Mammalian teratogenesis and radio-frequency fields

Evidence of teratogenesis after exposure to radio-frequency (RF) electromagnetic (EM) fields has been sought in investigations of several species. This review summarizes reports of teratogenic effects in mammals. Investigations performed on the laboratory mouse and rat have revealed that exposure to intense RF fields can result in reduced body mass, in specific anatomical abnormalities (especially exencephaly), and in an increase in resorptions of the fetus. The small number of investigations and clinical reports on human subjects is inconclusive. Whether the reported teratogenesis in infrahuman mammals is derived primarily from thermal stress or results from interactions involving field specific effects and heating has not been determined. The data to date do indicate that there is a marked dose-response relation such that only intense fields that result in significant heating are associated with reliable induction of teratogenesis.     

具有自动稳幅功能的软激励C类大功率射频振荡器

介绍了一种具有自动稳幅功能的软激励C类大功率射频振荡器。大功率射频振荡器已经广泛应用于电力电子、射频电源、低温等离子体、高频感应加热等领域。该大功率射频振荡器能够输出较高的输出电压和输出功率,并且通过对输出电压采样控制MOS管的静态工作点,稳定输出电压;另外,该设计电路起振时工作在AB类状态,稳定工作时在自动稳幅电路的作用下进入C类工作状态,实现了C类射频振荡器的软激励。最后通过仿真和实物电路测试了电路性能,并给出了振荡器输出电压、输出功率与MOS管工作状态关系的经验公式。     

Cost comparison of ECH relative to other RF plasma heating systems†

Electron cyclotron heating (ECH) of toroidal plasmas has many performance advantages over other plasma heating methods. However, up to the present time, ECH systems have been economically uncompetitive with other RF heating techniques, primarily due to the unavailability of tubes with high unit power in the ECH frequency range. High power RF systems consisting of a large number of small modules become complex and expensive due to the multiplicity of support, ancillary, interlock and control equipment necessary. This need no longer be true with the projected availability of ‘megawatt’ ECH power tubes. This paper will demonstrate the economic benefits to be obtained from the development of such tubes relative to present ECH and other RF plasma heating systems     

High-Power CW Klystron for Fusion Experiments

A 3.7-GHz 700-kW klystron in continuous-wave (CW) operation has been developed to upgrade the lower hybrid RF plasma heating power in a tokamak up to 10 MW. The klystron is equipped with a diode gun, a five-cavity RF structure, two BeO-disk RF windows, and a large-size X-ray-shielded hypervapotron collector. The output power is recombined in a four-port junction which we also developed. The tube is designed to deliver 620-kW CW RF power with a mismatched load (VSWR = 1.4) and 700-kW CW with a matched load. Several prototypes have been built with successive design improvements. The major improvement was to change one single RF output into two RF outputs. The most recently built prototype meets all design specifications at 73.1 kV and 20.7 A, with an efficiency of 47% on a matched load and 40% with a 1.4 : 1 VSWR load, worst case phase. The power losses dissipated in the body have been measured as low as 17 kW, which corresponds to the RF heating and implies low beam interception. The measured temperatures of the output cavity noses and collector wall have been kept below 130degC and 200degC, respectively, which results in large thermal margin.     

Comparison of power deposition patterns produced by microwave andradio frequency cardiac ablation catheters

Transcatheter microwave and radio frequency (RF) electrodes are used for the ablative treatment of cardiac arrhythmias. The authors compare the power deposition patterns of microwave antennas and RF electrodes in saline phantoms of biological material. The decrease in power deposition as a function of distance away from the electrode is nearly exponential for RF and is considerably steeper than microwave antennas. These results suggest that microwave antennas are capable of heating a larger volume and thus creating a greater lesion than RF     

RF Analysis of ITER Remote Steering Antenna for Electron-Cyclotron Plasma Heating

An application of remote RF beam steering concept, based on image multiplication phenomena in a corrugated square waveguide, to electron-cyclotron plasma heating and current drive for ITER has been considered. In the present paper high attention is paid to studies of reliability of the remote steering capability in realistic waveguide condition. Different factors, could limit efficiency (RF breakdown, random technological spread of parameters, and heating of system), are simulated. Polarization properties of the remote steering antenna, arising due to non-ideal corrugation, are investigated. It is suggested a new configuration of antenna to be not sensible to corrugation parameters. RF analysis of the system, supplemented by dog-legs and a vacuum window, is also presented. A new way to use beating wave transmission in the remote steering waveguide is suggested, in order to reduce losses caused by mitre bends.     

Radio frequency wave applications in magnetic fusion devices

An overview of RF wave applications in magnetic fusion devices is given. A summary of the wave physics, the present experimental progress, and the technological development of RF heating is presented. Particular emphasis is placed on the technological requirements of wave launchers, transmission systems, and RF generators for the three main frequency ranges: the ion cyclotron (ICRF), the lower hybrid (LHRF), and the electron cyclotron (ECRF). Some possible extrapolations of the present technology to CTR regimes are discussed.     

Nonlinear characteristics of on-chip spiral inductors under high RF power

This paper explores silicon CMOS on-chip spiral inductors performance degradation under high RF power. A novel methodology to calibrate and characterize on-chip spiral inductor with large signal inputs (high/medium power) is presented. Experiments showed 12% degradation of quality factor in a particular inductor design when 34 dBm RF power was applied. The degradation of quality factor of inductor can be attributed to a local self heating effect. Thermal imaging of such an inductor under high RF power validates the hypothesis.     

TIS320F2812构成的感应加热逆变控制器

针对现阶段感应加热领域逐渐数字化的趋势,将DSP芯片应用在感应加热电源的逆变器控制上,以达成频率跟踪与定角控制,从而实现智能控制,使得逆变器的控制与调整更加简单可行。分析了感应加热电源装置的发展趋势及其电源中逆变器的控制要求,设计了基于DSP的并联谐振式感应加热电源中的逆变器的控制主电路,成功实现了频率跟踪和定角控制。     

90nm硅栅过刻蚀工艺中功率对等离子体性质的影响

通过实验对适用于90nm多晶硅栅刻蚀工艺中过刻蚀阶段等离子体的性质进行了研究分析.实验采用满足200mm硅晶片刻蚀的电感耦合多晶硅刻蚀设备,借助等离子体分析仪器(朗缪尔探针)进行实验数据测定,得到了等离子体性质与功率、气体流量等外部参数的关系.实验表明在射频功率增加的过程中,能量耦合系数处于一个相对稳定的常值;当等离子体处于局部加热状态时,绝大部分的电子处于附着状态,维持等离子体的电子数目相对减少.等离子体中的射频能量耦合空间随着射频功率的增加,分布状态会变得更加一致化.     

The RF toroidal transformer as a heat delivery system for regionalhyperthermia

A novel working principle for a RF (radio-frequency) hyperthermia applicator, suitable for heating large cylindrical volumes of coaxial loads, is described. The system includes a toroidal inductor as an active device producing an almost uniform electric field, which is polarized along the toroidal z axis in the space inside the toroidal ring where the conductive tissue is placed. This electric field produces axial RF currents which, in turn, produce the required heating, provided that a closed loop is formed by electrically connecting the conductive load through capacitive ring (CR) electrodes to form an electric circuit closed externally to the toroidal inductor. This system behaves like a toroidal transformer (TT), the secondary circuit of which includes the dissipative load between the CR electrodes     

Guidelines for predicting lesion size at common endocardial locations during radio-frequency ablation

We used the finite element method to study the effect of radio-frequency (RF) catheter ablation on tissue heating and lesion formation at different intracardiac sites exposed to different regional blood velocities. We examined the effect of application of RF current in temperature- and power-controlled mode above and beneath the mitral valve annulus where the regional blood velocities are high and low respectively. We found that for temperature-controlled ablation, more power was delivered to maintain the preset tip temperature at sites of high local blood velocity than at sites of low local blood velocity. This induced more tissue heating and larger lesion volumes than ablations at low velocity regions. In contrast, for power-controlled ablation, tissue heating was less at sites of high compared with low local blood velocity for the same RF power setting. This resulted in smaller lesion volumes at sites of low local velocity. Our numerical analyzes showed that during temperature-controlled ablation at 60 degrees C, the lesion volumes at sites above and underneath the mitral valve were comparable when the duration of RF current application was 10 s. When the duration of RF application was extended to 60 s and 120 s, lesion volumes were 33.3% and 49.4% larger above the mitral valve than underneath the mitral valve. Also, with temperature-controlled ablation, tip temperature settings of 70 degrees C or greater were associated with a risk of tissue overheating during long ablations at high local blood velocity sites. In power-controlled ablation (20 W), the lesion volume formed underneath the mitral valve was 165.7% larger than the lesion volume above the mitral valve after 10 s of ablation. We summarized the guidelines for energy application at low and high flow regions.     

Electromagnetic annealing for the 100 nm technology node

Electromagnetic induction heating (EMIH) is a novel rapid thermal processing technique that uses microwave and radio frequency (RF) radiation to directly heat silicon wafers. Heating rates of 125°C/s have been achieved and 75 mm diameter wafers have been heated above 1000°C using only 950 W of power. EMIH has been used to activate shallow implanted dopants with minimal diffusion of the junction depth. It is speculated that the exposure of the wafer to intense electric fields during the anneal may provide an additional driving force for dopant activation, allowing for higher activation at lower temperatures. Post-anneal junction depths less than 25 nm with sheet resistances between 700 and 1000 ohms/square have been achieved without the use of a controlled low oxygen ambient. The EMIH Rs-Xj curve penetrates the SEMATECH 100 nm technology box and with further optimizations may satisfy the 70 nm technology node     

射频毁损术中近红外实时监测技术基础研究

利用近红外光谱(Near infrared spectrum,NIRS)测量技术进行射频损毁术中实时监测技术研究,探讨立体定向术中损毁疗效评估的可行性.在进行丘脑腹外侧核(Ventrolateral Thalamus,Vim)毁损术射频损毁的同时,使用近红外光谱实时采集系统检测在损毁过程中吸收系数(μa)与优化散射系数(μ's)的变化情况.结果表明: 44℃射频损毁过程中吸收系数和优化散射系数增大,停止掀毁后逐步恢复,稳定后μa和μ's稍高于初始值; 70℃射频损毁时μz和μ's增大,停止损毁且稳定后保持不变.根据μa和μ's的变化规律进行立体定向毁损过程实时监测是非常有可能的.     

Power amplifiers and transmitters for RF and microwave

The generation of RF/microwave power is required not only in wireless communications, but also in applications such as jamming, imaging, RF heating, and miniature dc/dc converters. Each application has its own unique requirements for frequency, bandwidth, load, power, efficiency, linearity, and cost. RF power is generated by a wide variety of techniques, implementations, and active devices. Power amplifiers are incorporated into transmitters in a similarly wide variety of architectures, including linear, Kalm, envelope tracking, outphasing, and Doherty. Linearity can be improved through techniques such as feedback, feedforward, and predistortion     

RF and microwave energy hots up

Radiofrequency and microwave heating spanning the frequency range 10-3000 MHz has, long since its birth just after the Second World War, embraced areas such as industry, catering, domestic and medicine. The author shows that the advantages of RF and microwaves (such as volumetric heating, rapid and selective heating, compactness of equipment and ease of operation) offer sound economic alternative heating techniques     

The RF Thermoseed?A Thermally Self-Regulating Implant for the Production of Brain Lesions

Telethermocoagulation is a neurosurgical technique that is now entering the phase of practical clinical application. In this system brain lesions are produced by heating implanted metallics by an external RF electromagnetic field.     

An Unbalanced Electric Applicator for RF Hyperthermia

An applicator of the electric type for the RF heating of living tissues is described. It consists essentially of an unbalanced capacitor where the RF current return is provided by a large groundplane electrode. A water layer is an integral part of the electric design, offering a relative independence from variations in the position of the electrodes with respect to the body being treated. The water also eleminates the detrimental effects of the high field concentrations at the edges of the "hot" electrode, and is additionally used for surface cooling.     

射频信号光纤延时的幅相特性研究

光纤传输具有大带宽、低损耗的特点,射频信号的光延时系统在雷达等电子信息系统中得到了广泛 应用。采用射频光纤延时技术来延时射频信号时,射频信号的幅度和相位会发生改变。频率越高、延时时间越长, 幅相变化就越大,其中相位变化尤为突出。文中阐述了这些变化产生的原因和导致的效果。幅度的变化,主要是光 纤传输损耗和色散导致的射频信号功率衰落而引起的;相位的变化,主要是激光器和光纤所处的环境温度变化以及 光纤自身损耗发热而引起的。在外部温度环境变化时,射频信号的相位会发生很大的飘移;即使在恒温条件下,相 位漂移依然较大,这会造成雷达相参等下降,降低雷达对微弱信号的检测能力,应该引起足够重视。     

An Optically Coupled System for Quantitative Monitoring of MRI-Induced RF Currents Into Long Conductors

The currents induced in long conductors such as guidewires by the radio-frequency (RF) field in magnetic resonance imaging (MRI) are responsible for potentially dangerous heating of surrounding media, such as tissue. This paper presents an optically coupled system with the potential to quantitatively measure the RF currents induced on these conductors. The system uses a self shielded toroid transducer and active circuitry to modulate a high speed light-emitting-diode transmitter. Plastic fiber guides the light to a photodiode receiver and transimpedance amplifier. System validation included a series of experiments with bare wires that compared wire tip heating by fluoroptic thermometers with the RF current sensor response. Validations were performed on a custom whole body 64 MHz birdcage test platform and on a 1.5 T MRI scanner. With this system, a variety of phenomena were demonstrated including cable trap current attenuation, lossy dielectric Q-spoiling and even transverse electromagnetic wave node patterns. This system should find applications in studies of MRI RF safety for interventional devices such as pacemaker leads, and guidewires. In particular, variations of this device could potentially act as a realtime safety monitor during MRI guided interventions.