under100 Hz transmitter

Hi,

What system?
* Electromagnetical? --> (far from being RF or microwave). What antenna (length) do you use for those low frequencies? Lambda/4 = 750 km! Btw. low frequencies are suitable for big distance.
* Optical? --> I don′t think so
* Acoustical? --> maybe possible.

***
In either case I really doubt that this low frequency makes sense.

Do you want to transmit data with this low carrier frequency? AM? FM?
What power supply do you use?

Klaus

hi Klaus.I want a transmitter which create and transmit signals that pass soil and metals for max 5m distance.do you have any functional idea to do this?

A professional loudspeaker can work ? + A High Power Audio amplifier ?

It can certainly be done but losses are huge.

Please answer Klaus's question in post #2 first. Does this transmission have to carry any information (data) or is it's presence all that you need?

Brian.

hi Brian. Not at all! .
no data are needed in my project. I want to track PIGs in underground oil and water pipelines. PIGs are tools for cleaning pipelines. the transmitter is located into the PIG and the receiver is also located in operator's hands. the transmitter emit extreme low frequencies pulses and these waves must pass pipe and soil to reach to the receiver. I want only waves that passes the pipe line body (metal) and soil for max 5m distance and finally I detect these wave on the surface by a receiver. 4 AA-size lithium batteries are needed for both transmitter and receiver.

thanks a lot.

The idea resembles a pet locator system. It does not require GPS.
The pet's transmitter is idle most of the time. It monitors your radio frequency continually. When it receives your radio command it transmits a beacon in response. You carry a directional antenna, allowing you to home in on the pet.

Advertised range is 400 feet. It's anyone's guess whether the signal can penetrate pipe and soil.

http://www.loc8tordirect.com/

For ease of design and construction, it may be sufficient just to have your transmitter send out a 5-second rf burst once every minute. That may allow your directional antenna to keep track.

It's not quite the same as pet locators because they use directional receivers which is fine through air but underground signals are dispersed widely and appear as 'hot spots' on the surface.

Non-metalic pipes may allow direct radiation but metal ones will screen EM waves. There is also the problem that the transmitting antenna (or coil) will be surrounded and possibly immersed in a substance with high dielectric contant which causes problems both with absorbing trhe signal and detuning the radiating element. If the PIG can make electrical contact with the pipe it may allow it to be used in a way similar to a feed point of a dipole, using the pipe itself as a radiating element, otherwise I see the best solution being to induce a current into the pipe by treating it as the secondary of a very low impedance transformer.

I did gound radiation tests many years ago (early 1970s) and found ground EM attenuation rises rapidly at frequencies above about 2Hz but electrical current conduction has a much wider bandwidth, in fact my experiments with injecting 1KHz tones between ground probes showed it could be detected about 1Km away.

I stress I have never done any work of this kind on pipelines so I'm making what I hope are intelligent guesses at solutions!

Brian.

I would say you have zero chance of transmitting any type of radio frequencies through the very thick steel walls of a buried pipe.

I don't know about the oil industry, but in the gas industry I am told the path of a pig moving along a pipeline can actually be heard as a very distinct audible "clunk" it passes each weld in the pipeline. Sound travels very well along a smooth bore steel pipe, as long as there is only air or natural gas in the pipe.

There is also zero chance of receiving GPS in a buried steel pipe, so about the only way I can think of is some type of acoustic transponder that could be used for accurate distance measurement along the pipe.

Something like an active sonar transponder inside the pig, should be able to travel a very long distance through a fluid, especially as it is contained within a pipe.

So you ping the pig, and it pings back, after some very well defined fixed time delay to let all the chaotic echoes die away. That should technically be quite easy to do.

It is perhaps possible for VLF (very low frequency) EM (electromagnetic waves) to pass through soil and water. But I am not sure about steel pipes ((they may block 50% of the signal).

Submarines, I believe, use VLF for communications (perhaps someone more knowledgeable may correct me) but I do not think 5m of water or soil is not a real problem.

But if you want to encode information you must be very careful because available bandwidth is rather small at lower frequency. You need to select the frequency carefully because it should not be a multiple (or submultiple) of the commercial line frequency (50/60 Hz). The metal pipes can be modeled as a secondary emitter and act like cylindrical lens (for the EM radiation).

Basically you are trying to make a metal detector for a metal (virtual) body inside a poorly conducting metal.

Thanks Brian. I have an idea that seems to be possible: Wireless power transmitter (WPT)(see the attached link). In WPT, two coils are the heart of the system,like a transformer, bot no core is needed; electromagnetic waves will induce from the primary coil to the secondary via air.the primary coil acts a transmitter and the secondary will be the receiver. the current that created by 30Hz sinusoidal oscillator is applied to primary coil and 30Hz electromagnetic waves will be induced to the secondary coil (receiver). if two sides (primary and secondary) act in resonance frequency, the result and distance will be improved.
what's your opinion?
../imgqa/eboard/Antenna/rf-rvfl0os4x0i.png



Hi and thanks.
surely pet locators will not be possible due to special conditions of underground PIGs. because the waves must pass soil and pipeline body to reach to the ground surface.

The question reduces to a simple AC magnetic simulation problem: How much of an AC field generated inside the pipeline tube can be received at the outer wall surface or at a certain distance above the ground? Respectively how much current is needed for the transmitter, how sensitive must the detector be? An additional question is optimal field orientation.

Suitable circuits can be discussed when the magnetic parameters are clear.

The idea of a 4AA powered transmitters sounds rather unrealistic to me. But we have to consider also pig speed and available detection time.

Hi

What about mechanical knocking at the wall of the pipe? Maybe once every couple of seconds.

And two (three) microphones.

Klaus

Magnetic pig detection is state-of-the-art, with large permanent magnets mounted on the pig and sensors at the wall outside.

Detecting a low frequent AC should work too, possibly also from a certain distance. You have to calculate with actual parameters (tube diameter, wall thickness, transmitter coil size, receiver distance, 5m is stated in initial post).

A serious project specification would either supply a ready-made calculation of magnetic field parameters or give the realizing person/team the tools to perform the calculation.

I agree, I was thinking in terms of several Amps of LF to a 'primary' coil with the pipe being a closed loop secondary. The induced current would radiate several metres at least and a sensitive and selective pick-up should find it easily.

I believe ground penetrating radar works at frequencies in the 400MHz region and might be able to locate the pipe itself but not a PIG inside it. Possibly GPR with a sensitive AM/FM detector could sense vibrations in the pipe from the PIG motion or a deliberate vibration sent from it.

Warpspeed's idea of using sonar TDR might work, it's simple to implement and as seen in recent aircraft crashes at sea, it can work over long distances in a hostile medium but I wonder if the shape of the pipe might cause so many false reflections that the real one would be impractical to identify. The principle would be that the PIG stays in 'standby' mode, listening for a particular tone pulse through a microphone. When it hears it, a loudspeaker sends another tone pulse back and the round trip time "time of flight" in conjunction with the velocity factor of the medium allows the distance to be calculated from a fixed location.

If the PIG has some kind of distance sensor on it (a rotating wheel in contact with the pipe wall for example) it might be able to report the distance it has travelled back to the fixed transceiver.

When these PIGs are used, is the pipe normally empty and what moves the PIG along the pipe?

Brian.

hi
I have an idea that seems to be possible: Wireless power transmitter (WPT)(see the attached link). In WPT, two coils are the heart of the system,like a transformer, bot no core is needed; electromagnetic waves will induce from the primary coil to the secondary via air.the primary coil acts a transmitter and the secondary will be the receiver. the current that created by 30Hz sinusoidal oscillator is applied to primary coil and 30Hz electromagnetic waves will be induced to the secondary coil (receiver). if two sides (primary and secondary) act in resonance frequency, the result and distance will be improved.

Brian I dont want to track the PIG(as in GPS). I want only to be aware about where the pig is located.

since the frequency is very low, I think the waves will pass the steel body of the pipe. Do you have any idea about WPT that could functional this project?

I think the Resonance inductive coupling or Wireless Power Transmitter is a good choice for making this project possible!
But I am baffled.

The question about "wireless power transmission" (should be better designated inductive coupling) has been already answered. You need to calculate actual field parameters. Probably 95 to 99.9 percent of the magnetic field generated inside the tube will shorted by the steel wall. So it's very little of "power transmission".



Instead of "thinking" you should better start to calculate.

Talking about "waves" is already confusing the problem, for distances below some 1000 km, there's only a magnetic near field. Respectively the potential EM problem reduces to a pure M field problem. But as a matter of fact, steel has high μr and only very small part of the magnetic field can penetrate the tube wall.

If you can give dimensions the dimensions of your reference pipe, someone might be motivated to do the calculation. However, as already mentioned, I believe that this calculation is an essential part of your project job, and in my view the thing to start with.



Making resonant transmitter and receiver coil circuits is all very well, but you seem to read magical properties into it.

Most notably, a resonant coil can only receive a field that actually reaches through the tube wall. On the transmitter side, it frees the driver circuit from supplying reactive power to the coil inductance, it does not reduce the resistive coil losses or the eddy current losses in the pipeline tube.