Nuclear Magnetic Resonance Spectrometer Probe Design

Nuclear Magnetic Resonance (NMR) spectrometer has the advantage to study the properties of materials by nucleus, and is widely used in industry, agriculture, medicine and geological exploration. The study of NMR spectrometer is of extreme significance both theoretically and practically.The probe is an important part of the NMR spectrometer, the design of the NMR spectrometer probe is an important work. The probe consists of a transmitter, a receiver and two coils. The working principle is as follows:the transmitter generates an unmodulated sine wave signal, which is then sent to the transmitter coil as excitation signal. When the frequency of the sine wave signal is equal to the resonance frequency of the tested sample, the sample will absorb the energy of the sine wave and raise to a higher energy level, which is called the NMR phenomenon; at this time the receiver coil will induce a NMR signal from the sample. The NMR signal is an amplitude modulated signal generated by modulating the sample information on the sine wave. The probe receiver is responsible for the reception of the NMR signal.This dissertation studies NMR spectrometer and focuses on the design and implementation of broadband NMR spectrometer probe. There are two problems need to be solved:one is design a transmitter which generates sine wave signal, and the sine wave’s frequency rang is10MHz to50MHz, frequency step is1kHz, power should be adjustable and achieve10dBm; the other is design a receiver which receives NMR signal, and the NMR signal’s power is-90dBm to-30dBm.To solve these problems, the author completes the following work:1. The principle of NMR is studied, and comparisons of NMR detection methods are conducted, main types of NMR spectrometers are summarized, and the overall architecture of the broadband NMR spectrometer is designed.2. The broadband probe transmitter is designed based on the results of the modern frequency synthesizer technology. After repeated circuit debugging, finally get the following results:Output frequency is10MHz-50MHz. The phase noise is better than-106.5dBc/Hz@10kHz. The spurious rejection is better than40.72dBc. The output power is adjustable.3. The broadband probe receiver is designed based on the results of the receiver technology. After circuit debugging, the indicators of the probe receiver are as follows: The sensitivity is-80dBm. The dynamic range is50dB. Both the image rejection and the IF rejection are better than60dB.