NMR Coil Current Source With Hybrid Linear-Switching Regulation
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Solution Overview
Problem
Current shim current sources for NMR apparatuses are inefficient due to high voltages and currents in the current control loop, generating excessive waste heat and requiring large heat dissipation devices, and are being phased out by audio Class-D amplifiers that do not meet NMR coil current supply requirements.
Innovation Solution
A linear current controller with a digital voltage source using switching technology and a high inductive load is integrated between the NMR coil and the linear current regulator, filtering high-frequency interference and minimizing power loss, allowing for stable, low-noise current supply with high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a linear current regulator is used to supply current to the NMR coil, then the current can be regulated stably, but high voltages and currents in the control loop generate excessive waste heat requiring large heat dissipation devices
Solution Approach 1:
The current source is divided into two distinct parts: a linear current regulator for stable current regulation and a separate power supply unit for efficient power delivery. This segmentation allows each component to operate in its optimal range, with the power supply providing high current with minimal voltage drop and the linear regulator maintaining stability without excessive power dissipation.
Solution Approach 2:
A current sense resistor is introduced as an intermediary element to measure the current flowing through the NMR coil. This enables feedback control that allows the linear regulator to operate with reduced voltage drop, thereby minimizing power loss while maintaining stable current regulation.
2Power
If high voltages and currents are applied in the current control loop to supply the NMR coil, then sufficient power is delivered, but excessive waste heat is generated requiring large heat dissipation devices
Solution Approach 1:
The power delivery function is separated from the current regulation function. The power supply unit delivers high current with minimal voltage drop, while the linear regulator handles only the small voltage adjustment needed for current stabilization. This segmentation dramatically reduces the power dissipated as heat in the regulation circuit.
Solution Approach 2:
The operating parameters of the linear regulator are changed by providing it with a reduced voltage range through the current sense resistor feedback mechanism. This allows the regulator to operate with small voltage drops, minimizing power loss while still achieving stable current control.
3Loss of energy
If audio Class-D amplifiers are used to replace traditional linear current regulators, then efficiency is improved, but they do not meet NMR coil current supply requirements
Solution Approach 1:
The system segments the current supply function into a power supply unit that provides efficient high-current delivery and a linear regulator that ensures stable, low-noise current control. This hybrid approach combines the efficiency of Class-D amplifiers with the precision and stability required for NMR applications.
Solution Approach 2:
The linear regulator acts as an intermediary between the efficient but noisy power supply and the sensitive NMR coil. It filters out high-frequency noise and ensures stable current delivery, making the system suitable for NMR applications while maintaining efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a stable, low-noise current supply with minimal power consumption, maintaining high magnetic field homogeneity and resolution in NMR experiments, even under changing conditions, while reducing the size and cost of the power source.
Implementation Method 1
the digital voltage source is implemented using switching technology
Implementation Method 2
the linear current regulator is configured as follows: that it regulates the digital voltage source in such a way that the voltage on the side of the linear part of the arrangement lies within a preselected operating range
Implementation Method 3
A stable and low-noise current source, which is designed to supply an NMR coil in such an NMR apparatus with electrical current
Implementation Method 4
the substance is exposed to a strong, static, homogeneous magnetic field B0, which aligns the nuclear spins within the substance
Implementation Method 5
High-frequency electromagnetic pulses are then irradiated into the substance under investigation. The resulting high-frequency electromagnetic fields are detected in the NMR spectrometer
Data Source
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AI summary
An NMR apparatus (10) having an NMR magnet system for generating an NMR magnetic field, which comprises an NMR coil (11) for modifying the magnetic field, and having a stable and low-noise current source which supplies the NMR coil with electric current, comprises a linear current controller (12) which is electrically connected to a first end of the NMR coil, is characterised in that the current source comprises a digital voltage source (13) in switching technology, which is connected to a second end of the NMR coil such that the NMR coil is connected as an electric consumer between the linear current controller and the digital voltage source; in that the current controller is connected via a control line (14) for controlling the electric voltage to the digital voltage source; and in that the linear current controller controls the digital voltage source such that the voltage on the side of the linear part of the arrangement is in a preselected working range such that in the linear part of the arrangement, the lowest possible electric power is consumed. As a result, the NMR coil can be supplied with current at a high electric efficiency in an adjustable, stable and low-noise manner, wherein the homogeneity of the NMR magnetic field can be kept stable and constant even when external conditions change.