Drum Core Stray Magnetic Field

[Lasse Langwadt Christense]

Den sřndag den 1. marts 2015 kl. 17.30.58 UTC+1 skrev Klaus Kragelund:

On Sunday, March 1, 2015 at 1:09:38 PM UTC+1, meow...@care2.com wrote:
On Sunday, March 1, 2015 at 11:11:09 AM UTC, Klaus Kragelund wrote:
On Sunday, March 1, 2015 at 4:09:31 AM UTC+1, k...@attt.bizz wrote:
On Sat, 28 Feb 2015 18:58:38 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Sat, 28 Feb 2015 17:07:26 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Saturday, February 28, 2015 at 6:20:25 PM UTC+1, John Larkin wrote:
On Sat, 28 Feb 2015 09:38:23 -0600, "Tim Williams"
tiwill@seventransistorlabs.com> wrote:

You'll primarily have field lines coming off the edges of the top/bottom
plates and arcing through space. The field above and below won't be so
much, so that a vertical offset would be inconvenient (but on a planar
PCB, that doesn't matter!), but placing them side by side should give
quite reasonable "weak" coupling.

I would very, very roughly guess that the radial dropoff has a (x^2 +
a^2)^(-3/2) sort of function, with x being distance and a being related to
height (plate-to-plate centers distance) and diameter.

Is that the near-field approximation? Far-field is 1/d^3.



Tim

I was playing with the idea of mounting a pair of surface-mount drum
cores on opposite sides of a PC board, axially coupled, to make a high
voltage isolated coupler. But the customer went away so I didn't
develop the idea. Side-by-side should work, too.


That is pretty much the same I am trying out

Other idea is spiral turns, adding a custom ferrite cylinder to reduce the gap, but I do not think that will add much gain, since running in resonance would combat the gap

Cheers

Klaus

I am currently laying out a PCB with a bunch of test circuits, and I'm
going to include some "transformers" just for fun... spiral traces on
parallel PCB layers, some shielded and some not. No ferrites.

One of my coworkers tried it a year or so back. He tried a ferrite
core around the transformer, too. FR4 was too lossy to make it
worthwhile, for power anyway.

I did it once with spiral turns, two layer, got 70% efficiency (at tuned frequency)

But, I am looking another way, since the spiral turns requires 4 layer board and blind vias or some special way to get the inner spiral end out to the rest of the circuit

like a wire link? Just give the inner ends the required clearances.


That defeats the purpose. Required creepages are from 8mm to 12mm on outer layers depending on which standard and working voltage is relevant, so the spiral would need to be very large

Cheers

Klaus

a spiral on the top and bottom layer each with an smd 0R resistor to get out
from the center?, requires mounting components on both side, but apart from
that

-Lasse

 

[Klaus Kragelund]

On Sunday, March 1, 2015 at 5:40:21 PM UTC+1, Lasse Langwadt Christensen wrote:

Den sřndag den 1. marts 2015 kl. 17.30.58 UTC+1 skrev Klaus Kragelund:
On Sunday, March 1, 2015 at 1:09:38 PM UTC+1, meow...@care2.com wrote:
On Sunday, March 1, 2015 at 11:11:09 AM UTC, Klaus Kragelund wrote:
On Sunday, March 1, 2015 at 4:09:31 AM UTC+1, k...@attt.bizz wrote:
On Sat, 28 Feb 2015 18:58:38 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Sat, 28 Feb 2015 17:07:26 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Saturday, February 28, 2015 at 6:20:25 PM UTC+1, John Larkin wrote:
On Sat, 28 Feb 2015 09:38:23 -0600, "Tim Williams"
tiwill@seventransistorlabs.com> wrote:

You'll primarily have field lines coming off the edges of the top/bottom
plates and arcing through space. The field above and below won't be so
much, so that a vertical offset would be inconvenient (but on a planar
PCB, that doesn't matter!), but placing them side by side should give
quite reasonable "weak" coupling.

I would very, very roughly guess that the radial dropoff has a (x^2 +
a^2)^(-3/2) sort of function, with x being distance and a being related to
height (plate-to-plate centers distance) and diameter.

Is that the near-field approximation? Far-field is 1/d^3.



Tim

I was playing with the idea of mounting a pair of surface-mount drum
cores on opposite sides of a PC board, axially coupled, to make a high
voltage isolated coupler. But the customer went away so I didn't
develop the idea. Side-by-side should work, too.


That is pretty much the same I am trying out

Other idea is spiral turns, adding a custom ferrite cylinder to reduce the gap, but I do not think that will add much gain, since running in resonance would combat the gap

Cheers

Klaus

I am currently laying out a PCB with a bunch of test circuits, and I'm
going to include some "transformers" just for fun... spiral traces on
parallel PCB layers, some shielded and some not. No ferrites.

One of my coworkers tried it a year or so back. He tried a ferrite
core around the transformer, too. FR4 was too lossy to make it
worthwhile, for power anyway.

I did it once with spiral turns, two layer, got 70% efficiency (at tuned frequency)

But, I am looking another way, since the spiral turns requires 4 layer board and blind vias or some special way to get the inner spiral end out to the rest of the circuit

like a wire link? Just give the inner ends the required clearances.


That defeats the purpose. Required creepages are from 8mm to 12mm on outer layers depending on which standard and working voltage is relevant, so the spiral would need to be very large

Cheers

Klaus

a spiral on the top and bottom layer each with an smd 0R resistor to get out
from the center?, requires mounting components on both side, but apart from
that

Yes, that's pretty much the same as the SMD bridge (ultra larger 0R SMD). A standard SMD 0R is going to have big pads to brigde a decent number of spiral tracks, but yes it's a more standard solution, one which the production guys should have no problems with

Cheers

Klaus

 

[Klaus Kragelund]

On Sunday, March 1, 2015 at 5:29:17 PM UTC+1, Robert Macy wrote:

On Sun, 01 Mar 2015 04:11:00 -0700, Klaus Kragelund
klauskvik@hotmail.com> wrote:

...snip...

But, I am looking another way, since the spiral turns requires 4 layer
board and blind vias or some special way to get the inner spiral end out
to the rest of the circuit

It's fun. Kind of strange it is not seen often (I have never seen it in
a product). It way cheaper than any other method, except for isolation
via FR4 capacitances

Cheers

Klaus

Doesn't require blind vias.

I used the 'spiral' PCB coil in a Medical Product. Cheapest way to make a
robust 100 turn coil was to use 6 layer 32 mil PCB cut into 2 inch round
discs. 100 Turns was easy with good layout and judicious crossovers, only
requires a few vias, work it out. The Q was awful as expected, but the
circuit did NOT rely upon Q to operate.

One PCB coil was Tx, the other Rx. Current in TX created a magnetic field
that you could see in Rx and uniquely identify. Based upon the principle
that magnetic fields drop off at a known rate, it was possible to
determine the distance between a set of Tx and Rx discs. Plus, magnetic
fields go right through the human body so...with four discs placed
judiciously against the skin around the lungs, you could observe several
distances. TxA to RxA, TxA to RxB, TxB to RxA, and TxB to RxB. See how by
adding more discs you get a permutation of measurements and really make it
possible to reconstruct lung volume [breathing] in real time? The discs
being very flat fit comfortably into pockets in a flexible vest. The vest
was used for monitoring a patence's health in situ. My disc system design
replaced iron core 'lumps' used in a demo prototype. The PCB discs were
more accurate, had lower noise floor, and were much more comfortable,
easier to sleep on, than having little 3/8 to 1/2 inch lumps caused by
using expensive iron core coils. The system could measure distances easily
anywhere from 6 inch to 28 inch distances. How accurate? At 8 inch
separateion the measured noise floor was 1 mil, yes, 1 mil rms noise
MEASURED. Not bad for a 'cheap' system. Plus it operated below 10kHz, so
no 'pesky' regulatory issues and even operated to spec while sitting in
front of an OLD magnetic deflection monitor at a PC.

Each Tx/Rx PAIR required around 5 mA total from a 3.3 Vdc supply, so was
VERY battery friendly for portable operation. Plus, I got to 'piggy-back'
all the logic/control into the existing TI's MSP430, so logic was 'free'
and the cost of all the extra hardware was negligible except for the $0.25
PCB coil.

I've got a couple of PCB discs around here, and may even have a sample
gerber file. Do you want pics? Let me know and if your email address
appears correctly as hotmail.com; I'll send you what I've got laying
around here.

Your solution sounds really ingenious. If you have time, then please send to my hotmail ;-)

Thanks

Klaus

 

[Klaus Kragelund]

On Sunday, March 1, 2015 at 5:50:59 PM UTC+1, Robert Macy wrote:

On Sun, 01 Mar 2015 09:30:54 -0700, Klaus Kragelund
klauskvik@hotmail.com> wrote:

...snip....
That defeats the purpose. Required creepages are from 8mm to 12mm on
outer layers depending on which standard and working voltage is
relevant, so the spiral would need to be very large

Cheers

Klaus

Magnetic fields are insidious, once made they're hard to get rid of. They
go EVERYWHERE! I've got cheap broadband magnetic receivers that can tap a
phone line. undetectably, from 3 ft away.

Again, you NEED to get a copy of FREE femm 4.2 and do some 'engineering'
to replace preconceived notions that cause you to say things like the
spiral has "to be very large".

I did download it a couple of months ago (due to one of your great posts)

Right now I have another project running, and the spiral experiments are done on my own time and have pushed off the femm tool due to the learning curve. But I guess I should get started, will probably pay off in the long run (the design cycle time is very short compared to ordering and testing PCBs)

For example, it is EASY to communicate between spiral coils at a
separation distance equal to the diameter. At separations of 2 times
diameter, you have to be more careful in the design. And, at 3 times
diameter of separation, since only around 1% of the field makes it out
that far, designs are doable, but just must be careful on your design.

That sounds interesting. The previous experiment I did, I had a 9 turn spiral, 10mm dia, seperated 1.6mm. So that does have pretty good coupling. I knew that allready, these guys has done a lot of experiments:

http://www3.nd.edu/~stjoseph/newscas/CAS_Sept00.pdf

Cheers

Klaus

 

[Klaus Kragelund]

On Sunday, March 1, 2015 at 5:53:38 PM UTC+1, Robert Macy wrote:

On Sun, 01 Mar 2015 09:49:33 -0700, Klaus Kragelund
klauskvik@hotmail.com> wrote:

...snip...

Your solution sounds really ingenious. If you have time, then please
send to my hotmail ;-)

Thanks

Klaus

will do, may take a day, or so.

Thanks

 

On Sunday, March 1, 2015 at 4:30:58 PM UTC, Klaus Kragelund wrote:

On Sunday, March 1, 2015 at 1:09:38 PM UTC+1, meow...@care2.com wrote:
On Sunday, March 1, 2015 at 11:11:09 AM UTC, Klaus Kragelund wrote:
On Sunday, March 1, 2015 at 4:09:31 AM UTC+1, k...@attt.bizz wrote:
On Sat, 28 Feb 2015 18:58:38 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Sat, 28 Feb 2015 17:07:26 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Saturday, February 28, 2015 at 6:20:25 PM UTC+1, John Larkin wrote:
On Sat, 28 Feb 2015 09:38:23 -0600, "Tim Williams"
tiwill@seventransistorlabs.com> wrote:

You'll primarily have field lines coming off the edges of the top/bottom
plates and arcing through space. The field above and below won't be so
much, so that a vertical offset would be inconvenient (but on a planar
PCB, that doesn't matter!), but placing them side by side should give
quite reasonable "weak" coupling.

I would very, very roughly guess that the radial dropoff has a (x^2 +
a^2)^(-3/2) sort of function, with x being distance and a being related to
height (plate-to-plate centers distance) and diameter.

Is that the near-field approximation? Far-field is 1/d^3.



Tim

I was playing with the idea of mounting a pair of surface-mount drum
cores on opposite sides of a PC board, axially coupled, to make a high
voltage isolated coupler. But the customer went away so I didn't
develop the idea. Side-by-side should work, too.


That is pretty much the same I am trying out

Other idea is spiral turns, adding a custom ferrite cylinder to reduce the gap, but I do not think that will add much gain, since running in resonance would combat the gap

Cheers

Klaus

I am currently laying out a PCB with a bunch of test circuits, and I'm
going to include some "transformers" just for fun... spiral traces on
parallel PCB layers, some shielded and some not. No ferrites.

One of my coworkers tried it a year or so back. He tried a ferrite
core around the transformer, too. FR4 was too lossy to make it
worthwhile, for power anyway.

I did it once with spiral turns, two layer, got 70% efficiency (at tuned frequency)

But, I am looking another way, since the spiral turns requires 4 layer board and blind vias or some special way to get the inner spiral end out to the rest of the circuit

like a wire link? Just give the inner ends the required clearances.


That defeats the purpose. Required creepages are from 8mm to 12mm on outer layers depending on which standard and working voltage is relevant, so the spiral would need to be very large

Cheers

Klaus

If you cant spare the extra size, dispense with a separate pad and solder a rigid bridge onto the end of the spiral coil.

The bridge to coil gap only sees the V across the winding, so I wouldnt expect hipot creepage distances to come into it.

You can also let solder stick to the spiral tracks to reduce ESR.


NT

 

[Lasse Langwadt Christense]

Den sřndag den 1. marts 2015 kl. 17.47.09 UTC+1 skrev Klaus Kragelund:

On Sunday, March 1, 2015 at 5:40:21 PM UTC+1, Lasse Langwadt Christensen wrote:
Den sřndag den 1. marts 2015 kl. 17.30.58 UTC+1 skrev Klaus Kragelund:
On Sunday, March 1, 2015 at 1:09:38 PM UTC+1, meow...@care2.com wrote:
On Sunday, March 1, 2015 at 11:11:09 AM UTC, Klaus Kragelund wrote:
On Sunday, March 1, 2015 at 4:09:31 AM UTC+1, k...@attt.bizz wrote:
On Sat, 28 Feb 2015 18:58:38 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Sat, 28 Feb 2015 17:07:26 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Saturday, February 28, 2015 at 6:20:25 PM UTC+1, John Larkin wrote:
On Sat, 28 Feb 2015 09:38:23 -0600, "Tim Williams"
tiwill@seventransistorlabs.com> wrote:

You'll primarily have field lines coming off the edges of the top/bottom
plates and arcing through space. The field above and below won't be so
much, so that a vertical offset would be inconvenient (but on a planar
PCB, that doesn't matter!), but placing them side by side should give
quite reasonable "weak" coupling.

I would very, very roughly guess that the radial dropoff has a (x^2 +
a^2)^(-3/2) sort of function, with x being distance and a being related to
height (plate-to-plate centers distance) and diameter.

Is that the near-field approximation? Far-field is 1/d^3.



Tim

I was playing with the idea of mounting a pair of surface-mount drum
cores on opposite sides of a PC board, axially coupled, to make a high
voltage isolated coupler. But the customer went away so I didn't
develop the idea. Side-by-side should work, too.


That is pretty much the same I am trying out

Other idea is spiral turns, adding a custom ferrite cylinder to reduce the gap, but I do not think that will add much gain, since running in resonance would combat the gap

Cheers

Klaus

I am currently laying out a PCB with a bunch of test circuits, and I'm
going to include some "transformers" just for fun... spiral traces on
parallel PCB layers, some shielded and some not. No ferrites.

One of my coworkers tried it a year or so back. He tried a ferrite
core around the transformer, too. FR4 was too lossy to make it
worthwhile, for power anyway.

I did it once with spiral turns, two layer, got 70% efficiency (at tuned frequency)

But, I am looking another way, since the spiral turns requires 4 layer board and blind vias or some special way to get the inner spiral end out to the rest of the circuit

like a wire link? Just give the inner ends the required clearances.


That defeats the purpose. Required creepages are from 8mm to 12mm on outer layers depending on which standard and working voltage is relevant, so the spiral would need to be very large

Cheers

Klaus

a spiral on the top and bottom layer each with an smd 0R resistor to get out
from the center?, requires mounting components on both side, but apart from
that

Yes, that's pretty much the same as the SMD bridge (ultra larger 0R SMD). A standard SMD 0R is going to have big pads to brigde a decent number of spiral tracks, but yes it's a more standard solution, one which the production guys should have no problems with

Cheers

Klaus

I guess you could also make the coils on separate small pcbs and surface mount them like that many modules

-Lasse

 

[RobertMacy]

On Sun, 01 Mar 2015 04:11:00 -0700, Klaus Kragelund
<klauskvik@hotmail.com> wrote:

...snip...

But, I am looking another way, since the spiral turns requires 4 layer
board and blind vias or some special way to get the inner spiral end out
to the rest of the circuit

It's fun. Kind of strange it is not seen often (I have never seen it in
a product). It way cheaper than any other method, except for isolation
via FR4 capacitances

Cheers

Klaus

Doesn't require blind vias.

I used the 'spiral' PCB coil in a Medical Product. Cheapest way to make a
robust 100 turn coil was to use 6 layer 32 mil PCB cut into 2 inch round
discs. 100 Turns was easy with good layout and judicious crossovers, only
requires a few vias, work it out. The Q was awful as expected, but the
circuit did NOT rely upon Q to operate.

One PCB coil was Tx, the other Rx. Current in TX created a magnetic field
that you could see in Rx and uniquely identify. Based upon the principle
that magnetic fields drop off at a known rate, it was possible to
determine the distance between a set of Tx and Rx discs. Plus, magnetic
fields go right through the human body so...with four discs placed
judiciously against the skin around the lungs, you could observe several
distances. TxA to RxA, TxA to RxB, TxB to RxA, and TxB to RxB. See how by
adding more discs you get a permutation of measurements and really make it
possible to reconstruct lung volume [breathing] in real time? The discs
being very flat fit comfortably into pockets in a flexible vest. The vest
was used for monitoring a patence's health in situ. My disc system design
replaced iron core 'lumps' used in a demo prototype. The PCB discs were
more accurate, had lower noise floor, and were much more comfortable,
easier to sleep on, than having little 3/8 to 1/2 inch lumps caused by
using expensive iron core coils. The system could measure distances easily
anywhere from 6 inch to 28 inch distances. How accurate? At 8 inch
separateion the measured noise floor was 1 mil, yes, 1 mil rms noise
MEASURED. Not bad for a 'cheap' system. Plus it operated below 10kHz, so
no 'pesky' regulatory issues and even operated to spec while sitting in
front of an OLD magnetic deflection monitor at a PC.

Each Tx/Rx PAIR required around 5 mA total from a 3.3 Vdc supply, so was
VERY battery friendly for portable operation. Plus, I got to 'piggy-back'
all the logic/control into the existing TI's MSP430, so logic was 'free'
and the cost of all the extra hardware was negligible except for the $0.25
PCB coil.

I've got a couple of PCB discs around here, and may even have a sample
gerber file. Do you want pics? Let me know and if your email address
appears correctly as hotmail.com; I'll send you what I've got laying
around here.

Robert

 

[Klaus Kragelund]

On Sunday, March 1, 2015 at 8:01:55 PM UTC+1, Frnak McKenney wrote:

On Sat, 28 Feb 2015 02:18:26 -0800 (PST), Klaus Kragelund <klauskvik@hotmail.com> wrote:
Hi

I have an application in which I need high stray field from a drum core
in order to pass a signal on to another drum core

Anyone ever measured the stray field above a drum core? Someting like
this type:

http://image.made-in-china.com/43f34j00PsZtJgRaZiqd/SMD-Unshielded-Power-Inductors.jpg

It is non shielded, which is good for stray field, but it has a small
"hat", so that bends the field somewhat

Klaus,

While your request was for measurement -- which implies numbers --
something in these might offer you a way to visualize what the field
shape looks like before you begin measuring:

http://www.evilmadscientist.com/2010/start-seeing-magnetic-fields/

Flow and Visualization: Shallow Ferrofluid in Magnetic Field
https://www.youtube.com/watch?v=A_soOzadtHU

http://www.colorado.edu/engineering/MCEN/flowvis/galleries/2011/Team-1/Reports/DiMarco_Dominic.pdf

http://www.instructables.com/id/ferromagnetic-fluid/

That might -- or might not -- be useful.

Those are some great links, especially the first one, I like the one with the magnetoresistive sensor

Thanks

Klaus

 

[Klaus Kragelund]

On Sunday, March 1, 2015 at 9:00:29 PM UTC+1, meow...@care2.com wrote:

On Sunday, March 1, 2015 at 4:30:58 PM UTC, Klaus Kragelund wrote:
On Sunday, March 1, 2015 at 1:09:38 PM UTC+1, meow...@care2.com wrote:
On Sunday, March 1, 2015 at 11:11:09 AM UTC, Klaus Kragelund wrote:
On Sunday, March 1, 2015 at 4:09:31 AM UTC+1, k...@attt.bizz wrote:
On Sat, 28 Feb 2015 18:58:38 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Sat, 28 Feb 2015 17:07:26 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Saturday, February 28, 2015 at 6:20:25 PM UTC+1, John Larkin wrote:
On Sat, 28 Feb 2015 09:38:23 -0600, "Tim Williams"
tiwill@seventransistorlabs.com> wrote:

You'll primarily have field lines coming off the edges of the top/bottom
plates and arcing through space. The field above and below won't be so
much, so that a vertical offset would be inconvenient (but on a planar
PCB, that doesn't matter!), but placing them side by side should give
quite reasonable "weak" coupling.

I would very, very roughly guess that the radial dropoff has a (x^2 +
a^2)^(-3/2) sort of function, with x being distance and a being related to
height (plate-to-plate centers distance) and diameter.

Is that the near-field approximation? Far-field is 1/d^3.



Tim

I was playing with the idea of mounting a pair of surface-mount drum
cores on opposite sides of a PC board, axially coupled, to make a high
voltage isolated coupler. But the customer went away so I didn't
develop the idea. Side-by-side should work, too.


That is pretty much the same I am trying out

Other idea is spiral turns, adding a custom ferrite cylinder to reduce the gap, but I do not think that will add much gain, since running in resonance would combat the gap

Cheers

Klaus

I am currently laying out a PCB with a bunch of test circuits, and I'm
going to include some "transformers" just for fun... spiral traces on
parallel PCB layers, some shielded and some not. No ferrites.

One of my coworkers tried it a year or so back. He tried a ferrite
core around the transformer, too. FR4 was too lossy to make it
worthwhile, for power anyway.

I did it once with spiral turns, two layer, got 70% efficiency (at tuned frequency)

But, I am looking another way, since the spiral turns requires 4 layer board and blind vias or some special way to get the inner spiral end out to the rest of the circuit

like a wire link? Just give the inner ends the required clearances.


That defeats the purpose. Required creepages are from 8mm to 12mm on outer layers depending on which standard and working voltage is relevant, so the spiral would need to be very large

Cheers

Klaus

If you cant spare the extra size, dispense with a separate pad and solder a rigid bridge onto the end of the spiral coil.

The bridge to coil gap only sees the V across the winding, so I wouldnt expect hipot creepage distances to come into it.

I'm not sure exactly what you mean. The SMD bridge "sees" only low voltage, but still needs to keep the creepage and clearance from the secondary side (the bridge is used to avoid the via, and the problems that causes)

> You can also let solder stick to the spiral tracks to reduce ESR.

Yes. Generally that will only reduce the ESR by 15% (if my memory serves me well) and create problems with possible solder bridges/shorts)

 

[Klaus Kragelund]

On Sunday, March 1, 2015 at 9:13:42 PM UTC+1, Robert Baer wrote:

Klaus Kragelund wrote:
Hi

I have an application in which I need high stray field from a drum core in order to pass a signal on to another drum core

Anyone ever measured the stray field above a drum core? Someting like this type:

http://image.made-in-china.com/43f34j00PsZtJgRaZiqd/SMD-Unshielded-Power-Inductors.jpg

It is non shielded, which is good for stray field, but it has a small "hat", so that bends the field somewhat

Cheers

Klaus
Totally impractical for numerous reasons:
1) Magnetic field strength seen at a distance is at best a 1/r relation,
so to get any transfer, the two drums will have to be VERY close
together (as in touching).

The will be close, only separated by 0.4mm FR4

2) The rotational speeds must be synced exactly to prevent surface slippage.
Far saner to transfer signal from read head to write head.

Can you elaborate? What is this about?

Thanks

Klaus

 

[RobertMacy]

On Sun, 01 Mar 2015 09:30:54 -0700, Klaus Kragelund
<klauskvik@hotmail.com> wrote:

...snip....
That defeats the purpose. Required creepages are from 8mm to 12mm on
outer layers depending on which standard and working voltage is
relevant, so the spiral would need to be very large

Cheers

Klaus

Magnetic fields are insidious, once made they're hard to get rid of. They
go EVERYWHERE! I've got cheap broadband magnetic receivers that can tap a
phone line. undetectably, from 3 ft away.

Again, you NEED to get a copy of FREE femm 4.2 and do some 'engineering'
to replace preconceived notions that cause you to say things like the
spiral has "to be very large".

For example, it is EASY to communicate between spiral coils at a
separation distance equal to the diameter. At separations of 2 times
diameter, you have to be more careful in the design. And, at 3 times
diameter of separation, since only around 1% of the field makes it out
that far, designs are doable, but just must be careful on your design.

You'd be surprised just how far magnetic fields can emanate. I've gotten
Communication System Designs based upon magnetic fields to work at two
miles separation using realistic power, for monitoring 'down-hole' well
drilling.

 

[RobertMacy]

On Sun, 01 Mar 2015 09:49:33 -0700, Klaus Kragelund
<klauskvik@hotmail.com> wrote:

...snip...

Your solution sounds really ingenious. If you have time, then please
send to my hotmail ;-)

Thanks

Klaus

will do, may take a day, or so.

 

[Klaus Kragelund]

On Sunday, March 1, 2015 at 9:19:17 PM UTC+1, Lasse Langwadt Christensen wrote:

Den sřndag den 1. marts 2015 kl. 17.47.09 UTC+1 skrev Klaus Kragelund:
On Sunday, March 1, 2015 at 5:40:21 PM UTC+1, Lasse Langwadt Christensen wrote:
Den sřndag den 1. marts 2015 kl. 17.30.58 UTC+1 skrev Klaus Kragelund:
On Sunday, March 1, 2015 at 1:09:38 PM UTC+1, meow...@care2.com wrote:
On Sunday, March 1, 2015 at 11:11:09 AM UTC, Klaus Kragelund wrote:
On Sunday, March 1, 2015 at 4:09:31 AM UTC+1, k...@attt.bizz wrote:
On Sat, 28 Feb 2015 18:58:38 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Sat, 28 Feb 2015 17:07:26 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Saturday, February 28, 2015 at 6:20:25 PM UTC+1, John Larkin wrote:
On Sat, 28 Feb 2015 09:38:23 -0600, "Tim Williams"
tiwill@seventransistorlabs.com> wrote:

You'll primarily have field lines coming off the edges of the top/bottom
plates and arcing through space. The field above and below won't be so
much, so that a vertical offset would be inconvenient (but on a planar
PCB, that doesn't matter!), but placing them side by side should give
quite reasonable "weak" coupling.

I would very, very roughly guess that the radial dropoff has a (x^2 +
a^2)^(-3/2) sort of function, with x being distance and a being related to
height (plate-to-plate centers distance) and diameter.

Is that the near-field approximation? Far-field is 1/d^3.



Tim

I was playing with the idea of mounting a pair of surface-mount drum
cores on opposite sides of a PC board, axially coupled, to make a high
voltage isolated coupler. But the customer went away so I didn't
develop the idea. Side-by-side should work, too.


That is pretty much the same I am trying out

Other idea is spiral turns, adding a custom ferrite cylinder to reduce the gap, but I do not think that will add much gain, since running in resonance would combat the gap

Cheers

Klaus

I am currently laying out a PCB with a bunch of test circuits, and I'm
going to include some "transformers" just for fun... spiral traces on
parallel PCB layers, some shielded and some not. No ferrites..

One of my coworkers tried it a year or so back. He tried a ferrite
core around the transformer, too. FR4 was too lossy to make it
worthwhile, for power anyway.

I did it once with spiral turns, two layer, got 70% efficiency (at tuned frequency)

But, I am looking another way, since the spiral turns requires 4 layer board and blind vias or some special way to get the inner spiral end out to the rest of the circuit

like a wire link? Just give the inner ends the required clearances.


That defeats the purpose. Required creepages are from 8mm to 12mm on outer layers depending on which standard and working voltage is relevant, so the spiral would need to be very large

Cheers

Klaus

a spiral on the top and bottom layer each with an smd 0R resistor to get out
from the center?, requires mounting components on both side, but apart from
that

Yes, that's pretty much the same as the SMD bridge (ultra larger 0R SMD). A standard SMD 0R is going to have big pads to brigde a decent number of spiral tracks, but yes it's a more standard solution, one which the production guys should have no problems with

Cheers

Klaus

I guess you could also make the coils on separate small pcbs and surface mount them like that many modules

Yes. My thought was to mount one on a base PCB like an normal SMD inductor. Then have the PCB milled 1.2mm down from the other side, mount the other coil on a add-on PCB, flip that over and mount this. So the coils are 0.4mm apart on a 1.6mm PCB

But, I am not sure if the board manufactor can mill a non-through hole...

Cheers

Klaus

 

[John Larkin]

On Sun, 1 Mar 2015 09:06:14 -0800 (PST), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

On Sunday, March 1, 2015 at 5:50:59 PM UTC+1, Robert Macy wrote:
On Sun, 01 Mar 2015 09:30:54 -0700, Klaus Kragelund
klauskvik@hotmail.com> wrote:

...snip....
That defeats the purpose. Required creepages are from 8mm to 12mm on
outer layers depending on which standard and working voltage is
relevant, so the spiral would need to be very large

Cheers

Klaus

Magnetic fields are insidious, once made they're hard to get rid of. They
go EVERYWHERE! I've got cheap broadband magnetic receivers that can tap a
phone line. undetectably, from 3 ft away.

Again, you NEED to get a copy of FREE femm 4.2 and do some 'engineering'
to replace preconceived notions that cause you to say things like the
spiral has "to be very large".


I did download it a couple of months ago (due to one of your great posts)

Right now I have another project running, and the spiral experiments are done on my own time and have pushed off the femm tool due to the learning curve. But I guess I should get started, will probably pay off in the long run (the design cycle time is very short compared to ordering and testing PCBs)


For example, it is EASY to communicate between spiral coils at a
separation distance equal to the diameter. At separations of 2 times
diameter, you have to be more careful in the design. And, at 3 times
diameter of separation, since only around 1% of the field makes it out
that far, designs are doable, but just must be careful on your design.


That sounds interesting. The previous experiment I did, I had a 9 turn spiral, 10mm dia, seperated 1.6mm. So that does have pretty good coupling. I knew that allready, these guys has done a lot of experiments:

http://www3.nd.edu/~stjoseph/newscas/CAS_Sept00.pdf

Cheers

Klaus

That's cool. Unfortunately (or maybe fortunately) I work with fast
pulses, so I can't resonate the coils. Tuning has a remarkable effect
on coupling efficiency.




--

John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Tim Williams]

"RobertMacy" <robert.a.macy@gmail.com> wrote in message
newsp.xutcqseu2cx0wh@ajm...

Still say, get a copy of femm 4.2 and model two cores in axisymmetric
mode. Both to get good estimates and to gain understanding of just how
insidious magnetic fields can be!

You can even 'recreate' Tim's formula.

But it doesn't have analytical output, does it?

You could do a plot of given geometry (some fixed ratio of width and
height) vs. distance and get a series of values, then curve fit a similar
equation. Which of course has the same problems as trying to draw up the
approximate equation from first principles, but with a known error bar and
no need for hefty E&M equations. On the upside, even if you end up with
linear interpolations between data sets, you're doing pretty good.

Tim

--
Seven Transistor Labs
Electrical Engineering Consultation
Website: http://seventransistorlabs.com

 

[Frnak McKenney]

On Sat, 28 Feb 2015 02:18:26 -0800 (PST), Klaus Kragelund <klauskvik@hotmail.com> wrote:

Hi

I have an application in which I need high stray field from a drum core
in order to pass a signal on to another drum core

Anyone ever measured the stray field above a drum core? Someting like
this type:

http://image.made-in-china.com/43f34j00PsZtJgRaZiqd/SMD-Unshielded-Power-Inductors.jpg

It is non shielded, which is good for stray field, but it has a small
"hat", so that bends the field somewhat

Klaus,

While your request was for measurement -- which implies numbers --
something in these might offer you a way to visualize what the field
shape looks like before you begin measuring:

http://www.evilmadscientist.com/2010/start-seeing-magnetic-fields/

Flow and Visualization: Shallow Ferrofluid in Magnetic Field
https://www.youtube.com/watch?v=A_soOzadtHU

http://www.colorado.edu/engineering/MCEN/flowvis/galleries/2011/Team-1/Reports/DiMarco_Dominic.pdf

http://www.instructables.com/id/ferromagnetic-fluid/

That might -- or might not -- be useful.


Frank McKenney
--
An education isn't how much you have committed to memory, or
even how much you know. It's being able to differentiate between
what you do know and what you don't.  -- Anatole France
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney aatt mindspring ddoott com

 

[Robert Baer]

Klaus Kragelund wrote:

Hi

I have an application in which I need high stray field from a drum core in order to pass a signal on to another drum core

Anyone ever measured the stray field above a drum core? Someting like this type:

http://image.made-in-china.com/43f34j00PsZtJgRaZiqd/SMD-Unshielded-Power-Inductors.jpg

It is non shielded, which is good for stray field, but it has a small "hat", so that bends the field somewhat

Cheers

Klaus

Totally impractical for numerous reasons:
1) Magnetic field strength seen at a distance is at best a 1/r relation,
so to get any transfer, the two drums will have to be VERY close
together (as in touching).
2) The rotational speeds must be synced exactly to prevent surface slippage.
Far saner to transfer signal from read head to write head.


2

 

On Sunday, March 1, 2015 at 9:47:50 PM UTC, Klaus Kragelund wrote:

On Sunday, March 1, 2015 at 9:00:29 PM UTC+1, meow...@care2.com wrote:
On Sunday, March 1, 2015 at 4:30:58 PM UTC, Klaus Kragelund wrote:
On Sunday, March 1, 2015 at 1:09:38 PM UTC+1, meow...@care2.com wrote:
On Sunday, March 1, 2015 at 11:11:09 AM UTC, Klaus Kragelund wrote:
On Sunday, March 1, 2015 at 4:09:31 AM UTC+1, k...@attt.bizz wrote:
On Sat, 28 Feb 2015 18:58:38 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Sat, 28 Feb 2015 17:07:26 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Saturday, February 28, 2015 at 6:20:25 PM UTC+1, John Larkin wrote:
On Sat, 28 Feb 2015 09:38:23 -0600, "Tim Williams"
tiwill@seventransistorlabs.com> wrote:

You'll primarily have field lines coming off the edges of the top/bottom
plates and arcing through space. The field above and below won't be so
much, so that a vertical offset would be inconvenient (but on a planar
PCB, that doesn't matter!), but placing them side by side should give
quite reasonable "weak" coupling.

I would very, very roughly guess that the radial dropoff has a (x^2 +
a^2)^(-3/2) sort of function, with x being distance and a being related to
height (plate-to-plate centers distance) and diameter.

Is that the near-field approximation? Far-field is 1/d^3.



Tim

I was playing with the idea of mounting a pair of surface-mount drum
cores on opposite sides of a PC board, axially coupled, to make a high
voltage isolated coupler. But the customer went away so I didn't
develop the idea. Side-by-side should work, too.


That is pretty much the same I am trying out

Other idea is spiral turns, adding a custom ferrite cylinder to reduce the gap, but I do not think that will add much gain, since running in resonance would combat the gap

Cheers

Klaus

I am currently laying out a PCB with a bunch of test circuits, and I'm
going to include some "transformers" just for fun... spiral traces on
parallel PCB layers, some shielded and some not. No ferrites.

One of my coworkers tried it a year or so back. He tried a ferrite
core around the transformer, too. FR4 was too lossy to make it
worthwhile, for power anyway.

I did it once with spiral turns, two layer, got 70% efficiency (at tuned frequency)

But, I am looking another way, since the spiral turns requires 4 layer board and blind vias or some special way to get the inner spiral end out to the rest of the circuit

like a wire link? Just give the inner ends the required clearances.


That defeats the purpose. Required creepages are from 8mm to 12mm on outer layers depending on which standard and working voltage is relevant, so the spiral would need to be very large

Cheers

Klaus

If you cant spare the extra size, dispense with a separate pad and solder a rigid bridge onto the end of the spiral coil.

The bridge to coil gap only sees the V across the winding, so I wouldnt expect hipot creepage distances to come into it.


I'm not sure exactly what you mean. The SMD bridge "sees" only low voltage, but still needs to keep the creepage and clearance from the secondary side (the bridge is used to avoid the via, and the problems that causes)

Use a wire link but instead of mounting it thru hole, mount it sm. Either its raised or insulated to prevent shorting. With no through holes, clearance isnt an issue introduced by the wire.

I've seen preformed flat wire bridges used.

You can also let solder stick to the spiral tracks to reduce ESR.

Yes. Generally that will only reduce the ESR by 15% (if my memory serves me well) and create problems with possible solder bridges/shorts)

Better suited to wide tracks than fine ones, where one can mask off the outer edges of the tracks. Bridging is normally prevented by patterning the solder mask. But I guarantee nothing!


NT

 

[RobertMacy]

On Sun, 01 Mar 2015 14:38:02 -0700, Klaus Kragelund
<klauskvik@hotmail.com> wrote:

...snip....
Those are some great links, especially the first one, I like the one
with the magnetoresistive sensor

Thanks

Klaus

manufacturer GMR Magnetic Field Sensor:

NVE Corporation (800) GMR-7141 (800) 467-7141
11409 Valley View Road
Eden Prairie, MN 55344
http://www.nve.com

Only thing to keep in mind is that the BMR sensor has a 'built-in' noise
floor you can't get around. For example 9k ohm sensor has the johnson
noise of 9k ohms, and then you're stuck. Also, a bit tricky to make
really, really linear. But DOES have the advantage of being a 'point'
sensor, unlike the broader coil.

I think NVE has some good AppNotes and tutorials.