US2983901A - Crystal hydrophone - Google Patents

Description

y 1961 LE ROY c. PASLAY ETAL 2,983,901

CRYSTAL HYDROPHONE Filed April 16, 1945 2 Sheets-Sheet 1 gnaw (MAI L. CIPasZay LYBZBrown NNESZ es a www May 9, 1961 LE ROY c. PASLAY ETAL 2,983,901

CRYSTAL HYDROPHONE Filed April 16, 1945 2 Sheets-Sheet 2 1/ I): III/4 #5 C. B Brown JV. N E8188 CRYSTAL HYDROPHONE Le Roy C. Paslay,4012 University Blvd., Dallas, Tex.;

'Charles B. Brown, 114 Forrester St. SW., Washington,

This invention relates to a hydrophone and more particularly to a hydrophone adapted to receive underwater signals having signal frequencies within a predetermined frequency band and transmit electrical-impulses corresponding thereto in which the strength of the received signals is multiplied by the hydrophone during the reception of the signals thereby to effecta, high degree of sensitivity of the hydrophone.

In devices of this character heretofore devised, it has i been the usual practice to employ a diaphragm in communication with the surrounding water of substantially the same area as the face of the crystal microphone in which'the diaphragm either is in physical contact with the face of the crystal element of the hydrophone or separated therefrom by a pressure transmitting fluid. These hydrophones are adapted to apply substantially the same pressure to the face of the crystal microphone as the pressure of the signals or impulses received by the diaphragm. Such devices have proved not altogether satisfactory under certain conditions of service when employed with underwater ordnance devices, for example, by reason of the fact that the voltage generated by the crystal microphone in response to weak signals received is insuflicient to control the electroresponsive mechanism connected thereto. 7 p

In the device of the present invention this difliculty has been overcome by employing a diaphragm of considerably greater area than the pressure surface ofthe crystal microphone and arranging a movable bafiie section or diaphragm of substantially rigid construction intermediate the first named diaphragm and crystal microphone, and filling the space between the two diaphragms and about the crystal with a pressure transmitting fluid, a vent or bypass being provided within the baflie plate to permit a flow of fluid therethrough for a purpose which will become more clearly apparent as the description proceeds. The bafile plate is provided preferably with a pressure surface of substantially the same area as the area of the flexible diaphragm and arranged adjacent thereto, and a second surface of reduced area corresponding substantially to the-area of the pressure face of the crystal microphone.

The strength of the pressure impulses received by the hydrophone is thus multiplied and the increased pressure is applied to' a relatively small crystal microphone, thereby providing an arrangement in which the electrical signal output of the microphone is greatly increased.

The device of the present invention is also adapted to respond to signals within a predetermined frequency band such, for example, as a range of frequencies from 150 cycles to' 15,000 cycles per second, the lower limit of the frequency band being controlled by the size of the by-pass or vent withinthe baflie plate and the density of the pressuretransmitting fluid. By employing a vent of sufficiently smaller diameter, the lower range of frequencies to which the device is responsive may be extended to a predetermined frequency cut-ofisuch, for example, as "5 cycles per second. Furthermore, by employing the Patented May 9, 1961 arrangement disclosed herein, the hydrophone may be designed in a compact unit which is economical to manufacture and which possesses a high degree of sensitivity.

. One of the objects is the provision of new and improved means within the hydrophone for increasing the strength of the impulses received and applying the increased signals to a crystal microphone element.

Another of the objects of the present invention is to provide a sensitive hydrophone in which the crystal element thereof is relatively small.

Another of the objects is the provision of a hydrophone having new and improved means for controlling the frequency band of the signals to which the hydrophone is responsive.

A still further object is the provision of a hydrophone having new and improved means for preventing the response of the crystal microphone element thereof to frequencies of less than a predetermined frequency.

Still another object is to provide a hydrophone having new and improved means for causing the hydrophone to be uniformly sensitive to "incoming signals throughout a predetermined range of frequencies.

A further object is the provision of a hydrophone for use for various purposes such, for example, as for controlling the operation of marine mines, torpedoes, seismic detecting devices and the like, which will be rugged in construction, economical to manufacture and which possesses all the qualities of reliability and a high degree of sensitivity in service.

Still other objects, advantages and improvements will become apparent from the following description taken in connection with the accompanying drawings, of which:

Fig. 1 is a front view of the device of the present invention in accordance with a preferred embodiment thereof and showing a fragmentary portion of the casing to which the device is secured;

Fig. 2 is a rear view of the device of Fig. 1 with the cover partially broken away;

Fig. 3 is an enlarged end sectional view in elevation of the-device;

Fig. 4 is a 'view partially broken away of the device with the baffle plate removed; and Fig. 5 is a fragmentary view in section showing the filler plug and the pair of signal conductors extending from the casing of the device.

Referring now to the drawings for a more complete understanding of the invention, on which like numerals of reference are employed to designate like parts throughout the several views and more particularly to Fig. 1 thereof, there is shown thereon a casing 10 such, for example, as the casing of the mine to which is secured as by a plurality of bolts 11, a hydrophone indicated generally by the numeral 12. The casing 10 is provided with a circular aperture 13 within which the hydrophone is arranged. The hydrophone includes a circular support 14 having a raised annular portion 15 adapted to be brought into registered engagement with an annular recessed portion 16 within the casing, within which is disposed a gasket 17 of material suitable for the purpose such, for example, as rubber, thereby to effect a watertight seal between the support 14 and the casing as the bolts 11 are tightened. A plurality of washers 18 are preferably employed between the support and the heads of the bolts 11 to maintain the hydrophone secured to the casing and in water-tight relation therewith.

The support 14 is provided with a circular recessed portion 19 having a lip 21 arranged thereabout and adapted to be engaged by a flexible diaphragm 22 composed of rubber or any of the synthetic varieties thereof thereby to effect a seal between the diaphragm and the support 14 as the diaphragm is clamped thereto by the clamping ring 23 and screws 24. Preferably, though not necessarily, there is provided beneath the heads of the screws 24 a plurality of washers 25. The support also includes an annular recessed portion 26 thereby to provide a baflie plate or diaphragm 27 of truncated conical shape, in the form of a frustum of a cone with a base of substantial breadth and a relatively smaller altitude, concentrically arranged within the recessed portion 26 of the support and integrally connected to the support by a thin annular portion 28 of the support whereby the baffle plate 27 is adapted to be actuated in an axial direction in response to impulses of pressure received by the rubber diaphragm 22 by reason of the thin annular portion 28 which supports the baflie plate. There is also arranged within the baffle plate 27 an aperture 29 within which is arrangedv a bushing or sleeve 31, The sleeve 31 is secured to the bafile plate in any convenient manner as by pressing the parts together and provides a by-pass or vent between the inner and outer faces of the baflie plate for the flow of fluidtherebetween as pressure impulses are received by the diaphragm 22, the rate of flow of the fluid being controlled by the size of the openingwithin the sleeve 31. 1 1

The support 14 has secured thereto as by the bolts 32, a casing 33, generally circular in shape, and provided with a Well 34 within which is arranged a crystal microphone indicated generally by the numeral 35.

A suitable gasket 36 is disposed within complementary annular recessed portions of the support 14 and casing 33 thereby providing an oil-tight joint therebetween when the bolts 32'are drawn tight, the tightness of the joint being effectively maintained by a plurality of washers 37 arranged beneath the heads of the bolts 32' The cavity on the inwardside of the diaphragm 27 is partly filled by an arcuately shaped member 38 composed of material suitable for the purpose such, for example, as amaterial known in the trade as Corprene, to which a flexible coating of oil resisting compound has been applied.

The crystal microphone may be composed of any material suitable for the purpose such, for example, as ammonium dihydrogen phosphate whereby the frequency response of the crystal is preferably independentof the temperature of the crystal and the crystals possess the characteristic of being relatively insensitive to variations in humidity.

The crystal elements comprising the microphone comprise a plurality of laminae of the crystal material'secured together in a unitary structure as by a coating of cement applied thereto and by a length of cord 39 wrapped thereabout. The external electrical connections to the crystal are established by a pair of conductors 41 and 42 secured to the pads 43 and 44 respectively whereby alternate crystals are connected to one of the conductors and the remaining crystals are connected to the other one of the conductors. The crystal microphone is cemented to a pair of plates 45 composed of insulating material suitable for the purpose such, for example, as a material known as linen Bakelite, the plates being of suflicient thickness to cause a predetermined pressure to be applied to the crystal when the casing 33 is clamped to the sup? port 14 and no impulses are received by the flexible diaphragm 22. e

The conductors 41 and 42 are connected in any suitable manner to a pair of rods 46, each of the rods passing through a bushing 47 arranged within an aperture 48 within the casing 33 substantially as shown. A gasket or gland 49 is also arranged about each of the rods 46 and adapted to be compressed by the bushing 51 and nut 52 sufiiciently to form an oil-tight seal between the rod 46 and the casing. An external electrical connection to the rods 46 is established by-the-pair of conductors 53 secured thereto. 5

There is also provided within the casing 33 an annular recessed portion 54 adapted to be enclosed by the cover 55 secured to the casing as by a screw 56.

The conductors 53 extend through an insulated bushing 57 arranged within the casing 33 and are preferably formed into a knot 58 within the recessed portion 54 of the casing, as is well known in the electrical art. There is also provided within the casing 33 a filler hole 59, through which the interior cavities of the hydrophone are filled with a fluid such, for example, as a fluid known in the trade as Dow Corning, having a viscosity which varies .but slightly with changes in temperature. A sufficient quantity of this fluid is introduced into the cavities of the hydrophone to force the flexible diaphragm22 outwardly, substantially as shown in Fig. 3.

A convenient method of achieving'this result is to reduce the pressure on the outside of the flexible diaphragm 22 during the filling operation although, if desired, the fluid may be inserted into the aforesaid cavities under pressure. The filler hole 59 is sealed by a gasket 61 arranged between a pair of discs 62 and adaptedto be compressed by 'the plug '63 sufficiently to effect an oiltight seal.

The cover 55 is provided with an aperture 64 through which a quantity of'material known as insulating compound is preferably introduced within the annular recessed portion 54 of the casing 33 sufficiently to form an additional seal for the electrical terminals and-filler hole and additionally to secure the conductors 53 to the casing.

By providing a 'suflicient quantity of fluid within the cavities of the microphonesuflicient'to effect a considerable distension of the-flexible diaphragm 22 from the baflle plate 27 before submersion of the device within the water, the diaphragm is prevented from striking the baffle plate while impulses of pressure are received by the device-while in a-submerged condition.

By providing abaffle plate having a rigid truncated cone-shaped central portion, supported by a'thin annular section in such a manner that the base of the baffle plate is disposed adjacent the flexible diaphragm 22 and the reduced area of the plate is in abutting relation with the crystalrnicrophone assembly, an arrangement is provided such that a mechanical advantage-is gained by exerting the combined pressure on the base of the diaphragm -against-the crystal assembly and thus the pressure per unit area applied to the crystal is much greater-than the pressure'perunit' area applied by the incoming signalto the flexible diaphragm 22. Furthermore, by providing a 'baflle plate or diaphragm 27 comprising a solid central portion and an annular weakenedportion at the outer periphery of the diaphragm of relatively-small compliance or resistance with respect to the central portion of the diaphragm the restoring force applied to the central portion of thediaphragm by the aforesaid thin annular section is sufliciently small as to be negligible in comparison with the force transmitted from the diaphragm to the crystal assembly;

An arrangement is thus provided in which a chamber 65 intermediate the base ofthe baflie plate and the flexible diaphragm 22 is incommunication with a chamber on the opposite side of the plate 27 by a duct formed by thesleeve 31 within the solid portion ofthe baflle plate. When the pressure applied to the outside of the flexible diaphragm 22 is increased, the fluid withinthe chamber 65 is; additionally compressed, thereby causing a flow of fluid from the, chamber 65 through theduct31. into the chamber 66, and, conversely, when the pressure against the outside of the flexible diaphragm .is reduced, the fluid flows from the chamber 66 into the chamber .65.. The combinationof the density of fluid, the size of the aperture 31, andthe compliance of the member 38 within the chamber 66 causes a resonant condition at a predetermined frequency, which may increase the degree of re,- sponse of the hydrophone to signals of that frequency and produce a sharp reduction ofv response to signals having frequencies lower than the resonance frequency. This condition is caused by the difference in the instantaneous pressure of the'fluid within the chamber 65 on the base of the'baflie plate and the pressure of the fluid the a chamber- 66 against the inside portion-of the balfle plate and the active faces of the crystal which are not normally or but slightly pressed otherwise.

The device is particularly adapted for use with underwater ordnance employing acoustic detecting devices in which it is desired to receivesignals of relatively weak strength within a predetermined frequency range such, for example, as the range from 150 cycles to 15,000 cyclesper second. The device, howevenis also well adapted for use with signals having a different range of frequencies such, for example, as the range from to 18 cycles per second, it being merely necessary to employ a bushing within the baflle plate having an aperture therein of smaller size to providethe desired cut-off characteristic of the device to signals of the lower frequency. Conversely, by employing a bushing within the baflle plate having a larger aperture therein, the device is adapted to cut olf signals having frequencies of less than a relatively higher frequency. Furthermore, by employing a pressure multiplying battle plate having a weakened annular section on the periphery thereof, the voltage generated by the crystal assembly is increased in proportion to the ratio of the multiplication factor of the aforesaid baflle plate and thus is made substantially equal to the sensitivity and energy output of a crystal assembly of much greater size and-having substantially the same pressure surface area as the exposed area of the flexible diaphragm in communication with the surrounding water.

While the invention has been described with reference to a specific embodiment which gives satisfactory results, it will be understood by those skilled in the art to which the invention appertains, after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is our intention, therefore, in the appended claims to cover all such changes and modifications.

The invention herein described may be manufactured andused by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent of the United States:

1. In a crystal hydrophone of the character disclosed, in combination, a metallic casing having a planar flexible annular portion, a rubber diaphragm secured to said casing and in communication with the surrounding water, a pressure multiplying device within the casing in interposed relationship between the diaphragm and the interior of the casing and adapted to be actuated variably in accordance with the strength of impulses received by said diaphragm, said device comprising a rigid member formed integrally with said flexible annular portion centrally thereof and having a broad flat base coplanar therewith, said member being in the form of a frustum of a cone of small altitude terminating in a surface parallelto and of less area than the base, and a crystal microphone within the interior of the casing in abutting relation with the terminal surface of said member and adapted to be actuated by the member as the pressure multiplying device is actuated in response to said impulses.

2. In a hydrophone of the character disclosed, in combination, a metallic casing including an exterior wall of predetermined thickness having a planar circular portion on the exterior thereof, said wall interiorly of said casing being formed with an annular recess coaxial with said circular portion for providing a central inwardly-tapered member connected to the remainder of the wall by a flexible annular portion, said member terminating in a surface of less area than the area of the circular portion, said casing having a well therein opening in facing relation to said surface, means for transmitting pressure impulses in the surrounding water to said member for actuation thereof in response to the impulses, and a crystal microphone supported within said well in abutting relaaesaee secured to saidv casing and in communication with the surrounding water, a movable bafile plate formed integral ly with said annular portion and arranged intermediate said diaphragm and said well, said baffle plate having a surfaceadjcent said diaphragm and a second surface thereon opposite said well and of less area than the area of the first named surface, a crystal microphone assembly supported within said well in abutting relation with said second surface and adapted to receive pressure impulses from the baffle plate as pressure signals are received through the water by said diaphragm, a quantity of fluid within said casing for transmitting pressure impulses from said flexible diaphragm to said baflle plate, and a duct within said baffle plate for establishing a fluid connection. between said surfaces.

4. In a hydrophone of the character disclosed, the combination of a metallic casing, a flexible diaphragm in communication with the surrounding Water and enclosing said casing, a movable baffle section within the casing, a flexible annular member formed integrally with both said section and said casing for supporting said section therefrom, a fluid connection between the baflle section andv said diaphragm whereby the baflle section is adapted to be moved variably as impulses are received by the diaphragm, said baffle section being a frustum of a cone having a broad flat base coplanar with said flexible annular memher. and a terminal surface of reduced area, and a laminated crystal microphone interposed between said casing and the baffle section, said microphone having a crosssectional area coextensive with and abutting said surface, said microphone being adapted to generate electrical impulses in response to variations in pressure impulses received by the microphone from said baflle section, said microphone comprising a plurality of laminae arranged perpendicularly to said surface of reduced area and composed of crystal material possessing the characteristics of being relatively insensitive to variations in humidity.

5. In a hydrophone of the character disclosed, the combination of a metallic casing, a movable baffle section within the casing and adapted to be moved variably as impulses are received by the section, a flexible annular member formed integrallywith both said section and said casing for supporting said section therefrom, said baffle section having a fnisto-conical configuration including a broad flat base coplanar with said flexible annular member and a parallel surface of reduced area thereopposite, a laminated crystal microphone interposed between said casing and the baflle section in abutting relationship with said surface and adapted to generate electrical impulses in response to variations in pressure received by the microphone from said baffiesection, said microphone compris ing a plurality of laminae composed of crystal material disposed perpendicularly to said surface of reduced area means including a pair of electrical conductors for establishing an external electrical connection to the hydro phone, and means for connecting alternate ones of said laminae to each of said conductors respectively.

6. In a hydrophone for detecting signals within a predetermined frequency range, the combination of a metallic casing provided with an integral flexible annular portion and a chamber, a movable baflie section substantially enclosing said chamber and formed integrally with said annular portion, a flexible diaphragm on said casing in communication with the surrounding water and arranged adjacent said baflle section thereby to form a second charm ber, a supply of fluid within each of said chambers, a duct within said baflle section for controlling the flow of fluid between said chambers as the diaphragm vibrates in response to signal impulses received through the surrounding water whereby the hydrophone is unresponsive to signals having frequencies of less than a predetermined frequency, and a crystal. microphone havingja' pressure facerlessthan the area of, saidflexible diaphragm in abutting relation with said movable baffle section and adapted to generate electrical. signals corresponding respectively to saidsignal impulses in response to pressure impulses received from: the baflle section.

7. In a hydrophone for detecting. signals within a predet'erminedfrequency range, the combination of a metalhc casing provided with an integral flexible annular portion andv a chamber, amovable, baflle section substantially enclosing said chamber and formed integrally with sa d annular portion, a flexible diaphragm, on said casing m communication with the surrounding water and arranged adjacent said bathe section thereby to form a second chamber, a supply of fluid within each of said chambers, a duct within, said baffle section for controlling the flow of fluid between said chambers as the diaphragm vibrates in response to signal impulses received through the sur- 7 rounding water whereby the hydrophone is unresponsive tosiguals having frequencies of less than a predetermined frequency, a crystal microphone having a pressure face less than the area of said flexible diaphragm arranged in abutting relation with said baflle section and adapted to generate electrical signals corresponding respectively to said signal impulses in response to pressure impulses received from the baflle section, and means for displacing a volume of said fluid variably in accordance with the pressure of the fluid within the second chamber.

8., In a hydrophone for detecting signals within a predetermined frequency range,the combination of a metallic casing provided with an integral flexible annular portion and" a chamber, a movable bafiie section enclosing said chamber and formed integrally with said annular portion, a flexible diaphragm on said casing in communication with. the surrounding water and arranged adjacent said baflle section to form a second chamber, a supply of fluid within each of said chambers, a duct for controlling the flow of. fluid between said chambers as the diaphragm vibrates in response to impulses received through the surrounding water thereby to control the low frequency cut-oiiof the signals received, and a crystal microphone in said firstnamed chamber and'having a pressure face less than the area .of said flexible diaphragm in abutting relation with said" bafllesection and adapted to be actuated thereby.

9'. In a crystal hydrophone ofthe character disclosed, in combination, a casing having a chamber therein, a flexible diaphragm secured to said casing and in 001111 munication with the surrounding water, a planar flexible annular. portion on saidcasing having a pressure multiplyingvv device co-extensive therewith in interposed relationship between the, diaphragm and the chamber and adapted for variable actuation in accordance with the strengthof impulses received by said diaphragm, said device comprising a rigid central member formed integrally with said' flexible annular portion, saidmember having theform of a frustum of a cone including-a broad flat base coplanar. with said annular portion and a surface parallel to. and of less area than saidbase, a microphone interposed in said chamber in abutting, relation with said surface of said" pressure multiplying device and adapted to be actuated thereby as the flexible diaphragm vibrates in response to said impulses.

' 10. The structureof claim 9' further 'charactcrized' in combination therewith, by an acoustic-impedance-match'-- ing coupling means disposedbetween'said' diaphragm: and said multiplying device for providing sign-a1 communication. therebetween. V V

11'. The-structureoffthecombination of claim 10 further'including a frequency filter means'comprising a duct passing through said pressure multiplying 'device for by passing signals of apredeterrninetl frequency;

12'. The combination, in a hydrophone of the character disclosed, of a casing, a microphonein' said casing, a flexible diaphragm secured to said casing inenclosingrelationship therewith and in communication with the surrounding water, a movable bathe section having a planar annular portion co-extensive with said casing whereby it is supported thereby, said baffle section being disposed" intermediate said diaphragrnand said microphone and having a central portion in the form of a frustum of a cone-with' a broad base anda' small" altitudeand thereby providing a first plane surface thereof ad'- jacent said? diaphragmand a second plane surface thereopposite ofless' area than the area of said-first-named surface, said firstplanesurface beingcoplanar withsaid an- I nular portion, said microphone being. disposedbetween saidcasing and saidi-baflle section fon receptionof pressure impulses from the'baffle section as pressure" signals are received: through the water bysaid' diaphragm and a fluid within said casingfor transmitting: pressure; impulses from said flexible diaphragm to said bafllesection.

13. The combinationnofclaim 12fuzther characterized by a low frequency bypass filter means comprising a fluid duct extending through said baflle section.

References Cited inthe file of this-patent UNITED STATES PATENTS- 1,216,946' Clement Feb. 20, 1917 1,380,869 Fay June 7, 1921 1,591,068 Williams July 6, 1926 2,044,807 Moyes June 23, 1936 2,088,324 John July 27, 1939 2,233,992 Wyckofl Mar. 4, 1941 2,405,226 Mason Aug. 6, 1946 2,626,380 Stedman Jan. 20, 1953 FOREIGN PATENTS 168,839 GreatBritain Mar. 26, 1918 852,150 France Jan. 24, 1940

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