Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
  • G01R33/035—Measuring direction or magnitude of magnetic fields or magnetic flux using superconductive devices
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F5/00—Coils
  • H01F5/02—Coils wound on non-magnetic supports, e.g. formers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F6/00—Superconducting magnets; Superconducting coils
  • H01F6/06—Coils, e.g. winding, insulating, terminating or casing arrangements therefor

Definitions

• the invention relates to the field of supersensitive magnetic measurements and refers to design of input antennas of SQUID (Superconducting Quantum Interference Device)-magnetometers.
• SQUID Superconducting Quantum Interference Device
• High-sensitive magnetometers are characterized by high magnetic field resolution in the range of pico-femto Tesla. At the same time spectrum of useful magnetic signal of biological objects is concentrated in low- frequency range 0.1-100 Hz. Generated by industrial sources (radio- stations, mobile communication, electrostatic discharges and other sources of electromagnetic fields and waves) of magnetic noises, they are thousands of times greater than the useful super-weak magnetic signal.
• SNR signal-to-noise ratio
• the device includes wire-wounded axial gradiometer of the 2nd order with the upper, central and lower (receiving) coils.
• the frame consists of two co-axial parts, on the first of which the central and lower coils are fixed and on the second one the upper coil is fixed; the upper and lower coils have N turns, and central coil has 2N turns.
• the antenna frame has 3 vertical holes in which the balancing mechanisms onto 3 orthogonal field components are placed, and trim- elements are made of lead plates. Balancing procedure consists in shifting of said plates relative to coils for equalization of their effective areas.
• Advantage of the above device is suppressing not only vertical magnetic noises but also vertical gradient of noise, technical effect consists in decreasing of cut-off frequency of 1/f noise at the magnetometer output from 10 Hz to 0.4 Hz. Disadvantages include complexity of design, which complicates and increases its production costs, and lack of strength of graphite frame.
• the advantage of this design is that the frame material, i.e. glass, is much stronger than graphite, but drawback is quite low (less than 1000 ppm) level of weakening of magnetic interference on the vertical component of the magnetic field, which contains a useful signal.
• Another drawback is that the coefficient of thermal expansion (CTE) of the glass at 300K approximately 2 times smaller than the wire material (niobium), but these CTE of glass and wire are equalized at cryogenic temperatures (Malkov M.P., Danilov I. B., Zeldovich A.G. et al. Handbook on physical- technical basics of cryogenics. - Moscow: Energoatomizdat, 1985, p 432). This pattern of changes in CTE leads to the fact that antenna imbalance occurs after several thermal cycles as a result of mechanical deformation and displacement of gradiometer coils.
• Design according to UA 16882 selected as a prototype, includes a cylindrical frame, receiving (pick-up) coil and two compensation coils wounded onto above cylindrical frame by superconducting wire of one piece, and connected by forward and backward wire sections, which are wounded together and attached to a vertical groove.
• the first compensation coil has 2 loops and placed in the middle of the frame, but pick-up coil and second compensating coil are made from 1 loop and placed at opposite ends of the frame.
• Frame is made of a material with a low CTE, and regulating device for mechanical balancing of gradiometer.
• the design is characterized in that on the outer frame surface it is made circular grooves, planes of which are perpendicular to the axis of the cylindrical frame, loops of all coils are placed in the circular grooves, loops of middle coil are placed at a distance no less than half of their radius.
• This design provides an initial balance of 40O800 (200-400) ppm for the vertical (horizontal) field components.
• the advantage of this design is that it provides sufficient (about 20 ppm after mechanical balancing) level of suppressing of magnetic noises on the vertical component of the magnetic field, which contains the useful signal. Disadvantage is insufficient mechanical strength of graphite and deterioration of the antenna balance after multiple thermal cycles due to the different changes of CTE in graphite and niobium during cooling.
• Invention WO/2012/173584 is intended to balancing procedure of gradientometer at unshielded location, but design of gradientometer of the 2 nd order used in preferred embodiment is fully analogous to device disclosed in UA 16882.
• proposed technical solution instead of textolite, glass, or graphite as frame of superconductive gradiometer, proposed device use composite material such as carbon-filled plastic, CTE of which can be adjusted equally to CTE of wire, from which coils of gradiometer are made.
• the novelty of the present invention is elimination of gradiometer drawbacks known from today techniques level by improving the design of the frame, in which:
• the invention is based on the task of improving the design of the superconductive magnetic gradiometer that includes at least the frame, the receiving coil, and at least one compensation coil, made of superconducting wire and wound on a frame made of a material, CTE of which is selected so that it was the closest to the CTE of superconducting wire material.
• Figure 1 Design of gradiometer of 2nd order according to invention: 1 - inner layer of frame, 2 - outer layer of frame, 3 - upper compensation coil, 4 - middle compensation coils, 5 - bottom (receiving) coil of antenna.
• Figure 2 - Structure of simplest embodiment of invention i.e. two- layer composite: 1 - inner layer 2 - outer layer.
• Figure 3 Temperature dependence of derivative of magnetic susceptibitity in constant magnetic field of 20 mT for graphite and carbon- filled plastic according to invention, i.e. composite material with epoxy matrix reinforced by carbon fibers with different orientation in various layers: triangles - graphite, squares - carbon-filled plastic.
• FIG. 1 The design of the device is shown at Figure 1 , which illustrates the principle of the invention.
• Main embodiment of device is wire-wounded axial gradiometer of the 2nd order that registers the 2nd spatial derivative of the vertical (axial) component of the field.
• Gradiometer consists of 4 circular loops 3-5 of radius 11 mm and the distance between the 3-4 and 4-5 (base) equal to 60 mm.
• the receiving coil 5 is designed to record signal, two middle loops 4 and top loop 3 is intended to compensate the magnetic noises from far sources. Average loops are wounded in the opposite direction relative to the top and bottom coils.
• the antenna is made of one piece, the superconducting coils are connected by the forward and reverse twisted wire segments (so called bifilyar) and are inserted into vertical grooves at the frame.
• a tubular detail is produced from 2 layers of composite material, internal layer 1 and external layer 2.
• Each layer is made of epoxy resin ED-22 type, reinforced with carbon fibers type BHM-4.
• the fibers of the 1 st (inner) layer are placed along the mandrel, and fibers of the 2nd (outer) layer are oriented perpendicular or at an angle to the fibers of the 1st layer.
• the carbon fibers have a number of unique properties.
• their electrical resistivity can vary widely depending on the method of production (9 orders of values), and CTE changes its sign along and across the fiber, i.e. when cooled fibers are extended in the axial direction.
• these fibers have very high values of module of elasticity and mechanical strength [see Meleshko A. I., Polovin S.P., Carbon, carbon fiber, carbon composities. Moscow: Science- Press, 2007, 192 p.].
• the mechanical strength of the proposed composite material allows produce parts such as antenna frame with wall thickness no more than 1.0 mm.
• Such type of reinforcing fiber has specific electrical resistivity of three orders of magnitude more than that of copper. This fact provides significant absorption of electromagnetic interferences by frame.
• the total electrical resistance of the frame can be varied with help of filling dielectric matrix by fibers.
• Carbon fibers have layered structure with the dominant orientation of layers along the fiber, i.e. like graphite in a direction perpendicular to the main crystallographic axis. It leads to a negative CTE values along the fiber. Across fiber CTE is positive and its value is more than along the fiber.
• CTE along the fiber proposed in the main embodiment of reinforcing material is near (-0.4...-0.9) * 10 6 1/K, where K is Kelvin, which provides a significant technological flexibility in the selection of the number of reinforcing fibers in the matrix and their ratio into different layers of composite material to equalize CTE of the composite material and wire.
• reinforcing (in main embodiment - carbon) fibers have different CTEs along and transverse fibers (preferably different signs);
• carbon fibers have a CTE along the fibers much less than the CTE of binding agent.
• the CTE of the composite can be adjusted as the relative content and type of binding agent so as relative number of reinforcing fibers into layers and fiber orientation.
• indices m (matrix) and f (fiber) represent, respectively, the polymer matrix and reinforcement fibers, m - Poisson's ratio of the polymer matrix.
• each layer has property of unidirectional composite and its overall CTE is determined by combined deformation of both layers.
• the radial CTE must be equal to CTE of the wire material, from which antenna coils are wound (in the main embodiment - niobium).
• Equality of composite CTE (3) and wire CTE is reached by changing volume content of fibers in each layer (which is regulated by the step of winding), and also by changing angle between the fiber directions in the adjacent layers.
• Figure 3 show relationships of magnetic susceptibility of graphite (triangles) and composite material reinforced by carbon fibers with optimized structure of layers - carbon-filled plastic (squares) in the temperature range 5 ⁇ 50 K.
• binding agent instead epoxy resin it is used polymer, plastic or other binding material
• composite material instead of carbon-filled plastic is reinforced by mineral or other fibers, and equality of CTEs of the composite and wire is reached with help of additional selection of the type of binding agent and/or fiber and/or the number of the composite layers.
• gradiometer frame has a different shape, e.g. polygon, and the gradiometer order is another than the 2nd, for example 1st or 3rd.
• the main advantage of the proposed design is absence of mechanical deformations and displacements caused by thermal expansion of the material of device parts. It provides invariability (permanency) of location and areas of gradiometer coils, which in turn, provides stability of degree of the antenna balance due to repeated thermal cycles from cryogenic to room temperature.
• Design, applied in the main embodiment, achieves initial balance on axial (transverse) component of the field as 800 (400) ppm, which is enough for supersensitive measurements in unshielded conditions without using additional de-noising means (compensation based on reference vector magnetometer or magnetic shielded room).
• An additional advantage of composite material is its best magnetic properties (5 times smaller magnetic susceptibility) so as distortion of the useful signal is smaller.
• Proposed device is industrially applicable, because for its producing it is needed design materials and technology equipment which are widely used in industrial manufacture of goods made from composite materials (fiberglass pipes, etc).

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Measuring Magnetic Variables (AREA)
• Measurement And Recording Of Electrical Phenomena And Electrical Characteristics Of The Living Body (AREA)
• Laminated Bodies (AREA)

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• 2015
  • 2015-01-12 UA UAA201500219A patent/UA112235C2/uk unknown
• 2016
  • 2016-01-04 WO PCT/UA2016/000001 patent/WO2016114742A1/en active Application Filing
  • 2016-01-04 CN CN201680014747.XA patent/CN107430174B/zh active Active
  • 2016-01-04 KR KR1020177022400A patent/KR101916298B1/ko active IP Right Grant

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