A High-Isolation Active RF Diplexer for Condensed Matter NMR

Abstract

The invention discloses a high isolation active radio frequency diplexer used for condensed state nuclear magnetic resonance. The diplexer includes a radio frequency excitation access port (1), a nuclear magnetic probe access port (2), a preamplifier access port (3), a TTL control level access port (4), two direct current isolation capacitors (5) and (6), two parallel radio frequency diode pairs (7) and (8), 1 / 4 of a wavelength line (9), a voltage regulator (10), a filter capacitor (11), a Schmitt trigger (13), a single pole double throw radio frequency switch (14), and a preamplifier (15). The method controls a high-speed radio frequency switch by a pulse generator to realize the disconnection during the excitation and the connection when receiving a magnetic signal, can greatly improve the isolation degree (being greater than 70 dB) of conventional diplexer while the introduced insertion loss (being lower than 1 dB) is very low. The method has advantages of a simple and reliable circuit and obvious effects, and plays an important role in improving the signal-to-noise ratio of condensed nuclear magnetic resonance experiments.

Description

technical field [0001] The invention relates to the field of nuclear magnetic resonance, in particular to a high-isolation active radio frequency duplexer for condensed matter nuclear magnetic resonance. Background technique [0002] When a nuclear system with spin is placed in an external magnetic field, its nuclear energy level will break the degeneracy and split into sub-levels with an energy spacing of ( is the reduced Planck constant, and is the gyromagnetic ratio of the nucleus). If we excite the atomic nucleus with an electromagnetic wave of an angular frequency, it will transition from a low-energy state to a high-energy state, realizing population flipping. When the excitation is removed, the nucleus will undergo a transition from a high-energy state to a low-energy state and radiate electromagnetic waves. This phenomenon is called nuclear magnetic resonance. After decades of rapid development, nuclear magnetic resonance has increasingly become a spectrum method wi...

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Problems solved by technology

[0009] The technical problem to be solved by the present invention is that the isolation of the existing nuclear magnetic resonance radio frequency duplexer is poor, which easily leads to the oversaturation of the preamplifier and thus causes the unfavorable result of long dead time in nuclear magnetic resonance detection; the purpose of the present invention is to provide a A High Isolation Active RF Diplexer for Condensed Matter NMR

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