Optical device for strain detection, method for the measurement of strain by means of the said device and their application to scales
First Claim
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1. An optical device for strain detection, which device comprises:
- at least one optical fiber (1) disposed in such a manner as to form a network (2), said at least one fiber being disposed in such a manner as to form a regular meshed network, each mesh of the network being delimited by two weft lines (i) and two warp lines (j) which are successive and which are respectively constituted by said at least one fiber spaced according to a specified pitch, the spacing pitch of the warp and weft lines being equal to k λ
/2 where k is an integer equal to or greater than 1 and where λ
represents the critical period of the mechanical perturbation capable of coupling the groups of adjacent propagation modes, λ
=2π
a/(2Δ
)1/2 where;
a is the radius of the core of the fiber, 2Δ
=(1-no2 /nc2), no being the refractive index of the sheath of the optical fiber and nc the refractive index of the core of the fiber respectively,means for emitting light (E) which are disposed at one end, referred to as the entrance end of said at least one fiber and means for receiving light (R) which are disposed at the other end, referred to as the exit end, of said at a least one fiber, said receiving means (R) being capable of supplying information relating to the luminous intensity transmitted by said at least one fiber of the network and a corresponding measurement of the strain.
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Abstract
An optical device and method for strain detection. The device is provided with at least one optical fiber arranged so as to form a network. A light emitting device is arranged at one end of the fiber and a receiver is arranged at the other end, enabling the generation of information relative to the light intensity transmitted by the fiber or fibers in the presence of strain, and a measurement corresponding to the strain.
86 Citations
13 Claims
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1. An optical device for strain detection, which device comprises:
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at least one optical fiber (1) disposed in such a manner as to form a network (2), said at least one fiber being disposed in such a manner as to form a regular meshed network, each mesh of the network being delimited by two weft lines (i) and two warp lines (j) which are successive and which are respectively constituted by said at least one fiber spaced according to a specified pitch, the spacing pitch of the warp and weft lines being equal to k λ
/2 where k is an integer equal to or greater than 1 and where λ
represents the critical period of the mechanical perturbation capable of coupling the groups of adjacent propagation modes, λ
=2π
a/(2Δ
)1/2 where;
a is the radius of the core of the fiber, 2Δ
=(1-no2 /nc2), no being the refractive index of the sheath of the optical fiber and nc the refractive index of the core of the fiber respectively,means for emitting light (E) which are disposed at one end, referred to as the entrance end of said at least one fiber and means for receiving light (R) which are disposed at the other end, referred to as the exit end, of said at a least one fiber, said receiving means (R) being capable of supplying information relating to the luminous intensity transmitted by said at least one fiber of the network and a corresponding measurement of the strain. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for stating the strains applied at a plurality of points of a test area comprising:
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(a) disposing a network (2) of at least one optical fiber contained in an optical device for strain detection on the test area, (b) recording in memory for each point of coordinates i, j a zero condition in the absence of a test load applied to the test area and the network (2), (c) applying the test load to the area and the network and memorizing the values of relative strain Fi and Rj supplied by and a detector associated with each optical fiber of order i j in the first and second directions respectively, (d) determining the relative strain Pij applied at each point of coordinates i, j of intersection of the fibers of order i and of order j of the first and second direction respectively of the network in accordance with the equation;
##EQU9## where ##EQU10## and where ##EQU11## m is the total number of lines in the first direction, and n is the total number of lines in the second direction. - View Dependent Claims (12, 13)
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Specification