# US 8,788,227 B2 · Measuring method of critical current density of superconductor wires using measurement of magnetization loss

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- Number: US 8,788,227 B2
- Document ID: US8788227B2
- Status: Granted
- Kind: B2
- Application number: 12/997,055
- Filed: 2010-07-28
- Published: 2011-11-03
- Granted: 2014-07-22
- Earliest claimed: 2009-11-20
- Assignees: Korea Polytechnic University Industry Academic Cooperation Foundation; Woosuk University Industry Academic Cooperation Foundation
- Applicants: Kyeong Dal Choi; Ji Kwang Lee; Woo Seok Kim; Chan Park; Byung Wook Han; Se Yeon Lee
- Inventors: Kyeong Dal Choi; Ji Kwang Lee; Woo Seok Kim; Chan Park; Byung Wook Han; Se Yeon Lee
- Web page: https://patentgrep.com/patent/US8788227B2

## CPC

- G01R 33/1246: {Measuring critical current}
- G01N 27/82: for investigating the presence of flaws
- G01R 19/08: Measuring current density
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

A method for measuring critical current density of superconductor wires according to the present invention is characterized in that it includes: (a) applying an external magnetic field to the superconductor wires, (b) measuring a magnetization loss of the superconductor wires according to the application of the external magnetic field, (c) normalizing the measured magnetization loss, and then calculating a fully-penetration magnetic field of the superconductor wires according to the normalized magnetization loss, (d) calculating a critical current density of the superconductor wires according to the calculated fully-penetration magnetic field. Therefore, the critical current density of parallel superconductor wires such as stacked superconductor wires may be measured without applying current to the superconductor wires directly.

## Claims

### Claim 1

A method for measuring critical current density of superconductor wires, the method comprising:
(a) applying an external magnetic field to the superconductor wires;
(b) measuring a magnetization loss of the superconductor wires, according to the application of the external magnetic field;
(c) normalizing the measured magnetization loss, and then calculating a full-penetration magnetic field of the superconductor wires according to the normalized magnetization loss; and
(d) calculating a critical current density of the superconductor wires according to the calculated full-penetration magnetic field, wherein:
at (b), a Brandt's strip model equation
Q
m
=
2
⁢
⁢
B
m
2
⁢
μ
0
⁢
π
⁢
⁢
ω
2
⁢
⁢
β
⁢
⁢
d
⁡
[
2
β
⁢
ln
⁢
⁢
(
cosh
⁢
⁢
β
)
-
tan
⁢
h
⁢
⁢
β
]
is applied to the calculation for measuring the magnetization loss of the superconductor wires, where Qm is the magnetization loss by the external magnetic field applied in a vertical direction of the superconductor wires, Bm is a dimension for the external magnetic field, ω is a frequency, β is a ratio of the external magnetic field to a characteristic magnetic field, μ0 is a vacuum permeability which is a constant value, and d is the width of the superconductor wires;
and further wherein operation (c) comprises:
(c1) normalizing the measured magnetization loss;
(c2) differentiating the normalized magnetization loss; and
(c3) calculating the full-penetration magnetic field by determining a relation of the characteristic magnetic field applied to Brandt's strip model equation and the full-penetration magnetic field, according to a differentiated value of the normalized magnetization loss,
and further wherein at (c3), the relation of the characteristic magnetic field and the full-penetration magnetic field is expressed as an equation Bd=β×Bp, where Bd is the characteristic magnetic field, Bp is the full-penetration magnetic field, and β is the ratio of the external magnetic field to the characteristic magnetic field;
and further wherein β is determined when the differentiated value of the normalized magnetization loss becomes zero at (c2).

### Claim 2 (depends on 1)

The method for measuring critical current density of superconductor wires of claim 1, wherein, at (d), the critical current density is expressed by an equation
J
c
=
β
⁢
⁢
B
p
⁢
π
μ
0
⁢
d
,
where Jc is the critical current density.