Stable microwave coaxial cavity plasma system at atmospheric pressure

We present a systematic study of the development of a novel atmospheric microwave plasma system for material processing in the pressure range up to 760 torr and the microwave input power up to 6 kW. Atmospheric microwave plasma was reliably produced and sustained by using a cylindrical resonator with the TM(011) cavity mode. The applicator and the microwave cavity, which is a cylindrical resonator, are carefully designed and optimized with the time dependent finite element Maxwell equation solver. The azimuthal apertures are placed at the maximum magnetic field positions between the cavity and the applicator to maximize the coupling efficiency into the microwave plasma at a resonant frequency of 2.45 GHz. The system consists of a magnetron power supply, a circulator, a directional coupler, a three-stub tuner, a dummy load, a coaxial cavity, and a central cavity. Design and construction of the resonant structures and diagnostics of atmospheric plasma using optical experiments are discussed in various ranges of pressure and microwave input power for different types of gases.     

Numerical Modelling and Optimisation of a Microwave Enhanced Rapid Prototyping

Microwave heating technology is a cost-effective alternative way for assisting the thermosetting process of thin epoxy resin layers of material. With the benefit of existing modelling for computing the electromagnetic field and power density distribution in a cavity, an investigation has been conducted about the application of an electromagnetic field and its effects on a thin epoxy resin layer. The results of the simulations have been used to optimise the design of a microwave heating system for curing a thin epoxy resin layer. The investigation leads to a feasibility study to combine the microwave heating process with the rapid product development technique, to build 3D models efficiently through the fast-curing of thin epoxy resin layers. Numerous configurations were investigated, by changing the design of microwave applicator. A numerical model was used to identify the strength and weakness of each design, leading to an optimised configuration that can be used for microwave heating, and fast curing of a thin epoxy resin layer. From the present study it can be concluded that a mathematical model can be used to optimise microwave heating devices, enabling the configuration to deliver a uniform electric field.     

Noninvasive beam-wave reflectometric instrumentation for measuring complex permittivity of dielectric materials at microwave frequencies

A noncontact and nondestructive method of measuring at microwave frequencies the complex permittivity of a selected region in a dielectric slab is described. For this purpose the test dielectric sample is irradiated with a focused (gaussian) microwave beam by means of a suitable applicator. From the characteristics of the reflected beam wave measured at a reflectometric bridge arrangement, the complex permittivity of the exposed region is determined. Some theoretical and experimental results analysing the test conditions are presented. Application of this method to biological in vivo (or in vitro) measurements of dielectric properties of bones and tissues, with selective partial-body microwave irradiation, is discussed.     

Noninvasive beam-wave spectrometric instrumentation for measuring dielectric constant at microwave frequencies

From the characteristics of the reflected Gaussian beam-wave for oblique incidence, measured with a spectrometer arrangement, the dielectric properties of a selectively exposed region of a dielectric slab are ascertained at microwave frequencies. For this purpose, a focused (Gaussian) microwave beam is launched from a suitable applicator to irradiate obliquely a selected protion of the test dielectric and the complex reflection coefficient is measured and analyzed. Further, the magnitude of the angular shift involved in the direction of the reflected beam is also used to calculate the dielectric constant. Application of this method to noninvasive measurements of dielectric properties of selective partial-bodies of commercial dielectrics and biological substances is discussed.     

Hyperthermia applicator based on a reentrant cavity for localized head and neck tumors

A new applicator based on a reentrant cavity is proposed for treating localized tumors such as those of the head and neck. In order to effectively heat the localized tumor without causing dissipation of heat into the surrounding normal tissues, the electric field must be localized over the target region. Although a small applicator may produce an appropriate localized electric field, the higher resonant frequency due to downsizing of the equipment results in very poor heating distribution; this occurs due to the changes in electric permittivity and conductivity consequent upon an increase in the resonant frequency. In this article, we introduce a method for reducing the resonant frequency by inserting a dielectric material into the applicator; the efficacy of this method has been determined by calculating the electromagnetic field and heating distribution with the help of the finite element method. By using the proposed applicator, a reduction in the resonant frequency and localized heating over spherical regions 100 mm in diameter can be achieved.     

激光诱导击穿光谱信号增强技术研究进展

激光诱导击穿光谱(laser-induced breakdown spectroscopy,LIBS)是一种具有诸多独特优势的物质成分分析技术,但该技术灵敏度低,限制了其在痕量元素定量分析方面的应用.提高LIBS的信号强度,改善其检测灵敏度,有利于拓宽该技术的应用领域.基于国内外学者对LIBS信号增强技术的研究,简述并...     

A technique for localized tumor hyperthermia in small animals

Hyperthermia, the intentional elevation of tissue temperature above 41 degrees C, is being intensely researched as a therapeutic modality for cancer, especially when used in combination with radiation therapy and/or chemotherapy. A serious impediment to laboratory progress in this area has been the lack of affordable equipment providing control and reproducibility when faced with highly variable factors including tumor size and shape, blood flow, heat conduction, and tissue dielectric discontinuity. Our solution has been the development of a laboratory microwave hyperthermia system, dedicated to the treatment of small, superficial tumors. This system uses a 2.45-GHz microwave generator and custom applicator to noninvasively heat a mass of tissue about 2 cm in diameter and 1.5 cm in depth. Tissue temperature at up to four locations is measured using miniature. Teflonencased thermocouples. The microwave generator and the thermometry are interfaced to a personal computer which provides fully automated hyperthermia treatment reproducible to +/- 0.2 degrees C.     

A microwave radiometer for deep noninvasive diagnostics of thermal fields inside a biological object

A microwave radiometer for a wavelength of 10.5 cm with a frequency band of received signals of 200 MHz is described. It allows one to perform remote noninvasive temperature measurements deep in a biological object. The use of a modified null–reception method as the basis of the instrument operation made it possible to reduce the influence of the reflectance at the location of the contact between an applicator antenna and a body on the measurement accuracy and increase the dynamic characteristics during mapping of a biological object. At a storage signal time of 1 s, the measurement accuracy was 0.047 K. The output–signal changes were within 0.1 K when the reflectance was varied from 0.1 to 0.5.     

Electric near-field enhancing properties of a finite-size metal conical nano-tip

Finite-difference time-domain (FDTD) technique simulations are performed to study the near-field resonance properties of a silver conical nano-tip with a rounded end. Varying the tip geometry, we have computed the electric field distribution, as well as the electric field enhancement factor in the immediate vicinity of the tip apex. The aim of this study is to find optimal geometric parameters of the conical tip, such as its angle and length, in order to maximize the electric field enhancement factor. The increase of the tip length is shown to result in a redshift of the tip resonance wavelength. In addition, some subsidiary (non-dipole) peaks appear for relatively long tips. The peak enhancement values for the small-angle tips increase with the tip length while those for the large-angle ones decrease with it. At the same time, the dependencies of the field enhancement on the cone angle exhibit non-monotonic behavior. In other words, an optimal angle exists allowing one to maximize the electric near field. Finally, the effect of the supporting dielectric medium on the electric field near the tip apex is discussed. In the approximation used, the effect is shown to leave the main conclusions unchanged.     

微波加热Mn-Zn铁氧体粉末压坯的微观机制及特点分析

采用频率为2.45 GHz的微波对Mn-Zn铁氧体粉末压坯进行加热,详细探讨微波加热过程微波场与电介质作用的微观机制以及软磁铁氧体在微波场中的电、磁损耗机理;探讨Mn-Zn氧体粉末压坯在微波场中加热的特点以及微波场E、磁导率μi、介电常数εr等对微波加热温度的影响。Mn-Zn铁氧体是磁性混合介质,在微波场中被加热的根本原因是Mn-Zn铁氧体粉末压坯在微波场作用下,微波电磁能以损耗的方式转化为热能对材料进行加热,这种损耗主要是介电损耗、磁损耗;影响损耗的主要电场因素包括微波电磁场的强度和频率,在特定频率(2.45 GHz)的微波场中,微波功率是Mn-Zn铁氧体加热烧结温度的主要影响因素,功率改变,加热烧结曲线随着变化;影响损耗的材料因素主要是磁导率μi、介电常数εr,两者随温度、频率变化。     

Electrically detected magnetic resonance in a W-band microwave cavity

We describe a low-temperature sample probe for the electrical detection of magnetic resonance in a resonant W-band (94 GHz) microwave cavity. The advantages of this approach are demonstrated by experiments on silicon field-effect transistors. A comparison with conventional low-frequency measurements at X-band (9.7 GHz) on the same devices reveals an up to 100-fold enhancement of the signal intensity. In addition, resonance lines that are unresolved at X-band are clearly separated in the W-band measurements. Electrically detected magnetic resonance at high magnetic fields and high microwave frequencies is therefore a very sensitive technique for studying electron spins with an enhanced spectral resolution and sensitivity.     

Industrial Microwave Sensors—A Review

This paper reviews the field of microwave sensors. The field is broad and the applications numerous. This review will therefore only be able to present the broad outlines. Firstly the historical perspective and the physical background are briefly described, and the general advantages and disadvantages are listed. An overview of the various working principles of microwave sensors is given with a few examples of the applications mentioned. Important fields of applications and interesting examples are treated separately, starting with the measurement of moisture, which is the single most important field of applications in microwave sensors. Applications in the petroleum industry are also mentioned, because they are relatively new, they play an exceptionally important economical role, and represent the field in which the author is currently working. Followed by some trends for the future.     

Modeling and calculation of field emission enhancement factor for carbon nanotubes array

To estimate the apex field enhancement factor associated with carbon nanotubes (CNTs) array on a planar cathode surface, the image model of floated sphere between parallel anode and cathode plates was proposed. Firstly, the field enhancement factor of individual CNT was given as the following expression, beta0=h/rho+3.5, where h is the height and rho is the radius of CNTs. Then the field enhancement factor of CNTs array was discussed and the above expression was modified to be beta=h/rho+3.5-W, in which W is the function of the intertube distance R and represents the coulomb field interaction between the CNTs. All results show that the intertube distance of CNTs array critically affects the field emission. When the intertube distance is less than the height of tube, the field enhancement factor will decrease rapidly with decreasing the intertube distance. According to the calculated results and considering the field emission current density, the filed emission is optimal theoretically when the intertube distance is comparable with the height of CNTs.     

ASHEMIT: A device for wideband electromagnetic pulse therapy

The device contains a pulse oscillator generating pulses with an amplitude of up to 12 kV, a pulse former reducing the pulse front duration down to 0.1–0.3 ns, and an output device made in the form of a radiator, applicator, or field-forming system. The device is designed for application in nonthermal electrophysiotherapy for treatment and prevention of a wide range of diseases. The active factors are nanosecond pulses of electromagnetic field, a current, and a voltage caused by spark discharges. The pulse repetition frequency ranges from zero (single pulse) to 300 Hz. The device successfully passed a preliminary medical approbation.     

New equipment for microwave electric field visualization

We present the operation and design of newly developed, fully automatic equipment for the visualization of microwave electric fields. This equipment enables the observation of microwave field patterns around different objects including metamaterial prototypes and to study the field patterns of various microwave antennas and other objects that have been developed and that interact with a surrounding microwave electromagnetic field. Moreover, the developed prototypes whose interaction with an incident electromagnetic wave is crucial for practical applications can be investigated using size scaling, and hence our equipment can be used for the testing of antennas and other devices that interact with electromagnetic radiation, not only at microwave frequencies, but also at radio frequencies. The performance of our innovative equipment was demonstrated through the investigation of the metamaterial cloak. The frequency behavior of the metamaterial cloak revealed frequency bands with maximum cloaking efficiencies.     

微波引导下的滚筒杀青机内电磁场分布研究

基 于 电 磁 场Ｍ ａｘ ｗｅｌｌ 方 程 理 论 及 微 波 的 热 效 应 理 论 ,利 用 有 限 元 软 件 对 谐 振 腔 内 的 电 磁 场 分布 模 态 进 行 了 仿 真 计 算 ,并 讨 论 了 微 波 馈 入 口 位 置 、数 量 、方 向 等 对 滚 筒 内 电 磁 场 均 匀 性 的 影 响 。 结 果 表明 ,电 磁 波 谐 振 模 式 严 重 影 响 电 磁 场 在 谐 振 腔 内 的 分 布 ,通 过 对 模 态 的 选 择 可 实 现 温 度 场 的 均 匀 分 布 ,最 终形 成 对 茶 叶 的 均 匀 杀 青 效 果 。     

A pulse-periodic gyroresonant plasma accelerator

A plasma electron accelerator based on the gyromagnetic autoresonance effect is described. Electrons of the initially cold internal-injection plasma (a classical ECR discharge) are accelerated in the magnetic field of a magnetic mirror trap under a one-stage effect of the resonant microwave field and an additional pulsed magnetic field. The synchronism in maintaining the resonance conditions is ensured by a smooth increase in the pulsed magnetic field in the course of a microwave pulse. At the moderate values of the input microwave power (up to 2.5 kW) and the steady-state and pulsed magnetic fields (each up to 1 kG), it is possible to obtain stable relativistic plasma bunches, in which the energy of the electron components is a few hundred keV. The measured X-ray bremsstrahlung spectra have features characteristic of the energy distribution of photons, and the high-energy tails are recorded in the region of 600–800 keV. The dependences of the bremsstrahlung characteristics on the experimental conditions—the value of the steady-state magnetic field and the amplitude of the pulsed magnetic field—are investigated. The experimental data are in good agreement in the quantitative sense with the results of the computer simulation and with the earlier studies.     

Quasi in situ scanning force microscope with an automatic operated reaction chamber

We describe the design and performance of a quasi in situ scanning force microscope with an automatic operated reaction chamber. The design provides a repetitive hermetically sealed sample environment for successive processing. The reaction chamber is based on a combination of a flexure-guided cover, a piezo-positioning system and a force applicator system. An axial force seals the cover against the reactor enabling flow-through applications at low pressure, ambient pressure, or elevated pressure. The position stability of the sample relative to the probe is characterized and a full automated operation of the instrument is explored by the alignment of an ABC terblock copolymer thin film undergoing solvent vapor annealing in the presence of a high electric field. Due to the high electric field strength and the sharp scanning force microscope tip it is impossible to perform in situ scanning in the presence of the electric field.     

Development of compact linear accelerator in KBSI

The compact linear accelerator using a 28 GHz ECRIS is under construction in KBSI, South Korea. The main capability of this facility is the production of fast neurons for the neutron radiography. The designing of a superconducting magnet, microwave transmission system, beam extraction, and plasma chamber of ECRIS were finished. The nominal axial design fields of the magnets are 3.6 T at injection and 2.2 T at extraction; the nominal radial design field strength at the plasma chamber wall is 2.1 T. We already installed 10 kW, 28 GHz gyrotron, and tested a microwave power from gyrotron using a dummy load. The current status will be discussed in this paper.     

Note: Vector network analyzer-ferromagnetic resonance spectrometer using high Q-factor cavity

A ferromagnetic resonance (FMR) spectrometer whose main components consist of an X-band resonator and a vector network analyzer (VNA) was developed. This spectrometer takes advantage of a high Q-factor (9600) cavity and state-of-the-art VNA. Accordingly, field modulation lock-in technique for signal to noise ratio (SNR) enhancement is no longer necessary, and FMR absorption can therefore be extracted directly. Its derivative for the ascertainment of full width at half maximum height of FMR peak can be found by taking the differentiation of original data. This system was characterized with different thicknesses of permalloy (Py) films and its multilayer, and found that the SNR of 5 nm Py on glass was better than 50, and did not have significant reduction even at low microwave excitation power (-20 dBm), and at low Q-factor (3000). The FMR other than X-band can also be examined in the same manner by using a suitable band cavity within the frequency range of VNA.