How will you design the rotor of a squirrel cage motor to have high starting torque?

When a high starting torque is required, a squirrel cage machine with specially designed rotor can be used without much sacrifice of efficiency but with some reduction of rated output. This can be achieved by either of the following two ways

(i) The rotor bars can be made very deep so that owing to skin effect, their resistance will be high at starting when the rotor frequency is equal to the supply frequency.

(ii) By using double squirrel cage rotor