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Q & A: solid-state variable capacitor

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Most recent answer: 01/06/2013
Q:
Dear Sir, is it possible to make up a solid state variable capacitor? What I envisage, is a capacitor with fixed (non-movable plates of foil) adjacent to a coil/s in appropriate orientation. I am hoping that as the magnetic field from the coil is increased, that this will have the effect of "squeezing" out the electrostatic field, thus limiting the maximum capacitance. Please suggest possible layout of components. Retired electronics engineer.
- Steele Braden (age 72)
Auckland New Zealand
A:

The standard name for an electronically-controlled variable capacitor is "varactor", as described here: http://en.wikipedia.org/wiki/Variable_capacitor#Electronically_controlled

You seem interested in a very unusual design, in which the capacitance is controlled by a magnetic field rather than by a voltage.  To get it to work, you'd also need to fill the capacitor with some material whose dielectric susceptibility along the direction between the plates was sensitive to the magnetic field. That would probably be some sort of "multiferroic" material, http://en.wikipedia.org/wiki/Multiferroics. There's been a lot of research recently on such materials, but I don't think practical devices are being built from them yet. One obvious drawback with the general design you suggest is that the coil producing the field would probably draw a lot of current.

Mike W.


(published on 01/06/2013)

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