On Wed, 18 Apr 2012 11:51:03 -0700, John Larkin <jlarkin@highlandtechnology.com> wrote:> >>> Does Barkhausen noise stop above a certain frequency, maybe >>> proportional to the magnetic domain sizes? Also for an extreme >>> example, for AC core losses, normally they are thought of as caused =by>>> eddy currents, but if the frequency is (extremely!) high enough, =maybe>>> the eddy current losses will start reducing, but will the transformer >>> core also start to lose its inductance properties so that it is not >>> useful? Just curious maybe 50 years in the future core losses will =not>>> matter! >>>=20 >> >>AFAIK it isn't white, but it goes well up into the megahertz. The >>spectrum depends on everything including what you had for breakfast.=20 >>(Like so many ferromagnetic things.) > >I had this inspiration that amorphous magnetics, metglas, might not >have Barkhausen noise, so I looked it up. They do.Thanks. My inspiration was opposite, as even amorphous materials still have magnetic domains. It is kind of a fineness of dimension thing. The surface of glass is smooth to low microscopic levels but not at 10000 times magnification. ?-)

# transformer core flux propagation speed

Started by ●April 13, 2012

Reply by ●April 26, 20122012-04-26

Reply by ●April 26, 20122012-04-26

On Wed, 25 Apr 2012 20:34:18 -0700, josephkk <joseph_barrett@sbcglobal.net> wrote:>On 16 Apr 2012 13:38:00 -0500, boB <K7IQ> 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�: >>>>>>>> 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 >>> >> >> >>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) >> >I suspect that until someone has sufficient problem with core noise to >actually specify the test conditions there won't ever be any. > >?-)Yeah, noise is not usually something anybody needs to know about. My need has to do with AC current sensing at very low levels. boB

Reply by ●April 26, 20122012-04-26

On Apr 25, 11:12=A0pm, boB <K7IQ> wrote:> On Wed, 25 Apr 2012 20:34:18 -0700, josephkk > > > > > > <joseph_barr...@sbcglobal.net> wrote: > >On 16 Apr 2012 13:38:00 -0500, boB <K7IQ> 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 > > >>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) > > >I suspect that until someone has sufficient problem with core noise to > >actually specify the test conditions there won't ever be any. > > >?-) > > Yeah, noise is not usually something anybody needs to know about. > > My need has to do with AC current sensing at very low levels. > > boBHow low? Accuracy? Trip point, or characterize the current exactly? Are you measuring the field adjacent to a single conductor? Have to double check, but 5 mils away from a 36Awg wire should be able to have noise floors below femtoAmps/rtHz. Linearity better than 0.1%; absolute accuracy on the order of 1-3%; and repeatable accuracy better than 0.1% I have designed portable AC magnetic field sensors with noise floor densities below noise of earth's field, into the femtoTesla/rtHz to replace SQUIDs for oil field exploration - much cheaper, and much easier to work with in the field. Don't recommend that exact design here, they were over 18 inches in diameter and weighed around 20lb

Reply by ●April 27, 20122012-04-27

On Thu, 26 Apr 2012 04:46:49 -0700 (PDT), Robert Macy <robert.a.macy@gmail.com> wrote:>On Apr 25, 11:12�pm, boB <K7IQ> wrote: >> On Wed, 25 Apr 2012 20:34:18 -0700, josephkk >> >> >> >> >> >> <joseph_barr...@sbcglobal.net> wrote: >> >On 16 Apr 2012 13:38:00 -0500, boB <K7IQ> 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> �wrote: >> >> >>>>>> On 4/14/2012 12:41 PM, Wimpie wrote: >> >>>>>>> El 14-04-12 0:15, Jamie M escribi�: >> >>>>>>>> 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 >> >> >>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) >> >> >I suspect that until someone has sufficient problem with core noise to >> >actually specify the test conditions there won't ever be any. >> >> >?-) >> >> Yeah, noise is not usually something anybody needs to know about. >> >> My need has to do with AC current sensing at very low levels. >> >> boB > >How low? Accuracy? Trip point, or characterize the current exactly? >Are you measuring the field adjacent to a single conductor?Accuracy is not a problem. BTW the Hall effect device located in the gap may have higher noise than anything but noise specs for HE sensors are fairly ambiguous too although Allegro does have what they call "low noise" HE devices.> >Have to double check, but 5 mils away from a 36Awg wire should be able >to have noise floors below femtoAmps/rtHz. Linearity better than 0.1%; >absolute accuracy on the order of 1-3%; and repeatable accuracy better >than 0.1% > >I have designed portable AC magnetic field sensors with noise floor >densities below noise of earth's field, into the femtoTesla/rtHz to >replace SQUIDs for oil field exploration - much cheaper, and much >easier to work with in the field. Don't recommend that exact design >here, they were over 18 inches in diameter and weighed around 20lb >Sounds kind of expensive... I see DC squids and RF squids. Do they work up to about 20 kHz ? BTW, I thought high temperature superconductivity wasn't quite there yet ? boB

Reply by ●April 27, 20122012-04-27

On Apr 26, 11:04=A0pm, boB <K7IQ> wrote:> On Thu, 26 Apr 2012 04:46:49 -0700 (PDT), Robert Macy > > > > > > <robert.a.m...@gmail.com> wrote: > >On Apr 25, 11:12=A0pm, boB <K7IQ> wrote: > >> On Wed, 25 Apr 2012 20:34:18 -0700, josephkk > > >> <joseph_barr...@sbcglobal.net> wrote: > >> >On 16 Apr 2012 13:38:00 -0500, boB <K7IQ> 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> =A0=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 pr=opagate> >> >>>>>>>> through a transformer core (ie a ferrite core) assuming a sin=gle> >> >>>>>>>> primary winding on a toroid? Would it be possible to make a r=esonant> >> >>>>>>>> transformer using core geometry (ie replacing the toroid with=a shape> >> >>>>>>>> that has a sine wave on the toroid). If the switching frequen=cy is high> >> >>>>>>>> enough, maybe it is possible to utilize the finite flux propa=gation> >> >>>>>>>> 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 m=edium> >> >>>>>>> because of the air/ferrite boundary. > > >> >>>>>>> Besides high mu_r, ferrite materials have a eps_r> =A01, it ca=n be>1000> >> >>>>>>> (MnZn ferrite). This reduces the propagation speed significant=ly.> >> >>>>>>> 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 co=re> >> >>>>>> 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 wor=k? =A0I am> >> >>>>>> not sure about the properties of ferrite compared to ferrite+ep=oxy for a> >> >>>>>> transformer! > > >> >>>>>> cheers, > >> >>>>>> Jamie > > >> >>>>> Adding a bunch of lower mu_r and eps_r material interstitially w=ill 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 eff=ect> >> >>>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 > > >> >>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) > > >> >I suspect that until someone has sufficient problem with core noise t=o> >> >actually specify the test conditions there won't ever be any. > > >> >?-) > > >> Yeah, noise is not usually something anybody needs to know about. > > >> My need has to do with AC current sensing at very low levels. > > >> boB > > >How low? Accuracy? Trip point, or characterize the current exactly? > >Are you measuring the field adjacent to a single conductor? > > Accuracy is not a problem. =A0BTW the Hall effect device located in the > gap may have higher noise than anything but noise specs for HE > sensors are fairly ambiguous too although Allegro does have > what they call "low noise" HE devices. > > > > >Have to double check, but 5 mils away from a 36Awg wire should be able > >to have noise floors below femtoAmps/rtHz. Linearity better than 0.1%; > >absolute accuracy on the order of 1-3%; and repeatable accuracy better > >than 0.1% > > >I have designed portable AC magnetic field sensors with noise floor > >densities below noise of earth's field, into the femtoTesla/rtHz to > >replace SQUIDs for oil field exploration - much cheaper, and much > >easier to work with in the field. Don't recommend that exact design > >here, they were over 18 inches in diameter and weighed around 20lb > > Sounds kind of expensive... =A0I see DC squids and RF squids. > Do they work up to about 20 kHz ? > > BTW, I thought high temperature superconductivity wasn't > quite there yet ? > > boBActually, less than $100 each sensor. Don't know a lot about SQUIDs, except know they're being used to map 3D neurologic current flows in situ and are sensitive enough to measure current flow of rusting metal. My design does NOT use any superconducting principle. The design has such a low noise floor that it can replace SQUIDs because the noise floor does not have to be much lower than the earth's magnetic field's noise. In other words, the sensor only has to be as good as the measurement environment; making SQUIDs an overkill.