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Variable inductance

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I'm involved in experimental study of Single Bubble Sonoluminescence. I'm using function waveform generator with piezoelectric transducers to produce ultrasound standing wave in my resonator. To achieve a standing wave there's a need to have current and voltage in a phase. For this purpose I use a coil with movable core. The problem is magnetic field producted with coil, and that I have to manually move the core each time the frequency is changed. I wonder if there is a possibility to build by myself or to buy some apparatus which will be able of providing variable inductance. It would be best if programmable or automatic. Thanks a lot for any hints.



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How much do you have to change the inductance value...like 2 times original,
10 times, 100 times, etc.?


I have an idea.

Wind another coil round your core to form a transformer.

Connect another inductor in series with the coil you've just wound to act as a high frequency choke.

Connect the coil you've just wound to a constant current DC power supply. Increasing the DC current will reduce the inductance because it gets closer to core saturation.


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Another way is to build separate, binary valued coils connected in series. For example, the first coil is x uH, the next coil is 2x uH, the next coil is 4x uH, then 8x uH... and so on. Use relays to short the coils out you don't want to produce any value inductance that is a mutiple of x uH. The relays are switched on and off with electrical signals. The first coil determines the smallest adjustment that can be accomplished. The more coils used, the larger the total inductance that can be accomplished.
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