Abstract

HING BATISTA, Joaquin Enrique; BORDELOIS BOIZAN, Alejandro  and  NODA GUERRA, Manuel Ernesto. RF modulator upgrading for an NMR spectrometer. EAC [online]. 2020, vol.41, n.3, pp.41-52.  Epub Dec 01, 2020. ISSN 1815-5928.

Low field magnetic resonance (MR) for the study of chemical compounds is a very common and important area of research. However, the greater the intensity of the magnetic field, the better the signal-to-noise ratio of the signal obtained from the substance under study and, therefore, the greater the possibilities of identifying the different chemical compounds. To conduct these studies, an MR spectrometer was built at the Centro de Biofísica Médica (Biophysics and Medical Physics Center), the parts of which were taken from other equipment in the laboratory or modified, such as the radio frequency (RF) modulator. This paper describes the changes and improvements made to the RF modulator that allowed the spectrometer to function correctly at the new 1.5 T field. The aforementioned changes included: changing the modulator's working frequencies to make it work well at the new 64 MHz, change of frequency, changing the RF switch to achieve better attenuation of the non-desired RF signal, designing and implementing a RF switch control circuit and designing and implementing a new 64 MHz passband filter. The performance of the upgraded modulator was demonstrated by measuring harmonic suppression, sideband rejection and conversion loss. Finally, the modulator fitted into the spectrometer was validated by carrying out a complete experiment that ended with the acquisition of an MR signal.

Keywords : Magnetic Resonance; modulator; NMR spectrometer; switch; filter.

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