Reversible current power supply for fast-field cycling nuclear magnetic resonance equipment (original) (raw)
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2016 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM), 2016
The main power supply of a Fast Field-Cycling Nuclear Magnetic Resonance (FFC-NMR) is the key element comparing the performance of different solutions. The power supply is a current source that supplies a magnet being the current controlled in order to perform adjustable and repetitive current cycles. This power supply can be based on different topologies, operating principles and controlled using distinct techniques. If for the final users of this experimental technique the current cycles of the equipment is the core feature, for the developers also the power losses distribution needs to be analyzed in order to develop efficient solutions. In this paper, the power losses and the dynamic behavior of two solutions for the FFC-NMR power supply are compared and discussed.
Electromagnetic and thermal aspects of a Fast Field Cycling NMR equipment
2015 9th International Conference on Compatibility and Power Electronics (CPE), 2015
The Fast Field Cycling Nuclear Magnetic Resonance (FFC-NMR) technique has been spreading its application to new areas such as oil and food industry. Consequently, new features and improvements concerning the equipment available has been investigated and exploited. Under this context, this paper describes the main aspects concerning the electromagnetic and thermal behavior of the main power supply and the magnet, respectively. The proposed power supply and the magnet were developed under the specifications of the FFC-NMR equipment and in order to match the requirements of the most recent areas of application. The dynamic behavior of the power supply is analyzed based on simulation results, being the thermal study of the magnet performed using finite element method software.
New Magnet Design for Fast-Field-Cycling Nuclear Magnetic Resonance
IEEE Latin America Transactions, 2013
A new magnet design for fast-field-cycling nuclear magnetic resonance is described. A topic of interest is the compensation of the magnetic field homogeneity during the generation of the pulsed magnetic field. In contrast with previous solutions, the magnet system here discussed can be electronically controlled. In Kelvin-type magnets used today, the homogeneity of the field is setup through a current density distribution along the air-cored cylinders that compose the magnet coil. A common feature of this type of magnets is that the magnetic field value and its homogeneity are affected by thermo-mechanical stress during the strong current pulses applied to the coil. In the new design here presented, the problem can be circumvented through a multicoil arrangement driven by individual current sources, allowing an automatic correction of the magnetic field drift and the homogeneity.
Electromagnetic Analysis and Thermal Behaviour of FFC-NMR Magnets
2014
The Fast Field Cyclic Nuclear Magnetic Resonance (NMR-FFC) is a research technique that explores the magnetic properties of atomic core. This technique can provide detailed information on the structure, dynamics, reaction state and chemical environment of molecules. This technique has a high use in various research areas such as Physics, Chemistry, Medicine, Pharmacy and others. The same technique requires spectrometers that allow to switch the magnetic field between different intensity levels quickly and accurately. However, it is necessary to ensure a relationship between magnetic field and the frequency of the radio frequency signal which allows the detection of the signal emitted by the sample. With the expansion of this technique to new areas such as oil and food industry, it is pertinent to investigate new solutions for implementation of the technique. This work presents a solution to make up the power supply responsible for supply the magnet and a thermal study of the magnet....
Fast field-cycling nuclear magnetic resonance spectrometer
Review of Scientific Instruments, 1996
We describe here the design and construction of a modern, state-of-the-art nuclear magnetic resonance ͑NMR͒ field-cycling instrument. Fourier transform NMR spectra of both liquid and solid samples can be measured, and spin-lattice relaxation times (T 1Z ) investigated over a broad range of magnetic field strengths ranging from 0 to 2 T. The instrument is based upon an existing personal computer-based NMR spectrometer ͓C. Job, R. M. Pearson, and M. F. Brown, Rev. Sci. Instrum. 65, 3354 ͑1994͔͒ which has been expanded into a fully computer-controlled field-cycling instrument. The magnetic field cycling is accomplished electronically by utilizing fast switching thyristors and a storage capacitor based on the Redfield energy storage concept. Unique aspects of the design include the field-cycling magnet, which can reach fields as high as 2 T; the personal computer-based NMR spectrometer and associated waveform electronics; and the use of a commercially available pulse width modulation switching current amplifier, having low internal power dissipation and a fast current settling time. Using this new technology T 1Z relaxation times as short as 1 ms can be readily measured.
Digital Control of an FFC NMR Relaxometer Power Supply
2020
The fast field cycling (FFC) experimental technique allows to overcome a technical difficulty associated with the nuclear magnetic resonance (NMR) signal-to-noise ratio (SNR) at low frequency spin-lattice relaxation measurements when using conventional NMR spectrometers. Constituting a step forward than the classical analog approaches, in this paper, a digital control system for an FFC-NMR relaxometer power supply was developed. The hardware and software were designed to allow for the modulation of the Zeeman field as required by this technique. Experimental results show that under digital control the system performs fast transitions between the high and low magnetic flux density levels, i.e., the switching times obtained are in the millisecond range, and, assures a good stability of the field during the steady states. Comparative proton relaxometry measurements in two compounds (liquid crystal 5CB and ionic liquid [BMIM]BF4) were made to assess the digital control system performance.
High-efficiency ripple-free power converter for nuclear magnetic resonance
Power Electronics Specialists …, 2000
A new power converter topology and control scheme, enabling a ripple free output with high efficiency, is presented. Feedback controllers for the proposed topology are designed taking into account non-ideal parameters. Experimental results, presenting almost no ripple, fast dynamics, almost no overshoot, and good tracking performance, demonstrate the merits and justify the cost of the extra amplifier needed in the new converter concept.
FFC-NMR Power Supply with Hybrid Control of the Semiconductor Devices
Journal of Low Power Electronics and Applications
The performance of FFC-NMR power supplies is evaluated not only considering the technique requirements but also comparing efficiencies and power consumption. Since the characteristics of FFC-NMR power supplies depend on the power circuit topology and on the control solutions, the control design is a core aspect for the development of new FFC systems. A new hybrid solution is described that allows controlling the power of semiconductors by switches (ON/OFF mode) or as a linear device. The approach avoids over-design of the power supply and makes it possible to implement new low power solutions constituting a novel design by joining a continuous match between the ON/OFF mode and the linear control of the power semiconductor devices.
A new high-precision current supply for magnets
IEEE Transactions on Nuclear Science, 1995
A new, high-precision, low-ripple current power supply (CPS) for magnets, based on a combination of an SCR converter and a single transistor switched mode power supply (SMPS) is described. The load power is primarily supplied by the SCR converter. The SMPS handles only a small fraction of the load power, and also, what is more significant, a very small part of the load current. In this paper, the topology and operating principle of the new power supply is discussed. A CPS, rated at 200 A at 45 V, was constructed and tested. The power supply energizes a family of quadrupole magnets at the Brazilian Synchrotron Light Source-LNLS [l]. Making use of the current limit modulation (CLM) control method, magnetic field variations at full current are 5 ppm, with only 8 A passing through the switching transistor. The design and performance of the power supply under different operating conditions are described. Variations of the proposed topology, suitable for highcurrent and high-voltage loads, are also discussed.