US3260990A - Electroacoustic transducer - Google Patents

Description

July 12, 1966 F. MAssA 3,260,990

ELEGTROACOUSTIC TRANSDUCER 2 SheetsSheet 1 Filed Jan. 5, 1962 f6 46 46 I2 40 42 a 56 20 56 ATTORNEY.

July 12, 1966 F. MASSA ELECTROACOUSTIC TRANSDUCER 2 Sheets-Sheet 2 Filed Jan. 5, 1962 IN VEN TOR.

ATTORNEY United States Patent 3,260,990 ELECTROACOUSTIC TRANSDUCER Frank Massa, Cohasset, Mass, assignor, by mesne assignments, to Dynamics Corporation of America, New York, N.Y., a corporation of New York Filed Jan. 3, 1962, Ser. No. 164,010 14 Claims. (Cl. 340-12) This invention relates generally to improvements in electroacoustic transducers, and more particularly to new and improved sonar transducers for generating highpower sound in very deep water at frequencies in the lower or mid-audible range. This invention is a continuation-in-part of my co-pending application, Serial No. 34,731, filed June 8, 1960.

One object of this invention is to provide an electroacoustic transducer of improved construction which is capable of generating acoustic powers of several hundred to several thousand watts and of operating at submerged depths down to many thousands of feet of water.

Another object of this invention is to produce a very rugged transducer of improved construction which is capable of operating at large, low frequency amplitudes of vibration sufficient to generate acoustic power densities of the order of 10 watts per square inch of radiating surface.

A further object of this invention is to still further reduce the weight of the radiating portion of the vibrating system of a high power sonar transducer in order to increase the band width of high efficiency operation of the transducer.

A still further object of this invention is to increase the efiiciency of coupling between the radiating surface of a sonar transducer and the water at high hydrostatic pressures without the need of any pressure release materials.

Another object of this invention is to produce an underwater transducer of improved construction which is capable of efficient operation in the lower or mid-audio frequency range.

Still another object of this invention is to provide a unique electromagnetic transducer construction characterized by an inertia mass flexibly suspended within and totally enclosed by a radiating mass which forms the outer protective housing of the transducer.

Another object of this invention is to provide a new and improved electroacoustic sonar transducer with permanent magnetic polarization such that high efficiency operation results in the lower or mid-audio frequency range.

These and other objects of the invention are set forth with particularity in the appended claims. However, for a better understanding of the invention itself, together with further features and advantages thereof, reference is made to the accompanying description and drawings in which are shown several illustrative embodiments of the invention.

In the drawings:

FIGURE 1 is a vertical cross-section taken through an illustrative transducer embodying one form of the invention;

FIGURE 2 is a sectional view taken substantially as shown along the line Z-2 of FIGURE 1;

FIGURE 3 is an end or plan view of one illustrative type of folded baffle structure embodying another form of the invention;

FIGURE 4 is a sectional view taken substantially as shown along the line 44 of FIGURE 3;

FIGURE 5 is a sectional view of a tunable folded baffle structure illustrating another embodiment of the invention; and

3,2003% Patented July 12, 1956 "ice FIGURE 6 is a sectional view taken substantially as shown along the line 66 of FIGURE 5.

Referring now to the drawing, and more particularly to FIGURES l and 2 thereof, the reference character 10 identifies a massive base structure of generally hemispherical shape and having a plane surface 14 at its upper portion. A second relatively light structure 12, which for example may consist of an aluminum or magnesium alloy or the like, and which may be further lightened, if desired, as by casting the aluminum into a sponge-like mass which would reduce the effective density of the material without reducing its rigidity, is provided to serve as an adaptor plate. Preferably the adaptor plate 12 has a surface contoured to mate with the inner surface of the transducer housing hemispherical shell 16. One surface 18 of adaptor plate 12, advantageously is machined fiat so that it may be set parallel to the plane surface 14 of the heavy base 10.

In accordance with a feature of this invention, a stack of laminations of magnetic material 20 is securely bonded, as by means of a suitable metal-to-metal cement, such as one of the epoxies, to the plane face 18 of adaptor plate 12. Another relatively massive magnetic assembly, comprising a number of cemented stacks of magnetic laminations 22 and 24, is assembled to a set of permanent magnets 26. Permanent magnets 26 may preferably be one of the sintered oxide types which develops high magnetiz-ing forces through relatively thin sections, although those skilled in the art will appreciate that other types of magnets may be used. The magnets are preferably in the form of thin plates which act as separators for the lamination stacks 22 and 24.

In accordance with the invention embodiment illustrated in FIGURES l and 2, the magnets 26 are magnetized with alternating north and south poles, as illustrated in FIGURE 1. The alternate stacks of magnetic laminations 22 and 24 interspersed with the permanent magnets 26 are cemented together and consolidated into a massive composite rectangular assembly 28 which is securely cemented to the plane surface 14 of the massive base 10. Advantageously, the height of the magnets 26 is less than the height of the lamination stacks 22 and 24 so that after the elements are consolidated into the assembly 28, a number of rectangular slots remain in the assembly within which coils of wire 30 may be placed, as illustrated in FIGURES l and 2.

FIGURE 2 shows a sectional plan view of the composite magnetic assembly including a pair of coils 30 nesting within the slots defined by the lamination stacks, as above described. During the preparation of the magnetic assembly, it is preferable to consolidate the magnetic assembly 28 which is bonded to the base 10 including the coils 30 with a rigid potting compound so that there can be no relative vibrational motion between the coils 30 and the associated magnetic assembly.

The invention further comprises a number of spring members 32 which are accurately machined such that their heights are equal. The spring members 32 are assembled to both the plane surfaces 18 and 14, respectively of plate 12 and base 10, as by means of the studs 34 and nuts 36. The studs 34 are preferably fastened to the base member 10 and adaptor plate 12 by means of a suitable cement so that they will not become loose during operation of the transducer. Similarly, the nuts 36 may be also coated with cement during the assembly in order that they will not become loose during operation.

In accordance with the invention, the shape of the spring members 32 is determined by the desired stiffness which is required for establishing the resonant frequency of the transducer. The total height of the spring memhers 32 is adjusted such that when the structure is assembled and the magnets are fully magnetized, the resulting air gap between the ends of the stacks 22 and 24, and the surface of the magnetic lamination assembly 20 is equal to the desired amount for eflicient operation. It has been found that a suitable air gap dimension to produce an eflicient transducer may lie in the approximate range .010 to .020. These dimensions are, of course, not critical and are only given to illustrate a typical range of values which are suitable for the practice of the invention.

The adaptor plate 12 has a passageway 38, as illustratecl in FIGURE 1, which permits the installation of the insulated wires 40 to establish electrical connection between the coils 30 and the terminals 42.

In order that the transducer may operate satisfactorily in very deep water and not fail under the extremely high hydrostatic pressures associated With such depths, it has been found desirable to use a high pressure molded cable and terminal arrangement which is assembled within a rugged cylindrical shell 44 whose wall thickness is sufficient to withstand the high hydrostatic pressure. A pair of shouldered insulating bushings 46 are placed through suitable clearance holes provided in the bottom wall of shell 44, as illustrated. The electrical terminals 42 have shoulders which rest on the upper surface of the flanged insulators 46, as shown. The conductors within the waterproof cable 47 are soldered to the terminals 42 as illustrated, after which a rubber compound 48 is molded to fill and hermetically seal the region between the cable 47 and the high pressure terminal assembly comprising the housing 44 and the insulated terminals 42. It has been found in actual practice that a molded cable terminal construction as just described operated satisfactorily underwater in ocean depths in excess of 20,000 feet.

In order that the molded cable assembly may be conveniently attached to the transducer, I have provided a cylindrical flanged metal bushing 50 welded, as at 51, to an opening in the outer housing 16. A suitable recess or shoulder 53 is formed in the wall of bushing 50 to receive the mating flange portion of shell 44, as illustrated in FIGURE 1. A suitable waterproof rigid cement, such as epoxy, preferably is used between the surfaces of shell 44 and bushing 50 at final assembly in order to establish a completely water tight, high pressure seal at the cable terminals.

In order to increase the efliciency of the transducer of this invention and to obtain higher acoustic power output, it is a feature of this invention that the suspended inertial weight, represented by the base member plus the magnetic assembly attached to its surface, be kept high whereas the total vibrating mass represented by the outer housing and the structure attached to the outer housing be kept low. Since the transducer is designed to withstand high hydrostatic pressure, it is advantageous to employ a convex shell for the outer housing which will result in minimum weight for maximum strength. The illustrative embodiment of FIGURE 1 comprises two hemispherical shells 16 and 52 which are assembled to form a complete sphere, as by means of Weld 54. A pair of cylindrical collars 56 are welded to the hemispherical shells, as illustrated, in order to provide an outer cylindrical bearing surface parallel to the axis of vibration to permit mounting the transducer into baflle structures as will be described hereinbelow.

Although in the illustrative embodiment of FIGURE 1, the outer housing of the transducer is in the form of a spherical shell having the attached outer cylindrical collars 56, those skilled in the art will appreciate that the cylindrical collars 56 could be incorporated into the Wall of the hemispherical shell by a forming operation, if desired, to eliminate the welding of the auxiliary collars. Alternatively the outer housing may comprise a separate cylindrical central collar with a dome-shaped cap fastened to each edge of the central collar.

FIGURES 3 and 4 illustrate one preferred embodiment for mounting the transducer structure above described in a folded bafile arrangement capable of providing highly satisfactory operation in deep water. The basic transducer unit above described is of the inertia type in which the outside surface vibrates as a Whole relative to the suspended inertial mass which is contained within the interior of the cylindrical shell housing. The operation of this transducer is similar to the transducer operation described in greater detail in my co-pending application Serial No. 34,731 filed June 8, 1960. In this co-pending application, in addition to the operation of the transducer, there is disclosed a number of bafiie arrangements whereby the out-of-phase vibration from one surface of the 0scillating transducer housing is suitably delayed by various baffle configurations such that the delayed energy is brought in phase with the energy radiating from the opposite transducer face, thereby increasing the efliciency of operation.

In the illustrative embodiment of FIGURES 3 and 4, the cylindrical tubular member 58 has a number of brackets 60 attached to its inner surface, as by means of bolts 62 and nuts 64. Advantageously, rubber bumpers 66 are cemented to the face of the brackets 60, as shown, to isolate the vibrating transducer from the bafile structure. A rubber covering, not shown, may be placed around the cylindrical periphery of the transducer such that the transducer will rest on a rubber sheet during vibration and thus be able to move with respect to the inner wall of the cylindrical tube 58, during its operation.

In accordance with a feature of this invention, the cylindrical tube 58 is reduced in diameter by the tapered funnel portion 68 which is coupled to a continuing smaller diameter tube 70. The smaller diameter tube 70 is bent as shown, and returns to a second funneled section 72 which, in turn, terminates in a larger cylindrical portion 74. Advantageously cylindrical portion 74 is made concentric with the smaller diameter cylindrical tube 58. A hole 78 through the funneled section 72 provides for the passage of the smaller diameter tube 70. A weld 76 serves to seal the clearance space between tube 70 and the hole 78 in section 72. If desired, several separating rods (not shown) may be welded between the outer surface of cylindrical tube 58 and the inner surface of cylindrical portion 74 to provide additional radial rigidity for the concentric assembly. Whether the provision of such separating rods is desirable will depend on the relative magnitude of the diameters of the structures which are employed in the assembly. The area of the concentric annular opening formed by the cylindrical portions 58 and 74 is preferably made approximately equal to the area of the cylindrical opening of tube 58 into which the transducer is mounted.

Although the outer shape of the portion 74 of the baflle structure is illustratively shown in FIGURES 3 and 4 as a cylinder it will be understood that the shape of this section may take the form of a square, a hexagon, or any other geometric shape which permits a nesting of such sections when it is desired to assemble a multiple array of these structures into a tight totally enclosed, composite area. When the outer surface of the cylindrical bafile portion 74 is made in the form of a polygon, the funneled section 72 will serve as an adaptor between the polygon and the smaller diameter cylindrical tube 70. When the outer bafiie portion 74 is made in the form of a polygon, the area of the peripheral opening is preferably held at a value approximately equal to the area of the opening of the inner tube 58.

The length of the signal path in the baflie is illustrated by the arrow M2 in FIGURE 3. This path preferably is made equal to approximately a one-half wavelength at the center of the frequency range over which the transducer is to operate. Under these conditions the sound radiated from the rear of the transducer will offer maximum reinforcement to the sound radiated from the front surface of the transducer.

Those skilled in the art will appreciate that restricting the diameter of the tubular baflle in the embodiment described hereinabove results in a great advantage because of the small cross-sectional area which has to be turned through 180 at the folded section. By reducing the diameter of the folded section of the tube, there is a reduction in the area of the surface at the bend to thereby minimize any undesirable reflections which would be set up between the folded surface and the transducer. Secondly, there is a reduction in the phase shift in the wave front as it passes through the smaller section around the 180 radius. The restriction of the area of the baffie as illustrated will naturally increase the magnitude of the sound pressure through the reduced section. For high power transducers operating in shallow water, this construction may lead to increased cavitation and thereby limit the power handling capacity of the transducer assembly. For deep water use, however, which is the primary objective of this invention, cavitation problems are not present and no practical disadvantage of limitation in power handling capacity will result by this improved construction.

In accordance with a further embodiment of this invention, the baffie structure arrangement of FIGURE 4 may be made adjustable to permit the length of the line to be tuned to selected frequencies, as desired. An illustrative embodiment comprising this highly desirable tunable arrangement is shown in FIGURES 5 and 6 of the drawing.

As there shown, the bafiie structure is generally the same as the structure of FIGURE 4 with the exception that the folded over cylindrical tube 70 is formed in two parts and is connected by adjustable means to permit the spacing between the parts to be varied in a selective manner. This is effected by means of a pair of coupling members 80 which are formed with internal threading engaging, right and left hand respectively, on the ends of the cylindrical tube portions. Rotation of coupling members 80 to increase or decrease the spacing between the ends of the cylindrical tube portions is effected by the cylindrical spur gear 82 which is meshed with gear teeth on the outside of coupling members 80 and positioned for rotation on the shaft 84 having a bevel gear 86 at its remote end. Bevel gear 86 is meshed with gear 88 which may be rotated, manually or otherwise in any suitable manner to tune the baffle arrangement to a desired frequency of operation.

While there has been shown and described a specific embodiment of the present invention, it will, of course, be understood that various modifications and alternative constructions may be made without departing from the true spirit and scope of the invention. Therefore, it is intended by the appended claims to cover all such modifications and alternative constructions as fall within their true spirit and scope.

What is claimed as the invention is:

1. The improvement of an electromagnetic transducer comprising a sealed housing structure having positioned therewithin first magnetic means, adapted to be spaced from said housing structure, mounted for translatory vibration relative thereto, said first magnetic means comprising an assembly of magnetically conducting elements separated by permanent magnets, second magnetic means secured to said housing structure and positioned in operable relation to said first magnetic means, said second magnetic means comprising a magnetic conducting structure, said first and second magnetic means defining an air gap therebetween with said permanent magnets creating a flux density in said air gap, current coil means operatively associated with said magnetic means, terminal means for supplying electrical current to said coil means, and spring elements attached between said first and said second magnetic means to hold said magnetic means in operable relationship to each other whereby translatory vibration of the housing structure will be of opposite phase to the translatory vibration of said first magnetic means whenever alternating current is applied to the current coils.

2. The improvement of an electromagnetic transducer comprising a sealed spherical housing structure having positioned therewithin first magnetic means adapted to be spaced from said housing structure mounted for translatory vibration relative thereto, said first magnetic means comprising an assembly of magnetically conducting elements separated by permanent magnets, second magnetic means secured to the inner surface of said spherical housing structure and positioned in operable relation to said first magnetic means, said second magnetic means comprising a magnetic conducting structure, said first and second magnetic means defining an air gap therebetween with said permanent magnets creating a flux density in said air gap, current coil means operatively associated with said magnetic means, terminal means for supplying electrical current to said coil means, and spring elements attached between said first and said second magnetic means to hold said magnetic means in operable relationship to each other whereby translatory vibration of the housing structure will be of opposite phase to the translatory vibration of said first magnetic means whenever alternating current is applied to the 'current coils.

3. The improvement of an electroacoustic transducer comprising the combination of a massive base member including a plane surface, a first magnetic assembly comprising a magnetic structure, said magnetic structure being secured to said plane surface of said massive base, a second magnetic structure, an adaptor plate having a plane surface, means securing said second magnetic structure to the plane surface of said adaptor plate, a shell like housing structure, means for securing said adaptor plate to the inside surface of said shell-like housing structure, spring means, means for securing said spring means to each of said first massive base structure and said adaptor plate.

4. The improvement of an electromagnetic transducer assembly for providing radiation of opposite phase from a pair of opposite end faces comprising a baffle structure defining a tubular member having two end openings, a sealed transducer structure positioned at one of said end openings and mounted for free vibration therewithin, a tapered region adjacent each end opening of said tubular member whereby the diameter of said baflie structure is reduced over a portion of its length intermediate said end openings, means folding over the reduced diameter portion of said baffie structure whereby the two end openings thereof are brought into approximate alignment, and selectively adjustable means for varying the spacing between the tapered regions adjacent each end opening of said tubular member to enable the selective tuning of the baffle structure to the operating frequency of the transducer structure.

5. The improvement of an electromagnetic transducer assembly in accordance with claim 4 wherein said selectively adjustable means comprises a coupling member threadedly coupled to each of said tapered regions and adapted to vary the spacing between said tapered regions upon rotation of said coupling member.

6. The method for assembling an electroacoustic transducer assembly of the type having a baffie containing shell-like housing formed of two separate sections enclosing a vibratile structure comprising a pair of rigid elements separated by a compliant member which comprises the steps of attaching one of said pair of said rigid elements to the inner surface of one section of said shelllike housing to support the entire vibratile structure from said one section, mating the second portion of said housing structure with the first portion of said housing structure to totally enclose said vibratile structure, sealing the mating surfaces of said housing structure portions to produce a continuous water-tight external surface, positioning the housing structure adjacent one end face of a foldable baflle structure of the type defining a tubular member having two end openings, and varying the spacing of the tubular member at a gap therein intermediate said two end openings to selectively tune the folded baflle structure to the operating frequency of the transducer.

7. In an electromagnetic transducer for operation underwater at high power levels, first and second magnetic means, spring elements connecting said first and second magnetic means for constrained relative translatory high amplitude vibrational movement thereof along a certain axis, current coil means operatively associated with said magnetic means for producing said relative vibrational movement thereof, a sealed rigid housing structure secured to said second magnetic means and disposed in spaced completely surrounding relation to said first magnetic means, said first magnetic means having a mass sufiieient in relation to the combined mass of said second magnetic means and said housing structure to cause high amplitude vibrational movement of said housing structure, as a whole, along said axis in response to application of high amplitude alternating current to said coil means.

8. In an electromagnetic transducer as defined in claim 7, said sealed housing structure having a generally eonvex surface over at least a portion of its radiating surface.

9. In an electromagnetic transducer as defined in claim '7, said sealed housing structure being spherical in shape.

10. In an electromagnetic transducer as defined in claim 9, further comprising a cylindrical collar secured to the surface of said sealed housing, and having an axis in alignment with said axis of vibrational movement.

11. In a transducer assembly, a bafile structure ineluding a tubular member having first and second openings at opposite ends thereof, a transducer mounted for vibration within said first opening and having outwardly and inwardly directed faces for radiating sonic Waves of opposite phase, said tubular member having a foldedover intermediate portion of reduced cross-sectional area with said first and second end openings being adjacent each other and facing in the same direction, and said tubular member having a length such that radiation from said second end opening is in phase with radiation from said outwardly directed face of said transducer.

12. In a transducer assembly as defined in claim 11, one of said end openings being arranged in generally concentric relation about the other of said end openings.

13. In a transducer assembly as defined in claim 12, wherein said tubular member has a wall opening therein through which said intermediate portion thereof extends.

14. In a transducer assembly in accordance with claim- 12, wherein the effective cross-sectional areas of said first and second end openings are approximately equal.

References Cited by the Examiner UNITED STATES PATENTS 2,597,005 5/ 1952 Kendall 340-R FOREIGN PATENTS 73 6,743 9/1932 France. 345,579 12/1921 Germany. 457,552 3/1928 Germany. 692,146 6/ 1940 Germany.

CHESTER L. JUSTUS, Primary Examiner. KATHLEEN CLAFFY, Examiner. L. H. MYERS, J. P. MORRIS, Assistant Examiners.

Claims (1)

1. 4. THE COMBINATION OF AN ELECTROMAGNETIC TRANSDUCER ASSEMBLY FOR PROVIDING RADIATION OF OPPOSITE PHASE FROM A PAIR OF OPPOSITE END SURFACES COMPRISING A BAFFLE STRUCTURE DEFINING A TUBULAR MEMBER HAVING TWO END END OPENINGS, A SEALED TRANSDUCER STRUCTURE POSITIONED AT ONE END SAID END OPENINGS AND MOUNTED FOR FREE VIBRATION THEREWITHIN, A TAPERED REGION ADJACENT EACH END OPENING OF SAID TUBULAR MEMBER WHEREBY THE DIAMETER OF SAID BAFFLE STRUCTURE IS REDUCED OVER A PORTION OF ITS LENGTH INTERMEDIATE SAID END HOUSINGS, MEANS FOLDING OVER THE REDUCED DIAMETER PORTION OF SAID BAFFLE STRUCTURE WHEREBY THE TWO END OPENINGS THEREOF ARE BROUGH INTO APPROXIMATE ALIGNMENT, AND SELECTIVELY ADJUSTABLE MEANS FOR VARYING THE SPACING BETWEEN THE TAPERED REGIONS ADJACENT EACH END OPENING OF SAID TUBULAR MEMBER TO ENABLE THE SELECTIVE TUNING OF THE BAFFLE STRUCTURE TO THE OPERATING FREQUENCY OF THE TRANDUCER STRUCTURE.

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