2005 Fiscal Year Final Research Report Summary
Development of SQUID magnetometers operating in a magnetic field noise.
| Project/Area Number |
15560287
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Electron device/Electronic equipment
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| Research Institution | Muroran Institute of Technology |
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Principal Investigator |
MATSUDA Mizushi Faculty of Engineering, Electrical and Electronic Engineering, Professor, 工学部, 教授 (20261381)
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| Co-Investigator(Kenkyū-buntansha) |
NAKANE Hideaki Faculty of Engineering, Electrical and Electronic Engineering, Associate Professor, 工学部, 助教授 (20237332)
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| Project Period (FY) |
2003 – 2005
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| Keywords | SQUID / Signal-noise ratio / Magnetic noise / Array structure / Non-destructive evaluation / 非破壊計測 |
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| Research Abstract |
For practical use of high-T_c dc superconducting quantum interference devices (SQUIDs), it is desirable to work in unshielded environment. In general, SQUIDs suffer from increased low frequency noise when operated in a relatively large residual magnetic field. This has been explained in the framework of thermally activated hopping of magnetic flux vortices trapped at local pinning sites in the superconducting film of the SQUID body. Then, the low frequency noise of a narrow current-carrying superconducting film is measured in order to examine the flux noise induced by shielding current in dirct coupled high-Tc SQUIDs. The behavior of the low-frequency flux noise as a function of applied current for samples prepared with different edge shapes suggest that the surface barrier at the strip edge plays a crusial role in determining the magnitude and occurrence of current-induced noise, while the pinning within the strip affects the occurrence of remanent flux noise.
The other approach to reduce the noise and to improve the signal to noise ratio is the use of the multiple-SQUID array. When n identical non-interacting dc-SQUIDs are connected in parallel and biased at a constant voltage, the current through the array exhibits a current modulation that is n times larger in amplitude than that of a single device. Since the current noise of array increases as n^<1/2> because of its uncorrelated nature, the resultant S/N ratio increases by n^<1/2>. We have fabricated and characterized the magnetometer with a parallel multiple-SQUID array. It is confirmed that the modulation depth for currents for multiple-SQUIDs is several times larger than that for a SQUID. White noise level depends upon the SQUID number n in a array, lower noise level for larger n.
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