微型核磁共振芯片平面微型线圈设计与信噪比分析

Design and signal to noise ratio analysis of planar microcoil for micro-NMR chip

设计一种可用于微型核磁共振芯片的平面微型线圈,在主磁场为0.7 T条件下,选取平面微型线圈的深宽比为1,以平面微型线圈宽度2倍趋肤深度为界,基于核磁共振信噪比数学理论模型,分析亚毫米直径平面微型线圈各个几何参数与信噪比的关系.分析结果表明:缩小平面微型线圈直径会提高信噪比;在不严重降低射频场均匀性的情况下,样品应尽可能地靠近平面微型线圈;平面微型线圈匝间距离与平面微型线圈宽度相等和平面微型线圈宽度为2倍趋肤深度时,信噪比均较高.最后确定平面微型线圈的几何参数:线圈半径为120μm,线圈宽度为24μm,匝间间距为24μm,匝数为3.

A planar microcoil applied in micro nuclear magnetic resonance（NMR） chip was designed.When the main magnetic field is 0.7 T and the aspect ratio of planar microcoil is 1,based on the mathematical model of signal to noise ratio（SNR） and taking the critical width of coil as twice the skin depth,the relation between SNRs and various geometric parameters were analysed for planar microcoil with sub-millimetric diameter.Result shows that reducing the diameter of planar microcoil increases the SNR;sample should be located as close as possible to the planar microcoil provided the radiofrequency homogeneity is not decreased heavily;high SNR is obtained when the space of adjacent wires is equal to the wire width;SNR behaves good when the width of planar microcoil is twice the skin depth.At last,geometric parameters of planar microcoil are determined： radius of coil is 120μm,the wire width is 24μm,the space of adjacent wires is 24μm,and the number of turns is 3.