Electric fields in the human body due to electrostatic discharges

Electrostatic discharges (ESDs) occur when two objects at different electric potentials come close enough to arc (spark) across the gap between them. Such discharges may be either single-event or repetitive (e.g., 60 Hz). Some studies have indicated that ESDs may be a causative factor for health effects in electric utility workers. Moreover, a hypothesis has recently been forwarded imperceptible contact currents in the human body may be responsible for health effects, most notably childhood leukemia. Numerical modeling indicates that the electric fields in human tissue resulting from typical contact currents are much greater than those induced from typical exposures to electric and magnetic fields at power line frequencies. Numerical modeling is used here to compute representative spark-discharge dosimetry in a realistic human adult model. The frequency-domain scalar potential finite difference method is applied in conjunction with the Fourier transform to assess electric fields in selected regions and tissues of interest in the body. Electric fields in such tissues as subcutaneous fat (where peripheral nerves may be excited), muscle and bone marrow are of the order of kilovolts per meter in the lower arm. The pulses, however, are of short duration (approximately 100 ns).     

Neural stimulation with magnetic fields: analysis of inducedelectric fields

Spatial distributions of the derivative of the electric field induced in a planar semi-infinite tissue model by various current-carrying coils and their utility in neural stimulation are evaluated. Analytical expressions are obtained for the electric field and its spatial derivatives produced by an infinitely short current element. Fields and their derivatives for an arbitrarily shaped coil are then obtained by numerical summation of contributions from all the elements forming the coil. The simplicity of the solution and a very short computation time make this method particularly attractive for gaining a physical insight into the spatial behavior of the stimulating parameter and for the optimization of coils. Such analysis is useful as the first step before undertaking a more complex numerical analysis of a model more closely representing the tissue geometry and heterogeneity.     

Permittivity measurements using open-ended sensors and referenceliquid calibration-an uncertainty analysis

Results of the uncertainty analysis of the error-corrected permittivity measurements of materials using open-ended sensors are reported. Uncertainties in the permittivities of the reference liquids due to the uncertainties in the Cole-Cole parameters are discussed. The effect of the selection of these parameters of reference liquids, when used as calibration standards for error-corrected permittivity measurements, is highlighted. The results of measurements performed on 15 and 30 ppt saline test liquids are presented along with the measurement uncertainties resulting from uncertainties in the Cole-Cole parameters of the reference liquids     

Electric fields in the human body resulting from 60-Hz contact currents

Contact currents occur when a person touches conductive surfaces at different potentials and completes a path for current flow through the body. Such currents provide an additional coupling mechanism to that, due to the direct field effect between the human body and low-frequency external fields. The scalar potential finite difference method, with minor modifications, is applied to assess current density and electric field within excitable tissue and bone marrow due to contact current. An anatomically correct adult model is used, as well as a proportionally downsized child model. Three pathways of contact current are modeled: hand to opposite hand and both feet, hand to hand only, and hand to both feet. Because of its larger size relative to the child, the adult model has lower electric field and current-density values in tissues/unit of contact current. For a contact current of 1 mA [the occupational reference level set by the International Commission on Non-ionizing Protection (ICNIRP)], the current density in brain does not exceed the basic restriction of 10 mA/m2. The restriction is exceeded slightly in the spine, and by a factor of more than 2 in the heart. For a contact current of 0.5 mA (ICNIRP general public reference level), the basic restriction of 2 mA/m2 is exceeded several-fold in the spine and heart. Several microamperes of contact current produces tens of mV/m within the child's lower arm bone marrow.     

A planar diversity antenna for handheld PCS devices

A polarization diversity antenna (PDA) is described, and its performance is compared to that of a monopole antenna at frequencies near 900 MHz. Numerical modeling of each antenna, using the finite-difference time-domain (FDTD) technique, incorporates a cellular telephone handset in the vertical orientation, the user's head and hand, and the mobile communications environment. Results indicate that the two modes of the PDA are sufficiently uncorrelated for diversity operation and that, overall, the values of the mean effective gain (MEG), efficiency, and averaged specific absorption rate (SAR) in the head are better for the PDA than for the monopole antenna. However, in terms of the MEG, the PDA is more sensitive than the monopole antenna to the presence of the user's body. For the PDA, most of the power absorbed in the user's body is deposited in the hand, whereas for the monopole antenna, most of the absorbed power is deposited in the head. For both antennas, the MEG depends on the environment (urban or suburban)     

An efficient way to compare ABCs

The authors present a performance comparison of absorbing-boundary conditions (ABCs), including the introduced perfectly matched layer (PML), for finite-difference time-domain (FDTD) simulations. This innovative PML for truncating FDTD domains was introduced by J. Berenger (see J. Comp. Phys. vol.114, p.195-200, 1994), and has since been the subject of intensive study. The key feature of the PML is its extremely low reflectivity over a broad range of (real) incidence angles, and its broadband characteristics. The authors provide color-coded graphs, which can be easily used to measure the PML's performance as a function of frequency and incidence angle. An important component of these graphs is that they also display the performance of the PML for evanescent waves. For comparison, similar graphs are given for the second order Mur and Lindman (see J. Comp. Phys., vol.18, p.66-78) ABCs. The superior performance of the PML (for propagating) waves is clearly seen, but for evanescent waves, the Lindman ABC gives better performance     

利用近场成像改进乳腺癌检测技术

长时间以来,人们梦想用非电离电磁波的人体成像技术检测癌症,如今乳腺癌的检测已取得重大进展,使这一梦想成为现实。在今后的十年里,微波系统将成为许多妇女疾病的一种可行的诊断方法。与其它癌症不同的是,乳腺肿瘤在微波波段与健康的乳房组织有着明显不同的电学特性。微波很容易穿透乳房,而对其他器官则相差很多。与其他的组织如肌肉和脑组织相比,正常的乳房组织对微波具有更高的透明度。本文概述了在乳腺癌检测的研制过程中有源系统、无源系统以及混合系统的主要特性,主要介绍有源系统,特别是微波断层摄影技术和共焦微波成像技术。乳…     

Implantable Electric-Field Probes?Some Performance Characteristics

Performance characteristics of three implantable triaxial field probes for measuring intensities of the internal electric fields in biological tissues at radio frequencies are given. The sensitivity in air between 100 MHz and 3 GHz, and in phantom materials at 350, 915, and 2450 MHz, are given for the Holaday model IME-01, EIT model 979, and Narda model 2608 implantable probes, as well as their noise and modulation characteristics.     

Wireless communications and the safety of the user

As the second century of wireless communication is approaching, both the new applications and the old ones, particularly the personal communication service (PCS), are rapidly growing and spreading. Health effects of human exposure to radio and microwave radiation have been investigated for over half a century, and considerable knowledge has been accumulated on biological effects of this radiation. This has resulted in development of protection standards in various countries, including the most recent revision of the ANSI standard (1992) in the United States. But as new technologies, particularly cellular telephones proliferate, new questions are asked. These questions are related to the effect of close proximity of an antenna to the telephone user's head, and the specific waveform of the transmitted signal. Both of these questions are considered below. It is interesting to note that the antenna design that improves radiation performance also limits energy deposition in the user's head.This paper is an updated version of the keynote address presented at Wireless '93, Canada, July 12–14, 1993.     

Modeling of magnetic field stimulation of bent neurons

The authors consider a simple model of magnetic stimulation of a long bent neuron located in a semi-infinite volume conductor with a planar interface. It is shown that the stimulating coil characteristics (size, shape and location) and the neuron shape affect the location of the stimulation. The activating function, defined as the electric field derivative along the neuron, has two components. One component depends on the derivative of the electric field along the straight section of the neuron, and the other on the field magnitude. The maximal stimulation point is at the bent part of the nerve and its position depends on the nerve shape and coil parameters. The analysis also has shown a better performance (a stronger stimulus) for a double-circular (figure eight) coil than for a double-square coil