宽带磁共振T/R开关的设计与实现

Design of Broadband T/R Switch for Magnetic Resonance

磁共振系统中的发射/接收(transmit/receive,T/R)开关用于收发通路的切换,要求在隔离大功率信号的同时具有较小的插入损耗;另外,在宽带磁共振谱仪中,一般的窄带T/R开关也不再适用.本文基于PIN(positive-intrinsic-negative)二极管设计了工作频率为10~100 MHz的宽带磁共振T/R开关.通过减小电平跳变、优化开关过冲和解决二极管被动导通等问题,获得了插入损耗小于1 dB、大功率信号隔离度大于75 dB、开关时间1μs的整体性能.用本文设计的宽带T/R开关替代一般探头中的窄带T/R开关,在0.5 T核磁共振(NMR)波谱仪上测得了氢核和氟核两个不同频率的磁共振信号,验证了宽带T/R开关的宽带性能.

Transmit/receive(T/R)switch is used to switch the transmission and reception channels in nuclear magnetic resonance(NMR)spectrometer,which is required high isolation of high-power signals and low insertion loss of NMR signals.In addition,the general narrowband T/R switch is no longer applicable in broadband magnetic resonance spectrometer.This paper presents a positive-intrinsic-negative(PIN)diode-based T/R switch design with low insertion loss(less than 1 dB),high isolation of high-power signals(more than 75 dB)and short switching time(1μs)in broadband(10~100 MHz).Substituting the broadband T/R switch for the narrowband T/R switch of the general probe,the NMR signals of hydrogen and fluorine nuclei at two different frequencies were measured on a 0.5 T NMR spectrometer,which verified the broadband performance of the T/R switch.