期刊
CONCEPTS IN MAGNETIC RESONANCE PART B-MAGNETIC RESONANCE ENGINEERING
卷 35B, 期 3, 页码 133-138出版社
WILEY
DOI: 10.1002/cmr.b.20141
关键词
transmit/receive switch; passive receiver protection; EPR instrumentation; low-field EPR; EPR imaging
类别
资金
- National Institutes of Health [P41-EB-002034, R01-CA98575]
To protect the low-noise amplifier (LNA) in the receive arm of a pulsed 250 MHz EPR bridge, it is necessary to install as much isolation as possible between the power exciting the spin system and the LNA when high power is present in the receive arm of the bridge, while allowing the voltage induced by the magnetization in the spin sample to be passed undistorted and undiminished to the LNA once power is reduced below the level that can cause LNA damage. We discuss a combination of techniques to accomplish this involving the power-routing circulator in the bridge, a second circulator acting as an isolator with passive shunt PIN diodes immediately following the second circulator. The low resistance of the forward biased PIN diode passively generates an impedance mismatch at the second circulator output port during the high-power excitation pulse and resonator ring down. The mismatch reflects the high power to the remaining port of the second circulator, dumping it into a system impedance matched load. only when the power diminishes below the diode conduction threshold, the resistance of the PIN diode will rise to a value much higher than the system impedance. This brings the device into conduction mode. We find that the present design passively limits the output power to 14 dBm independent of the input power. For high-input power levels, the isolation may exceed 60 dB. This level of isolation is sufficient to fully protect the LNA of a pulse EPR bridge. (C) 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 3513: 133-138, 2009
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据