2-Channel low power broadband transmit/receive switch and 720 MHZ high power narrow pass band filter.

摘要

Nuclear magnetic resonance (NMR) is an important tool used to study the atomic or molecular properties of nuclei by exploiting its magnetic properties. A spectrometer is an integral element of an NMR system which consists of a RF transmitter, receiver, amplifier, temperature controller, transmit/receive switch, filter, etc. A transmit/receive switch is used to toggle between transmission and reception modes of the resonant coil in the RF probe. The following thesis consists of the design and construction of one such T/R switch that is used to perform NMR field mapping of resistive magnets in the presence of temporal field fluctuations. This low power T/R switch consisting of two receive channels and a common transmitter is designed to operate over a wide range of proton (1H) NMR frequencies i.e., 200 MHz to 1600 MHz and can handle up to 1 watt power. It uses a micro strip transmission line design utilizing low power surface mount switches, splitters and drop-in preamps.;The other part of this thesis deals with the design of a band pass filter tuned at 720 MHz. In multi nuclear pulsed NMR experiments, a high power band pass filter is used to improve the isolation between the channels of the spectrometer and screen out the other frequencies and noise signals from the system. The filter is designed using two semi-rigid coaxial cables grounded at their ends. This design is evaluated for its performance (insertion loss and reflection coefficient). The construction challenges have also been discussed. The filter is capable of handling a maximum RF input of 1 kilowatt rms power, has a 3dB bandwidth of 40 MHz and produces an insertion loss as low as 1dB.