Magnetic flux fluctuations due to eddy currents and thermal noise in metallic disks

Uzunbajakau, S.; Rijpma, A.P.; Dolfsma, J.; Krooshoop, Hendrikus J.G.; Brake, H.J.M. ter; Peters, M.J.; Rogalla, Horst

doi:10.1109/tmag.2003.812720

Cited by 4 publications

(2 citation statements)

References 8 publications

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“…Electrically conducting materials generate thermally induced magnetic noise due to thermal fluctuations of conduction electrons inside the conductor [4][5][6]. If we model a conducting cylinder as shown in Fig.…”

Section: Measurement and Analysis Of Thermal Noisementioning

confidence: 99%

Analysis and reduction of thermal magnetic noise in liquid-He dewar for sensitive low-field nuclear magnetic resonance measurements

Hwang¹,

Hung²,

Lee³

et al. 2013

Progress in Superconductivity and Cryogenics

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For sensitive measurements of micro-Tesla nuclear magnetic resonance (μT-NMR) signal, a low-noise superconducting quantum interference device (SQUID) system is needed. We have fabricated a liquid He dewar for an SQUID having a large diameter for the pickup coil. The initial test of the SQUID system showed much higher low-frequency magnetic noise caused by the thermal magnetic noise of the aluminum plates used for the vapor-cooled thermal shield material. The frequency dependence of the noise spectrum showed that the noise increases with the decrease of frequency. This behavior could be explained from a two-layer model; one generating the thermal noise and the other one shielding the thermal noise by eddy-current shielding. And the eddy-current shielding effect is strongly dependent on the frequency through the skin-depth. To minimize the loop size for the fluctuating thermal noise current, we changed the thermal shield material into insulated thin Cu mesh. The magnetic noise of the SQUID system became flat down to 0.1 Hz with a white noise of 0.3 fT/√Hz, including the other noise contributions such as SQUID electronics and magnetically shielded room, etc, which is acceptable for low-noise μT-NMR experiments.

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Section: Measurement and Analysis Of Thermal Noisementioning

confidence: 99%

Analysis and reduction of thermal magnetic noise in liquid-He dewar for sensitive low-field nuclear magnetic resonance measurements

Hwang¹,

Hung²,

Lee³

et al. 2013

Progress in Superconductivity and Cryogenics

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show abstract

“…The RFI shield is typically made of a single layer of a conducting material such as aluminum paint, aluminum foil, or copper meshing. Both the superinsulation and the RFI shield comprise conductive components and produce magnetic noise [5], [6]. The shielding by the RFI shield improves with increasing thickness and conductivity of the material that is used in the shield.…”

Section: A Measuring Systemmentioning

confidence: 99%

Optimization of a Third-Order Gradiometer for Operation in Unshielded Environments

Uzunbajakau

Rijpma

Brake

et al. 2005

IEEE Trans. Appl. Supercond.

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Abstract-The optimum geometry of a third-order gradiometer for operation in unshielded environments is discussed. The optimization result depends on the specific signal and noise conditions. The fetal heart is considered as an example of the signal source. We optimized the gradiometer such that the signal-to-noise ratio is maximized in an averaged sense for all relevant environmental noise conditions and distances to the signal source. The resulting design consists of two second-order gradiometers that can be combined to form a third-order gradiometer in noisy environments, whereas a single second-order gradiometer can be used in lownoise environments. The gradiometer can provide the signal-tonoise ratio that allows detection of fetal heart signals in all relevant environmental noise conditions.

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Analysis and Reduction of Eddy Current Influence on Measurement Dewar for a 60 T Pulsed Magnet

Liu,

Li,

2023

2023 26th International Conference on Electrical Machines and Systems (ICEMS)

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Magnetic flux fluctuations due to eddy currents and thermal noise in metallic disks

Cited by 4 publications

References 8 publications

Analysis and reduction of thermal magnetic noise in liquid-He dewar for sensitive low-field nuclear magnetic resonance measurements

Analysis and reduction of thermal magnetic noise in liquid-He dewar for sensitive low-field nuclear magnetic resonance measurements

Optimization of a Third-Order Gradiometer for Operation in Unshielded Environments

Analysis and Reduction of Eddy Current Influence on Measurement Dewar for a 60 T Pulsed Magnet

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