A V-Band Communication Transmitter and Receiver System Using Dielectric Waveguide Integrated Circuits

A V-band communication transmitter and receiver is described. Both units make extensive use of passive microwave components fabricated rising millimeter-wave insular line integrated circuits (MILIC's). These components consist of rectangular dielectric rod antennas, a MILIC ferrite isolator, a bandpass ring filter, a directional coupler, and sections of dielectric insular waveguide. The passive insular waveguide components are integrated together, along with split block metal waveguide mounts for the active devices, in order to form the RF circuitry of the transmitter and receiver.     

Electromagnetic considerations for RF current density imaging [MRI technique

Radio frequency current density imaging (RF-CDI) is a recent MRI technique that can image a Larmor frequency current density component parallel to B(0). Because the feasibility of the technique was demonstrated only for homogeneous media, the authors' goal here is to clarify the electromagnetic assumptions and field theory to allow imaging RF currents in heterogeneous media. The complete RF field and current density imaging problem is posed. General solutions are given for measuring lab frame magnetic fields from the rotating frame magnetic field measurements. For the general case of elliptically polarized fields, in which current and magnetic field components are not in phase, one can obtain a modified single rotation approximation. Sufficient information exists to image the amplitude and phase of the RF current density parallel to B(0) if the partial derivative in the B(0) direction of the RF magnetic field (amplitude and phase) parallel to B(0) is much smaller than the corresponding current density component. The heterogeneous extension was verified by imaging conduction and displacement currents in a phantom containing saline and pure water compartments. Finally, the issues required to image eddy currents are presented. Eddy currents within a sample will distort both the transmitter coil reference system, and create measurable rotating frame magnetic fields. However, a three-dimensional electro-magnetic analysis will be required to determine how the reference system distortion affects computed eddy current images.     

地下磁感应通信阵列天线传播特性分析

针对地下磁感应通信系统中单个磁性天线路径损耗大、通信效率低、传输距离短的问题,研究了双线圈天线与3D天线两种协同式天线的电磁传播特性.基于Matlab对根据天线数学模型得到的磁感应强度进行了仿真和分析,并将两种天线的传输性能与单一磁性天线进行了比较.研究表明,两种天线的磁场强度都有很大提高,并具有方向性和对称性,双线圈...     

Power Equations and Capacity Performance of Magnetic Induction Communication Systems

Although a number of studies have been done on the traditional Radio Frequency (RF)terrestrial communication system, the potential applications and the advantages of Near-Field magnetically coupled coils in wireless short range communications is just emerging and is yet to be explored. This paper investigates the impacts of magnetically coupled transceiver antenna coil on the received signal power and the communication link capacity. Based on the equivalent circuit model in free space, theoretical foundations are laid with observed simulation results. The simulation result benefits the antenna designers and the network planning engineers to estimate the power at the receiver and a near field magnetic communication system capacity for different antenna coil characteristics and different communication ranges.     

An inverted-microstrip resonator for human head proton MR imaging at 7 tesla

As an extension of the previously developed microstrip transmission line (MTL) RF coil design, a high-frequency RF volume coil using multiple inverted MTL (iMTL) resonators for human head imaging at high magnetic field strength of 7 tesla (T) is reported. Compared to conventional MTL resonators, iMTL resonators can operate at higher frequency with lower losses and, thus, are suitable for designs of high-frequency RF volume coils with large coil size for human MR imaging and spectroscopy at high fields. An approach using capacitive terminations was analyzed and applied to the design of the iMTL volume coil for improving RF field homogeneity and broadening frequency-tuning range. A performance-comparison study was conducted between the prototype iMTL volume coil and a custom-built TEM volume coil at 7 T. The iMTL volume coil presents a comparable SNR and intrinsic B1 homogeneity to the TEM volume coil. Phantom and the human head images acquired using the iMTL volume coil are also presented. The proposed iMTL volume coil provides an efficient and alternative solution to design high-frequency and large-size volume coils for human MR applications at very high fields.     

RF powering of millimeter- and submillimeter-sized neuralprosthetic implants

The size of the transducers for neural stimulation has shrunk steadily with application of thin-film techniques to electrode design. The feasibility is examined of designing millimeter- and submillimeter-sized power sources based on RF coupling that could be integrated into these implants to provide power without a tethering power cable. The coupling between a transmitter coil and receiver coil when the coil diameters are markedly different is analyzed, and for these circumstances, a simple Thevenin equivalent model is developed to describe the power transmission between the transmitter and receiver. The equivalent circuit developed gives insight into the way that coil diameters, frequency, and turns affect coupling between large and small coils. Several examples demonstrate that milliwatt range power sources can be implemented with millimeter- and submillimeter-diameter receivers     

Hybrid Beamforming for Massive MIMO Using Rectangular Antenna Array Model in 5G Wireless Networks

Fifth and future generation (5G and B5G) wireless networks aim to serve users with higher data rates and lower latency. Data traffic due to the rapid growth in communication has motivated the study of Multiple Input Multiple Output (MIMO) systems. They utilize multiple antennas in both transmitter and receiver sides. It is necessary to improve the existing technology to achieve fast and reliable communication. In this research work, a rectangular array antenna based hybrid beamforming in a massive MIMO model has been proposed to improve the spectral efficiency of the system. Thus channel capacity with small RF chains is used. To achieve the high signal strength in the main lobe, Chebyshev tapering has been used to suppress the side lobes signals. In this manner, the proposed Hybrid Beamforming for Massive Output MIMO has been realized with a small complexity and higher spectral efficiency. In this research work, the spectral efficiency of both proposed Hybrid and fully-digital beamforming with a different number of RF chains for a various number of antennas at the transmitter, the receiver side has been analyzed. From the simulation results, it has been observed that the proposed rectangular array antenna based Hybrid beamforming in a massive MIMO system reduces the computational complexity up to 99% as compared with conventional fully digital beamforming to achieve the same spectral efficiencies, which is a productive model for 5G wireless networks.

     

Ultrahigh-field MRI whole-slice and localized RF field excitations using the same RF transmit array

In this paper, a multiport driving mechanism is numerically implemented at ultra high-field (UHF) magnetic resonance imaging (MRI) to provide 1) homogenous whole-slice (axial, sagittal, or coronal) and 2) highly localized radio frequency (RF) field excitation within the same slices, all with the same RF transmit array (here chosen to be a standard transverse electromagnetic (TEM) resonator/coil). The method is numerically tested using a full-wave model of a TEM coil loaded with a high-resolution/18-tissue/anatomically detailed human head mesh. The proposed approach is solely based on electromagnetic and phased array antenna theories. The results demonstrate that both homogenous whole-slice as well as localized RF excitation can be achieved within any slice of the head at 7 T (298 MHz for proton imaging).     

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.     

An Inverse Methodology for High-Frequency RF Coil Design for MRI With De-emphasized$B _1$Fields

An inverse methodology for the design of biologically loaded radio-frequency (RF) coils for magnetic resonance imaging applications is described. Free space time-harmonic electromagnetic Green's functions and de-emphasized$B_1$target fields are used to calculate the current density on the coil cylinder. In theory, with the$B_1$field de-emphasized in the middle of the RF transverse plane, the calculated current distribution can generate an internal magnetic field that can reduce the central overemphasis effect caused by field/tissue interactions at high frequencies. The current distribution of a head coil operating at 4 T (170 MHz) is calculated using an inverse methodology with de-emphasized$B_1$target fields. An in-house finite-difference time-domain routine is employed to evaluate$B_1$field and signal intensity inside a homogenous cylindrical phantom and then a complete human head model. A comparison with a conventional RF birdcage coil is carried out and demonstrates that this method can help in decreasing the normal bright region caused by field/tissue interactions in head images at 170 MHz and higher field strengths.     

An inverse methodology for high-frequency RF coil design for MRI with de-emphasized B1 fields.

An inverse methodology for the design of biologically loaded radio-frequency (RF) coils for magnetic resonance imaging applications is described. Free space time-harmonic electromagnetic Green's functions and de-emphasized B1 target fields are used to calculate the current density on the coil cylinder. In theory, with the B1 field de-emphasized in the middle of the RF transverse plane, the calculated current distribution can generate an internal magnetic field that can reduce the central overemphasis effect caused by field/tissue interactions at high frequencies. The current distribution of a head coil operating at 4 T (170 MHz) is calculated using an inverse methodology with de-emphasized B1 target fields. An in-house finite-difference time-domain routine is employed to evaluate B1 field and signal intensity inside a homogenous cylindrical phantom and then a complete human head model. A comparison with a conventional RF birdcage coil is carried out and demonstrates that this method can help in decreasing the normal bright region caused by field/tissue interactions in head images at 170 MHz and higher field strengths.     

Quantitative spectral/spatial analysis of phased array coil in magnetic resonance imaging based on method of moment

A new approach for analysis of RF coils in magnetic resonance (MR) experiments is reported. Instead of assuming current distribution in conventional quasi-static algorithm, this approach transforms the coil geometry into an equivalent circuit for complex current calculation. Self and mutual inductance are taken into consideration. Frequency responses of RF coils and transverse magnetic field (B1) maps can be simulated. This approach is especially efficient for phased array coil design for its small matrix size when implemented on computers. Experiments on both single surface coil and phased array coils are consistent with simulation results. Index Terms-Magnetic resonance, method of moment, phased array coil, RF coil.     

A time-harmonic inverse methodology for the design of RF coils inMRI

An inverse methodology is described to assist in the design of radio-frequency (RF) coils for magnetic resonance imaging (MRI) applications. The time-harmonic electromagnetic Green's functions are used to calculate current on the coil and shield cylinders that will generate a specified internal magnetic field. Stream function techniques and the method of moments are then used to implement this theoretical current density into an RF coil. A novel asymmetric coil operating for a 4.5 T MRI machine was designed and constructed using this methodology and the results are presented.     

磁性液体强化扬声器音圈散热的实验研究

实验将封有聚α-烯烃合成油基磁性液体的两玻璃管放置于磁场中,研制了磁性液体在均匀磁场中瞬态双热线导热 系数的实验测量装置,测试发现磁性液体的导热系数在均匀磁场中随磁场强度的增大而显著增大.研制了恒压法在线实时 检测扬声器音圈温升的测量装置,评价了在同一工况下空气和磁性液体对扬声器音圈温升的影响,测量发现磁性液体能显著 ...     

基于RX5000/TX5000的无线收发电路

RX5000和TX5000分别是RFMicro Devices公司专为小范围单向无线通信设计生产的接收器和发射器芯片。它们体积小，功耗低，价格便宜，而且性能稳定，使用方便。文中介绍了RX5000、TX5000的特点与功能，给出了以这两种器件为核心设计的无线收发电路，并对其在足球机器人无线通信系统中的应用进行了说明。     

Distribution of the Strength of the Low-Frequency Field Demodulated in the Disturbed Lower Ionosphere over the Earth Surface

The possible distribution of the field strength of the low-frequency demodulated radiation of the high-power transmitter of the HAARP station (Alaska, USA) over the Earth surface in the Earth–ionosphere waveguide has been numerically simulated. It has been shown that, owing to the extremely weak electromagnetic coupling between the ionosphere and the waveguide in the case of an ionospheric source, the strengths of the electric and magnetic fields of the waveguide waves are relatively low and are at the level of the low-frequency noise even in the immediate vicinity of the center of the distribution. It has been confirmed that, in order to detect such a signal and measure its parameters, it is necessary to use special procedures for processing data from ground-based receivers.     

Electromagnetics in magnetic resonance imaging

Magnetic resonance imaging (MRI) is a powerful new imaging method, which produces cross-sectional tomographic and three-dimensional images similar to those of x-ray computed tomography (CT). However, rather than relying on harmful ionizing radiation, MRT is based on the interaction between RF fields and certain atomic nuclei in the body, when they are in the presence of a strong magnetic field. An MRI system is one of the few complete systems in which the design relies heavily upon a knowledge of electromagnetics. We give a tutorial on the electromagnetic analysis and design of three key components of an MRI system, namely, the magnet, the gradient coil, and the radiofrequency (RF) coil. We also discuss the analysis and characterization of the interactions of RF electromagnetic fields with biological subjects     

Partial volume tissue classification of multichannel magnetic resonance images-a mixel model

A single volume element (voxel) in a medical image may be composed of a mixture of multiple tissue types. The authors call voxels which contain multiple tissue classes mixels. A statistical mixel image model based on Markov random field (MRF) theory and an algorithm for the classification of mixels are presented. The authors concentrate on the classification of multichannel magnetic resonance (MR) images of the brain although the algorithm has other applications. The authors also present a method for compensating for the gray-level variation of MR images between different slices, which is primarily caused by the inhomogeneity of the RF field produced by the imaging coil.     

Magnetic induction based cluster optimization in non-conventional WSNs: A cross layer approach

Conventional Radio Frequency (RF) communication technique is unsuitable for communication in non-conventional media (water, soil, rocks, etc.) because of heavy losses incurred due to dynamic channel characteristics. Magnetic Induction (MI) communication overcomes these losses as it is least affected by such varying channel characteristics. In non-conventional media based Wireless Sensor Networks (WSNs) the deployed sensor nodes cannot replace or replenish their batteries. Thus, energy consumption should be minimized and that can be achieved by clustering process. This process involves data sensing, aggregation and routing to the base station. These sub-tasks are performed under Physical (PHY), Medium Access Control (MAC) and Network (NET) layers of OSI Network model. Having lesser or larger number of clusters has different impact on energy consumption in different layers’ perspective. A large number of clusters decreases energy consumption as per PHY layer whereas it results in increased energy consumption as per MAC and NET layers. Thus, a trade-off is required to minimize the overall energy consumption. To this end, we found an optimal number of clusters considering the simultaneous influence of all three layers. The above analysis is performed for three media viz. sea water, fresh water and dry soil.     

波导传输检波装置的研究

波导传输检波装置用以发射机的检波式功率监测,是雷达导引头发射机的一个重要组成部分。发射机产生的大功率射频信号经过波导传输检波装置最终传输给天线,在大功率传输过程中,波导传输检波装置从大功率射频信号中耦合出一定量进行射频信号包络检波,检波信号通过外围电路处理可以反映发射机工作状态,并可反馈优化发射机工作状态。文中介绍了波导传输检波装置的设计原理,并对设计中的一些重要环节进行了仿真,其中包括了温度对设计的影响。