方体压电谐振器共振频率电调谐技术

受环境因素的影响,压电谐振器的共振频率会发生漂移。调谐技术因采用特定的手段主动调节共振频率而得到广泛应用,但传统附加质量块、激光烧蚀等机械调谐技术费时费力,灵活性不好。针对方体压电谐振器该文提出了一种激励信号幅值调谐和直流调谐的电调谐方法,可精密调节谐振器的共振频率。设计了一种基于ZYNQ系列主控芯片的数字化测控电路,实现了振子扫频激励、输出信号的幅值相位检测,为激励信号幅值调谐和直流调谐提供了实验硬件平台。实验结果表明,激励信号幅值调谐的共振频率变化范围为347.850～348.000 kHz,直流调谐的调节范围为347.720～347.820 kHz。该技术为压电谐振器共振频率精密调节提供可靠的理论与实践途径。     

导数法峰值锐化算法提高磁感应成像图像分辨率

磁感应成像(MIT)是一种利用电磁感应原理重构生物组织电导率分布的非接触式电阻抗成像技术。该文利用亥姆霍兹线圈和20个检测线圈搭建了旋转式磁感应成像系统,利用滤波反投影算法重构图像。分别利用2阶和4阶导数法峰值锐化算法处理单目标和双目标检测线圈的测量数据,通过3个客观参数对比处理前后的重构图像结果。结果证明磁感应成像中导数法峰值锐化能够有效地增加图像质量。     

一种并行磁共振成像伪影消除方法

多线圈采集技术与并行成像算法通过降低磁共振成像所必需的梯度编码步数有效提高了成像的扫描速度.但是在数据采集过程中,运动常常会使线圈数据发生异常,从而对最终重建图像质量产生很大影响.本文提出了一种新的重建算法去消除重建图像中产生的伪影.算法把破坏数据看成观测数据样本中的异常值,应用了AM鲁棒估计进行数据修正,很好的抑制了异常值对数据集造成的影响.本研究分别对多线圈并行采集的体模数据与真实脑部数据进行了实验,结果显示算法可以有效消除破坏数据在重建图像中产生的伪影,并通过对比实验充分显示了本算法的优越性.     

基于激光偏振调制的全光Cs原子磁力仪研究

采取对激光左旋+偏振态和右旋-偏振态周期性调制产生共振的方法,实现对Cs原子拉莫尔进动频率的检测,取代了采用射频线圈产生共振的方法而实现了对磁场的全光检测,从而避免了传统光泵原子磁力仪信号串扰的问题。展示了该方法对原子磁矩在磁场中进动频率的检测原理,分析了该模式下的信号特征,根据信号特征设计了对拉莫尔进动信号的检测和处理系统。同相信号显示为洛伦兹线形;正交信号显示为色散线形,在共振频率处大小为0;相位信号显示为连续单调递减函数,在共振频率处大小为0。正交信号和相位信号均可以用来锁定共振频率点,实现磁场测量。     

基于无线射频通信技术的气象数据采集系统

针对基本气象要素的检测,设计了一种气象数据采集系统。该系统以nRF905无线传输模块和MSP430F149单片机为核心,由采集端、显示端两个部分组成,整体分为传感器采集模块、无线射频通信模块、微处理器模块。该系统可以实现基本气象数据的测量、无线传输及实时显示。     

基于SerialLite Ⅱ协议的磁共振采集数据传输系统设计

磁共振成像（MRI）是一种无创检测人体内部结构的技术,随着接收通道数量增多,产生的采集数据量越来越大,给快速成像带来了巨大的挑战。文中设计一种基于SerialLite Ⅱ协议的磁共振采集数据传输系统。系统功能主要由FPGA实现,分为数据缓存模块和数据传输模块两类,数据缓存模块基于双缓存区和状态机控制的乒乓操作,有效地解决了因数据量大而带来的读写冲突问题;数据传输模块基于FPGA建立SerialLite Ⅱ数据传输链路,实现了采集数据的光纤传输。通过仿真和实验验证了系统功能的正确性,表明其能够实现磁共振采集数据的高速稳定传输。     

扫描激光成像雷达图像处理显示系统设计

图像显示系统是激光成像雷达系统的重要组成部分，同时也是分析和评价激光成像雷达性能指标的重要工具．激光成像雷达图像处理显示系统设计了强度像显示和数据分析模块、距离像显示和数据分析模块以及图像数据的存储模块．它可以显示雷达探测目标得到的强度像和距离像，并对所取得的数据进行分析，评价激光雷达的性能，指导激光雷达的设计和研究．     

复合型短波天线调谐器的设计

针对现代短波通信对天线调谐系统在调谐精度与速度方面的更高要求,提出一种复合型快速短波天线调谐的方案。讨论了基于驻波比和幅值的复合检测原理,阐述了该复合型天调的硬件设计及其实现方法,完成了基于CPLD的测频模块和结合查表法的嵌入式系统的软件控制模块的设计。测试结果表明,通过同时监测谐振幅值和电压驻波比复合参数,提高了调谐精度,调谐时间也得到改善,初步实现了对匹配网络的自动调谐控制。     

基于物联网的智能家居系统设计

随着智能家居系统的普及,人们对智能家居的接受程度越来越高。文章结合物联网和单片机技术,设计了一款基于STM32的智能家居系统。该智能家居系统由单片机模块、温湿度检测模块、烟雾检测模块、按键模块、无线模块、显示模块和报警模块构成。其中,温湿度检测模块采用DHT11温湿度传感器,负责对家庭内部的温湿度指标进行监控,烟雾检测模块采用MQ-2对烟雾浓度进行检测,并将检测到的所有数据上传给STM32单片机。单片机模块接收到传感器采集的温湿度和烟雾数据后,通过显示模块将采集到的数据实时展示给用户,并采用Zig Bee无线通信技术把数据上报给上位机,上位机根据数据阈值实现报警功能。最后经过实验,文章设计的智能家居控制装置可以准确实现各项环境数据指标的检测与无线传输的功能。     

一种短波矢量天调技术的应用

从短波矢量天调的特点入手,阐述短波矢量天调的组成部分,重点针对“矢量阻抗冶检测电路和“矢量调谐冶两个关键点进行阐述。文中给出了一种微功率矢量阻抗检测电路的设计方法和工作原理,阐述了匹配网络的结构及可调谐区域的划分,给出调谐元件的组合方式,最后阐述了矢量天调的粗调、细调的调谐过程。并与传统天调对比,具有调谐速度快、调谐功率低、不可调谐点数少的特点,验证了此项技术的优点以及可行性。     

A hybrid inverse approach applied to the design of lumped-element RF coils

A combination of inverse procedures is employed in the design of radio-frequency (RF) coils with specific examples in, but not restricted to, magnetic resonance imaging. The first inverse procedure is the use of functional methods for the optimization of coil characteristics subject to restrictions on the field behavior. Continuous current distributions are derived from analysis of the fields they are required to produce. To make use of these distributions at a desired frequency, the method of moments is applied as a second inverse procedure to a discretized version of the current distribution. The advantage of this hybrid technique is that it provides a computational algorithm for optimization of feeding, tuning, impedance matching and other aspects of RF coil design. A prototype RF coil has been built using the engineering values predicted by the theory. Experimental results including images acquired from the prototype coil are presented.     

Common-mode differential-mode (CMDM) method for double-nuclear MR signal excitation and reception at ultrahigh fields

Double-tuned radio-frequency (RF) coils for heteronuclear mangentic resonance (MR) require sufficient electromagnetic isolation between the two resonators operating at two Larmor frequencies and independent tuning in order to attain highly efficient signal acquisition at each frequency. In this work, a novel method for double-tuned coil design at 7T based on the concept of common-mode differential-mode (CMDM) was developed and tested. Common mode (CM) and differential mode (DM) currents exist within two coupled parallel transmission lines, e.g., microstrip lines, yielding two different current distributions. The electromagnetic (EM) fields of the CM and DM are orthogonal to each other, and thus, the two modes are intrinsically EM decoupled. The modes can be tuned independently to desired frequencies, thus satisfying the requirement of dual-frequency MR applications. To demonstrate the feasibility and efficiency of the proposed CMDM technique, CMDM surface coils and volume coils using microstrip transmission line for (1)H and (13)C MRI/MRSI were designed, constructed, and tested at 7T. Bench test results showed that the isolations between the two frequency channels of the CMDM surface coil and volume coil were better than -30 and -25 dB, respectively. High quality MR phantom images were also obtained using the CMDM coils. The performance of the CMDM technique was validated through a comparison with the conventional two-pole design method at 7T. The proposed CMDM technique can be also implemented by using other coil techniques such as lumped element method, and can be applied to designing double-tuned parallel imaging coil arrays. Furthermore, if the two resonant modes of a CMDM coil were tuned to the same frequency, the CMDM coil becomes a quadrature coil due to the intrinsic orthogonal field distribution of CM and DM.     

Electrical harmonic oscillator with MR damper and energy harvester operating as TMD: Experimental study

In the study we propose and examine a novel concept, eMR-TMD as we call it, replacing a standard tuned mass damper (TMD) by an electrical harmonic oscillator (RLC circuit). The concept employs an electromagnetic energy harvester (EEH) to extract energy from vibrations, an RLC circuit in which serial resonance phenomenon occurs and a magnetorheological (MR) damper. The approach does not require modifications to the structural part of the system, i.e. no additional mass and spring are needed. The essence of the concept relies on the introduction of a tuned RLC circuit between the EEH coil and the control coil of the MR damper. The RLC circuit parameters we select in such a way so that the electrical resonance frequency is close to or equal mechanical resonance frequency in which the eMR-TMD concept is applicable. Moreover, it is required that the RLC circuit's quality factor is greater than 1 and then the voltage activated the MR damper is higher than the EEH induced voltage at the resonance frequency. Fulfilling the criteria allows tuning the current in the MR damper's control coil so that it is maximized at resonance frequency and minimized at high excitation frequencies. To prove the concept's potential we test the engineered eMR-TMD system experimentally under sinusoidal excitations. We compare the obtained test results with those acquired with the MR damper powered directly from the EEH (dMR-EEH concept) and when the MR damper's control coil is not powered (without TMD concept).     

A 0.5-4.0-GHz Tunable Bandpass Filter Using YIG Film Grown by LPE

A tunable bandpass filter using YIG film grown by liquid phase epitaxy (LPE) has been developed. Taking advantage of the very low resonance frequency in the perpendicular resonance of YIG film, an operation frequency of 0.5 GHz has been achieved. In order to make this filter operate up to 4.0 GHz, a new technique for multioctave tuning has been developed and applied to the filter. Over the wide tuning range from 0.5 GHz to 4.0 GHz, low insertion loss and high spurious suppression have been achieved. The performance of this filter satisfies the requirements for use as a tracking preselector in a microwave spectrum analyzer.     

Shielded Microstrip Array for 7T Human MR Imaging

The high-frequency transceiver array based on the microstrip transmission line design is a promising technique for ultrahigh field magnetic resonance imaging (MRI) signal excitation and reception. However, with the increase of radio-frequency (RF) channels, the size of the ground plane in each microstrip coil element is usually not sufficient to provide a perfect ground. Consequently, the transceiver array may suffer from cable resonance, lower Q-factors, and imaging quality degradations. In this paper, we present an approach to improving the performance of microstrip transceiver arrays by introducing RF shielding outside the microstrip array and the feeding coaxial cables. This improvement reduced interactions among cables, increased resonance stability, and Q-factors, and thus improved imaging quality. An experimental method was also introduced and utilized for quantitative measurement and evaluation of RF coil resonance stability or “cable resonance” behavior.      

An RF electronically controlled impedance tuning network design and its application to an antenna input impedance automatic matching system

A novel design is proposed for an electronically tunable impedance unit. The prototypes include lumped elements, but no electromechanical control methods. The devices can tune many different complex impedances at minimum manufacture costs. Two antenna input impedance automatic matching systems are also presented, based on the tuning network. One includes a simplified version of the generic tuner, which can achieve good matching levels between the antenna and the power module with low losses. In a more complete version, an application specific integrated circuit control unit is developed including a complex search algorithm. In order to obtain a good matching level, both systems require a control module to select the proper tuner impedance configuration. The measurements and results of both constructed prototypes are presented. The designs were carried on terrestrial trunked radio mobile stations in the 380-400-MHz frequency band and supported high power levels (greater than 40 dBm).     

Design and modeling of a micromachined high-Q tunable capacitor with large tuning range and a vertical planar spiral inductor

In wireless communication systems, passive elements including tunable capacitors and inductors often need high quality factor (Q-factor). In this paper, we present the design and modeling of a novel high Q-factor tunable capacitor with large tuning range and a high Q-factor vertical planar spiral inductor implemented in microelectromechanical system (MEMS) technology. Different from conventional two-parallel-plate tunable capacitors, the novel tunable capacitor consists of one suspended top plate and two fixed bottom plates. One of the two fixed plates and the top plate form a variable capacitor, while the other fixed plate and the top plate are used to provide electrostatic actuation for capacitance tuning. For the fabricated prototype tunable capacitors, a maximum controllable tuning range of 69.8% has been achieved, exceeding the theoretical tuning range limit (50%) of conventional two-parallel-plate tunable capacitors. This tunable capacitor also exhibits a very low return loss of less than 0.6 dB in the frequency range from 45 MHz to 10 GHz. The high Q-factor planar coil inductor is first fabricated on a silicon substrate and then assembled to the vertical position by using a novel three-dimensional microstructure assembly technique called plastic deformation magnetic assembly (PDMA). Inductors of different dimensions are fabricated and tested. The S-parameters of the inductors before and after PDMA are measured and compared, demonstrating superior performance due to reduced substrate loss and parasitics. The new vertical planar spiral inductor also has the advantage of occupying much smaller silicon areas than the conventional planar spiral inductors.     

Evaluation of MRI RF probes utilizing infrared sensors

The magnetic resonance imaging (MRI) coil's radio frequency (RF) field distribution has a strong effect on image quality as well as specific absorption rate. In this paper, a method of probing a coil's RF field distribution over any unoccupied region of the coil is presented. This technique is based on the use of infrared sensing. The proposed method was implemented and tested on a high field RF volume coil operating at 340 MHz. Very good agreement was achieved between the infrared measurements and numerical data obtained utilizing an in-house three-dimensional finite-difference time-domain package. The results demonstrate that the proposed technique is practical, robust, and efficient in making accurate measurements of the electric field distributions in loaded and unloaded MRI coils.     

Dual frequency microstrip rectangular patches

A dual frequency microstrip rectangular patch antenna resonating at frequencies 520 MHz and 2.5 GHz is presented. This antenna incorporates a matching structure to improve the impedance characteristic at one resonance frequency and uses symmetrically positioned varactor diodes to control resonance at a lower frequency. The use of varactor diodes also provides the benefit of a broad tuning range at the lower resonance frequency. A tuning range of 32% at 520 MHz was measured.<>     

Rectangular spiral coil analysis for inductively coupled RFID systems based on Partial Element Equivalent Circuit method

In order to achieve maximum power efficiency with inductively coupled RFID tags, the impedances of the spiral coil and the integrated circuit must be matched to each other. In this paper, we present a numeric approximation of the impedance of a rectangular spiral coil by means of a coupled electromagnetic and circuit analysis called Partial Element Equivalent Circuit method and verify our simulation with measurement results. We include the effective permittivity in our 3D capacitance extraction method and fit the simulated impedance to a simple RLC equivalent circuit model which is also used by our measurement device and compare the resulting element values. Our Matlab-based simulator shows good agreement over the frequency band of interest and allows for optimization for various design goals.