基于磁纳米温度测量交变磁场激励系统设计

Design of Alternating Magnetic Field Excitation System Based on Magnetic Nanometer Temperature Measurement

磁纳米温度测量方法有望解决肿瘤热疗中无法实现实时准确的温度测量问题.针对磁纳米温度测量方法在实际应用过程中存在的交变磁场均匀性低、信噪比低、负载阻抗较大的问题展开分析.首先通过分析交变磁场激励系统信号链,提出采用亥姆霍兹线圈作为交变磁场发生装置并从理论分析、模拟仿真和实际测量等层面分析并验证其磁场均匀性;其次针对信噪比低的问题提出采用九阶椭圆无源滤波器,分别通过理论分析、数字模拟仿真和实际测量等方面验证信噪比达到100 d B;最后依据阻抗匹配理论,提出利用串联谐振电路解决负载阻抗较大的问题,通过实际测量发现激励磁场强度达到20 Gs;同时为了解决交变磁场激励系统稳定性问题,提出采用串联大功率电阻的方式实时监测激励电流以保证激励磁场的稳定性.

The method of the temperature measurement based on magnetic nanoparticles in hyperthermia is expected to solve the problem that the temperature cannot be measured accurately.This paper analyzes the problems such as low homogeneity of magnetic field,low signal to noise ratio,load impedance in the application of the method of the temperature measurement base magnetic nanoparticles. Firstly,Helmholtz coil is proposed as the excitation part for generating the AC magnetic field by careful analysis of signal chain in the AC magnetic field system from three aspects： theoretical analysis,analogue simulation and actual measurement.Secondly the nine-order elliptic passive filter is designed for solving the problems of low signal-to-noise ratio and the test result meets design requirement that the signal-to-noise is 100 d B.Lastly,according to impedance matching theories,the series resonant circuit is used for solving the impedance mismatch.The test result is that the magnetic field strength is 20 Gs.In the meantime,the sampling resistor,which is a power resister installed in series to the load circuit for monitoring the excitation current of the Helmholtz coils and negative feedback control algorithm,was used to stabilize the exciting magnetic field.