US3760348A

US3760348A - H52 standard reference hydrophone

Info

Publication number: US3760348A
Application number: US00228833A
Authority: US
Inventors: R Kieser; A Tims
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1972-02-24
Filing date: 1972-02-24
Publication date: 1973-09-18
Anticipated expiration: 1990-09-18

Abstract

An electroacoustic transducer with features permitting a structure of minimum size to thereby permit reflection and absorption measurement to be made over a broad band of frequencies without disturbing the sound field. A plurality of lithium sulfate crystals are bonded to gold plated silver foil electrodes with an isolating space being provided between each adjacent pair of crystals. The crystal assembly is supported by compliant members within a wire frame which is surrounded by an expanded metal electrostatic shield. The whole assembly is enclosed within a castor oil filled butyl boot. Output terminals are connected through a hermetic-seal-through to a conventional preamplifier. Cable connections to the preamplifier are made through a pressure resistance coupling of unique design.

Description

Kieser et al.

[ 1 H52 STANDARD REFERENCE HYDROPHONE [75] Inventor: RobertJ. Kieser; Allan CQTiins,

both of Orlando, Fla.

[73 Assignee: The United States of America as represented by the Secretary of the Navy [22] Filedf Feb. 24, 1972 '7 WWW M mum \M- [21] Appl. No.: 228,833

[52] US. Cl I. LI.IIITILjLIjl'liji. ..'I IQ:BZWE [51] Int. Cl. H04b 13/02 [58] Field of Search 340/8, 9, 10, 12, 340/13 [56] References Cited UNITED STATES PATENTS 3,432,000 3/1969 Ongkiehong et a1 340/8 LF 2,613,261 10/1952 Massa 340/10 3,054,982 9/1962 Kieser 340/10 2,490,236 12/1949 Shaper 340/10 X 3,027,540 3/1962 Howatt 340/10 Primary Examiner-Benjamin A. Borchelt [111 3,760,348 Sept. 18, 1973 Assistant Examinerl-l. J. Tudor Attorney-R. S. Sciascia et al.

[ 5 7] ABSTRACT An electroacoustic transducer with features permitting a structure of minimum size to thereby permit reflection and absorption measurement to be made over a broad band of frequencies without disturbing the sound field. A plurality oTlithiurn s filfate crystals are bonded to gold plated silver foil electrodes with an isolating space being provided between each adjacent pair of crystals. The crystal assembly is supported by compliant members within a wire frame which is surrounded by an expanded metal electrostatic shield. The whole assembly is enclosed within a castor oil filled butyl boot. Output terminals are connected through a hermetic-seal-through to a conventional preamplifier. Cable connections to the preamplifier are made through a pressure resistance coupling of unique design.

6 Claims, 13 Drawing Figures BACKGROUND OJF TI IE INVENTION This invention is directed to piezoelectric type transducers or hydrophones and more particularly to ahydrophone which is' s'aar;ravages-Basia:

band, temperature stable and is operable in a frequency range of from Hz to 500 KHz at a pressure up to 7,500 psig.

Heretofore, hydrophones that are available for operation at great depth (high pressure) are large, cumbersome, and of limited frequency response. Large hydrophones are unsuitable for reflection and absorption measurements because they disturb the sound field in which the measurements are made. Other hydrophones that embody cellular soundabsorption material are undesirable because their sensitivity is subject to change with temperature or pressure, or both. Such prior art devices areset forth in US Pat. Nos. 2,413,462; 3,054,982 and' 3,118,125; also in an article-Standard Hydrophone for the Infrasonigand Audio-frequency Range at Hydrostatic Pressure to 10,000 psig by T. A. Henrequez and ..EZ: -l.- 1L9l. fil .Saeisty 9f Am'r'iclfi pp. 276-280, Jan. 1970.

Tiie'hydroplion '6f'tiiisih7e'ntion may Be'u ed'as a reference standard through a wide range of frequency, temperature, and hydrostatic pressure. It

is small in size, light weight, and has an acoustically transparent hydrophone head which makes it par-- ticularly useful in reflection and absorption, measurements. In the frequency range 201-12 to 500 KHZ, the

receiving sensitivity changes by less than one decibel at pressures to 6,895 kPa (1,000 psi) gage. The hydrophone head is formed by a plurality of rectangular lithium sulfate crystals bonded. together and connected electrically in parallel by suitable electrodes. The crystal assembly is supported within a wirelike frame by suitable rubber mounts. An expanded metal cylinder having diamond shape apertures formed therein surrounds the wirelike frame and serves as an electrostatic shield. The electrostatic shield is surrounded by a butyl boot of uniform cross section and the head assembly confined by the boot is filled with castor oil. The output of the crystals is directed into a well known transistorized preamplifier and then out through suitable connections through a Y suitable cable to a desired receiver.

STATEMENT OF THE OBJECTS It is therefore an object of the present invention to ductivity.

Other objects and advantages of the invention will become obvious by reference to the following description of the drawings.

BRIEF DESCRIPTION OFTHE o-RAwiN'os H52 STANDARD REFERENCE HYDROPH'ONE' FIG. 1 illustrates a side view of the crystal assembly.

FlG. 2 illustrates a top sembly.

FIG. 3 illustrates one end of the crystal assembly. FIGS. 4 and 5 illustrate a side view ofThe crystal assembly.

view of the crystal as- FIGS. 6, 7, and 8 illustrate typical directivity patterns in the XY plane;

FIGS. 8, 10, 11, and 12 illustrate typical directivity patterns in the X2 plane; and

FIG. 13 illustrates a typical free-field voltage sensitivity of the hydrophone.

DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring to the drawings, FIGS. 1, 2, and 3, i :there is shown by illustration a crystal assembly for use in a high'pressure hydrophone.

As sliown, the crystal assembly includes eight lithium sulfate crystals 1 assembled in two rows of four each with their adjacent end faces spaced from each other by a small separation 5. The rows of crystals are aligned one over the other and are bonded together and connected electrically in parallel by gold-plated silver foil electrodes 2 bonded to their outer faces. The electrodes 2 are joined at one end and are connected electrically to a low potential terminal 3. The inner adjacent faces of the crystals are bonded to an electrode 4 which forms the high potential terminal. As shown in FIGS. 2 and 3, one end of each of the electrodes is cut at an angle su l g t hat when the ends of electrodes 2 are bent -toward each other to be coniiected together at 3 as shown in FIG. 1, they do not touch the center electrode 4.

FIGS. 4 and 5 illustrate a sectional view of the hydrophone head and electrical connections, with the crystal assembly in place within the head assembly. As shown, the crystal assembly is supported within a wire frame or cage which comprises two U-shaped wires secured together with the wires at relative to each other with their ends secured such as by welding to a cylindrical adapter 9. The wire frame is held together and supported by reinforcing rings 8 which provide mechanical strength for the wires. The crystal assembly is mounted coaxially within the wire cage and held in place by suitable thin natural gum rubber mounts 6 which are bonded within the wire frame or cage 7. A flattened, expandednickel cylinder 15 having a thickness of about 0.0051 cm which forms an electrostatic shield for the crystal assembly is secured about the wire cage and is point soldered to electrical ground through adapter 9. The expanded cylinder 15 has diamond shaped openings therein due to the expansion thereof through which castor oil 17 is free to move. A closed end butyl boot 16 of uniform cross section surrounds the expanded cylinder and confines the castor oil within the hydrophone head about the crystal assembly for acoustic coupling between the crystal assembly and the boot as is well known in the art. The open end of the boot is vulcanized and bonded to a cut down end portion of a stainless steel elongated cylinder 18 which is screw threaded onto a hydrophone head zztgapter assembly 11 and held in place by set screw Adapter 9 to which the cage is secured is secured to the hydrophone head adapter assembly 11 by an overlapping section and is secured thereto by a set screw 10. The adapter 9 is provided with a shoulder that rests against the end of adapter assembly 11 which prevents further movement of the adapter onto the assembly 11. An o-ring 19 is positioned between the head adapter assembly and the stainless steel cylinder 18 to avoid leakage of castor oil from 5 the hydrophone head assembly. Since the boot is secured to the stainless steel ring which is screw threaded onto the hydrophone head adapter assembly, the boot may be removed from the assembly by removing the set screw 20 and then unscrewing the stainless steel cylinder.

The hydrophone head adapter assembly 11 is-of cylindrical construction having a closed end near the adapter 9 through which are located parallel apertures which receive therein hermetic-seal elec- 15 trical conductive feed through 12. The opposite end of the head assembly is open and receives therein one end of a coaxial connector 13 which seats against a shoulder on the inner surface of the assembly. The open end of the assembly is provided with threads on the outer surface thereof upon which a stainless steel cylindrical housing 21 is threaded. The end of the stainless steel housing rests against an outwardly extending n'b on the adapter assembly and the outer surface of the adapter assembly is provided with a groove within which an o-ring 22 seats in order to provide a seal between the end of the stainless steel housing 21 and the hydrophone head assembly 11. The stainless steel housing 21 houses the preamplifier section including therein a conventional transistorizedpreamplifier 14 such as set forth in the above cited article.

Suitable electrical conductors are secured to

electrodes

2 and 4 and the electrical feed throughs 12. Also electrical conductors are used between the electrical feed throught 12 and the coaxial connector 13 which in turn connects electrically with the preamplifier 14. The preamplifier 14 amplifies the output developed by the crystals which is directed through an output connector 23 through a hermetic-seal 4 header 36 and a cable terminal 31 to the cable 24 which is connected to any desired suitable equipment which is well known in the a tr The conductor cable 24 is secured to an 'end connector 32 by use of a metal ferrule such as copper a 34 which is silver soldered to the inner surface of one end of the end connector 32 and swaged 33 to the cable 24. The end connector 32 is secured to the preamplifier section stainless steel housing by user of screw 26, an o-ring 25 prevents any leakage between the joint. The hermetic-seal header is secured to the end of the end connector 32 and is provided with posts 41 which plug into the preamplifier output connector 23. Wire conductors 35 are connected to the opposite ends of posts 41 and are electrically connected to the conductors 29 of the cable by use of a cable terminal 31 which is made of a hard, paperbase phenolic laminate material with good mechanical and electrical properties. The cable terminal 31 is precision tapered to fit into the end of the end connector 32 and is provided with apertures 42 therein which receive therein eyelets 30 that are soldered to the conductor wires 29. The eyelets are provided with shoulders 43 which prevent the'eyelets and con- ,65 ductors from being forced through the apertures. The space within the end connector through which the conductor wires 35 pass is filled with a hard set- -x... ting epoxy to hold thewires and the posts 41 in place while giving mechanical strength to the cable terminal.

A cable spacer 28 is provided between the end of the 4 cable and the cable terminal through which the cable wire conductors pass. An insulator protective neoprene rubber covering is vulcanized to the ferrule 34, the end of the cable near the ferrule and to the end of the end connector 32.

In assembly, the hydrophone head, the hydrophone head adapter assembly, and the preamplifier section may be assembled separate from the cable, cable end connector and cable terminal assembly and sub- .ssseee lxi i eitsrethstblrlussins the on te post 41 into the preamplifier output connector and securing the screw 26 in place which holds the sections together.

The transducer may be assembled in three separate sections. The hydrophone head assembly 44 which includes crystal assembly; the preamplifier section 45 which includes the preamplifier and its electrical connections, and the cable terminal section 46. These sections may be assembled separately and then joined together for operation as a single unit. Likewise, the separate sections may be separated for repair of a particular problem in a particular section without disassembly of the other sections.

The hydrophone head assembly may be disassembled by removal of screw 20 and unthreading stainless steel ring 18. This removes the boot. Upon removal of the boot theexpanded cylinder 15 and the wire cage may be removed with removal of adapter 9. This leaves the crystal assembly exposed which may be removed by disconnecting the wires connected t lsstflsettssdthr9 ghlunmu- The cable-gland terminal assembly may be removed by removing screw 26 and sliding the end connector 32 away from the stainless steel housing 21.

It is believed that assembly of the hydrophone head assembly and the preamplifier section are obvious from the drawing and the above description. However, assembly of the cable-gland assembly is 0 believed to require explanation. The cable is of a well known type which includes a braided shield surrounded by a neoprene jacket or cover with the wires included in the inner portion of the cable. Strands of the cable shield 27 are unbraided and bent back over the neoprene jacket with the cable conductors 29 extending from the end of the cable longer than a s?! The cable spacer 28 is placed over the individual cable conductors 29. The insulation is removed from each of the conductors even with the outer surface of the spacer 2 8 Eyelets 30 are placed over a n d soldered over the full length of the eyelet to each wire conductor even with the surface of the spacer 28. The ends of the conductors are fed through the apertures in the cable terminal 31 and the eyelets 'are then forced into the apertures in the cable terminal with the bare wires extending beyond the cable terminal. Wires 35 are soldered to the ends of the gable wires extending beyond the cable terminal.

The cable 24 with strands of the outer s h ield 2 7 bent back over the neoprene cable jacket, the cable spacer 28, and the cable terminal 31 is slipped as an assembly into the ferrule 34 until the precision taper on the cable terminal 31 seats in the precision taper in the end connector 32. The ferrule 34 is then swaged 33 in a directed manner. which seals and locks the cable into the end connector and electrically grounds the cable braid 27 to the cable connector. After the ferrule is swaged. the neoprene rubber 38 is simultaneoulsy formed to the end of the cable connector.32, the ferrule 34, and the cable 24 near the ferrule, by vulcanizing in a compression mold. The wires 35 extending through the opposite end of the cable connector are soldered to the posts 41 of the hermetic-seal header. A hard setting epoxy is poured into the cable connector then the hermetic-seal header is pressed into place and the epoxy is cured. The cable assembly is then ready for connection with the preamplifier output connector 23.

The electrical wires 35 and those in' the hydrophone head adapter assembly have been shown as short as possible for clarity; it is of course obvious that the wires must be sufficiently long to permit one to solder them to their proper connections and then to position the elements into place.

Since the device is so small and the boot over the hydrophone head is removable and can be placed onto the end after the cage is in position, the boot 16 may be filled with vapor free castor oil and then placed over the head assembly with any excess castor oil spilling over. Thus, no special filler plug is required, however, it is obvious that any appropriate filler plug may be provided if desired.

The length of the hydrophone assembly is 32.38 cm, the diameter of the preamplifier section is 2.54 cm, and each of the lithium sulfate plates has the following dimensions: length 1.24 cm, width 0.474 cm, and thick ness 0.152 cm. Therefore, the overall length of the crystal assembly with four linearly aligned crystals is 5.08 cm including the spacing of 0.04 cm between each of their adjacent ends. The overall thickness of the assembly is 0.304 plus the thickness of the thin electrode coated between the two rows of crystals which is negligible.

FIGS. 5, 6 and 7 illustrate typical directivity patterns in the XY plane wherein the center of the pattern to the top of the grid equals 50 dB.

FIGS. 8-12 illustrate typical directivity patterns in the XZ plane wherein the center of the pattern to the top of the grid equals 50 dB.

FIG. 13 illustrates the typical free-field voltage sensitivity which shows that the nominal open-circuit crystal voltage sensitivity at 0 kPa gage in the frequency range Hz to 150 kHz is l95.5 dB re 1 V/p. Pa (95.5 dB re 1 V/p. bar). In the frequency range 20 Hz to 150 kHz, at temperature from 3 to C and pressure to 6,895 kPa (1,000 psig) gage, the receiving sensitivity changes by less than 1.5 dB. For any specific temperaure from 3 to 25 C, the free-field voltage sensitivity measure in the horizontal (XY) plane in the directions 90 or 270 C from the acoustic axis does not change with pressure to 6,895 kPa in the frequency range 100 kHz to 500 kHz. No change in sensitivity with temperature has been observed at pressure to 51.7 MPa (7,500 psi) gage in the frequency range 20 Hz to 4 kHz. The difference in sensitivity measured along the acoustic axis and at l80 to this axis in the horizontal plane is less than 1 dB in the range 20 Hz to 150 kHz at temperature from 3 to 25 C and pressure to 6,895 kPa gage.

The above-stated characteristics are the result of present measurement capabilities. The sensitivity of the hydrophone has been determined in closed tanks under controlled conditions of temperature and pressure. Measurements above 4 kHz have not been made at pressure greater than 6,895 kPa. However, theoretical considerations indicate that the hydrophone is capable of operating above 4 kHz at pressure to 51.7 MPa within the frequency range and sensitivity tolerance given for 6,895 kPa.

The hydrophone is omnidirectional with t 1 dB in the plane (XY) normal to its longitudinal axis up to 50 kHz; at higher frequencies, it is bidirectional. The directivity in the vertical (XY) plane is equivalent to that of a 5.08 cm line.

Operation of the hydrophone is as well known in the art. Sound waves incident on the boot causes the castor oil to transmit vibrational forces onto the crystals which due to their characteristics produce an electrical potential. This is transmitted to the pre-amplifier by the conductive wires. The preamplifier increases the amplitude of the electrical potential developed by the crystal assembly. The output of the preamplifier is transmitted by the conductors and cable to any desired equipment on shore, on a ship, to a signal transmitting buoy or any other suitable equipment.

The hydrophone is suitable for broadband, highpressure temperature-stable reference standard operation and the crystal assembly may be easily removed for repair if needed. The tapered cable terminal permits high pressure operation because the surrounding pressures force the terminal further into its seat in the end of the cable connector and the shoulders on the eyelets prevents the conductors from expulsion. Further, the copper tube swagged to the end of the cable provides maximum tensile strength to the cable assembly while electrically grounding the shield to the hydrophone case.

Use of other types of materials and assembly as well as other modifications and variations are possible in the light of the above teachings and should become obvious to those skilled in the art.

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

l. A hydrophone which comprises:

a hydrophone head assembly,

a preamplifier electrically connected with said hydrophone head for amplifying potentials developed by said hydrophone head,

a cable,

said cable including electrical conductors connected with said preamplifier for conducting electrical pulses to a desired electrical instrument,

said hydrophone head including a crystal assembly formed by two rows of linearly aligned crystals bonded face-to-face and connected electrically in parallel to each other and lying along the axis of said hydrophone head assembly,

each of said linear rows including a spacing between adjacent ends of each of said crystals therein.

2. A hydrophone as claimed in claim 1; wherein,

each of said crystals are rectangular in shape with the crystals of one row aligned with crystals of the other row.

3. A hydrophone as claimed in claim 2; wherein,

said crystals are supported within a wire cage in axial alignment therewith,

said wire cage including two U-shaped wires secured with the wires from each other.

4. A hydrophone as claimed in claim 3; which in- 5 cludes,

a closed end expanded metal cylinder surrounding said wire cage and connected to electrical ground which serves as an electrostatic shield for the crystal assembly, N

a butyl boot surrounding said expanded meta l cylinder, l

and castor oil surrounding said crystal assembly and filling the space confined by said butyl boot.

5. A hydrophone as claimed in claim 4; which includes,

a hydrophone head adapter assembly throughwhich electrical conductors pass,

means for connecting said electrical conductors with said crystal assembly, 1

an adapter secured to said head adapter assembly for easy removal therefrom,

said wire cage and said expanded metal cylindrical cylinder connected to said adapter,

a stainless steel ring,

said butyl boot secured to said stainless steel ring,

said stainless steel ring adapted to be secured about said head adapter assembly for easy removal.

6. A hydrophone as claimed in claim 5; which in cludes,

. a cylindrical cable end connector,

said'cable end connector including a taperedinncr surface on one end,

a cable terminal tapered to match the taper on the innersurface of said cable end connector,

said cable terminal including a plurality of axially aligned apertures therethrough,

a cable, 1

said cable housing a ferrule swagged on a portion of the length from the end thereof,

, said ferrule secured to said cable connector,

electrical conductors passing through said apertures in said cable terminal,

i eyelets secured about said conductors and secured within said apertures in said cable terminal,

I said eyelets including outwardly extending shoulders end of said cable end connector.

# l t I i UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION p t 760,348 Dated September 18, 1973 Robert J. Kieser et a1. Inventor(s) It: is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Cancel the original columns 1 through 4 and substitute in their place the corrected columns as shown on the attached sheet.

Signed and sealed this 19th clay of November 1974.

(SEAL) Attest: I

McCOY M. GIBSON JR. 4 c. MARSHALL DANN Attesting Officer Commissioner of Patents )RM PO-1050 (10-69) USCOMM-DC wave-P09 U.S. GOVKRNMENT PRINTING OFFKE: 9 o

3,760,,348 Dated September 18 1973 Patent No.

Robert J; Kieser et a1... Ihventofls) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby Corrected as shown below:

Cancel the original Columns 1 through 4 and substitute in their place the corrected columns, as shown on the attached sheet.

Signed and sealed this 19th day of November. 1974.

(SEAL) Attest MCCOY M. GIBSON JR. 7 n c. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-IDSO (10-69) u 50 75 2 u.s. eovzmmzm Pmmmc OFFICE: 93 0

Claims

1. A hydrophone which comprises: a hydrophone head assembly, a preamplifier electrically connected with said hydrophone head for amplifying potentials developed by said hydrophone head, a cable, said cable including electrical conductors connected with said preamplifier for conducting electrical pulses to a desired electrical instrument, said hydrophone head including a crystal assembly formed by two rows of linearly aligned crystals bonded face-to-face and connected electrically in parallel to each other and lying along the axis of said hydrophone head assembly, each of said linear rows including a spacing between adjacent ends of each of said crystals therein.

2. A hydrophone as claimed in claim 1; wherein, each of said crystals are rectangular in shape with the crystals of one row aligned with crystals of the other row.

3. A hydrophone as claimed in claim 2; wherein, said crystals are supported within a wire cage in axial alignment therewith, said wire cage including two U-shaped wires secured with the wires 90* from each other.

4. A hydrophone as claimed in claim 3; which includes, a closed end expanded metal cylinder surrounding said wire cage and connected to electrical ground which serves as an electrostatic shield for the crystal assembly, a butyl boot surrounding said expanded metal cylinder, and castor oil surrounding said crystal assembly and filling the space confined by said butyl boot.

5. A hydrophone as claimed in claim 4; which includes, a hydrophone head adapter assembly through which electrical conductors pass, means for connecting said electrical conductors with said crystal assembly, an adapter secured to said head adapter assembly for easy removal therefrom, said wire cage and said expanded metal cylindrical cylinder connected to said adapter, a stainless steel ring, said butyl boot secured to said stainless steel ring, said stainless steel ring adapted to be secured about said head adapter assembly for easy removal.

6. A hydrophone as claimed in claim 5; which includes, a cylindrical cable end connector, said cable end connector including a tapered inner surface on one end, a cable terminal tapered to match the taper on the inner surface of said cable end connector, said cable terminal including a plurality of axially aligned apertures therethrough, a cable, said cable housing a ferrule swagged on a portion of the length from the end thereof, said ferrule secured to said cable connector, electrical conductors passing through said apertures in said cable terminal, eyelets secured about said conductors and secured within said apertures in said cable terminal, said eyelets including outwardly extending shoulders which prevent their removal from said apertures, and a neoprene rubber surrounding said ferrule and a portion of said cable vulcanized thereto and to the end of said cable end connector.