Dynamic shielding of the magnetic fields

Baltag, Octavian; Costandache, D.; Rau, Miuta Carmina; Iftemie, Anca; Rau, I.

doi:10.4316/aece.2010.04022

Cited by 23 publications

(9 citation statements)

References 19 publications

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“…The first winding is used for the manual compensation of the continuous component of the vector magnetic field along the three directions (X, Y, Z) within the range ±40 A/m. The second winding serves to compensate the alternating and slowly variable components of the magnetic field within the range ±40 A/m, making use of a system controlled by a triaxial magnetometer which operates in the negative feedback loop [31], [32].…”

Section: Methodsmentioning

confidence: 99%

First-order SQUID gradiometer with electronic subtraction for magnetocardiography

Carmina

Baltag

2012

2012 International Conference and Exposition on Electrical and Power Engineering

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The paper presents theoretical and experimental results of the research concerning the design and properties of a 1 st -order SQUID gradiometer with electronic subtraction and the recording of the first magnetocardiogram (MCG) performed in Romania, at the Bioelectromagnetism Laboratory of the Faculty of Biomedical Engineering. The MCG recording was possible by using a complex installation composed from a non ferromagnetic shielded room placed in the centre of the large (4 x 4 x 4) m, triaxial Helmholtz coils system. The Helmholtz system ensures the static compensation of the geomagnetic field and the active shielding too, by using the magnetic field negative feedback. . Magnetocardiography (MCG) is a noninvasive and risk-free technique for contactless surface mapping of the magnetic fields generated by the electrical activity of the heart. The difficulty of recording of a magnetocardiogram is determined by the very low value of biomagnetic field (10 -15 -10 -12 )T. Even the strongest of such biomagnetic fields, the one produced by the human heart, barely reaches 100 pT outside the thorax, less than a millionth of the geomagnetic field value and orders of magnitude weaker than environmental magnetic noise fields. In this context, the detection and recording of these fields require an extremely sensitive device such as SQUID biomagnetometer and special conditions. Performances of the installation are presented.

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Section: Methodsmentioning

confidence: 99%

First-order SQUID gradiometer with electronic subtraction for magnetocardiography

Carmina

Baltag

2012

2012 International Conference and Exposition on Electrical and Power Engineering

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“…The magnetic fields have been already used in diagnostics in connection with eminent sources of the fields, such as electrical energy converters and transformers, as well as furnaces with induction heating [37]. These measurements were performed for the purpose of the occupational hygiene [38][39][40] or compatibility issues [41][42][43][44]; they were mostly realized on static devices or near electric motors in case of mobile systems.…”

Section: Introductionmentioning

confidence: 99%

Low-Frequency Magnetic Fields in Diagnostics of Low-Speed Electrical and Mechanical Systems

et al. 2021

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The magnetic field created by technical devices is a source of information. This information could be used in contactless diagnostics and predictive maintenance or for resolving problems along with standard NDT (nondestructive testing) methods, especially if we consider large, slow-speed devices, such as electromotors, transmissions, or generators. Identification of causalities of device failure processes with near magnetic field is one of the suitable NDT methods improving sustainability of systems. The measurements presented in the article were performed with the VEMA 04 fluxgate vector magnetometer with the DC-250 Hz bandwidth and 2 nT sensitivity. Postprocessing of the results was performed in the means of standard methods of discrete Fourier Transform, spectrogram creation and Wavelet Transform. The article presents data gathered during the measurement of a pair of extraction fans with power of 140 kW each and maximum revolutions up to 740 rev/min controlled by frequency converters and a single semi-Kaplan water power plant with 400 kW peak power at 1005 rev/min maximum generator speed. The measurements were performed before and after repairs of one of the ventilators in the ventilation system at 60% and 100% of maximal output power. The rotating magnetic fields of the fan electromotor stator, fan rotor revolutions, rotor slip frequency and ball-bearing frequencies were identified in frequency spectrums in the distance of 700 mm from fan electromotor axis in both cases. During the measurements on the semi-Kaplan turbine, the changes in states of mechanical and electrical components of the machine were monitored in the magnetic fields with increase of the power in the range of 0–95%, before and after phasing to the electrical grid. Standard processing methods, Discrete Fourier Transform, spectrograms and Discrete Wavelet Transform were used. In the spectrograms of the measured magnetic fields, the 1st–4th harmonics of the turbine shaft, generator shaft and also their side frequencies were identified. Significant changes of magnetic fields in time were identified in the area of 60–95% power. With the help of the Wavelet, transform intervals were identified where it is desirable to operate the turbine. The analyses of magnetic fields measurements performed on the power plant were compared with vibro-diagnostic principles.

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“…[3][4][5] Several studies have identified the effect of electromagnetic interference on image resolution and proposed solutions to minimize its effect. [6][7][8][9][10]11 The causes and solutions for the image distortions due to sample drift are discussed in. 6,10,[12][13][14][15][16][17] Image distortions due to vibrations are seen at atomic resolution.…”

Section: Introductionmentioning

confidence: 99%

Development of tomography–transmission electron microscope (TEM) specimen holder stable under acoustic disturbances

Bataineh

2021

Building Acoustics

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This paper focuses on the development of tomography—transmission electron microscope (TEM) specimen holder stable under environment effect that allows atomic resolution. The successful holder must be dynamically stable for accuracy and image processes to obtain an atomic resolution, with a minimum controllable drift of the sample position. Different strategies to reduce the effect of acoustic disturbances are investigated. The approach to the problem has been two-fold, numerical and experimental. The effect of mechanical and acoustic noise is analyzed. Finite element results match very well previous experimental results and observations. Theoretical analysis showed that air pressure fluctuations have a significant impact on microscopes with side entry goniometers, especially when the exciting frequency matches a vibration mode of the sample holder. For example, finite element analysis (FEA) predicts that the tip deflections are 4.5 Å and 0.09 Å under air pressure excitation of 64 and 40 dB respectively. Utilizing a sandwiched constrained damping shell layer made of viscoelastic material that partially covers the inner part of TEM holder body successfully decreased the vibration. Finite element simulations predict that a shell layer of viscoelastic material with a thickness equal to the 1/10 of the body holder diameter reduces the vibrations by 30%. The viscoelastic layer shell thickness, loss factor, and elastic modulus have a strong effect on the damping behavior and the optimal combination should be determined.

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Dynamic shielding of the magnetic fields

Cited by 23 publications

References 19 publications

First-order SQUID gradiometer with electronic subtraction for magnetocardiography

First-order SQUID gradiometer with electronic subtraction for magnetocardiography

Low-Frequency Magnetic Fields in Diagnostics of Low-Speed Electrical and Mechanical Systems

Development of tomography–transmission electron microscope (TEM) specimen holder stable under acoustic disturbances

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