Collinear Array Research Articles

Dependence of the Occupational Exposure to Mobile Phone Base Stations on the Properties of the Antenna and the Human Body

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This study assesses human exposure in the close vicinity of mobile phone base station antennas by finite-difference time-domain simulations. The peak spatial average specific absorption rate (SAR) and the whole-body average SAR are analyzed in three different anatomical models (55–101 kg) with respect to the basic restrictions for occupational exposure. The models are at distances between 0.5 and 4 m from various antenna types operating at frequencies ranging from 450 to 2140 MHz. The validity of the simulations is confirmed by an analysis of the impact of the mesh resolution on local and whole-body average SAR and by experimental validation of the numerical models. The results demonstrate that the whole-body absorption generally determines the maximum permissible antenna output power for collinear array antennas. Local exposure depends on various effects that fluctuate strongly among individuals. In particular for short antennas, the peak spatial average SAR can be more restrictive than the whole-body absorption because they may only expose a fraction of the body. Therefore, compliance must be demonstrated for both quantities. </para>

Generation of a long wedge-shaped barium atomic beam and its density characterization

A radiatively heated crucible having collinear array of channels has been used to produce a long wedge-shaped (length ∼100 mm, width ∼10 mm) high density (∼10 11 cm −3) atomic beam of barium. The collision-free beam flows upwards. The source is designed to generate atomic beams of low melting point (∼1000 K) metals and is suitable for long duration (∼15 h) operation. The beam, used for laser-ionized plasma studies, has been characterized by measuring the integrated density of the ground state of barium atoms at a fixed distance away from the source. At the same location the density distribution profiles along the length and width of the beam are also mapped. The measurements are carried out online using hollow cathode lamp based absorption spectroscopy technique and also intrusively by deposition method. The density and its distribution are also estimated theoretically. The data from the two experimental methods and estimates are in agreement within 10% accuracy.

A Study of Radio Zone Length of Dual-Polarized Omnidirectional Antennas Mounted on Rooftop for Personal Handy-Phone System

This paper proposes a dual-polarized omnidirectional antenna for base-station antennas that are mounted on the rooftops of buildings. The antenna suppresses the degradation in the received-signal level due to the inclination of mobile antennas in the personal handy-phone system (PHS). The proposed polarization-diversity antenna is comprised of a dielectric-loaded slotted-cylinder antenna for horizontally polarized waves and a conventional collinear array antenna for vertically polarized waves in a height-diversity configuration. The structure of the proposed antenna and its fundamental characteristics, such as the input impedance and radiation pattern, are shown. The change in the radio zone length (RZL) due to the inclination angle of the mobile antenna is measured to estimate the improvement offered by the proposed antenna in an urban area. It is shown that the RZLs of the collinear antennas in line-of-sight (LOS) environments are decreased by 73% when the mobile antenna is inclined at 90 , whereas the proposed polarization-diversity antenna restrains the degradation to approximately 20%, regardless of the inclination angle without downtilt and from 20% to 40% for a 15 downtilt. The RZLs of the collinear tilt antennas in non-LOS (NLOS) environments are below approximately 20%, compared to those of the collinear tilt antennas for the LOS route. We show that the RZLs in the NLOS environments are short compared to those for the LOS environments in microcell systems such as PHS with a high-elevation base station, even when the polarization-diversity technique is applied to the base station.

Mutual Coupling Between Box-Horn Elements of a Phased Array Terminated in Three-layered Bio-Media

The ldquoplane wave spectral techniquerdquo is used to investigate theoretically the extent of mutual coupling between two box-horn elements of a phased array terminated in three-layered bio-media (skin, fat, and muscle layers). The results obtained have been validated against published results in the literature. Each box-horn of the array is assumed to be filled with water to provide good impedance match to the bio-media. Also, it reduces the dimensions of each box-horn which makes it suitable for array configuration. The effects of relative position of elements, spacing between elements, frequency, aperture size of each element, relative phase and amplitude of excitation of the elements on mutual coupling coefficients are numerically investigated and presented for an array of two box-horns terminated in bio-media. The specific absorption rate (SAR) distributions along the direction of the array axis in muscle layer of the bio-media in direct contact with a collinear array of two box-horns both with and without mutual coupling considerations are also computed and presented. The results of the present research work can provide useful design guidelines for the development of prototypes of box-horn array for hyperthermia treatment of tumors. Bio-media, box-horn, hyperthermia, mutual coupling, phased array, plane wave spectra.

Geothermal Investigation in the plain Between Sheikh Ibrahim and Atshan anticline southeast of Talafar Northweast of Iraq

Geoelectrical investigations were carried out in the area that located between atshan and sheikh Ibrahim anticline and south west respectively the vertical electric sounding was applied by using the collinear and symmetrical schlumberger array with maximum spacing interval for the current and potential electrodes (840 and 90m. respectively ) the sounding station were located in 64 sites through four traverses trending NE-SW. the field curve were interpreted by the partial matching method and the initial models were adjusted by using KMM program with digital partial matching technique. For electric zones were distinguished, the first one represent the surface soil while the second zone reflect of two lithofacies which belong to the upper member of al fat'ha formation while the fourth zone represent a lateral resistivity contrast which reflect lower member of al fat'ha formation and the unit D of the upper member. Those lateral variations were explained by the geoelectrical traverses which indicate longitudinal fault. More ever geoelectrical section delinated type of this normal fault with about 90m through and 25 degree dipping

Geological study for the southern plain of alan, north of iraq using geoelectrical sounding

The present research involves geoelectrical study of the southern allan's plain, which lies between allan and atshan anticlines, in the north of Iraq. The field measurements were carried out in sixty three sounding stations, using collinear and symmetrical schlumberger array, distributed on four traverses (NE-SW direction) across the axes of anticlines surrounding the study area. The maximum interval spacing between both current and potential electrode has reached 843 and 90 meters consequently. The final interpretation result were represented with four geoelectrical section. Continuous correlation with composite stratigraphic columns of surrounding anticlines was made and five electrical zones were distinguished reflecting the soil, quaternary deposits upper and lower members of Al-Fat'ha formation as well as Euphrates formation. This study has specified two strike slip faults affected by the alpine orogeny. One transversal fault with NE-SW direction is located and clearly affects the true resistivity data and the anticlinal structure plunges in the east of the currently studying area. In addition a rotational strike slip fault has been specified, extending E-W parallel to the axes of the anticlines surrounding the area the second fault is considered as an important tectonic element in the regional geology of the north of Iraq, this element divides between the northern and the southern blocks of Mosul, which is characterized by the existence of Taurus and zagros trends consequently.

Experimental Estimation of EMI From Cellular Base-Station Antennas on Implantable Cardiac Pacemakers

The impact of electromagnetic interference (EMI) from cellular base station (BS) antennas on implantable cardiac pacemakers is clarified in this article. The estimation of the impact is based on in vitro experiments that are conducted using simulated multicarrier and multicode signals, which are transmitted from actual BS antennas and dipole antennas as the radiation source of the BS antenna. Critical interference to the electric field strength is revealed with respect to the 800-MHz band second-generation and 2-GHz band third-generation cellular systems. The experimental results show two things. One is that the pacemaker EMI depends on the average power of the transmission signals and does not depend on the peak-to-average power ratios of the transmission signals, which increase with the number of multicarriers and multicodes. The other is that the boundary of the EMI area where malfunctions occur closely approximates the contour of a 25-V/m electric field that is exited from a commercially available collinear array antenna typically used in BSs. Furthermore, no pacemaker EMI is detected in the immediate vicinity under the BS antenna at an input power level for typical operation. Accordingly, it is clear that the pacemaker EMI should not pose a concern in residential environments.

High‐gain printed dipole antenna

AbstractA printed dipole antenna showing high gain (about 6.8 dBi) radiation in the azimuthal plane is presented. The dipole antenna has a narrow width of 10 mm and a total length of about 202 mm (with 1.64 wavelengths of the frequency at 2442 MHz, the center frequency of the 2.4‐GHz WLAN band). In each one of the two radiating arms of the dipole antenna, a meandered line is inserted as a phase‐reversal device. With this arrangement, the proposed dipole antenna performs as a collinear array antenna with three in‐phase half‐wavelength radiating elements, leading to constructive radiation in the azimuthal plane and small side lobes in the elevation plane. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 214–218, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20948

Current and Near Field Calculations for Cellular Base-Station Collinear Array Antennas

In this paper, we present a new formulation for the evaluation of the electromagnetic field levels in the near zone of a cellular radio base-station collinear array antenna. The algorithm allows to determine the real current distribution along each half-wave dipole forming the array for a given exciting function and it enables to take into account the effects of mutual coupling among array elements. Once the antenna current distribution has been determined, the radiated field in the near zone is reconstructed using the integro-differential equation relating field and current. The developed algorithm, tested respectively on a 4-element and 8-element collinear array antenna operating at 900 MHz, allows to accurately analyze the response of dipole arrays with a computational cost significantly lower than that of a classical method of moments.

A uniform asymptotic evaluation of the field radiated from collinear array antennas

A uniform asymptotic representation of the electromagnetic field radiated from arbitrary collinear array antennas is presented. The asymptotic field is obtained applying the saddle-point technique to the radiation integrals after expressing the current excited along the array axis by means of a Fourier spectral representation. The resulting electromagnetic field is expressed in terms of propagating and evanescent truncated Floquet waves (FWs). The leading asymptotic term of the FWs exhibits an optical behavior and is responsible for the slow decay of the array near-field, which can be described as cylindrical in character. The transition toward the spherical wave propagation regime is due to the interference of the cylindrical field with the relevant scattered field from the array truncations, while the reactive energy storage is due to the evanescent FWs, as well as to the progressive inductive and progressive electrostatic FWs excited close the antenna axis. Using the asymptotic field representation, prediction formulas for the spatial locations where the array near-field exhibits peak deviation from the cylindrical decay, and where the transition from cylindrical to spherical wave propagation regime takes place, have been derived. The proposed analytical technique can be adopted to analyze the spatial field distributions and the radiation mechanisms of periodic and nonperiodic linear arrays.

Low-cost printed collinear array antenna

This paper presents the design and antenna-prototype measurements of a low-cost antenna for DECT and LMDS system base stations (3400 to 3600 MHz). The specified pattern must be omnidirectional in the horizontal plane, having a maximum at the horizon. To produce this pattern, a linear array of printed patches, placed on both sides of a planar feeding structure, is designed The feeding structure is a symmetrical stripline, made with low-cost materials and designed to simplify the implementation tasks as much as possible.

Estimation of the average power density in the vicinity of cellular base-station collinear array antennas

This paper investigates the character of the average power density in the close proximity of base-station antennas, where human exposure to electromagnetic fields radiated from such radiofrequency (RF) sources is the highest. The concept of average power density is used since, in proximity of a large array antenna, the direction of the power flow at a given point is not readily predictable because of the substantially diverging path lengths and direction of propagation of the energy arriving from different array elements. This quantity Is shown to have a marked cylindrical decay near the antennas, which converts to spherical in the far field. On this basis, a set of simple prediction formulas is derived to allow the estimation of the average power density with good precision. The latest IEEE C95.1-1999 Standard for RF safety calls for spatially averaged measurements of incident power density to verify compliance to maximum permissible exposure limits. The advantage of using the concept of average power density and the resulting prediction formulas is that the evaluation of the exposure of humans near cellular base-station antennas becomes extremely simple during surveys when large computerized scanning equipment may not be available.

Compact shielded exposure system for the simultaneous long-term UHF irradiation of forty small mammals II. Dosimetry

A four-antenna collinear array in an electromagnetically shielded chamber was designed and constructed to preferentially irradiate the brains of a large number of small mammals using cellular telephony microwave signals. Ten animals in special restrainers were positioned symmetrically around a centrally located antenna. These restrainers are resting on a circular structure made of acrylic plastic called a "carousel." Four carousels are stacked vertically, forming the array, inside a microwave anechoic chamber called a "chamberette." (Details of the design of this irradiator and of a 12-chamberette irradiation facility are given in a previous article.) In this article, the dosimetry on rats is reported. Both thermometric and thermographic measurements were performed. The average specific absorption rate (SAR) in brain tissue measured thermometrically was 0.85+/-0.34 W/kg per watt of net input power into the radiating antenna. This range agrees with the SAR levels reported in the literature for cellular telephones. Thermographic evaluation using splittable phantoms showed that most of the energy absorbed by the rats is concentrated in and around the brain. Moreover, it was found that the SAR in brain tissue can vary considerably for rats of similar weights, depending on position of the rats' heads inside the restrainers, and that there exists a significant dependence of SAR on animal weight. These variations may be of importance in the interpretation of results of lifelong studies. The data presented clearly show that the chamberette is, dosimetrically, a suitable irradiation system for electromagnetic bioeffects studies in the cellular communication frequency range, especially when a large number of laboratory animals is required.

Compact shielded exposure system for the simultaneous long‐term UHF irradiation of forty small mammals II. Dosimetry

A four-antenna collinear array in an electromagnetically shielded chamber was designed and constructed to preferentially irradiate the brains of a large number of small mammals using cellular telephony microwave signals. Ten animals in special restrainers were positioned symmetrically around a centrally located antenna. These restrainers are resting on a circular structure made of acrylic plastic called a “carousel.” Four carousels are stacked vertically, forming the array, inside a microwave anechoic chamber called a “chamberette.” (Details of the design of this irradiator and of a 12-chamberette irradiation facility are given in a previous article.) In this article, the dosimetry on rats is reported. Both thermometric and thermographic measurements were performed. The average specific absorption rate (SAR) in brain tissue measured thermometrically was 0.85 ± 0.34 W/kg per watt of net input power into the radiating antenna. This range agrees with the SAR levels reported in the literature for cellular telephones. Thermographic evaluation using splittable phantoms showed that most of the energy absorbed by the rats is concentrated in and around the brain. Moreover, it was found that the SAR in brain tissue can vary considerably for rats of similar weights, depending on position of the rats' heads inside the restrainers, and that there exists a significant dependence of SAR on animal weight. These variations may be of importance in the interpretation of results of life-long studies. The data presented clearly show that the chamberette is, dosimetrically, a suitable irradiation system for electromagnetic bioeffects studies in the cellular communication frequency range, especially when a large number of laboratory animals is required. Bioelectromagnetics 20:81–93, 1999. © 1999 Wiley-Liss, Inc.

A compact shielded exposure system for the simultaneous long-term UHF irradiation of forty small mammals: I. Electromagnetic and environmental design

To carry out in vivo studies of the possible health effects of radiation from cellular telephone handsets, it is necessary to expose large numbers of small mammals at realistic power densities, modulations, and frequencies. Because even microwatt leakage could compromise the local cellular system, extreme care in shielding is required. Experimental logistics dictate, however, that the irradiated animals be easily accessed and that it be possible to irradiate them in small groups, while other groups are being loaded into or unloaded from the irradiators. This problem has been resolved by exposing the animals in aluminum-sheathed rectangular parallelepipeds, lined with microwave absorber and having doors that can be opened readily. Inside each of these microwave anechoic "chamberettes" is a vertical, four-element collinear array of dipole antennas; and around each antenna, 10 animal restrainers can be arranged like spokes on a wheel. The system has worked efficiently in studies of up to 480 rats. There is negligible coupling between antennas, and back reflection at an antenna's feed line is down 7-9 dB. Received CDMA power at the local base station is below the receiver's noise floor. Interior illumination reinforces the rats' diurnal rhythms, and the rats sleep during irradiation. Experimental logistics are excellent. In this paper, the irradiator design is presented.

Coherence in the quasiparticle scattering by the vortex lattice in pure type-II superconductors

The effect of quasi-particle (QP) 'scattering' by the vortex lattice on the de-Haas van-Alphen oscillations in a pure type-II superconductor is investigated within mean field,asymptotic perturbation theory. Using a 2D electron gas model it is shown that, due to a strict phase coherence in the many-particle correlation functions, the 'scattering' effect in the asymptotic limit ($\sqrt{E_F/\hbar\omega_c}\gg 1$) is much weaker than what is predicted by the random vortex lattice model proposed by Maki and Stephen, which destroys this coherence . The coherent many particle configuration is a collinear array of many particle coordinates, localized within a spatial region with size of the order of the magnetic length. The amplitude of the magnetization oscillations is sharply damped just below $% H_{c2}$ because of strong $180^{\circ}$ out of phase magnetic oscillations in the superconducting condensation energy ,which tend to cancel the normal electron oscillations. Within the ideal 2D model used it is found, however, that because of the relative smallness of the quartic and higher order terms in the expansion, the oscillations amplitude at lower fields does not really damp to zero, but only reverses sign and remains virtually undamped well below $H_{c2}$. This conclusion may be changed if disorder in the vortex lattice, or vortex lines motion will be taken into account. The reduced QP 'scattering' effect may be responsible for the apparent crossover from a strong damping of the dHvA oscillations just below $H_{c2}$ to a weaker damping at lower fields observed experimentally in several 3D superconductors.

Square array resistivity anomalies and inhomogeneity ratio calculated by the finite‐element method

In this work the square array configuration is studied. As with any four‐electrode measuring configuration, three different resistances can be measured directly and, in particular, by using the square array these resistance values can be used to obtain a measure of the apparent anisotropy: this is the so‐called azimuthal inhomogeneity ratio (AIR). The AIR is used widely to derive information regarding the directional variation of the subsurface resistivity. Similar types of information can be obtained using any collinear array but would need to be used in a crossed mode. This gives an operational advantage to the square array. Here, the AIR and the square α and β apparent resistivities have been calculated for a number of simple subsurface models. Moreover, the apparent resistivity responses for several different linear arrays were calculated to allow useful comparisons. The forward modeling has been carried out via a 2.5-D finite‐element scheme and an existing approach has been modified in order to calculate the potential variations parallel to the strike direction. Here, the use of AIR as a pattern recognition tool is investigated. The AIR anomalies are shown to delineate the edges of the targets successfully, retaining the same pattern when the model was shifted in depth, and indicating a satisfactory resolving ability. The AIR can be used as complementary information to the apparent resistivity measures and can improve the interpretation. However, careful consideration has to be given to the data noise.

Multiple cracks in transformation toughened ceramics

The problem of a collinear array of cracks in a transformation toughened ceramic under monotonically increasing load is analyzed by the theory of complex potentials and dislocation formalism. The analysis is applicable to both a homogeneous material containing multiple cracks and a brittle matrix ceramic reinforced by distributed transformable particulates. The detrimental effect of transformation at the onset of crack growth is generally found to be amplified by crack tip interactions. For the particulate reinforced ceramic the maximum relative strengthening is achieved for moderate volume fractions of large particles.

Crack front trapping in transformation-toughened ceramics

A theoretical study is made of the trapping of a crack front in brittle matrix ceramic reinforced by dispersed transformable zirconia particles. The trapped discontinuous crack front is modelled by a collinear array of microcracks interspersed by transformable particles. The effect of trapping of the macrocrack front is approximated by a closing pressure on a bridged zone. The maximum closing pressure and the critical opening of the macrocrack are related to the volume (area) fraction and size of the transformable particles. It is found that the maximum toughening due to trapping occurs at moderate volume (area) fractions of large particles. This is in agreement with available theoretical and experimental results.

Archetypal organization of the amphioxus Hox gene cluster.

Organization into gene clusters is an essential and diagnostic feature of Hox genes. Insect and nematode genomes possess single Hox gene clusters (split in Drosophila); in mammals, there are 38 Hox genes in four clusters on different chromosomes. A collinear relationship between chromosomal position, activation time and anterior expression limit of vertebrate Hox genes suggests that clustering may be important for precise spatiotemporal gene regulation and hence embryonic patterning. Hox genes have a wide phylogenetic distribution within the metazoa, and are implicated in the control of regionalization along the anteroposterior body axis. It has been suggested that changes in Hox gene number and genomic organization played a role in metazoan body-plan evolution, but identifying significant changes is difficult because Hox gene organization is known from only very few and widely divergent taxa (principally insects, nematodes and vertebrates). Here we analyse the complexity and organization of Hox genes in a cephalochordate, amphioxus, the taxon thought to be the sister group of the vertebrates. We find that the amphioxus genome has only one Hox gene cluster. It has similar genomic organization to the four mammalian Hox clusters, and contains homologues of at least the first ten paralogous groups of vertebrate Hox genes in a collinear array. Remarkably, this organization is compatible with that inferred for a direct ancestor of the vertebrates; we conclude that amphioxus is a living representative of a critical intermediate stage in Hox cluster evolution.