Biological aspects of mobile communication fields

Our knowledge on the biological effects of RF radiation has been increasing for many decades. It has become a focus of attention because of the accelerated use of RF radiation for wireless communication over the past few years. It is fairly well established that at sufficiently high power levels, RF and microwave energy can produce deleterious biological effects. Wireless communication systems use low power modulated forms of RF and microwave radiation that was not investigated extensively in the past. Thresholds and SARs for biological effects both vary widely. Many specific questions must be answered before any consistent, dependable and scientific conclusions can be drawn for the biological effects and safety of wireless mobile communication systems. Nevertheless, available data do not suggest any immediate cause for concern of a impending threat to public health from acute or short term exposure to low level RF and microwave radiation. Investigations to answer some of the questions have already begun. Many of them are designed to study the effects of long term exposure. When considering repeated, low level irradiation, the possibility of cumulative effects have been raised. While there is presently no confirmed evidence for cumulative effect, there is little information to the contrary. Large scale epidemiological investigations should also be undertaken among the twoway mobile communication and cellular telephone users who may be exposed to varying levels of RF radiation over time. Better understanding is needed of the mechanisms of interaction between RF/microwave radiation and biological systems, and of the significance of any observed effects. Enormous progress has been made in the difficult area of dosimetry. However, measurement of energy distribution in and around a subject for exposure assessment remains a challenge, more so for large numbers of people. This type of quantitative information is also required for extrapolation from animal experimentation to human response.     

石墨烯/铜镍铁氧体复合材料的制备及性能研究

为制备出宽波段磁波衰减材料,采用水热法制备得到了石墨烯/铜镍铁氧体复合材料（CNFRGO）,并对其进行SEM、XRD、红外光谱和拉曼光谱表征分析;然后测量其2~18 GHz的电磁参数,并计算其损耗角正切值和反射损耗,进而分析其微波衰减性能;最后,测量其中远红外波段的复折射率,利用测量数据和T矩阵法计算分析其红外波段消光和吸收性能。结果表明,尖晶石型铜镍铁氧体纳米颗粒吸附在还原石墨烯上,粒径大部分约为20 nm;CNFRGO同时具有介电损耗和磁损耗两种机制,其反射损耗低于-10 dB的频宽为3.7 GHz,在11.8 GHz处有峰值-14.7 dB;CNFRGO在近红外波段消光较强主要由散射引起,中远红外波段则主要由吸收决定,而其吸收能力在近红外和中红外波段较强,但在远红外大气窗口内相对较弱。因此,CNFRGO可同时吸收微波和红外辐射,是一种良好的微波与红外兼容材料。     

A finite difference thermal model of a cylindrical microwave heating applicator using locally conformal overlapping grids: part II--numerical results and experimental evaluation.

In this paper, we present numerical results obtained from a robust, locally conformal 3-D Orthogonal Grid Finite Difference (OGFD) thermal algorithm introduced in Part I of our current investigation [Al-Rizzo et al., 2006] integrated with an Orthogonal Grid Finite-Difference Time Domain (OGFDTD) scheme [Al-Rizzo et al., 2000], which accurately models the volumetric electromagnetic (EM) power deposition pattern. A unified meshing scheme, which utilizes identical overlapping grids in Cartesian and cylindrical coordinates, is employed within the load zone in the OGFDTD and OGFD models. Local temperature profiles excited by the absorbed microwave energy were measured at seven locations within the sample as a function of heating time. In order to benchmark, or validate our model, an alternative analysis of the coupled EM and thermal simulations was performed using state-of-the-art, Finite Element Method-based Ansoft's High Frequency Structure Simulator (HFSS) and the coupled thermal/stress analysis tool ePHYSICS (http://www.ansoft.com). Additionally, we compare our numerical simulations against measured dynamic temperature profiles induced within a mineral ore sample maintained for exposure period of 28.5 minutes inside a cylindrical multimode heating furnace energized at 915 MHz with a microwave source power of 12.5 kW and accompanied with significant temperature elevation. A combination of convective and radiation thermal boundary conditions are considered at the interfaces between the cavity walls, air, and sample. There is a general agreement between simulated and measured spatial and temporal temperature profiles, which validates the proposed model. Results indicate that inevitable fluctuations in the frequency spectrum and output power of the magnetron, non-uniformity of sample packing, and heat released by uncontrolled exothermic chemical reactions have a significant effect on the comparisons between measured and computed temperature patterns.     

A new microwave device for rapid thermal fixation of the murine brain.

A microwave applicator was developed to provide rapid thermal fixation of enzymes in the murine brain. Although the power output of the device is only 1.3 kW, whole-brain levels of acetyicholine after microwave fixation are comparable to those observed at a power output of 5 kW, and are markedly higher than those obtained by a conventional method (freezing) of fixation.     

微波辐照石油焦制备双电层电容器用活性炭

以石油焦为原料,KOH为活化剂,采用微波辐照加热法,制备了石油焦基双电层电容器用活性炭。研究了石油焦与KOH活化剂的比例、微波功率以及微波辐照时间对活性炭孔径分布和比电容量的影响。结果表明:在KOH活化剂与石油焦的质量比为3.5∶1,微波功率800W和辐照时间7min时,制备的活性炭比表面积为2031.96m2/g,比电容量达286.79F/g,以该活性炭作电极的双电层电容器有良好的循环稳定性和充放电性能。     

基于磁控管的S波段大功率窄带随机信号源研究

磁控管具有功率大,效率高,体积小,成本低等特点,且输出频谱也与其阳极电压和阴极电流密切相关,据此特性研制了基于磁控管的S波段大功率窄带随机信号源。通过实验探究不同阴极电流和阳极电压下磁控管的输出频谱,并利用微控芯片控制磁控管的阴极电流和阳极电压产生随机变化,实现了大功率窄带随机信号的产生。结果表明,窄带随机信号的中心频率为2.46 GHz,平均输出功率达到1.4 kW,直流到微波的转换效率超过70%。本文研制的大功率窄带随机信号源在通信干扰与抗干扰等领域有潜在的应用价值。     

Low-temperature process in growing carbon nanotube

Nickel particles, converted from film by microwave hydrogen plasma at a low temperature of 250 °C, were used as the catalyst for growing carbon nanotubes (CNTs). Low-temperature process is desirable for CNT application in flat panel display industry. We found that the processing pressure and microwave power can greatly influence the nickel particle size and density. The processing pressure during pretreatment affects the CNT to be grown or not at all. The microwave power affects the particle size of the catalyst and the diameter of the grown CNT. It was also found that after pretreatment, the diameter of the grown CNT is proportional to the catalyst particle size. The threshold electric field of CNT field emission was found reduced as the diameter of the CNT became smaller.     

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     

微波辐射淀粉接枝丙烯酸合成高吸水树脂

以N,N'-亚甲基双丙烯酰胺为交联剂,通过微波辐射制备了淀粉接枝丙烯酸高吸水树脂.研究了淀粉和引发剂类型、引发剂及交联剂用量、丙烯酸中和度、淀粉和单体的配比、微波辐射功率及辐射时间对吸水率的影响.结果表明,经过糊化后所制备的树脂吸水率明显提高,糊化过程减小了淀粉种类对吸水率的影响.过硫酸盐类引发剂是一类高效廉价的引发剂.当引发剂(过硫酸钾)和交联剂的用量分别为丙烯酸的0.3wt%和0.02wt%,中和度为60%,玉米淀粉和丙烯酸质量比为0.25时,经231W微波辐射4min,可获得吸水率为1110g·g~(-1)的高吸水树脂.利用微波技术制备吸水树脂可实现合成、干燥一步完成,且无须氮气保护,明显缩短反应时间、简化工艺、降低成本.     

Enhancement of the Bondability and Die-Shear Force of Chip–Flex Substrate Assemblies by Depositing a Nickel Layer on the Flex Substrate

A nickel layer and a silver bonding layer have been deposited on copper electrodes over flex substrates to improve the bondability and die-shear force performance of chip?Cflex substrate assemblies when using the thermosonic flip-chip bonding process. For bonding temperature of 200°C, the maximum die-shear force was achieved by combining parameter values of 20.66?W ultrasonic power, 625?gf bonding force, and 0.5?s bonding time. The improved bondability and die-shear force could be attributed to better transfer of ultrasonic power across the bonding interface during thermosonic flip-chip bonding, owing to the high rigidity of the copper electrodes provided by the nickel layer. Experimental results also indicated that high bonding load is necessary at elevated ultrasonic power range to provide firm contact between the bumps and electrodes to enable smooth ultrasonic power transfer across the bonding interface. Moreover, prolonged bonding time caused cracks between the bumps and flex substrate. Close examination of the fracture morphologies after die-shear testing and after ultrasonic separation provided insight into the die-shear force performance as influenced by the process parameters and by the deposition of the nickel layer on the copper electrodes over the flex substrate.     

一种抗微波干扰防腐蚀的温度传感器

目前在微波化学装置中所使用的温度传感器的抗干扰能力多是在低功率下才会有效的。但是如果微波功率达到10kW以上的时候,大部分的温度传感器就不能够胜任了。本文研究了一种基于Pt100铂电阻的温度传感器,它在10kW以上的微波场里的屏蔽衰减达到了100dB以上;能够直接与微波化学实验中的腐蚀性物料接触,而不会被腐蚀;并且它的成本远远低于现阶段同功能的温度传感器。填补了这一领域的空白。     

射频薄基板加阶梯槽衬底工艺研究

随着国家3G网络的发展,通信电路板的要求也随着改变。微波损耗较小,介质特性均匀,厚度一致,散热效果好,干燥效果好等要求也越来越高。未来使用射频/微波高频材料+铜基的PCB需求将进一步加大。研究射频薄基板和铜基压合,并且在薄基板和铜基上都开有阶梯槽,使得产品不仅能满足通信板的要求,而且对滤波和频率的调节也起到很好的作用。     

Rapid microwave fixation of rat brain.

A new microwave device which inactivates brain enzymes rapidly and uniformly is described. From the results obtained with microwave irradiation at two power levels (0.8 kW and 4.5 kW), it has been demonstrated that the high power microwave irradiation has several advantages over the low power irradiation. In its application to neurochemical studies, significant increase in the DOPAC level was found in the irradiated brain, while there were no statistical differences in the levels of NE, DA, 5-HT and 5-HIAA between microwave irradiation and decapitation. Significant increase in the Ach level and marked reduction of the choline level were observed after microwave irradiation. There were no significant differences in the level of cyclic GMP in the brain between the two methods of sacrifice, while significant reduction of the cyclic AMP level was observed in the irradiated brain.     

Fast fixation of brain in situ by high intensity microwave irradiation: application to neurochemical studies.

The levels of acetylcholine and choline were measured in various brain regions of the rat after fixation by microwave irradiation of the head and after decapitation and subsequent freezing in liquid nitrogen. Levels of acetylcholine were increased by approximately 50% after microwave irradiation, while choline levels were reduced. These biochemical findings were correlated with virtually complex loss of acetylcholinesterase and NADH-diaphorase activity after 1 s exposure to microwave irradiation at a level of 5 kW.     

连续氩氪离子激光晶化非晶硅薄膜的研究

为了研究连续激光晶化非晶硅薄膜中激光功率密度对晶化效果的影响,利用磁控溅射法制备非晶硅薄膜,采用连续氩氪混合离子激光器对薄膜进行退火晶化,用显微喇曼光谱测试技术和场发射扫描电子显微镜研究了薄膜在5ms固定时间下不同激光功率密度对晶化效果的影响,并对比了普通玻璃片和石英玻璃两种衬底上薄膜晶化过程的差异。结果表明,在一定激光功率密度范围内(0kW/cm2~27.1kW/cm2),当激光功率密度大于15.1kW/cm2时,普通玻璃衬底沉积的非晶硅薄膜开始实现晶化;随着激光功率密度的增大,晶化效果先逐渐变好,之后变差;激光功率密度增大到24.9kW/cm2时,薄膜表面呈现大面积散落的苹果状多晶硅颗粒,晶粒截面尺寸高达478nm ;激光功率密度存在一个中间值,使得晶化效果达到最佳;石英衬底上沉积的非晶硅薄膜则呈现与前者不同的结晶生长过程,当激光功率密度为19.7kW/cm2时,薄膜表面呈现大晶粒尺寸的球形多晶硅颗粒,并且晶粒尺寸随着激光功率密度的增大而增大,在 27.1kW/cm2处晶粒尺寸达到最大5.38m。研究结果对用连续激光晶化法制备多晶硅薄膜的研究具有积极意义。     

Microwave p-i-n diodes and switches based on 4H-SiC

The 4H-SiC p-i-n diodes were designed, fabricated, and characterized for use in microwave applications. The diodes with mesa structure diameters between 80 and 150 /spl mu/m, exhibited a blocking voltage of 1100 V, a 100-mA differential resistance of 1-2 /spl Omega/, a capacitance below 0.5 pF at a punchthrough voltage of 100 V and a carrier effective lifetime between 15-27 ns. X-band microwave switches based on 4H-SiC p-i-n diodes are demonstrated for the first time. The switches exhibited insertion loss as low as 0.7 dB, isolation up to 25 dB and were able to handle microwave power up to 2.2 kW in isolation mode and up to 0.4 kW in insertion mode.     

微波烧结法制备ITO陶瓷

采用微波烧结,在常压、纯氧气氛条件下制备了ITO陶瓷.通过XRD、SEM和金相分析等方法研究了烧结温度和保温时间对ITO陶瓷相对密度的影响.结果表明,微波烧结具有升温速度快、保温时间短的优点,大幅缩短了ITO陶瓷的烧结周期.1550℃微波烧结并保温20 min的ITO陶瓷相对密度达到了99.5%,晶粒大小均匀,结构紧密...     

Effects of Electromagnetic Fields on Isolated Nerve and Muscle Preparations

An S-band waveguide exposure system was designed to study the electromagnetic fields on the isolated tissues. The temperature of the exposed tissue was maintained at a constant temperature by circulating temperature controlled Ringer's solution through the waveguide. Isolated frog sciatic nerves, cat saphenous nerves, rabbit vagus nerves and superior cervical ganglia, as well as rat diaphragm muscles were placed in the waveguide either parallel or perpendicular to the electric field of the TE/sub 10/ mode. Compound action potentials of nerves or contractile tensions of muscles were recorded before, during and after the 2450-MHz microwave irradiation. Results showed no significant change in characteristics of nerves or muscles exposed to CW specific absorption rate (SAR) of 0.3-1500 W/kg and pulsed peak SAR of 0.3-220 kW/kg. The effects observed during high-power radiation were reproducible by changing the solution temperature. No direct field stimulation of nerves or muscles was observed during microwave irradiation.     

Improved reliability of AlGaN-GaN HEMTs using an NH/sub 3/ plasma treatment prior to SiN passivation

A passivation method has been developed which reduces the degradation of AlGaN-GaN high electron mobility transistor (HEMT) electrical properties caused by extended dc bias or microwave power operation. The key aspect of this passivation technique is exposure to a low-power NH/sub 3/ plasma prior to SiN deposition. Devices fabricated with the NH/sub 3/ treatment prior to SiN passivation show minimal gate lag and current collapse after extended dc bias operation. In addition, the rate of degradation of the microwave power output while under continuous microwave operation is improved by at least 100 times as compared to SiN passivated HEMTs that were not treated with the NH/sub 3/ plasma.     

Computer Simulation of a 5.7GHz, 110kW Transit-Time Oscillator

A high-power transit-time oscillator producing 110kW at 5.7GHz in the TM₀₁₀ cavity mode is described. The device comprises a temperature-limited diode electron gun operating at 40A in the range from 28kV to 35kV and an intermediate coaxial cavity from which the microwave power is extracted through a TEM coaxial guide. The diode serves also as a resonant cavity, where electromagnetic oscillations are grown from noise. The effect of the applied voltage on both the output microwave power and the instability saturation time has been investigated leading to an optimal diode voltage of 33kV.