Fiber optical accelerometer
View Patent ↗A fiber optical accelerometer comprising a base structure, a first seismic mass movably coupled to the base structure through a first hinge element, a second seismic mass movably coupled to the base structure through a second hinge element, an optical fiber coupled to the first and second seismic masses at first and second attachment joints, respectively, to subject the optical fiber to varying strain by displacement of the first and second seismic masses about the first and second hinge structures, respectively.
1. A fiber optical accelerometer comprising:
a base structure,
a first seismic mass movably coupled to the base structure through a first hinge element,
a second seismic mass movably coupled to the base structure through a second hinge element,
an optical fibre coupled to the first and second seismic masses at first and second attachment joints, respectively, to subject the optical fiber to varying strain by displacement of the first and second seismic masses about the first and second hinge structures, respectively,
wherein the first and second hinge elements are arranged in a common horizontal plane, and
wherein a center of gravity of the first seismic mass and a center of gravity of the second seismic mass are arranged in the common horizontal plane.
2. A fiber optical accelerometer according to claim 1 , wherein the first and second seismic masses, the first and second hinge elements and the base structure are formed in the same material.
3. A fiber optical accelerometer according to claim 2 , wherein the material comprises a metallic material selected from a group of Wolfram, stainless steel, brass, copper, titanium, silicon.
4. A fiber optical accelerometer according to claim 2 , wherein the first and second seismic masses, the first and second hinge elements and the base structure are fabricated from a single solid object by moulding or machining.
5. A fiber optical accelerometer according to claim 4 , wherein the first and second hinge elements comprise respective incisions or pinches in the first and second seismic masses adjacent to the base structure.
6. A fiber optical accelerometer according to claim 1 , comprising:
first lever extending between the first seismic mass and the first attachment joint on the optical fiber,
a second lever extending between the second seismic mass and the second attachment joint on the optical fiber.
7. A fiber optical accelerometer according to claim 1 , wherein a distance between the first attachment joint on the optical fiber and the first hinge element is at least two times larger than a distance between a center of gravity of the first seismic mass and the first hinge element.
8. A fiber optical accelerometer according to claim 1 , wherein the first and second seismic masses, the first and second hinge elements and the base structure are symmetrically arranged about a central vertical plane.
9. A fiber optical accelerometer according to claim 1 , wherein the first and second seismic masses are arranged above a common horizontal plane of the first and second hinge elements toward the optical fiber and the base structure is arranged below the common horizontal plane.
10. A fiber optical accelerometer according to claim 1 , wherein a maximum dimension of the base structure in a horizontal plane lies between 4 mm and 40 mm, preferably between 8 mm and 20 mm.
11. A fiber optical accelerometer according to claim 1 , having a maximum dimension along a vertical axis between 8 mm and 80 mm.
12. A fiber optical accelerometer according to claim 1 , having a mass between 2 gram and 400 gram such as between 5 gram and 100 gram.
13. A fiber optical accelerometer according to claim 1 , wherein a strained section of the optical fibre extending between the first and second attachment joints comprises a Fibre Bragg grating (FBG).
14. A fiber optical accelerometer according to claim 1 , comprising a transducer housing enclosing and sealing the first and second seismic masses and the first and second hinge elements against an external environment.
15. A method of detecting acceleration of a remote vibratory structure with a fiber optic accelerometer, comprising:
attaching a fiber optic accelerometer according to claim 1 to the vibratory structure,
optically coupling an optical transmission fiber to the optical fiber of the fiber optical accelerometer,
applying a broadband light source to the optical transmission fiber,
detecting a wavelength of reflected light from the fiber optical accelerometer, and
determining an acceleration of the fiber optical accelerometer by demodulating the wavelength of the reflected light.
16. The method of claim 15 , wherein the broadband light source includes an infra-red light source.