:ghz_01:INTROUCTIONIn 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.
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.
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.
DRAWBACKS OF ELECTROMAGNETIC MOTORS
Electromagnetic motors rely on the attraction and repulsion of magnetic fields for their operation. Without good noise suppression circuitry, their noisy electrical operation will affect the electronic components inside it. Surges and spikes from these motors can cause disruption or even damage in nonmotor related items such as CRTs and various types of receiving and transmitting equipments. Also , electromagnetic motors are notorious for consuming high amount of power and creating high ambient motor temperatures. Both are undesirable from the efficiency point of view. Excessive heat energy is wasted as losses. Even the efficiently rated electromagnetic motor has high input to output energy loss ratios.
Replacing these by ultrasonic motors would virtually eliminate these undesirable effects. The electromagnetic motors produce strong magnetic fields which cause interference. Ultrasonic motors use piezoelectric effect and hence 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.
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.