Search results

The purpose of this paper is to study the interaction of electromagnetic fields with biological tissues in the presence of antennas implanted subcutaneously for biotelemetry applications. The authors examined the influence of these radiative devices on energy absorption and also their effects as reflective metal surfaces when incoming radiofrequency energy was present.

The research was carried out using electromagnetic modeling based on the finite difference time domain method and the calculations were performed to determine the electric field and specific absorption rate. The implanted antenna operated in the Medical Implant Communication Service band. The incoming external electric fields considered included different frequency bands covering most current telecommunications standards.

Levels of absorbed energy with and without the implanted device.

The paper offers an analysis of results and comparison with current dosimetric standards and guidelines for limiting electromagnetic exposure.

The paper studies the interactions of implanted antennas with biological tissues, taking into account two behaviors: radiative and passive.

The purpose of this paper is to determine the electric field and specific absorption rate (SAR) distribution within biological tissues in the vicinity of dental implants, exposed to the mobile phone radiation.

This research was performed for the frequency of 2.6 GHz, which corresponds to 4G mobile network. The adequate 3D realistic numerical models of the mobile phone user’s head, dental implants and actual smartphone model are created using packages based on the finite integral technique numerical method.

The obtained results yield to a conclusion that the presence of dental implants affects the increase in electric field intensity and SAR values within biological tissues in its vicinity.

The presented procedure is limited to the 4G mobile network frequency of 2.6 MHz. The study should be extended to other mobile network frequencies to be more general.

The criteria for selection of the materials used for dental implants production should be extended with the recommended material characteristics related to their influence on the electric field and SAR distribution, to keep their values in the limits prescribed by standards.

The obtained results provide the foundation for future research in mobile devices’ electromagnetic fields’ influence on human health.

The accurate determination of the electric field and SAR values within different biological tissues and organs in the vicinity of dental implants exposed to mobile phone electromagnetic radiation, demands highly realistic model of observed biological structures. For purposes of the current study, the procedure for modeling of highly nonhomogeneous structure with finite number of homogenous domains having known electromagnetic parameters is described in the paper. As a result, the 3D complex users’ head model formed of 16 homogeneous domains of different electromagnetic parameters is created.

The purpose of this paper is to present a numerical analysis of the specific absorption rate (SAR) and temperature increase in a three dimensional (3D) anatomical human eye model exposed to electromagnetic (EM) fields at 1.9, 2.4 and 5.1 GHz, in particular devices such as tablets, smart phones, etc., which are based on Wi-Fi and 4G technology.

A new 3D model of the human eye composed of nine different tissues with a high resolution of 0.5 mm is presented, including a precise definition of the cornea and lens and also distinguishing the cornea from the aqueous humor and the sclera from the retina and choroid. The EM problem is solved from the Maxwell’s equations which gives the electric field and in turn enables the calculation of the SAR in any part of the eye model. The thermal problem is solved from the bioheat (Pennes’) equation taking the SAR as an input of the power dissipated by the EM field. In both cases the finite difference time domain method is employed.

A plane-wave field located 30 cm away from the eye is considered as the source for the far-field EM exposure. The results for maximum SAR indicate that the smallest value is 0.06 W/kg in the lens for 1.9 GHz whereas the highest value encountered is 0.43 W/kg in the vitreous humor for 5.1 GHz. In the worst case, the maximum SAR in the lens is 0.28 W/kg for 5.1 GHz. In all cases, the SAR values are within the limits defined by international standards. In terms of maximum temperature, the highest value found is 0.01 C in the cornea, aqueous humor and lens for 5.1 GHz.

The work presents a thorough numerical calculation of the temperature increase in the human eye induced by devices that are based on Wi-Fi and 4G technology operating at 1.9-5.1 GHz.

This paper aims to propose a two-element dual fed ultra-wideband (UWB) multiple input multiple output (MIMO) antenna system with no additional decoupling structures. The antenna operates from 3.1 to 10.6 GHz. The antenna finds its usage in on-body wearable device applications.

The antenna system measures 63.80 × 29.80 × 0.7 mm. The antenna radiating element is designed by using a modified dumbbell-shaped structure. Jean cloth material is used as substrate. The isolation improvement is achieved through spacing between two elements.

The proposed antenna has a very low mutual coupling of S₂₁ < −20 dB and impedance matching of S₁₁ < −10 dB. The radiation characteristics are stable in the antenna operating region. It provides as ECC < 0.01, diversity gain >9.9 dB. The antenna offers low average specific absorption rate (SAR) of 0.169 W/kg. The simulated and measured results are found to be in reasonable match.

The MIMO antenna is proposed for on-body communication, hence, a very thin jean cloth material is used as substrate. This negates the necessity of additional material usage in antenna design and the result range indicates good diversity performance and with a low SAR of 0.169 W/kg for on-body performance. This makes it a suitable candidate for textile antenna application.

Low‐level microwave (MW) fields may under certain conditions of exposure cause measurable effects in biological organisms. Exposure of the general public to MWs in the environment is generally below intensities which are considered as responsible for evoking bioeffects. Introduction of cellular phone (CP) systems has increased considerably MW exposure of CP users. Health consequences of long‐term use of CPs are not known in detail, but available data indicate that development of non‐specific health symptoms is possible, at least in “MW hypersensitive” subjects. In contrast to terminal CPs, transmitting antennas and base stations (BS) contribute to MW environmental contamination only with a small portion of the energy and do not pose any health risks. Health risks of CP use are underestimated and accepted, while risks of BS are generally overestimated by the public. Therefore, an improved risk communication as well as further studies of the risks are required.

The purpose of this paper is to determine the impact of human age on the distribution of electric field and absorbed energy that originates from a mobile phone.

This research was performed for frequencies of 900, 1800 and 2100 MHz, which are used in a mobile communication system. To obtain the most accurate results, 3 D realistic model of the child’s head has been created whereby the dimensions of this model correspond to the dimensions of a seven-year-old child. Distribution of the electric field and specific absorption rate (SAR) through the child’s head was obtained by numerical analysis based on the finite integration technique.

The results discover that amount of absorbed energy is greater in the surface layers of the child’s head model when the electromagnetic (EM) characteristics of tissues are adjusted for the child. This deviation corresponds to different EM characteristics of biological tissues and organs of an adult person compared to a child.

The study deals with penetrated electrical field and absorbed EM field energy. There is space for further studies of other EM field effects (e.g. thermal effects).

The analysis of obtained results leads to idea that mobile phones and devices aimed for children using should be modified to provide SAR values inside prescribed standards.

The obtained results are foundation for future research on influence of EM fields of mobile devices on human health.

The proposed procedure offers the model for accurate estimation and quality analysis of SAR and EM field distribution inside child head tissue.

Cancer is the foremost disease that causes death. The objective of hyperthermia in cancer therapy is to raise the temperature of cancerous tissue above a therapeutic value while maintaining the surrounding normal tissue at sublethal temperature values in cases where surgical intervention is dangerous or impossible. The malignant tissue is heated up to 42°C in the treatment. In this method, the unaffected tissues are aimed to have minimum damage, while the affected ones are destroyed. Therefore, it is very important for the optimization of the method to know the temperature profiles in both tissues. Accurately estimating the tissue temperatures has been a very important issue for tumor hyperthermia treatment planning. This paper, proposes to theoretically predict the temperature response of the biological tissues subject to external EM heating by using the space‐dependent blood perfusion term in Pennes bio‐heat equation.

The bio‐heat transfer equation is parabolic partial differential equation. Grid points including independent variables are initially formed in solution of partial differential equation by finite element method. In this study, one dimensional bio‐heat transfer equation is solved by flex‐PDE finite element method.

In this study, the bio‐heat transfer equation is solved for variable blood perfusion values and the temperature field resulting after a hyperthermia treatment is obtained. Homogeneous, non‐homogeneous tissue and constant, variable blood perfusion rates are considered in this study to display the temperature fields in the biological material exposed to externally induced electromagnetic irradiation.

Temperature‐dependent tissue thermophysical properties have been used and the Pennes equation is solved by FEM analysis. Variable blood perfusion and heat generation values have been used in calculations for healthy tissue and tissue with tumor.

The assessing of the specific absorption rate (SAR) of living organisms or phantoms is difficult to realize and this paper seeks to do this. SAR much more precisely describes the energy absorbed by biological objects than values of electric field strength (E [V/m]) or power density (S [W/m²]) measured at the point of exposition. However, for living objects the assessing of SAR is not an easy task by measuring methods or even in calculation evaluations. Numerical techniques, especially the finite‐difference time‐domain method (FDTD), offer different possibilities of calculations. The important problem with FDTD method introduced to lossy objects with complex shapes is that this method is not verified with the measuring data.

In this work the results of calculations and measuring data of ellipsoidal phantoms filled with specimen of electrical parameters like muscle tissue are presented. The calculations of SAR have been realized for two cases, e.g. for plane wave incident and for waveguide condition. Measurements for verifying the obtained data were done by waveguide method. The comparison of numerical (the package CONCERTO (Vector Fields Ltd)) and measurement methods were done at frequencies 900 and 1,800 MHz.

Calculations of SAR of lossy objects by FDTD method have been confirmed by measurements and analytical method of calculations. This documents that the package CONCERTO (Vector Fields Ltd) (Concerto User Guide) can be used for such calculations.

This paper presents the results of calculations of SAR of ellipsoidal phantoms filled with specimens of electrical parameters of equivalent muscle tissue.

Thermo physiological comfort is an important sportswear criterion in terms of sportsmen's comfort and performance. In this study, heat and mass transfer of active sportswear were evaluated. Heat transmission was measured by thermal resistance; relative water vapour permeability was measured to assess moisture vapour transmission; air permeability was measured to determine air passage; and sweat response was measured by water absorption, specific flow rates and drying time. It was observed that the structural parameters of fabric and the cross-sectional shape of filaments significantly affected the comfort characteristics of knitted active sportswear.

A vertically stacked, three layer hybrid Hilbert fractal geometry and serpentine radiator-based patch antenna is proposed and characterized for medical implant applications at the Industrial, Scientific and Medical band (2.4-2.48 GHz). Antenna parameters are optimised to achieve miniaturized, biocompatible and stable transmission characteristics. The paper aims to discuss these issues.

Human tissue effects on the antenna electrical characteristics were simulated with a three-layer (skin, fat and muscle) human tissue model with the dimensions of 180×70×60 mm3 (width×height×thickness mm3). Different stacked substrates are utilized for the satisfactory characteristics. Two identical radiating patches are printed on Roger 3,010 (ε _r=10.2) and Alumina (ε _r=9.4) substrate materials, respectively. In addition, various superstrate materials are considered and simulated to prevent short circuit the antenna while having a direct contact with the metallization, and achieve biocompatibility. Finally, superstrate material of Zirconia (ε _r=29) is used to achieve biocompatibility and long-life. A finite element method is used to simulate the proposed hybrid model with commercially available Ansoft HFSS software.

The antenna is miniaturized, having dimensions of 10×8.4×2 mm3 (width×height×thickness mm3). The resonance frequency of the antenna is 2.4 GHz with a bandwidth of 100 MHz at return loss (S11) of better than −10 dB characteristics. Overall, the proposed antenna have 50 Ω impedance matching, −21 dB far field antenna gain, single-plane omni-directional radiation pattern properties and incident power of 5.3 mW to adhere Specific Absorption Rate regulation limit.

Vertically stacked three layer hybrid design have miniaturized characteristics, wide bandwidth, biocompatible, and stable characteristics in three layer human tissue model make this antenna suitable for implant biomedical monitor systems. The advanced simulation analysis of the proposed design constitutes the main contribution of the paper.