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I have a magnetically permeable element (98% pure iron) vibrating at 3-5Hz between two electromagnets (with iron cores) which is experiencing too much damping, presumably due to eddy current losses.

I know I can reduce this damping by constructing my vibrating element from thin laminated layers, or by using an electrically non-conductive material (ferrite?).

Is it possible to produce a damping reduction via control system? I'm imagining sensing the displacement/velocity of the core versus time and using this to somehow vary the power output to the solenoid coils.

If it's possible, I'd be grateful for details on how it would work.

The vibrating element is cylindrical with approx 35mm diameter. My end goal is to electromagnetically control the (negative) stiffness of a system without adding much damping.

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  • \$\begingroup\$ do your electromagnets have magnetic cores? \$\endgroup\$ Feb 13, 2020 at 2:38
  • \$\begingroup\$ Do you want to oscillate the core position for a longer time? What is your system? Some lab shaker? Or more like a levitating magnet? \$\endgroup\$
    – jDAQ
    Feb 13, 2020 at 3:49
  • \$\begingroup\$ Eddy current compensation will just boost high frequency gain. Damping is an impedance ratio of real/reactive power is best improved by reducing the real eddy current loss if that is the cause. What freq? Core thickness? Matl? \$\endgroup\$ Feb 13, 2020 at 3:51
  • \$\begingroup\$ @Jasen see edits \$\endgroup\$
    – davegravy
    Feb 13, 2020 at 5:07
  • \$\begingroup\$ @jDAQ see edits \$\endgroup\$
    – davegravy
    Feb 13, 2020 at 5:07

2 Answers 2

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If you can characterize (i.e. predict) the damping then that can be fed into the control system inverted to reduce the damping effect.

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You want a control system for damping. What you would need is a coil in the field of the vibrating magnet, connected to a resistor. When vibrating, current will be induced in the coil. The resistor will dissipate some energy, which will be extracted from the magnet, so it will be "damped". With some electronics, you could regulate how much energy will be dissipated in the resistor. You also need a sensor that measures the amount of vibration, and a feedback loop to complete the control system.

You could, of course, combine this coil with one of the electromagnets, which are also coils, if you figure out how to separate the voltages for powering the electromagnet and those from the induction by the vibrating magnet.

The same coil can also be used as a sensor.

Good Luck!

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  • \$\begingroup\$ His problem is that he "... is experiencing too much damping", the resistor part will not help. If only the OP could better describe the system/requirements or post some good pictures of the system the answers could actually be on point. \$\endgroup\$
    – jDAQ
    Feb 24, 2020 at 9:32
  • \$\begingroup\$ @jDAQ Sure, OP could reduce the eddy current losses from the massive core by going to a laminated core, and introduce controllable losses to a resistor as I described. \$\endgroup\$
    – Roland
    Feb 24, 2020 at 13:51

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