Patent GB-1337822-A (GB)
Title: Magneto-strictive processes and apparatus
IPC: B06B1/08
Filed: 1971-06-07
Abstract: 1337822 Reciprocating motors INTERNATIONAL NICKEL Ltd 7 June 1971 [22 June 1970] 19264/71 Heading H2A [Also in Division H4] A vibratory power generator for generating vibratory power along a desired axis of dimensional change comprises a magnetostrictive transducer including a core 11 (Figs. 1, 2) containing bilinear magnetostrictive material (i.e. material characterized by dimensional changes in two mutually perpendicular directions, parallel to and at right angles to a varying magnetic field, increase in one direction being accompanied by decrease in the other direction). Two coils 14, 20 are each electromagnetically coupled to the core when electric current is passed through the coil and produce first and second electromagnetic fields having mutually transverse flux paths X, Y within the core. The direction of one of the flux paths X is along the desired axis of dimensional change. The transducer provides substantially closed loop paths X, Y of magnetostrictive material within the core. As shown, the core 11 includes a channelled ring 12, Fig. 2, and a contacting coverplate 13, both of randomly polycrystalline high purity nickel and rigidly attached by brass screws 27. If the ring 12 and cover-plate 13 are bonded together with a braze or cement it is beneficial for the braze or cement to be thin or have good magnetic permeability characteristics. Electrically insulating laminations may be needed for the core, e.g. for operation at high sonic or ultrasonic frequencies, with low resistivity core material in order to inhibit eddy current flow. Other magnetic or magnetostrietive materials may be provided between laminations. If desired, the ratio of thickness T (Fig. 2) to diameter D (Fig. 1) may be up to 10-1 or higher to produce a slender cylinder. Applications include sonar transmission and reception, the driving of vibratory tools such as drills, pile drivers, riveters, welders, soldering irons, ultrasonic cleaners, dental or surgical tools and metal forming processes, e.g. tube drawing or extruding. Frequencies may vary from 10 Hz to 100,000 Hz, or higher. By making use of two varying electromagnetic fields, high power conversion up to saturation level is obtained. Preferably, the two magnetic fields vary cyclically and maintain a 180 degrees out-of-phase relationship between them. The core may be of picture frame, window, scroll or doughnut configuration. The magnetostrictive material may be isotropic or anisotropic. Suggested core materials also include various polycrystalline alloys containing nickel, cobalt or iron, and ferrites. Stacks of ring core transducers (as in Fig. 1) with or without air gaps or with high permeability spacers may be operated as an array. Circuits and operation.-The core 11 (Figs. 1, 2) is energized by a vacuum tube oscillator 31 (Fig. 3) producing a sinusoidal output and connected to silicon diode half-wave rectifiers 32, 33. In one half-cycle the circumferential field from coil 14 permeates the core 11 with the magnetic flux in an annular flux path (arrow X) and in the other half-cycle the field from coil 20 follows a toroidal path around the cross-section of coil 20 (arrow Y). Thus an orthogonal pair of cyclically fluctuating and mutually perpendicular magnetic fields is produced and the core is subjected to 180 degrees out-of-phase excitation so that the direction of magnetization is angularly oscillated through a 90 degrees angle. During one half-cycle the field from coil 14 contracts and then releases the circumference (and thus the diameter) of the core 11. During the other half-cycle the field from coil 20 expands and then releases the circumference (and thus the diameter) of the core 11. In both instances changes in width and thickness occur but these are relatively unimportant. Preferably the flux densities of the fields are made substantially equal to the saturation magnetostrictive flux density of the core material by controlling the current through the coils and the number of turns. For trepanning, torsional output is advantageous and can be obtained by providing a continuous thin slit through a wall of cavity 19, parallel to the coil 21.  An alternative circuit has two orthogonal coils 71, 72 (Fig. 4) connected in series with an A.C. source and orthogonal coils 73, 74 connected in series with a D.C. bias source 76. The coils 71, 72 act as cyclic field coils and in conjunction with bilinear magnetostrictive core 77 produce two cyclically fluctuating, orthogonal fields intersecting with the core 77. Thus, coils 72 and 74 may replace coil 14 and coils 71 and 73 may replace coil 20. Preferably, the constant fields produced by coils 73, 74 are about 5% greater than the peaks of the fluctuating fields in order to avoid detrimental flux reversal effects. To obtain good electromechanical linearity, electromechanical coupling and bandwidth, and possibly efficiency, the peak flux densities of the fields from coils 71, 72 may be further reduced relative to the bias fields from coils 73, 74. Electromechanical efficiency and possibly linearity are improved by making the bias field from coil 73 greater than that from coil 74 and preferably making the field strength from coil 72 greater than that from coil 71. Coil 71 may be omitted altogether if the bias field from coil 73 relative to that of coil 74 is high enough and the power requirement is only moderate. In a variation of Fig. 4, a separate D.C. source is provided for each of coils 73 and 74. Coils 71 and 72 may be connected in parallel instead of in series, or a single coil may replace coils 73 and 74, e.g. by omitting coil 74 and connecting D.C. source 76 and coil 73 in series across coil 72 and inserting a capacitor between A.C. source 75 and coil 72 to block current flow from D.C. source 76 to A.C. source 75.