Abstract
A proof-of-concept of the use of a fully digital radiofrequency (RF) electronics for the design of dedicated Nuclear Magnetic Resonance (NMR) systems at low-field (0.1 T) is presented. This digital electronics is based on the use of three key elements: a Direct Digital Synthesizer (DDS) for pulse generation, a Software Defined Radio (SDR) for a digital receiving of NMR signals and a Digital Signal Processor (DSP) for system control and for the generation of the gradient signals (pulse programmer). The SDR includes a direct analog-to-digital conversion and a Digital Down Conversion (digital quadrature demodulation, decimation filtering, processing gain…). The various aspects of the concept and of the realization are addressed with some details. These include both hardware design and software considerations. One of the underlying ideas is to enable such NMR systems to “enjoy” from existing advanced technology that have been realized in other research areas, especially in telecommunication domain. Another goal is to make these systems easy to build and replicate so as to help research groups in realizing dedicated NMR desktops for a large palette of new applications. We also would like to give readers an idea of the current trends in this field. The performances of the developed electronics are discussed throughout the paper. First FID (Free Induction Decay) signals are also presented. Some development perspectives of our work in the area of low-field NMR/MRI will be finally addressed.
Highlights
The development of Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI)systems is still motivated by the outstanding features of this technique
Converter (ADC) and Digital Down Converter (DDC) with an Automatic Gain Controller (AGC). It accepts intermediate frequency (IF) analog signals (NMR signals in our case) and performs a digital quadrature demodulation to obtain the final In-phase (I) and Quadrature (Q) signals
Thanks to programming features of both Numerically Controlled Oscillator (NCO) and Direct Digital Synthesizer (DDS) and the use of a unique reference clock for the whole system, the receiver remains phase locked with the transmitter
Summary
The development of Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). A main idea is that hardware and software of the spectrometer could be updated for the largest number of applications and different working frequencies with minimum development time and low cost. It reports some parts of our experience in this area This experience is presented here through the development of a fully digital RF hardware and the associated software for the NMR at 0.1 T (4.2 MHz of Larmor frequency). One goal of the paper is to help people to get an idea of the current trends in this area Another goal of this paper is to try to make the NMR systems versatile and easy to replicate so as to help developers and research groups in realizing NMR spectrometers with flexibility, low cost and minimum development time. Development perspectives of our work in area of sensors for the low-field NMR will be addressed
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