How rapidly can an electromagnet get magnetised and de-magnetised?

[Peter Ahlman]

Hello all!


How fast can an electromagnet get magnetised and de-magnetised, by DC-pulsing it and without having any hysteresis & retentivity effects in the coil itself? Obviously its not going to be a ferrite core coil(because of retentivity,hysteresis). How fast can a low power air-core electromagnet be switched on and off in such a way that at the very instant the electromagnet is turned off, the magnetic field is also completely gone at the same instant without any delay?. Can we get in the 10-100GHz range? or is it basically limitless from the
"coil´s physical point of view"?

Peter

 

[jim hardy]

hysteresis & retentivity

are properties of ferromagnetic material and you later specified air core.

try google on inductors, both air and iron core.

You'll find that in iron, eddy currents place a very modest frequency limit and that's why there's powdered ferrite cores for high frequency

"retardation of magnetization due to eddy currents" should produce rich search results for the case of soft iron cores.

A fellow named Bozorth published a book "Ferromagnetism" which i think still stands as the ultimate reference.

Happy hunting !

 

[Peter Ahlman]

Jim, yes I mentioned hysteresis & retentivity that are related to ferromagnetic cores trying to make my point clearer. "in other words, I want to avoid any similar effects in air core copper electromagnet maybe I should I ask if diamagnetic copper have super tiny hysteresis & retentivity effects?"I am therefore intending for using only air-core electromagnet in my project. EXTREMELY high Frequencies are greatly limited by ferromagnetic cores or any magnetic cores. Maybe my question should be formulated this way:

If I DC pulse a small copper air-core electromagnet with 10ghz, will the coil retain some magnetic field (for a very short time) after every "off"? or will the magnetic field PRECISELY follow the extremely high Ghz DC pulses??

My entire wondering is really because of the very high frequencies involved?

Peter

 

[jim hardy]

now you're into microwave realm, completely beyond my experience.

I'll hope somebody experienced in high fvrequency RF can help.

Best i can offer is that microwave oven magnetrons have air core inductors in series with their heater leads - so they must still work at ~2 ghz.

I do point out that flux and current are related by proportional constants not time dependent functions
so , unless your excitation current induces secondary currents nearby, i would look for flux and current to be similar functions of time.
Voltage relation to flux of course is a different story

old jim

 

[Peter Ahlman]

"Best i can offer is that microwave oven magnetrons have air core inductors in series with their heater leads - so they must still work at ~2 ghz."

Thanx for the tip Jim..., I am going to be waiting for some experienced in the microwave area. BTW, are these air core inductors in the oven fed DC pulsed or AC?


Peter

 

[AlephZero]

If I DC pulse a small copper air-core electromagnet with 10ghz, will the coil retain some magnetic field (for a very short time) after every "off"? or will the magnetic field PRECISELY follow the extremely high Ghz DC pulses??

At 10 GHz, the wavelength of the EM radiation is only 30mm. If that length is comparable with the size of the device you are thinking about (i.e. the size of the complete circuit, not just the coil), you would have to take the finite speed of light into account to answer the question. A simple idea like "a DC pulse" doesn't mean much at those frequencies.

 

[berkeman]

Hello all!


How fast can an electromagnet get magnetised and de-magnetised, by DC-pulsing it and without having any hysteresis & retentivity effects in the coil itself? Obviously its not going to be a ferrite core coil(because of retentivity,hysteresis). How fast can a low power air-core electromagnet be switched on and off in such a way that at the very instant the electromagnet is turned off, the magnetic field is also completely gone at the same instant without any delay?. Can we get in the 10-100GHz range? or is it basically limitless from the
"coil´s physical point of view"?

Peter

Jim, yes I mentioned hysteresis & retentivity that are related to ferromagnetic cores trying to make my point clearer. "in other words, I want to avoid any similar effects in air core copper electromagnet maybe I should I ask if diamagnetic copper have super tiny hysteresis & retentivity effects?"I am therefore intending for using only air-core electromagnet in my project. EXTREMELY high Frequencies are greatly limited by ferromagnetic cores or any magnetic cores. Maybe my question should be formulated this way:

If I DC pulse a small copper air-core electromagnet with 10ghz, will the coil retain some magnetic field (for a very short time) after every "off"? or will the magnetic field PRECISELY follow the extremely high Ghz DC pulses??

My entire wondering is really because of the very high frequencies involved?

Peter

Welcome to the PF, Peter.

Can you tell us about your project? What are you wanting to do? There are lots of considerations at those frequencies, and hysteresis in an air core is not one of them AFAIK.

 

[jim hardy]

are these air core inductors in the oven fed DC pulsed or AC?

they are in series with a low voltage winding (5volts i think) of the 60 hz power transformer
and their purpose is to pass the 60 hz into the magnetron's heater but block the 2ghz keeping it from traveling back up the wires and past the shielding thence into the kitchen.

So they pass 60 hz AC and block 2ghz AC, both continuous for all practical purposes.

http://inlinethumb59.webshots.com/7034/2424785070063874629S600x600Q85.jpg

 

[Peter Ahlman]

AlephZero, berkeman

Hey and thank you for the info and welcoming.
As far as I am concerned there will be no other part in the circuit except the air core electro magnet(well it is going to be hooked to a some kind of signal/function generator), so that's all there is going to be, a coil hooked to a function generator, unless I find out I have to install some other electronic parts into circuit to help me reach my goal which is extremely fast & clean DC square-wave pulsing without having any delay between the current and flux field, the coils magnetic field is precisely off at an off pulse, nothing else matters..(I believe so far?)

 

[berkeman]

AlephZero, berkeman

Hey and thank you for the info and welcoming.
As far as I am concerned there will be no other part in the circuit except the air core electro magnet(well it is going to be hooked to a some kind of signal/function generator), so that's all there is going to be, a coil hooked to a function generator, unless I find out I have to install some other electronic parts into circuit to help me reach my goal which is extremely fast & clean DC square-wave pulsing without having any delay between the current and flux field, the coils magnetic field is precisely off at an off pulse, nothing else matters..(I believe so far?)

So you want to create an oscillating RF magnetic field in the 100GHz range inside a small air-core coil? What signal level are you going to drive through how many turns for what size volume?

 

[Peter Ahlman]

So you want to create an oscillating RF magnetic field in the 100GHz range inside a small air-core coil?

Im sorry but I am not quite exactly sure what you mean by "RF" but yes I want to create a rapid DC pulsing in an air- core coil in the 100ghz i.e. an oscillating magnetic field that goes: on off, on off. 10ghz may be enough. But it must be 10ghz minimum

Since this is an experiment, none of the coil specs really matters as long as I have some weak magnetic field in the coil. All I need is to get Clean DC high pulses. The air core coil itself could be as small or as big as required all to help reaching my main goal, also voltage & current could be as small or as big all to help reaching my main goal which is: DC pulsed air core in the microwave band.
So, I thought that things like the power, volts, amps, turns, inductance etc would be decided accordingly to and towards what is ultimately is needed to achieve 100ghz pulses.

 

[berkeman]

Im sorry but I am not quite exactly sure what you mean by "RF" but yes I want to create a rapid DC pulsing in an air- core coil in the 100ghz i.e. an oscillating magnetic field that goes: on off, on off. 10ghz may be enough. But it must be 10ghz minimum

Since this is an experiment, none of the coil specs really matters as long as I get some weak magnetic field. All I need is to get Clean DC high pulses, the electromagnet could be as small or as big as required all to help reaching my main goal, also voltage & current could be as small or as big all to help reaching my main goal: DC pulsed air core in the microwave band.
So, I thought that things like the power, volts, amps, turns, inductance etc would be decided accordingly to and towards what is ultimately is needed to achieve 100ghz pulses.

I think your concept of the signal that you will drive is a bit off. Don't use the term "DC" for something that happens at 10GHz. If you are going to drive a signal at 10GHz, it will be a sine wave, or perhaps an isolated pulse with subsequent ringing.

And by RF I mean radio frequency. A 10-100GHz signal is radio frequency signal.

If you want to make a gated pulse of some number of 10GHz sinewaves, then you can do that.

If you want to make a 10GHz sine wave with a DC offset of half the amplitude of the sine wave, then you can do that. That is the closest you will get to an "ON/OFF" 10GHz magnetic field.

 

[yungman]

Hello all! How fast can an electromagnet get magnetised and de-magnetised, by DC-pulsing it and without having any hysteresis & retentivity effects in the coil itself? Obviously its not going to be a ferrite core coil(because of retentivity,hysteresis). How fast can a low power air-core electromagnet be switched on and off in such a way that at the very instant the electromagnet is turned off, the magnetic field is also completely gone at the same instant without any delay?. Can we get in the 10-100GHz range? or is it basically limitless from the
"coil´s physical point of view"?

Peter

You really don't get into GHz with any solid core, even the powder stuff goes to a few hundred MHz. For more info, go to Mini-Circuit site and look at the RF transformers and see what is the upper limit. For air core, you can go a little higher, but as Alphazero said, when you approach 1GHz, even a one turn coil is quite high inductance and the wave length come into play. In air, speed of light is 3EE8m/s, so for 1GHz, λ=10cm. At 10GHz, λ=1cm. As you can see, you really cannot get many turns to be longer than λ. Any length of wire longer than 1/20λ need to be treated as transmission line and has to use phasor notation for calculation. It is no longer a wire. So your assertion of a "coil" is out the window quite fast when frequency goes up.

In fact we often use a section of wire( trace on pcb) shorter than 1/8λ as inductor with value calculated by the length. There nothing coil about it.

 

[Peter Ahlman]

I wrote dc to not confuse with ac, big difference. Though everything will tend to have a round triangular waveform at such high frequencies, my goal is to have square waves.

Anyway I found this:

http://apl.aip.org/resource/1/applab/v58/i12/p1253_s1?isAuthorized=no

This GaAs direction seems to have pretty clean square wave pulses at fairly high frequencies. Its seems to be laser pulses though..

 

[NascentOxygen]

I wrote dc to not confuse with ac, big difference. Though everything will tend to have a round triangular waveform at such high frequencies, my goal is to have square waves.

What would you like to do with the 100GHz square waves if you had them?

This GaAs direction seems to have pretty clean square wave pulses at fairly high frequencies. Its seems to be laser pulses though..

At 100GHz you are in the realm of microwaves, but getting close to light. Infra-red light is from 300Ghz up.

Are you wanting to construct a maser cannon?

 

[Peter Ahlman]

What would you like to do with the 100GHz square waves if you had them?
Are you wanting to construct a maser cannon?

Naah, I am trying to reconstruct Teslas Death ray...

At 100GHz you are in the realm of microwaves, but getting close to light. Infra-red light is from 300Ghz up.

Yes, I am aware that I am closing to light, that is sort like the idea. Honestly I have some kind of a little "theory" in my head(for some years now) that I really want to confirm by an experiment. I don't see really why it shouldn't work, I have went/revised through it countless times. That is, if I can oscillate a magnetic field at a frequency (which happens to be above 1ghz and simply can never work at any lower frequency), with actually a somewhat clean square wave pulse-train, the theory should really work. I can in fact say that I am confident that it will work if I reach the correct high frequency pulse-train/oscillating magnetic field in the electromagnet.

I have read some threads considering signal generation and if we can output a nice high speed square wave pulse train(1ghz+) and it seems that despite being difficult its manageable (?) I will probably though face a problem to actually output such a high speed clean square wave pulse train, but according to my (unfortunately and recently deceased) friend, he never mentioned that to be a problem.
So therefore I believe as he did that the main problem seems to be into "constructing such a physical coil" that can take extremely high pulses.

 

[jim hardy]

i'd think the trouble would be in generating picosecond risetimes.

that's a lot of di/dt... extreme voltage rquired ?

 

[davenn]

In air, speed of light is 3EE8m/s, so for 1GHz, λ=10cm. At 10GHz, λ=1cm.

1GHz = 30 cm; 10 GHz = 3 cm wavelengths ;)

Dave

 

[Peter Ahlman]

Hi again, I didnt want to start a new thread so here I continue. I decided to let you know what I am working/researching on. If you find that this concept is totally impossible it is fine, but please give it a thought and if it can't work, please specify the the reason why.

Anyway the whole idea could be summerized in that all I want to do is to create a short moment (nanosecond ? maybe less..?) where a delay exist between a magnetic field and a coils activation. in other words: a very short moment where the electromagnet is off while the magnetic field is still there at the same time. if you understood me correctly you will realize that there is a great potential for creating a net force, i.e. propulsion.

Take a look at Sun to Earth light propagation, it takes 8 minutes. magnetic fields also propagate at speed of light.Please ask if you didnt get me, I am not grasping this completely really either as its get real hard imagining the whole procedure

Pete

 

[berkeman]

Hi again, I didnt want to start a new thread so here I continue. I decided to let you know what I am working/researching on. If you find that this concept is totally impossible it is fine, but please give it a thought and if it can't work, please specify the the reason why.

Anyway the whole idea could be summerized in that all I want to do is to create a short moment (nanosecond ? maybe less..?) where a delay exist between a magnetic field and a coils activation. in other words: a very short moment where the electromagnet is off while the magnetic field is still there at the same time. if you understood me correctly you will realize that there is a great potential for creating a net force, i.e. propulsion.

Take a look at Sun to Earth light propagation, it takes 8 minutes. magnetic fields also propagate at speed of light.


Please ask if you didnt get me, I am not grasping this completely really either as its get real hard imagining the whole procedure

Pete

What makes you think you will get any measurable propulsion out of this?

 

[Peter Ahlman]

What makes you think you will get any measurable propulsion out of this?

I explained in the post but let me make it clearer. When you separate a magnet from its magnetic field you get a field to react and push against. Thats it really. For instance if we have two such super high pulsed elec.magnets with very short rise fall time, and slightly out of phase from each other one magnet will push against the magnetic field of the TURNED OFF MAGNET(we are talking about very short times)

I have thought about it and believe perhaps that its not the frequency that is important.. its perhaps the rise and fall time of the pulse that must be instant as to shut down the magnet while the magnetic field still is out there traveling.

Im sure that the pulse needs to be as sharp and instantaneous as possible to "turnoff the elec.magnet" before the magnetic field reached far out and "disappeared" . An electromagnet is really just like a gun but much much faster. every time you turn on an elec magnet magnetic field is sent at the speed of light. if you for instance turn off a very very powerfull elec. magnet that can reach 1000s of kilometers, what will happen is that there will e a magnetic field far out from the elec magnet even if its off, because electromagnetic fields travel at finite speed or at least that's what the theory sais

 

[berkeman]

What makes you think you will get any measurable propulsion out of this?

I explained in the post but let me make it clearer. When you separate a magnet from its magnetic field you get a field to react and push against. Thats it really. For instance if we have two such super high pulsed elec.magnets with very short rise fall time, and slightly out of phase from each other one magnet will push against the magnetic field of the TURNED OFF MAGNET(we are talking about very short times)

I have thought about it and believe perhaps that its not the frequency that is important.. its perhaps the rise and fall time of the pulse that must be instant as to shut down the magnet while the magnetic field still is out there traveling.

Im sure that the pulse needs to be as sharp and instantaneous as possible to "turnoff the elec.magnet" before the magnetic field reached far out and "disappeared" . An electromagnet is really just like a gun but much much faster. every time you turn on an elec magnet magnetic field is sent at the speed of light. if you for instance turn off a very very powerfull elec. magnet that can reach 1000s of kilometers, what will happen is that there will e a magnetic field far out from the elec magnet even if its off, because electromagnetic fields travel at finite speed or at least that's what the theory sais

You didn't specifically answer my question in a scientific way. To get "thrust" for continuous propulsion, you must expel some mass. The "mass" (momentum) of the EM fields that you are generating is infinitesimal.

 

[Peter Ahlman]

You didn't specifically answer my question in a scientific way. To get "thrust" for continuous propulsion, you must expel some mass. The "mass" (momentum) of the EM fields that you are generating is infinitesimal.

you are correct it is small but shouldn't it e ig since this small force is being applied 500,000,000 times a second if we use 500mhz?

 

[berkeman]

you are correct it is small but shouldn't it e ig since this small force is being applied 500,000,000 times a second if we use 500mhz?

No. You could generate the same "thrust" with an equal power flashlight...

 

[Peter Ahlman]

Ok, but doesn't it boil down to the magnetic field strength of the air coil, i.e. how many gauss the small 2nh air coil for instance will output at 500mhz+ with 2amps? this 2nh rf inductor can operate at 3ghz with max current 2.3A and has SRF of 16ghz so we can use it safely at 3ghz and 2A.

Doesnt it boil down to how many gauss an inductor is capable of at RF frequency?


I put in the dimensions of that specific small inductor in calculator of magnetic field strength and got 40gauss! but that can't be right. Since it is a "time varying magnetic field" we are dealing with here there is another formula right?

So what formula to use for calculating the a magnetic field at a certain frequency, can I just use the traditional gauss calculator or should it be this which is said to calculate the AC flux density :

B= E x 10^8
---------------------
4.44 x A x N x f

I would really like to know the formula used for calculating the field for time varying inductors.


I agree it is a small force.. but how much?

Thanks

 

[Peter Ahlman]

No. You could generate the same "thrust" with an equal power flashlight...

Lets see if I get this correctly

Maybe the real question is what will the magnet2 do when it encounters the uncoupled field-1 of magnet-1. The electromagnetic-field -1 has almost no mass but has the same magnetic field pole and strength as magnet2.

So, will magnet2 get repelled?. Obviously both magnet2 and field1 are going to get repelled from each other.. which leaves me wondering what happens next:

-magnet2 & field1 get repelled for equal distances?

Or
-magnet2 is almost stationary(actually repelled a very tiny amount)while filed1 is repelled for great distance because field1´ mass is so small while magnet2 is so heavy?


Am I getting closer to understanding this? which scenario is closer to reality?

 

[yungman]

Do you know RF electronics? You never responded my original post. You insist on doing this, you better know RF designs.

I have no idea what you are trying to do, I just join in when you start talking about GHz pulses and coil. Varying magnetic field ALWAYS accompanied by varying electric field, so it is EM wave. Any chance of using a loop antenna and use the EM wave as your magnetic pulses?

 

[Peter Ahlman]

yungman, all I know is from self taught knowledge, reading everything I ever can. And also before doing/making/building anything I wanted to make sure if it works or not. The final question was the one I posted in my last post before this one.

 

[Antiphon]

Don't give up on your dream; but there's a lot of engineering you need to do before you can even begin to design this type of apparatus.

At 100 ghz any coil you make will not be an inductor. It will be a capacitor mostly. Due to the skin effect you can forget about pushing a lot of current without giant power supplies.

The largest size your inductor can be will probably be a few mm across. And the worst news is you will loose most of the power to radiation. That is, you will have a 100ghz loop antenna.

The worst part of your plan is that it's not consistent with the known correct laws of electrodynamics. You just can't lift yourself by your own bootstraps using Maxwell's equations.

The answer to your quest likely lies in the nuclear fields realm and you don't have a hope of getting to building any equipment without deep deep knowledge of such fields.

This is a lifetime quest you're proposing. Take your time and do it right. Learn all the physics you possibly can and seek out people who have already got four or five decades head start on you. They're out there if you know where to look for them.

And yes, it's possible.

 

[Peter Ahlman]

Don't give up on your dream; but there's a lot of engineering you need to do before you can even begin to design this type of apparatus.

At 100 ghz any coil you make will not be an inductor. It will be a capacitor mostly. Due to the skin effect you can forget about pushing a lot of current without giant power supplies.

The largest size your inductor can be will probably be a few mm across. And the worst news is you will loose most of the power to radiation. That is, you will have a 100ghz loop antenna.

The worst part of your plan is that it's not consistent with the known correct laws of electrodynamics. You just can't lift yourself by your own bootstraps using Maxwell's equations.

The answer to your quest likely lies in the nuclear fields realm and you don't have a hope of getting to building any equipment without deep deep knowledge of such fields.

This is a lifetime quest you're proposing. Take your time and do it right. Learn all the physics you possibly can and seek out people who have already got four or five decades head start on you. They're out there if you know where to look for them.

And yes, it's possible.

I appreciate your point of view and I am aware of all the above hurdles in my way but as ironic as it is I started to think that the whole idea isn't possible but I am not 100% sure.

As I said it actually boils down to the "interaction between the uncoupled electromagnetic field of elec.magnet1 and electromagnet 2" both the uncoupled field and magnet2 will repel each other, right? but it looks like the electromagnet2 will be stationary and hardly moves while the uncoupled elec.magnetic field will be the one which is repelling since it is virtually massless(??). I really want to get this confirmed or not by someone more expert in this area. If you didnt understand this please see my post nr.26

 

[berkeman]

I'm sorry Peter, but I can't let this thread go on any longer. It is a waste of time. What you are trying to do is create a propulsion device using EM fields and the truth is it won't work. Please keep on learning as much as you can about EE and EM, because the more you know, the earlier you can reject ideas that won't work, and the sooner you can move on to other ideas that may have a chance of working.

Thread closed.