Low Field NMR

The low field NMR also called Time domain NMR, the short name is LF NMR, it uses physical methods to display abstract theories using multimedia, allowing us to see the imaging effects intuitively and help us quickly understand the imaging principles of NMR. The field strength of Low field NMR is below 1 tesla

First of all, it should be noted that there is an important parameter in NMR called Gyromagnetic ratio, which is related to the nucleus. For example, the Gyromagnetic ratio of hydrogen proton is 42.6MHz/T. Taking a hydrogen PROTON as an example, if the magnetic field strength is 1T, The corresponding Pulse Frequency is 42.6MHz. Generally we think that the low-field nuclear magnetic field is lower than 1T, so the NMR， time domain NMR we manufactured is usually called low-field NMR, so In terms of field strength, it is low field NMR, in terms of function it’s called time domain NMR.
The field strength of our Niumag NMR analyzer is from 2MHz to 42MHz, different applications have different field strengths.
The one on the left is earth’s field with the lowest magnetic field strength.

Low Field NMR Principles

The low field NMR experiment instrument is composed of serveral parts, mainly including magnet, probe, switching amplifier and phase detector. The inside of the probe mainly includes a gradient coil and a radio frequency coil. The gradient coil inside the probe can realize spatial phase encoding and frequency encoding, while the radio frequency coil inside the probe mainly puts the sample into the radio frequency coil, which can achieve rotation The purpose of the magnetic field, on the other hand, is to be able to observe the free precession signal of the transmitter coil and receiver coil. When observing the free precession signal, a switching amplifier can be used to connect the radio frequency coil in the probe to the phase detector. Next, an oscillator and a radio frequency pulse generator can be used to obtain the corresponding phase detector and radio frequency pulse. RF Reference. However, if there is difficulty in acquisition, phase detectors can be used to obtain low-frequency signals that are relatively easy to acquire. Finally, the phase accuracy required for low field NMR can be obtained.

Low field NMR Advantages

The magnet of the low field NMR experiment instrument is mainly realized by using the micron precision machining technology, therefore, its magnetic field uniformity is relatively high under normal circumstances. At the same time, the pulse MRI experiment instrument uses a thermostatic controller to control the magnet, so its stability is relatively high. In addition, with the support of DDS technology, the operating frequency of the RF circuit not only has high stability, but also can be adjusted in a wide range and high resolution.

In the whole process of low field NMR, if the operation of loading pulse is carried out, it is actually the stimulated absorption process of the pulse. At the same time, it can be found that when the pulse decays freely, it belongs to the spontaneous radiation, and the phenomenon of stimulated radiation also occurs.