The Theremin: From a Physics Perspective?

Question

I was wondering if anyone had any info and links on the physics behind the theremin.

A little more than the wikipedia explanation please

Answer 1

A lot of the unique theremin tone comes from interactions between the oscillators. An electronic circuit that has multiple oscillators has to fight their natural tendency to lock to the same frequency. Like pendulums that may couple through a common support structure, multiple oscillators can couple through a lot of sneak paths. Power supply and ground lines are common sources. Also magnetic coupling between the coils of the oscillators, even induced EMF between components that are close together.

In a theremin, the most apparent result of the oscillators locking is that the tone disappears. Since the two oscillators are locked to the same frequency, the difference frequency between them is zero. Most theremins count on the oscillators locking to provide a mute when the performer is not present.

Only slightly less apparent is the fact that the frequency difference at which the oscillators lock represents the lowest pitch that the instrument can produce. If they lock when there is less that 250 Hz difference in their frequencies then you won't be hitting any notes below about middle C.

Not apparent at all, in fact getting onto obscure, is the effect that oscillators have on one another as their frequencies approach lock. Before they actually synchronize, they "pull" one another toward the lock frequency. They do this by distorting each other on a cycle-by-cycle basis so that their outputs are no longer pure sine waves, or even truly periodic except at their difference frequency.

Answer 2

Its principals are almost entirely electronic circuitry and the capacitance effect of the human body - moving the hands varies the capacitance of a tuned circuit.
http://en.wikipedia.org/wiki/Theremin#Operating_principles