JP2021034402A - Variable capacitor and nmr probe - Google Patents

Abstract

To hold a movable shaft stably and move it smoothly in a cooled variable capacitor.SOLUTION: A movable portion 42 includes a movable shaft 52 and a movable electrode 54. A fixing portion 40 includes an insulating tube 44 and a holder 48. A fixing electrode 46 is provided at the end of the insulating tube 44. The capacitance changes as a spatial relationship between the movable electrode 54 and the fixing electrode 46 changes. A bearing structure 49 includes a wire bearing 50. The wire bearing 50 includes a plurality of coils wound around a core. A part of each coil contacts the outer surface of the movable shaft 52 as a linear contactor to hold the movable shaft 52 movably.SELECTED DRAWING: Figure 6

Description

The present invention relates to a variable capacitor and an NMR probe including the variable capacitor, and more particularly to a bearing structure in the variable capacitor.

A nuclear magnetic resonance (NMR) measuring device has an NMR probe including a detection circuit. The detection circuit generally includes a detection coil, a tuning capacitor, and a matching capacitor. The tuning capacitor and the matching capacitor are each composed of a variable capacitor. For example, the operating force is transmitted to each variable capacitor via the operating member. As a result, the capacitance (capacitance) is changed. Specifically, the operating force is transmitted as a linear motion or a rotary motion of the operating member.

The variable capacitor generally includes a bearing structure that holds the shaft body and guides the movement of the shaft body. Ball bearings are well known as bearing structures. It follows a point contact method and requires lubricating oil for the rotation of individual balls. At low temperatures, especially at cryogenic temperatures, the function of the lubricating oil is reduced or does not work. It is difficult to use ball bearings at low temperatures. On the other hand, as the bearing structure, it is conceivable to use a bearing structure including a tubular member made of a resin having a small friction coefficient (for example, a fluorine-based resin). It follows the surface contact method. In general, the coefficient of linear expansion of resin is large, and it can be pointed out that such a bearing structure may not function properly in an environment where there is a large temperature change.

The variable capacitor disclosed in Patent Document 1 has a bush that holds the shaft member so as to be able to move forward and backward. The bush is an annular member through which a shaft member is inserted. A variable capacitor can also be used in an apparatus other than the NMR measuring apparatus.

U.S. Pat. No. 9,500,276

As the bearing structure of the variable capacitor, it is desired to realize a structure that can stably hold the moving shaft body and smoothly guide the movement of the shaft body in the environment in which the variable capacitor is used. For example, it is desired to realize a bearing structure that exhibits an appropriate holding function and an appropriate guiding function under extremely low temperature cooling.

An object of the present invention is to provide a bearing structure capable of properly holding a shaft body and appropriately guiding the movement of the shaft body in an environment in which a variable capacitor is used. Alternatively, an object of the present invention is to provide a bearing structure capable of stably holding the shaft body in a cooled state of the variable capacitor and smoothly guiding the movement of the shaft body.

The variable capacitor according to the embodiment has a first member, a second member, and a bearing structure. The first member is a member having a cavity. The second member has a shaft body to be inserted into the cavity, and is a member that moves relative to the first member when the capacitance is variable. The bearing structure is a structure provided over the first member and the second member. Specifically, the bearing structure is provided on a plurality of linear contacts provided on one member of the first member and the second member, and a plurality of linear contacts provided on the other member of the first member and the second member. Includes a contact surface with which the linear bearings of the bearing come into contact. Each linear contactor extends along the relative direction of motion of the second member. The contact surface is an inner peripheral surface formed on the first member or an outer peripheral surface formed on the second member.

The above configuration employs a line contact method. According to the line contact method, it is generally easier to obtain a stable holding action as compared with the point contact method, and it is easier to reduce the frictional resistance as compared with the surface contact method. That is, according to the above configuration, since each linear contactor extends along the relative direction of motion, and a plurality of linear contactors are in contact with the contact surface around the shaft body. The holding of the other member by one member is stabilized, and the guidance of the relative movement of the other member with respect to one member is facilitated. Each linear contact may be made of a relatively flexible metal wire. One or both of the first member and the second member are configured as moving members.

A plurality of aspects of the bearing structure can be mentioned. In the first aspect, the first member is configured as a fixed member, the second member is configured as a movable member, the first member is provided with a plurality of linear contacts protruding inward, and the second member is provided with an outer side. A facing contact surface is provided. In the second aspect, the first member is configured as a fixed member, the second member is configured as a movable member, the first member is provided with an inward facing contact surface, and the second member has a plurality of lines protruding outward. A shape contactor is provided. In the third aspect, the first member is configured as a movable member, the second member is configured as a fixing member, the first member is provided with a plurality of linear contacts protruding inward, and the second member is provided with an outer side. A facing contact surface is provided. In the fourth aspect, the first member is configured as a movable member, the second member is configured as a fixed member, the first member is provided with an inward facing contact surface, and the second member has a plurality of lines protruding outward. A shape contactor is provided.

Examples of the relative motion described above include linear motion and rotational motion. When linear motion is adopted, each linear contactor is configured as a linear linear contactor. In that case, the plurality of linear contacts are arranged around the central axis of the shaft body. When rotational motion is employed, each linear contact is configured as a circular linear contact, in which case the plurality of linear contacts are aligned along the central axis of the shaft.

In the embodiment, the first member is a fixed member and the second member is a movable member. A plurality of linear contacts are provided on the fixing member, and the contact surface is the outer peripheral surface of the shaft body. The relative direction of motion is the direction of the central axis of the shaft body. This configuration corresponds to the first aspect described above.

In an embodiment, the bearing structure comprises a wire having a plurality of loops. The plurality of linear contacts are a plurality of portions (linear portions) that come into contact with the outer peripheral surface of the shaft body in the plurality of loops. This configuration facilitates the placement and manufacture of a plurality of linear contacts.

In the embodiment, the number of loops contained in the wire is 3 or more and 30 or less. If it is 3 or more, the central axis of the shaft body is stabilized. If the number of loops is too large, the contact with the surface is approached and the frictional resistance becomes large. Therefore, it is desirable to set the number of loops to 30 or less. When the shaft body is relatively thin, the number of loops may be 3 or more and 20 or less. It is desirable to adjust the number of loops so that there is some clearance between adjacent loops. In addition, it is desirable that the sizes of the plurality of gaps arranged in the circumferential direction are approximately the same.

In embodiments, the loops have a spiral morphology wrapped around an annular core. According to this configuration, a plurality of linear members can be formed more easily. For example, by physically winding one wire around the core in a spiral manner, a plurality of loops are formed. If the tilt angle of each loop with respect to the central axis is small, the tilt angle can be ignored, that is, a stable holding action and a smooth motion guiding action can be obtained even in that case. The material constituting the wire may be composed of a relatively soft metal. According to the above configuration, the frictional resistance in the direction orthogonal to the moving direction is naturally increased while reducing the frictional resistance in the moving direction. In addition, it becomes easy to form a good contact state (including an electrical contact state) between the contact surface and the plurality of loops. In an embodiment, the loops are wound around an annular core independently of each other. According to this configuration, the action of each loop can be made more ideal.

In the embodiment, the outer peripheral surface is coated to reduce frictional force. Further, in the embodiment, each linear contactor is also coated to reduce the frictional force. According to these configurations, the sliding resistance can be reduced or an appropriate sliding resistance can be obtained.

In the embodiment, the fixed member has a fixed electrode, the shaft body has a conductive member electrically insulated from the fixed electrode, and the spatial relationship between the fixed electrode and the conductive member is caused by the advancing / retreating movement of the movable member. It changes, which changes the capacity. Specifically, the conductive member is a movable electrode that forms the opposite electrode of the fixed electrode. Alternatively, the fixed electrode includes a first fixed electrode and a second fixed electrode having a counter electrode relationship, and the conductive member is a member for changing the dielectric constant between the first fixed electrode and the second fixed electrode.

In the embodiment, the variable capacitor is used in a cooled state. The bearing structure does not necessarily require a lubricating oil to support the movement, and looseness is unlikely to occur between the fixed member and the movable member in the cooled state.

The NMR probe according to the embodiment includes a detection circuit and a transmission member. The detection circuit has a variable capacitor for tuning or matching and is used in a cooled state. The transmission member is a member that transmits an external operating force to the variable capacitor when the capacitance of the variable capacitor is variable. The variable capacitor has a fixed member, a movable member, and a bearing structure. The fixing member has a cavity. The movable member has a shaft body that is inserted into the cavity, and is a member that linearly moves in the direction of the central axis of the shaft body by an operating force. The bearing structure is a structure provided over a fixed member and a movable member. Specifically, the bearing structure includes a plurality of linear contacts and contact surfaces. A plurality of linear contacts are provided on the fixing member, and each linear contact extends along the direction of the central axis. The contact surface is a surface on which a plurality of linear contacts come into contact, which is the outer peripheral surface of the shaft body.

The variable capacitor follows a line contact method, and can reduce frictional resistance when moving in the direction of the central axis while maintaining stable holding in a cooled state.

According to the present invention, the shaft body can be properly held and the movement of the shaft body can be properly guided in an environment where a variable capacitor is used. Alternatively, according to the present invention, the shaft body can be stably held in the cooled state of the variable capacitor, and the movement of the shaft body can be smoothly guided.

It is a schematic diagram which shows the nuclear magnetic resonance (NMR) measuring apparatus. It is sectional drawing of the variable capacitor which concerns on 1st Embodiment. It is a perspective view of the variable capacitor which concerns on 1st Embodiment. It is an exploded perspective view of the variable capacitor which concerns on 1st Embodiment. It is sectional drawing which shows the cross section shown by A in FIG. It is a perspective view which shows the upper part of a wire bearing. It is an exploded perspective view of the fixed part and the movable part which concerns on 2nd Embodiment. It is a figure for demonstrating the operation of the variable capacitor which concerns on 1st Embodiment. It is a figure for demonstrating the operation of the variable capacitor which concerns on 2nd Embodiment. It is a figure for demonstrating the operation of the variable capacitor which concerns on 3rd Embodiment. It is sectional drawing which shows the 1st modification. It is sectional drawing which shows the 2nd modification.

Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 shows a configuration example of the nuclear magnetic resonance (NMR) measuring apparatus according to the first embodiment. This NMR measuring device is a device that measures the NMR generated in a sample for the purpose of analyzing the sample. The illustrated NMR measuring device includes a spectrometer 10, a static magnetic field generator 12, and an NMR probe 14. In addition to them, it has a vacuum pump 20 and a cooling device 22. The spectrometer 10 constitutes a main console. Specifically, the spectrometer 10 has a transmitter, a receiver, a spectrum generator, and the like. The static magnetic field generator 12 generates a static magnetic field parallel to the z direction. The static magnetic field generator 12 has, for example, a superconducting coil. In each figure, the first horizontal direction is the x direction, the second horizontal direction is the y direction, and the vertical direction is the z direction. The three directions are orthogonal to each other.

The NMR probe 14 is composed of an insertion portion 16 and a base portion 18. The insertion portion 16 is a cylindrical portion inserted into the bore 12A of the static magnetic field generator 12. The upper end of the insertion portion 16 is a probe head, and a detection circuit 26 is provided inside the probe head. The detection circuit 26 is a circuit that generates NMR in the sample in the sample tube 24 and detects the generated NMR. Typically, the detection circuit 26 has a detection coil, a tuning capacitor, and a matching capacitor.

In the illustrated configuration example, for example, the variable capacitor 28 is a tuning capacitor, and the variable capacitor 30 is a matching capacitor. Three or more variable capacitors may be provided in the detection circuit 26. In the embodiment, the two variable capacitors 28 and 30 have the same configuration as each other. Their composition may be different.

A transmission / reception port is provided on the base 18, and a signal line is arranged between the transmission / reception port and the spectrometer 10. A vacuum pump 20 is connected to the base 18 via a pipe, and a cooling device 22 is connected to the base 18 via another pipe. By the action of the vacuum pump 20, the inside of the NMR probe 14 (particularly the inside of the probe head) is evacuated. The cooling device 22 functions as a drive source and a cooling source for the refrigerant circulation system. The refrigerant discharged from the cooling device 22 is sent to the probe head through the base 18. The refrigerant cools the individual elements in the probe head. After that, the refrigerant is sent from the probe head to the cooling device 22 via the base 18. Examples of the refrigerant include liquid helium and liquid nitrogen. The detection circuit 26 is maintained at a temperature of, for example, 100 K or less, preferably 50 K or less. Those temperatures are only examples. The temperature of the detection circuit 26 may be room temperature.

Two rods 32 and 34 are provided to transmit the operating force to the two variable capacitors 28 and 30. Knobs 36 and 38 are provided at the lower ends thereof. Each rod 32, 34 functions as an operating member when viewed from the variable capacitors 28, 30. That is, when the knobs 36 and 38 are rotated, the operating force generated by the knobs 36 and 38 is transmitted to the variable capacitors 28 and 30 via the rods 32 and 34. Each rod 32, 34 is provided with a motion conversion mechanism (not shown). The motion conversion mechanism is a mechanism that converts a rotary motion into a linear motion.

When the capacitance of the variable capacitors 28 and 30 is variable, linear motion force is applied to the variable capacitors 28 and 30 via the rods 32 and 34. The rotation of the rods 32 and 34 is performed manually or mechanically. The two variable capacitors 28 and 30 are fixed to the structure inside the probe. The structure also functions as a heat conductive member that cools the two variable capacitors 28 and 30. In the following, the variable capacitor 28 will be represented among the two variable capacitors 28 and 30, and the details of its structure will be described.

FIG. 2 shows the xz cross section of the variable capacitor 28. The variable capacitor 28 has a fixed portion 40 as a fixing member and a movable portion 42 as a movable member. Further, the variable capacitor 28 has a bearing structure 49 provided over or across the fixed portion 40 and the movable portion 42. The inside of the fixed portion 40 is hollow.

The fixing portion 40 is fixed to the structure 60. The structure 60 also functions as a heat conductive member for cooling the variable capacitor 28. The structure 60 is made of, for example, copper or phosphor bronze. The fixing portion 40 has a tubular body 43. The main body of the tubular body 43 is an insulating tube 44. The insulating tube 44 is made of, for example, transparent sapphire glass. The insulating tube 44 has an outer peripheral surface and an inner peripheral surface, and a fixed electrode 46 as an electrode layer is formed at one end portion (upper end portion in the drawing) of the outer peripheral surface. The fixed electrode 46 has an annular shape, which is a thin film.

A coating layer 47 is formed on the other end (lower end in the drawing) of the outer peripheral surface of the insulating tube 44. The coating layer 47 has an annular shape, which is also a thin film. The fixed electrode 46 and the coating layer 47 are configured as, for example, a silver-plated layer.

The fixing portion 40 has a tubular holder 48. The holder 48 is made of, for example, phosphor bronze. Specifically, the holder 48 includes a main body 48A and an upper end portion 48B. The lower end of the tubular body 43 is inserted inside the upper end 48B. Specifically, the upper end portion 48B is configured as a thin portion, and the main body 48A is configured as a thick portion. A stepped surface is formed between them, and the lower end surface of the tubular body 43 abuts against the stepped surface. The upper end portion 48B and the coating layer 47 are connected to each other by soldering or the like. The main body 48A and the structure 60 are also connected to each other by soldering or the like, if necessary.

The bearing structure 49 is arranged inside the main body 48A. The bearing structure 49 is fixed to the body 48A, which in the embodiment includes a wire bearing. Details of the bearing structure 49 will be described later.

The movable portion 42 has a movable shaft 52 as a shaft body and a movable electrode 54 provided at the tip of the movable shaft 52. The movable shaft 52 and the movable electrode 54 are made of conductive members, for example, they are made of phosphor bronze. The surfaces of the movable shaft 52 and the movable electrode 54 are coated. For example, a gold-deposited layer is formed on their surface. The movable electrode 54 constitutes a columnar enlarged portion, and its outer diameter is slightly smaller than the inner diameter of the insulating tube 44. The fixed electrode 46 and the movable electrode 54 are in a counter electrode relationship, and the capacitance between them changes depending on the position of the movable electrode 54 in the z direction.

Reference numeral 62 indicates the advancing / retreating motion of the movable shaft 52. In the state where the movable electrode 54 is pulled down most downward, the upper end level of the movable electrode 54 is lower than the lower end level of the fixed electrode 46, and the capacitance is minimized. On the other hand, in the state where the movable electrode 54 is pulled up most upward, the fixed electrode 46 and the movable electrode 54 completely overlap each other when viewed from the horizontal direction, and the capacity is maximized. In the first embodiment, the first signal line is connected to the fixed electrode 46, and the second signal line is connected to the holder 48. The holder 48 and the movable electrode 54 are in a conductive relationship.

A screw structure 56 is formed at the lower end of the movable shaft 52. The movable shaft 52 is connected to the rod 32 by utilizing the screw structure 56. The movable shaft 52 is integrated with the rod 32. When the rod 32 is advanced (raised), the movable shaft 52 is advanced, and when the rod 32 is retracted (descended), the movable shaft is retracted. The movable shaft 52 is electrically connected to the holder 48.

In FIG. 2, the length (size in the z direction) of the movable portion 42 is, for example, in the range of 50 to 60 mm. The length of the insulating tube 44 is, for example, in the range of 30 to 45 mm. The length of the fixed electrode 46 is, for example, in the range of 5 to 15 mm. The length of the movable electrode 54 is, for example, in the range of 5 to 15 mm. The length of the wire bearing 50 is, for example, in the range of 10 to 15 mm. The outer diameter of the insulating tube 44 is, for example, in the range of 3 to 8 mm. Its wall thickness is in the range of 0.3 to 1 mm. The outer diameter of the movable shaft 52 is, for example, in the range of 1.5 to 2.5 mm. The variable range of capacitance is, for example, 0.5 to 30 pF. All of these figures are merely examples.

FIG. 3 is a perspective view of the variable capacitor. As described above, the variable capacitor is composed of a fixed portion 40 and a movable portion 42.

FIG. 4 is an exploded perspective view of the variable capacitor. As described above, the movable portion 42 is composed of the movable shaft 52 and the movable electrode 54.

The fixing portion 40 has a tubular body 43 and a holder 48. A sheath 68 that functions as a spacer is provided inside the holder 48. Inside the sheath 68, a wire bearing 50, which forms a main part of the bearing structure, is fixedly installed. The sheath 68 is made of, for example, a conductive member. The wire bearing 50 is composed of a tubular or annular core 64 and a wire 66 wound around the core 64. The wire 66 is made of a conductive member, for example it is a copper wire. Its cross section is circular. The core 64 is composed of, for example, an insulating member. If it is composed of a conductive member, the core 64 or wire 66 is treated so that at least electrical insulation is achieved between the core 64 and the wire 66.

In the embodiment, the entire surface of the wire 66 is coated to reduce frictional resistance. The surface layer formed by the coating is, for example, a gold-deposited layer. The diameter of the wire 66 is, for example, in the range of 0.15 to 0.3 mm.

Examples of the installation mode of the wire 66 include a first mode and a second mode. In the first aspect, the wire 66 is composed of a plurality of coils 67 as a plurality of wire pieces separated from each other. The plurality of coils 67 are evenly wound around the core 64 in the circumferential direction. In that case, a plurality of coils 67 are arranged radially outward from the central axis of the movable shaft 52. It is desirable that the plurality of gaps generated in the plurality of coils 67 are substantially uniform. In the plurality of coils 67, the plurality of portions in contact with the surface of the movable shaft 52 function as a plurality of linear contacts. The plurality of linear contacts are means for stably holding the movable shaft and guiding the smooth movement of the movable shaft.

In the second aspect, the wire 66 is physically composed of one wire. A plurality of coils are configured by spirally winding the wire around the core 64. However, the plurality of coils 67 are not separated from each other, and they are connected. The tilt angle of each coil with respect to the central axis is small, and the coils perform much the same function as the plurality of coils 67 separated from each other, that is, a part of them performs a plurality of linear contacts as described above. Functions as. According to the second aspect, the wire bearing 50 can be easily manufactured, that is, the arrangement of the wires 66 can be easily performed.

As described above, the bearing structure is composed of a wire bearing 50 provided on the fixed member side and an outer peripheral surface of the movable shaft 52 provided on the movable member side. The arrangement of both may be exchanged. For example, the wire bearing may be provided on the movable member so that the wire bearing is brought into contact with the inner peripheral surface of the fixing member. The shaft body may be configured as a fixed member, and the hollow body into which the shaft body is inserted may be a movable member.

FIG. 5 shows the cross section shown by A in FIG. The movable shaft 52 has an outer peripheral surface 72. The holder 48 has a cavity, a sheath 68 is arranged in the cavity, and a wire bearing 50 is further provided inside the sheath 68. A wire 66 is wound around the wire bearing 50, which is composed of a plurality of coils. Each coil is roughly divided into an outer portion and an inner portion, and the outer portion is fixed while being in contact with the inner peripheral surface of the sheath 68. The inner portion of each coil is in contact with the outer surface of the movable shaft 52 as a linear contactor.

Each linear contactor extends in a direction parallel to the central axis, that is, in the z direction. Since a plurality of linear contacts are provided so as to surround the movable shaft 52 and they are in contact with the outer peripheral surface of the movable shaft, the movable shaft 52 is stably held. In addition, the movable shaft 52 can be smoothly moved linearly. FIG. 6 shows the upper end portion 50A of the wire bearing 50. Specifically, in FIG. 6, the upper end portion 64A of the core and the upper end portion 67A of each coil appear.

FIG. 7 is an exploded perspective view of the variable capacitor according to the second embodiment. The variable capacitor according to the second embodiment basically has the same configuration as the variable capacitor according to the first embodiment, but the configuration of the electrode portion is different. In the second embodiment, the elements already described are designated by the same reference numerals, and the description thereof will be omitted.

More specifically, in FIG. 7, the variable capacitor is composed of a fixed portion 40A and a movable portion 42A. In the fixed portion 40A, an electrode pair composed of two electrodes 76 and 78 provided so as to be separated from each other in the direction of the central axis is provided at the end of the insulating tube. The movable portion 42A is composed of a movable shaft 80 and a conductor 54A. The movable shaft 80 is composed of a conductive portion 84 and an insulating portion 82, and a conductor 54A is attached to the insulating portion 82. The conductor 54A has the same form as the movable electrode shown in FIG. 2 and the like. The conductor 54A is electrically floating.

In the second embodiment, the capacitance is changed by moving the movable shaft 80 forward and backward to change the spatial relationship of the conductor 54A with respect to the electrode pair 74. For example, when the movable shaft 80 is moved backward, the capacity is reduced, and when the movable shaft 80 is moved forward, the capacity is increased. When the conductor 54A is delivered to a position straddling or completely overlapping the two electrodes 76, 78, the capacitance is maximized. In the second embodiment, two signal lines are connected to the two electrodes 76 and 78.

According to the second embodiment, the variable range of the capacitance is lower than that of the first embodiment, and fine adjustment of the capacitance becomes easy. For example, its capacitance is 0.4-2.7 pF. A dielectric may be provided instead of the conductor 54A.

FIG. 8 shows the operation of the variable capacitor 86 according to the first embodiment. The first signal line 88 is connected to the fixed electrode 46, and the second signal line 90 is connected to the holder 48. Reference numeral 92 indicates an equivalent circuit. As shown by reference numeral 93, the capacitance of the capacitor changes due to the vertical movement of the movable portion. The line 88a corresponds to the first signal line 88, and the line 90a corresponds to the second signal line 90.

FIG. 9 shows the operation of the variable capacitor 94 according to the second embodiment. The first signal line 96 is connected to the electrode 76, and the second signal line 98 is connected to the electrode 78. Reference numeral 100 indicates an equivalent circuit. As shown by reference numerals 101a and 101b, the capacitances of the two capacitor elements connected in series change in tandem with the vertical movement of the movable portion. The line 96a corresponds to the first signal line, and the line 98a corresponds to the second signal line. The line 102a corresponds to an electrically floating conductor.

FIG. 10 shows the configuration and operation of the variable capacitor 104 according to the third embodiment. A semi-cylindrical electrode 108 is provided on one side of the end of the insulating tube, and a semi-cylindrical electrode 110 is provided on the other side. The first signal line 122 is connected to the electrode 108, and the second signal line 114 is connected to the electrode 110. The movable part is provided with a movable electrode. The third signal line 116 has a conductive relationship with the movable electrode via the wire bearing and the movable shaft. Reference numeral 118 indicates an equivalent circuit. As shown by reference numerals 119a and 119b, the capacitances of the two capacitor elements change in tandem with the vertical movement of the movable portion. The line 112a corresponds to the first signal line, and the line 114a corresponds to the second signal line. The line 116a corresponds to the third signal line.

FIG. 11 shows a first modification. The movable portion has a movable shaft 124. The fixing portion has a holder 120 and a bearing 122. The bearing 122 holds the movable shaft 124 and guides its rotational movement. The bearing comprises a cylindrical main body 126 and an annular protrusion row 128 provided on the inner peripheral surface of the main body. The annular projection row 128 is composed of a plurality of annular projections 130 arranged in the direction of the central axis C. The apex portion 132 of each annular projection 130 functions as a linear contact with a ring-like shape. Each apex portion 132 is in contact with the outer peripheral surface 134 of the movable shaft 124. A bearing structure is formed by a plurality of annular protrusions 130 and an outer peripheral surface in contact with them.

Since the movable shaft is held by the plurality of annular protrusions 130, the holding state is stabilized. Further, since each of the annular protrusions 130 has an annular shape, the frictional resistance generated during the rotational movement of the movable shaft 124 can be reduced. In the first modification, a configuration in which the capacitance is changed by the rotation of the movable shaft is adopted.

FIG. 12 shows a second modification. The wire bearing 144 is fixed to the movable shaft 140. The wire bearing 144 has a core 146 and a plurality of coils 150 wound around the core 146, and the outer portion of each coil is in contact with the inner peripheral surface of the holder 142. That is, each outer portion functions as a linear contactor. When adopting the second modification, it is desired to lengthen the holder 142 in the direction of the central axis or increase the length in the direction of the central axis of the wire bearing. It is desirable to coat the two members that are in contact with each other in the first modification and the second modification as well.

According to each of the above embodiments, the movable shaft can be properly held and the movement of the movable shaft can be properly guided in an environment in which a variable capacitor is used. In particular, the movable shaft can be stably held in the cooled state, and the movement of the movable shaft can be smoothly guided.

10 spectrometer, 12 static magnetic field generator, 14 NMR probe, 26 detection circuit, 28, 30 variable capacitor, 40 fixed part (fixed member), 42 movable part (movable member), 46 fixed electrode, 49 bearing structure, 50 wire Bearings, 52 movable shafts, 54 movable electrodes, 64 cores, 66 wires, 67 loops.

Claims (13)

The first member with a cavity and
A second member having a shaft body inserted into the cavity and moving relative to the first member when the capacitance is variable,
A bearing structure provided over the first member and the second member,
Including
The bearing structure is
A plurality of linear contacts provided on one of the first member and the second member,
A contact surface provided on the first member and the other member of the second member and in contact with the plurality of linear contacts.
Including
Each of the linear contacts extends along the relative direction of motion of the second member.
The contact surface is an inner peripheral surface formed on the first member or an outer peripheral surface formed on the second member.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 1,
The first member is a fixing member and
The second member is a movable member and
The plurality of linear contacts are provided on the fixing member, and the plurality of linear contacts are provided on the fixing member.
The contact surface is an outer peripheral surface of the shaft body, and is
The relative movement direction is the direction of the central axis of the shaft body.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 2,
The bearing structure includes a wire having a plurality of loops.
The plurality of linear contacts are a plurality of portions that come into contact with the outer peripheral surface in the plurality of loops.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 3,
The number of loops contained in the wire is 3 or more and 30 or less.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 3,
The plurality of loops have a spiral shape wound around an annular core.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 3,
The plurality of loops are wound around an annular core independently of each other.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 2,
The outer peripheral surface is coated to reduce frictional force.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 2,
Each of the linear contacts is coated to reduce frictional force.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 2,
The fixing member has a fixed electrode and
The shaft body has a conductive member that is electrically insulated from the fixed electrode.
The advancing / retreating movement of the movable member changes the spatial relationship between the fixed electrode and the conductive member, which changes the capacitance.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 9,
The conductive member is a movable electrode that forms the opposite electrode of the fixed electrode.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 9,
The fixed electrode includes a first fixed electrode and a second fixed electrode having a counter electrode relationship.
The conductive member is a member for changing the dielectric constant between the first fixed electrode and the second fixed electrode.
A variable capacitor that is characterized by that. In the variable capacitor according to claim 1,
The variable capacitor is used in the cooled state,
A variable capacitor that is characterized by that. A detection circuit that has a variable capacitor for tuning or matching and is used in a cooled state,
When the capacitance of the variable capacitor is variable, a transmission member that transmits an external operating force to the variable capacitor and
Including
The variable capacitor is
A fixing member with a cavity and
A movable member having a shaft body inserted into the cavity and linearly moving in the direction of the central axis of the shaft body by the operating force.
A bearing structure provided over the fixed member and the movable member,
Including
The bearing structure is
A plurality of linear contacts provided on the fixing member and extending along the direction of the central axis,
An outer peripheral surface of the shaft body as a contact surface with which the plurality of linear contacts are in contact,
including,
An NMR probe characterized by this.