Howard Robert Johnson developed a permanent magnet motor and, on April 24, 1979, received .United States Patent office main classification of his 4151431 patent is as a "electrical generator or motor structure, dynamoelectric, linear" (310/12). Johnson said that his device generates motion, either rotary or linear, from nothing but permanent magnets in rotor as well as stator, acting against each other. He estimated that permanent magnets made of proper hard materials should lose less than two percent of their magnetization in powering a device for 18 years.