Magnetostrictive Versus Piezoelectric
Transducers For Power Ultrasonic Applications(p. 1)
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There are two fundamental transducer designs used for power ultrasonic applications today, magnetostrictive and piezoelectric. Piezoelectric transducers utilize the piezoelectric property of a material to convert electrical energy directly into mechanical energy. Magnetostrictive transducers utilize the magnetostrictive property of a material to convert the energy in a magnetic field into mechanical energy. The magnetic field is provided by a coil of wire which is wrapped around the magnetostrictive material. Both types of transducers have advantages and disadvantages. Blackstone~NEY Ultrasonics has weighed both technologies and chooses to provide piezoelectric transducers. The following will help the reader understand the rationale behind this choice.
Background
The very first ultrasonic devices were developed early in the 20th century when the piezoelectric effect was discovered by Jacques and Pierre Curie. These devices consisted of naturally occurring piezoelectric minerals such as quartz crystals attached by various means to surfaces to be vibrated. These early devices were inherently fragile due to the fragile nature of the piezoelectric materials used in their construction and rudimentary adhesive bonding technology. In the 1930's, as there was an effort to utilize ultrasonic energy more extensively, the piezoelectric technology then available fell short of the need for reliable, robust ultrasonic devices. It was at this time that magnetostrictive technology eclipsed piezoelectric technology as the "motor" for ultrasonic devices including early ultrasonic cleaning systems. Magnetostrictive devices of that era were unquestionably more reliable than their piezoelectric counterparts.
All of that began to change, however, with the development of new piezoelectric ceramics for use in SONAR applications during World War II. New, stronger, man-made ceramics replaced naturally occurring "crystals" as the source of vibration. In addition, ways were found to pre-stress the new piezoelectric materials (much like in the architectural use of pre-stressed concrete) to prevent failure due to their limited tensile strength. The remaining "weak link," the attachment of composite piezoelectric drivers to suitable vessels for ultrasonic cleaning use, was overcome with the development of advanced adhesive bonding methods necessitated by the aircraft industry during the 1950's. This technology continues to advance to this day.
So, although there was a period in time when magnetostrictive transducers ruled the world of ultrasonic cleaning, the pendulum has now swung back toward piezoelectricity as the preferred ultrasonic source. There is abundant support for this switch in preference for piezoelectricity.
The following brief description of both magnetostrictive and piezoelectric technology as it is utilized in ultrasonic transducers is provided to assist the reader in an understanding of the discussions that follow.
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