核磁共振接收线圈谐振优化分析与标定

地面核磁共振接收机接收的核磁共振信号的初始振幅直接决定其反演的含水量大小。目前的核磁共振找水仪采用由线圈和配谐电容等组成的LC谐振回路接收核磁共振信号,该谐振接收回路对接收线圈感应的核磁共振信号存在选频放大效应,忽略该效应会造成初始振幅回推时产生较大误差。本文在对谐振接收回路建立精确电气模型的基础上,分析并计算了谐振接收回路各元件参数对选频放大效应的影响,并对100 m边长线圈谐振接收回路选频放大效应进行了标定,经过校正后初始振幅最大值由1 560 n V降至305 n V,与法国仪器基本一致。验证了野外施工谐振接收模型及模型计算的正确性,为地下水害的直接探测提供了仪器稳定性保障。     

用于微型胃肠道胶囊机器人供能的U型发射线圈无线能量传输系统设计与实验

为了解决微型胃肠道胶囊机器人或其他可植入医疗设备无法使用电源线供电以及无线能量发射系统性能差的问题,本文提出了一种新的U型发射线圈无线能量传输系统.与传统的螺线管对式的发射线圈相比,通过结构的改进,首次将磁芯加入到了发射线圈中.该系统可以极大地改善传输过程中传输效率低,机器人接收功率低的问题.本文建立了所提出的U型发射...     

用于胃肠道机器人的C型组合式无线能量发射线圈的设计与实验

现有适用于胃肠道机器人的无线能量传输系统的能量传输效率低、接收功率低且接收能量的位置均匀性差,无法满足功能复杂的新型胃肠道机器人的能量需求。本文提出了一种新型C型组合式发射线圈结构,通过有限元仿真分析供能单元组的磁感应强度大小和位置均匀性,确定供能单元组中线圈对间距的实验优化范围。最后搭建实验平台,优化供能单元组中线圈对间距,通过系统的能量传输效率、接收功率以及接收功率的位置均匀度对设计进行评估与验证。实验结果表明：当线圈对间距为150 mm时,中心位置的接收功率为1 165.34 mW,系统的能量传输效率为6.08%。系统的平均功率约为1 100 mW,平均能量传输效率达6%以上,接收功率的平均位置均匀度达94%。新型C型结构磁芯以及采用同一时刻只有一个供能单元组工作的组合式线圈结构,极大地改善了系统的接收功率与能量传输效率,并有较高的接收能量的位置均匀性。     

谐振式无线电能传输系统频率跟踪技术的研究

针对SP补偿结构的磁耦合谐振式WPT系统在失谐时造成传输效率降低的问题,通过建立串联-并联等效电路模型,分析SP补偿结构的磁耦合谐振式WPT系统的传输效率,得出当负载电阻较大时发射线圈与接收线圈近似工作于同一谐振点,此时可以通过检测发射线圈逆变器输出电压与一次侧电流相位差或检测逆变器输出电压与接收线圈线圈电流来跟踪系统的谐振状态。采用跟踪逆变器输出电压与一次侧电流相位差的方法,用鉴相器将相位差转化为直流电压信号,采用单片机内置ADC对直流信号进行采样,采用PID算法跟踪系统谐振频率。实验表明:采用的谐振频率跟踪方法取得了很好的跟踪效果。     

谐振式无线能量传输距离特性研究

谐振式无线能量传输技术是一种利用近区非辐射磁场的强磁耦合实现的无线电能传输技术。文章首先阐述了谐振式的工作原理,然后通过实验研究了系统参数、传输距离与传输功率和传输效率之间的关系,得出:系统的工作频率接近谐振频率就可以获得较高的传输效率,发射线圈和接收线圈之间有个最佳的功率传输距离。     

体内微机电系统的三维无线能量传输装置的设计和实验

设计了基于电磁感应原理的体内无线能量传输系统,为体内内窥镜胶囊提供能量。首先,通过建立数学模型对三维无线能量接收线圈正交绕组的接收性能进行仿真,获得不同姿态下系统的耦合系数。结果表明:三维正交线圈在不同姿态下能有效地进行互补。然后,根据体内内窥镜胶囊尺寸要求,设计制造了微型接收绕组和整流稳压电路,并用此系统给自制的图像采集系统供能,且对实际传输的电压和电流进行测量。实验结果表明:该三维接收系统的能量传输效率和稳定性能够满足实际需要。     

单线圈双调谐探头的电路分析

叙述一种单线圈双调谐探头的电路分析.单线圈双调谐探头同时提供两个不同信号源的发射和接收。探头使用同一个射频线圈进行核磁共振观察和场频联锁。应用二端网络原理对单线圈双调谐探头的电路进行分析,推导出计算探头参量的近似公式.依据公式设计了CH—100型付立叶变换核磁共振波谱仪的高质量探头电路。仪器性能:S/N为50:1在5毫米氢探头和1%乙基苯,并且40%乙醛得4.97×10~(-9)的分辨率.     

用于胃肠道微型机器人的组合螺线管式无线能量发射系统研究

为保障胃肠道微型机器人在体内稳定、可靠工作,以扩大无线能量传输系统的工作范围、提高接收能量及其稳定性为目标,研究了新型组合螺线管式无线能量发射系统.通过有限元仿真分析,确定发射线圈的最佳结构及结构参数.基于最小传输能量要求及所提出的发射线圈性能评估指标,优化确定发射线圈的匝数.研制的发射线圈尺寸为50 cm×50 cm...     

用于核磁共振谱仪的单线圈双调谐探头

我所研制的CH—100型100兆周脉冲付立叶变换核磁共振谱仪采用了单线圈双调谐探头是核磁共振波谱仪的核心部件,它直接影响仪器的主要指标:灵敏度和分辩率。双调谐探头同时提供观察通道和场频联锁通道的发射和接收。     

基于谐振耦合的电能无线传输系统设计

距离和效率是电能无线传输技术发展的瓶颈,电磁场的谐振耦合技术能够有效的解决这一问题.从谐振耦合的收发线圈电路模型出发,对谐振耦合电能无线传输系统进行了深入研究,发现失谐是系统效率不高的主要原因.进而,设计了一个功率为30W,频率为1 MHz的小功率电能无线传输系统,并且通过对发射线圈的电流检测实现发射源对发射线圈频率的...     

Method for nonlinear characterization of radio frequency coils made of high temperature superconducting material in view of magnetic resonance imaging applications

A contactless method based on reflectometry to accurately characterize an inductive radio frequency (rf) resonator even in the occurrence of a strong electrical nonlinearity is presented. Nonlinear extraction of the unloaded quality factor and resonance frequency is possible by combining an initial low-level swept-frequency calibration with high-level single-frequency measurements. The extraction protocol relies on a simple intrinsic R, L, C model and does not involve a fitting procedure according to a particular nonlinearity model. It includes a correction for strong coupling conditions between the probe and the rf coil, which allows extending the analysis over a wide range of transmitted power. Electrical modeling based on the extracted intrinsic data allows predicting the coil behavior when loaded by any kind of matching network. The method will have implications in different domains such as Magnetic Resonance (MR) applications with superconducting probe heads or analysis of rf properties in nonlinear materials. The method is demonstrated here by characterizing a high temperature superconducting (HTS) coil dedicated to MR imaging at 64 MHz. The coil consists in a multiturn spiral design that is self-resonant close to the MR frequency of interest. The Q factor and the resonance frequency are determined as a function of the actual power dissipated in the HTS coil accounting for losses occurring in the measurement system. Further characteristics of the HTS coil are considered in the present paper. The relation between the transmitted power and the magnetic field generated by the coil, which is the most relevant characteristics for MR applications, is directly accessible. The equivalent impedance of the coil under test is also expressed as a function of the total current flowing in the windings. The method could be extended to assess the fundamental properties of the nonlinear material (e.g., the London penetration depth or the critical current density) by including any pertinent model.     

A Nuclear Magnetic Resonance Probe for Testing Substances with Large Values of T1

An autodyne nuclear magnetic resonance (NMR) probe for testing solids with a long spin–lattice relaxation time T ₁ is described. The main advantage of the probe circuit suggested in this work over conventional NMR probes is an increase in the signal-to-noise ratio, whereas the induction of the radio-frequency field at the site of the sample remains the same and the voltage across the sample coil varies from 2 to 20 mV. The probe can be used at frequencies of 5 to 25 MHz.     

NMR代谢组学技术在环境污染评价中的应用

随着环境污染日益严重,对环境污染评价的研究亦愈发深入。基于核磁共振(Nuclear Magnetic Resonance,NMR)代谢组学是近年发展起来的一种新型环境污染评价方法,它是以核磁共振为技术手段,从生物角度研究生物体暴露在环境污染物下,生物体内源性代谢产物谱的变化,以期预警环境污染的程度。本文将综述基于核磁共振的代谢组学在环境污染评价上的原理、研究思路、以及国内外研究新进展。     

低场核磁共振螺线管线圈的设计

在常规低场核磁共振(NMR)实验中,NMR响应的空间均匀度与螺线管收发线圈的尺寸、样品的大小以及采用的脉冲序列类型有关,根据这些条件可以确定具有给定射频(RF)场均匀度的线圈最小尺寸.考虑到螺线管匝数、线径等因素对信噪比的影响,对线圈的各项参数进行了优化,设计了具有最佳信噪比性能的螺线管线圈.     

Nuclear magnetic resonance apparatus for pulsed high magnetic fields

A nuclear magnetic resonance apparatus for experiments in pulsed high magnetic fields is described. The magnetic field pulses created together with various magnet coils determine the requirements such an apparatus has to fulfill to be operated successfully in pulsed fields. Independent of the chosen coil it is desirable to operate the entire experiment at the highest possible bandwidth such that a correspondingly large temporal fraction of the magnetic field pulse can be used to probe a given sample. Our apparatus offers a bandwidth of up to 20 MHz and has been tested successfully at the Hochfeld-Magnetlabor Dresden, even in a very fast dual coil magnet that has produced a peak field of 94.2 T. Using a medium-sized single coil with a significantly slower dependence, it is possible to perform advanced multi-pulse nuclear magnetic resonance experiments. As an example we discuss a Carr-Purcell spin echo sequence at a field of 62 T.     

Development of custom-made RF coil for magnetic resonance velocimeter with a high spatial resolution

Magnetic resonance velocimetry (MRV) is a versatile flow visualization technique that is used to measure three-component velocity vectors in a 3D space. However, the spatial resolution of MRV is relatively poor in comparison with optical flow visualization techniques, thereby limiting its applicability to small-scale flows and wall shear stress (WSS) estimation. Thus, we built a solenoid RF coil and evaluated its performance in terms of spatial resolution improvement by measuring the laminar flow in a circular tubing. The coil was developed for a 4.7 Tesla MRI system and for tightly wrapping a flow tubing with an inner diameter of 2 mm. The custom-made RF coil could precisely capture the velocity vectors in a voxel that was 11 times smaller than a commercial coil at the same SNR. Therefore, the WSS errors estimated using the custom-made and commercial coils were 8.5 % and 42.3 %, respectively.

     

A low-frequency NMR probe

A probe for a low-frequency pulse NMR spectrometer with crossed coils has been designed. The probe is based on operational amplifiers and has an operating frequency of 3.6 MHz, a gain of 43 dB, and a noise factor of 1.8 dB. The damping unit of the pickup coil, which is integrated into the probe, reduces the complete recovery time of the receiving section of the spectrometer down to 15 μs.