Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Reexamination Certificate
2001-08-06
2003-09-02
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
Reexamination Certificate
active
06614723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to acoustic sensors. An embodiment relates to an acoustic sensor array that has high sensitivity, a robust response, and a desired and substantially uniform buoyancy.
2. Description of Related Art
Acoustic sensors may be used to measure sound transmitted through water. One type of acoustic sensor is a hydrophone. A number of hydrophones may be coupled together to form an acoustic sensor array. Acoustic sensor arrays may be used as detection instruments to monitor vessel movement in a marine environment. Acoustic sensor arrays may be used during seismic surveys of water covered areas to estimate the location of underground formations and structures. Acoustic sensor arrays may be placed in liquid filled wellbores. Such acoustic sensor arrays may be used to conduct vertical seismic surveys. Acoustic sensor arrays may be used as sensors for a variety of other applications as well.
One type of acoustic sensor array is a liquid filled array. The acoustic sensor array, which may be over 8 kilometers in length, may include a number of active cable sections. Each active cable section may include several groups of hydrophones connected in series. The hydrophones may be placed within a flexible, sealed tubular outer jacket that is made of polyurethane or a similar material. Multiple strain members (generally between two and five) may be axially spaced apart along the length of the array within the outer jacket. The strain members may be cables; such as, but not limited to, steel cables, cables reinforced with high-strength polymers such as KEVLAR and/or cables formed of high-strength polymers such as VECTRAN. The strain members may bear the load of the array when the array is towed or otherwise supported. The array may be filled with a nonconductive, light fluid, such as kerosene, to provide the array with a desired buoyancy.
Liquid filled arrays may have several characteristics that are undesirable. The arrays may be difficult and labor intensive to construct. The arrays may have to be stored on reels that have large diameters (greater than 10 feet) to inhibit damage to the array. The arrays may have inherent sensitivity limitations due to noise generated within the array by the fluid during use. The arrays may need to be towed at depths from about 12 to 30 feet below water surface to minimize surface reflection noise and surface wave noise. The arrays may present significant safety, health and environmental problems should the outer casing leak or rupture.
A second type of acoustic sensor array is a solid or non-liquid filled acoustic sensor array. U.S. Pat. Nos. 6,108,274; 6,108,267; 5,982,708; 5,883,857; 5,774,423; 5,361,240; and 4,733,378, each of which is incorporated by reference as if fully set forth herein, describe non-liquid filled arrays and hydrophones for non-liquid filled arrays. Non-liquid filled arrays may be easier to manufacture, may be used at shallower depths and may have hydrophone responses that are more sensitive and robust than the response obtainable from a liquid filled array.
A hydrophone may produce electrical signals in response to variation of acoustic wave pressure across the hydrophone. Several hydrophones may be electrically coupled together to form an active section of an acoustic sensor array. There may be several separate active sections within an acoustic sensor array. Electrical signals from multiple hydrophones of an active section may be combined to provide an average signal response and/or to increase the signal-to-noise ratio within an active section of the array. Hydrophones may be coupled together in serial and/or parallel arrangements so that active sections of the array have a desired response and sensitivity to acoustic waves. Typically, fewer hydrophones are needed in an active section of the array if the individual hydrophones have a high signal-to-noise ratio. The use of hydrophones having high signal-to-noise ratios allows for shorter, sensitive and robust acoustic sensor arrays. Hydrophones of non-liquid filled arrays may have an increased signal-to-noise ratio as compared to typical hydrophones of liquid filled arrays.
One type of non-liquid filled acoustic sensor array is a “floatation” cable design. The design includes a buoyant material, such as foamed polyethylene, that is formed over an inner jacket. The buoyant material is then covered with a polyurethane outer jacket. The types of material used for a floatation cable design may not allow the buoyant material to bind to the outer jacket or the inner jacket. If the outer casing were to be ruptured during use, water that entered into the array would undesirably be able to migrate up and down the length of the cable.
SUMMARY OF THE INVENTION
An acoustic sensor array may include a strain member, sensor sections and buoyancy sections. The sensor sections and the buoyancy sections may alternate along a length of the strain member. The sensor sections may be placed along a length of the strain member. Each sensor section may include one or more sensors capable of detecting acoustic signals. The sensors may be electronic sensors or fiber optic sensors. A potting material may be used to fill the space between a body of the sensor sections and the strain member. Buoyancy sections may be formed between adjacent sensor sections. The buoyancy sections may be formed of material that provides a desired amount of buoyancy for the array. When the buoyant sections are formed, the material of the buoyant sections may bind to the sensor sections. The material may also bind to the strain member. Filling the space between the strain members and the bodies of the sensors with potting material, and binding the buoyant sections to the sensor sections makes the array substantially an integral, solid unit. If one of the sections were to crack, migration of fluid in the array would be inhibited beyond the extent of the crack. In addition, the material used to form outer portions of the array may be made of a polymer material, such as polyurethane, that is resistant to cracking and/or breakage during use.
A sensor of a sensor section may be encapsulated within a polymer body. In an embodiment, the polymer is a polyurethane. To form a sensor section, positioners may hold a sensor at a desired position within a mold. Wiring for the sensors may be spiral wound about one, or both, of the positioners. Spiral winding the wiring may inhibit strain damage to the sensors due to bending of the array during use or during storage on a reel. The positioners may be made of, or coated with, a material that does not bind to the polymer so that the positioners may be removed after encapsulation of the sensor. The polymer is injected into the mold to form the sensor section. The mold may be part of a reaction injection molding machine. The polymer may be a material that is capable of binding to the material used to form buoyancy sections of a sensor array. The sensor sections may be formed so that the ends of the sensor sections have large surface areas that will bind to ends of buoyancy sections. A binding film may be wrapped on the ends of the sensor sections, and/or a binding fluid may be placed on the ends of the sensor sections, to enhance binding between the sensor sections and the buoyancy sections.
A sensor of a sensor section may be a hydrophone. The hydrophone may include a base that forms a back plane for a sensor. The base may have a number of ridges that form a plurality of concave surfaces in an outer surface of the base. In an embodiment, the base may have eight ridges so that the back plane has a generally octagonal cross sectional shape with eight concavely curved sides. Other back planes may have cross sectional shapes having fewer or more than 8 sides. A back plane may be molded or placed on the base, or the back plane may be an integral part of the base. A flexible diaphragm may slide over the back plane. In an embodiment, the diaphragm may have a cross sectional shape that substantially matches the cross sectio
Pearce Jonathan W.
Pearce Richard E.
Input / Output Inc.
Madan Mossman & Sriram P.C.
Pihulic Daniel T.
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