US2416314A - Electroacoustic transducer - Google Patents

Description

Feb. 25, 1947; B. M. HARRISON ELECTROACOUSTIC TRANSDUCER Filed Dec. 19, 1939 2 Sheets-Sheet 1 INVENTOR.

Bef-fmm M. Harrison Feb. 25, 1947. B. M. HARRISON ELECTROACOUSTIC TRANSDUCER Filed Dec. 19, 1939 2 Sheets-Sheet 2 Patented Feb. 25, 1947 2,416,314 ELECTROACOUSTIC 'raANsoUcna Bertram M. Harrison, Newton Highlands, Mass., assignor, by mesne assignments, to Submarine Signal Company, Boston, Mass., a corporation of Delaware Application December 19, 1939, Serial No. 309,992

12 Claims. 1

The present invention relates to a submarine electroacoustic transducer. More particularly the present invention relates to a device for signaling under water with compressional waves and especially for telephone communication.

The features and objects of the invention as well as its construction and manner of operation will best be understood from the following description taken in connection with the accompanying drawings in which Fig. 1 represents a plan view of the device with the diaphragm removed; Fig. 2 is another view, the right half being a vertical mid-section along the line 11-11 in Fig. 1 and the left half being an elevation with a portion of the diaphragm cut away; Fig. 3 shows a schematic diagram of the circuit arrangement of the structure as set forth in Fig. 1; Fig. 4 shows a fragmentary view in perspective illustrating the mounting of the electrodes and the electrical connector to the crystals; and Fig. 5 shows the mounting of the apparatus of Fig. 1 on the deck of a submarine. v

Upon the base member i which forms one end of the casing of the unit there is mounted-a plate 2 spaced from the plate i by spacers 3. Upon the plate 2 is mounted a hollow polygonal prism 4, here illustrated as a-hexagonal prism. The prism plate 2 and spacers 3 are held to the plate I by means of the screws 5. The side walls of the prism 4 are given a thickness of one-eighth of the wave length of compressional waves in the material at the signaling frequency. The bottom of the prism is closed by the plate 2 while the top of the prism is closed by a member preferably made integral with the side walls of the prism.

' This has a thin edge portion 6 and a thicker central portion I which also has a thickness of one-eighth of the wave length of compressional waves in the material. The interior of the prism is left filled with air, or any other gas may be substituted or it may be evacuated, the joint with the plate 2 being tightly sealed against the entrance of any liquid.

On each side face of the prism there are mounted a plurality of electroacoustic elements such as the piezoelectric crystals 8, preferably Rochelle salt crystals. Each of these crystals has a length projecting at right angles from the face of the prism equal to one-quarter of the wave length of compressional waves in the crystals at the signaling frequency. In the construction illustrated the crystals are arranged on each side face of the prism in a double row 8 and 8" as evident from Fig. 2. As many rows may be used as desired to give the required energy output consistent with the desired beam pattern in the plane perpendicular with the direction of the rows. The crystals have electrodes secured to their wide faces. The crystals in each row are arranged in pairs, the pairs being separated from each other by insulating members 9 having a. thickness small compared to the wave length in water. In this manner the crystals of each pair are connected together in series and I prefer to connect the several pairs together in parallel. This arrangement of connections may, however, be varied in any desired manner as will be understood by those skilled in the art. The crystals and their separators are fastened to the hexagonal mass member in any suitable manner as by means of cement. By extending the separators part way along the sides of the crystals the separators help to support the crystals and to make the structure sufliciently rugged for use under water.

The-crystals mounted on the several faces of the prism make it possible to radiate and receive compressional wave energy in all directions, particularly in the plane parallel to the ends of the prism which usually will be the horizontal plane. By using a hexagonal prism, the width of whose side faces is approximately equal to 0.89 times the wave length in the water, the beam patterns of the radiation from the several faces will overlap somewhat to assure full coverage in all directions.

In order to be able also to transmit and receive in a vertical direction one or more additional groups of crystals Ill are mounted on the top of the prism on the member Only one row of these is shown but at least two rows will usually be necessary for uniform hemispherical radiation. As on the sides, the crystals are arranged in pairs with supporting and separating members ll between them.

In front of each group of crystals and spaced as close to the crystals as possible is a diaphragm member made of a material having a specific acoustic impedance which is substantially the geometric mean between the impedances of the crystal and of the outer water. The diaphragm member has a thickness of one-quarter of the wave length of compressional waves of the signaling frequency in the material of which it is made. The diaphragm member is preferably made of one piece as, for example, of molded macerated Bakelite and shaped to cover the entire crystal unit and form with the plate I a watertight housing for the same. As illustrated, the diaphragm member I2 is in the form of a 3 1 hollow cylinder closed at one end and having its walls and end one-quarter wave length in thickness. The Bakelite diaphragm is fitted into a groove l3 in the plate I to which it is secured by the screws M, a soft rubber or other watertight gasket l5 being interposed. The interior of the member I2 is dimensioned so that when in place on the member I the interior walls and end will be as close to the crystals as possible, but not in contact with them. In order to transmit com pressional wave energy to and from the crystals; the interior of the unit is filledwith a suitable compressional wave conducting liquid such as oil, which may be introduced through the aperture occupied by the plug l6. Leads for connecting the crystals to a source of electric energy or to amplifying and indicating apparatus may be carried out from the interior of the unit through a suitable watertight stuffing tube indicated at II.

It will be observed that each crystal, forming a one-quarter wave length vibrator, is mounted by one end upon a one-eighth wave length mass member which has the effect of a substantially infinite mass which will reflect back into the crystals substantially all 'the vibratory energy received from it. Furthermore, the free end of each crystal is matched to the outer water by the interposition of the one-quarter wave length diaphragm member l2 to which it is acoustically connected by the liquid within the unit.

As above stated, the device as a whole provides a plurality of plane radiating surfaces so dimensioned and positioned that the several surfaces formed by the groups of crystals produce beam patterns in the medium which overlap in such a manner that substantially uniformly intense radiation and substantially uniform reception response is obtained in all directions in a plane normal to the radiating surfaces and fairly uniform in planes perpendicular to said normal plane. I have found that this result can be obtained by making the effective width of the radiating surfaces approximately equal to but not substantially greater than 0.89 times the wave length of compressional waves'in the signaling medium at the signaling frequency.

I with the necessary electrode thickness may oo- For example, for a device adapted for operation at 24 kilocycles the total width across each group of crystals including those on top of the device should be about 2.13 inches. This, of

..course, holds only for the hexagonal arrangement herein shown. If more power output is desired it will be necessary to make the crystal groups larger and hence each group will produce a sharper beam. The hexagonal arrangement then becomes insuflicient for uniform cylindrical radiation and it will be necessary to increase the number of faces of the polygonal figure. If uniform hemispherical radiation is required, it may further be necessary to break up the top surface into a number of angularly disposed surfaces. The rule to be observed is that the intensity of wave pressure produced by each of two adjacent effective radiating surfaces in directions at which the two intensities are equal shall be not substantially more than 3 decibels less than the maximum intensity produced by each surface, for then the resultant intensity will be substantially the same in all directions.

To complete the example of a suitable arrangement as herein described for 24 kilocycle operation, the hexagonal mass element 4 may be made of steel 1.0 inch thick. The Rochelle salt crystals 8 may be 1.5 inches in length and 0.25 inch thick by 1.0 inch in width; the separators 9 together cupy spaces 0130.043 inch each. so that the total width across the faces of the crystals in each row is 2.13 inches. The separation of the rows is 0.13 inch so that the span across the two rows is also 2.13 inches. Finally, the diaphragm element l2 may be made-of molded macerated Bakelite 0.75 inch thick and the interior of the unit may be filled with castor oil. This unit will absorb approximately 50 watts of input power.

This device is particularly adapted to telephonic communication between a disabled submarine and another submarine or a surface vessel. For this purpose the device is preferably mounted on the outside of the submarine, for example, on its upper deck in a position where sound waves will be free to travel to and from it in all directions when the submarine is submerged.

It will be understood by those skilled in the art that it is not essential to use piezoelectric crystals for the operating elements but that onequarter wave length magnetostrlctive members may be used instead if desired.

A futher feature of my device which should be noted is that each group of crystals is completely shielded from waves approaching from directions to the rear of that group by virtue of the hollow mass member. Thus, if desired, by separately bringing out leads from each group of crystals and providing suitable switching means, any one group of crystals can separately be listened to while receiving. If the group most nearly facing the source of waves be selected, disturbing noises arriving from opposite directions will be eliminated automatically. Also by virtue of this shielding effect it is possible to use the device for determining the general direction of a wave source by successively listening to the several receiver r p Fig. 3 illustrates schematically an arrangement whereby the operations described above may be carried out. As illustrated in this figure the crystals 8 and 8' which are arranged on the prismatic faces are connected in groups 20, 2|, 22, 23, 24 and 25. Each group may be connected, as indicated, in a series parallel connection by connecting the crystals 8 in series and the crystals 8' in series and connecting the two groups in parallel. The cable 26, as indicated in Fig. 3, may have connected across it both the sender 21 and the receiver 28 and each listening group may be connected across the circuit by means of the switches 29, 30, 3|, 32, 33 and 34. The top listening group of crystals l0 may also be connected across the line by means of. the switch 35 con.- nected across the cables 26. It will be seen from the above arrangement that any of the groups can be used singly or together with any other group and that if general listening is desired or general transmission, all of the units can be connected across the line.

In Fig. 4 which shows a perspective arrangement of a single group of crystals l0, 8 or 8' it will be seen that each crystal is provided with an electrode 36 on each side of the crystal, the center electrode 36 serving for the adjacent faces on two crystals. An electrode connection 31 is mounted on the plate electrode 36 and serves as a terminal connection for the electrical circuit. The blocks 9 are mounted on the sides of each pair of crystals and serve as mounting and spacing elements between the crystals.

In Fig. 5 there is shown a method of mounting the unit as a whole on the deck of a submarine. Here the unit 38 may be mounted in a fixed p0- sition on a projecting support 39 from the deck Having now described my invention, I claim:

1. An electroacoustic submarine transceiver comprising a plate, a hollow polygonal prism mounted on said plate, the walls of said prism being one-eighth of a wave length in thickness at the signaling frequency, means closing the lower end of said prism, means supporting said prism: to said casing at said lower end, means closing the upper end of said prism and having a thin edge portion and a central portion having a thickness of one-eighth of a wave length, a plurality of one-quarter wave length Rochelle salt crystals having electrodes with electrical connections attached thereto, the crystals being mounted by their ends upona plurality of thefaces and upon the thick portion of the means closing the upper end of said prism, a cup-shaped diaphragm of molded macerated Bakelite a quarter wave length in thickness secured by it edge to said plate and positioned to enclose with said plate all of said crystals and having its interior surfaces which are opposite the free ends of said crystals only slightly spaced from them and a compressional wave conducting liquid filling the enclosed space.

2. An electroacoustic submarine transceiver comprising a plate, a hollow hexagonal prism mounted on said plate, the, faces of said prism having a width approximately equal to 0.89 times the wave length of compressional waves in the signaling medium at the signaling frequency and the walls of said prism being one-eighth of a wave length in the material in thickness at the signaling frequency, means closing the lower end of said prism, means supporting said prism to said casing at said lower end, means closing the upper end of said prism and having a thin edge portion and a central portion having a thickness of one-eighth of a wave length in the material, a plurality of one-quarter wave length Rochelle salt crystals having electrodes with electrical connections attached thereto, the crystals being mounted by their ends upon a plurality of the faces and upon the thick portion of the means closing the upper end of said prism, a cup-shaped diaphragm of molded macerated Bakelite, having a thickness of one-quarter wave length in the material, secured by its edge to said plate and positioned to enclose with said plate all of said crystals and having its interior surfaces which are opposite the free ends of said crystals only slightly spaced from them and a compressional wave conducting liquid filling the enclosed space.

3. An underwater sending or receiving device including means for radiating compressional waves, said means having six substantially plane radiating surfaces arranged one on each side of a hexagonal prism and having a Width of substantially 0.89 times the wave length of the waves in the signaling medium.

4. An underwater sending or receiving device including means for radiating compressional waves, said means having six substantially plane radiating surfaces arranged one on each side of a hexagonal prism and having a width of substantially 0.89 times the wave length of the waves in the signaling medium and a seventh radiating surface on top of said prism having substantially the same width as said side surfaces.

5. An underwater electroacoustic device comprising a compressional wave transmitting hollow casing, a hollow hexagonal prismatic mass memer means mounting said member within said sing, a group of closely positioned piezoelectric cystals having electrodes with electrical connec- .tions attached thereto, the crystals being mounted upon each of the side faces of said member and projecting with their lengths substantially at right angles to the surfaces of the supporting prism faces, the total width of each of said groups being not substantially greater than 0.89 times the wave length of compressional waves in the water and a wave conducting liquid filling the casing.

6. An underwater electroacoustic device including a hexagonalprismatic mass member, a group of closely positioned piezoelectric crystals having electrodes with electrical connections attached thereto, the crystals being mounted upon each of the side faces of said mass member and projecting with their lengths substantially at'right angles to the surfaces of the supporting prism faces, the 'total width of each of said groups being not substantially greater than 0.89 times the wave length of compressional waves in the water and means for conducting said waves between the ends of the crystals and the water.

7. An underwaterv electroacoustic device comprising a compressional wave transmitting hollow casing, a hollow hexagonal prismatic mass member, means mounting said member within said casing, a group of closely positioned piezoelectric crystals having electrodes with electrical connections attached thereto, the crystals being mounted upon each of the side faces of said member and projecting with their lengths substantial- 1y at right angles to the surfaces of the supporting prism faces, each of said groups being substantially directed in a line normal to said surfaces and having dimensions with respect to the signaling wave length to form substantially a uniform radiation pattern in a plane normal to said surfaces.

8. An underwater electroacoustic device comprising a compressional wave transmitting hollow easing having a comparatively rigid fiat base member and a hollow diaphragm member, a hollow hexagonal prismatic mass member, means mounting said member at one end on said fiat base within said casing, a group of closely positioned piezoelectric crystals having electrodes with electrical connections attached thereto, the crystals being mounted upon each of said faces of said member and projecting with their lengths substantially at right angles to the surfaces of the supporting prism faces, each of said groups being substantially directed in a line normal to said surfaces and having dimensions proportioned with respect to the signaling wave length to form substantially a uniform radiation pattern in a plane normal to said surfaces.

l 9. An underwater electroacoustic device comprising a hollow casing, a hollow polygonal prismatic mass member having means closing the ends of said mass member, means at one of said ends for mounting said member within said casing, a plurality of electroacoustic transducer elements mounted upon at least two of the faces of said mass member and a compressional wave-conducting liquid filling the casing.

10. An underwater electroacoustic device comprising a hollow casing. a hollow po ygonal 7 prismatic mass member having means closing the ends of said mass member, means at one of said ends for mounting said member within said casing, a plurality of electroacoustic transducer elements mounted upon at least two or the faces of said mass member, said elements having a length projecting from the mass member of one-quarter wave length at the signaling frequency, the walls of the mass member in back of said electroacoustic elements having a thickness of oneeighth of a wave length and said casing opposite .the ends of said electroacoustic elements having a thickness of one-quarter wave length and being composed of a. material having a specific acoustic impedance which is the geometric mean between the impedance of said elements and the impedance of the signaling medium and a compres- V sional wave-conducting liquid filling the casing.

11. An underwater electroacoustic device comprising a' hollow casing, a hollow polygonal prismatic mass member having means closing the ends of said mass member, means at one of said ends for mounting said member within said casing, a plurality of piezoelectric crystals mounted upori at least two of the faces of said mass member, said crystals having a length projecting from the mass member of one-quarter wave length at the signaling frequency, the walls of the mass member in back of said piezoelectric crystals having a thickness of one-eighth of a wave length at the signaling frequency and said casing opposite the ends or said piezoelectric crystals having a thickness of one-quarter wave length and being composed of a material having a specific acoustic impedance which is the geometric mean between the impedance of said crystals and the impedance of the signaling medium and a compressional wave-conducting liquid filling the casing.

12. An underwater electroacoustic device comprising a, hollow casing, a hollow polygonal prismatic mass member having means closing the ends of said mass member, means at one of said endsfor mounting said member within said casing, .9, plurality of piezoelectric crystals having electrodes with electrical connections attached thereto mounted upon at least two of the faces of said member and a compressional wave-conducting liquid filling the casing.

BERTRAM M. HARRISON.

REFERENCES CITED UNITED STATES PATENT Name Date Nicolson Jan. 13, 1931 Number

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