Weiping Wu

The nuclear magnetic resonance probe based on a printed circuit board planar microcoil

The nuclear magnetic resonance (NMR) probe, one of the most important components in the spectrometer, has a considerable impact on overall instrument sensitivity. By the concept of a NMR analyzer with low-cost and portable was proposed in recent years, the earlier NMR probes were not suitable for the manufacture cost and cycle time. So, in this paper, a NMR probe based on the printed circuit board (PCB) planar microcoil was developed for time domain NMR measurement. When the Larmor frequency is 28.1 MHz, the NMR transverse relaxation time T2 of a deionized water sample was detected by the 2mm inner diameter PCB microcoil with six turns, and results of T2 measured value were stable under different scan times. In addition, relaxation times of used frying oil and three edible oils were analyzed by the PCB microcoil, both T22 and T23 components of used frying oil, obviously less than three edible oils, these results are agreed with the measurement of a commercial instrument Bruker minispec mq60.

Optimization and experimental test of a miniature permanent magnet structure for a microfluidic magnetic resonance chip

We propose a general global optimal algorithm to optimize the miniature permanent magnet structure of a micro magnetic resonance chip (μNMR-chip). For this purpose, we analyze the sensitivity of the permanent magnet structure to the design variables and determine the optimization variables. After this, radial basis function neural networks (RBFNNs) are constructed to model the objective functions, and the nondominated sorting genetic algorithm II (NSGA II) is improved by in- troducing a different weighting factor for each objective function in calculating the crowding distance. Combining the RBFNN with the improved NSGA II optimizes the miniature permanent magnet structure. Through comparison, the optimization solu- tions are proven effective. Finally, the optimized permanent magnet structure is manufactured and tested experimentally. After optimization, the volume of the permanent magnet block is reduced by 39%, and the permanent magnet becomes easier to manufacture.

Development of a miniature permanent magnetic circuit for nuclear magnetic resonance chip

The existing researches of miniature magnetic circuits focus on the single-sided permanent magnetic circuits and the Halbach permanent magnetic circuits. In the single-sided permanent magnetic circuits, the magnetic flux density is always very low in the work region. In the Halbach permanent magnetic circuits, there are always great difficulties in the manufacturing and assembly process. The static magnetic flux density required for nuclear magnetic resonance(NMR) chip is analyzed based on the signal noise ratio(SNR) calculation model, and then a miniature C-shaped permanent magnetic circuit is designed as the required magnetic flux density. Based on Kirchhoff’s law and magnetic flux refraction principle, the concept of a single shimming ring is proposed to improve the performance of the designed magnetic circuit. Using the finite element method, a comparative calculation is conducted. The calculation results demonstrate that the magnetic circuit improved with a single shimming has higher magnetic flux density and better magnetic field homogeneity than the one improved with no shimming ring or double shimming rings. The proposed magnetic circuit is manufactured and its experimental test platform is also built. The magnetic flux density measured in the work region is 0.7 T, which is well coincided with the theoretical design. The spatial variation of the magnetic field is within the range of the instrument error. At last, the temperature dependence of the magnetic flux density produced by the proposed magnetic circuit is investigated through both theoretical analysis and experimental study, and a linear functional model is obtained. The proposed research is crucial for solving the problem in the application of NMR-chip under different environmental temperatures.

Development of Permanent Magnet Probe for Intravascular Magnetic Resonance Imaging Device

Intravascular magnetic resonance imaging is a new approach for the diagnosis of cardiovascular diseases (CVDs). This paper shows the design of a permanent magnet probe, including the structure configuration, the design parameters and the selected materials of the probe assembly. The effect of magnetization angles on the static magnetic field distribution is computed using Maxwell finite element (Ansoft) simulation, and the optimal magnetization angle of the permanent magnet is chosen for the probe design. Then equations of the static magnetic field distribution and the gradient distribution produced by the permanent magnet are given using data fitting method under the optimal angle. In conclusion, calculations and fitting results demonstrate the validity of the static magnetic field produced by the permanent magnet probe which could be used in the intravascular magnetic resonance imaging for detecting the CVDS accurately as well as operating easily