JP2000004095A - Magnetic shield structure and rubidium atom oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, with a simple structure, a magnetic shield structure and a rubidium atom oscillator using the magnetic shield structure, that can achieve a adequate magnetic shielding property. SOLUTION: A magnetic shield structure is formed by overlaying and winding a thin plate 1 and a thin plate 2. The thin plate 1 is made of a magnetic material having high magnetic permeability, and the thin plate 2 is made of a material having high magnetic resistance. A rubidium atom oscillator is formed by having each of the magnetic shield structures arranged such that a central axis connecting centers of openings of the magnetic shield structure is disposed vertically, one of the magnetic oscillators is installed into the other, and then an optical microwave unit(OMU) is installed therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic shield structure and a rubidium atomic oscillator, and more particularly to a magnetic shield structure capable of obtaining sufficient magnetic shield performance with a simple structure and a rubidium atom to which the magnetic shield structure is applied. Oscillator.

[0002] Integrated Services Digital Network (so-called ISD)
N. In (2), clock synchronization in a network is indispensable in order to obtain high communication quality, and the clock source is required to have high stability of about 10 ⁻¹⁰ . For this reason, a gas cell type rubidium atomic oscillator based on optical pumping (hereinafter referred to as a rubidium atomic oscillator) is applied as a clock source.

FIG. 6 is a diagram illustrating the function and structure of a rubidium atomic oscillator. In FIG. 6, 8 is a first magnetic shield structure, 9 is a second magnetic shield structure, and 10 and 11 are heat insulating materials. Numeral 12 denotes a resonance cell in which rubidium atoms are sealed, and a light having a specific wavelength is absorbed by utilizing transition between energy levels of the rubidium atoms. Numeral 13 denotes light which passes through the resonance cell 12. Photodetector, 1
4 is a cavity for accommodating the resonance cell 12, 15 is a varactor diode for multiplying the microwave, and 16 is a magnetic field for adjusting the resonance frequency of rubidium atoms sealed in the resonance cell 12 (generally called a C magnetic field). ), A rubidium lamp 17 for emitting resonance light, a lamp house 18 for accommodating the rubidium lamp 17, and a lamp housing 19 for heating the rubidium lamp 17 by high-frequency heating. It is a lamp excitation source that excites. And the resonance cell 12,
The optical detector 13, the cavity 14, the varactor diode 15, the solenoid coil 16, the rubidium lamp 17, the lamp house 18, and the lamp excitation source 19 provide an optical microwave unit 7 (hereinafter referred to as OM).
Abbreviated as U. ) Is configured. 20 is the OMU7
A heater 21 for keeping the temperature of the OMU 7 constant is a thermistor whose resistance value changes according to a temperature change of the OMU 7.
Here, the portion from the first magnetic shield structure to the thermistor in FIG. 6 is a cross-sectional view of a rubidium atomic oscillator in which a resonance cell and the like are housed in a double magnetic shield structure. I have.

Further, reference numeral 22 denotes a temperature controller for detecting the resistance value of the thermistor 21 and generating a voltage for controlling the temperature of the heater 20. Reference numeral 23 denotes a current supplied to the heater 20 based on an output of the temperature controller 22. A transistor to control the
24 is a preamplifier for amplifying the output of the photodetector 13,
25 is a low-frequency oscillator for generating a low-frequency signal, 26 is a synchronous detection circuit for synchronously detecting the output of the preamplifier 24 by the output of the low-frequency oscillator 25, and 27 is a voltage control circuit described later based on the output of the synchronous detection circuit. A frequency control circuit for controlling the oscillation frequency of the crystal oscillator; 28, a voltage-controlled crystal oscillator whose oscillation frequency is stabilized using atomic resonance in the resonance cell 12; 29, an output of the voltage-controlled crystal oscillator 28; This is a frequency modulation circuit that frequency-modulates with the output of the frequency oscillator 25 and supplies the resultant to the varactor diode 15.

Here, the operation principle of the rubidium atomic oscillator shown in FIG. 6 and the stability of the oscillation frequency with respect to the strength of the magnetic field will be described. FIG. 7 is a diagram illustrating the operation principle of the rubidium atomic oscillator.

As shown in FIG. 7A, the rubidium atoms sealed in the resonance cell 12 shown in FIG. 6 are in the thermal equilibrium state, the ground level (5S, F1) level and the (5S) level. , F2) exist with a probability equal to the level.

When the resonance cell 12 is irradiated with the resonance light of the rubidium lamp 17 in this state, only the (5S, F1) level rubidium atom is excited to the 5P level as shown in FIG. . This is called optical pumping.

However, since the 5P level is an unstable energy level, the (5S, F1) level and the (5S, F2) level, which are ground levels due to spontaneous emission, as shown in FIG.
Transition with a probability equal to the level. Then, the (5S, F1) level is excited to the 5P level by optical pumping of only the rubidium atom by the resonance light of the rubidium lamp, and the 5P level to the (5S, F1) level and the (5S, F1) level are generated by spontaneous emission.
F2) The transition to the level with equal probability is repeated.

By repeating this, as shown in FIG.
The rubidium atom becomes present only at the (5S, F2) level. This state is called a negative temperature state. In this state,
The output of the frequency modulation circuit 29 is connected to the varactor diode 15
When the cavity 14 is excited by the microwave multiplied by, the rubidium atom at the (5S, F2) level transits to the (5S, F1) level by stimulated emission, as shown in FIG. At this time, the resonance cell 12
Since the energy of the light output by the lamp 17 is absorbed,
The light level detected by the light detector 13 decreases.

Then, the rubidium atom is (5S, F2)
The probability of transition from the level to the (5S, F1) level is a frequency at which the frequency of the microwave corresponds to the energy difference between the (5S, F2) level and the (5S, F1) level (this is called a resonance frequency). ), And becomes lower as the difference between the microwave frequency and the resonance frequency increases.

That is, the output of the photodetector 13 is as shown in FIG.
As shown in curve A of FIG.
2) When the resonance frequency f ₀ coincides with the resonance frequency f ₀ corresponding to the energy difference between the level and the (5S, F1) level, the value becomes minimum, and increases as the difference between the microwave frequency and the resonance frequency f ₀ increases. Specifically, it is constant because stimulated emission by microwaves does not occur. Note that a concave portion near the resonance frequency f ₀ in the curve A is called a dip.

Since the output of the voltage controlled crystal oscillator 28 is frequency-modulated by the output of the low frequency oscillator 25, the frequency at which the varactor diode 15 excites the cavity 14 changes. Therefore, the efficiency of light absorption in the resonance cell 12 changes, and the light level detected by the photodetector 13 changes.

First, when the excitation frequency of the microwave by the varactor diode 15 is equal to the resonance frequency f ₀ in the resonance cell when the frequency deviation is 0, the excitation frequency of the microwave by the varactor diode 15 modulated by the low-frequency signal. Since f changes near the bottom of the dip, the output of the photodetector 13 has a waveform like a full-wave rectified low-frequency signal as shown in FIG.

Next, when the frequency of the microwave bias is 0 and the excitation frequency of the microwave by the varactor diode 15 is higher than the resonance frequency f ₀ in the resonance cell, the excitation of the microwave by the varactor diode 15 modulated by the low-frequency signal. Since the frequency f changes at the rising portion on the right side of the dip, the output of the photodetector 13 changes at the same phase as the low frequency signal, as shown at C in FIG.

On the other hand, when the excitation frequency of the microwave by the varactor diode 15 is lower than the resonance frequency f ₀ in the resonance cell when the frequency deviation is 0, the excitation frequency of the microwave by the varactor diode 15 modulated by the low-frequency signal. Since f changes at the falling portion on the left side of the dip, the output of the photodetector 13 changes at a phase opposite to that of the low-frequency signal as shown at D in FIG.

The output of the photodetector 13 as described above is guided to a synchronous detection circuit 26 via a preamplifier 24, and synchronously detected by an output of a low-frequency oscillator 25. Synchronous detection is equivalent to combining the zero-crossing phase of the output of the photodetector 13 amplified by the preamplifier 24 and the zero-crossing phase of the output of the low-frequency oscillator 25, and taking the product of the two. Therefore, when the frequency deviation is 0, the varactor diode 1
When the excitation frequency of 5 is equal to the resonance frequency f ₀ in the resonance cell, the output of the synchronous detection circuit 26 becomes zero, and when the frequency deviation is 0, the excitation frequency of the varactor diode 15 is higher than the resonance frequency f ₀ in the resonance cell. Sometimes, the output of the synchronous detection circuit 26 becomes a positive value, and when the excitation frequency of the varactor diode 15 is lower than the resonance frequency f ₀ in the resonance cell when the frequency deviation is 0, the output of the synchronous detection circuit 26 becomes a negative value. become. This is shown in FIG.
This is shown in (b).

The output of the synchronous detection circuit 26 as shown in FIG. 8 (b) is supplied to a frequency control circuit 27, and a proportional control, an integral control,
A control voltage to be supplied to the voltage controlled crystal oscillator 28 is generated by differential control or a combination of these controls.

By the above control, firstly, the output frequency of the voltage controlled crystal oscillator 28 is set so that the excitation frequency of the varactor diode 15 when the frequency deviation is 0 becomes equal to the resonance frequency f ₀ in the resonance cell. Is controlled,
It is supplied to the external circuit as the output of the rubidium atomic oscillator.

The resonance frequency f ₀ of the resonance cell 12 changes depending on the strength of the surrounding magnetic field. By utilizing this phenomenon, the resonance frequency f ₀ of the resonance cell 12 is adjusted by the strength of the magnetic field generated by the solenoid coil 16.

However, since a magnetic field exists on the earth due to the magnetic pole (geomagnetic field) of the earth itself, the influence of the geomagnetic field changes depending on the angle at which the resonance cell 12 is placed in the magnetic field generated by the earth magnetism. Changes the resonance frequency f ₀ of The change rate of the resonance frequency due to geomagnetism is up to 3 × 10 ^-8
, Which is far from the frequency stability of 10 ⁻¹⁰ required for the rubidium oscillator.

Therefore, it is important for the rubidium atomic oscillator to use a magnetic shield to reduce the influence of geomagnetism. FIG. 9 is a diagram illustrating the principle of the magnetic shield.

In FIG. 9, reference numeral 30 denotes a magnetic cylinder having an infinite length in a direction perpendicular to the paper surface. The relative magnetic permeability of the magnetic substance is μ, the radius of the cross section of the cylinder is r, and the thickness of the cylinder is Let t be the shielding coefficient S, which is the ratio (H _O / H _I ) of the strength H _O of the magnetic field outside the magnetic cylinder to the strength H _I of the magnetic field inside the magnetic cylinder, is approximately given by the following equation: Given by

S = 1 + (μ · t) / (2 · r) (1) If the magnetic material is permalloy, μ = 80,0
Since t = 0.2 mm and r = 50 mm, the shield coefficient S is about 160. That is, the strength of the magnetic field inside the magnetic cylinder is 1/160 of the strength of the magnetic field outside the magnetic cylinder. The shield coefficient increases substantially in proportion to the thickness of the magnetic cylinder.

FIG. 10 shows a magnetic shield structure having a double magnetic cylinder. In FIG. 10, reference numeral 31 denotes a first magnetic cylinder having an infinite length in a direction perpendicular to the paper surface;
Is a second magnetic cylinder having an infinite length in a direction perpendicular to the paper surface. If the radii of the cross section of each magnetic cylinder are r ₁ and r _2, and the shield coefficients of each magnetic cylinder are S ₁ and S ₂ , the shield coefficient S of the magnetic shield structure of FIG. Is given by the following equation:

[0025] Now, both magnetic materials are permalloy, and S ₁ and S ₂ are 160
Assuming that r ₂ = 1.1r ₁ , the shield coefficient S of the magnetic shield structure of FIG. 10 is about 5,000. That is, in a single shield, the thickness of the magnetic cylinder is set to 2
Rather than doubling, double shielding greatly increases the shielding coefficient. Then, the more the magnetic shield structure is multiplexed, the more rapidly the shield coefficient increases.

Therefore, in the rubidium atomic oscillator, multiple magnetic shields are applied rather than a single shield, and usually, a double magnetic shield structure is applied in order to avoid a complicated structure.

In the equation (2) showing the shield coefficient of the double magnetic shield structure, the shield coefficient S increases as r ₂ is larger than r _1, but the rubidium atomic oscillator itself becomes large due to the multiple magnetic shield structures. The size of the external magnetic material is limited because it is required that the magnetic material does not become smaller. In addition, it is required that the price of the magnetic shield structure be low even in the case of a multiple magnetic shield structure.

[0028] Since the resonance frequency f ₀ of the resonance cell 12 which changes depending on the temperature change, on the application of temperature control circuit of the thermistor 21, the temperature control unit 22, the transistor 23 and the heater 20, the external temperature variation In order to make the magnetic shield structure less susceptible, a heat insulating material is used together.

The present invention particularly relates to a small and inexpensive magnetic shield structure taking into consideration the use of a heat insulating material, and a rubidium atomic oscillator to which the magnetic shield structure is applied.

[0030]

2. Description of the Related Art FIG. 5 is a diagram showing an example of a conventional magnetic shield structure. In FIG. 5, reference numeral 7 denotes an Optical Microwave Unit (OM described above) for realizing optical-microwave resonance.
U. ). 8-1 is a first magnetic substance square cylinder;
Reference numerals 2 and 8-3 denote lids for closing the opening of the first magnetic substance square cylinder 8-1, and the first magnetic substance square cylinder 8-1 and the lids 8-2, 8
-3 form the first magnetic shield structure 8.
Reference numeral 9-1 denotes a second magnetic substance square cylinder, and 9-2 and 9-3 denote lids for closing the opening of the second magnetic substance square cylinder 9-1. -1 and the lids 9-2 and 9-3 form a second magnetic shield structure 9. Furthermore, 10-1, 1
Reference numerals 0-2, 10-3, 10-4, and 11 are heat insulating materials.

The first magnetic substance square cylinder 8-1 and the lids 8-2 and 8-3 and the second magnetic substance square cylinder 9-1 and the lids 9-2 and 9-3 are made of sheet metal. It is formed by processing. The heat insulating materials 10-1 to 10-4 are attached to the outer surface of the OMU 7, and the heat insulating materials 10-1 to 10-4 are attached to the outer surface of the OMU 7. 1 and the first magnetic substance square cylinder 8-
Block the opening of No. 1.

Next, although only one heat insulating material 11 is shown in FIG. 5, actually, four heat insulating materials are attached to the outer surface of the first magnetic square tube 8-1. And the heat insulating material 10-
Including the OMU 7 having 1 to 10-4 attached to the outer surface, fixing the first magnetic shield structure having the heat insulating material 11 attached to the outer surface inside the second magnetic square tube 9-1, The double magnetic shield structure is completed by closing the opening of the second magnetic rectangular tube 9-1 with the lids 9-2 and 9-3.

The means for fixing the OMU 7 inside the first magnetic shield structure 8, the means for attaching the heat insulating materials 10-1 to 10-4 to the OMU 7, and the outer surface of the first magnetic shield structure 8 Means for attaching the heat insulating material 11 to the
The means for fixing the first magnetic shield structure 8 inside the second magnetic shield structure 9 is described in many documents and application specifications, and therefore, description thereof is omitted here.

However, in this case, since a double magnetic shield structure is realized, a magnetic material forming the first magnetic shield structure 8 and a magnetic material forming the second magnetic shield structure 9 are formed. Must not be in direct contact. Therefore, when the first magnetic shield structure 8 is accommodated in the second magnetic shield structure 9, a belt made of a material having a high magnetoresistance is wound around the first magnetic shield structure 8, or the first magnetic shield structure 8 is wound around the first magnetic shield structure 8. By sandwiching a gap member having high magnetic resistance between the magnetic shield structure 8 and the second magnetic shield structure 9,
It is necessary to magnetically insulate the first magnetic shield structure 8 and the second magnetic shield structure 9.

[0035]

In the conventional magnetic shield structure, as described above, the first magnetic shield structure 8 is used.
Further, since the second magnetic shield structure 9 is formed by sheet metal processing, the number of manufacturing steps is large and disadvantageous in price.

Further, since the heat insulating materials 10-1 to 10-4 are attached to the outer surface of the OMU 7 and the heat insulating material 11 is attached to the outer surface of the first magnetic shield structure 8, the process takes a lot of man-hour even in this step. Cause the price to rise. Moreover, in order to easily attach the heat insulating materials 10-1 to 10-4 to the OMU 7 which conforms to a cylindrical shape in terms of structure, it is necessary to use the OMU 7
It is inconvenient that it is necessary to add a square case so that the cross section of 7 becomes square.

Furthermore, in order to realize a double shield, it is necessary to magnetically insulate the first magnetic shield structure 8 and the second magnetic shield structure 9, which also requires a lot of man-hours. This will cause a further increase in the price of the shield structure.

In addition, a belt made of a material having a high magnetic resistance wound around the first magnetic shield structure 8 and a gap having a high magnetic resistance sandwiched between the first magnetic shield structure 8 and the second magnetic shield structure 9 If the member does not have a sufficient thickness, the first magnetic shield structure 8 and the second magnetic shield structure 9 may come into contact with each other in the middle of the interval between the belt and the gap member. For this reason, there arises a problem that the shape of the double magnetic shield structure becomes large or the number of belts and gap members must be increased.

In view of the above problems, the present invention provides a magnetic shield structure that is small, inexpensive, and has good magnetic shield characteristics.
An object of the present invention is to provide a small and inexpensive rubidium atomic oscillator to which the magnetic shield structure is applied.

[0040]

The principle of the present invention is that a thin plate made of a material having a high magnetic permeability (hereinafter abbreviated as a magnetic thin plate) and a thin plate made of a material having a high magnetic resistance (hereinafter referred to as a spacer thin plate). This is a technique for forming a magnetic cylinder by winding a composite thin plate on which a composite body is superimposed.

According to the principle of the present invention, a composite thin plate in which a magnetic thin plate and a spacer thin plate are overlapped is wound to form a magnetic tubular shape. Therefore, the number of turns focused on the magnetic thin plate is n (n is a positive integer). ), The magnetic thin plate at the (n-1) th turn in the cross section of the magnetic shield structure wound with the composite thin plate and n
A spacer thin plate exists between the magnetic thin plate at the turn and the magnetic thin plate at the (n-1) turn and the magnetic thin plate at the nth turn are magnetically insulated. Therefore, an n-fold magnetic shield structure can be realized by winding n turns of a composite thin plate in which a magnetic thin plate and a spacer thin plate are overlapped.

Here, the cross section of the magnetic shield structure formed as described above is not limited to a circle, but generally a polygonal cross section can be easily formed. There is an advantage that a cylindrical shape can be easily realized.

In addition, it is only necessary to overlap and wind the magnetic thin plate and the spacer thin plate, and further, apply the adhesive to the surfaces of the magnetic thin plate or the thin plate made of a material having a high magnetic resistance, which are not in contact with each other. Since it is also easy to solidify the adhesive after winding, the shape of the magnetic shield structure formed by winding the composite thin plate composed of the magnetic thin plate and the spacer thin plate can be easily maintained.

Alternatively, the shape of the magnetic shield structure can be maintained by winding the magnetic thin plate and the spacer thin plate one on top of the other and winding the periphery with a ring-shaped member. Further, when the spacer thin plate is made of a flexible material, a composite thin plate in which the magnetic thin plate and the spacer thin plate are bonded in advance may be wound.

If a heat insulating material is applied to the spacer thin plate, a magnetic shield structure having both a magnetic shielding effect and a heat insulating effect can be realized, and it is not necessary to manually attach the magnetic thin plate and the heat insulating material.

Accordingly, a multiple magnetic shield can be easily realized, and it is easy to provide a heat insulating effect.
A low-cost magnetic shield structure can be realized.

[0047]

FIG. 1 shows a first embodiment of the present invention. In FIG. 1A, reference numeral 1 denotes a magnetic thin plate, and 2 denotes a spacer thin plate. In FIG. 1B, reference numeral 4 denotes an example of a magnetic shield structure having a circular cross section formed by superposing and winding the magnetic thin plate 1 and the spacer thin plate 2;
A cross section perpendicular to the central axis is shown.

Here, as the material of the magnetic thin plate 1, a permalloy, a carbon monoxide-based amorphous alloy or the like can be applied. The fact that the magnetic thin plate 1 and the spacer thin plate 2 are simply overlapped and wound means that the laminating process is not required because the magnetic thin plate 1 and the spacer thin plate 2 are in contact with each other. Because it is not fixed in the face,
The slack is not generated due to the difference in the radius of curvature between the two thin plates during winding.

However, when the spacer thin plate 2 is made of a flexible material (in practice, the spacer thin plate 2 is often made of a flexible material), the spacer thin plate 2 is on the inside due to the difference in radius of curvature and is on the outside. Since it is possible to adapt to the difference in the winding length of the thin plate, the magnetic thin plate 1 and the spacer thin plate can be attached in advance. When the two thin plates are attached in advance in this way, the two thin plates do not shift in a direction different from the winding direction during winding, and thus there is an advantage that the winding device can be simplified.

As shown in FIG. 1B, the cross section shows a figure in which the magnetic thin plate 1 and the spacer thin plate 2 are spirally overlapped. As can be easily understood, the spacer thin plate 2 is placed between the magnetic thin plate 1 at the (n-1) th turn and the magnetic thin plate 1 at the nth turn at any position of the spiral figure.
, The magnetic shield structure 4 has a multiple magnetic shield structure.

Now, assuming that the material of the magnetic thin plate 1 is permalloy, the thickness of the magnetic thin plate is 0.2 mm, the radius of the magnetic shield structure 4 is about 50 mm, and the length of the magnetic shield structure 4 is Assuming that the length is sufficiently long, the shield coefficient near the center of the space surrounded by the magnetic shield structure 4 is about 160 for a single layer, about 800 for a double layer, and about 3,500 for a triple layer. That is, the magnetic shield structure shown in FIG. 1 has sufficient magnetic shield performance with a simple structure.

Here, the cross-section of the magnetic shield structure formed as described above is not limited to a circle, but a generally polygonal cross-section can be formed. Can be easily realized.

In order to determine the shape of the cross section of the magnetic shield structure, two thin plates are wound around the winding core using a column or a polygonal column, and after winding the desired number of turns, the winding core is removed. Good. Moreover, when the magnetic thin plate 1 and the spacer thin plate 2 are wound, it is difficult to solidify the adhesive after winding while applying the adhesive to the surfaces of the magnetic thin plate 1 or the spacer thin plate 2 that are not in contact with each other. Because it is easy, it is easy to maintain the shape of the magnetic shield structure 4 formed by winding a composite thin plate composed of the magnetic thin plate 1 and the spacer thin plate 2.

After the magnetic thin plate 1 and the spacer thin plate 2 are wound, the shape of the magnetic shield structure 4 can be maintained by winding the periphery with a ring-shaped member. In this case, the ring-shaped member is preferably formed of a relatively flexible material in order to generally conform to a magnetic shield structure having a polygonal cross section.

If a heat insulating material is applied as the spacer thin plate 2, a magnetic shield structure 4 having both a magnetic shielding effect and a heat insulating effect can be realized. As the heat insulating material, for example, a polyolefin foam can be applied. And
Even if one heat insulating material is thin, it is possible to secure the entire thickness of the heat insulating material by winding multiple times, so that good heat insulating properties can be realized.

As described above, the magnetic shield structure 4 can be realized only by superposing and winding the magnetic thin plate 1 and the spacer thin plate 2, so that the structure is simple and the multiple magnetic shield can be easily realized, and the spacer thin plate can be realized. If a heat insulating material is applied to 2, it is easy to have a heat insulating effect. Therefore, a low-cost magnetic shield structure can be realized.

At the position P in FIG. 1B, there is a gap between the end of the magnetic thin plate and the first turn magnetic thin plate.
When a magnetic field in a direction perpendicular to the center line of the magnetic shield structure 4 is applied, a magnetic pole is generated in this gap in a direction to cancel a magnetic field nearby, so that leakage of magnetic field lines from this gap to the internal space usually occurs. I can ignore it.

FIG. 2 shows a second embodiment of the present invention. In FIG. 2A, reference numeral 1 denotes a magnetic thin plate, and 2 denotes a spacer thin plate. In FIG. 2B, reference numeral 4 denotes an example of a magnetic shield structure having a circular cross section formed by superposing and winding the magnetic thin plate 1 and the spacer thin plate 2, and shows a cross section perpendicular to the central axis. .

Here, the feature of the configuration of FIG. 2 is that the length of the spacer thin plate 2 is shorter than the length of the magnetic thin plate 1. The reason that the magnetic thin plate 1 and the spacer thin plate 2 are simply overlapped and wound is that no laminating process is necessary because the magnetic thin plate 1 and the spacer thin plate 2 are merely overlapped, and the contact surface between the magnetic thin plate 1 and the spacer thin plate 2 The spacer thin plate 2 can be prevented from sagging due to the difference in curvature radius because it is not fixed by the above, and the spacer thin plate 2 is often made of a flexible material, and the winding length of the two thin plates due to the difference in curvature radius. This is the same as the configuration shown in FIG. 1 because the magnetic thin plate 1 and the spacer thin plate can be attached in advance, and the winding device can be simplified.

As shown in FIG. 1B, a figure in which a magnetic thin plate 1 and a spacer thin plate 2 are spirally overlapped appears on the cross section. As can be easily understood, except for the end of the magnetic thin plate 1 and the magnetic thin plate 1 in the first turn being in contact with each other, the magnetic properties of the (n-1) th turn in any part of the spiral figure can be understood. Since the spacer thin plate 2 exists between the body thin plate 1 and the nth-turn magnetic thin plate 1, the magnetic shield structure 4
Has a multiple magnetic shield structure.

As described above, since the end of the magnetic thin plate 1 and the first turn magnetic thin plate 1 are in contact with each other at the position of the point Q in FIG. The feature is that the magnetic field is less likely to leak into the internal space.

In order to bring the end of the magnetic thin plate 1 into contact with the first turn magnetic thin plate 1, the difference in length between the magnetic thin plate 1 and the spacer thin plate 2 is compared with the thickness of the spacer thin plate 2. Should be large enough.

Since the end of the magnetic thin plate 1 and the first turn magnetic thin plate 1 are in contact with each other at the position of point P in FIG. 2B, the center of the circular section and the point Q are connected. Although the magnetic shield performance near the elliptical line segment is different from the configuration in FIG. 1, the magnetic shield performance in other places is the same as the configuration in FIG.

Here, since the cross section of the magnetic shield structure 4 formed as described above is not limited to a circular shape, there is an advantage that a magnetic cylindrical shape suitable for the shape of the member to be included can be easily realized. In addition, it is easy to hold the shape of the magnetic shield structure 4 because it is easy to apply the adhesive on the surfaces of the magnetic thin plate 1 or the spacer thin plate 2 that are not in contact with each other and wind and solidify the adhesive. FIG. 1
The configuration is the same as

Further, the shape of the magnetic shield structure can be maintained by superposing and winding the magnetic thin plate 1 and the spacer thin plate 2 and then winding the periphery with a ring-shaped member. If you apply the material,
The magnetic shield structure 4 having both the magnetic shield effect and the heat insulating effect can be realized, and the need to manually attach the magnetic thin plate and the heat insulating material is also the same as the configuration in FIG.

Therefore, even with the configuration shown in FIG. 2, a multiple magnetic shield can be easily realized, and it is easy to provide a heat insulating effect, and a low-cost magnetic shield structure can be realized.

In FIG. 2B, the end of the magnetic thin plate 1 is 1
Although the example which contacts the magnetic thin plate 1 of the turn is shown,
It goes without saying that a configuration in which the end of the magnetic thin plate 1 is in contact with the magnetic thin plate 1 in the final turn is also possible.

FIG. 3 shows a third embodiment of the present invention. In FIG. 3, 1 is a magnetic thin plate, 2 is a spacer thin plate, and 3 is a magnetic thin plate having a large saturation magnetic flux density. still,
FIG. 3 does not show a magnetic shield structure formed by superposing and winding a magnetic thin plate 1, a spacer thin plate 2, and a magnetic thin plate having a high saturation magnetic flux density.

The feature of the configuration shown in FIG. 3 is that a magnetic thin plate 3 having a high saturation magnetic flux density is combined. Here, as a material of the magnetic thin plate having a high saturation density, a silicon steel plate, electromagnetic pure iron, or the like can be applied.

In general, a magnetic material having a high magnetic permeability has a low saturation magnetic flux density, so that the magnetic shield performance is deteriorated in a strong magnetic field. Therefore, the magnetic shielding performance can be maintained even in a strong magnetic field by combining a magnetic thin plate having a high saturation magnetic flux density.

Other manufacturing characteristics of the magnetic shield structure are not different from those of FIGS. 1 and 2. Therefore, even with the configuration of FIG. 3, a multiple magnetic shield can be easily realized, and it is also easy to provide a heat insulating effect, and a low-cost magnetic shield structure can be realized.

FIG. 4 shows a fourth embodiment of the present invention. In FIG. 4, reference numeral 4 denotes a first magnetic shield structure, 5 denotes a second magnetic shield structure, and 6 denotes a third magnetic shield in which the first magnetic shield structure 4 is housed in the second magnetic shield structure 5. The shield structure 7 is an OMU.

Here, the first magnetic shield structure 4 and the second magnetic shield structure 5 have the structure shown in FIG. 1 or FIG. 2 in which a magnetic thin plate and a spacer thin plate are overlapped and wound, or a magnetic thin plate A magnetic shield structure in which a spacer thin plate and a magnetic thin plate having a high saturation magnetic flux density are overlapped and wound.

FIG. 4 shows an example in which the first magnetic shield structure 4 has a circular cross section and the second magnetic shield structure 5 has a rectangular cross section. This is the result of considering that the whole when combined is not so large. The details of the cross section of the magnetic shield structure where the magnetic thin plate and the spacer thin plate overlap each other are not shown.

Since both magnetic shield structures 4 and 5 produce a magnetic shield effect against a magnetic field in a direction perpendicular to the line connecting the center points of the aperture surfaces, the first magnetic shield structure 4
If the first magnetic shield structure 4 is accommodated in the second magnetic shield structure 5 so that the opening surface of the second magnetic shield structure 5 and the surface indicated by W of the second magnetic shield structure 5 face each other, If the line connecting the center of the opening surface of the first magnetic shield structure 4 and the line connecting the center of the opening surface of the second magnetic shield structure 5 are accommodated at right angles, the first magnetic shield structure 4
Can be shielded from a magnetic field outside the second magnetic shield structure 5.

At this time, W of the second magnetic shield structure 5
If the size of the surface indicated by is sufficiently larger than the opening surface of the first magnetic shield structure 4, the space inside the first magnetic shield structure 4 is It is possible to sufficiently shield from an external magnetic field.

However, the W of the second magnetic shield structure 5
If the size of the surface indicated by is sufficiently larger than the opening surface of the first magnetic shield structure 4, the entire third magnetic shield structure 6 becomes too large, which is not practical.

Therefore, the shape of the cross section including the central axis of the first magnetic shield structure 4 and the second magnetic shield structure 5
If the shape of the opening surface of the first magnetic shield structure is made equal, the opening surface of the first magnetic shield structure comes into contact with the surface indicated by W of the second magnetic shield structure 5 at both ends of the first magnetic shield structure 4. As a result, the shielding effect is improved, and the first magnetic shield structure 4 and the second magnetic shield structure 5 can be rubbed with each other, so that the fixing means for both can be simplified. Therefore, it is preferable that the shape of the cross section including the central axis of the first magnetic shield structure 4 is equal to the shape of the opening surface of the second magnetic shield structure 5.

Here, the shape of the opening surface of the first magnetic shield structure 4 does not need to be a circle, and may generally be a polygon. However, the shape of the opening surface of the second magnetic shield structure 5 is preferably rectangular. That is, when the shape of the opening surface of the second magnetic shield structure 5 is circular or polygonal, the contact between the side wall of the first magnetic shield structure 4 and the side wall of the second magnetic shield structure 5 becomes line contact. This is because the shield effect may be weakened and the second magnetic shield structure 5 is prevented from becoming unnecessarily large.

If a lid made of a thin plate containing a magnetic material is provided on the opening surface of the second magnetic shield structure 5, the shielding effect can be further enhanced. The means for fixing the first magnetic shield structure 4 to the second magnetic shield structure 5 and the means for fixing the lid to the second magnetic shield structure 5 are provided by magnetically winding a magnetic material wound in multiple layers. In order to prevent a short circuit, a screw made of a metal that is not plastic or magnetic may be used.

When the above-mentioned magnetic shield structure is applied to a rubidium atomic oscillator, the first magnetic shield structure 4 accommodates the OMU 7 in the first magnetic shield structure 4 and the second magnetic shield structure 4 accommodates the OMU 7 in the second magnetic shield structure. What is necessary is just to house in the magnetic shield structure 5.

In this case, the shield surface of the first magnetic shield structure 4 and the second magnetic shield structure 5
It is necessary to design the magnetic shield performance of the magnetic shield structure perpendicular to the center axis of the solenoid coil of the MU 7 (the solenoid coil is not shown in FIG. 4; see FIG. 6) to have high magnetic shielding performance. There is.

For example, when the center axis of the solenoid coil of the OMU 7 is in the same direction as the line connecting the center of the opening surface of the first magnetic shield structure 4, it is indicated by W of the second magnetic shield structure 5. Since it is preferable to improve the magnetic shield performance with respect to a magnetic field perpendicular to the surface, it is preferable to increase the number of turns of the second magnetic shield structure 5. Conversely, if the center axis of the solenoid coil of the OMU 7 is in the same direction as the line connecting the centers of the openings of the second magnetic shield structure 5,
Since it is preferable to improve the magnetic shield performance with respect to a magnetic field perpendicular to the opening surface of the first magnetic shield structure 4, it is preferable to increase the number of turns of the first magnetic shield structure 4.

The third magnetic shield structure 6 containing the OMU 7 supplies a high-frequency signal or a direct current to the inside,
In extracting a low-frequency signal from the third magnetic shield structure 6 including the MU, a desired cable or wire may be passed through a packing with an insulator. Since this can be realized by the conventional technique, the description is omitted.

The above magnetic shield structure has a simple structure, can reduce manual work, and can easily realize multiple shields. Therefore, it is possible to reduce the price of a rubidium atomic oscillator to which the above magnetic shield structure is applied. As a result, it becomes possible to improve the frequency stability of the rubidium atomic oscillator.

[0086]

As described in detail above, according to the present invention, it is possible to realize a magnetic shield structure which has a simple structure, can reduce manual work, and can easily realize multiple shields. Therefore, the present invention can contribute to the realization of a magnetic shield structure that is inexpensive and has high magnetic shield performance.

Further, by applying the magnetic shield structure to a rubidium atomic oscillator, it is possible to realize a low-cost and high-performance rubidium atomic oscillator.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of the present invention.

FIG. 2 shows a second embodiment of the present invention.

FIG. 3 shows a third embodiment of the present invention.

FIG. 4 shows a fourth embodiment of the present invention.

FIG. 5 shows a conventional magnetic shield structure.

FIG. 6 is a diagram illustrating functions and a structure of a rubidium atomic oscillator.

FIG. 7 illustrates an operation principle of a rubidium atomic oscillator.

FIG. 8 shows an output of a photodetector and a control voltage.

FIG. 9 illustrates the principle of a magnetic shield.

FIG. 10 shows a magnetic shield structure in which a magnetic cylinder is doubled.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Thin plate made of a material with high magnetic permeability (magnetic thin plate) 2 Thin plate made of a material with high magnetic resistance (spacer thin plate) 3 Thin plate made of a magnetic material with high saturated magnetic flux density (magnetic thin plate with high saturated magnetic flux density) 4 Magnetism Shield structure, first magnetic shield structure 5 Second magnetic shield structure 6 Third magnetic shield structure 7 Optical Microwave Unit (OMU) 8 First magnetic shield structure 9 Second magnetic shield structure 10-1, 10- 2, 10-3, 10-4 First heat insulating material 11 Second heat insulating material 12 Resonant cell 13 Photodetector 14 Cavity 15 Varactor diode 16 Solenoid coil 17 Rubidium lamp 18 Lamp house 19 Lamp excitation source 20 Heater 21 Thermistor 22 Temperature control unit 23 Transistor 24 Preamplifier 25 Low frequency oscillator 26 Synchronous detection circuit 7 the frequency control circuit 28 the voltage controlled crystal oscillator 29 frequency modulating circuit 30 magnetic cylinder 31 first magnetic cylinder 32 the second magnetic cylinder

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ken Atami 1-2-25 Ichibancho, Aoba-ku, Sendai, Miyagi Prefecture Inside Fujitsu Tohoku Digital Technology Co., Ltd. (72) Inventor Yoshifumi Nakajima Aoba-ku, Sendai, Miyagi 1-25-2 Ichibancho Fujitsu Tohoku Digital Technology Co., Ltd. F-term (reference) 5E321 BB25 BB44 BB53 BB55 BB60 CC16 GG07 5J060 AA01 CC09 KK38

Claims (6)

[Claims] 1. A magnetic shield structure wherein a thin plate made of a magnetic material having a high magnetic permeability and a thin plate made of a material having a high magnetic resistance are stacked and wound. 2. A magnetic shield structure wherein a thin plate made of a magnetic material having a high magnetic permeability, a material having a high magnetic resistance, and a thin plate made of a magnetic material having a high saturation magnetic flux density are stacked and wound. 3. The magnetic shield structure according to claim 1, wherein, in a cross section in which a plurality of thin plates are piled up and wound, the orbiting thin plate made of the magnetic material is formed of the magnetic material. A magnetic shield structure characterized by being magnetically insulated by a thin plate made of a material having high resistance. 4. The magnetic shield structure according to claim 1, wherein, in a cross section in which a plurality of thin plates are stacked and wound, an end of the orbiting thin plate made of the magnetic material is formed. A magnetic shield structure characterized by being in contact with a thin plate made of a material having a high magnetic permeability at positions different by one turn. 5. The two magnetic shield structures according to claim 1, wherein a center axis connecting the centers of the opening surfaces of the respective magnetic shield structures is made vertical, and the first magnetic shield structure is formed. A magnetic shield structure characterized by being combined so as to be accommodated inside a second magnetic shield structure. 6. A magnetic shield structure according to claim 5, wherein an optical microwave is provided inside said first magnetic shield structure.
A rubidium atomic oscillator accommodating a unit (OMU).