磁共振主动式射频开关设计方法研究

目的:为避免磁共振成像（MRI）系统射频线圈的发射和接收两种工作模式发生耦合，对于短弛豫时间信号的采集，要求射频开关的切换时间应尽可能短。方法:在分析被动式MRI射频开关电路结构的基础上，采用PIN二极管设计了主动式MRI射频开关电路，由直流驱动电路控制PIN二极管的导通和截止实现射频开关的切换，从而达到对射频开关及其状态的主动控制，以缩短射频开关的切换时间。结果:采用电子设计自动化软件对射频开关电路的隔离度、插入损耗、电压驻波比等性能指标进行仿真分析，符合设计要求；通过示波器对由直流驱动电路和射频开关电路外接负载的端口波形进行分析，射频开关的切换速度达到预期目标。结论:基于PIN二极管的射频开关能够有效地缩短射频开关时间，具有良好的隔离度、插入损耗和噪声系数等性能。

Research on design method of active radio frequency switch for magnetic resonance

Abstract: Objective In order to avoid coupling between the transmitting and receiving working modes of the radio frequency coil of the magnetic resonance imaging (MRI) system, when collecting short relaxation time signals, the switching time of the radio frequency switch should be as short as possible. Methods Based on the analysis of the passive MRI radio frequency switch circuit structure, an active MRI radio frequency switch circuit is designed with a PIN diode. The DC drive circuit controls the on and off of the PIN diode to realize the switching of the radio frequency switch, so as to achieve the active control over radio frequency switch and its situation to shorten the switching time of the RF switch. Results Advanced Design System (ADS) is used to simulate and analyze the isolation, insertion loss and voltage standing wave ratio (VSWR) of RF switching circuit, which meets the design requirements. The oscilloscope is used to analyze the port waveform of the external load of the DC drive circuit and the RF switch circuit, and the switching speed of the RF switch achieves the expected target. Conclusion The RF switch based on PIN diode can realize the active control of RF switching time, and perform well in isolation, insertion loss and noise figure.