US3781779A

US3781779A - Gas impermeable expansion diaphragm

Info

Publication number: US3781779A
Application number: US00206696A
Authority: US
Inventors: C Tallman
Original assignee: Sanders Associates Inc
Current assignee: Lockheed Corp
Priority date: 1971-12-10
Filing date: 1971-12-10
Publication date: 1973-12-25
Anticipated expiration: 1990-12-25

Abstract

A hydrophone assembly for suspension below the surface of a body of water, the hydrophone assembly having a gas impervious diaphragm comprising a layer of elastomer material encapsulating a layer of metal for sealing a closed chamber which is filled with a gaseous evacuated liquid. The diaphragm compensates for changes in volume of the evacuated liquid which occurs with fluctuating temperatures and prevents any penetration of ambient air gases.

Description

United States Patent Tallman Dec. 25, 1973 [54] GAS IMPERMEABLE EXPANSION 2,444,911 7/1948 Benioff 340/8 LF DIAPHRAGM 3,239,801 3/1966 McGaugheym. 340/8 L 3,550,072 12/l970 Babikyan 340/13 R Primary ExaminerBenjamin A. Borchelt Assistant Examiner-H. J. Tudor Attorney-Louis Etlinger [57] ABSTRACT A hydrophone assembly for suspension below the surface of a body of water. the hydrophone assembly having a gas impervious diaphragm comprising a layer of elastomer material encapsulating a layer of metal for sealing a closed chamber which is filled with a gaseous evacuated liquid. The diaphragm compensates for changes in volume of the evacuated liquid which occurs with fluctuating temperatures and prevents any penetration of ambient air gases.

8 Claims, 2 Drawing Figures l 1 R 10 :25 56 ///1 a; I E 22 1'. ,7 I a emu" ]I s as j, I so I PAIENIED DEC 2 5 I975 CHARLES V. TALLMAN ATTORNEY 1 GAS IMPERMEABLE EXPANSION DIAPHRAGM FIELD OF THE INVENTION This invention relates to diaphragm assemblies, and more particularly, to gas impervious diaphragm particularly adapted for use in hydrophone assemblies.

The invention described herein was made during the performance of a contract with the Department of the Navy.

BACKGROUND Hydrophone assemblies are commonly used in sonobuoy systems and are used to detect the presence of underwater acoustic waves produced by a remotely located source. Typically, the assembly comprises hydrophone units positioned within a cavity of a housing with the cavity being filled with oil so as to surround and fill all voids of the hydrophone unit. The housing is then suspended from and electrically connected to a floating surface unit of the sonobuoy system.

The hydrophone unit is designated to generate an electrical signal when an acoustic pressure wave strikes the hydrophone housing The oil transmits these acoustic pressure waves causing electrical coils positioned circuit to move thereby generating the electrical signal. During assembly of the unit, all gases have been re moved from the oil for the presence of gas bubbles may effect the freedom of movement of the electrical coils. More particularly, gas bubbles may prevent or so restrict the movement of the coil assembly as to prevent the detection of acoustic waves. The sonobuoy system arrangements are very useful and have been used very extensively. Sometimes, however, it may be necessary to place the systems in storage for extended periods of time, and it is therefore necessary to provide a permanent impermeable gas barrier between the oil and the surrounding atmosphere.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of this invention to provide a novel and improved diaphragm assembly.

Another object of this invention is to provide a diaphragm assembly having a metallic element molded in layers of an elastomer material.

It is a further object of this invention to provide a hydrophone assembly which incorporates a gas impervious diaphragm for sealing a chamber containing oil fromthe atmosphere for extended lengths of time and capable of flexing to compensate for changes in the volume of the oil;

Another object of this invention is to provide a hydrophone assembly which incorporates a diaphragm having a metallic substance molded between layers of elastomer material to provide a permanent air barrier.

According to this invention, these and other objects which will become apparent upon reading the specification are embodied in apparatus comprising a flexible assembly for enclosing and sealing an open end of a housing, the flexible assembly having a metallic substance integrated within a layer of resilient material.

BRIEF DESCRIPTION OF THE DRAWINGS For a clearer understanding of the invention, reference may be made to the following detailed description and accompany drawing in which:

FIG. 1 is a schematic view, partly in section, of a hydrophone-assembly incorporating the invention; and

FIG. 2 is an enlarged sectional view of the gas impervious diaphragm.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a hydrophone assembly, indicated generally at 10, is shown as it would appear positioned beneath the surface of the water at a desired depth and held there by means ofa cable 12, or by any other means well known in the art, one end of which is secured to unit 20 at the water surface.

The hydrophone assembly structure comprises a generally cylindrical casing or housing 22 having a bottom portion 24 and a top portion or bulkhead 25 with a central opening 26 therein, which portions close the ends of the housing. Three posts, two of which are shown at 27 are supported from the bottom portion 24 and extend upwards where they are fastened to a generally cylindrical supporting ring 28. Three additional posts, one of which is shown at 32, extend from the supporting ring 28 to another supporting ring 33 positioned closer to the bulkead 25 with posts 32 being secured to both supporting rings. Three additional posts, one of which is shown at 40, extend from supporting ring 33 to an auxiliary ring 42 adjacent to the top bulkhead 25. It will be understood that three posts of each group are angularly displaced in a circular pattern so that not all of them appear in FIG. 1. A pair of 0

rings

29 and 34 assist in supporting

rings

28 and 33 respectively in lending stiffness to the sides of housing 22. The hydrophone sensing units, indicated generally by

reference characters

43 and 44, are each generally mounted to support

rings

27 and 33, respectively by four mounting brackets 45, respectively, (brackets for sensing unit 43 are not illustrated). As explained with reference to the posts above, the brackets are positioned in a generally circular pattern and therefore not all of them appear in FIG. 1.

The

sensing units

43 and 44 are positioned so that their longitudinal (sensitive) axis are substantially perpendicular to each other. The sensing units may be similar to the one set forth with particularity in U. 5. Pat. No. 3,550,072, issued to .lirair A. Babikyan, assigned to the assignee of this invention. Briefly, the units include a coil comprising many turns of fine wire, which is supported within the housing structure and further positioned within an air gap in a magnetic circuit. The magnetic circuit may be formed of any material which will provide a sufficiently strong magnetic field across the defined air gap. The air gap of the magnetic circuit is constructed in such a manner that the lines of force forming the magnetic material are perpendicular to the longitudinal axis of the sensing unit. Accordingly, the coil as previously indicated is supported within the sensing unit housing and it is arranged to travel substantially perpendicular to the lines of force forming the magnetic field. Stated in another way, the coil is arranged to travel in a direction parallel to the sensitive axis of the sensing unit. It follows that any axial movement of this coil attributable to underwater pressure waves will cause an electrical signal to be generated in the coil windings as the coil cuts the line of force forming the magnetic field. This signal is led by means of

cables

50, 51 through the bulkhead 25 to unit 20 at the water surface 20. The details of package 20 are not illustrated since they are well known in the art and are not part of this invention.

While the above description describes the hydrophone assembly as having two sensing units, it is to be understood that the number of units will depend upon the requirements of the system and other physical limitations.

Between the auxiliary ring 42 and the bulkhead 25 is positioned a generally circular, flexible gas impervious diaphragm 55, a feature of this invention. The diaphragm 55 comprises a raised portion 56 which is positioned within the opening 26 of the bulkhead 25. The function of the diaphragm 55 in part, is to provide a gas impermeable barrier for extensive periods of time. This is successfully accomplished as best shown in FIG. 2 (enlarged view for purposes of clarity) by having the diaphragm comprise essentially a metal insert 57 encapsulated by a suitable, flexible coating 58, such as an elastomer. Normally, the flexible coating exhibits a greater degree of elasticity than does the metal insert, and for comparison purposes the elastomer will be described as having a unit elastic limit.

Applicant has found that a lead composition characterized by its ductility and ability to undergo repeated flexing cycles, is a preferred element for the metal insert. The physical properties of lead may be found in any metallurgical handbook. Further, applicant has found that it is prefereable to place a fabric 59, such as Dacron, on each side of the lead when the elastomer is bonded to the lead in the molding process. This fabric maintains the integrity of the lead, that is, the fabric protects the lead from a shearing action caused by the elastomer flowing into the mold and also provides the means for entrapped air and gasses to escape from the mold. Also, if the fabric exhibits very little elasticity, it assists in preventing the elastomer from over stretching during service in the hydrophone assembly and thereby insuring that the lead will not be torn or ruptured. In this fashion, the lead retains the desirable characteristic of gas impermeability even after undergoing repeated flexing cycles. Still another advantage of a lead insert is its non-magnetic properties, a characteristic which insures that a metal insert cannot affect the magnetic circuit in the

hydrophone units

43 and 44.

Further, applicant has found that chlorbutyl rubber is especially suited for the flexible coating 58, and its physical properties may be found in a chemical handbook. This material also exhibits a high degree of impermeability for a short time duration but is not by itself effective when the unit is to be stored for time periods measured in months.

Describing now the function of the diaphragm 55 including the hydrophone assembly for which it has been adapted, the interior of housing 22 and all the voids therein including the interior area of the

sensing units

43 and 44 are filled under pressure with a gas evacuated liquid 60, such as oil until the assembly 10 is at a completely neutral state. The phrase neutral state as used herein means the pressure on each of the diaphragm surfaces is equal. It is important to maintain this established neutral state at all times to insure accurate and reliable operation of the sensing units, and will be further explained hereinafter. By this, it is meant no gaseous material whatsoever shall be allowed to pass through the diaphragm regardless of how long the assembly 10 may be stored before use, if at all. Also, it 6 pressure against the surface of the diaphragm opposite the liquid. The phrase unit as used herein means that volume of liquid which will achieve the aforementioned neutral state for the assembly. Any change in the volume of the liquid such as caused by temperature variations, causes a corresponding change in the surface of the diaphragm within the bulkheadopeningJhat is, the crown of the diaphragm may go through several flexing cycles while expanding or contracting depending upon the volume of the oil while maintaining the desirable neutral state.

Normally, when the hydrophone assembly 10 is placed into operation, it is transported by an aircraft to the particular destination. If the gasses had penetrated through the diaphragm 55 while the assembly is in storage, the gaseous material would tend to be attracted to each other so as to form larger pockets or bubbles when the assembly 10 is subjected to less pressure at higher elevations, and these bubbles could prevent the hydrophone assembly from operating at all.

When the sonobuoy enters the water, the cold temperatures may cause the oil to contract and the diaphragm must follow to prevent the formation of any voids or air pockets. Also, the diaphragm assists in keeping the water from mixing with the oil.

When the sonobuoy unit is placed in the water, the hydrophone assembly 10 is positioned beneath the water surface at a predetermined depth where pressure Waves travelling in the water strike the side 22 or bottom 24 of assembly 10, and travel through the liquid where the pressure waves cause a moveable coil in

hydrophone units

43 and 44 to pass through-a magnetic field at a frequency determined by the source of the waves and produce an electric signal which is also a function of the direction of travel of the pressure waves. It is necessary that these moveable coils freely move through the magnetic field.

To insure free movement of the coils, liquid 60 is free of all gasses or gas bubbles since a gas bubble could become positioned within the field of travel of the coil and thereby prohibit or cause erratic movement thereof through the magnetic field. For example, if the coil fails to move then no electrical signal would be generated; or erratic coil movement would produce a .false signal; that is, a signal which is not a true function of the direction of travel of the pressure waves. Thus the diaphragm must be gas impermeable for all periods of time. 1

While in the foregoing, l have described certain preferred forms and methods of practicing my invention, it is to be understood that this description is made only by way of example and not as a limitation thereon for one skilled in the art may make modifications and changes thereto without departing from the true spirit and scope thereof.

What is claimed is:

l. The combination, comprising means having a unit elastic limit for enclosing and sealing an open end of a housing, said housing having a compartment therein filled with a liquid capable of transmitting pressure waves which strike said housing;

said means being substantially parallel with a surface of said housing and responsive to changes in unit volume of said liquid; and

said means being substantially impervious to the passage of gaseous elements,.said means having a first, second and third -layers,-said first and third layer having a given unit elastic limit and said second layer having a lower unit elastic limit, said second layer being formed from a metallic substance, said matellic substance being gas impervious, and

a layer of fabric positioned between said second layer and at least one of said first and third layers.

2. The combination in accordance with claim 1 wherein said second layer is formed from lead.

3. The combination in accordance with claim 2 wherein said first and third layers are formed from an elastomer.

4.1A pressure compensated hydrophone assembly for detecting underwater pressure waves, comprising;

a housinghaving a compartment therein" and 'an opening at one end;

atleast one sensing unit mounted within said com partment, said sensing unit responsive to said underwater pressure waves;

a unit volume of liquid filling said compartment and voids within said sensing unit, said liquid capable of transmitting pressure waves which strike said housing; and

a resilient means across said opening of said housing, said resilient means responsive to changes in the unit volume of said liquid and substantially impervious to gaseous elements, said resilient means comprises a first, second, and third layers, said first and third layers having a given unit elastic limit, said first and third layers being formed from an elastomer, said second layer having a lower elastic unit, said second layer being formed from a nonmagnetizable metal, said second layer being substantially gas impervious, and a layer of fabric positioned between said second layer and at least one of said first and third layers, said fabric providing means for gasses to escape when said first, second and third layers are molded thereby preserving the integrity of said second layer.

5. Apparatus in combination with claim 4 wherein said second layer is formed from lead.

6. Apparatus in combination with claim 4 wherein said liquid is free from all gasses.

7. Apparatus for detecting the presence of underwa ter pressure waves, comprising a hydrophone assembly for generating signals in response to incident pressure waves, said hydrophone comprising a housing having a cavity therein and open at one end thereof;

a sensing unit mounted within said cavity, said sensing unit responsive to said underwater pressure waves and arranged to generate a corresponding electrical signal;

a unit volume of liquid filling said cavity and voids within said sensing unit; and

a diaphragm assembly across said opening, said diaphragm responsive to changes in the unit volume of said liquid and substantially impervious to the passage of gaseous elements, said diaphragm assembly comprising a first and third layer of resilient material having a given unit elastic limit, and a second layer of metallic substance having a lower elastic limit positioned between said first and third layers, said second layer being formed from lead and being substantially gas impervious, and a layer of fabric being positioned between said second layer and at least one of said first and third layers to preserve the integrity of said second layer when said first, second and third layers are assembled into an integral unit; and

means for maintaining said hydrophone assembly in position in the region of the underwater waves.

8. Apparatus in accordance with claim 7, wherein said first and third layers of said diaphragm are form from an elastomer.

Claims

1. The combination, comprising means having a unit elastic limit for enclosing and sealing an open end of a housing, said housing having a compartment therein filled with a liquid capable of transmitting pressure waves which strike said housing; said means being substantially parallel with a surface of said housing and responsive to changes in unit volume of said liquid; and said means being substantially impervious to the passage of gaseous elements, said means having a first, second and third layers, said first and third layer having a given unit elastic limit and said second layer having a lower unit elastic limit, said second layer being formed from a metallic substance, said matellic substance being gas impervious, and a layer of fabric positioned between said second layer and at least one of said first and third layers.

4. A pressure compensated hydrophone assembly for detecting underwater pressure waves, comprising; a housing having a compartment therein and an opening at one end; at least one sensing unit mounted within said compartment, said sensing unit responsive to said underwater pressure waves; a unit volume of liquid filling said compartment and voids within said sensing unit, said liquid capable of transmitting pressure waves which strike said housing; and a resilient means across said opening of said housing, said resilient means responsive to changes in the unit volume of said liquid and substantially impervious to gaseous elements, said resilient means comprises a first, second, and third layers, said first and third layers having a given unit elastic limit, said first and third layers being formed from an elastomer, said second layer having a lower elastic unit, said second layer being formed from a non-magnetizable metal, said second layer being substantiaLly gas impervious, and a layer of fabric positioned between said second layer and at least one of said first and third layers, said fabric providing means for gasses to escape when said first, second and third layers are molded thereby preserving the integrity of said second layer.

7. Apparatus for detecting the presence of underwater pressure waves, comprising a hydrophone assembly for generating signals in response to incident pressure waves, said hydrophone comprising a housing having a cavity therein and open at one end thereof; a sensing unit mounted within said cavity, said sensing unit responsive to said underwater pressure waves and arranged to generate a corresponding electrical signal; a unit volume of liquid filling said cavity and voids within said sensing unit; and a diaphragm assembly across said opening, said diaphragm responsive to changes in the unit volume of said liquid and substantially impervious to the passage of gaseous elements, said diaphragm assembly comprising a first and third layer of resilient material having a given unit elastic limit, and a second layer of metallic substance having a lower elastic limit positioned between said first and third layers, said second layer being formed from lead and being substantially gas impervious, and a layer of fabric being positioned between said second layer and at least one of said first and third layers to preserve the integrity of said second layer when said first, second and third layers are assembled into an integral unit; and means for maintaining said hydrophone assembly in position in the region of the underwater waves.