US2063952A - Apparatus for transmission and reception - Google Patents

Description

Dec. 15, 1936. R. L. STEINBERGER APPARATUS FOR TRANSMISSION AND RECEPTION Original Filed Dec. 4, 1931 2 Sheets-Sheet 1 Dec. 15, 1936. R. STEINBERGER APPARATUS FOR TRANSMISSION AND RECEPTION Original Filed Dec. 4, 1931 2 Sheets-Sheet 2 Patented Dec. 15, 1936 UNITED STATES PATENT OFFICE Raymond L. Steinberger, Westwood, Mam, assignor to George W. Pierce, Cambridge, Mass.

Original application December 4, 1931, Serial No. 579,039. Divided and this application July 19, 1935, Serial No. 32,253

15 Claims.

The present invention, although having fields of more general usefulness, is particularly related to devices for converting or translating acoustic energy into electric energy and vice 5 versa. From a more limited aspect, the invention relates to diaphragms. The present application is a division of application, Serial No. 579,039, filed December 4, 1931;

It has long been recognized, for theoretical reasons which need not be entered into here, that the ideal coupling element for radiating a concentrated beam of acoustic energy into a liquid or gaseous medium, or for the directionally-selective reception of acoustical energy from such a medium in electro-acoustic energy-convertor systems, is a diaphragm whose face dimensions are relatively large compared to the Wave length of the acoustic energy in the medium, and in which all points of the radiating face are vibrating in phase and with equal amplitude like a piston.

The ordinary metal membrane diaphragm commonly used at the present time in the communication art, does not satisfy this ideal condition. It cannot move as a piston because it is clamped along its periphery. Such a diaphragm may introduce a dispersion of the radiated energy at its several higher modes of vibration which will cause the various parts of. the diaphragm to be out of phase with one another so that the transmitted energy, for example, is not properlyfocused. It is well known that, in order to be an efilcient translating member, such a diaphragm must be tuned to the frequency of the i radiated or received acoustic energy. At the very high sound frequencies called into play in supersonic work, say 30 kilocycles, a resonant disc vibrating in the manner of an ordinary telephone diaphragm is, indeed, wholly impractical.

I At such frequencies a resonant plate or disc has proportions more nearly comparable to a short cylinder.

In the ordinary diaphragm clamped along its periphery and vibrating in its fundamental mode, all portions of the diaphragm will be moving in the same direction at any given time; that is to say. they will be in phase. In the diaphragm described in the present application, the median plane, parallel to and midway between the faces of. the diaphra m, executes no appreciable motion along the axis of the diaphragm; that is, it is a node; while the two faces of the diaphragm move in opposite directions along the axis at all times; that is, the two faces execute vibrations essentially 180 out of phase. This mode of vibration. for a particular frequency, is realized by making the thickness of the diaphragm, that is, the length along the axis, substantially equal to one-half of the wave length of sound in the material comprising the diaphragm. The vibration of the diaphragm in this manner will hereinafter be defined as expansional vibration.

Any longitudinal element of the diaphragm along the axis is, therefore, contracting and expanding along and parallel to the axis. The cen-- tral, nodal portion of the diaphragm, which has no longitudinal motion, nevertheless, at the same time expands and contracts in the nodal plane perpendicular to the axis. It is to permit this transverse motion in the nodal plane that the diaphragm is subdivided in the manner described below.

An object of the present invention is to provide a very sensitive, energy converter of the above-described character that shall translate acoustic into electric energy or vice versa. with greater efliciency than has been possible heretofore.

A further object is to provide a new and improved acoustic piston. This piston will, hereinafter, in the specification and the claims, for convenience and by analogy, be referred to as a diaphragm.

A further object is to provide a sectional diaphragm, the sections or blocks of which are properly designed and individually driven in unison so as to cause the diaphragm to move as a unit expansionally.

A further object is to provide a sectional diaphragm. the sections or blocks of which are permitted a transverse dilation and contraction as they execute a longitudinal contraction and expansion along their axis.

A further object is to provide a novel expansional metal diaphragm.

Another object is to provide a novel diaphragm energized by driving members which are operative through internal stresses, such as are brought about by magneto-striction, or piezo-electricity.

Another object is to provide a novel diaphragm particularly adapted for supersonic electro-acoustic energy conversions.

Other objects will be explained hereinafter, and will be more particularly pointed out in the appended claims.

The invention will be explained in connection with the accompanying drawings, in which Fig. 1 is a plan of a preferred embodiment of the piston diaphragm of the present invention; Fig. 2 is a section taken upon the line 2-2 of Fig. 1, looking in the direction of the arrows; Fig. 3 is a perspective upon a larger scale, one of the magnetostrictive-driving elements and an energizing coil being shown in section; Fig. 4 is a similar perspective of a. modification; and Fig. 5 is a diagrammatic view of circuits and apparatus illustrating one form of the invention as applied to .piezo-electriccrystal drive.

The invention is illustrated in the accompanying drawings as applied to a supersonic transmit-. ter or receiver, but it will be obvious that the invention is not limited thereto, and is applicable to other types of transmitters as well as to receivers. The device, if to be used under water, may be mounted in a rotatable, submerged housing, or it may be secured to any object I, as the side of a water craft, by means of bolts 3 passing through openings 5 in a relatively fixed or immovable, outer, inertia annular or ring portion 2. The inner, vibratory, diaphragm portion 4, cylindrical or disc-shaped, is integrally connected to the outer annular portion 2 by an intermediatelydisposed, relatively. thin, annular web 6.

.A uniform, metallic connection is thus obtained between the outer ring 2- and the diaphram 4. The web.6 is ,thin enough so as to be relatively yielding,-thus permitting the, receiving or radiating face-l of the diaphragm portion Jr to vibrate substantially like a piston, in a direction transversely of itself, substantially all the flexing taking place in the web 6. The large mass of the inertia ring 2 prevents transmission of vibration thereto.

All pointson the upper and lower end faces of the single expansional, resonant, cylindrical units of which the diaphragm is built, which individual units should have as large a diameter and as small a length as possible, should vibrate in phase over each face. The limit in choosing a large cross-sectional area compared to axial length, however, is small, because the cylinder has a tendency to vibrate, not only according to its fundamental, but also according to many higher modes of vibration, with resulting nodal lines on its lower, emitting face I. This phenomenon is enhanced owing to the fact that, if the diameter of the diaphragm is large compared to its axial length, the necessary transverse vibration of the diaphragm material in its median plane is restricted. Parts of this face, therefore,

have a tendency to vibrate in a phase opposite to that of other parts. At a distance from the transmitting face 1, therefore, the vibrations set up from the transmitted face 1 in the medium would cancel each other, so that the diaphragm will not efliciently emit a focused beam of sound energy. These considerations are .particularly potent at high frequencies. g

The diaphram portion 4 illustrated in Fi s. 1, 2 3 and 4 is therefore divided'into sections'or blocks. According to the embodiment of the invention there illustrated, these blocks are of two kinds: a'central, inner, cylindrical or disc-like block Qand' seven outer blocks I, each in the form of a sector of an annulus. It will be understood, however, that the circular arrangement is merely the preferred form, and that other shapes could be used; Thus, a rectangular assemblage of square blocks is theoretically operable. Clamp ing devices for holding a rectangular diaphragm,

however, are non-uniform around the periphery ally disposed webs I 2, located at or near the axial upper and lower extremities of the blocks, and to the central section or block 8 by similar thin, but annular, webs l3. The blocks are thus mechanically coupled together so that, though it is possible to drive them individually, each of the opposite faces I and 9 of diaphragm 4 will vibrate as a piston with the faces I and 9 opposed in phase. Diaphragms of this kind may be manufactured conveniently by casting.

The diaphragm 4 is in this manner separated into eight resonant blocks, and the spaces between the webs l2 and I3 permit the median nodal sections of the individual blocks to vibrate transversely independently of each other, without having any block react unfavorably upon any of the others and without, therefore, introducing vibrations of different phase in the various portions of the radiating face 1. These spaces between the webs l2 and those between the webs l3 should not be very wide for this purpose, the desirable minimum transverse width of the spaces being determined rather by considerations of easy casting;

As the diaphragm sections vibrate expansionally, as before described, there is a node of longitudinal motion about half way between their faces 1 and 9 and. loops of longitudinal motion at the said faces. It will thus be observed that the diaphragm sections are supported by the annular web 6 near these loops of motion.

According to the preferred embodiment of the invention, the driving of the individual blocks 8 and I0 is effected magnetostrictively. To this end, each of the diaphragm blocks 8 and I0 is provided with a magnetostrictive core l4, so as to cause individual driving of the blocks 8 and Ill. The cores l4 may, of course, be replaced by piezo-electric crystals 26, as shown in Fig. 5, or the blocks may be driven in any other desired manner. When operated magnetostrictively or piezo-electrically, the blocks 8 and H! are driven by means. of reversible internal stresses to obtain high frequencies. The cores I4 may be constituted of any desired magnetostrictive material. A thin, nickel tube, resonant with the blocks 8 and Hi to which it is attached, operates very well in practice. To the lower end may be rigidly attached an interiorly threaded cap plate l6 by means of which the core may be threaded upon a screw l8 that is integrally fixed to the diaphragm blocks 8 and it). The cores l4 may be individually and simultaneously caused to vibrate by means of energizing coils, one of which is shown at 20, and supplied with power from any desired source. These coils may also supply a constant magnetic polarization to the core. The vibrations of the core l4 are of such a nature that it executes longitudinal expansion and contractions, the free and attached ends being in motion while there will be one or more nodes suitably disposed along the core. The vibrations of the lower extremity of the core l4 will be communicated tothe block 8 or Ill to which it is attached and' the block in turn will also vibrate expansionally, the degree of vibration depending upon how close itapproaches resonance to the driving frequency and to the resonant frequency of the core l4, and upon the magnitude of the internal frictional losses. Theoretically, the core l4 and the block to which it is secured should have substantially the same natural frequency. No mass other than that of the nickel tube itself is necessary for the vibration of the tube to react against. The purpose of the cap plate I 6 is to provide a convenient means of rigid assembly of the core M to the face 9, thereby providing a tight coupling between the core l4 and the face 9. This cap plate, however, infiuences the resonant frequency of the driving member in a manner which will be demonstrated.

It can be shown mathematically and tested by experiment that the optimum lengths for the tubes 14 constitute a series of values given by the equation -2: a 5 ":(zfi'4) where v is the longitudinal velocity of sound in the metal of the tube, f is the resonant driving frequency, k is any odd integer, while which is independent of L, "is determined by the mass of the threaded cap in a manner shown by the equation mo being the mass per unit length of the tube and M the total mass of the cap. From the equation for L, we see that successive optimum values are obtained by starting with the shortest value at 1 L-)\( when 7c=1 and increasing the length of this value by successive additions of 7\, A representing the wave length.

By proper design of the sections 8 and [0, the cores I 4 and the coils 20, and by having the current in the coils 20 in phase, the blocks 8 and ID will be caused to be driven in unison, with the result that the emitting face 1 of the diaphragm 4 will be caused to vibrate as a unit at the resonant frequency, say 30 kilocycles, its motion very closely approximating to a true piston motion. The webs l2 and [3 are made short so that they have no possible mode of vibration as low as 30 kilocycles. In this manner, they will introduce no disturbing modes of vibration into the face 1 of the diaphragm as a whole.

(a tan- The diaphragm 4, therefore, presents to the medium, such as water, a substantially plane face I, all parts of which are in time phase.

The parts may be varied in design according to the purpose in hand. As shown in Fig. 4, an additional ring of sectors I5 may be interposed between the sectors I0 and the ring 2, separated by a web i1 similar to the web 6. The diaphragm will still consist of a compressional head, operating in the same manner as before described. It is preferred to make the diaphragm of metal having small mechanical viscosity. Aluminum has a low viscosity, its elastic losses and its decrement are low and it yields a very satisfactory diaphragm.

The operation of the diaphragm may be improved by a composition of cast aluminum with about 5 percent silicon. The silicon, though not materially affecting the vibrational qualities, lowers the melting temperature and, therefore, facilitates foundry manipulation.

It is desirable to present as large a vibrating surface to the medium as possible with the least complexity of design. The individual blocks or sections in and 8 should, therefore, have as large an emitting surface 1 as possible. The metal of the diaphragm should, therefore, preferably be such that the bulk velocity of sound therein is large. Aluminum, besides having a low mechanical viscosity, has also a large bulk velocity of transmission of sound.

It is possible to compute the most suitable dimensions for the blocks. For a cylindrical block, such as the block 8, the practical minimum limit of length to radius of block cross section is about 3 to l or all frequencies. If the ratio is much less than this, the block will not vibrate in a simple manner, as before described, but a series of nodal lines will appear upon the radiating face due to the restriction of the necessary lateral vibration in the median plane. The same ratio applies approximately for rectangular and sector blocks, replacing the radius by half the side of the square section or half the mean arc width of the sector. The length is determined by the frequency desired and the bulk velocity of sound in the material of the block. For aluminum blocks, the following dimensions are found convenient at 30 kilocycles:

a=1 inch, approximately, L=3 inches, approximately,

where a is the radius of the block 8 or half the means are width of the cross-sectional area of the block l0; and L is the height of the blocks. The ratio of the length to the width is thus' not substantially less than 3/2.

The resonant frequencies of two short cylinders equal in length whose section areas are equal, one of which is circular and the other square, are nearly, but not quite, equal. If the number of sector blocks [0 is properly chosen, their areas will not differ greatly from the area of the central block 8. By proper design, the areas of the blocks 8 and I0 may be made exactly equal, with the ratio of mean arc width to radial thickness nearly equal to unity for each of the sector blocks. This approximation to unity ratio depends upon the number of blocks per annulus, and becomes the better the larger the mean radius of the annulus. In designing the diaphragm, the number of whole blocks in the given annulus is computed. The departure from the unity ratio of width to thickness necessary in making the cross-section areas equal introduces a negligible error in the frequency computation.

It is found, however, because of the difference in shape between the block 8 and the block Ill and because of the loading effect of the webs 6, l2 and I3, that the height of the block 8 may, under certain conditions, be slightly different from that of the blocks l0, else the frequency of the central block 8 will be slightly different than that of the other blocks H). The exact design cannot readily be worked out mathematically. but may best be checked experimentally. In Fig. 3, the central block 8 is shown slightly shorter in length than the annular blocks l0 and the upper faces of the Webs l2 and I3 are disposed in the same plane with the upper face of the central sector 8. These webs must not, of course, be positioned lower down, at a point of nodal expansion and contraction, but could be positioned elsewhere.

The frequency of a longitudinally-vibrating bar can be computed even when the ratio of radius of the cross-section to the length becomes large by making a suitable correction for radial inertia. If the length is not large compared with the diameter of the bar, the expression for the frequency of longitudinal resonance of a short thick bar of elliptical or rectangular cross-section as given by Chree, Quart, Math. Journal. vol. 23, p. 317, 1889,

becomes k E 1rkP) Q] "ii a L 2.

Where f is the frequency in cycles per second, It is any integer, odd or even, L is the total length of the bar, E is the modulus of elasticity, d is the density, P is Poissons ratio normally taken as 3 and K is the radius of gyration of the section about the cylindrical axis.

The above equation is also valid for the case where K/L is small. Then it reduces to which is the familiar formula for the frequency of longitudinal Vibrations in a slender bar.

Thev difference between this latter formula and the more accurate formula given by Chree for the general case is a small correction term about 3 percent for bars in which the ratio of radius of cross-section or half side of rectangular section to the length is about 1:3.

The ratio which is the square of the bulk velocity may be computed after experiments performed upon the specific material used and the result employed in connection with the computation of new vibrators of that material.

Using these formulas for the block frequencies, it will be found that if a=1 inch, as above,

the corresponding length of the aluminum centrol block 8, as determined for a 30-kilocycle frequency is L=3.2 inches.

This is a very fair approximation of the 3 to 1 ratio before mentioned. In practice, however, good results may be obtained if the ratio is as great as, or even greater than, to 1. The thickness of the diaphragm is equal to a half-wave length of sound in the material thereof, or to integral multiples of the half-Wave length.

These dimensions are suitable for a 30-kilocycle frequency. To increase the area of the soundemitting plane surface 1 at this frequency, it is preferable to add additional annuli 22 of sector blocks between the annulus blocks 10 and the fixed annular portion 2, as shown in Fig. 4.

According to the modification illustrated in Fig. 5, each of the blocks is driven by a piezoelectric crystal 24 rigidly fastened at one end by means of suitable cement to the upper face 9 of the block. The crystal electrodes may consist of tin-foil layers 26 deposited upon opposite faces of the crystal, but any other electrodes of suitable type may be employed.

The tin-foil layers or other electrodes may be connected by conductors 28 in parallel to a coil 30 coupled to a coil 32 in the output circuit of a vacuum-tube oscillator 34 or of any other source of alternating-current frequency. The frequency of the output of this oscillator may be adjusted by means of a tuning condenser 36. A further condenser 38 in parallel with the crystal vibrators 24 may be employed to adjust the voltage on the crystals.

It will be understood that the invention is not restricted to the illustrated embodiments thereof, but is susceptible to further modifications and change within the skill of the artisan, and all such modifications and changes are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A vibrator for interchanging electrical and mechanical energy with a sound-conveying medium comprising a plurality of diaphragm sections having substantially the same natural frequency and adapted to be positioned in sonorous relation to the sound-conveying medium, the diaphragm sections being spaced from one another and connected together into a unitary vibrator by relatively thin webs, and a vibrator afiixed to each section, the last-named vibrators having substantially the same natural period of mechanical vibration and elastically cooperating with their corresponding sections to interchange energy with the sound-conveying medium.

2. A vibrator for interchanging electrical and mechanical energy with a sound-conveying medium comprising a plurality of diaphragm sections having substantially the same natural frequency and adapted to be positioned in sonorous relation to the sound-conveying medium, the diaphragm sections being spaced from one another and connected together into a unitary vibrator by relatively thin webs, a magnetostrictive vibra tor affixed to each section, the last-named vibrators having substantially the same natural period of mechanical vibration and elastically cooperating with their corresponding sections through their magnetostrictive expansion and contraction to interchange energy with the sound-conveying medium.

3. A vibrator for interchanging electrical and mechanical energy with a sound-conveying medium comprising a diaphragm having substantially the same natural frequency as the frequency of the sound in the sound-conveying medium and having inner and outer faces and an intermediately disposed plane, the outer face being adapted to be positioned in sonorous relation to the soundconveying medium, and a vibrator affixed to the inner face for vibrating the diaphragm expansionally at substantially the said frequency to cause it to contract and expand to and. from the intermediately dsposed plane, whereby loops of vibration occur at the inner and outer faces and. a node of vibration occurs at the intermediately disposed plane, and whereby the outer face will interchange energy with the sound-conveying medium.

4. A vibrator having a relatively fixed portion, a vibratory diaphragm portion for interchanging electrical and mechanical energy with a soundconveying medium comprising a diaphragm having substantially the same natural frequency as the frequency of the sound in the sound-conveying medium and having inner and outer faces and an intermediately disposed plane, the outer face being adapted to be positioned in sonorous relation to the sound-conveying medium, the relatively fixed portion constituting a support for the vibratory diaphragm portion and a vibrator affixed to the inner face for vibrating the diaphragm expansionally at substantially the said frequency to cause it to contract and expand to and from the intermediately disposed plane. whereby loops of vibration occur at the inner and outer faces and a node of vibration occurs at the intermediately disposed plane, whereby the outer face will interchange energy with the sound-conveying medium, and a web connecting the relatively immovable portion with the vibratory diaphragm portion near the said outer face.

5. A vibrator having a relatively fixed portion, a vibratory diaphragm portion for interchanging electrical and mechanical energy with a soundconveying medium comprising a diaphragm having substantially the same natural frequency as the frequency of the sound in the sound-conveying medium and having inner and outer faces and an intermediately disposed plane, the outer face being adapted to be positioned in sonorous relation to the sound-conveying medium, the relatively fixed portion constituting a support for the vibratory diaphragm portion, a vibrator affixed to the inner face for vibrating the diaphragm expansionally at substantially the said frequency to cause it to contract and expand to and from the intermediately disposed plane, whereby loops of vibration occur at the inner and outer faces and a node of vibration occurs at the intermediately disposed plane, whereby the outer face will interchange energy with the sound-conveying medium, and a web connecting the relatively immovable portion with the vibratory diaphragm portion near the said outer face, the web being of such dimensions as not to have any mode of vibration as low as the said natural frequency.

6. Apparatus for magnetostrictively interchanging electromagnetic energy and sound energy having, in combination, a mechanical vibratory system comprising a diaphragm having a ratio of length to width substantially equal to or greater than 3/2 and a magnetostrictive core afiixed thereto, the diaphragm being adapted to be positioned in relation to a sound-conveying medium for sonorously intercommunicating energy with the medium by means of its sonorous vibration, and coil means magnetostrictively cooperative with the core, the cross-sectional area of the metal of the core being small relative to the area of the diaphragm, but the core being proportioned effectively to transmit vibrational stresses lengthwise of the core to and from the diaphragm in order to enable the core to cooperate with the coil means, by its magnetostrictive expansion and contraction under the action of currents in the coil means, to vibrate the diaphragm to produce radiation of sound into the medium, and to cooperate with the coil means,

by its expansion and contraction in response to the incidence of sound in the medium upon the diaphragm, to generate electric voltages magnetostrictively in the said coil means.

[Apparatus for magnetostrictively interchanging electromagnetic energy and sound energy having, in combination, a mechanical vibratory system comprising a diaphragm having two oppositely disposed faces and adapted to vibrate expansionally about a nodal plane parallel and intermediate to said faces, and a magnetostrictive core affixed thereto, the diaphragm being adapted to be positioned in relation to a sound-conveying medium for sonorously intercommunicating energy with the medium by means of its sonorous vibration, and coil means magnetostrictively cooperative with the core, the cross-sectional area of the metal of the core being small relative to the area of the diaphragm, but the core being proportioned effectively to transmit vibrational stresses lengthwise of the core to and from the diaphragm in order to enable the core to cooperate with the coil means, by its magnetostrictive expansion and contraction under the action of currents in the coil means, to vibrate the diaphragm to produce radiation of sound into the medium, and to cooperate with the coil means, by its expansion and contraction in response to the incidence of sound in the medium upon the diaphragm, to generate electric voltages magnetostrictively in the said coil means, the mechanical vibratory system being dimensioned and tuned to cooperate effectively with the diaphragm at the frequency of the current in the coil means.

8. Apparatus for magnetostrictively interchanging electromagnetic energy and sound energy having, in combination, a mechanical vibratory system comprising a diaphragm having a ratio of length to width substantially equal to or greater than 3/2 and a magnetostrlctive core afflxed thereto, the diaphragm being adapted to be positioned in relation to a sound-conveying medium for sonorously intercommunicating energy with the medium by means of its sonorous vibration, coil means magnetostrictively cooperative with the core, the cross-sectional area of the metal of the core being small relative to the area of the diaphragm, but the core being proportioned effectively to transmit vibrational stresses lengthwise of the core to and from the diaphragm in order to enable the core to cooperate with the coil means, by its magnetostrictive expansion and contraction under the action of currents in the coil means, to vibrate the diaphragm to produce radiation of sound into the medium, and to cooperate with the coil means, by its expansion and contraction in response to the incidence of sound in the medium upon the diaphragm, to generate electric voltages magnetostrictively in the said coil means, and means for energizing the core at the resonant frequency of the mechanical vibratory system.

9. Apparatus for interchanging electromagnetic energy and sound energy having, in combination, a mechanical vibratory system comprising a diaphragm having a ratio of length to width substantially between 3/2 and and a vibrator afilxed thereto for driving the diaphragm, the diaphragm being adapted to be positioned in relation to a sound-conveying medium for sonorously intercommunicating energy with the medium by means of its sonorous vibration, the vibrator being actuable by reversible internal stresses.

10. Apparatus for interchanging electromagnetic energy and sound energy having, in combination, a mechanical vibratory system comprising a diaphragm having a ratio of length to width substantially equal to or less than 10 and a vibrator aflixed thereto for driving the diaphragm, the diaphragm being adapted to be positioned in relation to a sound-conveying medium for sonorously intercommunicating energy with the medium by means of its sonorous vibration, the vibrator being actuable by reversible internal stresses, and being of such dimensions as to cooperate resonantly with the diaphragm.

11. A vibrator for interchanging electrical and mechanical energy with a sound-conveying medium, comprising a plurality of diaphragm sections each having two oppositely-disposed faces and each having affixed to one of said faces a magnetostrictive core for energizing the diaphragm section, each section and core being so dimensioned and tuned as to vibrate resonantly together at a frequency of longitudinal vibration common to all of the sections, and the diaphragm sections being spaced from one another yet connected together into a unitary vibrator by webs essentially coplanar with one group of said faces for cophasing the vibrations of the said coplanar faces and supporting the sections.

12. A diaphragm having two oppositely-disposed faces and adapted to vibrate expansionally in longitudinal resonance about a nodal plane intermediately disposed between said faces, a web said faces for supporting the diaphragm, and a magnetostrictive core affixed to the other of said faces for energizing the diaphragm, said diaphragm and core being relatively dimensioned in such manner as to vibrate resonantly in unison.

13. A vibratory diaphragm for interchanging electrical and mechanical energy with a soundconveying medium having two oppositely disposed faces one of which is adapted to be disposed in the medium, the diaphragm being subdivided for part of its thickness by channels to produce a plurality of diaphragm sections having substantially the same natural frequency, and a vibrator aflixed to each section for vibrating the sections expansionally at a common frequency, the relative dimensions and the materials of the sections and the vibrators rendering their combination resonant to the said common frequency. 14. Apparatus for interchanging electrical and mechanical energy with a sound-conveying medium comprising a plurality of cylindrical diaphragm sections substantially alike in shape and dimensions, the diaphragm sections being spaced from one another symmetrically and connected together .into a unitary vibrator by webs, a vibrator afiixed to each section, and means causing the vibrators to cooperate elastically with their corresponding sections to effect an interchange of energy with the sound-conveying medium.

15. A vibrator for interchanging electrical and mechanical energy with a sound-conveying medium, comprising a plurality of diaphragm sections each having two oppositely-disposed faces, each section having aiiixed to one of said faces a magnetostrictivecore responsive to sound-excited vibrations of the section, each section and core being so dimensioned and tuned as to vibrate resonantly together at a frequency of longitudinal vibration common to all of the sections, and the diaphragm sections being spaced from one another yet connected together into a unitary vibrator by webs essentially coplanar with one group of said faces for cophasing the vibrations of the said coplanar faces and supporting the sections.

R. L. STEINBERGER.

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