Abstract:
An elongate structure having a magnetostrictive material composition is subjected to tensile stress in the longitudinal-axial direction, thereby generally orienting the magnetization of the elongate structure in the longitudinal-axial direction. Electrical current is conducted through the elongate structure and/or through at least one adjacent elongate conductor, thereby generally orienting the magnetization of the elongate structure in the transverse direction, generally in parallel with the transverse direction of the magnetic field concomitant the conduction of current through the elongate structure. The elongate structure magnetostrictively contracts due to the (generally 90°) repositioning of the magnetization of the elongate structure. Examples of inventive configurational variants include: (i) an elongate structure itself conducting current; (ii) a hollow elongate structure accommodating placement therethrough of at least one elongate conductor; (iii) an elongate structure flanked by a pair of elongate conductors conducting current in opposite directions; (iv) plural elongate structures bordering a centralized elongate conductor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. provisional application No. 60/543,650, filed 12 Feb. 2004, hereby incorporated herein by reference, entitled “Preparation of Positive Magnetostrictive Materials for Operation under Tension,” joint inventors Arthur E. Clark, James B. Restorff and Marilyn Wun-Fogle. 
   This application is related to U.S. nonprovisional application No. 11/007,953, filed 7 Dec. 2004, hereby incorporated herein by reference, entitled “Magnetostrictive Materials, Devices and Methods using High Magnetostriction, High Strength Fe-Ga Alloys,” joint inventors Arthur E. Clark, James B. Restorff and Marilyn Wun-Fogle; which is a continuation of U.S. nonprovisional application No. 10/182,095, filed 24 Jul. 2002, hereby incorporated herein by reference, entitled “Magnetostrictive Materials, Devices and Methods using High Magnetostriction, High Strength Fe-Ga Alloys,” joint inventors Arthur E. Clark, James B. Restorff and Marilyn Wun-Fogle; which claims the benefit of PCT application No. PCT/US01/02795, filed 29 Jan. 2001, hereby incorporated herein by reference, entitled “Magnetostrictive Devices and Methods using High Magnetostriction, High Strength Alloy,” joint inventors Arthur E. Clark, James B. Restorff and Marilyn Wun-Fogle; which claims the benefit of U.S. provisional application No. 60/178,615, filed 28 Jan. 2000, hereby incorporated herein by reference, entitled “Strong, Ductile, and Low Field Magnetostrictive Alloys,” joint inventors Arthur E. Clark, James B. Restorff and Marilyn Wun-Fogle. 
   This application is related to U.S. nonprovisional application No. 10/750,634, filed 24 Dec. 2003, hereby incorporated herein by reference, entitled “Magnetostrictive Materials, Devices and Methods using High Magnetostriction, High Strength Fe-Ga Alloys,” joint inventors Arthur E. Clark, James B. Restorff and Marilyn Wun-Fogle; which is a continuation-in-part of the aforementioned U.S. nonprovisional application No. 10/182,095, filed 24 Jul. 2002, hereby incorporated herein by reference, entitled “Magnetostrictive Materials, Devices and Methods using High magnetostriction, High Strength Fe-Ga Alloys,” joint inventors Arthur E. Clark, James B. Restorff and Marilyn Wun-Fogle. 

   STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to magnetostriction, more particularly to the utilization of positive magnetostrictive materials while being subjected to mechanical stresses. 
   The so-called “active materials” include magnetostrictives (e.g., Terfenol-D), electrostrictives, piezoelectrics (e.g., PZT, PMN-PT), and shape memory alloys (acronym, “SMA”). Active materials are used as sensors and actuators in various devices (such as smart structures) that integrate active and passive material systems. Typically, the active material system is subjected to significant mechanical stresses during operation of the device. With the notable exception of the recently discovered Galfenol class of alloy, modern active materials (e.g., Terfenol-D, PZT, PMN-PT) are robust under compressive stress but break relatively easily when a tensile stress is applied. Iron-gallium (Fe-Ga) alloys known as “Galfenol,” newly developed by the United States Navy&#39;s Naval Surface Warfare Center, Carderock Division, are materials that have large positive magnetostrictions but that are strong in both compression and tension. Certain other magnetostrictive materials, such as aluminum alloys, exhibit varying degrees of robustness in response to tensile stress; however, Galfenol is superior to all other magnetostrictive materials in this respect by at least a factor of two. 
   In a magnetostrictive material, the dimensions change as the material&#39;s magnetization direction varies. According to conventional practice involving magnetostriction, a magnetic field is applied to a magnetostrictive material to manipulate the material&#39;s magnetization direction. The magnetization direction tends to align itself parallel to the applied magnetic field. The magnetostrictive material acts as a transducer or motor, converting electrical to mechanical energy. A “positive” magnetostrictive material (i.e., a material that is characterized by “positive” magnetostriction) is one that, while subjected to longitudinally-axially directed compressive stress, expands (e.g., enlarges or lengthens) in the longitudinal-axial direction when then placed in a longitudinally-axially directed magnetic field created by an electrically conductive coil circumferentially circumscribing the magnetostrictive material; in the case of a positive magnetostrictive material, its magnetization shifts from transversely directed side-by-side orientation (brought about by the longitudinally-axially directed compressive stress) to longitudinally-axially directed end-to-end orientation (brought about by the longitudinally-axially directed magnetic field). A “negative” magnetostrictive material (i.e., a material that is characterized by “negative” magnetostriction) is one that, while subjected to longitudinally-axially directed tensile stress, contracts (e.g., shrinks or shortens) in the longitudinal-axial direction when then placed in a longitudinally-axially directed magnetic field created by an electrically conductive coil circumferentially circumscribing the magnetostrictive material; in the case of a negative magnetostrictive material, its magnetization shifts from transversely directed orientation (brought about by the longitudinally-axially directed tensile stress) to longitudinally directed end-to-end orientation (brought about by the longitudinally-axially directed magnetic field). 
   Positive magnetostriction materials are traditionally used with compressive stresses. Although heretofore unrealized, it would be desirable in many contexts to use positive magnetostriction materials with tensile stresses. The recent advent of Galfenol has whetted the technological world&#39;s appetite for such capabilities. For instance, one can contemplate various kinds of active apparatus that would prove useful in sonar, vibration damping, and other application. To achieve this goal, however, magnetic manipulation techniques commonly applied when using positive magnetostriction materials with compressive stresses would prove rather awkward to effectuate when using positive magnetostriction materials with tensile stresses. 
   The following references, incorporated herein by reference, are informative regarding magnetostriction in general, and Galfenol in particular. Wun-Fogle et al. U.S. Pat. No. 6,139,648 issued 31 Oct. 2000, entitled “Prestress Imposing Treatment of Magnetostrictive Material”; Wun-Fogle et al. U.S. Pat. No. 6,176,943 B1 issued 23 Jan. 2001, entitled “Processing Treatment of Amorphous Magnetostrictive Wires”; “Tensile Properties of magnetostrictive Iron-Gallium Alloys,” R. A. Kellogg, A. M. Russell, T. A. Lograsso, A. B. Flatau, A. E. Clark and M. Wun-Fogle,  Acta Materialia,  vol. 52, pp 5043-5050 (available online 25 Aug. 2004 at www. sciencedirect.com); “Extraordinary Magnetoelasticity and Lattice Softening in b.c.c. Fe-Ga Alloys,” A. E. Clark, K. B. Hathaway, M. Wun-Fogle, J. B. Restorff, T. A. Lograsso, V. M. Keppens, G. Petculescu, and R. A. Taylor,  Journal of Applied Physics,  vol. 93, no. 10, pp 8621-8623 (15 May 2003); “Texture and Grain Morphology Dependences of Saturation Magnetostriction in Rolled Polycrystalline Fe 83 Ga 17 ,” R. A. Kellogg, A. B. Flatau, A. E. Clark, M. Wun-Fogle, and T. A. Lograsso,  Journal of Applied Physics, vol,  93, no. 10, pp 8495-8497 (15 May 2003); “Structural Transformations in Quenched Fe-Ga Alloys,” T. A. Lograsso, A. R. Ross, D. L. Schlagel, A. E. Clark and M. Wun-Fogle,  Journal of Alloys and Compounds,  vol. 350, pp 95-101 (17 Feb. 2003); Magnetostrictive Properties of Galfenol Alloys under Compressive Stress,” A. E. Clark, M. Wun-Fogle, J. B. Restorff, and T. A. Lograsso,  Materials Transactions,  vol. 43, no. 5, pp 881-886, The Japan Institute of Metals, Special Issue on Smart Materials—Fundamentals and Applications (2002); “Temperature and Stress Dependence of the Magnetic and Magnetostrictive Properties of Fe 81 Ga 19 ,” R. A. Kellogg, A. Flatau, A. E. Clark, M. Wun-Fogle and T. A. Lograsso,  Journal of Applied Physics, vol.  91, no. 10, pp 7821-7823 (15 May 2002); “Magnetostriction of Ternary Fe-Ga-X Alloys (X=Ni, Mo, Sn, Al),” J. B. Restorff, M. Wun-Fogle, A. E. Clark, T. A. Lograsso, A. R. Ross, and D. L. Schlagel,  Journal of Applied Physics,  vol. 91, no. 10, pp 8225-8227 (15 May 2002); “Effect of Quenching on the Magnetostriction of Fe 1-x Ga x  (0.13&lt;x&lt;0.21),” A. E. Clark, M. Wun-Fogle, J. B. Restorff, T. A. Lograsso and J. R. Cullen,  IEEE Transactions on Magnetics,  vol. 37, no. 4, pp 2678-2680 (July 2001); “Magnetoelasticity of Fe-Ga and Fe-Al Alloys,” J. R. Cullen, A. E. Clark, M. Wun-Fogle, J. B. Restorff and T. A. Lograsso,  Journal of Magnetism and Magnetic Materials,  vols. 226-230, part 1, pp 948-949 (May 2001); “Magnetostrictive Properties of Body-Centered Cubic Fe-Ga and Fe-Ga-Al Alloys,” Arthur E. Clark, James B. Restorff, Marilyn Wun-Fogle, Thomas A. Lograsso and Deborah L. Schlagel,  IEEE Transaction on Magnetics,  vol. 36, no. 5, pp 3238-3240 (September 2000); “Magnetostrictive Galfenol/Alfenol Single Crystal Alloys Under Large Compressive Stresses,” A. E. Clark, M. Wun-Fogle, J. B. Restorff, and T. A. Lograsso, Proceedings of  Actuator  2000, 7 th  International Conference on New Actuators, Bremen, Germany, 19-21 Jun. 2000, pp 111-115; “Strong, Ductile, and Low-Field-Magnetostrictive Alloys Based on Fe-Ga,” S. Guruswamy, N. Srisukhumbowornchai, A. E. Clark, J. B. Restorff, and M. Wun-Fogle,  Scripta Materialia,  vol. 43, issue 3, pp 239-244 (20 Jul. 2000). 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, it is an object of the present invention to provide method and apparatus for using a positive magnetostriction material while subjecting it to tensile stress. 
   According to typical inventive embodiments, a method for producing magnetostrictive contraction comprises: (a) applying longitudinally-axially directed tension to an elongate structure so that the magnetization of the elongate structure tends generally to be longitudinally-axially directed; and, (b) applying a transversely (e.g., circumferentially) directed magnetic field to the elongate structure so that the magnetization tends generally to be transversely (e.g., circumferentially or tangentially) directed. The ensuing longitudinally-axially directed magnetostrictive contraction of the elongate structure is associated with the directional change of the magnetization from the longitudinally-axially directed general tendency to the transversely (e.g., circumferentially or tangentially) directed general tendency. The production of a transversely (e.g., circumferentially or tangentially) directed magnetic field will frequently result from, according to inventive practice, at least one of the following: (1) conduction of longitudinally-axially directed electrical current through the elongate structure; (2) conduction of longitudinally-axially directed electrical current through at least one elongate electrical conductor that is placed exterior (e.g., adjacent) to the elongate structure; (3) conduction of longitudinally-axially directed electrical current through at least one elongate electrical conductor that is placed interior to (e.g., inside a longitudinal-axial bore of) the elongate structure. 
   The present invention represents a unique methodology for using a positive magnetostrictive material under tensile loading. The conventional methodology for operating a positive magnetostrictive material in a device involves utilization of an excitation coil so as to supply an axial magnetic field to a magnetostrictive rod (or other elongate structure). This conventional methodology does not work for positive magnetostrictive materials under tensile load, since the magnetization is often already along the axial direction. The present invention applies a transverse (e.g., circumferential or tangential) magnetic field to magnetostrictie material with respect to which tensile stress is being exerted. The generation of a transverse magnetic field is accomplished according to at least one of three inventive modes. This transverse magnetic field rotates the magnetostrictive material&#39;s magnetization from the axial direction to the transverse direction, resulting in the desired magnetostrictive effect. 
   To elaborate, according to inventive principles, the magnetization of the magnetostrictive material is induced by tensile stress to be directed parallel to the longitudinal axis of the magnetostrictive material. An electrical current is applied so as to create a transverse (perpendicular) magnetic field. The tensilely induced longitudinally-axially directed magnetization of the magnetostrictive material is caused—by the electrically induced transverse magnetic field (i.e., the magnetic field induced via application of electrical current)—to move (rotate) ninety degrees so as to be transversely directed because of the tendency of the magnetization to become parallel with (align with) the transverse direction of the electrically induced magnetic field. That is, the magnetization changes orientation from one of parallelness with respect to the longitudinal axis to one perpendicularity with respect to the longitudinal axis. The magnetization becomes “perpendicular” (orthogonal or normal or at right angles) to the longitudinal axis in the sense that every or nearly every magnetization vector (“magnetic moment” or “magnetic domain”) shifts orientation so as to at least approximately lie in a geometric plane that perpendicularly intersects the magnetostrictive material&#39;s geometric longitudinal axis. Otherwise expressed, every or nearly every vector of magnetization shifts orientation so that the dot product between the vector of magnetization and the vector along the longitudinal axis equals or approaches zero. Expressed more simply, the magnetization becomes perpendicular to the direction of the length of the magnetostrictive material. The term “transverseness,” as used herein to describe directions of physical phenomena (such as magnetic field or magnetization) that are associated with inventive practice, denotes “perpendicularity” with respect to the length of the magnetostrictive structure. For instance, a magnetic field or a magnetization that is transverse with respect to a magnetostrictive rod is perpendicular to (at right angles to) the length of the rod. 
   According to typical embodiments of a first inventive mode for applying a transverse magnetic field to a magnetostrictive material structure, an electric current is provided through the magnetostrictive material structure itself (thereby applying a circumferentially transverse magnetic field). According to typical embodiments of a second inventive mode for applying a transverse magnetic field to the magnetostrictive material structure, an electric current is provided through one or more low resistance wires that are situated adjacent to the inside surface or surfaces of (e.g., inserted into) one or more magnetostrictive material structures (thereby applying a circumferentially transverse magnetic field). According to typical embodiments of a third inventive mode for applying a transverse magnetic field to the magnetostrictive material structure, an electric current is provided through one or more low resistance wires that are situated adjacent to the outside surface or surfaces of one or more magnetostrictive material structures (thereby applying a tangentially transverse magnetic field). According to some inventive embodiments, two or all three inventive modes are combined for applying a transverse magnetic field to the magnetostrictive material. According to one instance of such inventive embodiments, an electric current is provided through low resistance wires situated both inside the magnetostrictive material&#39;s axial bore and outside the magnetostrictive material&#39;s exterior surface. In the light of the instant disclosure, the ordinarily skilled artisan will be capable of practicing any of multifarious embodiments of the present invention. 
   The present invention affords new capabilities, especially the construction of devices that operate while effecting tensional stress. Such inventive devices are useful, for example, in sonar transducers and in vibration damping of structures and machinery. The present invention admits of implementation of a variety of active, structural materials and admits of practice in a variety of technologies and applications. 
   Other objects, advantages and features of this invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of an elongate magnetostrictive structure, illustrating the subjection of the elongate magnetostrictive structure to longitudinal-axial tension and the consequent alignment therewith of the elongate magnetostrictive structure&#39;s magnetization. 
       FIG. 2  is the perspective view of the elongate magnetostrictive structure shown in  FIG. 1 , illustrating the lack of any magnetostrictive effect associated with a current-carrying coil that is wrapped circumferentially around the elongate magnetostrictive structure, when the elongate magnetostrictive structure is subjected to longitudinal-axial tension. 
       FIG. 3  is the perspective view of the elongate magnetostrictive structure shown in  FIG. 1 , illustrating a magnetostrictive effect associated with current that is carried by a coil that is oriented so that the coil&#39;s geometric longitudinal axis is perpendicular to the elongate magnetostrictive structure&#39;s geometric longitudinal axis, when the elongate magnetostrictive structure is subjected to longitudinal-axial tension. 
       FIG. 4  is a perspective view of an electrically conductive, elongate magnetostrictive structure, cylindrically shaped similarly as shown in  FIG. 1 , illustrating a principle of the present invention whereby electrical current carried by the elongate magnetostrictive structure along the elongate magnetostrictive structure&#39;s geometric longitudinal axis results in a magnetic field that is circumferentially transverse relative to the elongate magnetostrictive structure&#39;s geometric longitudinal axis. 
       FIG. 5  is a perspective view of the elongate magnetostrictive structure shown in  FIG. 4 , illustrating, in accordance with an embodiment of the present invention, a magnetostrictive effect associated with current that is carried by the elongate magnetostrictive structure along the elongate magnetostrictive structure&#39;s geometric longitudinal axis such as shown in  FIG. 4 , when the elongate magnetostrictive structure is subjected to longitudinal-axial tension. As shown in  FIG. 5 , transverse magnetic field lines are generated by a current conducted through the elongate, electrically conductive, magnetostrictive structure. The transverse magnetic field lines cause the magnetization to rotate parallel to the transverse magnetic field lines. 
       FIG. 6  is a cross-sectional or end view of the inventive embodiment shown in  FIG. 9 , illustrating an inventive configuration that includes an integral elongate structure having two coaxial sections, viz., (i) a solid cylindrical electrically conductive core section and (ii) a hollow cylindrical magnetostrictive annular section. 
       FIG. 7  is a cross-sectional or end view of the inventive embodiment shown in  FIG. 10 , illustrating an inventive configuration that includes a central electrically conductive elongate structure and eight peripheral symmetrically distributed magnetostrictive elongate structures. 
       FIG. 8  is a cross-sectional or end view of the inventive embodiment shown in  FIG. 11 , illustrating an inventive configuration that includes a central elongate magnetostrictive structure and two peripheral (opposite) electrically conductive elongate structures that carry current in opposite directions. The righthand peripheral elongate structure conducts current in a direction shown proceeding into the page; the lefthand peripheral elongate structure conducts current in a direction shown proceeding out of the page. 
       FIG. 9  is a perspective view of the inventive embodiment shown in  FIG. 6 , illustrating, in accordance with an embodiment of the present invention, a magnetostrictive effect associated with current that is carried by the interior, electrically conductive section of an elongate structure, when the exterior, magnetostrictive section of an elongate structure is subjected to longitudinal-axial tension. 
       FIG. 10  is a perspective view of the inventive embodiment shown in  FIG. 7 , illustrating, in accordance with an embodiment of the present invention, a magnetostrictive effect associated with current that is carried by the central electrically conductive elongate structure when the eight peripheral symmetrically distributed magnetostrictive elongate structures are subjected to longitudinal-axial tension. 
       FIG. 11  is a perspective view of the inventive embodiment shown in  FIG. 8 , illustrating, in accordance with an embodiment of the present invention, a magnetostrictive effect associated with current that is carried in opposite directions by the two peripheral electrically conductive elongate structures, when the central elongate magnetostrictive structure is subjected to longitudinal-axial tension. 
       FIG. 12  is a table defining variables and constants used in several examples, described herein, of practice in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In positive magnetostrictive materials, tensile loading (tensile stress) causes the magnetization to rotate toward the stress axis. Referring to  FIG. 1 , elongate magnetostrictive structure  20  is made of a positive magnetostrictive material. Although elongate magnetostrictive structure  20  is shown to be cylindrical, magnetostrictive properties have been known to manifest in non-cylindrical (e.g., prismatic) elongate shapes. In the absence of stress, elongate magnetostrictive structure  20  is characterized by directional randomization of magnetization M. When elongate magnetostrictive structure  20  is subjected to tension (tensile stress) T in the direction of its geometric longitudinal axis a, the magnetization M of elongate magnetostrictive structure  20  becomes parallel to tension T, which is coincident with geometric longitudinal axis a. 
     FIG. 2  and  FIG. 3  illustrate relationships among tensional (tensile) stress, magnetization and magnetic field direction. With reference to  FIG. 2 , the parallelness of the magnetization M with respect to the tension T, shown in  FIG. 1 , can be a counterproductive characteristic if a magnetostrictive change in length L of elongate magnetostrictive structure  20  is desired.  FIG. 2  depicts a simple configuration of a current I conducted through a coil  90  that is wrapped around elongate magnetostrictive material  20 . No magnetostrictive effect is brought about when a current-carrying coil  90  coaxially circumscribes elongate magnetostrictive structure  20  while elongate magnetostrictive structure  20  is being subjected to longitudinal-axial tension T. Coil  90 , wrapped or wound around elongate magnetostrictive structure  20 , carries electrical current I. Current I produces a magnetic field H that is parallel to the magnetization M of elongate magnetostrictive structure  20 . Magnetization M is directed along longitudinal axis a because tension T is directed along longitudinal axis a. Hence, the magnetic field H thus produced does not cause a change in direction of magnetization M of elongate magnetostrictive structure  20  such as would result in a change in length L of elongate magnetostrictive structure  20 . 
   Accordingly, as depicted in  FIG. 2 , current I creates a magnetic field H along the same axis, viz., longitudinal axis a, and therefore does not result in any change in the direction of magnetization M, since the magnetization M is already parallel to the magnetic field H direction. That is,  FIG. 2  illustrates the non-responsiveness of the elongate magnetostrictive structure  20  material to the magnetic field H. With reference to  FIG. 3 , a magnetic field H applied transverse to the elongate magnetostrictive structure  20  material rotates the magnetization M and results in a change in length L. As shown in  FIG. 3 , current I is conducted by a coil  90 . Current-carrying coil  90  is oriented so that the geometric longitudinal axis w of current-carrying coil  90  is perpendicular to the geometric longitudinal axis a of elongate magnetostrictive structure  20 . Current I produces a magnetic field H that is perpendicular to magnetization M of the elongate magnetostrictive structure  20 . Magnetization M is directed along longitudinal axis a because the tension T that the elongate magnetostrictive structure is experiencing is directed along longitudinal axis a. Hence, the magnetic field H thus produced causes a change in direction of magnetization M of elongate magnetostrictive structure  20  so as to be parallel to the magnetic field H. The change in direction of the magnetization M of elongate magnetostrictive structure  20  thereby results in a change in the length L of elongate magnetostrictive structure  20 . 
   Similarly as elongate magnetostrictive structure  20  is shown to be cylindrical in  FIG. 1  through  FIG. 3 , the inventively practiced elongate magnetostrictive structures shown herein in  FIG. 4  through  FIG. 11  are shown to be cylindrical. Thus, elongate magnetostrictive structure  20   c  is shown to be cylindrical in  FIG. 4  and  FIG. 5 ; elongate annular magnetostrictive structure  200  is shown to be cylindrical in  FIG. 6  and  FIG. 9 ; elongate magnetostrictive structure  20  shown to be cylindrical in  FIG. 7  and  FIG. 10 ; magnetostrictive structure  20  is shown to be cylindrical in  FIG. 8  and  FIG. 11 . Nevertheless, in inventive practice the elongate magnetostrictive structures are not necessarily cylindrical, albeit they are typically (but not necessarily) axially symmetrical. Magnetostrictive properties manifest analogously for cylindrical and non-cylindrical (e.g., prismatic) shapes. Generally speaking, an elongate magnetostrictive structure used in inventive practice is characterized by a shape defining the lateral surface of a “cylindric solid.” A cylindric solid is a three-dimensional geometric figure that includes a lateral surface and two congruent bases lying in parallel geometric planes. Cylindric solids include, but are not limited to, cylinders (wherein the bases are circular), cylindroids (wherein the bases are elliptical), and prisms (wherein the bases are polygonal). The present invention&#39;s elongate magnetostrictive structures can be embodies, for instance, as a rod, a wire or a bar. It is to be understood that the present invention&#39;s elongate magnetostrictive structures illustrated herein in  FIG. 4  through  FIG. 11 , though sometimes referred to herein as “wires,” can be inventively practiced in multifarious forms and shapes. 
   Referring to  FIG. 4  and  FIG. 5 , elongate magnetostrictive structure  20   c  conducts electrical current I along the longitudinal axis a of elongate magnetostrictive structure  20   c . The current I is supplied by an electrical current source  70  (such as a battery or other direct current power supply device) and is conducted to elongate magnetostrictive structure  20   c  via an electrical connection means  80  (such as a wire, lead, electrode or other electrical conductor device). Generally speaking, inventive practice similarly involves utilization of an electrical current source  70  and electrical connection means  80 . As illustrated in  FIG. 4 , current I produces a magnetic field H that is circumferentially transverse relative to longitudinal axis a of elongate magnetostrictive structure  20   c . That is, current I, conducted through elongate magnetostrictive structure  20 , generates a transverse magnetic field H. 
   The elongate magnetostrictive structure  20   c  in  FIG. 4  and  FIG. 5  is similar to the elongate magnetostrictive structure  20  shown in  FIG. 1  through  FIG. 3  insofar as having a positive magnetostrictive material composition and describing a cylindrical shape. Typical magnetostrictive structures consist of (or substantially consist of) magnetostrictive material, and are thus electrically conductive. Some magnetostrictive structures, however, are not electrically conductive, as they have a composite construction including a resinous matrix and magnetostrictive material reinforcement or filler. The elongate magnetostrictive structures that can be inventively implemented are not limited to structures having a positive magnetostrictive material composition, but can include any structure, regardless of material composition, that is capable of exhibiting positive magnetostriction. 
   As illustrated in  FIG. 5 , elongate magnetostrictive structure  20   c  is subjected to longitudinal-axial tension (tensile stress) T. According to typical inventive practice, longitudinal-axial tensile stress T is exerted by means of attaching elongate magnetostrictive structure  20   c  to one or more other structures, diagrammatically represented in  FIG. 5  as housing  100 . Such attachment can be effected by any of various known techniques for attaching metal materials to other objects. For instance, elongate magnetostrictive structure  20   c  can be bored (e.g., drilled) at each end and the resultant holes used for fastening (e.g., screwing or bolting) to housing  100 . Alternatively, elongate magnetostrictive structure  20   c  can threaded at each end and the resultant threaded ends used for fastening (e.g., screwing or bolting) to housing  100 . As another alternative, elongate magnetostrictive structure  20   c  can be welded at each end to housing  100 . 
   As further illustrated in  FIG. 5 , a magnetostrictive effect ensues when elongate magnetostrictive structure  20   c  is subjected to longitudinal-axial tension T. The current I produces a magnetic field H that is circumferentially transverse relative to the magnetization M of elongate magnetostrictive structure  20   c , magnetization M being directed along longitudinal axis a because of the tension T along longitudinal axis a that elongate magnetostrictive structure  20   c  is experiencing. Hence, the magnetic field H thus produced causes a change in direction of magnetization M of elongate magnetostrictive structure  20   c  so that magnetization M is parallel to the produced magnetic field H. The change in the direction of magnetization M of elongate magnetostrictive structure  20   c  thereby results in a change in the length L of elongate magnetostrictive structure  20   c . 
   With reference to  FIG. 6  and  FIG. 9 , the present invention&#39;s integral elongate structure  40  includes two coaxial sections, viz., annulus  200  (the exterior, annular, magnetostrictive section) and core  300  (the interior, solid cylindrical, electrically conductive section), which share longitudinal axis a. Annulus  200  is an elongate hollow cylindrical structure. Core  300  is an elongate solid cylindrical structure. Core  300  conducts current I in the direction of longitudinal axis a. Annulus  200  is subjected to tension T along longitudinal axis a. Current I produces a magnetic field H that is perpendicular to the magnetization M of annulus  200 . Magnetization M is longitudinally-axially directed because of the longitudinal-axial tension T that annulus section  200  is experiencing. Hence, the magnetic field H, produced by current I, causes a change in direction of the magnetization M of annulus  200  so that magnetization M is parallel to magnetic field H, as shown in  FIG. 9 . The change in the direction of magnetization M of annulus  200  thereby results in a change in length L of annulus  200 . 
   According to generally preferred inventive practice, core  300  is detached from (e.g., slidably engages) annulus  200 ; thus, annulus  200  (and not necessarily core  300 ) is subjected to tension T along longitudinal axis a. According to some inventive embodiments, however, annulus  200  and core  300  are attached to each other; here, by virtue of the integral or coupled nature of elongate structure  40 , the subjection of annulus  200  to tension T along longitudinal axis a will be accompanied by subjection of core  300  to longitudinal-axial tension. In principle, the joining of core  200  with annulus  300  might interfere somewhat with magnetostrictive change in length L of annulus  300 ; nevertheless, it can be expected that such resistance imparted by core  200  when annulus  300  experiences magnetostrictive contraction will usually be negligible. 
   Now referring to  FIG. 7  and  FIG. 10 , a current I is conducted by wire  30 , which is a central, electrically conductive, elongate structure. The peripheral wires  20  ( 20   1 ,  20   2 ,  20   3 ,  20   4 ,  20   5 ,  20   6 ,  20   7  and  20   8 ), are magnetostrictive structures that are shown to be symmetrically arranged with respect to longitudinal axis a of the central, electrically conductive wire  20 . The inventive embodiment shown in  FIG. 7  and  FIG. 10  is similar to that shown in  FIG. 6  and  FIG. 9  in that the active material surrounds the current-carrying wire. However, as shown in  FIG. 7  and  FIG. 10  the active material is discrete, whereas as shown in  FIG. 6  and  FIG. 9  the active material is continuous. 
   Still referring to  FIG. 7  and  FIG. 10 , each peripheral, magnetostrictive wire  20  has a longitudinal axis b and is contiguous to the central, electrically conductive wire  20  so that every longitudinal axis b of a corresponding peripheral wire  20  is parallel to longitudinal axis a of central wire  30 . Each peripheral wire  20  is subjected to tension T along its longitudinal axis b. Tensions T 1 , T 2 , T 3 , T 4 , T 5 , T 6 , T 7  and T 8  correspond to peripheral wires  20   1 ,  20   2 ,  20   3 ,  20   4 ,  20   5 ,  20   6 ,  20   7  and  20   8 , respectively. Current I is conducted by central wire  30  along its longitudinal axis a so as to produce a magnetic field H that is perpendicular to the magnetization M of each peripheral wire  20 . Magnetization M is directed along each longitudinal axis b because of the tension T along longitudinal axis b that each peripheral wire  20  is experiencing. Hence, the magnetic field H produced by the current I causes a change in direction of magnetization M of each peripheral wire  20  so that magnetization M is parallel to the produced magnetic field H, as shown in  FIG. 10 . Although magnetizations M 2 , M 3  and M 4 , only, are indicated in  FIG. 10  due to illustrative limitations, it is understood that each peripheral wire  20  has associated therewith its own magnetization M; that is, magnetizations M 1 , M 2 , M 3 , M 4 , M 5 , M 6 , M 7  and M 8  correspond to peripheral wires  20   1 ,  20   2 ,  20   3 ,  20   4 ,  20   5 ,  20   6 ,  20   7  and  20   8 , respectively. The change in direction of magnetization M of each peripheral wire  20  thereby results in a change in length L of that peripheral wire  20 . 
   With regard to attachment versus detachment of components of the inventive device, similar considerations apply to the inventive embodiment shown in  FIG. 7  and  FIG. 10  as apply to the inventive embodiment shown in  FIG. 6  and  FIG. 9 . According to generally preferred inventive practice, central wire  30  is detached from (e.g., slidably engages) every peripheral wire  20 ; thus, peripheral wires  20  (and not central wire  30 ) are each subjected to tension T along its longitudinal axis b. According to some inventive embodiments, however, peripheral wires  20  are attached to central wire  30 ; here, by virtue of the attachment, the subjection of peripheral wires  20  to tension T along corresponding longitudinal axes b will be accompanied by subjection of central wire  30  to tension along longitudinal axis a. In principle, the joining of central wire  30  with peripheral wires  20  might interfere with magnetostrictive change in length L of peripheral wires  20 ; nevertheless, it can be expected that such resistance imparted by central wire  30  when peripheral wires  200  experience magnetostrictive contraction will usually be negligible. 
   Reference now being made to  FIG. 8  and  FIG. 11 , this inventive configuration includes a central, elongate, magnetostrictive structure (wire  20 ) and two peripheral, locationally opposite, electrically conductive, elongate structures (wires  30   1  and  30   2 ) that conduct electrical current I in opposite directions. The central, magnetostrictive wire  20  is symmetrically flanked by the two peripheral, electrically conductive wires  30 . Currents I 1  and I 2  are conducted by peripheral wires  30   1  and  30   2 , respectively. Each of peripheral wires  30   1  and  30   2  has a longitudinal axis b and is contiguous to the central wire  20  so that longitudinal axis b is parallel to longitudinal axis a of central wire  20 . As shown in  FIG. 8 , peripheral current-carrying wire  30   1  carries current I 1  out of the page, whereas peripheral current-carrying wire  30   2  carries current I 2  into the page. 
   Still referring to  FIG. 8  and  FIG. 11 , central, magnetostrictive, elongate structure  20  is subjected to tension T along its longitudinal axis a. Each of currents I 1  and I 2  is conducted in a direction parallel to longitudinal axis a. Currents I 1  and I 2  produce magnetic fields H 1  and H 2 , respectively, each of which is perpendicular to the magnetization M of central, magnetostrictive structure  20 .  FIG. 11  illustrates the two parallel, counter-rotational magnetic flux patterns of magnetic field H 1  (which corresponds to current I 1 ) and magnetic field H 2  (which corresponds to current I 2 ). The overall magnetic field H=H 1  and H 2 , wherein magnetic field H is perpendicular to the magnetization M of central, magnetostrictive structure  20 . Magnetic field H is the sum magnetic field as manifested additively and intermediately, i.e., between current-carrying wires  30   1  and  30   2  and in the vicinity of central, magnetostrictive structure  20 . Magnetization M is directed along longitudinal axis a because of the tension T along longitudinal axis a that central, magnetostrictive structure  20  is experiencing. Hence, the magnetic field H produced cumulatively by the currents I 1  and I 2  causes a change in direction of magnetization M of central, magnetostrictive structure  20  so that magnetization M is parallel to the cumulatively produced magnetic field H, as shown in  FIG. 11 . The change in direction of magnetization M thereby results in a change in length L of central, magnetostrictive structure  20 . 
   Some analogies or commonalities can be noted among the various inventive embodiments shown in  FIG. 6  through  FIG. 11 . The inventive embodiment shown in  FIG. 8  and  FIG. 11  is similar to that shown in  FIG. 7  and  FIG. 10  in that there are two or more discrete elongate structures proximately situated with corresponding geometric axes in parallel; at least one structure is made of active material, and at least one other structure is made of electrically conductive material. As a general rule the elongate structures need not be actually touching, but according to usual inventive practice the elongate structures are at least close in space. Further, the inventive embodiment shown in  FIG. 6  and  FIG. 9  is similar to that shown in  FIG. 7  and  FIG. 10  in that active material surrounds electrically conductive material; however, as shown in  FIG. 7  and  FIG. 10  the active material is discrete, whereas as shown in  FIG. 6  and  FIG. 9  the active material is continuous. Moreover, the inventive embodiment shown in  FIG. 6  and  FIG. 9  is similar to those shown in  FIG. 7  and  FIG. 10  and in  FIG. 8  and  FIG. 11  in that two or more discrete elongate structures (at least one structure made of active material, and at least one other structure made of electrically conductive material) are proximately situated, a main difference being that according to the inventive embodiment shown in  FIG. 6  and  FIG. 9  the corresponding geometric axes are coincident, whereas according to the inventive embodiments shown in  FIG. 6  and  FIG. 9  and in  FIG. 7  and  FIG. 10  the corresponding geometric axes are parallel. Again, inventive practice generally provides for nearness or contiguousness of a magnetostrictive structure with respect to an electrically conductive structure, but actual contact therebetween is generally not an inventive requirement. The present invention&#39;s individual components typically adjoin one another but, generally speaking, need not actually contact one another. Furthermore, although the inventive embodiments shown in  FIG. 6  through  FIG. 11  are characterized by symmetry, this is generally not a requirement of inventive practice. 
   It is to be understood that the present invention can be practiced with practically any number of (one or plural) active material structures and practically any number of (one or plural) electrically conductive material structures. For instance, a plurality of elongate magnetostrictive structure  20   c  can be inventively implemented similarly as shown in  FIG. 4  and  FIG. 5 . As another example, a plurality of integral elongate structures  40  can be inventively implemented similarly as shown in  FIG. 6  and  FIG. 9 . As a further example, one, or fewer than eight, or more than eight, elongate magnetostrictive structures  20  can be inventively implemented similarly as shown in  FIG. 7  and  FIG. 10 . As another example, a plurality of elongate magnetostrictive structures  20  can be inventively implemented, each similarly as shown in  FIG. 7  and  FIG. 10 , each elongate magnetostrictive structure  20  having associated therewith any number of elongate electrically conductive structures  30 . As yet another example, a plurality of elongate magnetostrictive structures  20  can be inventively implemented, each similarly as shown in  FIG. 8  and  FIG. 11 , each elongate magnetostrictive structure  20  having associated therewith on opposite sides a pair of elongate electrically conductive structures  30  conducting electrical current in opposite directions. 
   The following numerical examples of inventive practice are explained with reference to  FIG. 12  and other, specified figures presented herein. SI units (metric units in accordance with the International System of Units) are used in these examples. As demonstrated by each example, using a ten (10) meter length of magnetostrictive material characterized by a magnetostriction of three hundred parts per million (300 ppm), which is typical of Fe 81 Ga 19  alloys, a length change of three millimeters (3 mm) is expected as the voltage is applied. Variables and constants used in the calculations are listed in  FIG. 12 . The resistance R of a wire is calculated by 
           R   =       ρ   ⁢           ⁢   L     A           
The magnetic field at a radius r enclosing a current I is given by
 
   
     
       
         
           H 
           = 
           
             I 
             
               2 
               ⁢ 
               
                   
               
               ⁢ 
               π 
               ⁢ 
               
                   
               
               ⁢ 
               r 
             
           
         
       
     
   
   EXAMPLE 1 
   With reference to  FIG. 4  and  FIG. 5 , in this example the voltage is applied directly to the magnetostrictive material  20   c . A load of 40 lb=178 N is applied to a magnetostrictive, electrically conductive wire  20   c  of single crystal (or highly textured) Fe 81 Ga 19  that is 3 mm (˜⅛ inch) in diameter and 10 meters in length. To calculate the cross-sectional area a of magnetostrictive wire  20   c , a=πr 2 =7.07×10 −6  m 2 . The resistance R of Fe 81 Ga 19  wire=ρ=10 m/a=1.06 Ω. Force F=178 N. The tensile stress T=25.2 MPa. Setting the magnetic and mechanical energies equal, the following equation obtains: M×H=T×S ms . The magnetic field needed, H av , is calculated as follows: H av =25.2×10 6  Pa×300×10 −6 /1.7 T=4450 A/m. The magnetic field at the surface, H surface , is assumed to be ≅1.2&gt;H av =5340 A/m. The current needed is calculated as follows: I=5340 A/m×π0.3×10 −2  m=50.3 A. Voltage V=IR=50.3 A×1.06 Ω=53.3 V. Power P=VI=53.3 V×50.3 A=2680 W. Thus, in this case of a small diameter (3 mm), 10 meter Fe 81 Ga 19  wire  20   c , subjection of wire  20   c  to a 40 lb tensile load, and application of a voltage of ˜53.3 V to wire  20   c , result in a 3 mm contraction of wire  20   c . 
   EXAMPLE 2 
   With reference to  FIG. 6  and  FIG. 9 , in this example a load of 40 lb=178 N is applied to the present invention&#39;s integral configuration  40 , a cable-like structure that includes a Cu wire core  300  (1.5 mm in diameter) and, surrounding Cu wire  300 , a magnetostrictive ring (annulus)  200  (10 meters in length, 3 mm in diameter) made of Fe 81 Ga 19  textured magnetostrictive alloy. Core  300  has a radium of r in ; annulus  200  has a radius of r out . The cross-sectional area a of the annular active material  200  is calculated as a=π(r out   2 −r in   2 )=5.3×10 −6  m 2 . The resistance R of the Cu wire is calculated as R=0.102 Ω. The force F=178 N. The tensile stress T=33.6 MPa. Setting the magnetic and mechanical energies equal, the following equation obtains: M×H=T×S ms . Magnetic field H av , the magnetic field needed in the Fe 81 Ga 19  ring  200 , is calculated as follows: H av =33.6×10 6  Pa×300×10 −6 /1.7=5930 A/m=74.2 Oe. To achieve this, magnetic field H surface , the magnetic field at the surface of the copper wire core  300 , is assumed to be ≅1.5×H av =8900 A/m. The current needed is calculated as follows: I=H surface ×π×r out =8900 A/m×π×0.0015 m=41.9 A. Voltage V=IR=41.9 A×0.102 Ω=4.27 V. Power P=VI=4.27 V×41.9 A=179 W. It is seen that, as compared with Example 1, in Example 2 a much smaller voltage V and power P are necessary for electrifying the Cu core  300  of the inventive cable  40 . Generally speaking, the present invention&#39;s heterogeneous (combining an electrically conductive core material and a magnetostrictive annular material) embodiments such as shown in  FIG. 6  and  FIG. 9  will require significantly less voltage and significantly less power than will the present invention&#39;s homogenous (a uniformly magnetostrictive material) embodiments such as shown in  FIG. 4  and  FIG. 5 . 
   EXAMPLE 3 
   Still with reference to  FIG. 6  and  FIG. 9 , in this example the Cu wire  300  and the Fe 81 Ga 19  annulus  200  each have twice the diameter as in Example 2. In addition, in this example a larger load of 100 lb=445 N is applied to the present invention&#39;s integral configuration  40 , which includes Cu core  300  (3 mm in diameter) and Fe 81 Ga 19  annulus  200  (10 meters in length, 6 mm in diameter). The cross-sectional area a of the annular active material  200  is calculated as a=π(r out   2 −r in   2 )=2.12×10 −5  m 2 . The resistance R of the Cu wire is calculated as R=0.0255 Ω. The force F=445 N. The tensile stress T=21 MPa. Setting the magnetic and mechanical energies equal, the following equation obtains: M×H=T×S ms . Magnetic field H av , the magnetic field needed in the Fe 81 Ga 19  ring  200 , is calculated as follows: H av =21×10 6  Pa×300×10 −6 /1.7 T=3710 A/m=46.6 Oe. To achieve this, magnetic field H surface , the magnetic field at the surface of the copper wire core  300 , is assumed to be ≅1.5×H av =5570 A/m. The current needed is calculated as follows: I=H surface ×πr out =5570 A/m×π0.003 m=52.5 A. Voltage V=IR=52.5 A×0.0255 Ω=1.33 V. Power P=VI=1.33 V×52.5 A=69.8 W. Thus, in this case of a 10 meter cable  40 , subjection of cable  40  to a 100 lb tensile load, and application of a voltage of ˜1.33 V to copper wire  300 , result in a 3 mm contraction of Fe 81 Ga 19  annulus  200 . Here, in this case of a 6 mm diameter, 10 meter length cable  40 , cable  40  will contract 3 mm under a tensile load of 100 lb. Note that, in this example as compared with Example 2 (which involves diameter half as large), the force F is much larger and the power P requirement is much smaller. However, here the amount of Fe 81 Ga 19  material is greater. 
   The present invention is not to be limited by the embodiments described or illustrated herein, which are given by way of example and not of limitation. Other embodiments of the present invention will be apparent to those skilled in the art from a consideration of this disclosure or from practice of the present invention disclosed herein. Various omissions, modifications and changes to the principles disclosed herein may be made by one skilled in the art without departing from the true scope and spirit of the present invention, which is indicated by the following claims.