Schematic illustration of a duplexer in a NMR system: (1) spectrometer, (2) transmitter, (3) receiver, (4) power amplifier, (5) preamplifier, (6) duplexer, and (7) probe.
Cryogenic duplexer developed in this work. A schematic sketch of the (a) cryogenic duplexer and a (b) photograph: (1) a rf input for a power amplifier, (2) a series GaAs PIN cross-diode gate, (3) rf input/output for a probe, (4) a ladder of GaAs PIN cross-diode gates connected by a line, (5) a ladder of GaAs Schottky cross-diode gates connected by a line, (6) a ladder of rf-MEMS switches with a line, and (7) a rf output for a preamplifier.
Plots of power leakage to the preamplifier vs power input from the power amplifier of the cryogenic duplexer operating at 298 K (○: with the rf-MEMS switches turned off, ●: with the rf-MEMS switches turned on) and at 43 K (△: with the rf-MEMS switches turned off, ▲: with the rf-MEMS switches turned on).
(a) A schematic sketch of gating the rf-MEMS switches: (1) the TTL gating signal from the spectrometer and (2) operational amplifier. To drive rf-MEMS gates by a dc voltage , a power operational amplifier, such as Apex PA-05, Cirrus Logic, Inc., is used. (b) A timing chart for rf-MEMS switching with a single pulse sequence for NMR measurement: (3) dead time for pulse ringing, (4) lag time for MEMS switching on, and (5) lag time for MEMS switching off.
MAS-NMR single-pulse spectra of adamantane observed by using the cryocoil MAS probe. (a) The detection coil and the preamplifier were kept at room temperature. The 90° pulse width was at the rf power of 33 W. (b) The detection coil and the preamplifier were cooled down to and , respectively. The 90° pulse width was at 33 W. The two spectra are plotted on the same amplitude scale and can be directly compared. The MAS spinning speed was 7.4 kHz.
Typical performances of the discrete devices.
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