W-band investigation of material parameters, SAR distribution, and thermal response in human tissue

This investigation is divided into three parts. First, the W-band dielectric properties of different biological tissues are determined. Then, the electromagnetic field in the human eye and skin is simulated for plane-wave exposure. An analytical method is used to investigate the specific absorption rate (SAR) inside a layered model of the human skin between 3-100 GHz. Furthermore, the SAR inside a detailed model of the human eye is investigated numerically by the finite-difference time-domain method for a frequency of 77 GHz. Maximum local SAR values of 27.2 W/kg in skin tissue and 45.1 W/kg in eye tissue are found for 77 GHz and an incident power density of 1 mW/cm/sup 2/. In the third part of the investigation, the temperature changes of superficial tissue caused by millimeter-wave irradiation are measured by a thermal infrared imaging system. The exposure setup is based on a horn antenna with a Gunn oscillator operating at 15.8-dBm output power. The measurements showed a maximum temperature increase of 0.7/spl deg/C for a power density of 10 mW/cm/sup 2/ and less than 0.1/spl deg/C for 1 mW/cm/sup 2/, both in human skin (in vivo), as well as in porcine eye (in vitro). The comparison of the temperature measurements with a thermal bio-heat-transfer simulation of a layered skin model showed a good agreement.     

Potential Temperature Rise Induced by Electromagnetic Field in Brain Tissues

The differential temperature rise in a spherical region stimulating a potential hot spot in the central region of a human head has been determined, takdng into account heat conduction as well as heat convection due to blood flow. The results apply in general to ali cases where the dimensions of the model and the frequency of the incident electromagnetic wave is such that a hot spot is formed near the central region. For a heat deposition rate of 10 mW/g in a hot spot of 1 cm radius, a differential temperature rise over the ambient tissues and blood is approximately 0.5°C. This corresponds to the case of a differential absorption cross section of 1 cm-1 for a 5 cm radius sphere exposed to an incident power density of 10 mW/cm2. For larger models of man's head the differential temperature rise is smaller.     

Development of a 2.45-GHz Local Exposure System for In Vivo Study on Ocular Effects

We developed a new exposure system to irradiate microwaves locally on a rabbit eye using a small coaxial-to-waveguide adapter filled with low-loss dielectric material as an antenna. A numerical rabbit model was also developed using X-ray computer tomography images, and the specific absorption rates (SARs) in the rabbit, especially in the eye, were analyzed with the finite-difference time-domain method. The temperature elevation in the exposed eye was also evaluated by solving a bioheat equation. Our exposure system can generate incident power density of 15 mW/cm² at the surface of a rabbit eye with input power of 1 W. When the incident power density on the rabbit eye is 300 mW/cm² , average SAR over the exposed eye and the whole body were approximately 108 and 1.8 W/kg, respectively. The exposure system can realize localized exposure to the eye with the ratio of exposed-eye averaged SAR to the whole-body averaged SAR was 60. The developed exposure system can achieve high-intensity exposure such as the threshold of cataracts, i.e., the eye-averaged SAR over 100 W/kg or the lens temperature over 41 degC with the incident power density of 300mW/cm² without significant whole-body thermal stresses     

Broadening of the RF Power-Density Window for Calcium-ion Efflux from Brain Tissue

Blackman et al. [1], [2] have reported enhanced efflux of calcium ions from chicken forebrains, exposed in vitro in a 50 ?stripline to 147 MHz radiation, modulated sinusoidally at 16 Hz. When the spacing between the sample tubes was 3.8 cm on center, enhancement occurred at an incident power density of 0.83 mW/cm2, but not at 0.11, 0.5S, 1.11, or 1.38 mW/cm2. When the spacing between sample tubes was reduced to 1.9 cm, significant enhanced efflux was observed at incident power densities of 0.55, 0.83, 1.11, and 1.38 mW/cm2. This broadening of the effective power-density range is explained herein by calculations which show that the more closely spaced samples interact electrically in a way that both lowers and broadens the range of spatial variation-of absorbed power density (MW/cm3) within the sample for a given incident power density (mW/cm2). Electrical coupling among the samples allows several different values of incident power to yield exactly the same value of power absorbed at given points within the brain sample. Because the absorbed power density must be directly related to the power that interacts with the brain to enhance the efflux of calcium ions, the electromagnetic conditions for efflux enhancement in coupled and uncoupled brains are the same if the absorbed power density is the same. Ranges of absorbed power density are identified that could be effective in enhancing the efflux of calcium ions from the brain tissue.     

A system for studying effects of microwaves on cells in culture.

An improved design of the fluid-filled waveguide-exposure chamber is described for studying effects of microwave radiation on cells in vitro. The system with a micropipette sample holder may be used as a prototype to isolate the apparent nonthermal factor of microwave radiation on cells in culture from those effects resulting from cell temperature rise. This system also allows more precise calibration of incident and absorbed microwave energies. Compared with control, somatic cells of the Chinese hamster exhibited a lower rate of growth and difference in morphology after 2450 MHz microwave radiation for 20 min at a power density of 500 mW/cm2.     

The transmission of reflexes in the spinal cord of cats during direct irradiation with microwaves.

The spinal of cats was directly exposed to 2450 CW microwave radiation in order to study the effect on reflex response and synaptic function. A small but statistically significant increase in the reflex response was detected in the first series of experiment, which indicates enhancement of the synaptic transmission. However, this effect was not observed in a second series of experiments in which the incident power density was increased from 10 mW/cm(2) to 20 mW/cm(2) and a more rigorous experimental design was employed. The slight changes that were observed in the second series could be attributed to small temperature variations during the experiment.     

Temperature-Time Profile in Rats Subjected to Selective Microwave Irradiation of the Brain

Real-time cortical and colonic temperature changes in rats irradiated for 20 min by a 2450 MHz contact radiator at the animals head were measured. Ten ?s pulses were delivered to the radiator at pulse repetition rates of 25-500 pulses/s and at energy rates of 0.3 to 1325 mW that corresponded to incident power densities of 0.18 to 875 mW/cm2. Lower power densities yielded a small cortical temperature increase below that for the body core whereas higher power densities produced a greater cortical temperature rise. Even at an incident power density as high as 875 mW/cm2 that resulted in a specific absorption rate of 70 mW/g in the brain, the cortical temperature increased by less than 3.0°C while the colonic temperature rose by 0.5°C. The cortical temperature rapidly rose during the initial transient period of irradiation. It soon became nonlinear and achieved a steady-state level around 39°C. From these observations we concluded that the brain temperature was lowered by thermoregulatory processes involving blood circulation, temperature, and mass differences between the brain and the nonirradiated body of the anesthetized rat, and furthermore, the irradiated brain received significant protection from the nonirradiated body.     

双极化方向回溯整流天线阵列设计与实验

提出了由双极化方向回溯Van Atta天线阵和差分整流电路组成的方向回溯整流天线阵,它能够避免接收波束未对准和收发天线极化失配而造成整流天线转换效率的急剧下降,使整流天线在宽入射角和任意极化时仍能保持稳定的直流输出.设计并测试了C波段2×2元阵列.实验结果表明,当入射波功率密度为3.43 mW/cm2时,双极化方向回溯整流天线阵列的垂直和水平极化端口归一化电压比大于0.8的入射角度范围分别为[-38°,38°]和[-31°,31°].当功率密度为4.32 mW/cm2时,两个极化端口均获得70.8%的最高整流效率.     

Noninvasive glucose sensing utilizing a digital closed-looppolarimetric approach

A polarimetric glucose sensor utilizing a digital closed-loop controller was designed and implemented during this study. Its potential as a noninvasive glucose sensor was evaluated in vitro for both glucose doped water and bovine aqueous humor mediums. A physiological hyperglycemic concentration range was used in both calibration and validation of each set of experiments. Ideally, the end application of this system could estimate blood glucose concentrations indirectly by measuring the amount of rotation of a light beam's polarization state after it propagates through the aqueous humor contained within the anterior chamber of the eye. The polarimeter designed in this study differs from similar investigated systems in that it utilizes a digital closed-loop control system. This type of controller was implemented in order to further improve system repeatability and stability without sacrificing accuracy. Unique to this investigation, independent validation sets other than those used to create each respective calibration model were obtained. The results of the glucose-doped water experiments yielded mean standard errors of prediction for calibration and validation of 6.91 and 8.84 mg/dl, respectively. The mean standard errors of prediction during calibration and validation of the glucose-doped aqueous humor experiments were higher at 27.20 and 27.47 mg/dl, respectively, due to medium degradation over time while exposed to air     

Absorption of Millimeter Waves by Human Beings and its Biological Implications

With recent advances in millimeter-wave technology, including the availability of high-power sources in this band, it has become necessary to understand the biological implications of this energy for human beings. This paper gives the millimeter-wave absorption efficiency for the human body with and without clothing. Ninety to ninety-five percent of the incident energy may be absorbed in the skin with dry clothing, with or without an intervening air gap, acting as an impedance transformer. On account of the submillimeter depths of penetration in the skin, superficial SAR'S as high as 65-357 W/Kg have been calculated for power density of incident radiation corresponding to the ANSI guideline of 5 mW/cm/sup 2/. Because most of the millimeter-wave absorption is in the region of the cutaneous thermal receptors (0.1 - 1.0 mm), the sensations of absorbed energy are likely to be similar to those of IR. For the latter, threshold of heat perception is near 0.67 mW/cm/sup 2/, with power densities on the order of 8.7 mW/cm/sup 2/ likely to cause sensations of "very warm to hot" with a latency of 1.0+-0.6s. Calculations are made for thresholds of hearing of pulsed millimeter waves. Pulsed energy densities of 143-579 µJ/cm/sup 2/ are obtained for the frequency band 30-300 GHz. These are 8-28 times larger than the threshold for microwaves below 3 GHz. The paper also points to the need for evaluation of ocular effects of millimeter-wave irradiation because of high SAR's in the cornea.     

Effect of microwave irradiation (2450 MHz) on murine cytotoxic lymphocyte and natural killer (NK) cells

Male Balb/c mice were exposed in an anechoic chamber to 2450 MHz CW microwaves at 5, 10, 15, and 20 mW/cm2, 4 hours daily for 4 days, under controlled environmental conditions. T-cell cytotoxicity and natural killer (NK) cell activity were compared in exposed and sham animals. A significant decrease (p less than 0.001) of cell-mediated cytotoxicity was observed only for a power density of 20 mW/cm2. A significant increase (p less than 0.01) in NK activity was demonstrated following exposures at 15 mW/cm2.     

毫米波辐照下大鼠皮肤温度场及血液灌注率影响研究

根据Pennes方程和毫米波在动物皮肤内的传播特性,建立了在33.5 GHz毫米波同辐照强度下的大鼠皮肤的非稳态多层传热模型. 在二维柱坐标下进行离散计算,得到了长时间辐照条件下不同皮肤深度的温度变化规律,并将理论结果与实验数据进行了比较. 在284 mW/cm2和853 mW/cm2辐照强度下,理论结果和实验结果基本一致; 在474 mW/cm2和664 mW/cm2辐照强度下,有一定的误差,但误差仍不超过1 ℃,验证了该理论模型的准确性.分析了实际趋肤深度内的温度分布,发现毫米波引起的生物热效应的最高温度点并非在皮肤表面,而是皮下某点,其与表面辐照中心点的温差可超过1 ℃.进一步分析了血液灌注率对温度场的影响,发现在讨论的温度范围内,血液灌注率的变化对毫米波辐照下的皮肤表面温度场的影响较小.     

Temperature rises in the human eye exposed to EM waves in thefrequency range 0.6-6 GHz

The temperature rises in the human eye for plane wave exposures are investigated in the frequency range between 600 MHz and 6 GHz, which covers the hot spot frequency range. As a first step, the specific absorption rates (SARs) are calculated with the use of the finite-difference time-domain (FDTD) method and the mechanism of hot-spot formation is discussed. Then the temperature rises in the human eye are calculated by using Pennes' bioheat equation. In addition, the dependence of SARs and temperature rises on the electromagnetic (EM) wave polarization and the eye dimension is discussed. Furthermore, the temperature rises calculated are compared with the values found in the literature pertaining to microwave-induced cataract formation. Numerical results show that hot spots appear in a certain frequency range and that the location and number of hot spots depend on the frequencies of the incident wave. In particular, the averaged SARs and the temperature rise are found to depend obviously on the polarization of the EM wave. Additionally, the deviations in the SAR and the temperature rise caused by the eye size are found to be within 10%. Furthermore, the maximum temperature rise due to the incident EM power density of 5.0 mW/cm² , which is the maximum permissible exposure limit for controlled environments, is found to be 0.30°C at 6.0 GHz. This value is small but not negligible, as compared with the threshold temperature rise 3.0°C for cataract formation     

Fabrication of room temperature continuous-wave operation GaN-based ultraviolet laser diodes

Two kinds of continuous-wave GaN-based ultraviolet laser diodes (LDs) operated at room temperature and with different emission wavelengths are demonstrated.The LDs epitaxial layers are grown on GaN substrate by metalorganic chemical vapor deposition,with a 10×600 μm2 ridge waveguide structure.The electrical and optical characteristics of the ultraviolet LDs are investigated under direct-current injection at room temperature. The stimulated emission peak wavelength of first LD is 392.9 nm,the threshold current density and voltage is 1.5 kA/cm² and 5.0 V,respectively.The output light power is 80 mW under the 4.0 kA/cm² injection current density. The stimulated emission peak wavelength of second LD is 381.9 nm,the threshold current density the voltage is 2.8 kA/cm² and 5.5 V,respectively.The output light power is 14 mW under a 4.0 kA/cm² injection current density.     

Computation of the Electromagnetic Fields and Induced Temperatures Within a Model of the Microwave-Irradiated Human Eye

The electromagnetic fields within a detailed model of the human eye and its surrounding bony orbit are calculated for two different frequencies of plane-wave irradiation: 750 MHz and 1.5 GHz. The computation is performed with a finite-difference algorithm for the time-dependent Maxwell's equations, carried out to the sinusoidal steady state. The heating potential, derived from the square of the electric field, is used to calculate the temperatures induced within the eyeball of the model. This computation is performed with the implicit alternating-direction (IAD) algorithm for the heat conduction equation. Using an order-of-magnitude estimate of the heat-sinking capacity of the retinal blood supply, it is determined that a hot spot exceeding 40.4/spl deg/C occurs at the center of the model eyeball at an incident power level of 100 mW/cm/sup 2/ at 1.5 GHz.     

Preliminary studies: far-field microwave dosimetric measurements of a full-scale model of man.

Measurements of microwave heating were made in a full-size, upright human model. The 75-Kg model, composed of electrically simulated muscle, was placed in the far-zone of a standard-gain horn inside an absorber-lined chamber. Pulsed energy at 1.29 GHz was obtained from a military radar transmitter (AN/TPS-1G) and produced radiation at 6-14 mW/cm2 average power density at the location of the model. Microwave heating at the front surface was measured at nine locations on the phantom. Measurements at several depths within the phantom were also made at a central location to gain information on the depth-of-penetration of the microwave energy. Results of the frontal surface measurements and of the penetration study permitted a calculation of the approximate whole-body average specific absorption rate (SAR) when the model's long axis was parallel to the E-field vector. For a normalized power density of 1 mW/cm2 at a frequency of 1.29 GHz, the whole-body average SAR approximated 0.03 W/Kg. This result agrees well with theoretical predictions based on absorption in prolate spheroidal models of man.     

Effect of 2450-Mhz Radiation on the Rabbit Eye

The cataractogenic effects of near-zone 2450-MHz radiation in rabbits are presented. The power deposition pattern inside the eyes and head of rabbits has been determined using a thermocouple technique. It was found that a peak absorption of 0.92 W/kg occurred between the lens of the eye and the retina for each milliwatt/square centimeter incident. Time and power-density studies indicated a cataractogenic threshold of a 150-mW/cm2 incident, or 138-W/kg peak absorption behind the lens for 100 min. The threshold time decreased with increasing power density. Agreement between in vivo intraocular temperature measurements and finite-element computer predictions reinforces the suggestion of a thermal mechanism for microwave-induced lens opacities.     

High-performance 1.5 /spl mu/m GaInNAsSb lasers grown on GaAs

Substantially reduced threshold current density and improved efficiency in long-wavelength (>1.4 /spl mu/m) GaAs-based lasers are reported. A 20/spl times/1220 /spl mu/m as-cleaved device showed a room temperature continuous-wave threshold current density of 580 A/cm/sup 2/, external efficiency of 53%, and 200 mW peak output power at 1.5 /spl mu/m. The pulsed threshold current density was 450 A/cm/sup 2/ with 1145 mW peak output power.     

Thermal elevation in the human eye and head due to the operation of a retinal prosthesis

An explicit finite-difference time-domain formulation of the bio-heat equation is employed with a three-dimensional head eye model to evaluate the temperature increase in the eye and surrounding head tissues due to the operation of the implanted stimulator IC chip of a retinal prosthesis designed to restore partial vision to the blind. As a first step, a validation of the thermal model and method used is carried out by comparison with in vivo measurements of intraocular heating performed in the eyes of dogs. Induced temperature increase in the eye and surrounding tissues is then estimated for several different operational conditions of the implanted chip. In the vitreous cavity, temperature elevation of 0.26 degrees C is observed after 26 min for a chip dissipating 12.4 mW when positioned in the mid-vitreous cavity while it is 0.16 degrees C when the chip is positioned in the anterior portion between the eye's ciliary muscles. Corresponding temperature rises observed on chip are 0.82 degrees C for both the positions of the chip. A comprehensive account of temperature elevations in different tissues under different operational conditions is presented.     

354.7nm ps强紫外激光

用两块Ⅱ类KDP晶体对主被动锁模YAG激光输出进行倍频及和频,在入射光强度为1.27GW/cm~2条件下,得到脉冲宽度为32ps、峰值功率30MW、平均功率60mW和重复率为20Hz的稳定的354.7nm激光。