What is an ultrasonic lens?

The so-called ultrasonic lens is actually a lens driven by an ultrasonic motor. The ultrasonic motor was first used on the lens by Canon in 1987. But at that time, the development of ultrasonic motor technology was still relatively weak, so only micro ultrasonic motors appeared. Now many ring ultrasonic motors have been used for some time, and Canon applied for a patent for this technology. So in 2002, almost after 15, other factories began to launch ultrasonic motor-driven lenses on a large scale, and the patent protection time has passed. However, for ultrasonic motor drive, there are different names. Canon is called USM, Nikon is called SWM, but the logo on the lens is AF-S, Sigma is called HSM, Pentax is called SDM, Sony follows Minolta's name SSM, Olympus is called SWD, and Longteng and Tuli haven't launched ultrasonic motor-driven lenses yet.