US2444061A - Magnetostrictive device - Google Patents

Description

Je 29, 1948. R L PEEK, JR 2,444,061

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Patented June 29, 1948 STATES PATENT GFFQE MGNETOSTRICTIVE DEVICE Application May 26, 1944, Serial No. 537,503 11 Claims. (Cl. 177-386)` This invention relates to magnetostrictive devices and more particularly to submarine signaling devices of the magnetostriction type.

One object of this invention is to simplify the construction of magnetostrictive devices and more particularly of magnetostrictive sonic transducers intended for operation in the audio frequency range.

Another object of this invention is to improve the emciency of submarine signaling devices of the magnetostriction type.

in one illustrative embodiment of this invention, a submarine signaling device comprises a magnetostrictive bar mounted for free vibration in its fundamental exural mode and a signal coil electromagnetically coupled to the bar for eiecting vibration thereof in accordance with signal currents supplied to the coil or, conversely, for translating vibrations of the ba'r into electrical signals.

In accordance with one feature of this invention, the magnetostrictive bar is polarized longitudinally and is provided adjacent its center with a transverse longitudinally extending slot whereby the central portion of the bar comprises two parallel arms polarized in the same direction. The signal coil lencompasses only one of these arms. When the bar vibrates, as in response to forces due to compressional waves effective thereon, one of the arms is placed under tension when the other is under compression, and vice versa, so that the flux changes in the two arms are opposite in sign and a signal ilux traverses a series path through the portions of the bar surrounding the slot. Similarly, when signal currents are supplied to the coil, the flux changes produced in the two arms are opposite in sign and the bar is caused to vibrate iiexurally.

In accordance with another feature of this invention, the bar is supported at the nodes of its fundamental exural mode by resilient mounts, whereby mechanical losses are reduced and improved emclency is realized.

The invention and the above-noted and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing in which:

Fig. l is a perspective view of a. magnetostrictive transducer unit illustrative of one embodiment of the invention;

Fig. 2 is a sectional view of a submarine signal.- ing device including a transducer unit of the construction shown in Fig. l;

Fig. 3 is a side view. to an enlarged scale, of

. 2 l the core assembly included in the unit illustrated in Fig. l; and

Fig. 4 is a side view illustrating a modification of the unit shown in Fig. 1.

Referring now to the drawing, the transducer unit illustrated in Fig. 1 comprises a non-magnetic foundation member or supporting plate i0 having aixed thereto, as by screws il as shown in Fig, 2, a pair of U-shaped supports i2 having rounded bearing surfaces it. In one construction, the supports l2 may be of magnetic iron and constitute pole-pieces of a bar magnet lli the ends of which are fitted in the supports.

Seated upon the bearing surfaces i3 and held thereon initially by magnetic attraction is a magnetostrictive beam or bar l5 which, in a particularly advantageous construction, comprises a plurality of thin laminations insulated from one another and bonded together by an impregnating compound such as a phenolic condensation product. As shown more clearly in Fig. 3, the beam or bar I5 is provided at its cen-4 tral portion with a transverse slot i3 so that this portion comprises substantially identical, longitudinally extending parallel arms Il and I8. A signal coil i9 is woun'd about the arm It.

The beam or bar i5 is polarized longitudinally by the magnet I li, the polarizing ilux traversing the two arms Il and i8 in the same direction as indicated by the solid arrows on the core in Fig. 3. When the bar is flexed, as by compressional waves eiective thereon in the direction indicated by the arrow S in Fig. 3, the two arms are stressed in opposite sense, that is when the arm Il is placed under compression the arm IS is placed under tension. Hence, the iiux changes in the two arms due to magnetostriction are opposite in sign and a circulating flux ows in the core around the slot IS, for example as indicated by the dotted arrows in Fig. 3, and a signal current is induced in the coil I9. Conversely, when signal currents are supplied to the coil I9, the flux changes in the two arms are opposite in sign so that one arm contracts while the other expands and, -as a result, the bar is vibrated in accordance with the signal currents.

The transducer unit is particularly suitable for operation as a single frequency device, that is one sharply resonant at a prescribed frequency. In this case, the beam or bar length is made such in relation to the beam thickness that the fundamental exural mode corresponds to the prescribed frequency and the supports l2 are so spaced that the contact between. the bearing surfaces l and the beam or bar are each substantially 0.22 times the length of the beam from the nearest end of the beam, whereby the magnetostrictive element is freely supported at its nodes for its fundamental ilexural mode. It will be appreciated that for such single frequency devices, relatively short cores may be employed. For example, in a device intended for operation at 5 kilocycles the core length is approximately 21/2 inches.

The unit illustrated in Fig. .1 may be used to particular advantage in a submarine signaling device as shown in Fig. 2. The device shown in the latter gure comprises a diaphragm 20, for example of metal, aixed to a mounting ring 2l. The unit is secured -to the ring 2| by a plurality of screws 22 threaded into the ring and is spaced therefrom by other screws 23 threaded into the plate lil and bearing against one i'ace of the ring 2 l. The magnetostrictive core lli is coupled to the diaphragm 2i] by a body or block 2l, for example a block of a commercially available form of rubber having good compressional wave energy transmission characteristics, aiilxed, as by cement, to the core. In the assembly of the device, the screws 23 are adjusted so that they will engage the ring 2l only when the lblock 2l has been compressed to be in intimate contact with ,the core and the diaphragm by tightening of the screws 22.

In a particularly advantageous construction. the beam or bar l5 is made of a magnetic material having high remanence so that the beam or bar is capable oi self-polarization and the magnet Hl may be omitted. The supports I2, in such construction, may then be of a resilient material, such as soft rublber, as illustrated in Fig. 4, suitably aixed to the foundation plate lil. The beam or bar, in such construction, is held in position between the supports l2 and the Iblock 24 when the plate IB is securedto the mounting ring 2l. A special Ifeature of this construction is that the beam is in effect oatingly mounted so that mechanical losses are reduced and improved eiiciency is obtained.

Although speciiic embodiments of this invention have been shown and described, it will be understood that they are but illustrative and that various modications may be made therein without departing from the scope and spirit of this invention as deiined in the appended claims,

What is claimed is:

1. A magnetostrictive device comprising a magnetostrictive bar polarized -longitudinally and having a transverse slot therein, extending normal to the thickness of said bar and dividing an intermediate portion only thereof in-to a pair of longitudinally extending arms, means mounting said bar for flexura1 vibration in the direction of its thickness, and a signal coil in electromagnetic coupling relation with one of said arms.

2. A magnetostrictive device in accordance with claim 1 wherein said mounting means comprises supports engaging said bar at the nodes of its fundamental flexural mode.

3. A magnetostrictive device compris-ing a magnetostrictive fbar having a transverse slot in its center portion dividing said portion into a pair of longitudinally extending arms, means for polarizing said arms magnetically in the same direction, means mounting said bar for flexural vibration in the direction normal to said slot, and signal cc-il means in electromagnetic coupling relation with one of said arms.

4. A magnetostrictive device in accordance with claim 3 wherein said mounting means comprises supports engaging said bar at regions substantially 0.22 times the bar length from the ends thereof.

5. A magnetostrictive device comprising a longitudinally rpolarized magnetostrlctive bar having intermediate its ends, two longitudinally extending, substantially coextensive spaced portions which together with portions adjacent thereto define a closed magnetic loop, resilient supports engaging said bar at the nodes thereof for its fundamental exural mode. means for flexing said lbar in the direction to vary the stresses in said two portions in opposite sense, said flexing means comprising a diaphragm coupled to said bar, and a signal coil in electromagnetic coupling relation Iwi-th one oi said spaced portions.

6. Amagnetostrictive device comprising a magnetostrictive bar having a pair of adJacent. spaced, longitudinally extending arms intermediate its ends and defining a closed magnetic path with portions of said bar adjacent the ends of said longitudinally extending arms, means for polarizing said arms in the same direction, a signal coil linked to one of said arms. and means for stressing said arms simultaneously and in opposite sense.

'7. A magnetostrictive device comprising a magnetostrictive bar having a pair of parallel longitudinally extending arms in the mid-portion thereof and dening a closed magnetic path with portions of said bar at the ends of said arms, means for polarizing said arms magnetically in the same direction, means mounting said bar for (free flexural vibration in the direction to alter the stresses in the two arms in opposite sense, and a signal coil encompassing one of said arms.

8. A magnetostrictive device comprising a magnetostrictive bar having a pair of parallel longitudinally extending armsin the mid-portion thereof and dening a closed magnetic path with portions of said -bar at the ends of said arms, means mounting said barat the nodes thereof for its fundamental exural mode of vibra-tion in the direction lo stress said arms in opposite sense, means fox polarizing said arms magnetically in the same direction, a vlbratile mem- -ber coupled to said bar, and a signal coll in electromagnetic coupling relation with one of said arms.

9. A submarine signaling device comprising a magnetostrlctive bar having a transverse slot therein dividing an intermediate .portion thereof into two longitudinally extending portions, a signal coil encompassing one of said portions, a pair of spaced magnetic supports engaging said bar beyond opposite longitudinal extremities ci said intermediate .portion and mounting said vbar for flexural vibration in the direction to stress said longitudinally extending portions in the opposite sense, a magnet for which said supports constitute pole-pieces, and a diaphragm coupled to said intermediate portion.

10. A submarine signaling device comprising a magnetostrictive bar having a transverse slot in its mid-portion dividing said portion into a pair of longitudinally extending arms, a. pair of magnetic supports engaging said .bar at the nodes of its fundamental exural mode and mounting said rbar for exural vibration in the direction to stress said arms in opposite sense, a permanent magnet extending between said supports, a signal coil encompassing one of said arms, and a diaphragm coupled to said mid-portion.

11. A magnetostrictive device comprising a REFERENCES CITED The following references are of record in the file of this patent:

Number Number UNITED STATES PATENTS Name Date Rieker June 23. 1925 Hayes June 25, 1935 Christensen Aug. 18, 1936 Turner May 30, 1939 Lakatos July 22, 1941 Turner Dec. 3, 1946 FOREIGN PATENTS Country Date Great Britain July 5, 1933 Great Britain Jan. 8, 1935

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