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Recent content by drdick

  1. drdick

    Magnetic Damping to Minimise LF Vibration

    Eddy current damping will slow the pendulum, but should help smooth things out. Calculations are not precise. Suggest you pick up a bag of magnets from a hardware store and do some empirical work. A pair of .5" disk magnets about .25" thick placed so they attract throught the...
  2. drdick

    Effect of seams in magnetically shielded enclosures?

    Magnetic shielding is a misnomer. The object is to guide unwanted magnetic flux to a place where it can return to its source without doing harm. If the flux must jump a gap, it projects a fringing field which will at least alter the field shape/strength within the "shielded" volume...
  3. drdick

    Permeability at very low level

    Magnetic core materials, typically low carbon steels or permalloys, can be annealed to bring out various magnetic attributes, including initial (low level) permeability. In general, those anneals that promote grain growth with slow cools result in higher permeability and lower hardness. If you...
  4. drdick

    Demagnetization

    Physical geometry is a factor. See Domain Theory at www.dextermag.com
  5. drdick

    Magnetic losses due to shock

    The effect of shock would depend on the magnet's resistance to demagnetization, i.e. it's coercivity (Hc) and magnetic length. Hc for SMCo is relatively high, but thin (L/D=<.1) magnets have weak domains at corners/edges that can be reversed by external energy sources. If there is potential...
  6. drdick

    Permeability at very low level

    What grade of SS is used? If heat treat for strength increased hardness and/or decreases grain size, then permeability has probably dropped. The effect can be pronounced at low flux levels. Other factors to consider are the potential for magnetization (biasing) during cooling due to...
  7. drdick

    Magnetic Permeability

    Do the EMs have a ferrous core? Are they identical? Is the mounting identical? Are there ferrous mounting components that add &quot;yoke effect&quot; in one case and not the other? It would help a great deal to know the flux density established in some fixed gap between the electromagnet...
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