha]

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

I am (at least my group partner is) doing FM at 16 and 18Khz. Regarding
the study here is a link
http://www.eecs.harvard.edu/~shnayder/ptossim/mica2bench/summary.html.
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.

 

[Clifford Heath]

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

Coooool! what transducers did you use?

 

[Joerg]

Hello Affan,

I am (at least my group partner is) doing FM at 16 and 18Khz. Regarding
the study here is a link
http://www.eecs.harvard.edu/~shnayder/ptossim/mica2bench/summary.html.
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).

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.

 

[Rich Grise]

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.

How did the whales and dolphins like it?

Thanks,
Rich

 

[Intiha]

I am (at least my group partner is) doing FM at 16 and 18Khz. Regarding
the study here is a link
http://www.eecs.harvard.edu/~shnayder/ptossim/mica2bench/summary.html.
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.

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

 

[Intiha]

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.

actually the one in the link (mica2) is was one of the initial research
platofrms that was used. The current best choice is telos
(http://www.xbow.com/Products/Product_pdf_files/Wireless_pdf/TelosB_Datasheet.pdf)
that has exactly the TI MSP430. However, the radio has similar
characteristics still.

Thanks
Affan.,

 

[John Fields]

I am (at least my group partner is) doing FM at 16 and 18Khz. Regarding
the study here is a link
http://www.eecs.harvard.edu/~shnayder/ptossim/mica2bench/summary.html.
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).

---
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.
---

 

[Fred Bloggs]

Generally, low cost RF transducers are such that emperical studies, viz
a viz, sensor networks/motes take nearly the same ballpark amount of
power for transmitting and receiving a symbol.
Now if we are to use piezo-electric oscillators of underwater acoustic
communications, will this still hold or is the transmitter going to to
take up much more energy than the receiver?

I would appreciate any input at all.

Thankyou.

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.

 

[Intiha]

---
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.

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

From your explanaion i gather that you are saying that it is important

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.