JP3030358B2 - Optical fiber magnetic sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical fiber magnetic sensor.

[0002]

2. Description of the Related Art An interference type optical fiber sensor is a sensor for detecting physical quantities such as magnetism and acceleration. (1) Reference 1: “Frank Bucholtz, K. et al.
P. Koo, George H Sigel, Jr. ,
and Anthony Dutchridge, "Op
timing of the Fiber / M
etallicGlass Bond in Five
r-Optical Magnetic Sensors ",
Journal of Lightwave Tech
nology, Vol. LT-3. No. 4, Augu
st 1985, pp814-817 "(2) Reference 2:" KP Koo, Frank Buc
Holtz, A .; Dandridge and A.
B. Tveten, "Stableity of F.
iber-Optical Magnetometer ”,
IEEE Transactions on Magn
etics, Vol. MAG-22, No. 3, May
1986, pp 141-144] Conventionally, as a sensor of this type, the Fi
g. One is shown in FIG. That is, after injecting light output from a laser light source into an optical fiber, the light is split into two by an optical coupler, one of which is used as sensing light, the other is used as reference light, and the sensing fiber through which the sensing light passes is a magnetostrictive material [the above-mentioned document. Then, an amorphous magnetostrictive material (M
et al. Glass) is used].

When the magnetic field applied to the magnetostrictive material changes, the magnetostrictive material is distorted, so that the sensing fiber expands and contracts, and the phase of the sensing light passing through the sensing fiber changes. When the sensing light and the reference light that have passed through the sensing fiber interfere with each other and are subjected to O / E conversion, the phase of the O / E output also changes due to the magnetic field, and this is demodulated to detect the magnetic field.

[0004] A method for demodulating a magnetic signal is disclosed in FIG. 2 is shown. According to this method, a magnetostrictive material is contained in a solenoid coil that generates an AC bias magnetic field, and a signal included in the AC bias magnetic field component of the O / E output is detected. Noise due to vibration and the like is reduced.

Further, by applying a feedback control system for superimposing a current for canceling the magnetic signal on the solenoid coil,
The linearity degradation due to the hysteresis of the magnetostrictive material is reduced.

[0006]

In the above-mentioned conventional optical fiber magnetic sensor, low noise is realized by shifting a signal to a high frequency region where noise generated by temperature fluctuation is small. However, in an environment where temperature fluctuation, vibration, and the like are large, noise also becomes large and becomes a level that cannot be ignored.

[0007] It is an object of the present invention to provide an optical fiber magnetic sensor capable of eliminating the above-mentioned problems and suppressing noise even in an environment having large temperature fluctuations and vibrations.

[0008]

According to the present invention, there is provided an optical fiber magnetic sensor for applying an AC bias magnetic field to a magnetostrictive material, wherein the magnetic means applies at least a bias magnetic field. A magnetic sensing portion including a magnetostrictive material having an arm arranged so that a bias magnetic field is applied in opposite directions; and a pair of optical fibers individually adhered to the magnetostrictive material, and passing through the arm. Both of the two lights are arranged so as to cause a phase change in opposite directions due to the AC bias magnetic field.

As described above, since the fiber lengths of the optical fiber coil A and the optical fiber coil B are substantially uniform, the phase changes due to temperature fluctuations occurring in the two optical fiber coils A and B are in the same direction in the same amount. Therefore, by detecting the phase difference between the light passing through the two optical fiber coils A and B, it is possible to suppress a phase change due to a temperature change.

Further, since the two optical couplers and the two optical fiber coils A and B constituting the interferometer are integrally formed by bonding or molding to a magnetostrictive material, noise due to vibration can be suppressed. [2] In the optical fiber magnetic sensor according to the above [1], a magnetic circuit closed with a magnetostrictive material or a magnetostrictive material and a ferromagnetic material is formed as the magnetic sensing unit, and an AC bias magnetic field is applied by a coil, so that the magnetostrictive material is reciprocal. The structure is such that an optical fiber is attached to a portion where an AC bias magnetic field is applied in a direction in which the optical fiber is applied.

As described above, in addition to the effect of the above [1], since the structure is such that the AC bias magnetic field is generated in the closed magnetic circuit, the AC bias magnetic field can be generated with a small current. In addition, since the ferromagnetic material gap is provided in the magnetic sensing part, the ferromagnetic material part is magnetically coupled and not mechanically coupled. A magnetic signal can be detected.

[3] The optical fiber magnetic sensor according to the above [1] or [2], wherein a laminated amorphous magnetostrictive material is used as a magnetostrictive material of the magnetic sensing portion. As described above, in addition to the effect of the above [1] or [2], since the sheet-like amorphous magnetostrictive material is laminated and its elasticity is strengthened, even if the sensing fiber is wound in a coil shape and lengthened, The elasticity of the amorphous magnetostrictive material can be made stronger than that of the optical fiber coil.

Further, since the portion where the optical fiber and the amorphous magnetostrictive material are bonded is axisymmetric with respect to the direction in which the optical fiber is distorted, the optical fiber is distorted in the axial direction without bending. Therefore, it is possible to realize a small and highly sensitive optical fiber magnetic sensor. [4] The optical fiber magnetic sensor according to [2] or [3], wherein the magnetic sensing unit is provided with a feedback control system for generating a magnetic field for canceling a magnetic signal.

As described above, in addition to the effect of the above [2] or [3], by providing a feedback control system for generating a magnetic field for canceling a magnetic signal by a solenoid coil, linearity deterioration due to hysteresis of the magnetostrictive material is prevented. Can be reduced. [5] The optical fiber magnetic sensor according to [2], [3] or [4], wherein the orthogonal component of the magnetic signal is frequency-division multiplexed.

As described above, in addition to the effects of [2], [3], or [4], since the orthogonal three components of the magnetic signal are frequency-division multiplexed, the size and cost are reduced. With such a configuration, the direction of the magnetic signal can also be detected.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall configuration diagram of an optical fiber magnetic sensor according to a first embodiment of the present invention.
As shown in FIG.
The optical fiber coil A and the optical fiber coil B are bonded to the sides, respectively. A ferromagnetic material 2 is attached to a U-shaped magnetostrictive material 1 to form a ring, and a toroidal coil 3 is wound to form a magnetic circuit.

A gap is provided in the ferromagnetic material 2 so that the distortion of the U-shaped magnetostrictive material 1 is not hindered. The fiber lengths of the optical fiber coil A and the optical fiber coil B are made substantially uniform. Optical couplers 5 and 6 are connected to both ends of the optical fiber coils A and B, respectively, and molded with a molding material 4 so as to be integrated with the U-shaped magnetostrictive material 1. One optical coupler 5 is the output of the laser light source 11 and the other optical coupler 6 is
/ E converter 12 is connected to the input. The output of the O / E converter 12 is connected to a passive homodyne demodulator 13, and the output of the passive homodyne demodulator 13 is connected to an AM demodulator 14. The output of the modulation signal generator 15 used in the passive homodyne demodulation processing is connected to the laser light source 11 and the passive homodyne demodulator 13 and the signal generator 1 for the AC bias magnetic field is connected.
6 is connected to the toroidal coil 3 and the AM demodulator 14. Thus, the magnetic sensing unit 10 is configured.

The operation of the thus constructed optical fiber magnetic sensor will be described. FIG. 2 shows an optical fiber coil,
FIG. 3 is an explanatory diagram of an operation principle of a magnetic sensing unit 10 including an optical coupler, a magnetostrictive material, a ferromagnetic material, and a toroidal coil. As shown in FIG. 2, a magnetic circuit closed by a U-shaped magnetostrictive material 1, a ferromagnetic material 2, and a toroidal coil is formed. When an alternating current is applied to the toroidal coil 3, the parallelism of the U-shaped magnetostrictive material 1 is reduced. On two sides (region A and region B), AC bias magnetic fields are generated in opposite directions. Here, the distortion amounts ξ _A and の of the regions A and B when a magnetic signal is applied
_{B is, ξ A = C (H s} -H AC cosω m t) 2 ξ B = C (H s + H AC cosω m t) is expressed as ^2.

Here, H _s is a magnetic signal, H _AC and ω _m are amplitude and angular frequency of an AC bias magnetic field, and C is an amount which can be generally treated as a constant determined by the magnetostriction characteristics of the magnetostrictive material. The optical fiber coils A and B are also distorted in proportion to the distortion of the magnetostrictive material. The light output from the laser light source 11 (see FIG. 1) is split into two by an optical coupler 5 (see FIG. 1), one of which passes through an optical fiber coil A and the other passes through an optical fiber coil B. The phase of the light passing through the two optical fiber coils A and B changes due to the distortion of the optical fiber. The light that has passed through the two optical fiber coils A and B is caused to interfere with the other optical coupler 6 (see FIG. 1) and subjected to O / E conversion, and the phase of the output has passed through the two optical fiber coils A and B. A phase difference Δθ of light appears.

Δθ = a (ξ _B -ξ _A ) = 4aCH _s H _AC cos ω _mt Here, a is a constant determined by the fiber length of the portion of the optical fiber coils A and B adhered to the magnetostrictive material. The phase difference Δθ of this light is demodulated by passive homodyne processing,
Detecting a magnetic signal H _s and demodulates. As described above, according to the first embodiment: (1) Since the fiber lengths of the optical fiber coil A and the optical fiber coil B are substantially uniform, the phase change due to temperature fluctuation occurring in the two optical fiber coils A and B In the same direction.

Therefore, the two optical fiber coils A,
By detecting the phase difference of the light passing through B, it is possible to suppress a phase change due to a temperature change. (2) Since the two optical couplers constituting the interferometer and the two optical fiber coils A and B are integrally formed by bonding or molding a magnetostrictive material, noise due to vibration can be suppressed.

(3) Since a toroidal coil is used to generate an AC bias magnetic field, an AC bias magnetic field can be generated with a smaller current than a finite length solenoid coil. (4) Since a gap is provided in the ferromagnetic material in the magnetic sensing unit, the ferromagnetic material is magnetically coupled and not mechanically coupled in the ferromagnetic material, so that the distortion of the magnetostrictive material is not hindered. A magnetic signal can be detected with high sensitivity.

Next, a second embodiment of the present invention will be described. FIG. 3 is a structural diagram of a magnetic sensing unit according to a second embodiment of the present invention. Parts other than the magnetic sensing unit are the same as in the first embodiment, and are omitted here. The optical fiber coil A is sandwiched between the laminated amorphous magnetostrictive materials A1 and A2, which are formed by laminating sheet-like amorphous magnetostrictive materials, and the optical fiber coil B is adhered between the laminated amorphous magnetostrictive materials B1 and B2. The portion where the optical fiber coil and the laminated amorphous magnetostrictive material are bonded is axially symmetric with respect to the direction in which the laminated amorphous magnetostrictive material is distorted (for example, the same thickness of the laminated amorphous magnetostrictive material is applied to both sides of the single-layer wound optical fiber coil). Glues magnetostrictive material).

Laminated amorphous magnetostrictive materials A1, A2, B
1 and B2 are arranged in parallel. A ferromagnetic material 22 is attached to both ends of the laminated amorphous magnetostrictive materials A1 and B1 and A2 and B2 to form an annular shape, and two toroidal coils 23 are wound to form two magnetic circuits. Ferromagnetic material 22 constituting magnetic circuit
A gap is provided on one side (right side in FIG. 3) so as not to hinder the distortion of the magnetostrictive material.

The laminated amorphous magnetostrictive materials A1, A
2 and B1, B2, a horseshoe-shaped guide 27 is provided on both sides, and the guide 27 and the laminated amorphous magnetostrictive materials A1, A
A track-shaped peripheral surface is formed by the upper surface of the lower half of B2, B1 and B2, and the optical fiber coils A and B are wound along the track-shaped peripheral surface. Optical couplers 25 and 26 are connected to both ends of the optical fiber coils A and B, respectively.
Molding is performed so as to be integrated with the laminated amorphous magnetostrictive materials A1, A2, B1, and B2.

The laminated amorphous magnetostrictive materials A1, A2, B
Toroidal coils 23 wound around two magnetic circuits are connected in series in such a direction that magnetic fields in the same direction are generated in 1 and B2 and in the opposite directions in A1 and B1. The operation of the optical fiber magnetic sensor thus configured will be described. When an alternating current is passed through the toroidal coil 23,
An alternating bias magnetic field is generated in the same direction in the laminated amorphous magnetostrictive materials A1 and A2, in the same direction in B1 and B2, and in the opposite direction in A1 and B1. Distortion amount xi] _A of the laminated amorphous magnetostrictive material A1 and A2 when the magnetic signal is applied here, the strain amount xi] _B of the laminated amorphous magnetostrictive material B1 and _{B2, ξ A = C (H s} -H AC cosω m t) ^{_{2 ξ B = C (H s}} + H AC cosω m t) is expressed as ^2.

Here, H _s is a magnetic signal, H _AC and ω _m are amplitude and angular frequency of an AC bias magnetic field generated by the toroidal coil 23, and C is an amount which can be generally treated as a constant determined by the magnetostrictive characteristics of the magnetostrictive material. The optical fiber coils A and B are also distorted in proportion to the distortion of the magnetostrictive material. The light output from the laser light source is split into two by an optical coupler 25, one of which passes through an optical fiber coil A and the other through an optical fiber coil B. The phase of the light passing through the two optical fiber coils A and B changes due to the distortion of the optical fiber. When the light that has passed through the two optical fiber coils A and B is caused to interfere with the other optical coupler 26 and O / E converted, the phase of the light that has passed through the two optical fiber coils A and B has a phase difference Δ
θ appears.

Δθ = a (ξ _B -ξ _A ) = 4aCH _s H _AC cos ω _mt where a is a constant determined by the fiber length of the portion of the optical fiber coils A and B adhered to the magnetostrictive material. The phase difference Δθ of this light is demodulated by passive homodyne processing,
Detecting a magnetic signal H _s and demodulates. As described above, according to the second embodiment, in addition to the effect of the first embodiment, since the elasticity of the sheet-like amorphous magnetostrictive material is increased by laminating the sheet-like amorphous magnetostrictive material, the sensing fiber is wound in a coil shape to be long. Even in this case, the elasticity of the amorphous magnetostrictive material can be made stronger than that of the optical fiber coil. Further, since the portion where the optical fiber and the amorphous magnetostrictive material are bonded is axially symmetric with respect to the direction in which the optical fiber is distorted, the optical fiber is distorted in the axial direction without bending.

Therefore, it is possible to realize a small and highly sensitive optical fiber magnetic sensor. Next, a third embodiment of the present invention will be described. FIG. 4 is an overall configuration diagram of an optical fiber magnetic sensor according to a third embodiment of the present invention. The first
The same parts as those of the embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, in addition to the configuration of the first embodiment, the solenoid coil 31 is wound so that a magnetic field of the same strength is applied to the region A (see FIG. 2) and the region B (see FIG. 2) of the magnetic circuit. , The feedback control signal generator 32 is connected to the output of the AM demodulator 14, and the output of the feedback control signal generator 32 is connected to the solenoid coil 31. The operation of the optical fiber magnetic sensor thus configured will be described.

A closed magnetic circuit is formed by a U-shaped magnetostrictive material, a ferromagnetic material, and a toroidal coil. When an alternating current is applied to the toroidal coil 3, the parallel 2
On the sides (region A and region B), an AC bias magnetic field is generated in opposite directions. Here, the strain amount xi] _A and xi] _B in regions A and B when the magnetic signal is applied _{is, ξ A = C (H s} + H FB -H AC cosω m t) 2 ξ B = C (H s + H _FB + H _AC cos ω _mt ) ² .

Here, H _s is a magnetic signal, H _FB is a feedback control magnetic field generated by the solenoid coil 31, H _AC and ω _m are the amplitude and angular frequency of an AC bias magnetic field generated by the toroidal coil, and C is the magnetostrictive material. This is an amount that can be generally treated as a constant determined by the magnetostriction characteristics. The optical fiber coils A and B are also distorted in proportion to the distortion of the magnetostrictive material. The light output from the laser light source 11 is divided into two by the optical coupler 5, one of which passes through the optical fiber coil A and the other passes through the optical fiber coil B. The phase of the light passing through the two optical fiber coils A and B changes due to the distortion of the optical fiber. The light that has passed through the two optical fiber coils A and B is caused to interfere by the other optical coupler 6 and is subjected to O / E conversion.
Phase difference Δθ of light passing through two optical fiber coils A and B
Appears.

Δθ = a (ξ _B -ξ _A ) = 4aC (H _s +
H _FB ) H _AC cos ω _mt Here, a is a constant determined by the fiber length of the portion of the optical fiber coils A and B adhered to the magnetostrictive material. The phase difference Δθ of this light is demodulated by passive homodyne processing,
Detecting a magnetic signal by demodulating (H _s + H _FB). The current for the feedback control signal generator 32 (H _s + H _FB) generates the H _FB which becomes constant is supplied to the solenoid coil 31, and outputs a signal proportional to simultaneously -H _FB.

As described above, according to the third embodiment, in addition to the effect of the first embodiment, by applying a feedback control system for generating a magnetic field for canceling a magnetic signal by a solenoid coil, a straight line due to hysteresis or the like of the magnetostrictive material is provided. Degradation of performance can be reduced. Next, a fourth embodiment of the present invention will be described. FIG. 5 is an overall configuration diagram of an optical fiber magnetic sensor according to a fourth embodiment of the present invention. The same portions as those in the first embodiment are denoted by the same reference numerals, and description of those portions is omitted.

In this embodiment, three magnetic circuits X, Y, and Z each having an optical fiber coil bonded thereto, as in the first embodiment,
Arrange them at right angles to each other. Three magnetic circuits X,
The optical fiber coils A and B bonded to Y and Z are continuous. The fiber lengths of the optical fiber coil A and the optical fiber coil B are made substantially uniform. Optical couplers 45 and 46 are connected to both ends of the optical fiber coils A and B, respectively, and molded so as to be integrated with the magnetostrictive material.

The laser light source 11, the O / E converter 12, the passive homodyne demodulator 13, and the modulation signal generator 15
The configuration is the same as that of the embodiment. Then, three AM demodulators, that is, an AM demodulator X41, an AM demodulator Y42, and an AM demodulator Z43 are connected to the output of the passive homodyne demodulator 13. Further, the outputs of the AC bias magnetic field signal generator 40 for generating AC bias magnetic fields having different frequencies (ωx, ωy, ωz) are connected to the three toroidal coils 44 and the AM demodulators 41, 42, 43, respectively.

The operation of the optical fiber magnetic sensor thus configured will be described. Laser light source 11, optical coupler 4
5, 46, an O / E converter 12, a passive homodyne demodulator 13, a modulation signal generator 15, and three magnetic circuits X, Y,
Each of Z operates similarly to the first embodiment. However, since the frequencies of the AC bias magnetic fields applied to the three magnetic circuits X, Y, and Z are different, the phase difference Δθ of the light output from the O / E converter 12 is Δθ = 4a _X CH _sX H _ACX cos ω _{m X} t + 4a _Y CH
_{sY H ACY cosω m Y t +} 4a Z CH sZ H ACZ cosω
_{m Z} t.

Here, H _sX , H _sY , and H _sZ are orthogonal components of a magnetic signal, and a _X , a _Y , and a _Z are constants determined by a fiber length of a portion of the optical fiber coils A and B adhered to the magnetostrictive material. ,
_{H AC X, H ACY, H} ACZ, ω m X, ω m Y, ω m Z is the amplitude and angular frequency of the AC bias magnetic field. The phase difference Δθ of the light is demodulated by passive homodyne processing, and the three frequency components are AM-demodulated to detect three orthogonal components of the magnetic signal.

As described above, according to the fourth embodiment, the first embodiment
In addition to the effects of the embodiment, since the orthogonal three components of the magnetic signal are configured to be frequency-division multiplexed, the direction of the magnetic signal can be detected with a small and low-cost configuration. The present invention further has the following usage modes. Although the U-shaped magnetostrictive material described in the first embodiment is used for the magnetic circuits of the third and fourth embodiments, the second embodiment has been described.
The laminated amorphous magnetostrictive material described in the embodiment may be used.

The case where the U-shaped magnetostrictive material and the ferromagnetic material are used for the magnetic circuit of the magnetic sensing unit and the case where the laminated amorphous magnetostrictive material and the ferromagnetic material are used have been described. A magnetic circuit may be formed by arranging a ferromagnetic material at both ends of a rod (or plate or sheet) magnetostrictive material, or by configuring all ferromagnetic material portions with the same magnetostrictive material.

Although the optical fiber coil is wound in the longitudinal direction of the magnetostrictive material and bonded, the optical fiber coil is wound around the magnetostrictive material (in the case of a cylindrical magnetostrictive material, in the circumferential direction) and bonded. May be used. Although the example in which the optical fiber coil is bonded to the magnetostrictive material has been described, the optical fiber may not be wound in a coil shape.

In the first to fourth embodiments, an example has been described in which the same type of magnetostrictive material is used to generate an AC bias magnetic field in opposite directions. However, a positive magnetostrictive material (which is distorted in the direction in which it expands when the magnetic field is increased). An AC bias magnetic field may be applied in the same direction with a structure in which an optical fiber serving as an arm of an interferometer is bonded to a negative magnetostrictive material (which becomes distorted in the direction of contraction when the magnetic field is increased).

Although an example in which a Mach-Zehnder interferometer using two optical couplers and an optical fiber coil is used as the interferometer of the magnetic sensing unit has been described, another interferometer such as a Michelson interferometer may be used. . Although an example of demodulation using the passive homodyne method has been described, another demodulation method such as an active homodyne method or a heterodyne method may be used.

In the third embodiment, an example has been described in which the feedback control magnetic field is generated by a solenoid coil. However, another type of coil such as a Helmholtz coil may be used. The feedback control system described in the third embodiment may be provided in the second and fourth embodiments. In the fourth embodiment, an example has been described in which three magnetic circuits are arranged at right angles to each other. However, the number of magnetic circuits and the arrangement angle may be changed.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0046]

As described above, according to the present invention, the following effects can be obtained. (1) According to the first aspect of the invention, since the fiber lengths of the optical fiber coil A and the optical fiber coil B are substantially uniform, the phase change due to temperature fluctuation occurring in the two optical fiber coils A and B is the same. In the same direction. Therefore, 2
By detecting the phase difference between the lights passing through the two optical fiber coils A and B, it is possible to suppress a phase change due to a temperature change.

Further, since the two optical couplers and the two optical fiber coils A and B constituting the interferometer are integrally formed by bonding or molding to a magnetostrictive material, noise due to vibration can be suppressed. (2) According to the second aspect of the invention, in addition to the effect of (1), since the coil is used to generate the AC bias magnetic field, the AC bias magnetic field can be generated with a small current.

Further, since the ferromagnetic material gap is provided in the magnetic sensing portion, the ferromagnetic material portion is magnetically coupled but not mechanically coupled, so that the magnetostrictive material is not hindered from being distorted. A magnetic signal can be detected with high sensitivity. (3) According to the third aspect of the invention, in addition to the effect of the above (1) or (2), the elasticity of the sheet-like amorphous magnetostrictive material is increased by laminating the same.
Even if the sensing fiber is coiled and lengthened, the elasticity of the amorphous magnetostrictive material can be made stronger than that of the optical fiber coil.

Further, since the portion where the optical fiber and the amorphous magnetostrictive material are bonded is axisymmetric with respect to the direction in which the optical fiber is distorted, the optical fiber is distorted in the axial direction without bending. Therefore,
A small and highly sensitive optical fiber magnetic sensor can be realized. (4) According to the fourth aspect of the invention, in addition to the effect of the above (2) or (3), by applying a feedback control system for generating a magnetic field for canceling a magnetic signal by a solenoid coil, hysteresis of the magnetostrictive material and the like can be obtained. Can be reduced.

(5) According to the fifth aspect of the present invention, in addition to the effects of (2), (3) or (4), three orthogonal components of the magnetic signal are frequency-multiplexed and transmitted. Therefore, the azimuth of the magnetic signal can be detected with a small-sized and low-cost configuration.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an optical fiber magnetic sensor according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an operation principle of a magnetic sensing unit of the optical fiber magnetic sensor according to the first embodiment of the present invention.

FIG. 3 is a structural diagram of a magnetic sensing unit according to a second embodiment of the present invention.

FIG. 4 is an overall configuration diagram of an optical fiber magnetic sensor according to a third embodiment of the present invention.

FIG. 5 is an overall configuration diagram of an optical fiber magnetic sensor according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 U-shaped magnetostrictive material 2,22 Ferromagnetic material 3,23,44 Toroidal coil 4 Mold material 5,6,25,26,45,46 Optical coupler 10 Magnetic sensing part 11 Laser light source 12 O / E converter 13 Passive Homodyne demodulator 14 AM demodulator 15 Modulation signal generator 16 Signal generator for AC bias magnetic field 27 Guide 31 Solenoid coil 32 Feedback control signal generator 40 Signal generator for AC bias magnetic field with different frequency 41 AM demodulator X 42 AM demodulation Y43 AM demodulator Z A, B Optical fiber coil A1, A2, B1, B2 Multilayer amorphous magnetostrictive material X, Y, Z Magnetic circuit

Continuation of the front page (56) References JP-A-8-233923 (JP, A) JP-A-58-165071 (JP, A) JP-A-9-54148 (JP, A) JP-A-8-248107 (JP) , A) JP-A-8-233924 (JP, A) JP-A-1-145042 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 33/00-33/18

Claims (5)

(57) [Claims] 1. An optical fiber magnetic sensor of the type in which an alternating bias magnetic field is applied to a magnetostrictive material, wherein (a) at least a magnetic means for applying a bias magnetic field, and an arm arranged so that the bias magnetic field is applied in opposite directions. (B) a magnetic sensing portion comprising a magnetostrictive material having
Providing a pair of optical fibers individually bonded to the magnetostrictive material, and (c) both of the two lights passing through the arm are:
An optical fiber magnetic sensor arranged to cause a phase change in opposite directions by an AC bias magnetic field. 2. The optical fiber magnetic sensor according to claim 1, wherein a magnetic circuit closed by a magnetostrictive material or a magnetostrictive material and a ferromagnetic material is formed as the magnetic sensing unit, and an AC bias magnetic field is applied by a coil to form the magnetostrictive material. An optical fiber magnetic sensor, wherein an optical fiber is attached to a portion where an AC bias magnetic field is applied in opposite directions. 3. The optical fiber magnetic sensor according to claim 1, wherein a laminated amorphous magnetostrictive material is used as a magnetostrictive material of the magnetic sensing unit. 4. The optical fiber magnetic sensor according to claim 2, wherein a feedback control system for generating a magnetic field for canceling a magnetic signal is provided in the magnetic sensing unit. 5. The optical fiber magnetic sensor according to claim 2, wherein an orthogonal component of the magnetic signal is frequency-multiplexed and transmitted.