JPH0786532B2 - Magnetic substance detection method - Google Patents

Description

The present invention relates to a magnetic body detection method suitable for detecting weak magnetism and detecting a magnetic body.

[Conventional technology]

One of the conventional magnetic sensors that detect weak magnetism is the Josephson element, which is used to detect subtle submarine by detecting weak magnetic changes. Therefore, the magnetism to be detected is geomagnetism and has a detectable distance. The long technical content is not disclosed as a high military secret.

Next, there is an example of combining a magnetostrictive material and an optical fiber as a magnetic sensor that detects weak magnetism.A magnetic sensor that applies pressure change to the optical fiber by magnetism by sandwiching the optical fiber with metallic glass, or an optical fiber with a metallic glass is used. It is wound around a bobbin and the bobbin is deformed by magnetism to change the pressure on the optical fiber.The magnetic sensor and the surface of the optical fiber are coated with a magnetostrictive material such as nickel, and nickel is deformed by the magnetic force to change the pressure on the optical fiber. There are magnetic sensors that detect changes in the propagation phase.

[Problems to be Solved by the Invention]

Among the above-mentioned conventional techniques, the magnetic sensor using the Josephson element requires liquid helium or a refrigerator as a refrigerant in order to operate at an ultralow temperature due to the characteristics of the Josephson element, and the equipment cost and operating cost are expensive and the handling is complicated.

On the other hand, the magnetic sensor in which the magnetostrictive material and the optical fiber are combined has a problem that the sensitivity is extremely low, the directivity for magnetism is not present, the direction of magnetism cannot be specified, and it cannot be put to practical use as a magnetic body detection device.

An object of the present invention is to solve the above-mentioned problems and to provide a magnetic material detection method which is highly sensitive and can specify the direction of magnetism and is easy to handle.

[Means for Solving the Problems]

The above-mentioned object is to separate the light emitted from the light source into two optical paths by the first optical path separating means, and to separate one of the separated lights into parallel to the long side on the outer periphery of the elongated rectangular parallelepiped magnetostrictive material having the long side and the short side. A different optical path is formed, and the optical path length is changed by magnetism, and the phase of the light transmitted through the optical path is changed, and the other light separated by the first optical path separating means is magnetized by the optical path. The light that propagates through the optical path without changing the length is input to the reference optical path and the magnetic detection optical path and the light from the reference optical path are combined into one optical path by the second optical path separating means, The light from the second optical path separating means is input to the light detecting means, converted into an electric signal and subjected to a predetermined process to specify the magnetic direction, and the presence of the magnetic substance is detected from the pattern in which the magnetic distribution is disturbed. It

[Action]

According to the above configuration, the light emitted from the light source is split into the two optical paths by the first optical path splitting means, and one of the lights is input to the magnetic detection optical path so that the rectangular magnetostrictive member having the long side and the short side is magnetized. When it acts, the magnetostrictive material is distorted, and the optical path length of the optical path formed on the outer periphery of the magnetostrictive material changes, and the phase of light propagating in the optical path changes. The other light from the first optical path separating means is input to the reference optical path, and the optical path length does not change here due to magnetism, so the phase of the light propagating in the optical path does not change. The light from the magnetic detection optical path and the light from the reference optical path are input to the second optical path separating means and combined. When two lights having different phases are combined, the light intensity changes due to interference, so that the light is input to the light detecting means, converted into an electric signal, and subjected to predetermined processing to detect magnetism, and from a pattern in which the magnetic distribution is disturbed. The presence of magnetic material can be detected.

By forming an optical path in parallel with the long side on the outer periphery of the elongated rectangular parallelepiped magnetostrictive material consisting of the long side and the short side, the magnetic detection optical path, the magnetostrictive material greatly expands and contracts in the magnetism from the longitudinal direction, and directivity is obtained. Moreover, since the optical path in the longitudinal direction is long, the optical path length greatly expands and contracts as the magnetostrictive material expands and contracts, the phase change also increases, and the magnetic detection sensitivity increases.

Then, the magnetic detection means is moved to detect weak magnetism,
By inputting the nonuniformity of magnetism generated by the detected weak magnetic field and the magnetic material measured in advance in the storage means and the pattern of magnetic change due to distance to the verification determination means and verifying the presence of the magnetic material. The magnetic substance can be detected.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The light emitted from the laser light source 1 is divided into a reference loop 3 and a magnetic detection loop 4 by an optical coupler 2. Phase shifter 6
Is a reference loop 3 to increase the detection sensitivity of the synthetic light.
And the magnetic detection loop 4 shifts the phase so that the phase difference of the light becomes 1/4 wavelength. When the optical path length of the magnetic detection loop 4 changes due to magnetism, the light is combined with the reference light by the optical coupler 5 and can be detected as an electric signal as an interference output by the photodiode 5. When no magnetic field is applied to the magnetic detection loop 4, the output signal of the photodiode is
It shows the maximum value.

FIG. 2 shows a characteristic example of the magnetostrictive material used for the magnetic detection loop 4. Now, select AF alloy as a magnetostrictive material, and assume that the magnetostriction rate changes from 29.4 × 10 ^{-6 m} / 50 Oe according to Fig. 2. Note that the horizontal component of the geomagnetism is on the order of 0.3 Oe, so this material is sufficient for the detection purpose of the submarine.

On the other hand, it is desired that the reel around which the reference loop 3 is wound has a linear expansion coefficient as similar as possible to that of the magnetostrictive material and has almost no magnetostrictive effect. One example is the YCO ₃ alloy.

The fact that the magnetostrictive material used in the present invention significantly extends in the direction in which magnetism arrives can detect the direction of the magnetic field. For example, the submerged submarine changes the horizontal component of the geomagnetism. Therefore, in order to detect a submarine, it is advisable to determine the detection direction of the magnetic sensor so as to have the maximum sensitivity in the horizontal component direction of geomagnetism. Due to the non-uniform distribution of the geomagnetic field of the submarine, it is effective for finding a submarine that is located as far away as possible, that is, at a higher altitude and deeper, and for detecting small equipment. This is because the sensitivity of the magnetic field other than in the horizontal component direction is significantly deteriorated, so that the S / N is improved with respect to the magnetic noise in each direction.

If the size of the magnetic detection loop 4 shown in FIG. 3 is used, the change in length due to the magnetostrictive material per one turn of the optical fiber is about 9.42 μm / 50 Oe. Since the optical fiber is wound 100 times, the total extension value of the optical fiber is about 942 μm / 50O.
It is e. If the wavelength of the laser used is 0.55 μm, 9
When 42 μm is converted into a wavelength, a phase change of about 1108.23 wavelength, that is, 6963.2 radians occurs at 50 Oe. On the other hand, the phase difference conversion of light that can detect a change in the output current value of the photodiode 5 is π / 4rad × 10 ⁻⁴ to 10 ⁻⁵ in a practical value. Therefore, if the detectable value of the change in the magnetic field is Hd, then π / 4 × 10 ^-4 = (6963.2 / 50 Oe) · Hd Hd = 5.64 × 10 ^-7 Oe.

Furthermore, if a magnetic material such as a magnetostrictive material or a focusing magnetic pole 42 shown in FIG. 4 is provided, and the average magnetic permeability of this magnetostrictive material is set to 10, the minimum detection value is further reduced to 1/10. Therefore, the estimated change value Hm of the minimum detected magnetic field is 5 × 10 ⁻⁸ to 10 ⁻⁹ Oe. Since it is 1 Oe = 10 ^-4 T (Tesla), the detection capability is 5 × 10 ^-12 T to 5 × 10 ^-13 T when compared with FIG. As mentioned above, the change in geomagnetism due to the submarine is 2 × 10.
^{Since it is -10} T to 1.5 × 10 ^-11 T, it is possible to detect submarines with a sufficient altitude difference of 1 km.

FIG. 6 shows the structure of a magnetic sensor mounted on an aircraft to detect a submarine. The electronics section 61 functions as a filter for amplifying the output current of the photodiode 5. Reference loop 3 is magnetic detection loop 4
It is stored in the constant temperature pot 64 with anti-vibration measures in the same manner as. The constant temperature controller 66 keeps the inside of the pot at a constant temperature. Optical system laser light source 1, optical coupler 2, photodiode 5
Are stored in the optical system circuit section 67.

Structural points are to keep the magnetic detection loop 4 and the reference loop 3 at the same temperature as possible and to keep the room temperature at the same temperature, and not to give vibration to each optical fiber. This is because changes in temperature and vibrations cause expansion and contraction of the optical fiber and changes in the refractive index of the optical fiber core, which causes noise and makes signal processing difficult.

Next, a detection signal detecting method will be described with reference to FIG.

The photodiode 71 converts a change in interference output of light into a change in current. This current is amplified by the preamplifier 72, and the low-pass filter 73 cuts off high frequency components. The reason why the high frequency component exists is the vibration component of the magnetostrictive material due to the vibration of the aircraft and the magnetism generated inside the aircraft, for example, the induction of 400 Hz power supply. The amplifier 74 amplifies only low frequency components, and its output is divided into various frequency components by the fast Fourier transform circuit 75 and stored in the waveform memory 76.

As shown in Fig. 8, there is a change in the magnetic strength above the submarine, so the magnetic sensor No. 7 of the aircraft flying above it changes.
The output of the amplifier 74 in the figure is as shown in FIG. The waveform of the output component of the amp 74 from the submarine changes depending on the relative altitude difference and the speed of the aircraft. That is, if the altitude difference is large, the non-uniformity of the magnetic field in the vicinity thereof is reduced, and the change amount of the magnetic field is small even when the aircraft is at high speed, so the signal of the amplifier 74 is reduced. When flying at a low altitude difference at a high speed, the amount of change in the magnetic field becomes large, so that the output amplitude of the amplifier 74 becomes large and an output with a high frequency, for example, about 1 Hz is obtained. Since it is difficult to detect the noise component due to the change in the waveform as described above, the altitude (sea level) information of the aircraft and the speed information are given to the arithmetic computer 78 shown in FIG. The altitude difference pattern for generating various relative altitude difference patterns is set in the generator, and the detection pattern as shown in FIG. 9 is generated.
The submarine is detected by matching with the waveform of. The frequency of the waveform is the same as the direction of flight of the aircraft and the direction of success of the submarine.
As shown in the figure, the relative altitude difference is large, and it is the lowest in the case of low speed flight, the value is 0.1 Hz, for example, as shown in Fig. 9b, the relative altitude difference is small, and it flies during high speed flight and across the submarine. In some cases, it may be 10 to 20 Hz.

Therefore, it is necessary to provide the circuits 72 to 76 shown in FIG. 7 in multiple stages, to use in a time division manner and to generate various patterns to be collated to perform collation. This is because a detection error will occur if this is not done.

The level of magnetism that needs to be detected, that is, the level when detecting a submarine that is submerged, is the altitude difference of 1 km between the aircraft and the submarine.
Then, the change in the geomagnetic component near the aircraft will change by about 2 × 10 ^-10 T to 1.5 × 10 ^-11 T. As shown in FIG. 5, this value is so weak that it is equal to the magnetic level of the human body. This is said to be in the field of skid (SQUID) detection using Josephson devices, as in the Electrical Engineering Handbook of the cited document.
In this embodiment, the skid can be used instead.

As described above, the expansion and contraction due to the magnetism of the magnetostrictive material is changed to the expansion and contraction of the optical fiber, and the change in the length is detected by the optical interference circuit, so that it is possible to detect the weak magnetic field that can be used only by the conventional Josephson element. became.

In addition to the above weak magnetic field detection method for defense equipment applications, there is a system that detects submarine by detecting the change pattern of the geomagnetism of the submarine that is submerged, and uses magnetic sensors to detect magnetic noise and other noise. It is difficult to detect the amount of change in magnetic field directly because it is used in a lot of places, but the detection device is equipped with a conversion circuit that converts the change pattern of the geomagnetic field generated by the submarine for each distance in each direction into a time pattern. A good S / N can be obtained by matching and detecting the similarity with the pattern.

〔The invention's effect〕

According to the present invention, by forming an optical path parallel to the long side on the outer periphery of the elongated rectangular parallelepiped magnetostrictive material consisting of the long side and the short side, the magnetic field with high sensitivity and sharp directivity in the long side direction of the rectangular parallelepiped magnetostrictive material is formed. It is possible to specify the direction and detect the presence of the magnetic substance from the pattern in which the magnetic distribution is disturbed.

[Brief description of drawings]

FIG. 1 is a system diagram showing a configuration according to an embodiment of the present invention, and FIG.
FIG. 3 is a magnetostrictive characteristic chart of a known magnetostrictive alloy, FIG. 3a is a plan view showing the configuration of a magnetic detection optical path in the embodiment of the present invention, and 3b.
Fig. 3 is a side view of Fig. 3a, Fig. 4a is a plan view showing another embodiment of the magnetostrictive material of the present invention, Fig. 4b is a side view of Fig. 4a, and Fig. 5 is a known magnetic strength and its measurement. Fig. 6a is a layout showing the arrangement of equipment according to an embodiment of the present invention, and Fig. 6b is a layout showing the method.
Fig. 6a is a side view, Fig. 7 is a block diagram showing the structure of the electronics section shown in Fig. 6a, Fig. 8 is a chart showing changes in magnetic distribution due to magnetic substances, and Fig. 9a is magnetic substances under other conditions. FIG. 9b is a diagram showing a change in magnetic distribution due to the above, and FIG. 9b is a diagram showing a change in magnetic distribution due to a magnetic substance under other conditions. 1 ... Laser light source, 2 ... Optical coupler, 3 ... Reference loop, 4 ... Magnetic detection loop, 5 ... Photodiode, 6 ... Phase shifter, 31 ... Magnetostrictive material, 32 ... Optical fiber , 41 …… Magnetic detection loop, 42 …… Focused magnetic pole, 61 …… Electronics department, 62 …… Reference loop, 63 ……
Magnetic detection loop, 71 ... Photodiode, 72 ... Preamplifier, 73 ... Lowpass filter, 74 ... Amplifier, 75 ...
… Fast Fourier transformer, 76 …… Waveform memory, 77 …… Altitude difference pattern generator, 78 …… Computer, 81 …… Submarine

Claims (1)

[Claims] 1. A light emitted from a light source is separated into two optical paths by a first optical path separating means, and one of the separated lights is provided on the outer periphery of an elongated rectangular parallelepiped magnetostrictive material having long sides and short sides. A parallel optical path is formed, and the optical path length is changed by magnetism to input to the magnetic detection optical path in which the phase of the light transmitted through the optical path is changed, and the other light separated by the first optical path separating means is magnetically The optical path length does not change and the phase of the light propagating through the optical path does not change and is input to the reference optical path, and the magnetic detection optical path and the light from the reference optical path are combined into one optical path by the second optical path separating means, By inputting the light from the second optical path separating means to the light detecting means, converting it into an electric signal and performing a predetermined process to specify the magnetic direction, it is possible to detect the presence of the magnetic substance from the pattern in which the magnetic distribution is disturbed. Characteristic magnetic substance detection method.