A kind of nuclear magnetic resonance spectrometer self-shielding gradient coil and its design method

Abstract

The invention discloses a self-shielding gradient coil of a nuclear magnetic resonance spectrometer and a design method thereof. The invention is characterized in that, the self-shielding gradient coil comprises a main coil and a shielding coil which is coaxially arranged on the outer side of the main coil. The windings of the main coil are composed of a plurality of stages of main coil upper windings and main coil lower windings which are symmetrically arranged up and down. The centers of winding wire troughs, the circle radiuses of winding coils and turns per coil, corresponding to the maincoil upper windings and the main coil lower windings, are symmetrically arranged up and down in the one-to-one mode. The windings of the main coil are wound in the winding wire troughs and are arranged in a single-layer winding mode in the axial direction. Each stage of main coil winding corresponds to an independent driving current channel. According to the self-shielding gradient coil and the design method thereof, the series single-channel circuit design is changed into the matrix multi-channel circuit design, and the coil structure is simplified. The optimization difficulty of a target field is reduced. The probability that the actually generated gradient field is deformed and the linearity is not pure due to the winding translation and the interlayer dislocation is reduced.

Description

technical field [0001] The invention belongs to the field of gradient coils, in particular to a matrix type self-shielding gradient coil of a nuclear magnetic resonance spectrometer and a design method thereof. Background technique [0002] Gradient coils are a key component of nuclear magnetic resonance (NMR) spectrometers. In high-resolution NMR experiments, pulsed currents are used to generate specific pulsed gradient magnetic fields to achieve such things as spatial encoding, diffusion motion, coherent selection, and suppression of unwanted magnetization signals. and other important gradient effects. Measuring the performance indicators of gradient coils mainly includes gradient field linearity, gradient switching time (rising edge, falling edge), gradient eddy current, etc. Therefore, improving the performance of gradient coils is of great significance for improving the effect of nuclear magnetic resonance experiments and improving the overall level of the instrument. ...

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Problems solved by technology

To match it, the target field of the gradient coil must also expand the linear range, which requires increasing the number of turns (wire consumption) and the number of layers of the gradient main coil; on the other hand, the accumulated magnetic field causes the stray field in the shielding area to increase accordingly Larger, the optimization of the shielding coil structure becomes more complicated, requiring a denser coil shape, so more constraints need to be added in order to avoid overlapping of wire distribution

[0005] In addition to making it more difficult to optimize the gradient coil structure, the increase in the amount of wire used in the coil also leads to a larger coil inductance. The direct result is that the switching speed of the pulsed gradient field becomes slower, especially when the required gradient strength is proportionally larger, the gradient The hysteresis phenomenon of the rising edge becomes more and more obvious, which leads to the imbalance of the proportion of the effect of the actual gradient field on the magnetization (also known as the effect of the gradient field area, which is determined by the product of the gradient field strength and the action time). For the multi-pulse gradient field, it must be designed into different shapes Compared with proportional NMR experiments, the actual spectrum effect is unsatisfactory

In addition, the increase in the number of layers of the gradient main coil arrangement will also lead to the difficulty of producing the winding process. This process difficulty is mainly reflected in the fact that the gradient coil is too close to the center of the magnetic field, requiring precise coil arrangement (complete alignment and symmetry), a slight translation and Dislocation between layers may lead to deformation of the actual gradient field and impure linearity.

Therefore, the arrangement and winding of the second and third layers (generally no more than three layers) in the wire slot often requires the help of auxiliary equipment such as electronic magnifying glasses, which significantly increases the difficulty of the winding process, and is prone to gradient field deformation and linearity. impurity etc.

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