This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0070342 filed in the Korean Intellectual Property Office on May 31, 2021, the entire contents of which are incorporated herein by reference.
The present invention relates to a superconducting coil module. Particularly, the present invention relates to a superconducting coil module constituting a superconducting magnet.
A superconducting magnet can be operated with an even higher current density than an existing electromagnet. When the superconducting magnet is applied to an electric device, epochal improvement of an energy density and weight reduction are possible. In particular, a high temperature superconducting magnet is one of candidates to lead commercialization of a superconducting electric device due to a relatively high operating temperature and a relatively high operation stability, and a lot of researches into the high temperature superconducting magnet are in progress. However, when a quench phenomenon in which superconductivity suddenly disappears in a superconducting magnetic material occurs, there has been a problem in that a coil of the superconducting magnet is burned.
In order to solve this problem, a no-insulation winding technique is proposed. High temperature superconducting magnets to which this technique is applied can successfully achieve a target magnetic field. Further, even when the quench occurs, current in the coil detours a point where the quench occurs to protect the superconducting magnet.
As such, the high temperature superconducting magnets to which the no-insulation winding technique is applied are not electrically burned when the quench occurs, but under a high magnetic field condition of the superconducting magnet, a phenomenon occurs in which a superconducting wire is mechanically deformed due to current which is induced in the superconducting coil during the quench. When mechanical deformation occurs in the high temperature superconducting wire, a performance of the high temperature superconducting wire is rapidly dropped.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.
The present invention has been made in an effort to provide a superconducting coil module capable of preventing mechanical deformation when a quench occurs in a superconducting coil.
An exemplary embodiment of the present invention provides a superconducting coil module including: a superconducting coil configured by winding a superconducting wire a plurality of times; and a magnetic dam wound along a shape of the superconducting coil, and electromagnetically coupled. The magnetic dam may include a conductive structure device insulated from the superconducting coil, and implemented by a conductive wire wound along the shape of the superconducting coil a plurality of times, and a control circuit controlling current which flows to the magnetic dam during charging and discharging of the superconducting coil between both terminals of the conductive wire.
The conductive wire may be wound along an exterior of the superconducting coil a plurality of times. The magnetic dam may further include an insulation device including an insulation member located between the conductive structure device and the superconducting coil.
The superconducting coil module may further include a superconducting coil support body located on an interior of the superconducting coil, and the conductive wire may be wound along an exterior of the superconducting coil support body a plurality of times.
The magnetic dam may further include an insulation device including an insulation wire located between the conductive wires. When the conductive wire is wound along an exterior of the superconducting coil a plurality of times, the insulation wire may include an insulation member located between the superconducting coil and the conductive wire.
The control circuit may include a switching element which is in an off state when the superconducting coil is charged and discharged and in an on state when the superconducting coil is not charged and discharged.
The control circuit may include a diode connected between both terminals of the conductive wire so that a direction of current induced to the magnetic dam becomes an inverse direction when the superconducting coil is charged.
The control circuit may include a capacitor which causes resonance with an inductor component of the magnetic dam with respect to a specific frequency of an electromagnetic wave induced to the magnetic dam when a quench occurs.
Another exemplary embodiment of the present invention provides a superconducting coil module including: a superconducting coil configured by winding a superconducting wire a plurality of times; a conductive structure device including a conductive wire wound on the superconducting coil along an exterior of the superconducting coil a plurality of times; an insulation device including a first insulation member located between the conductive structure device and the superconducting coil; and a control circuit controlling current which flows to the magnetic dam during charging and discharging of the superconducting coil between both terminals of the conductive wire.
The insulation device may further include an insulation wire wound on the superconducting coil together with the conductive wire.
When the conductive wire is separated in units of one turn in the conductive structure device, the conductive structure device may include a plurality of conductive members, when the insulation wire is separated in units of one turn in the insulation device, the insulation device may include a plurality of second insulation members, and one corresponding second insulation member among of the plurality of second insulation members may be located between two adjacent conductive members among the plurality of conductive members.
Yet another exemplary embodiment of the present invention provides a superconducting coil module including: a superconducting coil configured by winding a superconducting wire a plurality of times; a superconducting coil support body located on an interior of the superconducting coil; a conductive structure device including a conductive wire wound on the superconducting coil along an interior of the superconducting coil support body a plurality of times; and a control circuit controlling current which flows to the magnetic dam during charging and discharging of the superconducting coil between both terminals of the conductive wire.
The superconducting coil module may further include an insulation device including an insulation wire wound on the superconducting coil together with the conductive wire.
When the conductive wire is separated in units of one turn in the conductive structure device, the conductive structure device may include a plurality of conductive members, when the insulation wire is separated in units of one turn in the insulation device, the insulation device may include a plurality of insulation members, and one corresponding second insulation member among of the plurality of insulation members may be located between two adjacent conductive members among the plurality of conductive members.
The at least one superconducting coil may include two adjacent superconducting coils, and the magnetic dam may be located between the two adjacent superconducting coils. The at least one superconducting coil may include two adjacent superconducting coils, and the magnetic dam may be located between the two adjacent superconducting coils.
The magnetic dam may further include a control circuit controlling current which flows to the magnetic dam during charging and discharging of the superconducting coil between both terminals of the conductive wire.
The conductive structure device may include a conductive wire wound along shapes of the two adjacent superconducting coils between the two adjacent superconducting coils, and the magnetic dam may further include an insulation device including an insulation wire wound along the shape of the superconducting coil together with the conductive wire.
The conductive wire of the conductive structure device may be a high temperature superconductor.
According to an exemplary embodiment of the present invention, provided is a superconducting coil module capable of preventing mechanical deformation when a quench occurs in a superconducting coil.
In order to apply a high magnetic field superconducting electromagnet to an electric device, the present invention relates to a magnetic damper structure for protecting a superconducting coil during a quench. Hereinafter, a structure for protecting the superconducting coil will be referred to as a magnetic dam. The magnetic dam may be electromagnetically coupled to the superconducting coil. Further, in addition to electromagnetic coupling, the magnetic dam may be implemented as a conductive structure device physically coupled to the superconducting coil. The magnetic dam may prevent deformation of a coil by reducing current induced to the superconducting coil electromagnetically connected to a superconducting coil in which the quench occurs when the quench occurs in the superconducting coil. That is, the magnetic dam may delay a quench propagation of the superconducting coil, absorb energy depending on induction current by the quench, and prevent mechanical deformation of the superconducting coil by the quench. A superconducting electromagnet in the present invention may be widely applied to various electric devices including NMR, MRI, and the like.
In the present invention, the magnetic dam may be applied to a non-insulation type superconducting coil. The no-insulation type includes no-insulation, partial insulation, and metal insulation.
In the present invention, a material of the magnetic dam may be one of copper, a low temperature superconductor, and a high temperature superconductor.
In the present invention, an insulation type of the magnetic dam may be any one of insulation, the no-insulation, the partial insulation, and the metal insulation.
In the present invention, the magnetic dam may be located in at least one of an inside and an outside of the superconducting coil. Alternatively, the magnetic dam may be located between at least two coils in a superconducting electromagnet in which at least two coils are stacked.
In the present invention, the magnetic dam may be an active type in which an operation is controlled through a switch or a passive type without the switch.
Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be interpreted as being limited to typical or dictionary meanings, but should be interpreted as having meanings and concepts which comply with the technical spirit of the present invention, based on the principle that an inventor can appropriately define the concept of the term to describe his/her own invention in the best manner. Accordingly, configurations illustrated in the exemplary embodiments and drawings disclosed in the present specification are only an exemplary embodiment of the present invention and do not represent all of the technical spirit of the present invention, and thus it is to be understood that various equivalents and modified examples, which may replace the configurations, are possible at the time of the present invention.
The magnetic dam illustrated in
A magnetic dam 10 includes a conductive structure device 11 and an insulation device 12. The conductive structure device 11 may be implemented in which a conductive wire is wound in a circular shape which is a shape according to a solenoid type superconducting coil. In this case, an insulation wire is together wound on the superconducting coil according to a conductive wire to implement the insulation device 12.
For convenience of description, the conductive wire and the insulation wire are described separately in units of one turn. When the conductive wire is separated in units of one turn in the conductive structure device 11, the conductive structure device 11 includes a plurality of conductive members 111 to 115. When the insulation wire is separated in units of one turn in the insulation device 12, the insulation device 12 includes a plurality of insulation members 121 to 125.
In
The magnetic dam 20 illustrated in
As illustrated in
When the magnetic dam is a passive type, both terminals (hereinafter, referred to as both terminals of the magnetic dam) of the conductive wire of an insulation type magnetic dam may be shorted. Even in the case of a no-insulation type magnetic dam, both terminals of the magnetic dam may be shorted. In particular, when the material of the conductive wire is the low temperature superconductor, the high temperature superconductor, etc., resistance of the magnetic dam may not be small. Even in the case of the no-insulation type magnetic dam, both terminals of the magnetic dam may be shorted in order to reduce the resistance.
When the magnetic dam is the active type, a control circuit is connected between both terminals of the insulation type and the no-insulation type magnetic dams. The control circuit may be implemented as at least one of a diode, a capacitor, and a switch. In charging and discharging the superconducting coil, in order to reduce an influence which the magnetic dam exerts to the charging and the discharging, the control circuit operates to control the current of the magnetic dam during the charging and the discharging.
As illustrated in
When the control circuit 40 is implemented by a switching element, the switching element is in an off state when charging and discharging the superconducting coil. During a period in which the switching element is in the off state, the magnetic dam 30 does not operate. When the superconducting coil is not charged and discharged, the switching element is turned on so as to prepare for an emergency situation such as the quench.
When the control circuit 40 is implemented as the diode, the control circuit 40 controls current to flow on the magnetic dam 30 in a forward direction of the diode. When the quench occurs in the superconducting coil, the current of the superconducting coil is rapidly generated in a discharge direction. That is, in the magnetic dam 30, the diode is connected between both terminals TM1 and TM2 so that a direction of current induced to the magnetic dam 30 becomes an inverse direction with respect to the diode when the superconducting coil is charged. For example, in a condition in which the both terminals TM1 and TM2 are shorted (there is no control circuit), if current which flows from a terminal TM1 to a terminal TM2 is induced when charging the superconducting coil, the diode of the control circuit 40 is connected to both terminals TM1 and TM2 so that a TM1->TM2 current direction becomes the inverse direction. That is, an anode of the diode may be connected to the terminal TM2 and a cathode of the diode may be connected to the terminal TM1. That is, the diode is connected to both terminals TM1 and TM2 so that the forward direction of the diode is opposite to the direction of the current induced to the magnetic dam when charging the superconducting coil. Since the current flows in the discharge direction of the superconducting coil when the quench occurs, the direction of the current which flows on the magnetic dam 30 matches the forward direction of the diode.
When the control circuit 40 is implemented as the capacitor, the capacitor may be designed so as to cause resonance with an inductor component of the magnetic dam 30 with respect to a specific frequency of an electromagnetic wave induced to the magnetic dam 30 when the quench occurs. Through resonance in a specific frequency band when the quench occurs, the resistance of the magnetic dam 30 is very small. Since the quench generally occurs even more rapidly than charging and discharging operations of the superconducting coil, an electromagnetic wave having a higher frequency band than the electromagnetic wave when the superconducting coil is charged and discharged is induced to the magnetic dam 30. In this case, the capacitor of the control circuit 40 resonates by matching the inductor component of the magnetic dam 30 in a specific frequency band during the quench.
Hereinafter, various exemplary embodiments in which the superconducting coil and the magnetic dam are coupled will be described with reference to drawings.
The type of superconducting coil may be implemented as a solenoid type, a race track type, a saddle type, a toroidal type, etc., and the present invention may be applied to all types of superconducting coils. First, exemplary embodiments in which the magnetic dam is coupled to the solenoid type superconducting coil will be described.
In
The superconducting coil 105 may be implemented by winding the superconducting wire in the no-insulation type in a solenoid shape. The superconducting coil support body 110 as a ring type including an exterior which is in contact with the interior of the superconducting coil 105 may be located on the interior of the superconducting coil 105. A width d1 of the superconducting coil support body 110 may be appropriately set according to a support force required for the superconducting coil support body 110.
The magnetic dam 50 which has a shape to surround the exterior of the superconducting coil 105 may be electromagnetically coupled to the superconducting coil 105. In
The magnetic dam 50 includes a conductive structure device 51 and an insulation device 52. When the conductive structure device 51 is separated in units of one turn, the conductive structure device 51 includes a plurality of conductive members 511 to 515. When the insulation device 52 is separated in units of one turn, the insulation device 52 includes a plurality of insulation members 521 to 525. For insulation among the plurality of conductive members 511 to 515 and insulation between the superconducting coil 105 and the conductive structure device 51, the plurality of insulation members 521 to 525 may be located. That is, the insulation member (e.g., reference numeral 522) is located between two adjacent conductive members (e.g., reference numerals 511 and 512) among the plurality of conductive members 511 to 515, and the insulation member 521 is located between the superconducting coil 105 and the conductive member 511.
The superconducting coil module 101 includes a superconducting coil 105, a superconducting coil support body 110, and a magnetic dam 60.
In the exemplary embodiment of
The magnetic dam 60 includes a conductive structure device 61 and an insulation device 62. When the conductive structure device 61 is separated in units of one turn, the conductive structure device 61 includes a plurality of conductive members 611 to 615. When the insulation device 62 is separated in units of one turn, the insulation device 62 includes a plurality of insulation members 621 to 624. For insulation among the plurality of conductive members 611 to 615, the plurality of insulation members 621 to 624 may be located. That is, the insulation member (e.g., reference numeral 621) is located between two adjacent conductive members (e.g., reference numerals 611 and 612) among the plurality of conductive members 611 to 615. When the magnetic dam 60 is coupled to the interior of the superconducting coil module 101, the superconducting coil support body 110 is located between the superconducting coil 105 and the conductive member 615, and as a result, the insulation member may not be located.
In
As illustrated in
A stacking structure of
The superconducting coil layer 11 includes a superconducting coil support body 115 and a superconducting coil 113, and the superconducting coil support body 115 as a ring type including an exterior contacting an interior of the superconducting coil 113 is located on the interior of the superconducting coil 113. The superconducting coil layer 12 includes a superconducting coil support body 125 and a superconducting coil 123, and the superconducting coil support body 125 as a ring type including an exterior contacting an interior of the superconducting coil 123 is located on the interior of the superconducting coil 123.
An insulation layer 17 for insulation between the superconducting coil layer 11 and the magnetic dam 70 is located between the superconducting coil layer 11 and the magnetic dam 70. An insulation layer 27 for insulation between the superconducting coil layer 12 and the magnetic dam 70 is located between the superconducting coil layer 12 and the magnetic dam 70. The magnetic dam 70 is electromagnetically coupled to two superconducting coil layers 11 and 12.
The magnetic dam 70 includes a conductive structure device 71 and an insulation device 72. In
The magnetic dam 70 includes a conductive structure device 71 and an insulation device 72. When the conductive structure device 71 is separated in units of one turn, the conductive structure device 71 includes a plurality of conductive members 711 to 715. When the insulation device 72 is separated in units of one turn, the insulation device 72 includes a plurality of insulation members 721 to 724. For insulation among the plurality of conductive members 711 to 715, the plurality of insulation members 721 to 724 may be located. That is, the insulation member (e.g., reference numeral 721) is located between two adjacent conductive members (e.g., reference numerals 711 and 712) among the plurality of conductive members 711 to 715.
A shape of the magnetic dam may be changed depending on a shape of the superconducting coil to which the magnetic dam is electromagnetically coupled.
As illustrated in
The magnetic dam 80 which has a shape to surround the exterior of the superconducting coil 205 may be electromagnetically coupled to the superconducting coil 205. In
The magnetic dam 80 includes a conductive structure device 81 and an insulation device 82. When the conductive structure device 81 is separated in units of one turn, the conductive structure device 81 includes a plurality of conductive members 811 to 815. When the insulation device 82 is separated in units of one turn, the insulation device 82 includes a plurality of insulation members 821 to 825. For insulation among the plurality of conductive members 811 to 815 and insulation between the superconducting coil 205 and the conductive structure device 81, the plurality of insulation members 821 to 825 may be located. That is, an insulation member (e.g., reference numeral 822) is located between two adjacent conductive members (e.g., reference numerals 811 and 812) among the plurality of conductive members 811 to 815, and an insulation member 821 is located between the superconducting coil 205 and the conductive member 811.
In
In order to help understand a coupling structure illustrated in
As illustrated in
The magnetic dam 90 which has a shape to surround the exterior of the superconducting coil 305 may be electromagnetically coupled to the superconducting coil 305. In
The magnetic dam 90 includes a conductive structure device 91 and an insulation device 92. When the conductive structure device 91 is separated in units of one turn, the conductive structure device 91 includes a plurality of conductive members 911 to 915. When the insulation device 92 is separated in units of one turn, the insulation device 92 includes a plurality of insulation members 921 to 925. The insulation member 921 is located between the conductive structure device 91 and the superconducting coil 305 for insulation between the conductive structure device 91 and the superconducting coil 305, and the plurality of insulation members 921 to 924 are located between two adjacent conductive members which correspond to each other for insulation among the plurality of conductive members 911 to 915. For example, the insulation members 922 is located between two adjacent conductive members 911 and 912 among the plurality of conductive members 911 to 915.
In
As illustrated in
A magnetic dam 95 which has a shape to surround the exterior of the superconducting coil 405 may be electromagnetically coupled to the superconducting coil 405. In
The magnetic dam 95 includes a conductive structure device 96 and an insulation device 97. When the conductive structure device 96 is separated in units of one turn, the conductive structure device 96 includes a plurality of conductive members 961 to 963. When the insulation device 97 is separated in units of one turn, the insulation device 97 includes a plurality of insulation members 971 to 973. The insulation member 971 is located between the conductive structure device 96 and the superconducting coil 405 for insulation between the conductive structure device 96 and the superconducting coil 405, and the plurality of insulation members 972 and 973 are located between two adjacent conductive members which correspond to each other for insulation among the plurality of conductive members 961 to 963. For example, the insulation members 972 is located between two adjacent conductive members 961 and 962 among the plurality of conductive members 961 to 963.
In
As illustrated in
The magnetic dam is electromagnetically coupled to the superconducting coil, so a rapid current change by the quench induces the current to the inductance L2. Therefore, energy of the superconducting coil is absorbed by the magnetic dam. Therefore, a voltage rise and a peak voltage of another superconducting coil adjacent to the superconducting coil in which the quench occurs may be lowered. Accordingly, according to the present invention, generation of overcurrent and overvoltage by the quench of the superconducting coil may be prevented.
A description of the same configuration as the equivalent circuit of
Therefore, as illustrated in
In
During a charging period of 50 to 150 seconds illustrated in
Further, during a discharging period of 440 to 550 seconds illustrated in
As such, when the magnetic dam is continuously shorted, the superconducting coil module may influence charging and discharging. In an exemplary embodiment, the control device is added to minimize the influence on the charging and the discharging of the superconducting coil module.
A simulation is performed under the following condition.
The superconducting coil is a no-insulation high temperature superconductor, the number of turns of the superconducting wire is 100, an inner diameter is 20 mm, an outer diameter is 32 mm, and an experimental temperature is LHe 4.2 K.
The magnetic dam is made of copper (Cu), and a residual-resistivity ratio (RRR) of copper is 100, the inner diameter is 33 mm, and the outer diameter is 38 mm.
As illustrated in
In a superconducting coil without the magnetic dam in the related art, since all stored energy is dissipated in the superconducting coil, an energy consumed in the superconducting coil by the quench and a temperature are higher than the present invention.
In order to satisfy an intensity of a magnetic field required for the superconducting coil module, the superconducting coil module may be implemented by stacking a plurality of superconducting coils. When the quench occurs in a specific coil among the plurality of stacked superconducting coils, a phenomenon in which the voltage, the current, and the temperature are raised for a short time occurs even another adjacent coil. When the magnetic dam is electromagnetically coupled to the superconducting coil module, such a phenomenon may be reduced. An exemplary embodiment of the present invention may include a magnetic dam applied to the plurality of stacked superconducting coils.
As illustrated in
Specific specifications for the plurality of superconducting coils illustrated in
In Table 1, C1 indicates five superconducting coils DP5 to DP9, C5 indicates two superconducting coils DP1 and DP13, C4 indicates two superconducting coils DP2 and DP12, C3 indicates two superconducting coils DP3 and DP11, and C2 indicates two superconducting coils DP4 and DP10. A case where “Number of DP” of C1 is disclosed as “5×1” means that there is one type in which five superconducting coils DP5 to DP9 are stacked. The remaining “1×2” means that there are two superconducting coils having the corresponding specification. As seen in Table 1, five types of superconducting coils are different in terms of average width, but the same as each other in terms of the remaining specifications. The superconducting coil module 500 stores energy of 25.4 [kJ] when the current of 342 A flows, and total inductance is 0.521 [H].
The magnetic dam 600 of
In order to show an effect according to an exemplary embodiment, a quench simulation is performed while changing a thickness of the magnetic dam 600. Specifically, as disclosed in Table 2, a winding inner radius of the magnetic dam 600 is fixed to 51.2 mm, and a winding outer radius is changed to 53.2 mm, 54.2 mm, 55.2 mm, 56.2 mm, and 57.2 mm. A radial build (winding outer radius—winding inner radius) which is the thickness of the magnetic dam 600 is changed to 2 mm, 3 mm, 4 mm, 5 mm, and 6 mm. In this case, a thickness of the insulation device 610 is constant, and a thickness of the conductive structure device 605 is changed.
As disclosed in Table 2, when the quench occurs in the simulation, energy consumed in the magnetic dam 600 is the largest if the thickness of the magnetic dam 600 is 6 mm. As the thickness of the magnetic dam 600 increases, a magnetic coupling coefficient between the plurality of superconducting coils and the magnetic dam decreases in the superconducting coil module, so the thickness of the magnetic dam 600 should be designed so that the coupling coefficient is not equal to or less than a predetermined threshold. The coupling coefficient of the magnetic dam in the superconducting coil module should be secured as a value which is large as possible. That is, the thickness of the magnetic dam 600 should be determined by considering both the energy consumed when the quench occurs, and the coupling coefficient.
When the quench occurs in a lumped parameter circuit model for the superconducting coil module, a voltage, a temperature, and a current of each of the plurality of superconducting coil modules DP1 to DP13 are simulated through COMSOL multiphysics.
Referring to a quench simulation result for the superconducting coil module in a condition without the magnetic dam illustrated in
Referring to a quench simulation result for the superconducting coil module including the magnetic dam illustrated in
As illustrated in
In an exemplary embodiment illustrated in
A simulation result of
As illustrated in
As illustrated in
As illustrated in
In an exemplary embodiment illustrated in
Each of the plurality of superconducting coils DPC1 to DPC3 is implemented as the double pancake type.
The magnetic dam 800 is wound on an exterior of one pancake coil DPC21 constituting the superconducting coil DPC2 and electromagnetically coupled, and the magnetic dam 850 is wound on an exterior of the other pancake coil DPC22 in the superconducting coil DPC2 and electromagnetically coupled.
The magnetic dam 800 may be implemented by winding both the conductive wire and the insulation wire on the exterior of the pancake coil DPC21. When the conductive wire and the insulation wire are separated in units of one turn, the conductive structure device of the magnetic dam 800 includes a plurality of conductive members 801 to 803, and the insulation device of the magnetic dam 800 includes a plurality of insulation members 821 to 823. In a cross section illustrated in
The magnetic dam 850 may be implemented by winding both the conductive wire and the insulation wire on the exterior of the pancake coil DPC22. When the conductive wire and the insulation wire are separated in units of one turn, the conductive structure device of the magnetic dam 850 includes a plurality of conductive members 851 to 853, and the insulation device of the magnetic dam 850 includes a plurality of insulation members 861 to 863. In a cross section illustrated in
A case where the number of winding times is illustrated as 3 in
Moreover, in
In
As illustrated in
In the drawings, the shapes of the superconducting coil and the superconducting coil support body, the shape of the conductive structure device, the shape of the insulation device, the number of winding times of the conductive wire, the number of winding times of the insulation wire, etc., are examples for describing the present invention. The examples disclosed in this specification do not limit the present invention.
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Number | Date | Country | Kind |
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10-2021-0070342 | May 2021 | KR | national |