This thesis addresses the design, construction, and characterization of a compact pulsed NMR measurement system based on a permanent magnet, intended for measuring the magnetic flux density of a sample from the Free Induction Decay (FID) signal.
The measurement system consists of: an NMR probe with a coil, a T/R switch with a diode protection circuit, a two-stage amplification chain, and an aluminium Faraday cage for electromagnetic shielding. The system parameters were optimized iteratively using dedicated laboratory equipment. Signal acquisition and analysis were performed using the Digilent Analog Discovery PRO device and the WaveForms software.
By applying FFT analysis to the acquired FID signal, the Larmor frequency of the sample was measured as f_L=12,665 MHz , from which the magnetic flux density of the permanent magnet was calculated as B_0=0,2975 T . The measured magnetic flux density is dependent on temperature and magnet ageing. Furthermore, the NMR probe must be positioned at a location within the gap where the field homogeneity is greatest, as this location will also yield the best signal-to-noise ratio. The acquired FID signal, exhibiting characteristic exponential amplitude decay, unambiguously confirms the successful detection of nuclear magnetic resonance in the sample.
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