WO2011081299A2 - 저잡음 냉각장치 - Google Patents
저잡음 냉각장치 Download PDFInfo
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- WO2011081299A2 WO2011081299A2 PCT/KR2010/008145 KR2010008145W WO2011081299A2 WO 2011081299 A2 WO2011081299 A2 WO 2011081299A2 KR 2010008145 W KR2010008145 W KR 2010008145W WO 2011081299 A2 WO2011081299 A2 WO 2011081299A2
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- magnetization
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- liquid refrigerant
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/445—MR involving a non-standard magnetic field B0, e.g. of low magnitude as in the earth's magnetic field or in nanoTesla spectroscopy, comprising a polarizing magnetic field for pre-polarisation, B0 with a temporal variation of its magnitude or direction such as field cycling of B0 or rotation of the direction of B0, or spatially inhomogeneous B0 like in fringe-field MR or in stray-field imaging
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/323—Detection of MR without the use of RF or microwaves, e.g. force-detected MR, thermally detected MR, MR detection via electrical conductivity, optically detected MR
- G01R33/326—Detection of MR without the use of RF or microwaves, e.g. force-detected MR, thermally detected MR, MR detection via electrical conductivity, optically detected MR involving a SQUID
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
- G01R33/3815—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets with superconducting coils, e.g. power supply therefor
Definitions
- the present invention relates to a nuclear magnetic resonance device, and more particularly to a low magnetic field / ultra-low magnetic field nuclear magnetic resonance device.
- NMR Nuclear Magnetic Resonance
- MRI Magnetic Resonance Imaging
- Sensitivity of the MRI image is proportional to the magnetization ratio and resonance frequency of the nucleus.
- a very strong main magnetic field using a superconducting magnet is applied. Applied to the target object.
- the magnetization degree and resonance frequency of the atomic nucleus increases.
- the relaxation time of the NMR signal is inversely proportional to the uniformity of the main magnetic field. Therefore, the strength and uniformity of the main magnetic field are important.
- Low and Ultra Low Magnetic Fields NMR and MRI are a new concept of MRI devices that operate in magnetic fields of several to hundreds of micro Tesla strength.
- conventional MRI devices in order to increase the sensitivity of the image, the magnetization degree and resonance frequency of the nucleus were increased.
- the low magnetic field MRI device separates the main magnetic field generated in the main magnet of the conventional MRI device into a pre-magnetized magnetic field and a detection magnetic field.
- the detection magnetic field may have a strength of several uT to several tens of uT.
- One technical problem to be solved of the present invention is to provide a pre-magnetization coil-SQUID integrated magnetic field measuring device.
- One technical problem to be solved of the present invention is to provide a cooling device to reduce the thermal noise to a non-conductive auxiliary heat shield.
- a low noise cooling apparatus includes an outer container and an inner container, a vacuum insulation layer is formed between the outer container and the inner container, and the inner container is a dewar comprising a liquid refrigerant, the inner A pre-magnetization coil disposed inside the vessel and immersed in the liquid refrigerant, a pickup coil immersed in the liquid refrigerant, and a SQUID electrically connected to the pickup coil and immersed in the liquid refrigerant.
- the prepolarization coil is formed of a superconductor.
- a low noise cooling device is disposed in the outer container, the outer container, the inner neck, the inner container including the inner body, connected to the inner neck and arranged to surround at least a side of the inner body.
- a pickup coil disposed on a central axis of the pre-magnetization coil and immersed in the liquid refrigerant, and a SQUID electrically connected to the pickup coil and immersed in the liquid refrigerant.
- a vacuum insulating layer is formed between the outer container and the inner container.
- Low noise cooling apparatus can be applied to low magnetic field MRI.
- the low noise cooling device provides an integrated system for mounting the pre-magnetization coil and the SQUID in one dewar.
- the pre-magnetization coil can solve the problem of resistance heating by using a superconducting wire.
- the concave dewar structure can increase the susceptibility of the sample and the sensitivity of the signal.
- Low noise cooling apparatus can block the contribution of the thermal noise to the SQUID by the metallic heat shield using a non-conductive auxiliary heat shield to solve the phenomenon of inducing thermal noise in the SQUID.
- FIG. 1 is a view for explaining a low noise cooling apparatus according to an embodiment of the present invention.
- FIG. 2 is a view for explaining the structure of the pre-magnetization coil according to an embodiment of the present invention.
- FIG. 3 is a view for explaining the structure of the pre-magnetization coil according to another embodiment of the present invention.
- FIG. 4 is a view for explaining a connection according to an embodiment of the present invention.
- FIG. 5 is a view for explaining a conductive heat shield according to an embodiment of the present invention.
- FIG. 6 is a view for explaining an ultra-thermal insulation film according to an embodiment of the present invention.
- FIGS. 7 to 10 are diagrams illustrating a magnetic field measuring apparatus according to other embodiments of the present invention.
- FIG. 11 is a view for explaining a cooling apparatus according to another embodiment of the present invention.
- FIG. 12 is a view for explaining a cooling device according to another embodiment of the present invention.
- Low magnetic field MRI is a pre-magnetization field (prepolarzation magnetic field, Bp) and detecting the magnetic field (measurement magnetic field, B m) in the sample may be sequentially applied to.
- the pre-magnetization magnetic field Bp may be turned off after pre-magnetizing the sample.
- the pre-magnetized magnetic field Bp has a much greater intensity than the detection magnetic field B m in order to fully magnetize the sample.
- the pre-magnetized magnetic field Bp When the pre-magnetized magnetic field Bp is turned off, the spindle of the protons that have been magnetized resonates with the detection magnetic field Bm to precess. Accordingly, the precessing spindle generates an electromagnetic wave, and the electromagnetic wave signal can be measured.
- the pre-magnetization field (Bp) and the detected magnetic field (B m) is applied to each use a separate coil to each other.
- the pre-magnetization magnetic field Bp is generated by the pre-magnetization coil.
- the detection magnetic field B m is generated by the detection magnetic field coil.
- the prepolarization magnetic field Bp may be a strong magnetic field for magnetization of the sample regardless of the uniformity of the magnetic field.
- the detection magnetic field B m may be a uniform magnetic field even if its intensity is small. Therefore, the low magnetic field MRI can be configured in a system much simpler and lower cost than the conventional high magnetic field MRI using a superconducting magnet.
- the relaxation signal of the protons due to the detection magnetic field B m is a low frequency signal of several tens to hundreds of Hz.
- Faraday induction coil is used as a receiver coil for measuring the relaxation signal.
- the signal-to-noise ratio (SNR) of the Faraday induction coil is proportional to the frequency of the relaxation signal being measured. Therefore, the Faraday induction coil is not suitable for measuring the relaxation signal of the low magnetic field MRI of low frequency.
- the low magnetic field MRI may use a superconducting quantum interference device (SQUID) to improve the low signal-to-noise ratio of the Faraday induction coil.
- SQUID superconducting quantum interference device
- Low magnetic field MRI can operate in a micro Tesla-sized magnetic field using the SQUID.
- the low magnetic field MRI may image the inside of an object by using a resonance signal in a band of several hundreds of Hz which is proportional to the magnitude of the detection magnetic field Bm.
- the low magnetic field MRI may reduce distortion caused by metal in or around the object to be imaged. Therefore, the low magnetic field MRI can see a phenomenon that can not be seen in the existing high magnetic field MRI.
- the low magnetic field MRI can be used without difficulty even in a person wearing a metal prosthesis or a pacemaker.
- the low magnetic field MRI can non-invasively obtain an image inside the metal can. Therefore, the low magnetic field MRI may be applied to a device that complements the X-ray widely used in security images.
- the low field MRI includes a pre-magnetization coil for magnetizing the sample, a detection magnetic field coil for determining the relaxation characteristics of the proton spins of the magnetized sample, a SQUID for reading the nuclear magnetic resonance signal, and a cooling for the SQUID below a critical temperature And a cooling system.
- the pre-magnetization coil can generate a magnetic field, typically in the order of tens to hundreds of milli-tesla, for sufficient magnetization of the sample.
- a current of about tens to hundreds of amps may flow through the pre-magnetization coil.
- the pre-magnetization coil may generate resistance heat of about several kilowatts or more.
- the resistance heating of the pre-magnetization coil can be easily reduced by using a thick wire with a small resistance.
- the lead becomes thicker the volume of the coil may increase. Therefore, a method of cooling the pre-magnetization coil to reduce specific resistance may be most effective. That is, due to the resistivity of the metal which decreases in proportion to the temperature, it is advantageous for the pre-magnetization coil to be cooled to the lowest possible temperature.
- Cooling of the resistive pre-magnetization coil can generally use a refrigerant such as liquid nitrogen or liquid helium. Liquid helium at 4.2 K can provide much lower temperatures than liquid nitrogen at 77 K. Thus, when cooling the resistive pre-magnetization coil using liquid helium, the resistivity of the resistive pre-magnetization coil can be lowered. In addition, the SQUID and pre-magnetization coils can be cooled using a single dua.
- liquid helium is required in large amounts compared to liquid nitrogen. Cooling the resistive pre-magnetization coil with the liquid helium is not practical given the price of liquid helium, which is about 100 times more expensive than the price of liquid nitrogen.
- the resistive pre-magnetization coil may be installed in a liquid helium dua containing SQUID.
- the liquid helium may generate vibration in the process of absorbing heat of the resistive pre-magnetization coil. Vibrations generated by helium gas may be transmitted to the SQUID to deteriorate operating characteristics of the SQUID.
- a separate dewar containing liquid nitrogen may be used for cooling the resistive pre-magnetization coil.
- a separate liquid nitrogen dua for the pre-magnetization coil is required.
- liquid nitrogen and helium dewars are difficult and expensive to manufacture because they require minimal refrigerant consumption. In other words, using two types of dua is not desirable given the complexity or cost of the system.
- the liquid helium deua includes a vacuum insulating layer between the dewar inner wall and the outer wall to improve insulation properties.
- a thermal shield may be disposed inside the insulation layer. The heat shield prevents radiant heat from the outside of the dua from being conducted to the inside of the dua inner wall.
- the heat shield is mostly made of metal.
- the thinner the thermal insulation layer of the dua for cooling should be as thin as possible.
- the pickup coil of the SQUID is close to the sample and the heat shield.
- the inherent thermal noise of the metallic thermal barrier increases the noise of the SQUID.
- Dewars for the purpose of cooling the SQUID will inevitably use thermal barriers. However, the use of the thermal barrier is minimized to minimize the SQUID impact.
- Liquid nitrogen dua which is relatively hot compared to liquid helium, is used in a relatively small amount compared to helium dua, but it is not a structure without a heat shield. Thus, the nitrogen dua used for cooling the pre-magnetization coil can provide additional sources of noise based on SQUID.
- the low noise cooling device proposes a shape of a dua optimized for a superconducting pre-magnetization coil-SQUID integrated system.
- an arrangement of a superconducting premagnetization coil is proposed to maximize the magnetization of the sample.
- Low noise cooling device uses a non-conductive auxiliary heat shield to solve the thermal noise of the SQUID due to the metal heat shield.
- FIG. 1 is a view for explaining a low noise cooling apparatus according to an embodiment of the present invention.
- the low noise cooling apparatus 100 includes a dewar 102.
- the dewar 102 includes an outer container 120 and an inner container 110. Between the outer container 120 and the inner container 110 forms a heat insulating layer in a vacuum state.
- the inner container 110 includes a liquid refrigerant 104.
- the low noise cooling apparatus 100 is disposed inside the inner container 110 and is pre-magnetized coil 140 submerged in the liquid refrigerant 104, pickup coil 172 submerged in the liquid refrigerant 104, and the And a SQUID 150 electrically connected to the pick-up coil and immersed in the liquid refrigerant.
- the pre-magnetization coil 140 is formed of a superconductor.
- the outer container 120 may include an outer body portion 122 and an outer concave portion 124 disposed on the lower surface of the outer body portion 122 and surrounding the sample 160.
- the outer body portion 124 may be in the form of a cylinder.
- the outer container 120 may include an outer top plate 121.
- the outer top plate 121 may be fixedly coupled to the outer body portion 122.
- the outer top plate 121 may be formed of a metallic material.
- the outer upper plate 121 may include a vacuum port 123 and a through hole (not shown) at the center of the outer upper plate 121.
- the vacuum port 123 may be connected to a vacuum pump (not shown).
- the outer concave portion 124 may have a cylindrical shape, and may have a structure recessed in a lower surface of the outer body portion 122.
- the outer body portion 122 and the outer concave portion 124 may be a fiber-reinforced plastic (FRP).
- FRP fiber-reinforced plastic
- the inner container 110 is connected to the inner neck 116 coupled with the outer upper plate 121, the inner body 114 connected to the inner neck 116, and the inner body 114 is the It may include an inner recess 112 surrounding the outer recess 124.
- the inner recess 112 may be disposed around the outer recess 124.
- the inner container 110 and the outer container 120 may be in the form of a cylinder.
- the diameter of the inner body 114 may be smaller than the diameter of the inner neck 116.
- the diameter of the inner body 114 may be larger than the diameter of the inner recess 112.
- the inner container 110 may be fixedly coupled to the outer container 120 through the through hole. Specifically, one end of the inner neck 116 may be combined with the through hole.
- the space between the inner container 110 and the outer container 120 may form a heat insulating layer.
- the heat insulation layer may be exhausted through the vacuum port 123 to form a vacuum.
- the inner container 110 may be made of FRP.
- the inner body 114 may be in the form of a cylinder.
- the inner recess 112 may have a structure recessed in the lower surface of the inner body 114.
- the inner recess 114 may have a cylindrical shape.
- a portion of the inner body portion 114 may be filled with the liquid refrigerant 104.
- the liquid refrigerant 104 may be liquid helium or liquid nitrogen.
- the liquid refrigerant 104 may be changed by materials of the SQUID 150 and the pre-magnetization coil 140.
- the superconducting quantum interference device (SQUID) 140 may be a low temperature superconducting SQUID.
- the low temperature superconducting SQUID Nb / AlO X / Nb Josephson Junction can be used.
- the magnetic field sensitivity of the low temperature superconducting SQUID is about 1-2 fT / vHz in the 1 kHz band.
- the target frequency band of the low magnetic field MRI may be a few to several hundred Hz bands. In the target frequency band, the magnetic field sensitivity of the low temperature superconducting SQUID may be less than 10 fT / vHz.
- the low temperature superconducting SQUID exhibits very stable physical and chemical properties in prolonged operation at low temperature, or repeated thermal cycling between low temperature and room temperature.
- the SQUID 140 may be a high temperature superconducting SQUID.
- the high temperature superconducting SQUID may be made of ceramic-based YBCO oxide.
- the magnetic field sensitivity of the high temperature superconducting SQUID may be about 20 to 100 fT / vHz in a few to several hundred Hz band.
- the high temperature superconducting SQUID may be inferior to the low temperature superconducting SQUID in physical and chemical safety.
- a flux transformer may increase the sensitivity of the SQUID 140.
- the magnetic flux converter may include a pick-up coil 172 for detecting magnetic flux and an input coil (not shown) for amplifying the magnetic flux.
- the magnetic flux converters are all composed of superconductors.
- the pickup coil 172 preferably has a large area in order to detect a large amount of magnetic flux.
- the input coil has an area similar to that of the SQUID 140 to focus the magnetic flux on the SQUID 140 and may be wound several times to amplify the SQUID 140.
- the pickup coil 172 may include a magnetometer or a gradometer.
- the magnetometer is composed of a coil of one turn, and amplifies the sensed magnetic flux by the number of turns of the input coil and transmits it to the SQUID 140.
- the Gradometer has two coils wound in opposite directions. Thus, the gradientometer does not respond to a uniform magnetic field. However, a gradientometer detects the difference between the magnetic fluxes of the two coils with respect to the magnetic fluxes having different slopes, and transmits the difference to the input coils.
- the pickup coil 172 may include a pair of gradiometers. Accordingly, the pickup coil 172 may include first to fourth pickup coils 172a to 172d. The shape of the pickup coil may be variously modified.
- the pre-magnetization coil 140 may be arranged to surround the inner recess 112. In addition, some or all of the pickup coils 172 may be disposed between the pre-magnetization coil 140 and the internal recess 112.
- the dua 102 having the outer recess 124 may provide a structure in which the pickup coil 172 completely surrounds the sample 160.
- the pre-magnetization coil 140 may provide a close enough distance to pre-magnetize the sample 160.
- the center of the sample 160 may coincide with the center of the pre-magnetization coil 140. Meanwhile, the center of the pickup coil 172 may not coincide with the center of the sample 160.
- the pre-magnetization coil 140 is It may include a superconductor.
- the pre-magnetization coil 140 may be formed of a sheet material or a line material.
- the plate may have a multilayer structure.
- Superconductors are materials that have zero resistance at or below a certain critical temperature. Accordingly, the pre-magnetization coil 140 may be manufactured using a conductive wire made of a superconductor, and the pre-magnetization coil 140 may be operated at or below a critical temperature. In this case, the problem of refrigerant consumption due to resistance heating in the pre-magnetization coil 140 can be eliminated.
- the superconductor can generate a large magnetic field with a small number of turns because the current density is 100 times greater than that of a general copper conductor. In addition, the volume of the pre-magnetized coil can be reduced than when using a copper lead.
- the superconductor premagnetization coil 140 can be operated at liquid helium temperature regardless of its high temperature superconductor or low temperature superconductor. Therefore, when the pre-magnetization coil is configured using the superconductor, the pre-magnetization coil-SQUID integrated system is possible. That is, one dewar may operate the prepolarization coil 140 and the SQUID 150.
- the liquid refrigerant may cause vibration in the process of absorbing heat from the pre-magnetized coil.
- the vibration may be transmitted to the SQUID to hinder the operation characteristics of the SQUID.
- the pre-magnetization coil When manufacturing the pre-magnetization coil using a copper conductor, it may have a separate dewar for cooling the pre-magnetization coil. However, using a separate dewar increases the complexity and cost of the system.
- the vibration can be sufficiently reduced in the process of absorbing heat of the pre-magnetization coil.
- the pre-magnetized coil and the SQUID are fabricated in one piece, reducing the complexity and cost of the system.
- FIG. 2 is a view for explaining the structure of the pre-magnetization coil according to an embodiment of the present invention.
- the superconductor constituting the pre-magnetization coil should be capable of minimizing the alternating heat loss occurring at the same time without losing its superconductivity while the current is changed.
- the pre-magnetization coil 10 may be a form in which the fine superconductor filament 12 is closely embedded in the matrix material (14).
- the AC heat loss due to the magnetization history may be smaller.
- the base material 14 a copper alloy material such as CuNi or CuMn may be used.
- the specific resistance of the copper alloy material is about 1000 times higher than that of pure copper at 4 K, which is the vaporization point of liquid helium.
- the matrix material 14 can quickly reduce the vortex generated by the current change.
- the coupling loss between the superconductor filaments 12 caused by the current change can be minimized.
- the superconductor filament 12 may be a low temperature superconductor.
- the superconductor filament 12 may include at least one of NbTi, Nb 3 Sn, and MgB 2.
- Metal shell 16 may be disposed to enclose the matrix material 14.
- the thermal and electrical conductivity of the metal shell 16 may be better than the thermal and electrical conductivity of the matrix material. Accordingly, the metal shell 14 may provide to prevent the diffusion thereof and to restore fast superconductivity when a superconducting quenching phenomenon occurs.
- the pre-magnetization coil 10 may be in the form of densely arranged 0.14 micron thick NbTi superconductor filament in the copper-nickel alloy matrix material 14.
- the thickness of the conductive wire of the pre-magnetization coil 10 may be 0.2 mm, and the total volume of the pre-magnetization coil 10 may be 200 cm ⁇ 3.
- the rise and fall times of the current are 5 msec each, and a maximum 1000 A current pulse may be applied to the pre-magnetization coil 10 to generate a 0.5 Tesla magnetic field.
- the expected heat loss can be up to 40 mJ per pulse. When the pulse is applied once every 4 seconds, the average value of AC heat loss is up to 10 mW.
- the heat loss of a pre-magnetized coil made of a resistive wire having a total resistance of 0.58 ohms may be 1 kW when a current of 40 A is flowed at a temperature of liquid nitrogen to generate 0.2 T.
- the heat loss of a superconductor premagnetization coil is only one hundredth of that of the resistive premagnetization coil. Therefore, the superconducting pre-magnetization coil can keep the evaporation amount of the liquid helium insignificant without affecting the SQUID in the liquid helium dua.
- FIG. 3 is a view for explaining the structure of the pre-magnetization coil according to another embodiment of the present invention.
- the pre-magnetization coil may include a buffer layer 23, a superconductor 24, a conductive protective layer 25, and a copper stabilizer layer 21 surrounding the buffer material layer 23 sequentially stacked on the substrate material 22.
- the substrate material 22 may mainly use a Hastelloy-based nickel alloy material having a high tensile strength and mechanical stability at a thickness of about 50 ⁇ m.
- the complete layer 23 may have an oxide thickness of 10 to 40 nm on the substrate material 22 to serve as a mechanical buffer.
- the oxide may include at least one of LaMnO 3, MgO, and Al 2 O 3.
- the superconductor 24 may be stacked on the buffer layer 23 to a thickness of about 1 um.
- the superconductor 24 may include a high superconductor of YBCO series.
- the conductive protective layer 25 may be stacked on the superconductor 24 to a thickness of about 2 ⁇ m.
- the conductive protective layer 25 may serve to electrically connect the superconductor 24 and the external conductor.
- the conductive protective layer 25 may need to have high corrosion resistance.
- the conduction protective layer 25 may be made of silver (Ag) material.
- the copper stabilizer layer 21 may be formed to enclose the substrate, the buffer layer, the superconductor, and the conductive protective layer in a thickness of about 20 ⁇ m.
- the copper stabilizer layer 25 may absorb the eddy current generated when the current flowing in the superconductor 24 changes through the resistance heating to reduce the AC loss of the superconductor 24.
- FIG. 4 is a view for explaining a connection according to an embodiment of the present invention.
- connection unit 180 may electrically connect the pre-magnetization coil 140 and a power supply unit (not shown).
- the connection part 180 may include a first wire 186 formed of a superconductor, part of which is immersed in the liquid refrigerant 104 and electrically connected to the pre-magnetization coil 140, and electrically connected to the first wire 186.
- the second wiring 182 disposed inside the inner container 110, the first connection portion 184 electrically connecting the first wiring 186 and the second wiring 182, and the second wiring 182.
- a third wire 189 electrically connected to the outside of the dua 102 and a second connection 188 electrically connecting the second wire 182 and the third wire 189 to each other.
- the second wiring 182 and the third wiring 189 may be litz wires.
- the second wiring 182 and the third wiring 189 may each include a plurality of conductive wires, and the conductive wires may be individually connected through the second connection part 188.
- the first wire 186 may be connected to the pre-magnetization coil 140. One end of the first wiring 186 may be immersed in the liquid refrigerant 104, and the other end of the first wiring 186 may be exposed to the outside of the liquid refrigerant 104.
- the first wiring 186 may be a high temperature superconductor.
- One end of the second wiring 182 may be connected to the other end of the first wiring 186 through the first connector 184.
- the other end of the second wiring 182 may be connected to the third wiring 189 through the second connection portion 188.
- the second wiring 182 and the third wiring 189 may be resistance wires in the form of a litz wire.
- the resistance wire may include copper.
- the first wiring 186 may be formed of a ceramic-based high temperature superconductor.
- the first wire 186 may be configured to minimize the transfer of heat outside the dua 102 through the second wire 182 to the liquid refrigerant 104 inside the dua 102.
- the second wiring 182 is formed of a single wire or a stranded wire, when the amount of current supplied from the power supply unit to the prepolarization coil 140 changes rapidly, the effective AC resistance may increase due to the surface effect of the conductive wire. Can be.
- the second wiring 182 is formed of a single line or a stranded wire, the effective cross-sectional area of the conductive line in the direction in which the current flows can be increased. As a result, a thermal noise (Johnson noise) current easily occurs.
- the magnetic field generated from the thermal noise current may affect the SQUID 150 to act as measurement noise.
- the thermal noise current may decrease as the lead becomes thinner and as the lead becomes longer.
- the second wiring 182 may be configured in the form of a litz wire in which a plurality of conductive wires are twisted. That is, the second wiring 182 may minimize electrical resistance and reduce thermal conductivity, thereby minimizing heat inflow from the outside of the dua. in this case, The number of conductive lines of the second wiring 182 is set to a sufficient number so as not to raise the temperature of the conductive lines excessively due to resistance heating when a maximum current flows.
- the second wiring 182 and the third wiring 189 may be configured to minimize the generation of thermal noise through the second connection 188.
- the second connector 188 may include a female connector 188b and a male connector 188a.
- the second connector 188 may include a plurality of contact pins 188c such that the copper wires 188d constituting the second wiring 182 have independent terminals with the copper wires 188d insulated from each other.
- the second connector 188 may reduce formation of thermal noise by preventing formation of a conductive loop of a short path between copper conductors in the dua. The longer the path of the lead loop, the smaller the amount of thermal noise generated. When all of the wires of the Ritzwire are connected through one terminal, a short path wire loop may be formed between the individual Ritzwire conductors in the dua.
- the second wiring 182 and the third wiring 189 may include 200 0.5 mm copper wires.
- the total thickness of the second wiring 182 and the third wiring 189 is about 8 mm.
- the resistance heat generated by the third wiring 189 is about 4.3 Watts per 1 m of the conductive wire.
- the resistance heat generation is an amount of heat that can raise the temperature of the wire 0.3 degrees per second when cooling is ignored. Considering the cooling of the third wiring 189 through air, the actual temperature rise of the third wiring 189 may be insignificant.
- FIG. 5 is a view for explaining a conductive heat shield according to an embodiment of the present invention.
- the heat shield 130 may have a structure coupled to the inner neck 116 to surround the inner body 114.
- the heat shield 130 may be a conductive material.
- the heat shield 130 may extend to a part of the side surface of the inner recess 112.
- the heat shield 130 may be formed of copper or aluminum.
- One end of the heat shield 130 may be coupled to the inner neck 116, and the other end of the heat shield 130 may have a slit shape separated from each other.
- the heat shield 130 may have a cylindrical shape.
- the heat shield 130 may include a first heat shield 132 and a second heat shield 134 surrounding the first heat shield 132. Since the heat shield 130 is a conductive material, the inherent thermal noise of the heat shield 130 may adversely affect the SQUID 150 or the pickup coil 172. Radiation heat collected through the heat shield 130 may be transferred to the inner neck 116 in the form of conduction heat. The transfer heat transferred to the inner throat 116 may be cooled by the evaporated liquid refrigerant. The heat shield 130 may give inherent thermal noise to the SQUID 150, and thus, it may need to be used in a limited way. Therefore, some or all of the conductive heat shield 130 between the sample 160 and the pickup coil 172 may be removed. Thermal contact between the thermal barrier 130 and the inner neck 116 may be improved by clamps 133 and 135. The clamps 133 and 135 may be combined with the heat shield 130 to increase the contact area of the inner neck 116.
- the first heat shield 132 may include a plate portion 132a and a strip portion 132b.
- the plate-shaped portion 132a may be disposed to surround the inner body portion 114 in combination with the inner neck portion 116.
- the strip portion 132b may be continuously connected to the plate portion 132a and disposed below the inner body portion 114.
- the plate portion 132a may have a cylindrical shape.
- the plate portion 132a may extend to the lower surface of the inner body portion 114.
- the strip portion 132b may be disposed between the inner recess 112 and the outer recess 124.
- FIG. 6 is a diagram illustrating a node of an ultra insulation film according to an embodiment of the present invention.
- the ultra-insulation film 192 may include fine fiber 192a and 192b and conductive material 192c anisotropically deposited on the fiber yarn 192a and 192b. have.
- the conductive material 192c may be intermittently formed with a conductive region according to the bending of the fine fiber.
- a super thermal insulation layer 192 may be disposed between the inner recess 112 and the outer recess 124.
- the ultra-insulating film 192 may extend to surround the inner body 114.
- the ultra insulation layer 192 is disposed inside the heat insulation layer. Therefore, the ultra-insulation film 192 may suppress the transfer of radiant heat introduced from the dewar 102 into the dewar 102.
- the ultra insulation layer 192 may be a non-conductive insulating material.
- the super insulation film 192 may be separated into a plurality of lattice shapes so that the surfaces are electrically insulated from each other.
- the ultra insulation layer 192 may include aluminum mylar.
- the ultra insulation layer 192 may include a plurality of laminated aluminum mylar films.
- the heat shield 130 may not be disposed between the sample 160 and the pick-up coil 172, and only the super insulation film 192 may be disposed. Accordingly, the pickup coil 172 may be less affected by thermal noise due to the conductive thermal barrier film 130.
- the magnetization degree of the sample 160 may vary depending on the distance between the sample 160 and the pre-magnetization coil 140 and their arrangement.
- the magnitude of the signal may vary depending on the distance between the sample 160 and the pickup coil 172. Therefore, the spatial arrangement of the sample-magnetization coil and the sample-pickup coil can greatly affect the performance of the low magnetic field MRI system.
- the cooling apparatus may be applied to a SQUID-superconducting premagnetization coil integrated low magnetic field MRI system to which a superconducting premagnetization coil is applied.
- the Meissner effect by the pre-magnetization coil may have a magnetic effect on the SQUID.
- the placement of the pre-magnetized coils and the shape of the dua can have a significant impact on the performance of the system.
- the sample is placed at a position off the inner center of the premagnetizing coil.
- this structure may not be suitable for low magnetic field MRI systems.
- the dua In order for the SQUID-superconducting premagnetizing coil integrated low magnetic field MRI system to operate at optimal performance, the dua needs to be optimized.
- the optimized dewar is a concave dewar including an inner recess and an outer recess.
- the concave dua may have the following advantages.
- the sample is placed at a position off the inner center of the premagnetization coil with the largest magnetic field. Therefore, the magnetization degree of the sample is inferior.
- the said sample is arrange
- the pre-magnetization coil may be arranged to surround the inside of the cylinder. Thus, the sample may be disposed at the inner center of the premagnetization coil. Therefore, the magnetization degree of the sample may increase.
- the magnitude of the nuclear magnetic resonance signal of the sample is proportional to the distance between the sample and the pickup coil.
- the insulating layer of the dua adjacent to the sample should be as thin as possible.
- Protruding and planar duas require a minimum thickness of the thermal insulation layer to maintain a stable temperature difference of up to 300 K.
- protruding and planar dewars have a thickness (8-10 mm) between the thickness of the FRP material used for the inner and outer containers (8-10 mm) and the thickness of the vacuum insulation layer between the inner and outer containers in which the thermal barrier and the superheat insulation layer are arranged. Requires.
- the sample and the pickup coil fall by the thickness of the heat insulating layer.
- the sample and the pick-up coil may be coplanar. Therefore, there is no difference in distance between the sample and the pickup coil in the vertical direction, so that the signal decrease according to the distance between the sample and the pickup coil can be suppressed.
- the heat insulation layer thickness d of the region where the sample and the pickup coil are adjacent to each other may be relatively thick as compared with the protruding dua or the flat dua. Therefore, the difficulty of manufacturing the concave dua can be reduced. Specifically, the thickness of the inner recess, the thickness of the outer recess, and the thickness of the heat insulation layer between the inner recess and the inner recess may be reduced.
- the solid angele of the radiant heat incident on the concave portion is small, and less radiant heat is introduced.
- the concave cylinder portion in which the sample is placed is surrounded by a portion filled with liquid helium. Therefore, as compared with the protruding or planar dua, the inner concave portion of the concave dua is relatively less exposed to room temperature and less radiant heat is introduced.
- the conductive heat shield may be removed in an area where the sample and the pickup coil face each other. Therefore, the area where the sample and the pickup coil face each other has a lot of radiant heat introduced compared to other areas.
- a region in which the sample and the pickup coil face each other can secure a sufficient insulating layer, thereby minimizing the inflow of radiant heat.
- FIG. 7 to 10 are diagrams illustrating a magnetic field measuring apparatus according to other embodiments of the present invention. Descriptions overlapping with those described in FIG. 1 will be omitted.
- the pre-magnetization coil 240 may have a Helmholtz shape, and the pre-magnetization magnetic field Bp formed by the pre-magnetization coil 240 may be in the direction of the central axis of the internal recess 112. .
- the pre-magnetization coil 240 may include a first pre-magnetization coil 240a and a second pre-magnetization coil 240b.
- the first pre-magnetization coil 240a and the second pre-magnetization coil 240b may be disposed in the same shape and spaced apart from each other.
- the first pre-magnetization coil 240a and the second pre-magnetization coil 240b may be connected in series or in parallel.
- the first pre-magnetization coil 240a and the second pre-magnetization coil 240b may be disposed to surround the inner recess 112.
- the pre-magnetization coil 240 is not limited to the Helmholtz form.
- the pre-magnetization coil 240 may be connected in series and / or parallel to one or more coils.
- the pre-magnetization coil 340 is in the form of Helmholtz, and the pre-magnetization magnetic field Bp formed by the pre-magnetization coil 340 is a direction perpendicular to the central axis of the inner recess 112. Can be.
- the pre-magnetization coil 340 may include a first pre-magnetization coil 340a and a second pre-magnetization coil 340b.
- the first pre-magnetization coil 340a and the second pre-magnetization coil 340b may be spaced apart from each other with respect to the inner recess 112.
- the first pre-magnetization coil 340a and the second pre-magnetization coil 340b may be connected in series or in parallel.
- the pre-magnetization coil 340 is not limited to the Helmholtz form.
- the pre-magnetization coil 340 may be connected in series and / or parallel to one or more coils.
- the ultra insulation layers 192 and 194 may be disposed between the heat shields 132 and 134.
- the auxiliary heat shielding film 197 may be a non-conductive material that is coupled to the heat shielding film 130 and disposed between the inner recess 112 and the outer recess 124.
- the auxiliary heat shield 197 may be non-conductive and include a metal oxide layer.
- the auxiliary thermal barrier film may include at least one of an aluminum oxide film (alumina), aluminum nitride, and boron nitride.
- Dewar uses thermal barriers to minimize thermal noise structurally.
- a heat shield is not used in an area where the sample and the pickup coil are adjacent to each other. Instead, superheat insulation films are used to block radiant heat, but it is difficult to achieve sufficient thermal insulation. Therefore, there is a need for a non-metallic auxiliary heat shield that blocks radiant heat introduced into the dua.
- the auxiliary heat shield may be a non-metallic material having high thermal conductivity and not conducting thermal noise and magnetic noise to the SQUID.
- Non-metallic materials however, often have low thermal conductivity, which can reduce their functionality as a thermal barrier.
- aluminum oxide (alumina) it is a ceramic-based nonmetallic material and has a high thermal conductivity of 300 K at about 30 W / mK and 5 K at about 1.7 W / mK. Therefore, the existing metallic heat shield may be used where the distance between the pick-up coil and the sample is far away.
- the auxiliary heat shield may be disposed in the region close to the pickup coil and the sample. The auxiliary heat shield and the heat shield may be reliably contacted. Accordingly, it is possible to block radiant heat introduced from the outside while suppressing inflow of thermal noise by the metallic heat shield.
- the auxiliary heat shield may be applied to a dua using liquid helium.
- FIG. 11 is a view for explaining a cooling apparatus according to another embodiment of the present invention.
- the cooling device 400 may include an outer container 420 and an inner container 410.
- the inner container 410 may be disposed inside the outer container 420, and may include an inner neck 416 and an inner body 414.
- the conductive heat shield 430 may be connected to the inner neck 416 and disposed to surround at least a side of the inner body 414.
- the auxiliary heat shield 479 may be disposed in contact with the heat shield 430 in a region adjacent to the sample 460 disposed under the outer container 412, and may be formed of aluminum oxide.
- the outer container 420 and the inner container 410 may form a heat insulating layer in a vacuum state, and the inner container 410 may include a liquid refrigerant 404.
- Lower surfaces of the outer container 420 and the inner container 410 may be flat.
- the premagnetization coil 440, the SQUID 450, and the pickup coil 470 formed of a superconductor may be disposed inside the liquid refrigerant.
- the ultra insulation film 492 may be disposed to surround the inner body portion 414.
- FIG. 12 is a view for explaining a cooling device according to another embodiment of the present invention.
- the cooling device 500 may include an outer container 520 and an inner container 510.
- the inner container 510 may be disposed inside the outer container 520, and may include an inner neck 516 and an inner body 514.
- the conductive heat shield 530 may be connected to the inner neck 516 and disposed to surround at least a side of the inner body 514.
- the auxiliary heat shield 579 may be disposed in contact with the heat shield 530 in an area adjacent to the sample 560 disposed under the outer container 512, and may be formed of aluminum oxide.
- the outer container 520 and the inner container 510 may form a heat insulating layer in a vacuum state, and the inner container 510 may include a liquid refrigerant 504.
- the outer container 520 may include an outer protrusion 524 and an outer body portion 522.
- the inner container 510 may include an inner protrusion 512.
- the inner protrusion 512 may be disposed inside the outer protrusion 524.
- the auxiliary heat shield 579 may be disposed between the bottom surface of the inner protrusion 512 and the bottom surface of the outer protrusion 524.
- the pre-magnetization coil 540 and the pickup coil 570 formed of a superconductor may be disposed inside the inner protrusion 512.
- SQUID 450 may be immersed in the liquid refrigerant 504.
- An ultra insulation film (not shown) may be disposed to surround the inner body portion 514.
Abstract
Description
Claims (17)
- 외부 용기 및 액체 냉매를 포함하는 내부 용기를 포함하는 듀어;상기 내부 용기의 내부에 배치되고 상기 액체 냉매에 잠기는 사전 자화 코일;상기 액체 냉매에 잠기는 픽업 코일; 및상기 픽업 코일에 전기적으로 연결되고 상기 액체 냉매에 잠기는 SQUID를 포함하고,상기 사전 자화코일은 초전도체로 형성되고,상기 외부 용기와 내부 용기 사이는 진공 상태의 단열층을 형성하고,시료는 상기 사전 자화 코일에 의해 자화되고, 상기 픽업 코일의 측정 대상이 되고,상기 듀아는 오목한 형태를 포함하고, 상기 시료는 상기 오목한 형태의 내부에 배치되는 것을 특징으로 하는 저잡음 냉각장치.
- 제 1 항에 있어서,상기 외부 용기는:외부 몸체부; 및상기 사전 자화 코일이 배치되는 영역의 중심부에 상기 시료가 배치되도록 상기 시료를 감싸는 외부 오목부를 포함하고,상기 내부 용기는:상기 외부 용기와 결합하는 내부 목부;상기 내부 목부와 연결되는 내부 몸체부; 및상기 내부 몸체부와 연결되어 상기 외부 오목부를 감싸는 내부 오목부를 포함하고,상기 내부 오목부는 상기 외부 오목부의 주위에 배치되는 것을 특징으로 하는 저잡음 냉각장치.
- 제 2 항에 있어서,상기 내부 목부에 결합하여 상기 내부 몸체부를 감싸는 적어도 하나의 도전성 열차폐막을 더 포함하는 것을 특징으로 하는 저잡음 냉각장치.
- 제 3 항에 있어서,상기 도전성 열차폐막은 판형부와 스트립부를 포함하고,상기 판형부는 상기 내부 목부와 결합하여 상기 내부 몸체부를 감싸도록 배치되고,상기 스트립부는 상기 판형부와 연속적으로 연결되어 상기 내부 몸체부의 하부에 배치되는 것을 특징으로 하는 저잡음 냉각장치.
- 제 3 항에 있어서,상기 내부 오목부와 상기 외부 오목부의 사이에 배치되고 상기 외부 오목부를 감싸는 적어도 하나의 초단열막(Super Thermal Insulation layer)을 더 포함하는 것을 특징으로 하는 저잡음 냉각장치.
- 제 5 항에 있어서,상기 초단열막은:세사 섬유; 및상기 세사 섬유 상에 비등방성을 가지고 증착된 도전 물질을 포함하고,상기 도전 물질은 상기 세사 섬유 굴곡에 따라 전도 영역이 단속적으로 형성되는 것을 특징으로 하는 저잡음 냉각장치.
- 제 3 항에 있어서,상기 열차폐막과 결합하고, 상기 내부 오목부와 상기 외부 오목부 사이에 배치되는 적어도 하나의 비도전성 보조 열차폐막을 더 포함하는 것을 특징으로 하는 저잡음 냉각장치.
- 제 7 항에 있어서,상기 비도전성 보조 열차폐막은 알루미나, 질화알류미늄, 및 질화붕소 중에서 적어도 하나를 포함하는 것을 특징으로 하는 저잡음 냉각장치.
- 제 2 항에 있어서,상기 사전 자화 코일은 상기 내부 오목부를 감싸도록 배치되고,상기 수신 코일의 일부 또는 전부는 상기 사전 자화 코일과 상기 내부 오목부 사이에 배치되는 것을 특징으로 하는 저잡음 냉각장치.
- 제 2 항에 있어서,상기 사전 자화 코일은 적어도 하나의 코일이 직렬 또는 병렬로 연결된 형태이고, 상기 사전 자화 코일에 의하여 형성된 사자 자화 자기장은 상기 내부 오목부의 중심축에 수직한 방향인 것을 특징으로 하는 저잡음 냉각장치.
- 제 2 항에 있어서,상기 사전 자화 코일은 적어도 하나의 코일이 직렬 또는 병렬로 연결된 형태이고, 상기 사전 자화 코일에 의하여 형성된 사자 자화 자기장은 상기 내부 오목부의 중심축 방향인 것을 특징으로 하는 저잡음 냉각장치.
- 제 1 항에 있어서,상기 사전자화 코일은:저항이 큰 합금재 기지재료; 및상기 기지재료 속에 배치된 복수의 미세한 초전도체 필라멘트를 포함하는 것을 특징으로 하는 저잡음 냉각장치.
- 제 12 항에 있어서,상기 초전도 필라멘트는 NbTi, Nb3Sn, MgB2 중에서 적어도 하나를 포함하는 것을 특징으로 하는 저잡음 냉각장치.
- 제 1 항에 있어서,상기 사전자화 코일과 전원부를 전기적으로 연결하는 연결부를 더 포함하고,상기 연결부는:상기 액체 냉매에 일부가 잠기고 상기 사전 자화 코일과 전기적으로 연결되는 초전도체로 형성된 제1 배선; 및상기 액체 냉매로부터 노출된 상기 제1 배선의 일단과 전기적으로 연결되고 배치되고 상기 액체 냉매로부터 노출된 제2 배선을 포함하고,상기 제2 배선은 단선, 연산, 또는 리츠 와이어 형태의 저항 도선인 것을 특징으로 하는 저잡음 냉각장치.
- 외부 용기;상기 외부 용기 내부에 배치되고, 내부 목부, 내부 몸체부를 포함하는 내부 용기;상기 내부 목부에 연결되고 상기 내부 몸체부의 적어도 측면을 감싸도록 배치되는 적어도 하나의 도전성 열차폐막;상기 외부 용기의 하부에 배치된 시료와 인접한 영역에 상기 차폐부와 접촉하여 배치되는 비도전성 보조 열차폐막;상기 내부 용기의 내부에 배치되고 액체 냉매에 잠기는 사전 자화 코일;상기 사전 자화 코일의 중심축 상에 배치되고 상기 액체 냉매에 잠기는 픽업 코일; 및상기 픽업 코일에 전기적으로 연결되고 상기 액체 냉매에 잠기는 SQUID를 포함하고,상기 외부 용기와 내부 용기 사이는 진공 상태의 단열층을 형성하는 것을 특징으로 하는 저잡음 냉각장치.
- 제 15 항에 있어서,상기 외부 용기는 외부 돌출부를 더 포함하고,상기 내부 용기는 내부 돌출부를 더 포함하고,상기 내부 돌출부는 상기 외부 돌출부의 내부에 배치되고,상기 보조 열차폐막는 상기 내부 돌출부의 하부면과 상기 외부 돌출부의 하부면 사이에 배치되는 것을 특징으로 하는 저잡음 냉각장치.
- 제 15 항에 있어서,상기 외부 용기는 외부 오목부를 더 포함하고,상기 내부 용기는 내부 오목부를 더 포함하고,상기 외부 오목부는 상기 내부 오목부의 내부에 배치되고,상기 보조 열차폐막은 상기 외부 오목부와 상기 내부 오목부 사이에 배치되는 것을 특징으로 하는 저잡음 냉각장치.
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KR101520801B1 (ko) * | 2013-10-24 | 2015-05-18 | 한국표준과학연구원 | Squid 센서 모듈 및 뇌자도 측정 장치 |
KR101632278B1 (ko) | 2015-01-15 | 2016-06-21 | 한국표준과학연구원 | 저 자기장 및 극저 자기장 핵자기 공명 및 자기 공명 영상 장치 |
JP6891054B2 (ja) * | 2017-06-23 | 2021-06-18 | 昭和電線ケーブルシステム株式会社 | 常電導接続部材及び超電導ケーブルの端末構造体 |
CN109862771B (zh) * | 2019-03-22 | 2020-05-22 | 中国农业大学 | 一种超导磁悬浮系统的磁屏蔽装置及方法 |
KR102354391B1 (ko) * | 2020-06-01 | 2022-01-21 | 한국표준과학연구원 | 이중 헬멧 뇌자도 장치 |
CN117062515B (zh) * | 2023-10-12 | 2023-12-12 | 国网江苏省电力有限公司营销服务中心 | 一种热屏蔽装置及约瑟夫森结阵芯片系统 |
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JP2002076453A (ja) * | 2000-08-31 | 2002-03-15 | Hitachi Ltd | 微弱磁場計測デュワー |
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US20060091881A1 (en) * | 2004-11-03 | 2006-05-04 | John Clarke | NMR and MRI apparatus and method |
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JP2014041104A (ja) * | 2012-08-23 | 2014-03-06 | Kyoto Univ | 磁気共鳴信号検出用プローブ |
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KR101081482B1 (ko) | 2011-11-08 |
US20120252678A1 (en) | 2012-10-04 |
KR20110076150A (ko) | 2011-07-06 |
JP5738893B2 (ja) | 2015-06-24 |
JP2013515964A (ja) | 2013-05-09 |
WO2011081299A3 (ko) | 2011-09-15 |
DE112010005032T5 (de) | 2012-10-18 |
US8554294B2 (en) | 2013-10-08 |
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