Passive fiber optic sensor with omnidirectional acoustic sensor and accelerometer
First Claim
1. A fiber optic acoustic sensing system, comprising:
- a housing formed generally as an elongate hollow cylinder;
an omnidirectional sensor comprising;
a sensing fiber wrapped around the housing and exposed to an acoustic field;
a reference fiber isolated from the acoustic field;
means for introducing optical signals into the sensing and reference fibers;
means for combining optical signals output from the sensing and reference fibers to form an interference pattern that is indicative of changes in the acoustic field;
a first unequal path length fiber optic interferometer, comprising;
a first mandrel affixed inside the housing the formed to enclose a first chamber;
a first optical fiber wrapped around the first mandrel to form a first optical fiber coil;
a second mandrel placed in the housing and formed to enclose a second chamber;
a second optical fiber wrapped around the second mandrel to form a second optical fiber coil;
a fluid filling both the first and second chambers;
means for placing the first and second chambers in fluid communication and defining a sensing axis between the first and second mandrels such that acceleration of the housing along the first sensing axis causes a fluid pressure differential on the first and second optical fiber coils;
means for introducing optical signals into the first and second optical fibers;
means for combining optical signals output from the first and second optical fibers to produce a signal indicative of the component of the acoustic field along the first sensing axis; and
a second unequal path length fiber optic interferometer affixed inside the housing nd formed essentially identical to the first unequal path length fiber optic interferometer but having a second sensing axis perpendicular to the first sensing axis.
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Accused Products
Abstract
A mismatched path length fiber optic interferometer is optically coupled to an optical fiber and configured to form an omnidirectional acoustic sensor. A second mismatched path length fiber optic interferometer is optically coupled to the optical fiber and configured as a first gradient sensor. A second fiber optic gradient sensor is also optically coupled to the optical fiber. A detector optically coupled to the omnidirectional acoustic sensor and to the gradient sensors converts optical signals output therefrom to electrical signals indicative of the magnitude and direction of changes in an acoustic field. The omnidirectional acoustic sensor may include a length of optical fiber wrapped around the housing while the gradient sensors are mounted inside the housing. The housing perferably has a volume that is adjustable for controlling the buoyancy thereof. Each gradient sensor preferably comprises a pair of mandrels formed to enclose chambers. Optical fiber coils are formed on the mandrels. Both the chambers are filled with a fluid and placed in fluid communication through a tube that defines a sensing axis between the mandrels such that acceleration of the housing along the first sensing axis causes a fluid pressure differential on the first and second optical fiber coils.
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Citations
20 Claims
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1. A fiber optic acoustic sensing system, comprising:
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a housing formed generally as an elongate hollow cylinder;
an omnidirectional sensor comprising;a sensing fiber wrapped around the housing and exposed to an acoustic field; a reference fiber isolated from the acoustic field; means for introducing optical signals into the sensing and reference fibers; means for combining optical signals output from the sensing and reference fibers to form an interference pattern that is indicative of changes in the acoustic field; a first unequal path length fiber optic interferometer, comprising; a first mandrel affixed inside the housing the formed to enclose a first chamber; a first optical fiber wrapped around the first mandrel to form a first optical fiber coil; a second mandrel placed in the housing and formed to enclose a second chamber; a second optical fiber wrapped around the second mandrel to form a second optical fiber coil; a fluid filling both the first and second chambers; means for placing the first and second chambers in fluid communication and defining a sensing axis between the first and second mandrels such that acceleration of the housing along the first sensing axis causes a fluid pressure differential on the first and second optical fiber coils; means for introducing optical signals into the first and second optical fibers; means for combining optical signals output from the first and second optical fibers to produce a signal indicative of the component of the acoustic field along the first sensing axis; and a second unequal path length fiber optic interferometer affixed inside the housing nd formed essentially identical to the first unequal path length fiber optic interferometer but having a second sensing axis perpendicular to the first sensing axis. - View Dependent Claims (2, 3, 4)
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5. A fiber optic acoustic sensing system, comprising:
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a first optical fiber; an optical signal source arranged to introduce optical signals into the first optical fiber; a first mismatched path length fiber optic interferometer optically coupled to the first optical fiber and configured to form an omnidirectional acoustic sensor; a second mismatched path length fiber optic interferometer optically coupled to the first optical fiber and configured to form a first hydrophone having a first sensing axis; a third mismatched path length fiber optic interferometer optically coupled to the first optical fiber and configured to form a second hydrophone for producing optical signals indicative of having a second sensing axis that is perpendicular to the first sensing axis; and a detector optically coupled to the omnidirectional acoustic sensor and to the first and second hydrophones for converting optical signals output therefrom to electrical signals indicative of the magnitude and direction of changes in an acoustic field. - View Dependent Claims (6, 7, 8, 9)
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10. A method for forming a fiber optic acoustic sensing system, comprising the steps of:
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forming a housing generally as an elongate hollow cylinder; forming an omnidirectional sensor by a process that comprises the steps of; wrapping a sensing fiber around the housing; exposing the sensing fiber to an acoustic field; isolating a reference fiber from the acoustic field; introducing optical signals into the sensing and reference fibers; combining optical signals output from the sensing and reference fibers to form an interference pattern that is indicative of changes in the acoustic field; forming a first unequal path length fiber optic interferometer by a process that comprises the steps of; affixing a first mandrel inside the housing; forming the first mandrel to enclose a first chamber; wrapping a first optical fiber around the first mandrel to form a first optical fiber coil; affixing a second mandrel inside the housing; forming the second mandrel formed to enclose a second chamber; wrapping a second optical fiber around the second mandrel to form a second optical fiber coil; filling both the first and second chambers with a fluid; placing the first and second chambers in fluid communication and defining a sensing axis between the first and second mandrels such that acceleration of the housing along the first sensing axis causes a fluid pressure differential on the first and second optical fiber coils; introducing optical signals into the first and second optical fibers; combining optical signals output from the first and second optical fibers to produce a signal indicative of the component of the acoustic field along the first sensing axis; and affixing a second unequal path length fiber optic interferometer inside the housing to define a second sensing axis perpendicular to the first sensing axis. - View Dependent Claims (11, 12, 13)
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14. A method for forming a fiber optic acoustic sensing system, comprising the step of:
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providing a first optical fiber; arranging an optical signal source to introduce optical signals into the first optical fiber; optically coupling a first mismatched path length fiber optic interferometer to the first optical fiber; configuring the first mismatched path length fiber optic interferometer to form a first omnidirectional acoustic sensor; optically coupling a second mismatched path length fiber optic interferometer to the first optical fiber; configuring the second mismatched path length fiber optic interferometer to form a first hydrophone having a first sensing axis; optically coupling a third mismatched path length fiber optic interferometer to the first optical fiber; configuring the third mismatched path length fiber optic interferometer to form a second hydrophone having a second sensing axis that is perpendicular to the first sensing axis; and optically coupling a detector to the omnidirectional acoustic sensor and to the first and second hydrophones for converting optical signals output therefrom to electrical signals indicative of the magnitude and direction of changes in an acoustic field. - View Dependent Claims (15, 16, 17, 18)
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19. A fiber optic acoustic sensing system, comprising:
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a first optical fiber; an optical signal source arranged to introduce optical signals into the first optical fiber; a first mismatched path length fiber optic interferometer optically coupled to the first optical fiber to receive optical signals therefrom and configured to form an omnidirectional acoustic sensor; a second mismatched path length fiber optic interferometer optically coupled to the first optical fiber to receive optical signals therefrom and configured to form a first gradient hydrophone having a first sensing axis; a third mismatched path length fiber optic interferometer optically coupled to the first optical fiber to receive optical signals therefrom and configured to form a second gradient hydrophone having a second sensing axis that is perpendicular to the first sensing axis; and a detector optically coupled to the omnidirectional acoustic sensor and to the first and second gradient hydrophones for converting optical signals output therefrom to electrical signals indicative of the magnitude and direction of changes in an acoustic field. - View Dependent Claims (20)
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Specification