Northrop Grumman Systems Corporation

Litton Systems, Inc.

Northrop Grumman Guidance and Electronic Company, Inc.

Michael J Tweedy

Eric Lee Goldner

Samuel N Fersht

Thomas McLean

James L Arroyo

Shen-Hui L Wu

David Barnett Hall

Bruce A Danver

Patrick J Welton

Mayer Rud

Gregory M Nau

A fiber optic sensor includes a housing having first and second end plates with a sidewall extending therebetween with the sidewall having an inwardly facing groove. A flexural disk having a central passage therethrough has an outer edge portion mounted in the inwardly facing groove in the housing. The flexural disk has a stepped thickness that is thinner at the outer edge portion than at a region spaced apart from the housing. A first fiber optic coil is mounted on a first side of the flexural disk in the thicker region of the flexural disk, and a second optical fiber is mounted on a second side of the flexural disk opposite the first fiber optic coil. The first and second fiber optic coils are optically coupled together by a fiber optic coupler to form an interferometer that produces an output signal in response to axial acceleration of the flexural disk.

Low cost fiber optic velocity sensor for sonar applications

A system and method for measuring acceleration using a fiber optic accelerometer having a pair of fiber optic coils positioned around a deformable support structure. The support structure possesses a nominally cylindrical shape with the fiber optic coils being wound around opposite ends of the cylindrical support structure from each other. The support structure deforms from its nominally cylindrical shape to a conical shape in response to acceleration along a sensing axis. The changing shape of the support structure causes one of the fiber optic coils to expand while the other of the fiber optic coils contracts. The fiber optic coils are included in an interferometer such that acceleration along the sensing axis produces a phase difference between light signals propagating in the fiber optic coils resulting from their expansion and contraction.

Method and apparatus for measuring acceleration using a fiber optic accelerometer

A pair of fiber optic coils are mounted on opposite sides of a flexural disk and are arranged to form an interferometer that produces an output signal in response to acceleration of the flexural disk. The flexural disk is mounted in a housing having first and second end plates with a sidewall extending between them. A support member extends between the end plates and through a central passage in the flexural disk. A pair of compressive dampers is mounted in the housing between the flexural disk and the housing end plates. A shear damper mounted on the central support member exerts a radial force on an inner edge of the central passage in flexural disk to dampen vibrations of the flexural member and control the output signal amplitude over a selected frequency range.

High performance fiber optic accelerometer

An accelerometer of the type in which a disk is mounted upon a vertical post. The accelerometer may be employed as a hydrophone, for example, including a watertight case, and forming a neutrally buoyant structure or may be suitable for hull-mounting. The disk comprises a planar honeycombed structure. A solid, dense ring-like peripheral mass is fixed to the central honeycombed structure to form a composite apparatus. The honeycombed central structure contributes enhanced stiffness without a corresponding increase in weight when compared with disks of solid fabrication while the peripheral concentration of mass increases radius of gyration sufficiently to offset gain dimunition due to increased stiffness so that an increase in figure of merit is obtained.

High sensitivity, high bandwidth accelerometer with fiber optic sensing

A fiber optic displacement sensor includes a flexural disk assembly affixed to a mounting post that extends from a support base that is enclosed by a housing. Spiral wound optical fiber coils are mounted on opposite sides of the flexural disk with optical fiber leads extending from both the inner and outer diameters of the optical fiber coils and being optically coupled together to form an interferometer. An inertia ring connected to the periphery of the flexural disk has a plurality of peripheral slots therein for routing the optical fiber leads from the optical fiber coils to other components in the housing. The slots in the inertia ring are arranged to allow differing lengths of fiber to be wound circumferentially in different depth slots to accommodate mismatches in optical fiber lead lengths.

Fiber optic displacement sensor

A displacement sensor and an acceleration sensor are mounted to a common support member. The displacement sensor comprises a first circular flexural disk having a natural frequency less than the frequency range of the acoustic waves of interest. Spiral-wound optical fiber coils are mounted to opposite sides of the first flexural disk. The acceleration sensor comprises a second flexural disk having a natural frequency greater than the frequency range of the acoustic waves. Spiral-wound optical fiber coils are mounted to opposite sides of the second flexural disk. A fiber optic interferometer provides an output signal that is a combination of signals output from the displacement sensor and the acceleration sensor. The displacement sensor includes an inertia ring mounted to an edge of the first flexural disk to keep it nearly stationary when an acoustic wave in the selected frequency range is incident upon the housing. The flexural disks include upper and lower rings spaced apart from the support post with portions of the disks between the rings and the support post defining hinges at which the flexural disk flex in response to acceleration of the support member along its longitudinal axis. The surfaces of the first and second flexural disks preferably include grooves extending between the upper rings and the outer edges of the flexural disks. The grooves are arranged to allow lengths of optical fiber adjacent the rings to pass under the optical fiber coils that are formed on the surfaces of the flexural disks.

Fiber optic acoustic sensor with specifically selected flexural disks

A fiber optic sensor comprises a flexural disk having a pair of fiber optic coils mounted on opposite sides thereof and connected together to form an interferometer that produces an output signal in response to acceleration of the flexural disk. The flexural disk is mounted in a housing having first and second end plates with a sidewall extending between them. The sidewall is formed to have an inwardly facing groove in which an outer edge portion of the flexural disk is mounted. A support member extends between oppositely facing portions of the first and second end plates and through a central passage in the flexural disk. A damping member is mounted on the central support member and arranged to exert a radial force on an inner edge of the central passage in flexural disk to dampen vibrations of the flexural disk and control the sensor output signal amplitude over a selected frequency band in order to maximize dynamic range.

Shear damped fiber optic sensor

Interconnection mechanisms for a laser gyroscope assembly ( ) enable it to be rapidly and non-harmfully assembled and disassembled prior to a more durable interconnection, to facilitate repair and rework. The assembly includes a fiber optic spool ( ), an inner shield ( ) and an outer shield ( ), which are formed of a stress-annealed magnetic and generally malleable material. The outer shield comprises upper and lower portions or parts ( ) whose first and second end segments ( ) respectively terminate the portions. Segment ( ) has angled intersecting conical surfaces ( ) which engage surfaces ( ) on segment ( ). Stops ( ) are formed respectively on the ends of the segments so that a distal end ( ) contacts an interior ledge surface ( ) of outer shield ( ), thereby to limit the mutual engagement and to center the segment configuration interfit. The position and location of the stop allows the intersecting edges of surface ( ) of outer shield ( ) to precisely contact reverse taper segment ( ) of surface ( ) at a point beneath intersection ( ) to ensure positive retention and mechanical locking of the upper and lower portions of outer shield ( ). A plurality of notches ( ) are positioned evenly about the periphery of the lower portion of the outer shield at its intersection of the upper portion. Tangs ( ) of a tool ( ) are inserted in seriatim within the spaces for gradual disassembly of the upper and lower outer shield portions without harm thereto. Inner shield ( ) includes a cover ( ) having two pairs of projections ( ) which can snap together, and a top annular segment ( ) which is engageable with a centering projection ( ) on end ( ) of the spool. When the cover is secured to the spool, the top annular segment is flexed, but not deformed, to provide a spring bias and positive retention and, consequently, a solid and chatter-resistant engagement in a robust mechanical connection even under severe dynamic environments.

Snap fit magnetic shields for laser gyroscopes

A temporary latchable or clasping interengageable interconnection mechanism is provided for an optical gyroscope assembly (,) to enable it to be rapidly and non-harmfully assembled and disassembled prior to a more durable interconnection, to facilitate repair and rework. The assembly includes a fiber optic spool (,), an inner shield (,) and an outer shield (,), which are formed of a stress-annealed magnetically permeable, and generally malleable material. Should the assembly be dropped, bent or dented, their magnetic shielding properties will be compromised, which is the harm to be avoided by the temporary interconnection. Accordingly, the fiber optic spool (,) and the inner shield (,) are temporarily interconnectable with the outer shield (,) and its spacer ring (,) by interengageable elements having the ability to latch or clasp the shield and the spacer ring together to prevent or, at a minimum, resist disassembly therebetween. The temporary interconnection includes grooves (,) respectively in a tubular wall (,) of the spool and in a corresponding element in the spacer ring. An O-ring (,) is positioned in the grooves, and provides easy assembly and disassembly. The O-ring also serves to center the inner shield within the outer shield to establish a concentric relationship between the two, to avoid a radial metal-to-metal contact therebetween, and to mitigate against chattering which otherwise would affect the fidelity of the gyroscope output.

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Simi Valley, CA, United States of America

Michael J Tweedy