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Exposure Assessment in Front of a Multi-Band Base Station Antenna

BIOELECTROMAGNETICS 2011年第3期32卷 234-242页

作者： Kos, Bor Valic, Blaz Kotnik, Tadej Gajsek, Peter INIS Inst Nonionizing Radiat SI-1000 Ljubljana Slovenia Univ Ljubljana Fac Elect Engn Ljubljana Slovenia

This study investigates occupational exposure to electromagnetic fields in front of a multi-band base station antenna for mobile communications at 900, 1800, and 2100 MHz. finite-difference time-domain method was used to first validate the antenna model against measurement results published in the literature and then investigate the specific absorption rate (SAR) in two heterogeneous, anatomically correct human models (Virtual Family male and female) at distances from 10 to 1000 mm. Special attention was given to simultaneous exposure to fields of three different frequencies, their interaction and the additivity of SAR resulting from each frequency. The results show that the highest frequency-2100 MHz-results in the highest spatial-peak SAR averaged over 10 g of tissue, while the whole-body SAR is similar at all three frequencies. At distances > 200 mm from the antenna, the whole-body SAR is a more limiting factor for compliance to exposure guidelines, while at shorter distances the spatial-peak SAR may be more limiting. For the evaluation of combined exposure, a simple summation of spatial-peak SAR maxima at each frequency gives a good estimation for combined exposure, which was also found to depend on the distribution of transmitting power between the different frequency bands. Bioelectromagnetics 32:234-242, 2011. (C) 2010Wiley-Liss, Inc.

关键词： occupational RF exposure multi-band base station finite-difference time-domain method whole-body SAR spatial-peak SAR

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Application of finite-difference time domain and dynamic differential evolution for inverse scattering of a two-dimensional perfectly conducting cylinder in slab medium

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JOURNAL OF ELECTRONIC IMAGING 2010年第4期19卷

作者： Sun, Chi-Hsien Chiu, Chien-Ching Chien, Wei Li, Ching-Lieh Tamkang Univ Dept Elect Engn Tamsui 251 Taipei County Taiwan De Lin Inst Technol Dept Elect Engn Tucheng City 236 Taipei County Taiwan

We apply the dynamic differential evolution (DDE) algorithm to solve the inverse scattering problem for which a two-dimensional perfectly conducting cylinder with unknown cross section is buried in a dielectric slab medium. The finite-difference time domain method is used to solve the scattering electromagnetic wave of a perfectly conducting cylinder. The inverse problem is resolved by an optimization approach, and the global searching scheme DDE is then employed to search the parameter space. By properly processing the scattered field, some electromagnetic properties can be reconstructed. One is the location of the conducting cylinder, the others is the shape of the perfectly conducting cylinder. This method is tested by several numerical examples, and it is found that the performance of the DDE is robust for reconstructing the perfectly conducting cylinder. Numerical simulations show that even when the measured scattered fields are contaminated with Gaussian noise, the quality of the reconstructed results obtained by the DDE algorithm is very good. (C) 2010 SPIE and IS&T. [DOI: 10.1117/1.3514737]

关键词： Reconstruction algorithms Inverse scattering Inverse problems Inverse scattering problem finite-difference time-domain method Scattering Chromium Dielectrics Electromagnetism Evolutionary algorithms

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Investigating the spectral characteristics of backscattering from heterogeneous spheroidal nuclei using broadband finite-difference time-domain simulations

Investigating the spectral characteristics of backscattering...

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Conference on Biomedical Applications of Light Scattering IV

作者： Chao, Guo-Shan Sung, Kung-Bin Natl Taiwan Univ Grad Inst Biomed Elect & Bioinformat Taipei Taiwan

ISBN: (纸本)9780819479693

Backscattered light spectra have been used to extract size distribution of cell nuclei in epithelial tissues for noninvasive detection of precancerous lesions. In existing experimental studies, size estimation is achieved by assuming nuclei as homogeneous spheres or spheroids and fitting the measured data with models based on Mie theory. However, the validity of simplifying nuclei as homogeneous spheres has not been thoroughly examined. In this study, we investigate the spectral characteristics of backscattering from models of spheroidal nuclei under plane wave illumination using three-dimensional finite-difference time-domain (FDTD) simulation. A modulated Gaussian pulse is used to obtain wavelength dependent scattering intensity with a single FDTD run. The simulated model of nuclei consists of a nucleolus and randomly distributed chromatin condensation in homogeneous cytoplasm and nucleoplasm. The results show that backscattering spectra from spheroidal nuclei have similar oscillating patterns to those from homogeneous spheres with the diameter equal to the projective length of the spheroidal nucleus along the propagation direction. The strength of backscattering is enhanced in heterogeneous spheroids as compared to homogeneous spheroids. The degree of which backscattering spectra of heterogeneous nuclei deviate from Mie theory is highly dependent on the distribution of chromatin/nucleolus but not sensitive to nucleolar size, refractive index fluctuation or chromatin density.

关键词： Backscatter finite-difference time-domain method Light scattering Optical spheres Mie scattering Refractive index 3D modeling Tissues Data modeling Scattering

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Anisotropic-medium PML for efficient Laguerre-based FDTD method

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ELECTRONICS LETTERS 2010年第5期46卷 318-U25页

作者： Duan, Y. T. Chen, B. Chen, H. L. Yi, Y. PLA Univ Sci & Technol EMP Lab Nanjing 210007 Peoples R China

An anisotropic-medium perfectly matched layer (PML) for efficient Laguerre-based finite-difference time-domain (FDTD) method is presented. To verify the validity of the presented method, a numerical example of scattering from a two-dimensional rectangular conductor is given. Compared with Mur's absorbing boundary condition, the presented PML shows better absorbing performance.

关键词： anisotropic-medium perfectly matched layer two-dimensional rectangular conductor Numerical approximation and analysis Electromagnetic waves: theory Other numerical methods finite difference time-domain analysis Mur absorbing boundary condition Laguerre-based FDTD method Electromagnetic wave propagation stochastic processes electromagnetic wave scattering anisotropic-medium PML finite-difference time-domain method

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Dynamics and control of few-cycle ultrashort pulse propagation in an asymmetric coupled-quantum-well nanostructure

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OPTICS COMMUNICATIONS 2010年第19期283卷 3803-3811页

作者： Li, Jiahua Yu, Rong Si, Liugang Huang, Pei Yang, Xiaoxue Huazhong Univ Sci & Technol Wuhan Natl Lab Optoelect Wuhan 430074 Peoples R China Huazhong Univ Sci & Technol Sch Phys Wuhan 430074 Peoples R China Wuhan Inst Technol Sch Sci Hubei Prov Key Lab Intelligent Robot Wuhan 430073 Peoples R China

The nonlinear propagation of few-cycle ultrashort pulse in an asymmetric coupled-quantum-well (CQW) nanostructure is simulated by solving numerically the full Maxwell-Bloch equations with an iterative predictor-corrector finite-difference time-domain method. The behaviors of electric field profiles for 2 pi and 4 pi ultrashort pulses in different propagating zones are predicted in details beyond the slowly varying envelope and rotating-wave approximations. This investigation may provide a guideline for optimizing and controlling ultrashort pulses in solid-state media, which are promising for practical applications in highspeed optical communications. (C) 2010 Elsevier B.V. All rights reserved.

关键词： Few-cycle ultrashort pulse Coupled quantum wells (CQWs) Predictor-corrector algorithm finite-difference time-domain method

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Applications of the multidomain pseudospectral time-domain algorithm for waveguide structures

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IET MICROWAVES ANTENNAS & PROPAGATION 2010年第10期4卷 1626-1631页

作者： Cao, Q. Zhao, F. Li, L. Nanjing Univ Aeronaut & Astronaut Coll Informat Sci & Technol Nanjing 210016 Peoples R China

The authors have analysed the complex waveguide structures by the multidomain pseudospectral time-domain (MPSTD) algorithm, and discussed the design of a filtering procedure through improving the stability of the MPSTD method for the corner singularities. These numerical results of the MPSTD method have shown an excellent agreement with those results of the analytical solution and the traditional finite-difference time-domain method for the resonant frequencies of the waveguide structures. It is evident that the MPSTD method can achieve high efficiency and accuracy when we use to analyse inhomogeneous media and curved objects.

关键词： Waveguide and cavity theory multidomain pseudospectral time-domain algorithm inhomogeneous media analysis finite difference time-domain analysis resonant frequency waveguide theory waveguide structures finite-difference time-domain method Other numerical methods MPSTD algorithm filtering procedure design

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Numerical simulations of laser light guiding and focusing using an open hollow cone

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OPTICS COMMUNICATIONS 2010年第20期283卷 3854-3859页

作者： Zeng, Xiahui Fan, Dianyuan Minjiang Univ Dept Phys Elect Informat Engn Fuzhou 350108 Peoples R China Chinese Acad Sci Shanghai Inst Opt & Fine Mech Shanghai 201800 Peoples R China

An open hollow cone that can optically guide and focus a laser light into a small beam spot is proposed. The shaping and focusing effects are numerically demonstrated by finite-difference time-domain simulations. The results reveal that the cone-focused laser originates from the multi-beam interference and squeeze of two cone side walls acting like oblique targets. Moreover, the influences of oblique incident angle of laser light, cone angle and cone tip size on the focusing properties are discussed and the optimum cone geometry with cone angle of 16 and tip size of 4.5 wavelengths to achieve high energy concentration at the cone tip is also presented. It is shown that with an open hollow cone a laser light can be focused into a tiny highly localized beam spot of 1 pm diameter and keeps propagating forward for a distance of about 8 wavelengths with a tiny spot diameter remaining almost unchanged. The intensity almost increases up to twentyfold in a 1 pm focal spot. (C) 2010 Elsevier B.V. All rights reserved.

关键词： Laser beam focusing Hollow cone finite-difference time-domain method

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Spherical vector wave functions solution of electromagnetic scattering by a two-layered uniaxial anisotropic sphere

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IET MICROWAVES ANTENNAS & PROPAGATION 2010年第10期4卷 1559-1566页

作者： Geng, Y-L Hangzhou Dianzi Univ Inst Antenna & Microwaves Hangzhou 310018 Zhejiang Peoples R China

The electromagnetic fields in spherical uniaxial anisotropic objects can be expressed as the sum of spherical vector wave functions of the first and second kind in uniaxial anisotropic media. Applying the tangential boundary conditions of electromagnetic fields at the interface between different uniaxial anisotropic media, the expansion coefficients of electromagnetic fields in a two-layered uniaxial anisotropic sphere and free space can be derived in terms of spherical vector wave functions. Then, the radar cross section (RCS) by a two-layered uniaxial anisotropic sphere can be obtained. Numerical results for some special cases are shown, and compared to those of the classical Mie theory, the method of moments (MoM) accelerated with the conjugate-gradient fast-Fourier-transform (CG-FFT) approach and finite-difference time-domain (FDTD) method.

关键词： tangential boundary conditions uniaxial anisotropic media conjugate-gradient fast-Fourier-transform spherical vector wave functions electromagnetic scattering Electromagnetic wave propagation Integral transforms finite difference time-domain analysis Radar theory fast Fourier transforms classical Mie theory radar cross-sections electromagnetic wave scattering radar cross section finite-difference time-domain method method of moments Other numerical methods two-layered uniaxial anisotropic sphere

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Improving the performance of a photonic crystal ring-resonator-based channel drop filter using particle swarm optimization method

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OPTICS COMMUNICATIONS 2010年第20期283卷 4099-4103页

作者： Darki, Behnam Saghirzadeh Granpayeh, Nosrat KN Toosi Univ Technol Fac Elect Engn Tehran *** Iran

The optical channel drop filters (CDFs) based on photonic crystals (PCs) are believed to be the essential components for compact photonic integrated circuits and WDM systems. One of the promising designs for a PC-CDF is based on the photonic crystal ring resonators (PCRRs). In this study, different parameters of a PCRR based CDF is optimized by using the particle swarm optimization (PSO) method in conjunction with the numerical method of two-dimensional (2D) finite-difference time-domain (FDTD) in a square lattice dielectric-rod 2D-PC. Hence a PC-CDF with ideal drop efficiency, large free spectral range (FSR) and acceptable quality factor will be proposed. (c) 2010 Elsevier B.V. All rights reserved.

关键词： Photonic crystal Channel drop filter Ring resonator Particle swarm optimization finite-difference time-domain method

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An ultra-short double-wavelength optical power splitter for two waveguides operation based on photonic crystal multimode interference

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OPTICS COMMUNICATIONS 2010年第20期283卷 3850-3853页

作者： Li, Wei Xu, Xu-ming Nanchang Inst Technol Dept Sci Nanchang 330099 Peoples R China Nanchang Univ Dept Phys Nanchang 330031 Peoples R China

In this paper, we design an ultra-short 1 x 2 1310/1550 nm double-waveguide optical power splitter based on photonic crystal multimode interference. The device can be used to divide the input beam equally for both 1310 nm and 1550 nm at the same time. The total multimode waveguide length of this device is only about 13 mu m, which is one 210th of the conventional dielectric counterparts reported. On the basis of the guided-mode propagation analysis method, the self-imaging effect is discussed for the case of symmetric incidence. The finite-difference time-domain method is used to simulate the propagation of the beam in the multimode interference. The results show that the repetitive appearances of single image and twofold image of the input field occur alternatively in this device. (C) 2010 Elsevier B.V. All rights reserved.

关键词： Double-wavelength optical power splitter Multimode interference finite-difference time-domain method Photonic crystal waveguide

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