# transformer core flux propagation speed

Started by April 13, 2012
```Hi,

I was curious about how fast the winding induced flux will propagate
through a transformer core (ie a ferrite core) assuming a single
primary winding on a toroid?  Would it be possible to make a resonant
transformer using core geometry (ie replacing the toroid with a shape
that has a sine wave on the toroid).  If the switching frequency is high
enough, maybe it is possible to utilize the finite flux propagation
speed (ie. by using resonant flux switching to give different simulated
urns ratios etc)

cheers,
Jamie
```
```On Fri, 13 Apr 2012 15:15:43 -0700, Jamie M wrote:

> Hi,
>
> I was curious about how fast the winding induced flux will propagate
> through a transformer core (ie a ferrite core) assuming a single primary
> winding on a toroid?  Would it be possible to make a resonant
> transformer using core geometry (ie replacing the toroid with a shape
> that has a sine wave on the toroid).  If the switching frequency is high
> enough, maybe it is possible to utilize the finite flux propagation
> speed (ie. by using resonant flux switching to give different simulated
> urns ratios etc)

If the core isn't significantly conductive, then the speed of flux
penetration should just be the speed of light in the core, which would be
c/sqrt(mu) -- so, c is around 300 meters/microsecond, and you know the
relative permeability of the core.

The core doesn't have to be a special shape.

There are, in fact, resonators that are made with high dielectric
constant ceramic, as 1/4 wavelength shorted coax segments.  Because of
the dielectric constant, the velocity is much lower than the speed of
light in a vacuum, so the resonators are more compact.

I remember when they first came out, with much ballyhoo -- I don't know
if they're still popular.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
```
```Roughly sqrt(mu_r) times slower than c.  Notice that in real materials, past
a cutoff, mu_r depends strongly on frequency, so above 10kHz-10MHz
(depending on formulation), the response is strongly dispersive.

Notice that using ferrite for signal propagation works just like any other
propagation medium, so along with time delay comes phase shift, and with
phase shift comes rotation from magnetic to electric fields.  To achieve
stable propagation you'll have to determine what geometry allows the
electric field to propagate.

There are microwave resonators available which do this; the operation is
analogous to optical total internal reflection, except the puck is
fractional wavelength sized, so it acts like a conventional resonator as
well.  I believe they are made from ferrite or dielectric (either of which
has an index of refraction greater than air).

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"Jamie M" <jmorken@shaw.ca> wrote in message
news:jma8ib\$p8f\$1@speranza.aioe.org...
> Hi,
>
> I was curious about how fast the winding induced flux will propagate
> through a transformer core (ie a ferrite core) assuming a single
> primary winding on a toroid?  Would it be possible to make a resonant
> transformer using core geometry (ie replacing the toroid with a shape
> that has a sine wave on the toroid).  If the switching frequency is high
> enough, maybe it is possible to utilize the finite flux propagation
> speed (ie. by using resonant flux switching to give different simulated
> urns ratios etc)
>
> cheers,
> Jamie

```
```El 14-04-12 0:15, Jamie M escribi&#2013265923;:
> Hi,
>
> I was curious about how fast the winding induced flux will propagate
> through a transformer core (ie a ferrite core) assuming a single
> primary winding on a toroid? Would it be possible to make a resonant
> transformer using core geometry (ie replacing the toroid with a shape
> that has a sine wave on the toroid). If the switching frequency is high
> enough, maybe it is possible to utilize the finite flux propagation
> speed (ie. by using resonant flux switching to give different simulated
> urns ratios etc)
>
> cheers,
> Jamie

hello Jamie,

The phenomenon is known, even standing waves in the magnetic medium
because of the air/ferrite boundary.

Besides  high mu_r, ferrite materials have a eps_r > 1, it can be
>1000 (MnZn ferrite).   This reduces the propagation speed
significantly. unfortunately, most manufacturers don't specify eps_r'
and eps_r'' versus frequency for their power ferrites.

--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM
```
```On 4/14/2012 12:41 PM, Wimpie wrote:
> El 14-04-12 0:15, Jamie M escribi&#2013265923;:
>> Hi,
>>
>> I was curious about how fast the winding induced flux will propagate
>> through a transformer core (ie a ferrite core) assuming a single
>> primary winding on a toroid? Would it be possible to make a resonant
>> transformer using core geometry (ie replacing the toroid with a shape
>> that has a sine wave on the toroid). If the switching frequency is high
>> enough, maybe it is possible to utilize the finite flux propagation
>> speed (ie. by using resonant flux switching to give different simulated
>> urns ratios etc)
>>
>> cheers,
>> Jamie
>
> hello Jamie,
>
> The phenomenon is known, even standing waves in the magnetic medium
> because of the air/ferrite boundary.
>
> Besides high mu_r, ferrite materials have a eps_r > 1, it can be >1000
> (MnZn ferrite). This reduces the propagation speed significantly.
> unfortunately, most manufacturers don't specify eps_r' and eps_r''
> versus frequency for their power ferrites.

Hi,

Thanks, I guess for experimenting it would be good to find a core
material with low propagation speed and also a high saturation current
density, maybe MnZn ferrite powder mixed with epoxy to mold it into a
custom shape and also increase the saturation current could work?  I am
not sure about the properties of ferrite compared to ferrite+epoxy for a
transformer!

cheers,
Jamie

>
>
>

```
```On Sat, 14 Apr 2012 16:14:26 -0700, Jamie M <jmorken@shaw.ca> wrote:

>On 4/14/2012 12:41 PM, Wimpie wrote:
>> El 14-04-12 0:15, Jamie M escribi=F3:
>>> Hi,
>>>
>>> I was curious about how fast the winding induced flux will propagate
>>> through a transformer core (ie a ferrite core) assuming a single
>>> primary winding on a toroid? Would it be possible to make a resonant
>>> transformer using core geometry (ie replacing the toroid with a shape
>>> that has a sine wave on the toroid). If the switching frequency is =
high
>>> enough, maybe it is possible to utilize the finite flux propagation
>>> speed (ie. by using resonant flux switching to give different =
simulated
>>> urns ratios etc)
>>>
>>> cheers,
>>> Jamie
>>
>> hello Jamie,
>>
>> The phenomenon is known, even standing waves in the magnetic medium
>> because of the air/ferrite boundary.
>>
>> Besides high mu_r, ferrite materials have a eps_r > 1, it can be >1000
>> (MnZn ferrite). This reduces the propagation speed significantly.
>> unfortunately, most manufacturers don't specify eps_r' and eps_r''
>> versus frequency for their power ferrites.
>
>Hi,
>
>Thanks, I guess for experimenting it would be good to find a core
>material with low propagation speed and also a high saturation current
>density, maybe MnZn ferrite powder mixed with epoxy to mold it into a
>custom shape and also increase the saturation current could work?  I am
>not sure about the properties of ferrite compared to ferrite+epoxy for a
>transformer!
>
>cheers,
>Jamie
>
Adding a bunch of lower mu_r and eps_r material interstitially will only
lower the effective value of mu_r and eps_r.

?-)

```
```On 04/16/2012 12:38 AM, josephkk wrote:
> On Sat, 14 Apr 2012 16:14:26 -0700, Jamie M<jmorken@shaw.ca>  wrote:
>
>> On 4/14/2012 12:41 PM, Wimpie wrote:
>>> El 14-04-12 0:15, Jamie M escribi&#2013265923;:
>>>> Hi,
>>>>
>>>> I was curious about how fast the winding induced flux will propagate
>>>> through a transformer core (ie a ferrite core) assuming a single
>>>> primary winding on a toroid? Would it be possible to make a resonant
>>>> transformer using core geometry (ie replacing the toroid with a shape
>>>> that has a sine wave on the toroid). If the switching frequency is high
>>>> enough, maybe it is possible to utilize the finite flux propagation
>>>> speed (ie. by using resonant flux switching to give different simulated
>>>> urns ratios etc)
>>>>
>>>> cheers,
>>>> Jamie
>>>
>>> hello Jamie,
>>>
>>> The phenomenon is known, even standing waves in the magnetic medium
>>> because of the air/ferrite boundary.
>>>
>>> Besides high mu_r, ferrite materials have a eps_r>  1, it can be>1000
>>> (MnZn ferrite). This reduces the propagation speed significantly.
>>> unfortunately, most manufacturers don't specify eps_r' and eps_r''
>>> versus frequency for their power ferrites.
>>
>> Hi,
>>
>> Thanks, I guess for experimenting it would be good to find a core
>> material with low propagation speed and also a high saturation current
>> density, maybe MnZn ferrite powder mixed with epoxy to mold it into a
>> custom shape and also increase the saturation current could work?  I am
>> not sure about the properties of ferrite compared to ferrite+epoxy for a
>> transformer!
>>
>> cheers,
>> Jamie
>>
> Adding a bunch of lower mu_r and eps_r material interstitially will only
> lower the effective value of mu_r and eps_r.
>
> ?-)
>

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
```
```On Mon, 16 Apr 2012 09:55:21 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 04/16/2012 12:38 AM, josephkk wrote:
>> On Sat, 14 Apr 2012 16:14:26 -0700, Jamie M<jmorken@shaw.ca>  wrote:
>>
>>> On 4/14/2012 12:41 PM, Wimpie wrote:
>>>> El 14-04-12 0:15, Jamie M escribi&#2013265923;:
>>>>> Hi,
>>>>>
>>>>> I was curious about how fast the winding induced flux will propagate
>>>>> through a transformer core (ie a ferrite core) assuming a single
>>>>> primary winding on a toroid? Would it be possible to make a resonant
>>>>> transformer using core geometry (ie replacing the toroid with a shape
>>>>> that has a sine wave on the toroid). If the switching frequency is high
>>>>> enough, maybe it is possible to utilize the finite flux propagation
>>>>> speed (ie. by using resonant flux switching to give different simulated
>>>>> urns ratios etc)
>>>>>
>>>>> cheers,
>>>>> Jamie
>>>>
>>>> hello Jamie,
>>>>
>>>> The phenomenon is known, even standing waves in the magnetic medium
>>>> because of the air/ferrite boundary.
>>>>
>>>> Besides high mu_r, ferrite materials have a eps_r>  1, it can be>1000
>>>> (MnZn ferrite). This reduces the propagation speed significantly.
>>>> unfortunately, most manufacturers don't specify eps_r' and eps_r''
>>>> versus frequency for their power ferrites.
>>>
>>> Hi,
>>>
>>> Thanks, I guess for experimenting it would be good to find a core
>>> material with low propagation speed and also a high saturation current
>>> density, maybe MnZn ferrite powder mixed with epoxy to mold it into a
>>> custom shape and also increase the saturation current could work?  I am
>>> not sure about the properties of ferrite compared to ferrite+epoxy for a
>>> transformer!
>>>
>>> cheers,
>>> Jamie
>>>
>> Adding a bunch of lower mu_r and eps_r material interstitially will only
>> lower the effective value of mu_r and eps_r.
>>
>> ?-)
>>
>
>
>Cheers
>
>Phil Hobbs

At the risk of saying I am hijacking this thread (might need a new
topic),  what about core noise and dynamic range ??

What I mean is....   If you had a super quiet wide range hall effect
or other magnetic sensing device in the gap of a (ferrite ?) core,
what would be the  smallest AC and/or  DC signal change you
could see ??    I know there is some noise floor in there but
it's kind of hard to read some of the lit I've googled.

boB

```
```On 16 Apr 2012 13:18:00 -0500, boB <K7IQ> wrote:

>On Mon, 16 Apr 2012 09:55:21 -0400, Phil Hobbs
><pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>>On 04/16/2012 12:38 AM, josephkk wrote:
>>> On Sat, 14 Apr 2012 16:14:26 -0700, Jamie M<jmorken@shaw.ca>  wrote:
>>>
>>>> On 4/14/2012 12:41 PM, Wimpie wrote:
>>>>> El 14-04-12 0:15, Jamie M escribi&#2013265923;:
>>>>>> Hi,
>>>>>>
>>>>>> I was curious about how fast the winding induced flux will propagate
>>>>>> through a transformer core (ie a ferrite core) assuming a single
>>>>>> primary winding on a toroid? Would it be possible to make a resonant
>>>>>> transformer using core geometry (ie replacing the toroid with a shape
>>>>>> that has a sine wave on the toroid). If the switching frequency is high
>>>>>> enough, maybe it is possible to utilize the finite flux propagation
>>>>>> speed (ie. by using resonant flux switching to give different simulated
>>>>>> urns ratios etc)
>>>>>>
>>>>>> cheers,
>>>>>> Jamie
>>>>>
>>>>> hello Jamie,
>>>>>
>>>>> The phenomenon is known, even standing waves in the magnetic medium
>>>>> because of the air/ferrite boundary.
>>>>>
>>>>> Besides high mu_r, ferrite materials have a eps_r>  1, it can be>1000
>>>>> (MnZn ferrite). This reduces the propagation speed significantly.
>>>>> unfortunately, most manufacturers don't specify eps_r' and eps_r''
>>>>> versus frequency for their power ferrites.
>>>>
>>>> Hi,
>>>>
>>>> Thanks, I guess for experimenting it would be good to find a core
>>>> material with low propagation speed and also a high saturation current
>>>> density, maybe MnZn ferrite powder mixed with epoxy to mold it into a
>>>> custom shape and also increase the saturation current could work?  I am
>>>> not sure about the properties of ferrite compared to ferrite+epoxy for a
>>>> transformer!
>>>>
>>>> cheers,
>>>> Jamie
>>>>
>>> Adding a bunch of lower mu_r and eps_r material interstitially will only
>>> lower the effective value of mu_r and eps_r.
>>>
>>> ?-)
>>>
>>
>>
>>Cheers
>>
>>Phil Hobbs
>
>
>
>At the risk of saying I am hijacking this thread (might need a new
>topic),  what about core noise and dynamic range ??
>
>What I mean is....   If you had a super quiet wide range hall effect
>or other magnetic sensing device in the gap of a (ferrite ?) core,
>what would be the  smallest AC and/or  DC signal change you
>could see ??    I know there is some noise floor in there but
>it's kind of hard to read some of the lit I've googled.
>
>boB
>
>
>
>

Actually, I think the noise in ferrite cores was just Johnson noise
and might get louder with hotter cores maybe but is
hysteresis maybe an issue too at low low levels ??

boB

>
```
```On 16 Apr 2012 13:18:00 -0500, boB <K7IQ> wrote:

>On Mon, 16 Apr 2012 09:55:21 -0400, Phil Hobbs
><pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>>On 04/16/2012 12:38 AM, josephkk wrote:
>>> On Sat, 14 Apr 2012 16:14:26 -0700, Jamie M<jmorken@shaw.ca>  wrote:
>>>
>>>> On 4/14/2012 12:41 PM, Wimpie wrote:
>>>>> El 14-04-12 0:15, Jamie M escribi&#2013265923;:
>>>>>> Hi,
>>>>>>
>>>>>> I was curious about how fast the winding induced flux will propagate
>>>>>> through a transformer core (ie a ferrite core) assuming a single
>>>>>> primary winding on a toroid? Would it be possible to make a resonant
>>>>>> transformer using core geometry (ie replacing the toroid with a shape
>>>>>> that has a sine wave on the toroid). If the switching frequency is high
>>>>>> enough, maybe it is possible to utilize the finite flux propagation
>>>>>> speed (ie. by using resonant flux switching to give different simulated
>>>>>> urns ratios etc)
>>>>>>
>>>>>> cheers,
>>>>>> Jamie
>>>>>
>>>>> hello Jamie,
>>>>>
>>>>> The phenomenon is known, even standing waves in the magnetic medium
>>>>> because of the air/ferrite boundary.
>>>>>
>>>>> Besides high mu_r, ferrite materials have a eps_r>  1, it can be>1000
>>>>> (MnZn ferrite). This reduces the propagation speed significantly.
>>>>> unfortunately, most manufacturers don't specify eps_r' and eps_r''
>>>>> versus frequency for their power ferrites.
>>>>
>>>> Hi,
>>>>
>>>> Thanks, I guess for experimenting it would be good to find a core
>>>> material with low propagation speed and also a high saturation current
>>>> density, maybe MnZn ferrite powder mixed with epoxy to mold it into a
>>>> custom shape and also increase the saturation current could work?  I am
>>>> not sure about the properties of ferrite compared to ferrite+epoxy for a
>>>> transformer!
>>>>
>>>> cheers,
>>>> Jamie
>>>>
>>> Adding a bunch of lower mu_r and eps_r material interstitially will only
>>> lower the effective value of mu_r and eps_r.
>>>
>>> ?-)
>>>
>>
>>
>>Cheers
>>
>>Phil Hobbs
>
>
>
>At the risk of saying I am hijacking this thread (might need a new
>topic),  what about core noise and dynamic range ??
>
>What I mean is....   If you had a super quiet wide range hall effect
>or other magnetic sensing device in the gap of a (ferrite ?) core,
>what would be the  smallest AC and/or  DC signal change you
>could see ??    I know there is some noise floor in there but
>it's kind of hard to read some of the lit I've googled.
>
>boB
>

And maybe the noise goes up with permeability ?

I guess I am asking if there are any magnetics
companies that have noise specs for their cores.
I don't believe I have ever seen any from the
usuall sources.

boB (again)

>
>
>
```