Ultrasonic Appucations Using Magnetostrictive Smart Materials
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T. TOBY HANSEN AND SOLOMON R. GHORAYEB ETREMA Products, Inc. 2500 North Loop Drive, Ames, Iowa 50010 ABSTRACT
Many of the innovations in ultrasonic technology make use of modem smart alloys and materials. As a result, the theory and application of ultrasonic energy have become extremely important in various disciplines such as ultrasonic surgery, deaning and imaging. However, despite the fact that most of these ultrasonic devices are based on widely known materials, there remains a class of materials which have not been fully explored as potential active components in ultrasonic designs. In this paper, the giant magnetostrictive smart material, ETREMA TERFENOL-D®, is discussed to illustrate its potential for such applications. Frequency analysis, reliability and advantages of ultrasonic mechanisms using ETREMA TERFENOL-D@ are also shown for a general broadband ultrasonic device. Frequencies between 1 kHz and 30 kHz were obtained for these applications. INTRODUClION
Recent developmental applications in the field of magnetostriction have covered areas ranging from the medical to the defense industry. A large volume of interest has focused on electroactive devices used for micropositioning, antivibration and antinoise.
However, driven by technological and market forces, this interest has broadened to cover ultrasonic applications in both the medical and the nondestructive testing (NDT) arenas. As a result, new techniques are being implemented to refine, and thus outperform, the conventional electrostrictive technologies. Magnetostriction, or the tendency of ferromagnetic materials to expand or contract in a magnetic field, is a well known phenomenon that has been exploited for many years for acoustic/sonic transducers. Magnetostrictive actuators using nickel and alloys of nickel, cobalt and iron were used extensively in the 1940's and 1950's, predominantly as ultrasonic vibration sources for acoustic cleaning, welding and machining. In the early 1970's a group of Navy scientists lead by A. E. Clark began experimenting with highly magnetostrictive rare earth metals [1]. In 1976, they discovered an alloy of Iron and Terbium which had high levels of magnetostriction. Furthermore, they determined that by adding Dysprosium to the mixture, they could vary the amount of magnetic hysteresis present in the material. The new material was called TERFENOL-D after its components Terbium (TER-), Iron (-FE-), Dysprosium (-D) and its place of discovery (Naval Ordnance Lab, -NOL). Basic Actuator Configuration An actuator is the general name for mechanisms that convert energy input to a displacement output. Magnetostrictive actuators convert electrical energy to mechanical 259 Mat. Res. Soc. Symp. Proc. Vol. 360 © 1995 Materials Research Society
energy using the magnetic field induced by an electric current in a wound wire solenoid. The solenoid is usually wrapped around a rod or bar of the magnetostrictive material and displacement output is varied by controlling the current flow in the coil. The use of ETREMA TERFENOL-D® actuato
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