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WO1998025437A2 - Method of making an acoustic transducer - Google Patents

Method of making an acoustic transducer Download PDF

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Publication number
WO1998025437A2
WO1998025437A2 PCT/US1997/023159 US9723159W WO9825437A2 WO 1998025437 A2 WO1998025437 A2 WO 1998025437A2 US 9723159 W US9723159 W US 9723159W WO 9825437 A2 WO9825437 A2 WO 9825437A2
Authority
WO
WIPO (PCT)
Prior art keywords
acoustic transducer
assembly
crystal
piezoelectric ceramic
curing
Prior art date
Application number
PCT/US1997/023159
Other languages
French (fr)
Other versions
WO1998025437A3 (en
Inventor
Win H. Chang
Algernon S. Badger
Bernard Simensky
Original Assignee
Input/Output, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Input/Output, Inc. filed Critical Input/Output, Inc.
Publication of WO1998025437A2 publication Critical patent/WO1998025437A2/en
Publication of WO1998025437A3 publication Critical patent/WO1998025437A3/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/16—Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
    • G01V1/18—Receiving elements, e.g. seismometer, geophone or torque detectors, for localised single point measurements
    • G01V1/186—Hydrophones
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K9/00—Devices in which sound is produced by vibrating a diaphragm or analogous element, e.g. fog horns, vehicle hooters or buzzers
    • G10K9/12—Devices in which sound is produced by vibrating a diaphragm or analogous element, e.g. fog horns, vehicle hooters or buzzers electrically operated
    • G10K9/122—Devices in which sound is produced by vibrating a diaphragm or analogous element, e.g. fog horns, vehicle hooters or buzzers electrically operated using piezoelectric driving means

Definitions

  • This invention relates to acoustic transducers and, more particularly, to a hydrophone for use in a seismic streamer cable at depths down to 300 meters.
  • U.S. Pat. Nos. 3,187,300 to Brate and 3,832,762 to Johnson et al. disclose hydrophones having component-to-component seals of epoxy.
  • U.S. Patent No. 3,970,878 discloses an acoustic transducer which has no plastic or epoxy parts exposed to the outside of the transducer unit, to avoid electrical leakage caused by the epoxy or plastic absorbing salt from exposure to salt water.
  • the disclosed transducer appears, from the patent, and from the technical specifications of the commercial embodiment, to be limited to depths of less than one hundred and fifty feet.
  • U.S. Patent No. 4,999,819 discloses an acoustic transducer for use in
  • this transducer also requires, after assembly, curing for ten minutes at 600 degrees centigrade. As a result of such heat, if the piezoelectric cell had been poled before assembly, it then has to be repoled. Piezoelectric cells may be purchased already poled, so it is a waste of time and money to repole them. What is needed is a transducer that does not require a curing which destroys the original poling.
  • the transducer After the repoling, the transducer then has to be stored for at least ten days, to let the piezoelectric cell age, before calibrating the transducer. Because the aging is not linear, most of the aging occurs within the first ten days. The required storage time increases manufacturing time, and increases storage costs. What is needed is a transducer that does not require an aging period after assembly.
  • the method of the present invention which method of making an acoustic transducer includes the steps of: a) assembling a previously polarized piezoelectric crystal with a pair of solid circular metal plates positioned to sandwich the piezoelectric ceramic crystal between them, wherein an epoxy adhesive is interposed between the metal plates and the piezoelectric ceramic crystal to form an acoustic transducer assembly; b) curing the acoustic transducer assembly at temperatures less than 150 degrees centigrade; c) encapsulating the acoustic transducer assembly in a flexible case with a polyurethane potting sealant to form a potted assembly; and d) curing the potted assembly at temperatures less than 150 degrees centigrade to form an acoustic transducer.
  • the method produces a hydrophone which includes: (a) a first surface, and a leader wire attached to a second surface of each metal plate, the second surface being opposite the first surface, and having a convex portion formed in it; (b) a case housing the pair of metal plates with the attached leader wires; and (c) a potting sealant surrounding the pair of metal plates and leader wires, and filling substantially all the space in the case not occupied by the pair of metal plates and leader wires.
  • Fig. 1 is a general overall view of an illustrative seismic streamer cable towed behind a boat, the cable containing many hydrophones.
  • Fig. 2 is a perspective view of a hydrophone, containing an acoustic transducer.
  • Fig. 3a is a perspective view of the two metal plates of an acoustic transducer.
  • Fig. 3b is an exploded view of one metal plate and a piezoelectric ceramic crystal.
  • Fig. 4 is a plan view of a solid circular metal plate, which comprises part of an acoustic transducer.
  • Fig. 5 is a side view of the metal plate of Fig. 4, taken along the line 5-5 of Fig. 4.
  • Fig. 6 is an enlarged view of a portion of Fig. 5.
  • Fig. 1 depicts a seismic streamer cable 10 towed behind a boat 12.
  • the cable 10 contains hydrophones 14.
  • Fig. 2 is a perspective view of a hydrophone 14, containing an acoustic transducer 20.
  • the transducer 20 has a leader wire 22 attached to a metal plate 24, and a leader wire 26 attached to a metal plate 28.
  • the transducer 20 is surrounded by polyurethane 30, filling a boot 32.
  • the polyurethane 30 must be, as much as possible, acoustically transparent. This is done by selecting a polyurethane which has, as much as possible, the same acoustic characteristics as sea water, or as the Isopar H, manufactured by Exxon, in which the hydrophone is immersed inside the marine seismic streamer cable 10.
  • the boot 32 must be, as much as possible, acoustically transparent.
  • the boot 32 is made of a thin, soft, flexible vinyl.
  • the polyurethane 30 is model no. PC-3032, manufactured by Polyset company in Mechanicville, NY.
  • the boot 32 is a boot manufactured by Mocap Inc.
  • Fig. 3a is a perspective view of the two metal plates 24, 28 of the acoustic transducer 20.
  • the two plates are identical. Each has a diameter less than one inch, and is slightly concave.
  • FIG. 3b is an exploded view of the metal plate 24 and a piezoelectric ceramic crystal 36.
  • Fig. 4 is a plan view of a concave side 38 of the solid circular metal plate 24.
  • the plate 24 includes an outer rim 40 and a recessed inner rim 42.
  • the diameter of the piezoelectric ceramic crystal 36 is less than the diameter of the plate 24, but is greater than the diameter of the recessed inner rim 42.
  • the two plates 24, 28 are put together with their concave sides 38 facing each other, the piezoelectric ceramic crystal 36 between them, and an epoxy adhesive 54 is interposed between the metal plates 24, 28 and the piezoelectric ceramic crystal 36.
  • the outer rim 40 of each plate is bonded to the piezoelectric ceramic crystal 36 by the epoxy adhesive 54, the pair of plates thus forming a cavity between them.
  • the epoxy adhesive 54 with a conductive filler, is Eco-bond, made by Emerson & Cuming, in Woburn, Massachusetts.
  • Fig. 5 is a side sectional view of the metal plate 24, taken along the line 5-5 of Fig. 4. Proceeding from the recessed inner rim 42 towards the center of the plate, the plate thickens and then thins to be thinner at the center than at either of the rims 40, 42. Also depicted in FIG. 5 is the crystal 36, glued to the outer rim 40.
  • the crystal 36 is a little more than twice as thick as the depth of the recessed inner rim 42.
  • a convex side 44 of the plate 24 includes a small radius curve 46 and a large radius curve 48.
  • the crystal 36 acts as a flexing stop to stop the inward movement of the center 50.
  • a flexing stop could also be achieved by a pedestal rim attached to each of the concave sides 38, midway between the center 50 and the outer rim 40. Still another flexing stop could be achieved by a small pedestal attached at the center 50.
  • the inner dotted circle 52 shown in FIG. 4 is where the small radius curve 46 meets the outer rim 40 on the convex side 44.
  • Fig. 6 is an enlarged view of a portion of FIG. 5, at the point of the juncture of the crystal 36 and the rims 40, 42.
  • the width of the recessed inner rim 42 is greater than the width of the outer rim 40.
  • the hydrophone 14 is made in the following steps. First, the previously polarized piezoelectric crystal 36 is positioned to be sandwiched between the pair of solid circular metal plates 24, 28. The epoxy adhesive 54 is then applied to the outer rims 40 of the plates. The plates 24, 28 and the crystal 36 are then put together, with the crystal sandwiched between them, and the plates are held together by a clamp while the epoxy adhesive 54 cures, thus forming the acoustic transducer assembly 20.
  • the acoustic transducer assembly 20 is cured at temperatures less than 150 degrees centigrade.
  • the curing temperature is 65 degrees centigrade, about one hundred forty-nine degrees fahrenheit. This low temperature curing, as opposed to the high temperatures required to cure an assembly made with solder, avoids the prior art problem of destroying the polarization of the piezoelectric ceramic crystal 36.
  • the curing temperature can be varied according to the manufacturer's specifications. For example, it could be cured at 95 degrees centigrade for one hour, or at room temperature for twenty-four hours. Different manufacturers of the epoxy adhesive 54 would have different curing temperatures and times.
  • the acoustic transducer assembly 20 After the acoustic transducer assembly 20 has been cured, it is encapsulated in the flexible case, or boot 32, with the polyurethane potting sealant 30 to form a potted assembly 20. Finally, the potted assembly 20 is cured at temperatures less than 150 degrees centigrade to form the hydrophone 14.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Remote Sensing (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Acoustics & Sound (AREA)
  • Geology (AREA)
  • Environmental & Geological Engineering (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics (AREA)
  • Multimedia (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Piezo-Electric Transducers For Audible Bands (AREA)

Abstract

Method of making an acoustic transducer (20) includes the steps of: a) assembling a previously polarized crystal (36) with a pair of solid circular metal plates (24, 28) positioned to sandwich the piezoelectric ceramic crystal (36) between them, wherein an epoxy adhesive is interposed between the metal plates (24, 28) and the piezoelectric ceramic crystal (36) to form an acoustic transducer assembly (20); b) curing the acoustic transducer assembly (20) at temperatures less than 150 degrees centigrade; c) encapsulating the acoustic transducer assembly (20) in a flexible case with a polyurethane potting sealant to form a potted assembly; d) curing the potted assembly at temperatures less than 150 degrees centigrade to form a hydrophone.

Description

METHOD OF MAKING AN ACOUSTIC TRANSDUCER
Background of the Invention
This is a continuation application of an application entitled "ACOUSTIC TRANSDUCER", filed on October 2, 1995, Serial No. 08/537,972 (now issued as U.S. Patent No. 5,642,332), the contents of which are incorporated into this application by this reference.
This invention relates to acoustic transducers and, more particularly, to a hydrophone for use in a seismic streamer cable at depths down to 300 meters. U.S. Pat. Nos. 3,187,300 to Brate and 3,832,762 to Johnson et al. disclose hydrophones having component-to-component seals of epoxy. U.S. Patent No. 3,970,878 discloses an acoustic transducer which has no plastic or epoxy parts exposed to the outside of the transducer unit, to avoid electrical leakage caused by the epoxy or plastic absorbing salt from exposure to salt water. However, the disclosed transducer appears, from the patent, and from the technical specifications of the commercial embodiment, to be limited to depths of less than one hundred and fifty feet.
U.S. Patent No. 4,999,819 discloses an acoustic transducer for use in
"deep submergence applications under high hydrostatic pressures." Col.2, lines 31-32. However, because it is designed for high hydrostatic pressures, it is not as sensitive as desired for shallower water, where streamer cables are usually used. What is needed is a transducer with greater sensitivity, for more accurate readings.
The construction of this transducer also requires, after assembly, curing for ten minutes at 600 degrees centigrade. As a result of such heat, if the piezoelectric cell had been poled before assembly, it then has to be repoled. Piezoelectric cells may be purchased already poled, so it is a waste of time and money to repole them. What is needed is a transducer that does not require a curing which destroys the original poling.
Furthermore, after the repoling, the transducer then has to be stored for at least ten days, to let the piezoelectric cell age, before calibrating the transducer. Because the aging is not linear, most of the aging occurs within the first ten days. The required storage time increases manufacturing time, and increases storage costs. What is needed is a transducer that does not require an aging period after assembly.
Summary of the Invention The foregoing problems are solved and a technical advance is achieved by the method of the present invention, which method of making an acoustic transducer includes the steps of: a) assembling a previously polarized piezoelectric crystal with a pair of solid circular metal plates positioned to sandwich the piezoelectric ceramic crystal between them, wherein an epoxy adhesive is interposed between the metal plates and the piezoelectric ceramic crystal to form an acoustic transducer assembly; b) curing the acoustic transducer assembly at temperatures less than 150 degrees centigrade; c) encapsulating the acoustic transducer assembly in a flexible case with a polyurethane potting sealant to form a potted assembly; and d) curing the potted assembly at temperatures less than 150 degrees centigrade to form an acoustic transducer.
In another feature of the invention, the method produces a hydrophone which includes: (a) a first surface, and a leader wire attached to a second surface of each metal plate, the second surface being opposite the first surface, and having a convex portion formed in it; (b) a case housing the pair of metal plates with the attached leader wires; and (c) a potting sealant surrounding the pair of metal plates and leader wires, and filling substantially all the space in the case not occupied by the pair of metal plates and leader wires. Brief Description of the Drawings
Fig. 1 is a general overall view of an illustrative seismic streamer cable towed behind a boat, the cable containing many hydrophones.
Fig. 2 is a perspective view of a hydrophone, containing an acoustic transducer.
Fig. 3a is a perspective view of the two metal plates of an acoustic transducer; and
Fig. 3b is an exploded view of one metal plate and a piezoelectric ceramic crystal. Fig. 4 is a plan view of a solid circular metal plate, which comprises part of an acoustic transducer.
Fig. 5 is a side view of the metal plate of Fig. 4, taken along the line 5-5 of Fig. 4.
Fig. 6 is an enlarged view of a portion of Fig. 5.
Detailed Description of the Preferred Embodiment
Fig. 1 depicts a seismic streamer cable 10 towed behind a boat 12. The cable 10 contains hydrophones 14.
Fig. 2 is a perspective view of a hydrophone 14, containing an acoustic transducer 20. The transducer 20 has a leader wire 22 attached to a metal plate 24, and a leader wire 26 attached to a metal plate 28. The transducer 20 is surrounded by polyurethane 30, filling a boot 32. The polyurethane 30 must be, as much as possible, acoustically transparent. This is done by selecting a polyurethane which has, as much as possible, the same acoustic characteristics as sea water, or as the Isopar H, manufactured by Exxon, in which the hydrophone is immersed inside the marine seismic streamer cable 10. Similarly, the boot 32 must be, as much as possible, acoustically transparent. The boot 32 is made of a thin, soft, flexible vinyl. The polyurethane 30 is model no. PC-3032, manufactured by Polyset company in Mechanicville, NY. The boot 32 is a boot manufactured by Mocap Inc. in St. Louis, MO.
Fig. 3a is a perspective view of the two metal plates 24, 28 of the acoustic transducer 20. The two plates are identical. Each has a diameter less than one inch, and is slightly concave. FIG. 3b is an exploded view of the metal plate 24 and a piezoelectric ceramic crystal 36.
Fig. 4 is a plan view of a concave side 38 of the solid circular metal plate 24. The plate 24 includes an outer rim 40 and a recessed inner rim 42. The diameter of the piezoelectric ceramic crystal 36 is less than the diameter of the plate 24, but is greater than the diameter of the recessed inner rim 42. The two plates 24, 28 are put together with their concave sides 38 facing each other, the piezoelectric ceramic crystal 36 between them, and an epoxy adhesive 54 is interposed between the metal plates 24, 28 and the piezoelectric ceramic crystal 36. The outer rim 40 of each plate is bonded to the piezoelectric ceramic crystal 36 by the epoxy adhesive 54, the pair of plates thus forming a cavity between them. The epoxy adhesive 54, with a conductive filler, is Eco-bond, made by Emerson & Cuming, in Woburn, Massachusetts.
The recessed inner rim 42 acts as a wicking barrier, so that when the epoxy adhesive is placed on the plates 24, 28, it does not "wick" further along from the outer rim 40 towards the center of the piezoelectric ceramic crystal 36 and the plates 24, 28. Another less effective form of a wicking barrier would be to put masking tape along the inner perimeter of the outer rim 40. Fig. 5 is a side sectional view of the metal plate 24, taken along the line 5-5 of Fig. 4. Proceeding from the recessed inner rim 42 towards the center of the plate, the plate thickens and then thins to be thinner at the center than at either of the rims 40, 42. Also depicted in FIG. 5 is the crystal 36, glued to the outer rim 40. The crystal 36 is a little more than twice as thick as the depth of the recessed inner rim 42. A convex side 44 of the plate 24 includes a small radius curve 46 and a large radius curve 48. In operation, as pressure increases on the outside of the hydrophone 14, a center 50 of the convex side 44 is pushed inwardly. The crystal 36 acts as a flexing stop to stop the inward movement of the center 50. To achieve less flexing, a flexing stop could also be achieved by a pedestal rim attached to each of the concave sides 38, midway between the center 50 and the outer rim 40. Still another flexing stop could be achieved by a small pedestal attached at the center 50.
Referring to both Fig. 4 and Fig. 5, the inner dotted circle 52 shown in FIG. 4 is where the small radius curve 46 meets the outer rim 40 on the convex side 44.
Fig. 6 is an enlarged view of a portion of FIG. 5, at the point of the juncture of the crystal 36 and the rims 40, 42. The width of the recessed inner rim 42 is greater than the width of the outer rim 40. The hydrophone 14 is made in the following steps. First, the previously polarized piezoelectric crystal 36 is positioned to be sandwiched between the pair of solid circular metal plates 24, 28. The epoxy adhesive 54 is then applied to the outer rims 40 of the plates. The plates 24, 28 and the crystal 36 are then put together, with the crystal sandwiched between them, and the plates are held together by a clamp while the epoxy adhesive 54 cures, thus forming the acoustic transducer assembly 20.
The acoustic transducer assembly 20 is cured at temperatures less than 150 degrees centigrade. In the preferred method, the curing temperature is 65 degrees centigrade, about one hundred forty-nine degrees fahrenheit. This low temperature curing, as opposed to the high temperatures required to cure an assembly made with solder, avoids the prior art problem of destroying the polarization of the piezoelectric ceramic crystal 36. The curing temperature can be varied according to the manufacturer's specifications. For example, it could be cured at 95 degrees centigrade for one hour, or at room temperature for twenty-four hours. Different manufacturers of the epoxy adhesive 54 would have different curing temperatures and times.
After the acoustic transducer assembly 20 has been cured, it is encapsulated in the flexible case, or boot 32, with the polyurethane potting sealant 30 to form a potted assembly 20. Finally, the potted assembly 20 is cured at temperatures less than 150 degrees centigrade to form the hydrophone 14.
Although an illustrative embodiment of the invention has been shown and described, other modifications, changes and substitutions are intended in the foregoing disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and consistent with the scope of the invention.

Claims

WHAT IS CLAIMED IS:
1. A method of making an acoustic transducer, comprising the steps of: a. assembling a previously polarized piezoelectric crystal with a pair of solid circular metal plates positioned to sandwich the piezoelectric ceramic crystal between them, wherein an epoxy adhesive is interposed between the metal plates and the piezoelectric ceramic crystal to form an acoustic transducer assembly; b. curing the acoustic transducer assembly at temperatures less than 150 degrees centigrade; c. encapsulating the acoustic transducer assembly in a flexible case with a polyurethane potting sealant to form a potted assembly; and d. curing the potted assembly at temperatures less than 150 degrees centigrade to form an acoustic transducer.
PCT/US1997/023159 1996-12-04 1997-12-04 Method of making an acoustic transducer WO1998025437A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US76027296A 1996-12-04 1996-12-04
US08/760,272 1996-12-04

Publications (2)

Publication Number Publication Date
WO1998025437A2 true WO1998025437A2 (en) 1998-06-11
WO1998025437A3 WO1998025437A3 (en) 1998-10-01

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2853968A1 (en) * 2003-04-17 2004-10-22 Geophysique Cie Gle DEVICE AND METHOD FOR MEASURING SEISMIC WAVES
US7573781B2 (en) 2004-07-30 2009-08-11 Teledyne Technologies Incorporation Streamer cable with enhanced properties
WO2010057708A2 (en) * 2008-11-21 2010-05-27 Robert Bosch Gmbh Ultrasonic transducer, ultrasonic sensor and method for operating an ultrasonic sensor

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4004266A (en) * 1975-12-05 1977-01-18 The United States Of America As Represented By The Secretary Of The Navy Transducer array having low cross-coupling

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4004266A (en) * 1975-12-05 1977-01-18 The United States Of America As Represented By The Secretary Of The Navy Transducer array having low cross-coupling

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2853968A1 (en) * 2003-04-17 2004-10-22 Geophysique Cie Gle DEVICE AND METHOD FOR MEASURING SEISMIC WAVES
WO2004095075A2 (en) * 2003-04-17 2004-11-04 Compagnie Generale De Geophysique Device and method for measuring seismic waves
WO2004095075A3 (en) * 2003-04-17 2005-01-06 Geophysique Cie Gle Device and method for measuring seismic waves
US7573781B2 (en) 2004-07-30 2009-08-11 Teledyne Technologies Incorporation Streamer cable with enhanced properties
US7710819B2 (en) 2004-07-30 2010-05-04 Teledyne Instruments, Inc. Streamer cable with enhanced properties
US8000167B2 (en) 2004-07-30 2011-08-16 Teledyne Instruments, Inc. Streamer cable with enhanced properties
US8493815B2 (en) 2004-07-30 2013-07-23 Teledyne Instruments, Inc. Streamer cable with enhanced properties
WO2010057708A2 (en) * 2008-11-21 2010-05-27 Robert Bosch Gmbh Ultrasonic transducer, ultrasonic sensor and method for operating an ultrasonic sensor
WO2010057708A3 (en) * 2008-11-21 2011-04-14 Robert Bosch Gmbh Ultrasonic transducer, ultrasonic sensor and method for operating an ultrasonic sensor
US8393219B2 (en) 2008-11-21 2013-03-12 Robert Bosch Gmbh Ultrasonic transducer, ultrasonic sensor and method for operating an ultrasonic sensor

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