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magnetic field insulator

terty 34852 26
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  • #1
    terty
    Level 13  
    Has anyone heard of any materials that do not allow or significantly weaken the magnetic field of a permanent magnet passing through them
  • #2
    Kobra
    Level 18  
    Hello
    Each non-magnetic metal, e.g. Al, Cu, brass etc.
    Greetings
  • #3
    terty
    Level 13  
    Kobra wrote:
    Hello
    Each non-magnetic metal, e.g. Al, Cu, brass etc.
    Greetings


    non-magnetic metals such as aluminum or copper PASS the magnetic field, this field does not directly affect such elements but passes through them without any problems, I am interested if there is any material that will stop a strong field at a short distance and will not allow it to go further than the screen made from this material
  • #4
    _jta_
    Electronics specialist
    Any type I guide. This may require quite low temperatures - e.g. a dozen or so degrees K.
  • #5
    h-doc
    Level 27  
    there is something else called mumetal or something like that (I am not even sure if it is spelled this way) - I do not know what exactly it is, but it is used for shielding columns of electron microscopes.
  • #6
    elektryk
    Level 42  
    Take the steel plate. The lines of the magnetic field will close in it and at least part of the field will be shielded.
  • #7
    _jta_
    Electronics specialist
    Mumetal, 74% Ni, 5% Cu, 1% Mn, 20% Fe, soft ferromagnetic material,
    miu [p] from 7000 to 25000, miu [max] 100000, B [us] 850mT, B [r] 400mT, H [c] 2.4A / m;
    it shields like a conductor, not like an insulator;
    Supermalloy is better for this: miu [p] 125000, H [c] 0.32A / m
  • #8
    h-doc
    Level 27  
    yeah, but supermajols seem a bit expensive ...
    Only to the author of the topic - you can also consider an active neutralizer of the magnetic field (i.e. a coil or a set of coils properly positioned and powered).
  • #9
    _jta_
    Electronics specialist
    I don't suppose supermalloy is much more expensive than mumetal; but as if you want to do that
    economically, you can make the outer cover of carbonyl iron, and give it inside
    a thin supermalloy cover that will shield the field that passes through the iron.

    Active neutralization was used for the most demanding measurements
    small magnetic field, so that the Earth was much too large, it was getting
    this with the use of several coils with sizes several dozen times larger than the system,
    which was supposed to be in space without a field, and it was still visible on the measurements
    a tram ride a few kilometers away - had to be measured at night.
  • #10
    prokopcio
    Level 29  
    Hello...

    I have a question, is there any material that is not ferromagnetic and would significantly weaken the magnetic field ???

    If so, Perpetum Mobile is at your fingertips - so there is probably no such material.

    Once upon a time (by the head) I had fun with creating PerpetumMobile - with poor results, of course (like everyone else) - I came up with something like the picture.

    In the figure, the two outer magnets would be permanently attached and the two (inner) rotatably. The red tiles would have to be of this material.

    Regards
  • #11
    grzeskk
    Level 34  
    it seems to me that there is no such material for magnetic isolation for a simple reason: the lines of force of the magnetic field must close and thus there are no unipolar magnets, and the magnetic screens, e.g. in loudspeakers, only properly shape the field so that it does not diverge everywhere was just focused on the loudspeaker
  • #12
    _jta_
    Electronics specialist
    "Magnetic field isolator" exists - I wrote.
    On the other hand, this "perpetual motion machine" would not work - with or without an isolator, working in the field
    magnetic has a value of zero for a full revolution - its forces are potential.
  • #13
    grzerus
    Level 2  
    I heard that you can limit the magnetic field with a dense steel mesh of 2mm, preferably grounded
  • #14
    _jta_
    Electronics specialist
    It's better with sheet metal - but it's still a conductive screen, not an insulator.
    Only type I superconductors are magnetic field insulator (type II superconductors behave
    as if they consist of a large number of threads and there must be a magnetic field between them).
  • #15
    malarz1235
    Level 1  
    The only insulator is another magnet
  • #16
    qaz22
    Level 15  
    After all, there is an old solution that is successfully used. SPEAKER MAGNET, if we remove its middle, it is an ordinary magnet. When we put it back into the loudspeaker housing, the magnetic field is directed in one direction.
  • #17
    _jta_
    Electronics specialist
    In a loudspeaker, the magnetic field is mainly in the aperture. Likewise, in any closed (except for a small gap) magnetic circuit.
  • #18
    0x5261647A6975
    Level 10  
    I have a similar problem. I built a radio, i.e. in one housing I have a radio, amplifier, power supply, loudspeakers, I also controlled the remote control and turned on the main transformer with a relay. Unfortunately, I did not think about the magnetic field from the loudspeaker and the effect is that the relay does not work. It stops working only after moving away from the speaker. Unfortunately, the problem is that there is no other place inside the housing where it can be moved due to the high density of components inside. How to separate the loudspeaker from the transmitter to make it work, unfortunately there is very little space between the loudspeaker and the transmitter, only a few millimeters.
  • #19
    398216 UsuniÍty
    Level 43  
    A piece of steel sheet (preferably the diameter of a loudspeaker magnet) glued to the loudspeaker magnet at a distance.
    See what the older TV speakers look like - there is an additional steel "box" on the magnet and all this so as not to magnetize the cathode ray tube grid ... It worked.
  • #20
    _jta_
    Electronics specialist
    First of all, is it possible to turn this relay? In one position, the influence of the loudspeaker field should be much smaller. How is it arranged?
  • #21
    0x5261647A6975
    Level 10  
    398216 UsuniÍty wrote:
    A piece of steel sheet (preferably the diameter of a loudspeaker magnet) glued to the loudspeaker magnet at a distance.
    See what the older TV speakers look like - there is an additional steel "box" on the magnet and all this so as not to magnetize the cathode ray tube grid ... It worked.


    I couldn't find a piece of steel that would do it. Maybe I'll look for more and try it.

    Added after 15 [minutes]:

    _jta_ wrote:
    First of all, is it possible to turn this relay? In one position, the influence of the loudspeaker field should be much smaller. How is it arranged?


    Without desoldering the relay from the board, it will not be possible. But when I desolder it, I can stuff it a bit further from the speakers, maybe it would work, but a little tinkering will come out.

    What it looks like - top view:

    magnetic field insulator

    Side view after tilting the cover to take a photo. When closed, the speaker is a few mm on the relay, no more than 10.
    magnetic field insulator

    What is left for me:

    1. Resignation from internal speakers - only connecting external ones will be left.
    2. Resignation from turning off the power with the remote control - only the main switch.
    3. Converting the standby power supply board to the version with triac control? Electronic Relay? Mechanical some smaller / lower?

    PS. The design may seem strange, but it's an "evolutionary" version, originally it was a radio with the KIT AVT 5540 + amplifier based on the KIT AVT 1597, then I made my own version of the receiver + AVR with COG display and remote control, and finally decided to making a standby power supply.
  • #22
    _jta_
    Electronics specialist
    It would also be good to check: where the loudspeaker magnet attracts (he has a zone that does not attract, you need to find it), to which field direction the transmitter is sensitive.
  • #23
    0x5261647A6975
    Level 10  
    Well, you can, but in the PCB version, the relay can only be in this place, and I do not like tinkering. If it is impossible to isolate it, I have to consider the options mentioned above. And at the moment I am inclined to the option of replacing the relay with a triac.
  • #24
    _jta_
    Electronics specialist
    The knowledge of the magnetic field system can be helpful - a magnet always has two opposite poles, and you can try to shape their field by inserting a ferromagnetic in such a way that the same amount will come from both to the sensitive point of the relay (only with the opposite sign) - in total, zero will be obtained and there will be no interfere with the operation of the relay. But with a triac it will be easier ...
  • #25
    jarek_lnx
    Level 43  
    Quote:
    Knowing the magnetic field pattern can be helpful - a magnet always has two opposite poles,
    In a loudspeaker, it is usually placed along the axis of the coil, because the place where the relay is operated is very close to one pole of the magnet and far from the other with the use of ferromagnetic alone, this will not be reset.
    But by using a ferromagnetic and a second, weaker magnet, you can level the magnetic field in the area close to the relay.

    Quote:

    See what the older TV speakers look like - there is an additional steel "box" on the magnet and all this so as not to magnetize the cathode ray tube grid ... It worked.
    There were two magnets in the box, one generated the field needed for the loudspeaker to operate, the other was about two or three times thinner between the magnetic shield and the pole piece of the main magnet.
    This is what the magnetic circuit looked like below, the gray ones are ferromagnetic, the blue and red magnets.
    magnetic field insulator
    Quote:

    But when I desolder it, I can stuff it a bit further from the speakers, maybe it would work, but a little tinkering will come out.
    So you have a choice, it doesn't work but looks better vs it works but looks bad. Both are wrong, I have never understood people who say the first is better :)

    PS The transformer also "dislikes" the direct proximity of the magnet, it may deteriorate the properties of the core (saturate) and increase the power losses in the transformer (both losses in the core and in the windings due to an increase in no-load current). Check that it is not overheating.
  • #26
    _jta_
    Electronics specialist
    jarek_lnx wrote:
    This is what the magnetic circuit looked like below, the gray ones are ferromagnetic, the blue and red magnets.

    This arrangement additionally increased the magnetic field in the gap, improving the performance of the loudspeaker. That would be the way, now there are neodymium magnets, just a question of what size (too large will not only compensate the speaker field, but also give the field in the opposite direction, and will disturb the transmitter itself).
  • #27
    0x5261647A6975
    Level 10  
    jarek_lnx wrote:
    So you have a choice, it doesn't work but looks better vs it works but looks bad. Both are wrong, I have never understood people who say the first is better :)


    I have given more solutions. I have already designed a PCB with a triac, I will order it soon for a triac and optotriac for galvanic isolation, then I will solder the transformer and a few other elements and it will be nice and it will work. Two in one :)

    jarek_lnx wrote:
    PS The transformer also "dislikes" the immediate vicinity of the magnet, it may deteriorate the properties of the core (saturate) and increase the power losses in the transformer (both losses in the core and in the windings due to an increase in no-load current). Check that it is not overheating.


    This small 0.7VA transformer heats up quite a bit, it burns a bit but you can hold your toe, so probably something around 40-50 degrees. But it is probably the same with the housing open, i.e. without a loudspeaker nearby. I will look at it again.