Forums

transformer core flux propagation speed

Started by Jamie M April 13, 2012
boB wrote:
> > 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. > >>> > >>> ?-) > >>> > >> > >>Google "YIG-tuned oscillator design" > >> > >>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 > > >
There's also Barkhausen noise, due to the stick-slip motion of magnetic domains. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
On Apr 16, 4:47=A0pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:
> boB wrote: > > > On 16 Apr 2012 13:18:00 -0500, boB <K7IQ> wrote: > > > >On Mon, 16 Apr 2012 09:55:21 -0400, Phil Hobbs > > ><pcdhSpamMeSensel...@electrooptical.net> wrote: > > > >>On 04/16/2012 12:38 AM, josephkk wrote: > > >>> On Sat, 14 Apr 2012 16:14:26 -0700, Jamie M<jmor...@shaw.ca> =A0wro=
te:
> > > >>>> 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 propa=
gate
> > >>>>>> through a transformer core (ie a ferrite core) assuming a single > > >>>>>> primary winding on a toroid? Would it be possible to make a reso=
nant
> > >>>>>> 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 propagat=
ion
> > >>>>>> speed (ie. by using resonant flux switching to give different si=
mulated
> > >>>>>> urns ratios etc) > > > >>>>>> cheers, > > >>>>>> Jamie > > > >>>>> hello Jamie, > > > >>>>> The phenomenon is known, even standing waves in the magnetic medi=
um
> > >>>>> because of the air/ferrite boundary. > > > >>>>> Besides high mu_r, ferrite materials have a eps_r> =A01, it can b=
e>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 cur=
rent
> > >>>> density, maybe MnZn ferrite powder mixed with epoxy to mold it int=
o a
> > >>>> custom shape and also increase the saturation current could work? =
=A0I 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. > > > >>> ?-) > > > >>Google "YIG-tuned oscillator design" > > > >>Cheers > > > >>Phil Hobbs > > > >At the risk of saying I am hijacking this thread (might need a new > > >topic), =A0what about core noise and dynamic range ?? > > > >What I mean is.... =A0 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 =A0smallest AC and/or =A0DC signal change you > > >could see ?? =A0 =A0I 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 > > There's also Barkhausen noise, due to the stick-slip motion of magnetic > domains. > > Cheers > > Phil Hobbs > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC > Optics, Electro-optics, Photonics, Analog Electronics > > 160 North State Road #203 > Briarcliff Manor NY 10510 > 845-480-2058 > > hobbs at electrooptical dot nethttp://electrooptical.net
Fun home experiment: attach an audio amp to transformer, then run DC through another winding. Change the DC up/down and listen for the domain boundaries to 'crash'
"boB" <K7IQ> wrote in message 
news:paooo7d5m6qsglnavjs3d2q9p9agjrflue@4ax.com...
> 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.
http://en.wikipedia.org/wiki/Barkhausen_effect This isn't directly due to thermal noise (flipping magnetic spins, domain fluctuations), which will be much weaker (though possibly noticable around the Curie temperature). Very soft materials (low remenance) should be quieter than those with high remenance; blatant example, applying a field to a permanent magnet won't cause any substantial flipping until the entire coercive force is applied (~1e5 A/m for NdFeB, IIRC), at which point the whole thing changes quite rapidly. Tempted to set up an amplifier and try listening to a core. Should be able to get a small ferrite toroid up to Curie with only the soldering iron handy. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
On Mon, 16 Apr 2012 19:47:49 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>boB wrote: >> >> 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. >> >>> >> >>> ?-) >> >>> >> >> >> >>Google "YIG-tuned oscillator design" >> >> >> >>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 >> >> > > >There's also Barkhausen noise, due to the stick-slip motion of magnetic >domains. > >Cheers > >Phil Hobbs
Won't there be a mean time delay associated with the domains snapping around? They will have, in effect, some sort of inertia. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
John Larkin wrote:
> > On Mon, 16 Apr 2012 19:47:49 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >boB wrote: > >> > >> 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. > >> >>> > >> >>> ?-) > >> >>> > >> >> > >> >>Google "YIG-tuned oscillator design" > >> >> > >> >>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 > >> > >> > > > > >There's also Barkhausen noise, due to the stick-slip motion of magnetic > >domains. > > > >Cheers > > > >Phil Hobbs > > Won't there be a mean time delay associated with the domains snapping > around? They will have, in effect, some sort of inertia. > > -- > > John Larkin Highland Technology, Inc > > jlarkin at highlandtechnology dot com > http://www.highlandtechnology.com > > Precision electronic instrumentation > Picosecond-resolution Digital Delay and Pulse generators > Custom laser controllers > Photonics and fiberoptic TTL data links > VME thermocouple, LVDT, synchro acquisition and simulation
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
On Apr 16, 5:42=A0pm, John Larkin <jlar...@highlandtechnology.com>
wrote:
> On Mon, 16 Apr 2012 19:47:49 -0400, Phil Hobbs > > > > > > <pcdhSpamMeSensel...@electrooptical.net> wrote: > >boB wrote: > > >> On 16 Apr 2012 13:18:00 -0500, boB <K7IQ> wrote: > > >> >On Mon, 16 Apr 2012 09:55:21 -0400, Phil Hobbs > >> ><pcdhSpamMeSensel...@electrooptical.net> wrote: > > >> >>On 04/16/2012 12:38 AM, josephkk wrote: > >> >>> On Sat, 14 Apr 2012 16:14:26 -0700, Jamie M<jmor...@shaw.ca> =A0wr=
ote:
> > >> >>>> 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 prop=
agate
> >> >>>>>> through a transformer core (ie a ferrite core) assuming a singl=
e
> >> >>>>>> primary winding on a toroid? Would it be possible to make a res=
onant
> >> >>>>>> 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 propaga=
tion
> >> >>>>>> speed (ie. by using resonant flux switching to give different s=
imulated
> >> >>>>>> urns ratios etc) > > >> >>>>>> cheers, > >> >>>>>> Jamie > > >> >>>>> hello Jamie, > > >> >>>>> The phenomenon is known, even standing waves in the magnetic med=
ium
> >> >>>>> because of the air/ferrite boundary. > > >> >>>>> Besides high mu_r, ferrite materials have a eps_r> =A01, 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 cu=
rrent
> >> >>>> density, maybe MnZn ferrite powder mixed with epoxy to mold it in=
to a
> >> >>>> custom shape and also increase the saturation current could work?=
=A0I am
> >> >>>> not sure about the properties of ferrite compared to ferrite+epox=
y for a
> >> >>>> transformer! > > >> >>>> cheers, > >> >>>> Jamie > > >> >>> Adding a bunch of lower mu_r and eps_r material interstitially wil=
l only
> >> >>> lower the effective value of mu_r and eps_r. > > >> >>> ?-) > > >> >>Google "YIG-tuned oscillator design" > > >> >>Cheers > > >> >>Phil Hobbs > > >> >At the risk of saying I am hijacking this thread (might need a new > >> >topic), =A0what about core noise and dynamic range ?? > > >> >What I mean is.... =A0 If you had a super quiet wide range hall effec=
t
> >> >or other magnetic sensing device in the gap of a (ferrite ?) core, > >> >what would be the =A0smallest AC and/or =A0DC signal change you > >> >could see ?? =A0 =A0I 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 > > >There's also Barkhausen noise, due to the stick-slip motion of magnetic > >domains. > > >Cheers > > >Phil Hobbs > > Won't there be a mean time delay associated with the domains snapping > around? They will have, in effect, some sort of inertia. > > -- > > John Larkin =A0 =A0 =A0 =A0 Highland Technology, Inc > > jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com > > Precision electronic instrumentation > Picosecond-resolution Digital Delay and Pulse generators > Custom laser controllers > Photonics and fiberoptic TTL data links > VME thermocouple, LVDT, synchro =A0 acquisition and simulation
Think more sequential than average. Actually, a domain wall does not have 'pressure' on it until an adjacent wall flips. Then the field can build against it. Sort of like dominoes. For me to understand what was going on, I used to envision a field of wheat, blowing in the wind. The wind hits a stock and it tends to bend over allowing the next stock to 'see' the wind and so on. Some stocks are stiffer than others so the wave is not so uniform. Importantly, It makes a great image for picturing wave propagation. Plus, *IF* the wind changes direction before the field is down, you can start to envision the standing wave patterns moving across the field, even see how the stocks in one section are not even going down the right direction, but the opposite direction, so instead of helping, they are hindering. Anway, any allegory that helps intuitive understanding has some value, look at what Tesla came up with after watching ??, which was an imperfect allegory, too. He came up with the induction motor.
On Mon, 16 Apr 2012 19:10:56 -0500, "Tim Williams"
<tmoranwms@gmail.com> wrote:

>"boB" <K7IQ> wrote in message >news:paooo7d5m6qsglnavjs3d2q9p9agjrflue@4ax.com... >> 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. > >http://en.wikipedia.org/wiki/Barkhausen_effect > >This isn't directly due to thermal noise (flipping magnetic spins, domain >fluctuations), which will be much weaker (though possibly noticable around >the Curie temperature). > >Very soft materials (low remenance) should be quieter than those with high >remenance; blatant example, applying a field to a permanent magnet won't >cause any substantial flipping until the entire coercive force is applied >(~1e5 A/m for NdFeB, IIRC), at which point the whole thing changes quite >rapidly. > >Tempted to set up an amplifier and try listening to a core. Should be able >to get a small ferrite toroid up to Curie with only the soldering iron >handy. > >Tim
Barkhousen was a term I was semi familiar with and now that Phil mentioed it, I wonder how much that could interfere with an AC signal amplifing when the DC current is changing appreciably... Now I will go look at the wiki link. I'd expect harder magnetic material to make more BH noise and soft material to make more johnnson noise but I'm just guessing. Hopefully any real work I do is way below the curie temperature but it makes intuitive sense that there would be some hot action up there. A Wikiing I will now go ! boB
On Mon, 16 Apr 2012 19:10:56 -0500, "Tim Williams"
<tmoranwms@gmail.com> wrote:

>"boB" <K7IQ> wrote in message >news:paooo7d5m6qsglnavjs3d2q9p9agjrflue@4ax.com... >> 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. > >http://en.wikipedia.org/wiki/Barkhausen_effect
Looking at the B-H curve on that page, it doesn't look like particularly hard material, but it might not be magnetically "to scale" but was just a convenient curve to use for illustatration. Since I'm set up to do the test in the lab already, I will have to try it on ferrite at least while varying the DC current. It might even be worse than any other noise but I haven't noticed it yet. I wonder how much gain is needed ? Maybe a hall effect device is too noisey to eve hear this Barkhausen effect and that's one reason the wiki artilce mentions using a coil ? Looks like it could even sound like somewhat of a zipper noise. OK, so I went to the listed youtooob link and they show a guy rotating a magnet near an antenna loop looking thing. This is kinda confusing to me cuz I don't see how that is going to excercise through the B-H loop as shown in the wikipedia article.... And it's a magnet, not a soft magnetic core. Something doesn't seem quite right there. boB
> >This isn't directly due to thermal noise (flipping magnetic spins, domain >fluctuations), which will be much weaker (though possibly noticable around >the Curie temperature). > >Very soft materials (low remenance) should be quieter than those with high >remenance; blatant example, applying a field to a permanent magnet won't >cause any substantial flipping until the entire coercive force is applied >(~1e5 A/m for NdFeB, IIRC), at which point the whole thing changes quite >rapidly. > >Tempted to set up an amplifier and try listening to a core. Should be able >to get a small ferrite toroid up to Curie with only the soldering iron >handy. > >Tim
On 17 Apr 2012 00:43:01 -0500, boB <K7IQ> wrote:

>On Mon, 16 Apr 2012 19:10:56 -0500, "Tim Williams" ><tmoranwms@gmail.com> wrote: > >>"boB" <K7IQ> wrote in message >>news:paooo7d5m6qsglnavjs3d2q9p9agjrflue@4ax.com... >>> 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. >> >>http://en.wikipedia.org/wiki/Barkhausen_effect > > > >Looking at the B-H curve on that page, it doesn't look like >particularly hard material, but it might not be magnetically >"to scale" but was just a convenient curve to use for >illustatration. Since I'm set up to do the test in the lab >already, I will have to try it on ferrite at least while >varying the DC current. It might even be worse than >any other noise but I haven't noticed it yet. > >I wonder how much gain is needed ? Maybe a hall effect device >is too noisey to eve hear this Barkhausen effect and that's one >reason the wiki artilce mentions using a coil ? Looks like it could >even sound like somewhat of a zipper noise. > >OK, so I went to the listed youtooob link and they show a guy rotating >a magnet near an antenna loop looking thing. This is kinda confusing >to me cuz I don't see how that is going to excercise through the B-H >loop as shown in the wikipedia article.... And it's a magnet, not a >soft magnetic core. Something doesn't seem quite right there. > >boB >
OK, finally found a decent demonstration online http://sci-toys.com/scitoys/scitoys/electro/barkhausen/index.html This one makes sense. boB
> > > >> >>This isn't directly due to thermal noise (flipping magnetic spins, domain >>fluctuations), which will be much weaker (though possibly noticable around >>the Curie temperature). >> >>Very soft materials (low remenance) should be quieter than those with high >>remenance; blatant example, applying a field to a permanent magnet won't >>cause any substantial flipping until the entire coercive force is applied >>(~1e5 A/m for NdFeB, IIRC), at which point the whole thing changes quite >>rapidly. >> >>Tempted to set up an amplifier and try listening to a core. Should be able >>to get a small ferrite toroid up to Curie with only the soldering iron >>handy. >> >>Tim
On Apr 16, 10:25=A0pm, boB <K7IQ> wrote:
> On Mon, 16 Apr 2012 19:10:56 -0500, "Tim Williams" > > > > > > <tmoran...@gmail.com> wrote: > >"boB" <K7IQ> wrote in message > >news:paooo7d5m6qsglnavjs3d2q9p9agjrflue@4ax.com... > >> What I mean is.... =A0 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 =A0smallest AC and/or =A0DC signal change you > >> could see ?? =A0 =A0I know there is some noise floor in there but > >> it's kind of hard to read some of the lit I've googled. > > >http://en.wikipedia.org/wiki/Barkhausen_effect > > >This isn't directly due to thermal noise (flipping magnetic spins, domai=
n
> >fluctuations), which will be much weaker (though possibly noticable arou=
nd
> >the Curie temperature). > > >Very soft materials (low remenance) should be quieter than those with hi=
gh
> >remenance; blatant example, applying a field to a permanent magnet won't > >cause any substantial flipping until the entire coercive force is applie=
d
> >(~1e5 A/m for NdFeB, IIRC), at which point the whole thing changes quite > >rapidly. > > >Tempted to set up an amplifier and try listening to a core. =A0Should be=
able
> >to get a small ferrite toroid up to Curie with only the soldering iron > >handy. > > >Tim > > Barkhousen was a term I was semi familiar with and now that Phil > mentioed it, I wonder how much that could interfere with an AC signal > amplifing when the DC current is changing appreciably... =A0Now I will > go look at the wiki link. =A0I'd expect harder magnetic material to > make more BH noise and soft material to make more johnnson noise > but I'm just guessing. =A0Hopefully any real work I do is way below > the curie temperature but it makes intuitive sense that there would > be some hot action up there. > > A Wikiing I will now go ! > > boB
From memory talking with the Ampex employee that designed/built the 3MHz bias recorders, Barkhausen noise is proportional to the signal, so as the signal is louder, so is the noise.Therefore not as obtrusive as a fixed level of noise. People easily hear fixed noise something like 70-90 dB down, but, again from memory, they're very forgiving of the normal 46-52dB down Barkhausen noise. Recalled that the HF bias, copper wedge in the recording gap, and eddy currents all contributed to 'injecting' the mag field into the tape media better and thus improved S/N something like an additional 6dB! It was impressive, you could hear the difference.