Re: what frequencies will pass metals and soil?

it means you have no practical idea?

Well no.
I am almost seventy years old and have completed more than a few really interesting R&D projects over the years.
But so far I have never found the need to design a transmitter for a pipeline pig.

oh thanks. I also have fair information about underground locating. my professional field is in photonic and electro-optic logic devices and I published 2 articles in IEEE and some in Iranian conferences. the latest was published in IEEE photonics technology letter.you can find them at ieeexplore.

I believe many Edaboard members have practical ideas, me too. The basic problem seems to me that you are starting the project without much clue about magnetic and electromagnetic fields.

The linked manufacturer article gives a basic idea of achieved range of commercial pipeline pigging systems, it also shows the field orientation used by the devices (in case it was not obvious for you before). There are also catalog data from many other vendors with battery life, transmitter size and free air range information available on the internet.

Based on the available information you should be able to define the parameters of your planned transmitter, make calculations of expected field strength in- and outside a steel tube, specify the required sensitivity of the receiver circuit. I assume that your project is somehow related to oil and gas industry and that someone has already electromagnetic pigging systems. If so, consider measurements of transmitter field strength and receiver sensitivity of the "competitor" systems.

I mentioned that the project seems feasible. But it requires profound knowledge in analog circuit and electromagnetic design to achieve the specifications.

You are harping on about inductive wireless power transfer systems. There are some similarities, particularly that transmitter and receiver are using coils in a resonant circuit. But there's isn't much power transfer possible, just a very small remainder of the field inside the tube "leaking" to the outside. In so far the reference to WPT systems doesn't get you anywhere.

thanks.My MSC thesis was focused on all-optical digital devices and I published some articles about all-optical logic gates.you can see them at IeeeXplore (my name is Mohammad Pirzadi). in all-optical devices the wavelength is in micro and nano meter. but the thing that makes me baffled is how to design extremely low frequency transceiver which able to works in unusual circumstances, additionally, I visited your proposed link about pig locating and was so useful.

The physics behind magnetic pig localization is probably simple compared to photonic devices. A rotational symmetric, pure AC magnetic problem, can be solved by 2.5-D FEM tools like Quickfield. There might be even research articles or project reports that calculate the basic parameters, unfortunately I didn't find any.

I hope there's someone at your institute who can help you with the magnetic calculations.

thanks. you are the best.

Hi everyone.
after passing tedious days, I decide to use magnetic coupling for realizing 22Hz underground transceiver through resonant inductive coupling, as already used in wireless power transmitter technology. the transmitter is located into a in-pipeline-PIG which the steel pipe is located 4m underground. the transmitter coil is supplied by 22Hz current which created by a 22Hz oscillator. magnetic fields will be coupled to a secondary coil (receiver). to enhance the structure a capacitor parallel to both coils which two sides go to resonance (tow sides have the same resonance frequency). 4 AA-size lithium cells is proposed initially. the proposed structure is schematically shown in the attached link.

now I am baffled for 3 reasons:
1- for max distance of 5m, what is the designation parameters of coils and capacitors?
2- how to enhance the output power of the oscillator to maximize the coupling distance?
3-Is my idea practical?

http://obrazki.elektroda.pl/7501437400_1479808501.png

thanks

As has been explained a few times already, the wireless power transmission is a poor example to build on. You don't want a rectifier on the secondary, that would kill your sensitivity. Instead the receiver should have resonant filter > low noise amplifier > antialiasing filter > ADC. The transmit circuit could be built similar to a wireless power transmitter, but simpler (just an Hbridge driving a series LC).

hi,what's your proposal?

Resonance is a means to increase the transmitter coil current and to free the driving amplifier from sourcing reactive power. But it's not the only way.

A resonance capacitor for the transmitter circuit might be unwanted due to it's size, it contradicts also the possible requirement to send multiple frequencies. If the transmitter coil is driven by switched mode (class D) amplifier, the reactive power can be supplied without generating much additional losses.

Presuming an efficient switched mode driver, the relevant losses can be assigned to the coil resistance. You'll define an feasible coil size and battery power and get an ampere-turns number.

Please don't keep opening new threads on the same topic.

1. The coils and capacitors have to make the coils resonant at 22Hz. Use the formula: 22 = 1/(2*Pi * Sqrt(L*C)) The coil and capacitor types make very little difference to the range you will achieve.

2. The limitiation is how much power you can get from 4 AA-cells, it is quite small. If you assume 200mA max current, the power will be less than (4 * 1.5V) * 0.2A = 1.2W. Given typical power amplifier efficiency, a figure of about 0.75W is more likely.

3. Not really, if you built it exactly as in the diagram with the coils lined up with each other and nothing between them, you would be lucky to get 10% of the transmitted power transferred to the receiving circuit. However, where you diagram has the letter 'B' you would have a metal screen and 4m of high loss soil, almost all the signal would be lost. Maybe 0.000001% (my guess) of the signal might be received on the surface so you would need a very sensitive and selective receiver circuit to pick it up.

The example of PIGs you have shown elsewhere are designed to fit in small diameter pipes (~40mm) which would have thin walls and the sensors clamp directly to the outside of the pipe wall. The situation of thicker walls and much greater distance to the sensor make the problem much harder and other location methods more feasible.

Brian.

thanks Brian. please help me if you have a practical proposal. propose your proposal for realizing this transceiver,
I wish the best for you.

I would suggest an experiment to see if it is feasible.

You can get enough power out of a single NE555 timer IC. Wire it as an astable oscillator with a 3.3uF timing capacitor, top resistor of 3.3K and bottom resistor of 8.2K, this will make it oscillate at about 22.2Hz while using standard component values. That is near enough for the experiment. Wire a 1,000uF capacitor across it's supply pins to keep the impedance low.

From its output pin, wire a 33 Ohm resistor to limit the output current then wire the transmitting coil and capacitor to the 6V supply. If you use a 10uF non-polarized capacitor and 5.25H coil in parallel it should resonate. If you wind the coil with an air core, 50mm tube diameter and space it to be 50mm length, you need 12,437 turns, that's lots of wire! You can decrease the number of turns by using a higher permeability core but you would have to find one the right shape and use the 'u' given by it's manufacturer.

That will give you a fairly compact transmitter producing EM waves at 22Hz. Next you need the receiver.

In a real tracer you would have to make the receiver coil highly directional but for the experiment you can make an identical one to the transmitter and use the same capacitor value across it. If you wire it as in your diagram and use a voltmeter as the load, you should be able to pick up a small voltage when the coils are close to each other. Now the fun starts! place the transmitter inside a metal box and see if you can still pick up a voltage on the receiving coil outside it. I suspect it will drop to almost zero with maybe a tiny residual reading. You have to amplify the received signal by maybe 100,000 times (100dB gain) to bring it back to a usable level. To do that you will have to use several stages of amplification and to eliminate other sources of signal you will have to filter the signal with a narrow passband 22Hz filter.

If it works so far, the next step would be to see if it can also penetrate 4m of ground. Unless you have a mechanical digger and space for a crater, that would be difficult! You can get an approximation of signal strength by working horizontally, bury the transmitter in the metal box to a depth of say 0.5m then see if the receiver can pick it up from another 0.5m hole spaced 4m away. you will have to back-fill the holes to eliminate other signal paths that might be present in the horizontal test but not if it was used deep into the ground.

Brian.

thanks Brian.



thank Mr. Brian. I will never forget your helps.
Mr Brian do you have another improved idea for realizing this nightmare transceiver or the mentioned way is the only way?

It may be worth remembering that we can receive signal from spacecrafts (that are on a power budget) that are millions of km away. It is never the problem of the signal strength.

Hi,

spacecrafts:
ISS is only 0.0004 million km away. (400km, you can go the distance by bike within a few days)
The Moon is 0.4 milion km away, and it is a long time ago..
The Mars is about 250 million km away. I doubt they use omnidirectional transmitting antenna. I rather think they use a narrow beam. And the receiving antennas are huge, no handheld types.

So I assume the signal strength surely can be a problem.

Klaus

There is a free running, Zero Volts switching, simple oscillator called Royer Oscillator. You only need a DC voltage.

Here is the circuit. I simulated it with a coupling coefficient of 0.0001 which is a wild guess ... I believe at 5 m distance and through a steel wall it will be much less.

When tuned at the same frequency the secondary side, higher voltage is achieved and distance is increased.

Here is the voltage accros the secondary side with and without tunning capacitor.

WITHOUT

WITH

I have picked values without thinking on the practical implementation, only to get 22 Hz. Maybe those high inductor/capacitor values are not practical for your approach.

You forgot Saturn, that is a still bit further. Bike won't do, you will need a Volkswagen!

Of course it will be silly to use an antenna that shouts in all directions. But even the best laser would light up the whole earth (it will still follow the inverse square law).

The antenna are almost regular one (well, you cannot carry even on a truck)- about 10m dish - but still - they are small in comparison the antenna used for radio telescopes.

I am not an engineer but if I understand correctly, it is the noise that need to be tackled. The efficiency is often measured in degrees Kelvin, but I digress.

I remember that the signal from the Sputnik could be heard on a regular radio (the pre-transistor era)- I guess the Sputnik had electronic made of regular valve tubes.

thank you for supporting.surely I will never forget your kindness to me.
but it's vague for me that how much your circuit could be efficient. if you are aware about your proposed circuit, plz explain more.
thanks