Magnetic Induction - how to improve distance

C

ChronoFish

Guest
Hello,

I am experimenting with magnetic induction for a PAN (personal area network) application. As with everything electronics this is
all new to me.

SO FAR:
So far I have been able to get a TX and RX to talk with each other at the 30-50cm range which I've been very happy with given it's
my first shot at it. I would like to extend that range 4x (about 1.5-2 meter).

On the TX I have a small (35mm x 5mm) ferrite (magnetic) core inductor that I ripped out of a sports heart monitor transmitter. I
can't go bigger because of the application. The power is about 7v and again I don't really have flexibility to increase the power
of the TX.

On the RX I have a 10cm air-core wire loop (about 7mm in thickness - I guess around 100 wounds - maybe more) feeding several series
of amplifiers. I will have more flexibility in terms of size of the loop (to a limit).

THE QUESTIONS:
How can I increase my communications distance? Would it be better to increase the windings, increase the size of the loop, or both?
Is a tightly bound loop better than one that varies in thickness? Also, will a rectangle shaped loop perform significantly worse
than a circle shaped loop?

Thanks!
CF
 
I read in sci.electronics.design that ChronoFish <deja@chronofish.com>
wrote (in <sph8c.2479$EW1.991@lakeread03>) about 'Magnetic Induction -
how to improve distance', on Wed, 24 Mar 2004:

How can I increase my communications distance? Would it be better to
increase the windings, increase the size of the loop, or both?
Click to expand...
Either of those will help, provided you don't reduce the transmitter
*current* more than in proportion. The impedance of the transmitting
loop is inductive and the inductance is proportional to the coil
perimeter, and the square of the number of turns.

But you will have great difficulty in getting a useful range with the
constraints you have already applied. Don't forget, also, that both
transmitting and receiving coils are directional.

Is a
tightly bound loop better than one that varies in thickness?
Click to expand...
Not necessarily.
Also, will
a rectangle shaped loop perform significantly worse than a circle shaped
loop?
Click to expand...
No.

What signals are you passing through your system? That matters a great
deal. In fact, it isn't really possible to give you constructive help
without knowing that.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:NJlGkqGghaYAFw6x@jmwa.demon.co.uk...
I read in sci.electronics.design that ChronoFish <deja@chronofish.com
wrote (in <sph8c.2479$EW1.991@lakeread03>) about 'Magnetic Induction -
how to improve distance', on Wed, 24 Mar 2004:

How can I increase my communications distance? Would it be better to
increase the windings, increase the size of the loop, or both?

Either of those will help, provided you don't reduce the transmitter
*current* more than in proportion. The impedance of the transmitting
loop is inductive and the inductance is proportional to the coil
perimeter, and the square of the number of turns.

But you will have great difficulty in getting a useful range with the
constraints you have already applied. Don't forget, also, that both
transmitting and receiving coils are directional.

Is a
tightly bound loop better than one that varies in thickness?

Not necessarily.
Also, will
a rectangle shaped loop perform significantly worse than a circle shaped
loop?

No.

What signals are you passing through your system? That matters a great
deal. In fact, it isn't really possible to give you constructive help
without knowing that.
Click to expand...
Depending on signal and modulation, it might be possible to use LC resonant
tuning.
Bill Beatty has a lot of info on his site
http://www.amasci.com/tesla/nearfld1.html

--
Dirk

The Consensus:-
The political party for the new millennium
http://www.theconsensus.org
 
"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message news:NJlGkqGghaYAFw6x@jmwa.demon.co.uk...
I read in sci.electronics.design that ChronoFish <deja@chronofish.com
wrote (in <sph8c.2479$EW1.991@lakeread03>) about 'Magnetic Induction -
how to improve distance', on Wed, 24 Mar 2004:

How can I increase my communications distance? Would it be better to
increase the windings, increase the size of the loop, or both?

Either of those will help, provided you don't reduce the transmitter
*current* more than in proportion. The impedance of the transmitting
loop is inductive and the inductance is proportional to the coil
perimeter, and the square of the number of turns.
Click to expand...
The transmitter would stay constant. The changes I would like to make are in the receiver - unless you're telling me that's not
possible.


But you will have great difficulty in getting a useful range with the
constraints you have already applied. Don't forget, also, that both
transmitting and receiving coils are directional.
Click to expand...
Yes the directional aspect is known. It's kind of cool actually...

What signals are you passing through your system? That matters a great
deal. In fact, it isn't really possible to give you constructive help
without knowing that.
Click to expand...

Right now its a 30kHz square wave (8 cycles = 1 bit) which is pulsed to produce a bit pattern. Each pulse becomes attenuated (is
that the correct term? - starts off large then tapers off) but is clearly visible (clean .5v). I have a lot of flexibility for the
signal.

Thanks!

-CF
 
"ChronoFish" <deja@chronofish.com> wrote in message
news:JSj8c.2485$EW1.1031@lakeread03...
"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:NJlGkqGghaYAFw6x@jmwa.demon.co.uk...
I read in sci.electronics.design that ChronoFish <deja@chronofish.com
wrote (in <sph8c.2479$EW1.991@lakeread03>) about 'Magnetic Induction -
how to improve distance', on Wed, 24 Mar 2004:

How can I increase my communications distance? Would it be better to
increase the windings, increase the size of the loop, or both?

Either of those will help, provided you don't reduce the transmitter
*current* more than in proportion. The impedance of the transmitting
loop is inductive and the inductance is proportional to the coil
perimeter, and the square of the number of turns.

The transmitter would stay constant. The changes I would like to make are
in the receiver - unless you're telling me that's not
possible.



But you will have great difficulty in getting a useful range with the
constraints you have already applied. Don't forget, also, that both
transmitting and receiving coils are directional.

Yes the directional aspect is known. It's kind of cool actually...


What signals are you passing through your system? That matters a great
deal. In fact, it isn't really possible to give you constructive help
without knowing that.


Right now its a 30kHz square wave (8 cycles = 1 bit) which is pulsed to
produce a bit pattern. Each pulse becomes attenuated (is
that the correct term? - starts off large then tapers off) but is clearly
visible (clean .5v). I have a lot of flexibility for the
signal.
Click to expand...
Are you using a resonant circuit tuned to 30kHz in the receiver?

--
Dirk

The Consensus:-
The political party for the new millennium
http://www.theconsensus.org
 
I read in sci.electronics.design that Dirk Bruere at Neopax
<dirk@neopax.com> wrote (in <c3sfnu$2ar12m$1@ID-120108.news.uni-
berlin.de>) about 'Magnetic Induction - how to improve distance', on
Wed, 24 Mar 2004:
Depending on signal and modulation, it might be possible to use LC
resonant
tuning.
Bill Beatty has a lot of info on his site
http://www.amasci.com/tesla/nearfld1.html
Click to expand...
I would treat this with great caution, especially as it's not about
magnetic induction but electric induction.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
In article <sph8c.2479$EW1.991@lakeread03>,
ChronoFish <deja@chronofish.com> wrote:
Hello,

I am experimenting with magnetic induction for a PAN (personal area
Click to expand...
Typically, in a "magnetic induction" system, the frequency is so low that
the impedance of the coils is very near zero.

If this is the case, the receiver design should use largish transistors on
its input and run them at fairly high currents. The noise voltage in the
preamplifier is the most important parameter.

No matter what you do, the signal will fall off as the cube or 4th power
of distance when the distance is much greater than the size of the coils.
--
--
kensmith@rahul.net forging knowledge
 
"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:luj8NzH6fdYAFwN7@jmwa.demon.co.uk...
I read in sci.electronics.design that Dirk Bruere at Neopax
dirk@neopax.com> wrote (in <c3sfnu$2ar12m$1@ID-120108.news.uni-
berlin.de>) about 'Magnetic Induction - how to improve distance', on
Wed, 24 Mar 2004:
Depending on signal and modulation, it might be possible to use LC
resonant
tuning.
Bill Beatty has a lot of info on his site
http://www.amasci.com/tesla/nearfld1.html

I would treat this with great caution, especially as it's not about
magnetic induction but electric induction.
Click to expand...
A lot of it applies equally, and as someone who has actually built an
induction battery charger I can confirm that making the receiver a resonant
LC circuit greatly increases the power transfer. Mine operated at 14kHz, but
the higher the frequency the better in general.

--
Dirk

The Consensus:-
The political party for the new millennium
http://www.theconsensus.org
 
"Dirk Bruere at Neopax" <dirk@neopax.com> wrote in message news:c3sjcb$2a1niv$1@ID-120108.news.uni-berlin.de...
"ChronoFish" <deja@chronofish.com> wrote in message
news:JSj8c.2485$EW1.1031@lakeread03...


How can I increase my communications distance? Would it be better to
increase the windings, increase the size of the loop, or both?


Are you using a resonant circuit tuned to 30kHz in the receiver?

Hi Dirk,
Click to expand...

Thanks for answering. Again I have to confess that I know nothing....

What I've got is a loop antenna (I now have 2 that I've tested. The first is a 10cm circular loop and the second is a 12cm x 17cm
rectangle. Both about 7mm thick using red magnet wire (I don't know how thick it is, it comes in a three pack at radio shack - the
copper is thickest, then the green, then the red.

I simply plug these between ground and the input into my "receiver" which is a LM386 opamp, then some RC (and diode) filters, then
another LM386 opamp. (I know my techniques suck - but I'm enjoying every minute of it!)

To answer your question - I have not set anything up to purposely "tune" the receiver. So it kind of operates like a "broadband"
inductor (it loves my dual monitor setup which I have to turn off when I test anything further than 13cm). If any "tuning" is
happening it's through the RC filter.

Thanks!
CF
 
I read in sci.electronics.design that Ken Smith
<kensmith@violet.rahul.net> wrote (in <c3soio$7rf$1@blue.rahul.net>)
about 'Magnetic Induction - how to improve distance', on Wed, 24 Mar
2004:
Typically, in a "magnetic induction" system, the frequency is so low
that the impedance of the coils is very near zero.
Click to expand...
What sort of magnetic induction system do you mean? For induction-loop
systems for assisted hearing, the inductance of the sending antenna is a
major factor in design, and the receiving antenna is typically an
inductor of several hundred millihenrys.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
"ChronoFish" <deja@chronofish.com> wrote in message
news:Zhm8c.2500$EW1.2367@lakeread03...
"Dirk Bruere at Neopax" <dirk@neopax.com> wrote in message
news:c3sjcb$2a1niv$1@ID-120108.news.uni-berlin.de...


"ChronoFish" <deja@chronofish.com> wrote in message
news:JSj8c.2485$EW1.1031@lakeread03...


How can I increase my communications distance? Would it be better
to
increase the windings, increase the size of the loop, or both?


Are you using a resonant circuit tuned to 30kHz in the receiver?

Hi Dirk,

Thanks for answering. Again I have to confess that I know nothing....

What I've got is a loop antenna (I now have 2 that I've tested. The first
is a 10cm circular loop and the second is a 12cm x 17cm
rectangle. Both about 7mm thick using red magnet wire (I don't know how
thick it is, it comes in a three pack at radio shack - the
copper is thickest, then the green, then the red.

I simply plug these between ground and the input into my "receiver" which
is a LM386 opamp, then some RC (and diode) filters, then
another LM386 opamp. (I know my techniques suck - but I'm enjoying every
minute of it!)

To answer your question - I have not set anything up to purposely "tune"
the receiver. So it kind of operates like a "broadband"
inductor (it loves my dual monitor setup which I have to turn off when I
test anything further than 13cm). If any "tuning" is
happening it's through the RC filter.
Click to expand...
Try putting a cap in parallel with the coil such that its resonant frequency
is about 30kHz. The width of the resonance is determined by the resistance
of the coil.
http://www.allaboutcircuits.com/vol_2/chpt_6/2.html

--
Dirk

The Consensus:-
The political party for the new millennium
http://www.theconsensus.org
 
"ChronoFish" <deja@chronofish.com> wrote in message news:<sph8c.2479$EW1.991@lakeread03>...
Hello,

I am experimenting with magnetic induction for a PAN (personal area network) application. As with everything electronics this is
all new to me.

SO FAR:
So far I have been able to get a TX and RX to talk with each other at the 30-50cm range which I've been very happy with given it's
my first shot at it. I would like to extend that range 4x (about 1.5-2 meter).

On the TX I have a small (35mm x 5mm) ferrite (magnetic) core inductor that I ripped out of a sports heart monitor transmitter. I
can't go bigger because of the application. The power is about 7v and again I don't really have flexibility to increase the power
of the TX.

On the RX I have a 10cm air-core wire loop (about 7mm in thickness - I guess around 100 wounds - maybe more) feeding several series
of amplifiers. I will have more flexibility in terms of size of the loop (to a limit).

THE QUESTIONS:
How can I increase my communications distance? Would it be better to increase the windings, increase the size of the loop, or both?
Is a tightly bound loop better than one that varies in thickness? Also, will a rectangle shaped loop perform significantly worse
than a circle shaped loop?

Thanks!
CF
Click to expand...
The thing with this (and I designed some stuff for that in the past),
is
that to get more range, you need more current in the loop.
There are systems for translation in big halls that use such a loop,
in this case the data is modulated on one or mofre carriers (AM or
FM), think
frequencies from 25kHz to 150 kHz as carrier.
In such a case the inductance of the loop becomes a problem to get
current
in it, this can be solved by tuning the loop with a series capacitor
and coil.
I do not remember values exactly, but if you use 10mH and several nF
you can tune a loop in that range.
To get more bandwidth you can lower the Q by adding a series resistor.
Some (Philips) use a series lightbulb.
Now you can use any power amp that will work at that carrier.
For data transmission you can then use any scheme, narrow band FM
modulating
with 2 tones would work (old TI chips, I would have to look).
Anyways, with such a system I have covered halls with thousands of
people.
You may or may not need a license to operate at those frequnecies and
power
levels, ask you local regulator :)
JP
 
In article <UP+gVoIMYfYAFwJc@jmwa.demon.co.uk>,
John Woodgate <noone@yuk.yuk> wrote:
I read in sci.electronics.design that Ken Smith
kensmith@violet.rahul.net> wrote (in <c3soio$7rf$1@blue.rahul.net>)
about 'Magnetic Induction - how to improve distance', on Wed, 24 Mar
2004:
Typically, in a "magnetic induction" system, the frequency is so low
that the impedance of the coils is very near zero.

What sort of magnetic induction system do you mean? For induction-loop
systems for assisted hearing, the inductance of the sending antenna is a
major factor in design, and the receiving antenna is typically an
inductor of several hundred millihenrys.
Click to expand...
I was thinking mostly of EM systems such as the Geonics EM61 and the Mine
Labs F1 devices. I also thought of the systems I tinkered together many
years ago. In all of those cases the coil impedance is only a few Ohms or
few tens of Ohms.


--
--
kensmith@rahul.net forging knowledge
 
In article <X9LAJxGY9uYAFw7u@jmwa.demon.co.uk>,
John Woodgate <noone@yuk.yuk> wrote:
I read in sci.electronics.design that Ken Smith
kensmith@violet.rahul.net> wrote (in <c3uqam$58a$1@blue.rahul.net>)
about 'Magnetic Induction - how to improve distance', on Thu, 25 Mar
2004:
I was thinking mostly of EM systems such as the Geonics EM61 and the
Mine Labs F1 devices. I also thought of the systems I tinkered together
many years ago. In all of those cases the coil impedance is only a few
Ohms or few tens of Ohms.

Ah, well, metal detectors are a different kettle of worms entirely.
Click to expand...
I think the folks at Geonics would have a cow if you called the EM61 a
"metal detector".
--
--
kensmith@rahul.net forging knowledge
 
I read in sci.electronics.design that Ken Smith
<kensmith@violet.rahul.net> wrote (in <c3uqam$58a$1@blue.rahul.net>)
about 'Magnetic Induction - how to improve distance', on Thu, 25 Mar
2004:
I was thinking mostly of EM systems such as the Geonics EM61 and the
Mine Labs F1 devices. I also thought of the systems I tinkered together
many years ago. In all of those cases the coil impedance is only a few
Ohms or few tens of Ohms.
Click to expand...
Ah, well, metal detectors are a different kettle of worms entirely.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
I read in sci.electronics.design that Ken Smith
<kensmith@violet.rahul.net> wrote (in <c3uri6$58a$5@blue.rahul.net>)
about 'Magnetic Induction - how to improve distance', on Thu, 25 Mar
2004:
I think the folks at Geonics would have a cow if you called the EM61 a
"metal detector".
Click to expand...
I did a Google search for 'Geonics EM61 ' and that's what it came up
with:

METAL DETECTION. EM61. The EM61, one of the newest instruments from
GEONICS, is a time-domain metal detector which detects both ferrous and
non-ferrous metals. ...

That's also what the Geonics page itself says, of course. I now know
that it isn't the popular 'mine-detector' device but a geophysics
instrument, but who am I to argue that the manufacturer describes it
wrongly?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
In article <KcTXBbH66vYAFwKV@jmwa.demon.co.uk>,
John Woodgate <noone@yuk.yuk> wrote:
I read in sci.electronics.design that Ken Smith
kensmith@violet.rahul.net> wrote (in <c3uri6$58a$5@blue.rahul.net>)
about 'Magnetic Induction - how to improve distance', on Thu, 25 Mar
2004:
I think the folks at Geonics would have a cow if you called the EM61 a
"metal detector".

I did a Google search for 'Geonics EM61 ' and that's what it came up
with:

METAL DETECTION. EM61. The EM61, one of the newest instruments from
GEONICS, is a time-domain metal detector which detects both ferrous and
non-ferrous metals. ...
Click to expand...
When you consider that the EM61 is over 10 years old "one of the newest"
seems like an odd claim.

Q: When it is 1:00PM is LA what time is it in Toronto*?
A: About 1953

(*) I only say Toronto because I can't spell "Mississauga".

That's also what the Geonics page itself says, of course. I now know
that it isn't the popular 'mine-detector' device but a geophysics
instrument, but who am I to argue that the manufacturer describes it
wrongly?
Click to expand...
I'll have to discuss that with them.

--
--
kensmith@rahul.net forging knowledge
 
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