Squirrel cage alternating current (AC) induction motors, the usual subject of Motor Doctor articles, are one of the world’s great “evergreen” technologies. The basic principles and fundamental designs have been known and applied for approximately 100 years. (And no, I was not around when they were first introduced.)
Most of the changes over the years have been in the area of materials — primarily metallurgical changes associated with new alloys and chemicals related to insulating materials.