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How Ultrasonic Motor Works

Published on July 25, 2016


All of us know that motor is a machine which produces or imparts motion, or in detail it is an arrangement of coils and magnets that converts electric energy into mechanical energy and ultrasonic motors are the next generation motors. In 1980,the world's first ultrasonic motor was invented which utilizes the piezoelectric effect in the ultrasonic frequency range to provide its motive force resulting in a motor with unusually good low speed, high torque and power to weight characteristics.

Electromagnetism has always been the driving force behind electric motor technology. But these motors suffer from many drawbacks. The field of ultrasonic seems to be changing that driving force.


Ultrasonic motor construction tends to be simpler than EM type motors. Fewer assembly parts mean fewer moving parts and consequently less wear. The number of components required to construct an USM is small thereby minimizing the number of potential failure points.

As the ultrasonic motor uses ultrasonic vibrations as its driving force,it comprises a stator which is a piezoceramic material with an elastic body attached to it,and a rotor to generate ultrasonic vibrations. It therefore does not use magnets or coils. Therefore there is no problem of magnetic field and interference as in the case of electric motors. In ultrasonic motors, piezoelectric effect is used and therefore generates little or no magnetic interference. Principle Of Operation


Many polymers, ceramics and molecules are permanently polarized; that is some parts of the molecules are positively charged, while other parts are negatively charged. When an electric field is applied to these materials, these polarized molecules will align themselves with the electric field, resulting in induced dipoles within the molecular or crystal structure of the material. Further more a permanently polarized material such as Quartz(SiO2) or Barium Titanate(BaTiO3) will produce an electric field when the material changes dimensions as a result of an imposed mechanical force. These materials are piezoelectric and this phenomenon is known as Piezoelectric effect. Conversely, an applied electric field can cause a piezoelectric material to change dimensions. This is known as Electrostriction or Reverse piezoelectric effect. Current ultrasonic motor design works from this principle, only in reverse.

Ultrasonic Motor Works

When a voltage having a resonance frequency of more than 20KHz is applied to the piezoelectric element of an elastic body (a stator),the piezoelectric element expands and contracts. If voltage is applied, the material curls. The direction of the curl depends on the polarity of the applied voltage and the amount of curl is determined by how many volts are applied.

Eg:Quartz,Rochelle salt,Tourmaline,Lead Zirconium Titanate

t therefore does not make use of coils or magnets. It is a motor with a new concept that does not use magnetic force as its driving force. It also overcomes the principles of conventional motors. The working principle is based on a traveling wave as the driving force. The wave drives the comb of the piezoelectric ring. When applied, the piezoelectric combs will expand or contract corresponding to the traveling wave form and the rotor ring which is pressed against these combs start rotating.

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