Hybrid uniform theory of diffraction finite-difference time-domainmethod for scattered waves

The problem of an electromagnetic field propagating and scattering in a small finite-difference time-domain (FDTD) mesh enveloped in a larger ray-tracing region is investigated     

A memory-efficient formulation of the finite-difference time-domainmethod for the solution of Maxwell equations

With the increase in speed and memory storage in modern computer systems, the finite-difference time-domain (FDTD) method for the solution of electromagnetic problems is rapidly becoming an attractive choice due to its programming simplicity and flexibility in the analysis of a wide range of structures. However, this technique has the drawback of high computer memory requirements and computational power, when analyzing large geometries. In this paper, a modified version of the FDTD method with increased memory efficiency is presented and applied to the calculation of the resonant frequencies of a dielectric resonator coupled to a microstrip line. In this novel approach, the divergence relationship, which spatially links the three electric-field and three magnetic-field components, is used to eliminate one component each of E and H. This leads to a more memory-efficient formulation, where only four field components are stored in the whole domain, with a direct memory reduction of 33% in the storage of the fields     

Comparison of finite-difference time-domain SAR calculations withmeasurements in a heterogeneous model of man

A finite-difference time-domain technique was used to calculate the specific absorption rate (SAR) at various sites in a heterogeneous block model of man. The block model represented a close approximation to a full-scale heterogeneous phantom model. Both models were comprised of a skeleton, brain, lungs, and muscle. Measurements were conducted in the phantom model using an implantable electric-field probe and a computer-controlled data acquisition system. The calculation and measurement of SAR distributions were compared primarily in the head (including the neck) and chest. To obtain the necessary spatial resolution with the computer model, the head and neck were modeled with approximately 105,000 cells, while 86,000 cells were used to configure the chest. Planewave fields, polarized in the E orientation, were utilized to irradiate the models at an exposure frequency of 350 MHz. Reasonable correlation existed between the calculations and measurements.     

Application of the three-dimensional finite-difference time-domainmethod to the analysis of planar microstrip circuits

A direct three-dimensional finite-difference time-domain (FDTD) method is applied to the full-wave analysis of various microstrip structures. The method is shown to be an efficient tool for modeling complicated microstrip circuit components and microstrip antennas. From the time-domain results the input impedance of a line-fed rectangular patch antenna and the frequency-dependent scattering parameters of a low-pass filter and a branch-line coupler are calculated. These circuits were fabricated and the measurements made on them are compared with the FDTD results and shown to be in good agreement     

Characterization of the shielding effects on thefrequency-dependent effective dielectric constant of awaveguide-shielded microstrip using the finite-difference time-domainmethod

The dispersion behavior of a waveguide-shielded microstrip line is investigated using the finite-difference time-domain method. The result is a frequency-dependent effective dielectric constant. Structures having a centred strip are examined to determine the effects of a top cover alone and the effects of two symmetrically placed sidewalls. Structures with an off-centred strip are used to investigate the effects of a single sidewall alone and the combined effects of a single sidewall plus the top wall. The differences between the effects of a single sidewall alone and those of the two symmetrically placed sidewalls are identified. In addition, new results on the combined effects of the top wall plus one sidewall, which are important when considering the placement of the outermost elements of a packaged circuit, are also discussed     

SAR and induced current distributions for operator exposure to RFdielectric sealers

The finite-difference time-domain method is used to calculate local, layer-averaged, and whole-body averaged specific absorption rates (SARs) and induced current distributions in a 16-tissue, anatomically based, 5628-cell model of a human to assess operator exposure to RF sealers. Industrially relevant shapes and dimensions of commonly used RF dielectric heaters using parallel-plate and bar-type electrodes are considered. Realistic postures of the human operators are used for the calculations, including extending arms to simulate working conditions or an operator sitting on a wooden or metallic stool. Due to the high-intensity leakage fields in proximity to the RF applicators, some of the highest induced currents and SARs are calculated for the hands and the ankles and, in the sitting position, the knees. It is concluded that steps should therefore be taken either to reduce the leakage fields or shield the hands and the knees if it is necessary for them to be in high leakage field regions     

Simulation of induced current densities in the human body atindustrial induction heating frequencies

At industrial workplaces in the vicinity of induction heating and melting devices, workers are exposed to strong magnetic fields. Up until now, little knowledge about the coupling of external fields into the human body at low frequencies existed. This paper provides numerical investigations to clarify the ratio between external homogeneous magnetic fields and induced current densities inside the human body in the frequency range from 250 Hz up to 10 kHz. The finite-difference time-domain (FDTD) method is used to calculate the induced current density in a realistic inhomogeneous 1 cm resolution human body model with appropriate tissue parameters. The magnitude of the external magnetic field equals the reference value for occupational exposure in the current guideline of the International Commission on Nonionizing Radiation Protection (ICNIRP). It was found that the calculated maximum current densities inside the body may exceed the basic restrictions of the ICNIRP guideline at least up to a factor of two. Finally, the suitability of the human body model for dosimetric investigations is discussed in view of fine-resolution models presented in the literature     

Currents induced in the human body for exposure to ultrawidebandelectromagnetic pulses

The frequency-dependent finite-difference time-domain [(FD)² TD] method is used to calculate internal electric fields and induced current densities in a 1.31-cm resolution anatomically-based model of the human body for exposure to ultrawideband vertically polarized electromagnetic pulses (EMPs). From a single (FD)²TD simulation, two ultrawideband pulses with frequencies up to 1500 MHz are examined using a convolution technique. The complex permittivities ϵ*(τ) for the various tissues are known to vary a great deal over the wide bandwidth of these two pulses. In the (FD) ²TD formulation, these frequency-dependent ϵ*(τ) are described by the best-fit second-order Debye equations for the sixteen tissues that are used to define the anatomically based model. The vertical currents passing through several sections of the body are compared for a shoe-wearing model standing on a perfectly conducting ground plane, and a barefoot model suspended in air. For the first pulse, currents on the order of 1 to 4 mA per V/m of incident fields are calculated with the highest values calculated for the sections through the bladder and slightly above it. For the second pulse, currents on the order of 4 mA per V/m of incident fields were calculated     

Noninvasive measurement of current in the human body forelectromagnetic dosimetry

Minimally perturbing, resistive, nonferrous probes were developed for noninvasively measuring hazardous currents induced in the human body by electromagnetic fields at 1-200 MHz. Each probe has a resistive toroidal coil that is placed around the leg or other body member. An electrostatic shield is required to limit capacitive coupling. A new shielded test fixture provides TEM fields for calibration with a voltage standing wave ratio (VSWR) less than 1.1 from 1 to 200 MHz. A man-sized phantom was exposed to the near field of a vertical monopole antenna at 29.9 MHz, and the value of the current measured in the leg with the probe is in reasonable agreement with measured heating. Analyses and experiments show that commercial ferrous current probes modify the circuit in which they are used, changing the current being measured. Less change is caused by the authors' nonferrous current probes     

Electric current and electric field induced in the human body whenexposed to an incident electric field near the resonant frequency

The electric field and current density induced in the human body when this is exposed to electric fields near the resonant frequency, 53 MHz, are determined analytically. Since this frequency range includes an important amateur radio band of 50-60 MHz and exposure to electric fields at this frequency has been shown to be hazardous, the study has a specific motivation. A cylindrical model of the body is used to derive formulas for the total axial current and current density induced in the body subject to skin effect. Tabulations and graphical representations illuminate the results     

Application of a finite-difference technique to the human radiofrequency dosimetry problem

A powerful finite-difference numerical technique has been applied to the human radiofrequency dosimetry problem. The method possesses inherent advantages over the method-of-moments approach in that its implementation requires much less computer memory. Consequently, it has the capability to calculate specific absorption rates (SARs) at higher frequencies and provides greater spatial resolution. The method is illustrated by the calculation of the time-domain and frequency-domain SAR responses at selected locations in the chest. The model for the human body is comprised of rectangular cells with dimensions of 4X4X6 cm and dielectric properties that simulate average tissue (2/3 muscle). Additionally, the upper torso (chest) is configured by both homogeneous and inhomogeneous models in which this region is subdivided into 20,736 cells with dimensions of 1X1X1 cm. The homogeneous model of the chest consists of cells with average tissue properties, and the calculated results are compared with measurements acquired from a homogeneous phantom model when the exposure frequency is 350 MHz. For the inhomogeneous chest model the lungs and surrounding region (ribs, spine, sternum, fat, and muscle) are modeled with as much spatial resolution as allowed by the 1X1X1 cm cells. Computed results from the inhomogeneous chest model are compared with the homogeneous model.     

Evaluation of the SAR induced in a multilayer biological structure and comparison with SAR in homogeneous tissues

Wireless systems usage has evolved, for instance, with the recent increase in the use of a hands-free kit, the mobile phone is used more and more in a body-worn position. Therefore, to check the compliance to the international limits, new methods have to be developed. In this study, we analyze the relevance of using the equivalent head liquid for the biological structure of organs that are different from that of the head. This paper compares the Specific Absorption Rate (SAR) values assessed using simulations in a flat phantom filled with the liquid used to test the compliance of mobile phone close to the head to those values obtained using a multilayer model representing the tissues of the trunk. The multilayer structures are derived from the anatomical analysis of the visible human model and corresponding to reasonable positions of a handset in a body-worn configuration. The employed sources are half-wavelength dipoles placed at different distances from those structures and operating at frequencies between 300 MHz and 6 GHz.     

SAR and temperature increase in the human eye induced by obliquely incident plane waves

Specific absorption rates (SARs) and temperature increases in the human eye are calculated for exposure to obliquely incident plane waves in the frequency range of 600 MHz and 6.0 GHz. The average SARs and the temperature increases in the lens are found to take maximum values only in the hot-spot frequency range for oblique incidence (30/spl deg/-50/spl deg/).     

人体对电磁脉冲吸收剂量的仿真研究

在对39种人体组织的复介电常数进行二阶德拜式拟合的基础上,基于分辨率为3×3×3mm的人体结构模型,采用与频率相关的时域有限差分法((FD)2TD),对两种电磁脉冲作用下局部比吸收能量和感生电流密度分布进行了计算分析。结果表明,人体内局部比吸收能量和感生电流密度分布与入射电磁脉冲的频谱特性密切相关。在两种电磁脉冲作用下,人体全身平均比吸收能量分别为0.0138PJ/kg和0.0340PJ/kg。     

Modeling of the body current in a Bi-MOS hybrid-mode environment

The body current I_B of deep submicron lightly doped drain pMOSFETs has been investigated. Based on the experimental results, an analytical I_B model, applicable for devices operating in a Bi-MOS hybrid-mode environment, has been developed for the first time. The proposed model is able to effectively characterize the measured I_B results over a wide range of independently applied biases (gate, drain and body) and gate lengths (from 1 μm down to 0.25 μm). The possibility of minimizing or even eliminating the undesired I_B is also explored and discussed for the first time.     

The modified auxiliary current method applied for the problem of diffraction by a body of revolution with a kinked boundary

A new version of the modified auxiliary current method is proposed for the solution of the vector problem of diffraction by an impedance body of revolution. It is shown that the proposed approach makes it possible to develop efficient algorithms for the solution of this problem for bodies of revolution of various shapes, including scatterers with kinked boundaries. Numerical results for bodies of various geometries are reported, and the high accuracy of the results is demonstrated.     

The use of current amplifiers for high performance voltage applications

A current amplifier is used to realize a voltage amplifier having an improved high frequency response and slew rate capability. It is shown that the closed loop bandwidth is independent of the closed loop voltage gain. The design and application of a unity gain and a high gain current amplifier to voltage signal processing circuits are given. The results demonstrate an efficient use of the inherent frequency response capabilities of the active devices in the circuit to achieve the amplification of high frequency and large amplitude voltage signals.     

The use of imprecise component reliability distributions inreliability calculations

System reliability prediction can be needed when detailed data concerning each component are unavailable. This prevents data from various sources from being integrated by considering each source as a sample from the same population. For the Weibull distribution, fuzzy arithmetic is used to synthesize a single fuzzy probability distribution for a component from several possible distributions by considering particular features that map to the Weibull parameters. The use of fuzzified probabilities in fault trees has been considered by others; once the fuzzy component failure probabilities have been calculated, a fuzzy system reliability distribution can be obtained which portrays the inexact nature of the data on which the result is based     

A surrogate model to assess the whole body SAR induced by multiple plane waves at 2.4?GHz

The assessment of the exposure to electromagnetic waves is nowadays a key question. Dealing with the relationship between exposure and incident field, most of previous investigations have been performed with a single plane wave. Realistic exposure in the far field can be modeled as multiple plane waves with random direction of arrival, random amplitude, and random phase. This paper, based on numerical investigations, studies the whole body specific absorption rate (SAR) linked to the exposure induced by five random plane waves having uniformly distributed angles of arrival in the horizontal plane, log-normal distributed amplitudes, and uniformly distributed phases. A first result shows that this random heterogeneous exposure generates maximal variations of ??25% for the whole body specific absorption. An important observation is that the exposure to a single plane wave arriving face to the body, used for the guidelines, does not constitute the worst case. We propose a surrogate model to assess the distribution of the whole body SAR in the case of an exposure to multiple plane waves. For a sample of 30 values of whole body SAR induced by five plane waves at 2.4?GHz, this simple approach, considering the resulting SAR as the sum of the SAR induced by each isolated plane wave, leads to an estimated distribution of whole body SAR following the real distribution with a p value of 76% according to the Kolmogorov statistical test.