Experimental and numerical examination of eddy (Foucault) currents in rotating micro-coils: Generation of heat and its impact on sample temperature

Aguiar, Pedro M.; Jacquinot, J. F.; Sakellariou, Dimitrios

doi:10.1016/j.jmr.2009.05.010

Cited by 42 publications

(45 citation statements)

References 36 publications

(41 reference statements)

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“…Assuming the same aspect ratio for L 1 and L 2 , the efficiency of power transmission to coil L 2 previously given by Eq. [20] becomes: and the magnitude of the field induced inside the coil L 2 previously given by Eq. [22] becomes:…”

Section: 7mentioning

confidence: 99%

“…The drawbacks of the split ring coil are its small inductance and the fact that large eddy currents are expected when it is rotated (20). Nevertheless, we can use its electrical characteristics to get a closed formula of the maximum SNR that can be reached with a microcoil of given dimensions.…”

Section: Limitation Due To the Coilmentioning

confidence: 99%

“…Several authors have recently proposed the use of inductive coupling between the coil of any standard NMR probe and a microcoil (1,(16)(17)(18)(19). This wireless coupling permits for easy sample and coil rotation inside conventional rotors as a way to enhance the filling factor and thus the sensitivity of limited-size solid samples (1,20,21). This approach was dubbed magic angle coil spinning, or MACS, because the coil is fixed to the sample, and both are placed inside the rotor which undergoes magic angle spinning.…”

Section: Introductionmentioning

confidence: 99%

“…Several examples of applications have been demonstrated for MACS, namely their use in confined samples (1), microscopic biological samples rapidly spinning (1), turning slowly (21), powdered solids in single resonance (1) or double resonance mode (22,23). It has been shown numerically and experimentally that eddy current effects in spinning microcoils can be controlled (20). There has been, however, little discussion (17) about the considerations of the electronics in such MACS probes.…”

Section: Introductionmentioning

confidence: 99%

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NMR signal detection using inductive coupling: Applications to rotating microcoils

Jacquinot

Sakellariou

2011

Concepts Magnetic Resonance

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Sensitivity in solid-state nuclear magnetic resonance can be improved by the use of rotating microcoils (1). The connection to the rest of the electronics is performed through resonant inductive coupling. This mode of detection of nuclear induction has major advantages as it provides a wireless way to obtain extremely high radio-frequency amplitudes per unit current under sample rotation and thus improved sensitivity for size-limited samples. We review the circuit electronics and discuss experimental optimization of the probe and coil parameters. We also present alternative geometries for coupling between rotating coils and we explicitly calculate the signal enhancement. Two practical cases are presented, namely a standard magic angle sample spinning probe and a double sample rotation probe. We conclude with a theoretical discussion about the limits of detection attainable with coil miniaturization.

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Section: 7mentioning

confidence: 99%

Section: Limitation Due To the Coilmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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NMR signal detection using inductive coupling: Applications to rotating microcoils

Jacquinot

Sakellariou

2011

Concepts Magnetic Resonance

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“…[29,30] In addition, eddy currents are generated by spinning the Halbach part inside a uniform longitudinal field, generating heat in a way analogous to motors or magic angle spinning coils. [31] In this paper, we combine both Halbach's and Aubert's permanent magnet designs to produce a hybrid structure, where the magnetic field at the center is pointing along a direction making an 'arbitrary' angle with the axis of the cylinder. This structure is made out of pure permanent magnets allowing the rotation of the entire magnet around its axis.…”

Section: Theorymentioning

confidence: 99%

Permanent magnet assembly producing a strong tilted homogeneous magnetic field: towards magic angle field spinning NMR and MRI

Sakellariou

Hugon

Guiga

et al. 2010

Magnetic Reson in Chemistry

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We introduce a cylindrical permanent magnet design that generates a homogeneous and strong magnetic field having an arbitrary inclination with respect to the axis of the cylinder. The analytical theory of 3 D magnetostatics has been applied to this problem, and a hybrid magnet structure has been designed. This structure contains two magnets producing a longitudinal and transverse component for the magnetic field, whose amplitudes and homogeneities can be fully controlled by design. A simple prototype has been constructed using inexpensive small cube magnets, and its magnetic field has been mapped using Hall and NMR probe sensors. This magnet can, in principle, be used for magic angle field spinning NMR and MRI experiments allowing for metabolic chemical shift profiling in small living animals.

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Capacitor re‐design overcomes the rotation rate limit of MACS resonators

Adhikari

Wallrabe

Badilita

et al. 2017

Concepts Magn Reson

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The magic angle coil spinning (MACS) technique has provided a breakthrough in enhancing sensitivity in magic angle spinning (MAS) NMR. However, efforts in improving the MACS detector for higher spinning speeds have been lacking. One published MACS construction technique is to solder a handwound solenoidal coil to a commercial non-magnetic capacitor and subsequently centering the detector inside the MAS rotor. An alternative method to realize these detectors is by using MEMS fabrication at the wafer scale, potentially capable of achieving reproducible MACS detectors. However, it is also important that the performance of the sensors does not deteriorate as a result of microfabrication constraints. The footprint of the detectors is a limiting factor in achieving higher spinning speeds. One of the key elements of a micro-resonator is its tuning capacitor, whose geometry has a significant influence on its electrical and mechanical performance. The quality factor of the capacitor, along with the induced eddy currents, are the key performance parameters considered. The article addresses these concerns by presenting a study of microfabricated on-chip capacitors for magic angle coil spinning (MACS) detectors. The capacitors are juxtaposed with commercially available capacitors and the most suitable fit to be integrated with a micro-coil is established.K E Y W O R D S eddy currents, magic angle coil spinning, MEMS fabrication, quality factor

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Experimental and numerical examination of eddy (Foucault) currents in rotating micro-coils: Generation of heat and its impact on sample temperature

Cited by 42 publications

References 36 publications

NMR signal detection using inductive coupling: Applications to rotating microcoils

NMR signal detection using inductive coupling: Applications to rotating microcoils

Permanent magnet assembly producing a strong tilted homogeneous magnetic field: towards magic angle field spinning NMR and MRI

Capacitor re‐design overcomes the rotation rate limit of MACS resonators

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