An electric motor with a squirrel cage rotor is called a squirrel cage motor. In overall shape it is a cylinder mounted on a shaft. Internally it contains longitudinal conductive bars of aluminium or copper set into grooves and connected together at both ends by shorting rings forming a cage-like shape. The core of the rotor is built of a stack of iron laminations. The field windings in the stator of an induction motor set up a rotating magnetic field around the rotor. The relative motion between this field and the rotation of the rotor induces electrical current flow in the conductive bars. Squirrel cage motor is a polyphase induction motor, so called because its rotor consists of a circle of bars, parallel to the shaft.