Rotary transformer

A rotary (rotatory) transformer is a specialized transformer used to couple electrical signals between two parts that rotate in relation to each other. They may be either cylindrical or 'pancake' shaped.

Slip rings can be used for the same purpose, but are subject to friction, wear, intermittent contact, and limitations on the rotational speed that can be accommodated without damage. Wear can be eliminated by using a pool of liquid mercury instead of a solid ring contact, but the toxicity and slow corrosion of mercury are problematic, and very high rotational speeds are again difficult to achieve. A rotary transformer has none of these limitations.