Gyrotron Backward Wave Oscillator Experiments with a Relativistic Electron Beam Using an X-Band Rectangular Waveguide

A mildly relativistic electron beam (500keV, 200A, 10ns) injected into an X-band rectangular waveguide immersed in a uniform axial magnetic field (4-10kG) produced magnetically tunable microwave radiation in the 9-13 GHz frequency range with an estimated output power of 1MW. The frequency range and tunability of the radiated microwave agreed with a theoretical model for a gyrotron backward wave oscillator taking into account the low energy component of the beam electron.     

Airborne active and passive microwave observations of Super TyphoonFlo

Airborne microwave measurements of precipitation associated with Super Typhoon Flo in the western North Pacific were conducted during September 16-18, 1990. The sensor package aboard the NASA DC-8 aircraft included a dual-frequency precipitation radar at 10 GHz and 34 GHz and a host of radiometers operating at 10 GHz, 18 GHz, 19 GHz, 34 GHz, and 92 GHz, as well as three frequencies near the strong water vapor absorption line of 183.3 GHz. The measurements were made during a few passes over the storm center, and active and passive microwave signatures of the rainbands were detected with a fine spatial resolution. The relationship between the measured brightness temperature and radar-estimated rain rate is examined at the frequencies between 10-92 GHz. At both 34 and 92 GHz this relationship is analyzed with the 10 GHz radar reflectivity factor measured at altitudes above the freezing layer as a further constraint. The results show that frozen hydrometeors strongly scatter radiation at these frequencies, especially at 92 GHz. It was shown from a close examination of both active and passive microwave signatures that a significant scattering of radiation at frequencies 118 GHz occurred in the inner eyewall at altitudes of 3-8 km. This scattering of microwave radiation by hydrometeors in both liquid and frozen forms is discussed under the authors' current understanding of the scattering mechanism     

Hearing microwaves: the microwave auditory phenomenon

The microwave auditory phenomenon, or the microwave hearing effect, pertains to the hearing of short pulses of modulated microwave radiation at high peak power by humans and laboratory animals. Anecdotal and journalistic reports of the hearing of microwave pulses persisted throughout the 1940s; and 1950s. The first scientific report of the phenomenon appeared in 1961. The effect has been observed for RF exposures across a wide range of frequencies (450-3000 MHz). It can arise, for example, at an incident energy-density threshold of 400 mJ/m2 for a single 10-microsecond-wide pulse of 2450 MHz microwave energy, incident on the head of a human subject. And it has been shown to occur at an SAR threshold of 1.6 kW/kg for a single 10-microsecond-wide pulse of 2450 MHz microwave energy, impinging on the head. A single microwave pulse can be perceived as an acoustic click or knocking sound, and a train of microwave pulses to the head can be sensed as an audible tune, with a pitch corresponding to the pulse-repetition rate (a buzz or chirp). Note that the SAR threshold of 1.6 kW/kg is about 1000 times higher than that allowable by FCC rules for cellular mobile telephones     

Josephson junction millimeter microwave source and homodyne detector

A millimeter and submillimeter microwave source is described in which a point-contact Josephson junction is used as both the emitter and as a homodyne detector of the microwave radiation. The microwave radiation is conveyed from the Josephson junction to the room-temperature environment outside the Dewar of liquid helium by an oversize waveguide. A room-temperature Fabry-Perot resonator refocuses the radiation on the oversize waveguide which returns the radiation to the emitting junction which also serves as a coherent detector with sensitivity 10^-15W/√Hz. The detector is sufficiently sensitive that the emitted power of 10^-12W can be detected with high signal-to-noise ratio. Power required by the junction is of the order 10^-6W from the bias supply. For the experiments reported, the wavelength of the emission could be varied over discrete wavelengths between 1.1 and 2.6 mm by varying the voltage bias across the junction. These wavelengths corresponded to the resonant frequencies of a cavity tightly coupled to the Josephson junction, and the frequencies can be changed by modifying the geometry of the cavity.     

Microwave enhanced recovery of nickel-copper ore: communition and floatability aspects.

A study describing the effect of microwave radiation, at a frequency of 2450 MHz, on the processes of communication and flotation of a complex sulphide nickel-copper ore is presented. Ore communication has been investigated under standard radiation-free conditions and after ore treatment in a radiated environment as a function of ore size, exposure time to radiation, and microwave power. The findings show that communication is tremendously improved by microwave radiation with values of the relative work index as low as 23% at a microwave power of 1.406 kW and after 10 s of exposure time. Communication is affected by exposure time and microwave power in a nontrivial manner. In terms of ore floatability, the experimental tests have been carried out on a sample of 75 microm in size under different exposure times. The results show that both ore concentrate recoveries and grades of nickel and copper are significantly enhanced after microwave treatment of the ore with relative increases in recovered concentrate, grade of nickel, and grade of copper of 26 wt%, 15 wt%, and 27%, respectively, at a microwave power of 1330 kW and after 30 s of exposure time.     

Total dose and transient radiation effects on GaAs MMICs

To elucidate the effects of radiation on GaAs monolithic microwave integrated circuits (MMICs), radiation-induced changes in DC parameters of test FETs and in the measured microwave performance of MMICs were compared. Changes in material parameters determined from the DC results were used to model the observed microwave performance degradation. In addition, the effect of accumulated radiation damage in MMICs was studied in terms of the amplifier response to transient radiation pulses. The effect of 1-MeV electron irradiation on microwave response and transient radiation pulse response was measured in 0.5- to 12.5-GHz distributed amplifiers (ion-implanted) and in 28-GHz power amplifiers (with epitaxially grown active layers)     

微波遥感在岩土工程中应用的基础实验研究

由电磁辐射理论知道,物质的微波辐射是热能激发组成物质分子的转动态能级跃迁辐射出的电磁波。在等温过程加载的条件下,对岩石和混凝土进行了２ｃｍ、３ｃｍ、１０ｃｍ３个波段以及水平和垂直两种极化状态的实验,得出岩石和混凝土的微波辐射能量随压力变化面变化的实验结果,实验了不同岩性岩石和不同强度混凝土共计４０个试件,无一例外。变化规律是：在２ｃｍ和１０ｃｍ波段微波辐射能量随压力增加而增加,在３ｃｍ波段微波辐射     

Visualizing the Intensity Distribution of a Microwave Field Using a Microstrip Rectenna with a Schottky Diode

Journal of Communications Technology and Electronics - A microwave radiation intensity indicator based on an antenna-coupled detector (rectenna), an amplifier, and a semiconductor light-emitting...     

Stabilization Scheme for Hot-Electron Bolometer Receivers Using Microwave Radiation

We present the results of a stabilization scheme for terahertz receivers based on NbN hot-electron bolometer (HEB) mixers that uses microwave radiation with a frequency much lower than the gap frequency of NbN to compensate for mixer current fluctuations. A feedback control loop, which actively controls the power level of the injected microwave radiation, has successfully been implemented to stabilize the operating point of the HEB mixer. This allows us to increase the receiver Allan time to 10 s and also improve the temperature resolution of the receiver by about 30% in the total power mode of operation.     

A Broadband WR10 Turnstile Junction Orthomode Transducer

We present a broadband waveguide ortho-mode transducer for the WR10 band that was designed for CLOVER, an astrophysics experiment aiming to characterize the polarization of the cosmic microwave background radiation. The design, based on a turnstile junction, was manufactured and then tested using a millimeter-wave vector network analyzer. The average measured return loss and isolation were -22 dB and -45 dB, respectively, across the entire WR10 band     

Microwave cataractogenesis

Experimental investigations of microwave cataractogenesis, as well as the application of theoretical methods, suggest the involvement of thermal damage. Time-intensity cataract thresholds for acute exposures of rabbits indicate dose reciprocity. The induction of lens opacification following repeated exposure at intensities below the threshold for single-dose exposures suggests a cumulative component of lens damage and the existence of repair mechanisms. Repair mechanisms are also indicated, in experimental biochemical studies of microwave effects on rabbit lens epithelial cells with a 10-20-day cellular recovery period. Experimental studies have revealed a relationship between the site of ocular damage and radiation wavelength. Cataract induction has also been reported in humans accidentally overexposed to microwave radiation. Although dosimetric data is not adequate to specify exposure thresholds, acute lens opacification in humans appears to involve thermally induced lens damage that occurs at exposure intensities of 100 mW/cm²or greater. Epidemiological studies of workers have in some instances suggested that occupational microwave exposure may result in lens alterations but there is no evidence that such effects are associated with visual impairment or cataract formation.     

Heterodyne detection of tunable FIR sidebands

Continuously tunable far infrared (FIR) laser sidebands have been generated in a Schottky diode by nonlinear mixing the radiation from an optically pumped FIR laser operating between 0.6 and 3 THz with that from a microwave source in the 2-4 GHz range. A very sensitive heterodyne detection is adapted to detect the sidebands generated not only at the sum or difference frequency of the two radiations, but also, for the first time in the FIR region, those related to the mixing of the FIR radiation with the second and third harmonics of the microwaves. The high selectivity of the superheterodyne detection allows easy separation of the various sidebands. The global tunability of this system is 2 × 10 GHz for the more powerful FIR emission lines. To demonstrate the tunability of the device absorption signals of several molecules are presented in the whole range of operation of the system (0.6-3 THz) using either direct or lock-in detection techniques.     

Microwave-transmission, heat and temperature properties of electrically conductive adhesive

Microwave heating significantly speeds up the curing process of polymer and polymer-based composites. The present theoretical work studies the microwave transmission through the electrically conductive adhesive (ECA), heat generation and transfer inside the ECA and subsequently the microwave heating rate of the ECA. By studying the temporal transmission property of the microwaves in the ECA, we have calculated quantitatively the electromagnetic field distribution around a metal filler. It has been shown that the penetration depth of the skin effect in the metal filler is significantly smaller than the one of a bulk metal material. The heat generation (microwave power absorption) is negligible in the metal filler due to its large electric conductivity. Furthermore, due to the high thermal conductivity, the thermal equilibrium between the metal filler and the surrounding adhesive is reached within a nano second (10/sup -9/ s). The temperature of the whole ECA system becomes uniform within a time interval of 10/sup -3/ s. When the temperature of the system is relatively low, the heating rate of the system is linearly proportional to the external microwave input power and the heating time. It gradually saturates when the temperature of the ECA is so high that the heat radiation from the ECA becomes significant. Numerical results of our theoretical model agree well with experimental data, thus providing a solid platform for designing the microwave curing process of the ECA.     

Coplanar-waveguide/microstrip probe coupler and applications to antennas

A method to couple microwave power from a coplanar waveguide to a microstrip line on opposite sides of a ground plane is demonstrated. The measured insertion loss and return loss are about 1 dB and 10 dB, respectively, across the frequency range of 0.045-6.5 GHz. To demonstrate potential applications of the coupler as a feeding network for a microstrip patch array measured radiation patterns for two rectangular patch antennas with a direct coplanar-waveguide/microstrip feed and with a proximity coupled coplanar-waveguide/microstrip feed are presented.<>     

Radiation effects in transit-time microwave diodes

There has been considerable progress in the direct generation of microwave power using two-terminal semiconductor devices during the last decade. Permanent and transient radiation effects on bulk (Gunn and LSA) and junction (IMPATT, TRAPATT, and BARITT) transit-time microwave diodes are reviewed. Emphasis is placed upon relating the primary effects of radiation to the physics of device operation. The principal permanent damage is attributed to carrier removal effects, impairing the RF performance of bulk diodes below 10¹⁴neutrons/cm²and junction transit-time diodes at fluences near 10¹⁵neutrons/cm². The principal transient effect is the generation of free carriers by ionizing radiation, affecting the RF performance of bulk diodes above 10⁹rad/s and junction transit-time diodes at dose rates near 10⁸rad/s.     

A 90-100 GHz double-folded slot antenna

A double-folded slot antenna (DFS) has been designed, fabricated, and tested at 90-100 GHz. The antenna shows a very wideband impedance around 20 Ω from 85 to 110 GHz. The low impedance is compatible with superconductor-insulator-superconductor (SIS) junctions, Schottky diodes or high electron mobility transistor (HEMT) amplifiers, which require a low impedance at millimeter wave frequencies. The antenna is placed on a dielectric lens to synthesize a semi-infinite substrate and realize high-directivity patterns. The measured radiation patterns agree very well with theoretical calculations and demonstrate symmetric main beams and sidelobe levels below -15 db over a 10% bandwidth. The double folded slot antenna is an attractive candidate for low-cost wideband millimeter-wave monolithic microwave integrated circuits (MMIC) front ends     

具有谐波抑制功能的宽带圆极化宽缝天线

针对微波无线输能系统中接收天线质量轻、体积小、剖面低、易与微波电路集成的特点,设计了一款新型的具有谐波抑制功能的宽带圆极化宽缝接收天线。通过在长方形缝隙中添加末端具有圆形贴片的交叉结构实现圆极化性能,添加切角结构展宽圆极化带宽。在馈线上添加具有一定长度的开路支节,配合使用缺陷地结构共同实现谐波抑制功能。研究并测试了天线的反射系数、轴比、增益以及远场辐射方向图,仿真与实测基本吻合。仿真结果显示,该天线很好地抑制了基频5.8 GHz的二次谐波和三次谐波,在4.5~6.2 GHz的范围内S11<-10 dB,相对阻抗带宽31.8%;基频5.8 GHz处的轴比AR=1.3 dB,在频率范围4.2~6.15 GHz内轴比AR<3 dB,相对轴比带宽37.7%;基频5.8 GHz仿真增益6.7 dB。     

Near-field antennas integrated with scanning probes for THz tovisible microscopy: scale modeling and limitations on performance

A promising approach to localized spectroscopy at far-infrared (λ > 5 μm) and terahertz frequencies (100-3000 GHz) is with scanning probe microscopes by transducing far-field radiation to the near field with a field confinement structure - a near-field antenna. We discuss the background of this idea and show encouraging results from a scale-model experiment using 3-GHz microwave radiation. We also present experiments to scale antennas to visible wavelengths and we discuss limits to scale modeling     

微波辐射Fenton试剂氧化催化降解水中三氯乙烯

对微波辐射与Fenton试剂氧化催化法相结合降解水中三氯乙烯进行了研究。采用单因子法考察了反应时间、Fenton试剂用量和配比、反应物初始浓度、PH值，微波功率和压强等条件对脱氯率的影响。结果表明，三氯乙烯脱氯率随微波功率，压强、反应时间的增加而增加，随以应物初始浓度的增加而降低。Fenton试剂用量，比例和反应物初始Ph有一个最佳值。采用正交试验法对影响脱氯降解作用明显的催化剂量、Fenton试剂配比，反应时间，微波功率进行了优化分析，结果表明，在Fenton试剂摩尔比为60，Fenton试剂用量10%，反应时间12min、微波功率750W的最佳条件下，三氯乙烯脱氯率可以达到87.08%。