Low Frequency Sound Transducer

Technical Field

This invention relates to sound producers and in particular to low frequency sound producers adapted for use in high pressure environments.

Background Art

One form of magnetostrictive transducer is illus¬ trated in U.S. Letters Patent 2,468270 of Harry F. Olson et al. As shown therein, the signal transducer is intended for use in underwater signaling systems, echo ranging systems, and the like. The transducer utilizes, as signal translating members, elements which can be tuned separately to a desired resonant frequency and which are formed as laminated members. The circuit uses a polarizing coil which conducts the magnetic flux through a magnetic plate through the laminated bar around which is closely fitted the signal coil. Benjamin Schwartz discloses, in U.S. Letters

Patent 3,484,630, an ultrasonic magnetostrictive trans¬ ducer element having a pair of magnets between opposed legs of U-shaped magnetic bars with coil windings dis¬ posed about each of the bars. In the Volume 27, Number 1, January 1977 issue of U.S. Navy Journal of Underwater Acoustics, Robert R. Smith and James C. Logan describe the design of a transducer using rare-earth magnetostrictive materials. The transducer utilizes a plurality of magnetostrictive rods each of which is surrounded by a signal solenoid, with the rods disposed between stress plates secured together by stress bolts. The stress plates, in turn, transmit low frequency vibrations to a pair of spaced

outer housing portions.

In the May 1980 issue of the Journal of the Acous¬ tical Society of America, at pages 1809-1811, J. L. Butler and S. J. Ciosek disclose a rare earth iron octagonal transducer.

Disclosure of Invention

The present invention comprehends an improved mag¬ netostrictive vibrator for producing low frequency sound, including a plurality of laterally related rods each formed of rare ear-th agnetostrictive material, means for compressively prestressing the rods, perma¬ nent magnet means for providing a permanent magnet bias in the rods, and coil means magnetically coupled to the rods for causing magnetostriction of the rods corresponding to an input AC signal applied to the coil means.

In the illustrated embodiment, the rods are sub¬ stantially rectilinear.

In the illustrated embodiment, the magnetic means comprises means compressively urged against at least one end of the rods for transmitting to the rods com- pressive prestressing forces.

The rods may be formed of rare earth material.

The prestressing means, in the illustrated embodi- ent, comprises resilient prestressing means.

In the illustrated embodiment, the vibrator is enlcosed in a synthetic resin.

The sound producer further includes spacer means between the ends of the successive vibrators which are arranged end to end to define a ring, with each of the vibrators comprising a plurality of laterally related rods, each formed of rare earth magnetostrictive mater¬ ial.

In the illustrated embodiment, the ring is

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polygonal and the spacer means comprise wedge-shaped elements.

Each of the vibrators comprises a water-sealed assembly. In one aspect, the invention comprehends the provision of a low frequency sound producer includ¬ ing a plurality of magnetostrictive vibrators arranged seriatim end-to-end to define a polyhedral ring, each vibrator comprising a pair of parallel spaced rods formed of rare earth magnetostrictive material, means for compressively prestressing the rods, rare earth permanent magnet means for providing a permanent mag¬ netic bias in the rods, and coil means magnetically coupled to the rods for causing magnetostriction of the rods corresponding to an input AC signal applied to the oil means.

In the illustrated embodiment, the vibrator fur¬ ther includes means for coupling the coil means in series. In the illustrated embodiment, the rods are spaced in the axial direction of the ring.

The magnetostrictive vibrator of the present in¬ vention is extremely simple and economical of con¬ struction, while yet providing an improved low fre- quency sound source adapted for use such as in marine applications at great depths. As a result of the im¬ proved efficiency of the transducer, the size thereof may be substantially reduced from that of the prior art devices. A novel arrangement further permits the use of rare earth transducers without the need for a separate direct current power source.

Brief Description of the Drawing

Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawing wherein:

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FIGURE 1 is an exploded perspective view with por¬ tions broken away illustrating a magnetostrictive vibrator embodying the invention;

FIGURE 2 is an end elevation of the vibrator; FIGURE 3 is a side elevation thereof with a por¬ tion broken away to illustrate in greater detail the support means for mounting the vibrator;

FIGURE 4 is an enlarged transverse section taken substantially along the line 4-4 of Figure 2; and FIGURE 5 is an end view of the vibrator unit il¬ lustrated in Figure 4.

Best Mode for Carrying Out the Invention

In the illustrative embodiment of the invention as disclosed in the drawing, a magnetostrictive vibra- tor generally designated 10 comprises a plurality of individual vibrator units 11 arranged seriatim end to end to define a polyhedral ring generally designated 12. As shown in Figure 2, in the illustrated embodi¬ ments, six such units 11 are provided forming a hex- agonal ring.

The ring is arranged to be mounted on a support 13 and is advantageously adapted for use in producing low frequency vibrations or sound in environments of extremely high pressure, such as at great marine depths. The ring 11 may be encased in a suitable enclosure 14 of synthetic resin defining an axial bore 15 adapted to mount on a cylindrical extension 16 of the support 13.

The transducer units 11 are similar and are shown in greater detail in Figures 4 and 5. More specifi¬ cally, each unit comprises an individual vibrator which is a self-contained water-sealed unit vibrating under the influence of magnetostrictive rods 17 and 18, extending axially within surrounding annular

coils 19 and 20, respectively. The opposite ends 21 and 22 of rod 17 abut permanent magnets 23 and 24, re¬ spectively. The opposite ends 25 and 26 of rod 18 abut permanent magnets 27 and 28, respectively. Magnets 23 and 27, in turn, are abutted by a bridging magnetic keeper 29 and magnets 24 and 28 are abutted by a similar abridging magnetic keeper 30. Secured to keeper 29 by a plurality of cap screws 31 is a support block 32 and secured to keeper 30 by a plurality of similar cap screws 33 is a similar sup¬ port block 34.

As seen in Figure 4, the support blocks 32 and 34 define therebetween a gap 35, with the keepers 29 and 30, and thus, supports blocks 32 and 33, urged toward each other by a stress wire 36 connected at its oppo¬ site ends to securing nuts 37 and 38 received in out¬ wardly opening recesses 39 and 40 in keepers 29 and 30, respectively. By suitable tightening of the ten¬ sion nuts, prestressing of the magnetostrictive rods 17 and 18 is effected whereby vibratory elongation and contraction of the rods by the application of alter¬ nating current through the coils 19 and 20 is trans¬ mitted to the keepers 29 and 30 and, in turn, to outer portions 41 and 42 of the support blocks 32 and 34, respectively.

In the illustrated embodiment, the prestressing is made to be elastic by means of Belleville washers 43 and 44 urged by the nuts 37 and 38, respectively, against the keeper plates 29 and 30. In the illustrated embodiment, the gap between the supports 32 and 34 is approximately .01", and thus, the supports, including outer portions 41 and 42, are caused to vibrate with a total maximum permissible excursion of approximately .02". In the illustrated embodiment, the rods 17 and 18 are formed of rare earth material, and more specifi-

cally, are formed of Terfenol D, comprising a compound

Industrial Applicability

The vibrator 10 is advantageously adapted for use in producing low frequency sound such as in marine ap¬ plications at great depths. By arranging the individ¬ ual vibrator units in ring form, a high degree of sta¬ bility is provided, while yet high efficiency in the production of the desired low frequency sound is ef- fected. The individual units are substantially free- flooded so that water pressure on the exterior of the transducer is effectively substantially completely offset by the pressure on the interior thereof.

By utilizing a permanent magnet bias, the ring vibrator minimizes heating, increasingthe performance of the transducer. By utilizing the close-packed hex¬ agonal array configuration, further efficiency in the overall sound production is obtained.

In the illustrated embodiment, the support bodies are shown, as in Figure 2, to have inclined end sur¬ faces 45 and 46. As will be obvious to those skilled in the art, however, if it is desired to maintain the end surfaces 45 and 46 orthogonal or parallel to each other, additional spacers (not shown) may be utilized between the end surfaces of the contiguous vibrator units.

It is found that the improved ring vibrator 10 produces a higher sound level for its size than the prior art transducers in view of the permissible large vibrational displacement. Thus, the vibrator provides a substantial improvement in applications where small size, high efficiency low frequency sound producers - are desired.

The foregoing disclosure of specific embodiments

is illustrative of the broad inventive concepts com¬ prehended by the invention.