Comments on "theoretical model for an MRI radio frequency resonator"

In contrast to a previous report [Baertlein et al., ibid., vol.47, p.535 (2000)], the transverse electromagnetic resonator used in magnetic resonance imaging is shown to be similar to the high-pass "birdcage" resonator in having an electric field minimum in correspondence with the maximum of the magnetic field. The noise performance of each resonator will, in consequence, be comparable, since at high frequencies patient conductive losses are predominant     

Theoretical performance analysis of radio frequency fingerprinting under receiver distortions

Radio frequency fingerprinting (RFF) is used to uniquely identify individual emitters by exploiting the radio frequency characteristics, which are originated from transmitter imperfections. The theoretical performance is analyzed to evaluate the feasibility of RFF with channel noise and receiver imperfections. The distortions from oscillators and analog‐to‐digital converter (ADC) are considered, and a RFF signal model describing the discrepancies of transmitter imperfections, channel noise, and receiver distortions are constructed. A likelihood ratio test algorithm for RFF is proposed to analyze the theoretical performance. The upper and lower bound of theoretic performance is derived through the analysis of the likelihood ratio test statistic, which enlightens how to design a “just enough” receiver to meet the demands of RFF. The simulation results are in agreement with the theoretical evaluation. Copyright © 2013 John Wiley & Sons, Ltd.     

3kW射频板条CO2激光器抛物面非稳波导腔研究

为了提高传统球面镜腔3kW射频板条CO2激光器光束质量,设计了新型抛物面镜负支非稳-波导混合腔;结合标量光束的瑞利-索末菲衍射理论与特征向量法,研究了大菲涅耳数下镜面类型对非稳波导混合腔光场传输特性的影响;利用矩形波导理论、1维近似分析得出了波导传输损耗及偏振情况。结果表明,将非稳方向输出镜和尾镜改为与光轴交点处曲率半径为R1=951.32mm和R2=1088.68mm的抛物镜面,能够避免尾镜漏光,可有效改善模式鉴别特性;常用波导电极镀膜材料中,镀铝电极内波导方向传输损耗最小,传输光场为x偏振的EH1模。采用电极镀铝的抛物面非稳波导腔能够降低损耗、提升光束质量。     

Theoretical radiation resistance of an isolated slot ring resonator

The theoretical radiation resistance of an isolated slot ring resonator is expressed by means of an analytical formula. The result is deduced from the radiation resistance of an equivalent circular loop of the same size when Babinet's principle is applied. Results are compared with recent theoretical and experimental ones.     

Detection and measurement of radio frequency feedback for an on‐frequency repeater

The radio frequency feedback (RFF) occurs when the insulation is insufficient between the antennas of an on‐frequency repeater, increasing digital transmission errors. In addition, a strong RFF could compromise system stability of the on‐frequency repeater because of the growing power in the closed‐loop. Automatic gain control is widely used by the on‐frequency repeater to regulate the power, this solution being generally used with echo cancellation processes. Most of echo cancellation techniques are based on digital processing such as adaptive filters whose the effectiveness and the algorithm speed are depending on the signal frequency, the bandwidth and the closed‐loop parameters. This paper describes a solution of RFF estimation and detection regardless of the receiving signal modulation. By using the frequency scanning and the analysis of the power spectral density peaks in the system, this solution is reliable whatever are the values of the gain‐margin and the loop‐delay. Simulations and experimental implementation using field‐programmable gate array validate the solution. In addition, an example of applications is given in the context of the interference cancellation.     

A new frequency for piezoelectric resonator measurement

A new frequency associated with the reflection coefficient of a piezolectric resonator is described which is independent of the length of the uniform transmission line connecting the resonator with the measurement system. The frequency is also independent of the resonator motional resistance and has other properties which make it potentially useful for special measurement purposes.     

SOI纳米光波导微环谐振腔谐振频移的测试分析

To research the effect of a deposited SiO₂ insulating layer on the resonance frequency modulation of an SOI nanowaveguide ring cavity during integration fabrication,a rib waveguide ring resonator was systematically designed and fabricated.SiO₂ insulating layers with different thicknesses were deposited for analysis of the frequency shift characteristics.By testing the resonance transmission spectrum power of this structure,it is found that there are blue shifts after SiO₂ deposition,and the frequency shift value of a structure with a 500 nm SiO₂ insulating layer deposited is 0.8 nm,that is 0.24 THz at the resonance point where wavelength is around 1550 nm. Taking advantage of this conclusion,efficient optical modulation is available by choosing different frequency band resonance wavelengths to narrow the frequency modulation range.     

Adjustable frequency dielectric resonator antenna

An easy method of tuning the resonant frequency of cylindrical and ring dielectric resonator (DR) antennas using different diameters of conducting plates is presented. This technique can tune a DR antenna to operate at the design frequency without changing antenna performance. The maximum frequency tuning range can reach up to 300-500 MHz     

Laser frequency control using an optical resonator locked to anelectronic oscillator

A new method for controlling a laser's center frequency is reported. This method extends the Pound-Drever-Hall technique, which delivers exceptional laser linewidth. The new technique, applicable over a broad range of wavelengths, produces a laser beam with both narrow linewidth and stable center frequency. A diode-pumped ring laser is locked to an ultrahigh-finesse, tunable optical resonator which, in turn, is locked to an electronic (5 MHz) oscillator using a difference frequency developed by locking a second laser to the resonator. A 1064-nm beam is reported with linewidth less than 0.004 Hz and center-frequency stability given by the electronic reference. For the case of an oven-controlled quartz crystal, the laser center-frequency stability is less than 1 part in 10¹¹ per day with root Allan variance of 10^-12 for a 1000-s time delay. The entire system is compact, and all elements are solid-state, making it useful both in the laboratory and in a number of space-based applications     

Design and simulation of optoelectronic oscillator with micro ring resonator and radio frequency amplifier modelling at 110 GHz

There is an increasing need for high performance oscillators as the faster transmission networks demand for high frequency signals. Opto-electronic oscillators (OEO) enable us to make better oscillators in terms of size, weight and power. In this paper, photonic integration is proposed for realizing the OEO with micro ring resonator (MRR) and radio-frequency (RF) amplifiers of monolithic microwave integrated circuit (MMIC), which can be used for generating 110 GHz sine wave. The OEO architecture is proposed and block diagram developed considering Silicon based MRR and three-stage RF amplifier based on GaN high-electron-mobility transistor (HEMT). A simulation model is developed according to the Klein model of MRR and is validated against the calculated performance parameters. MRR dimensions are calculated as with silicon on insulator (SOI) technology and a radius 5.27 μm for the device is derived. Free spectral range (FSR) of 48.52 nm and filter rejection ratio of 16.79 dB are obtained for this device. The proposed RF amplifier is modelled with GaN parameters derived from high frequency pinch-off model and with power amplifier considerations. The gain for this amplifier is obtained as 10.6 dB. The OEO design is developed in this project in such a way that the system can be manufactured with the existing methods.     

Planar inverted-F antenna for radio frequency identification

A small and low-cost antenna solution for radio frequency identification (RFID) tags is presented. The impedance of the antenna is designed to match directly to the impedance of the RFID microchip. Also, the impedance of the antenna is immune to the platform. Thus, the antenna is applicable in many different environments. The design and measurement results are reported and discussed.     

Split-aloha algorithm for radio frequency identification system

Anti-Collision algorithm is one of the most important components of radio frequency identification (RFID) technology, which possesses a key position in the performance of the whole system. ALOHA algorithm is one of the most popular methods to solve the collision problem because of its efficiency and practicability. The grouping method has been developed for enhancing the performance of conventional ALOHA when there are thousands of tags. However, the existing grouping method has limitations in applications due to its rigorous requirements for the estimation of the number of backlog tags or the admirable characteristics of the tags' ID number. Working on the improvement of the grouping methods, we proposed an algorithm named split-ALOHA with a novel grouping method that split tags as a binary tree. The novel grouping method makes it more practicable than the existing grouping methods due to the simplified requirements for tags. Simulations of the proposed algorithm show the superior performance of a linearly increasing of the number of consumed time slots while the number of tags increases. The algorithm performance analysis between split-ALOHA and ALOHA algorithms with other grouping methods has been implemented in a proper way.     

一种用于认知无线电的快速频率合成器设计

为了研制一种锁定时间短、相位噪声低、杂散抑制度高的频率合成技术,采用了直接数字式频率合成器(DDS)驱动锁相环(PLL)的结构。该频率合成器综合了DDS频率转换速度快、频率分辨率高和PLL输出频带宽、输出杂散低的优点。基于该结构研制实现了输出频率范围为700～800 MHz的宽带频率合成器,实验结果表明该频率合成器扫描模式Δf=1 MHz锁定时间不超过20μs,跳频模式Δf=50 MHz的定时间不超过30μs,近端杂散抑制度优于-50 dBc。     

Digital radio frequency memory

Digital radio frequency memory (DRFM) is a technique in which high-speed sampling and digital memory is used to store radio frequency and microwave signals. It is becoming a popular technique for the implementation of false-target ECM systems. The author discusses the principles of DRFM and the advantages of alternative system architectures     

一种综合射频系统SCA软件平台的设计与实现

针对机载综合射频开放式系统架构,为了在软件综合层面上实现波形应用软件与具体平台的解耦,设计并实现了一种基于软件通信架构(Software Communication Architecture, SCA)的软件平台及其环境工具,解决了机载平台软件的分布式通信、资源调度管理、系统建模等技术问题,从而实现功能、应用和波形的组件化与动态重构。测试验证与工程应用情况表明,软件平台能够满足机载领域信号、信息处理强实时、高可用的应用需求,可有效提升综合射频系统软件开发质量与集成联试效率。     

Generalized frequency plane model of a spiral winding structure integrated power series resonator

The technology of integrated passive components for power electronics is at present being developed. Because of the compact structures and the special implementation techniques of these integrated modules, the high-frequency parasitic resonances are normally significant and may have a negative impact on the performance and electromagnetic interference characteristics. However, the existing modeling technique can only predict the fundamental resonant frequency and showed neither the causes of the high-frequency resonance nor how to calculate those accurately. Based on the modeling of multiconductor transmission structures, this paper presents the modeling of the spiral winding structure integrated series resonant module. This structure can be treated as several multiconductor transmission structures connected in certain patterns. Different connection patterns only determine the voltage and current boundary conditions with which the equations can be solved. The MATLAB calculation results correlate well with the small-signal measurement results. The calculation sensitivities with respect to variation of various parameters are also discussed and the causes of resonance at different frequencies are identified.     

A three dimensional analysis of slotted tube resonator for MRI

A three dimensional model of a slotted tube resonator (STR) used as a probe in the magnetic resonance imaging (MRI), which is loaded by a dielectric body and surrounded by a conducting shield, is analyzed by using the variational method and the dyadic Green's function of a circular waveguide having a dielectric core. Three surface current modes are properly assumed to expand the currents on the STR. The characteristics such as the input impedance, the resonance frequency, the Q value, and the magnetic field distribution are obtained to show the effects of the dielectric body and the conducting shield. Some theoretical results are compared with the measured data to confirm the validity of the present analysis.     

Optimal transmission frequency for ultralow-power short-range radio links

Analysis determining the optimal transmission frequency for maximum power transfer across a short-range wireless link is introduced, including a comparison of near-field transmission with far-field transmission. A new near-field power transfer formula has been derived, which allows direct comparison with the well-known far-field Friis transmission formula. Operating charts are presented, which provide the designer with the preferred transmission frequency as a function of distance and antenna dimensions, together with surface plots which show the power transfer for this frequency. The analysis, performed for loop antennas, has been used to evaluate the oscillator transmitter as a low-power topology. It is shown that the requirement of a high-Q factor to realize a low-power oscillator need not be contradictory to achieving optimal far-field radiation characteristics. Based on this fact an approach to sizing loop antennas for low-power oscillator transmitters is suggested.     

Evaluation of microwave and radio frequency catheter ablation in amyocardium-equivalent phantom model

A highly localized burst of energy applied to the myocardium via a transvenous catheter-mounted power source can be used to destroy endocardial tissue regions which mediate life-threatening arrhythmias. In the past, high-voltage direct current pulses, radio-frequency (RF) current, and laser light have been used as energy sources. In this paper, the use of 2450 MHz microwave energy applied via a miniature coaxial cable-mounted helical coil antenna designed specifically for this application was investigated as a means to increase the treated volume of cardiac tissue in a controllable and efficient manner during ablation. Using an array of fiber optic temperature probes implanted in a saline-perfused, tissue-equivalent gel phantom model designed to simulate the myocardium during ablation, the heating pattern from the microwave antenna was characterized and compared to that induced by a commercial RF electrode catheter at 550 kHz. Effects of variable contact angle between the heat source and heart wall were assessed in terms of the radial penetration and overall volume of heated tissue. Heating patterns from the RF electrodes dropped off much more abruptly both radially and axially than the microwave antenna such that the volume of effectively heated tissue was more than ten times larger for the microwave antenna when the heat sources were well-coupled to the tissue, and more than four times larger for the microwave antenna when the sources were angled 30 degrees away from the tissue surface.