Vibratory piezoelectric transducers have the capacity to operate at extremely high frequencies, allowing their usage in a wide range of ultrasonic applications. Most common types of ultrasonic applications include motors, cleaning devices, and various sensors. Here we will discuss ultrasonic transducers used in motor and cleaning tools – we have previously covered ultrasonic sensors in the “Sensors” section.
Types of Motors and Basic Mechanics
We will discuss two types of motors: linear and rotary. Both types utilize a repetitive motion generating small movements. The simplicity and high frequency capability of piezoelectric transducers are often a perfect solution for these applications requiring minimal movement.
Piezoelectric crystals can be applied in two ways: they can either be used to generate the movement, or to generate friction. The latter type uses locking mechanisms, where the crystal can either be locked or free (to or from the surface being traversed). A crystal becomes locked by expanding and creating frictional force with the surface. Conversely, it becomes free by contracting and moving out of contact with the surface. This crystal generating movement utilizes the frictional force and expands to move across the surface.
Three Piece Motors
The most common type of motor (both linear and rotary) uses one rectangular crystal to generate movement and two crystals on either end to generate friction. When expanding, one crystal locks while the other frees up, causing the motor to generate motion away from the locked crystal. Once the center piece is fully expanded, the first locking crystal frees up while the other locks onto the surface. When the center piece contracts, a force is, again, exerted away from the first piece.
One variation of such a motor is where one piece is always free and the other is always locked. The center piece expands slowly so the free piece is pushed outwards. It then contracts rapidly, generating enough force for the locked piece to slip towards the free piece slightly.
Ultrasound cleaning utilizing piezoelectric transduction is a straightforward process. A vibratory transducer operating at ultrasonic frequencies in a fluid (normally water or a cleaning solvent) creates bubbles from the vibrations, exerting high amounts of force on molecules on the surface of the object being cleaned. This cleaning process generally lasts for less than twenty minutes.
This method for cleaning is extremely volatile and effective, and is widely used by jewelers, fishermen, dentists, and electricians. Due to the extra force provided by the vibrations, potent chemicals or cleaning agents are either minimized or no longer required.
Benefits of Piezoelectricity
For motor applications, piezoelectricity shines in its precision. Since the individual movements are so small, it is easy for the motors to be controlled to the micrometer level. By utilizing piezoelectric ultrasonic transducers these motors can be designed to be relatively efficient and simple, with few rotating parts and minimized maintenance over a wide range of operating conditions.
In ultrasonic cleaning applications, piezoelectric transducers are the most common vibratory apparatus in use today, with new products based on this technology being designed throughout many industries.