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RF Coil

RF coil in copper shielded box

The RF coil for this system is used for transmitting the excitation pulse to get the magnetization precessing and to detect the MRI signal thru the Faraday detection principle. The coil is part of a resonant circuit that is tuned to the Larmor frequency of the B0 magnet. The coil is a solenoid which the NMR tubes fit into snuggly; it is contained in a plastic case which is wrapped in copper foil to shield against external RF noise sources.

TR Switch

The RF coil is used for 2 things: transmitting the RF pulse and receiving the MRI signal. This means that it should sometimes be connected to the transmit amplifier and sometimes be connected to the receive amplifier. This TR switch uses pin diodes and a lumped quarterwave line to effectively switch the coil connection between the two amplifiers.

Receive amplifier

The NMR signal from the coil is very small, so a a pre-amplifier with a low noise figure is needed as the receive amplifier. A 2 stage amplifier was designed using Gali-74+ Monolithic Amplifier from Minicircuits. The TR switch and pre-amplifier circuit were combined in a single PCB.