Optics: measuring and testing – By light interference – Using fiber or waveguide interferometer
Reexamination Certificate
2001-03-30
2003-09-30
Pyo, Kevin (Department: 2878)
Optics: measuring and testing
By light interference
Using fiber or waveguide interferometer
C073S514070, C073S024050
Reexamination Certificate
active
06628400
ABSTRACT:
BACKGROUND
The present invention relates to accelerometers that including a fiber optic arrangement for signal detection. More particularly, this invention pertains to such a device that includes a centrally-supported flexural disk.
In the prior art, accelerometers of the above-mentioned type have featured flexural disks of integral design formed of solid metal, plastic or, for example, polycarbonate with various filling materials. Various factors, including material modulus, stiffness and weight are adjusted to vary the resonance and scale factor (degree of bending) of the sensing disk. Coils of optical fiber are fixed to the opposed surfaces of the responsive element. Each coil forms an arm of an interferometer with their relative lengths of the two optical paths varying as a function of the degree of deflection of the element. Devices of this type are taught, for example, by U.S. Pat. No. 5,883,308 of Samuel N. Fersht entitled “Fiber Optic Twist Ring Accelerometer”, property of the Assignee herein.
Experience has shown that the well-known tradeoff between bandwidth and gain in a device of the type described above has limited the possibility of increasing the figure of merit (product of bandwidth and gain) in an accelerometer of the above-identified type. Stiffening or softening the solid flexural disk tends to affect bandwidth and gain (or sensitivity) in opposite senses, leaving the important figure of merit measure of the device either static or decreased.
SUMMARY OF THE INVENTION
The preceding and other disadvantages of the prior art are addressed by the present invention that provides, in a first aspect, an accelerometer with fiber optic sensing. Such accelerometer includes a disk having opposed surfaces. The disk is substantially-horizontally supported with a case. A first coil of optical fiber is fixed to the top surface of the disk and a second coil is fixed to the bottom surface of the disk. A substantially-planar honeycomb structure is intermediate the top and bottom surfaces of the disk.
In a second aspect, the invention provides an accelerometer that includes a substantially-planar disk that is horizontally-supported within a case. First and second coils of optical fiber are fixed to the opposed surfaces of the disk that form the legs of an interferometer. The disk includes a central portion and an outer portion with the outer portion being characterized by greater density than the central portion.
In a third aspect, the invention provides a method for increasing the figure of merit of an accelerometer including a centrally-mounted, substantially horizontal disk having opposed top and bottom surfaces within a case. Such method is accomplished by interposing a honeycomb structure between the top and bottom surfaces of the disk.
The foregoing and other features of this invention shall become further apparent from the detailed description that follows. Such description is accompanied by a set of drawing figures. Numerals of the figures, corresponding to those of the written description, point to the features of the invention with like numerals referring to like features throughout both the drawing figures and the written text.
REFERENCES:
patent: 4994668 (1991-02-01), Lagakos et al.
patent: 6384919 (2002-05-01), Fersht et al.
Goldner Eric L.
Tweedy Michael J.
Kramsky Elliott N.
Litton Systems Inc.
Pyo Kevin
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