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Highly homogeneous magnetic fields in magnetic resonance spectrometers are an important guarantee for improving the quality of spectra for chemical structure analysis and kinetic information. The active shimming process using a shimming power supply to drive a shimming coil to produce a compensating electromagnetic field is an essential way to improve the homogeneity of the magnetic field. The high accuracy and stability of the shimming power supply’s output are crucial indicators for improving the active shimming capability and maintaining the shimming results. The paper develops a high-precision, high-stability, low-ripple active shimming power supply system for magnetic resonance spectrometers, and designs a shimming current driver (constant current source) with output state monitoring based on negative feedback control, coupled with an MCU control platform and host computer system to complete the closed-loop transmission of control commands and data between hardware and software, to achieve digital constant current output control. Under R=2.84 Ω, L=25.5 µH shimming coil load, the full-scale output response time is less than 18.9 µs, the output ripple peak-to-peak control is 30 mV, the positive and negative current output symmetry is good, and the maximum output deviation is 4.8‰ for long time operation. This power supply was used in a nuclear magnetic resonance spectrometer system using 0.5 T-Halbach configuration magnets, and the magnetic field homogeneity was optimised from 24.48 ppm (10-6) to 2.72 ppm by driving a first-order shimming coil. This work contributes to the integration of compact nuclear magnetic resonance spectrometer systems and the applications related to active shimming.

Temperature drift is an important factor affecting the measurement accuracy of desktop NMR spectrometers, and adding a field-locking coil to the probe to achieve field-frequency interlocking is a common means of suppressing temperature drift. In this paper, a dual-channel miniaturised RF probe with an external field-locking channel is designed based on a laboratory compact Halbach magnet. The coil diameter, height, number of turns, turn spacing and enamelled wire radius were optimized based on the solenoid structure. The optimum solenoid size was obtained with an enameled wire radius of 0.4 mm, a coil diameter and height of 8.2 mm, a turn spacing of 1.6 mm and a number of turns of 5. Based on the simulation results, the detection and field-locking coils were fabricated, and tested in conjunction with the peripheral circuitry. The results show that the crosstalk between the two coils is low, the signal-to-noise ratio of the detection channel is above 50 and the signal-to-noise ratio of the locking channel is above 20. Final field locking experiments were performed and the frequency drift of the overall system after equipping the locking field was approximately 0.2 ppm/h (1 ppm=10-6), verifying that this probe design can be applied in compact Halbach magnet-based NMR analysis facilities.

Objectives This study is focused on improving the performance and increasing the detection probability of a multiple Unmanned Underwater Vehicle （UUV） seabed acoustic beacon searching a specific sea area.Methods First, the search ability index function of the passive sonar is given. Second, the Monte Carlo method is used to randomly simulate the coordinate position of the submarine acoustic beacon. Third, the cluster search capability function is established and the optimization goal of the optimization task is obtained. The optimization constraints are established in combination with the formation requirements of the UUV actually performing the task. Finally, the integration is based on the seabed acoustic beacon search probability. The cluster formation optimization model is maximized and the UUV cluster is made to complete the acoustic beacon search work in the specified area according to this formation. In this paper, the genetic algorithm is used to optimize the parameters of the optimization model. By setting a reasonable objective function and improving the traditional genetic operator, the value of the objective function reaches the set standard. At this point, the corresponding parameters are taken out to complete the value selection.Results By comparing this new optimized formation with the traditional optimized formation, it is found that the optimized formation has a higher average probability of finding the submarine beacon.Conclusions The optimized model test results show that the proposed method can effectively improve the submarine acoustic beacon search performance of UUV clusters and provide a reasonable formation optimization scheme.

Two methods for measuring pulse wave using either a pressure or an optical sensor are studied and compared. A model for determining the optimal external force for restraining the pressure sensor is proposed. Pulse waves are measured on 20 volunteers. The restraint force on the pressure sensor is slowly varied and recorded using a piezoelectric film sensor for each person until it reaches a so-called optimal acquisition pressure under which the pulse wave has the greatest amplitude. The optimal pressure is then analyzed using polynomial regression with the body-mass index(BMI). In addition, the pulse waves are decomposed in both the time and frequency domains to identify and extract the features corresponding to physiological activities. Pulse waves measured with the optical sensor method suffer from feature point loss where certain points are submerged and indistinguishable. The pressure sensor method can reveal the feature points clearly, but the waveform exhibits variations if the external force applied isn′t a constant. With the application of optimal acquisition force set by our model, the latter method is able to detect pulse wave with a high signal-to-noise ratio. The dual domain analysis is shown to extract features that can be later used for continuous blood pressure monitoring.