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1377Info about the MEG core's hysteresis curve

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  • mayerstan
    Feb 6, 2010
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                Recently I had a phone conversation with a serious MEG experimenter who shared with me some information about the MEG core that apparently comes from a source close to the Bearden team and so with his permission, I am sharing this information with you.   The source ... the MEG experimenter who I have great respect for ... wishes to remain anonymous.  Below is the info:

                A while ago, it was brought to my attention that the  standard core needs to be processed so that the  hysteresis  curve is "square".  This is why Tom Bearden  says that any lab with $100k of equipment can replicate  the MEG.  That $100k of equipment performs the necessary  processing for the core.  A square hysteresis curve means that the magnetization of the core requires a  strong coercive force (the external field trying to  reverse the polarity of the magnetic domains in the core)  before the core magnetic field reverses direction.

      I  believe it is this sudden reversal of the core's magnetic  direction in essentially an avalanche that provides  the large output of the MEG.  Because the reversal  requires a finite time, the switching frequency of  the drive flux is adjusted so that it occurs just as  the core completes its reversal.  The output voltage  then is a square wave because V = dB/dt ( V is the  voltage, dB is the change in the core's magnetic field,  dt is the time of the change of the magnetic field)  and the driver keeps the external B changing as quickly as the core can change direction.  

      Metglas may be willing to provide information about annealing or they may even be willing to perform custom annealing for a standard core to  provide different hysteresis performance.  I have not  made this inquiry since I do not have knowledge of  materials processing nor the equipment required to do so.    To me, the processing of the off-the-shelf core  is one of the secrets of the MEG.  Clearly it is not  simple because Dr. Bearden says that the development team has very few working prototypes.


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