Specific Absorption Rate Analysis Research Articles

Specific Absorption Rate Analysis of Aperture Coupled Antenna for Wireless Body Area Network Applications

Objective: This work presents the design and analysis of miniaturized aperture coupled antenna. The proposed antenna is designed to operate at 2.45GHz of Industrial Scientific Medical (ISM) band and intended to use for Wireless Body Area Network Applications (WBAN). Methods/Statistical analysis: The H shaped patch with aperture coupled feeding is incorporated to get symmetrical radiation pattern. By adjusting the dimensions of ground plane notch and feed line the miniaturization and desired operating frequency is achieved. The antenna’s performance is simulated at the vicinity of human arm biological tissue model to measure Specific Absorption Rate (SAR). Findings: The proposed antenna has compact form factor of 0.32λo x 0.3λo x 0.021λo. The electromagnetic numerical simulation software shows the SAR of 2.71 W/Kg. The antenna’s performance in terms of bandwidth, gain, radiation pattern is found invariable in presence of human arm tissue model. Application/Improvements: The result shows the proposed antenna possesses low SAR and small compact form factor which can be applicable for WBAN applications.

Temperature distribution and Specific Absorption Rate inside a child’s head

This paper represents the numerical analysis of Specific Absorption Rate (SAR) and temperature distribution within a real child head model exposed to mobile phone radiation at the frequency of f=900MHz. In this research the SAR and temperature distribution are obtained by numerical solutions of the equation of electromagnetic waves propagation and by bioheat equation, respectively, and are shown inside different biological tissues and organs during exposure to electromagnetic radiation from a mobile phone. As electromagnetic properties of tissues depend on the electromagnetic waves frequency, the value of SAR and temperature will be different for different tissues and organs. The maximum absorption of electromagnetic energy is in the surface layers of the model, whereby this value is greater than the maximum allowed value defined by standards. Furthermore, the increase in temperature is the highest in those biological tissues and organs that are closest to the source of radiation i.e. a mobile phone. Moving away from a mobile phone, the temperature decreases, but more slowly than the SAR values. In the analysis of the temperature rise resulting from tissues and organs heating due to the effects of electromagnetic fields on a child’s head, special attention will be given to the maximum temperature increase in the brain.

Preliminary imaging results and SAR analysis of a microwave imaging system for early breast cancer detection.

Currently X-ray-based imaging systems suffer from low contrast between malignant and healthy fibrous tissues in breast. Microwave Near-field Radar Imaging (NRI) shows a higher contrast between the aforementioned tissues and therefore can enhance tumor detection and diagnosis accuracy. In this work, we present the first imaging results of our developed NRI system that is equipped with a pair of Antipodal Vivaldi Antennas. We used a metal bearing ball immersed in oil as our object of interest, to keep the first measurement configuration simple. Moreover, to demonstrate the safety of our system for human subject tests, we simulated the Specific Absorption Rate (SAR) in a realistic breast tissue model and compared the resulted values with both the USA and Europe standards. The results show that firstly the imaging results from the measurements and simulations are comparable, and secondly the antennas radiations meet the SAR criteria.

A compact TRM antenna with high impedance surface for SAR reduction at 1800 MHz

In this paper, a compact tapered ring monopole (TRM) antenna with high impedance surface (HIS) is reported. This antenna is characterized by improved gain and reduced back lobe radiation. This provides specific absorption rate (SAR) reduction on human tissues, when used in a mobile phone. The reflection phase property of the HIS is used to increase the radiated field towards the antenna, thus providing a good return loss with 21% impedance bandwidth, 7.4dBi gain and front to back ratio of 21dB. In contrast to the already reported HIS ground planes, the proposed structure has a simple design methodology with compact form factor of 0.52λ×0.52λ×0.026λ at 1.8GHz. The antenna prototype was fabricated and measurements were carried out. Further, numerical simulations were performed for SAR and thermal analysis. It is observed that SAR and consequent temperature rise in human tissues are greatly reduced, when HIS is added to the TRMA.

Specific absorption rate analysis of broadband mobile antenna with negative index metamaterial

This paper presents a negative index metamaterial-inspired printed mobile wireless antenna that can support most mobile applications such as GSM, UMTS, Bluetooth and WLAN frequency bands. The antenna consists of a semi-circular patch, a 50Ω microstrip feed line and metamaterial ground plane. The antenna occupies a very small space of 37 × 47 × 0.508 mm3, making it suitable for mobile wireless application. The perceptible novelty shown in this proposed antenna is that reduction of specific absorption rate using the negative index metamaterial ground plane. The proposed antenna reduced 72.11 and 75.53 % of specific absorption rate at 1.8 and 2.4 GHz, respectively.

Investigation of maximum local specific absorption rate in 7 T magnetic resonance with respect to load size by use of electromagnetic simulations.

Local specific absorption rate (SAR) evaluation in ultra high field (UHF) magnetic resonance (MR) systems is a major concern. In fact, at UHF, radiofrequency (RF) field inhomogeneity generates hot-spots that could cause localized tissue heating. Unfortunately, local SAR measurements are not available in present MR systems; thus, electromagnetic simulations must be performed for RF fields and SAR analysis. In this study, we used three-dimensional full-wave numerical electromagnetic simulations to investigate the dependence of local SAR at 7.0 T with respect to subject size in two different scenarios: surface coil loaded by adult and child calves and quadrature volume coil loaded by adult and child heads. In the surface coil scenario, maximum local SAR decreased with decreasing load size, provided that the RF magnetic fields for the different load sizes were scaled to achieve the same slice average value. On the contrary, in the volume coil scenario, maximum local SAR was up to 15% higher in children than in adults.

Numerical analysis of specific absorption rate in the human head due to a 13.56 MHz RFID-based intra-ocular pressure measurement system

A modern wireless intra-ocular pressure monitoring system, based on 13.56 MHz inductively coupled data transmission, was dosimetrically analyzed with respect to the specific absorption rate (SAR) induced inside the head and the eye due to the electromagnetic field exposure caused by the reader antenna of the transmission system. The analysis was based on numerical finite difference time domain computations using a high resolution anatomical eye model integrated in a modern commercially available anatomical model of a male head. Three different reader antenna configurations, a 7-turn elliptic (30 mm × 50 mm) antenna at 12 mm distance from the eye, a flexible circular antenna (60 mm diameter, 8 turns on 2 mm substrate) directly attached to the skin, and a circular 7-turn antenna (30 mm diameter at 12 mm distance to the eye) were analyzed, respectively. Possible influences of the eye-lid status (closed or opened) and the transponder antenna contained in a contact lens directly attached to the eye were taken into account. The results clearly demonstrated that for typical reader antenna currents required for proper data transmission, the SAR values remain far below the limits for localized exposure of the head, as defined by the International Commission for Non-Ionizing Radiation Protection. Particularly the induced SAR inside the eye was found to be substantially (orders of magnitudes for typical reader antenna currents in the order of 1 A turn) below values which have been reported to be critical with respect to thermally induced adverse health effects in eye tissues.

Performance and Validation of a Broadband- Multigeneration Exposure System for Unconstrained Rats

In view of actual electromagnetic environment of multiple-frequency exposure, we have developed a whole-body exposure system for a multigeneration bio-effect test with rats at frequencies between 800 MHz and 5.2 GHz. We first experimentally evaluated the system performances such as antenna performance, electric field distribution, and specific absorption rate (SAR) in the exposure system. Then, after an experimental validation of the finite-difference time-domain modeling of the exposure system, we employed it to make a statistical SAR analysis for anatomical rat models. We first took documentary photographs of rat activity inside the exposure system every 5 min in real time. Then, by identifying the rat positions in each photograph, we derived the frequency of rats staying in various positions in the exposure system. Using the stay frequency as a weighting factor, we derived the whole-body average SAR statistical characteristics for the multiple-frequency exposure system during the entire multigeneration experimental period. The developed system and demonstrated approach provide a high-quality means for biological effect test of radio frequency exposure in wide frequency bands.

Numerical Analysis of Specific Absorption Rate and Heat Transfer in Human Head Subjected to Mobile Phone Radiation: Effects of User Age and Radiated Power

The human head is one of the most sensitive parts of the human entire body when exposed to electromagnetic radiation. This electromagnetic radiation interacts with the human head and may lead to detrimental effects on human health. However, the resulting thermophysiologic response of the human head is not well understood. In order to gain insight into the phenomena occurring within the human head with temperature distribution induced by electromagnetic field, a detailed knowledge of absorbed power distribution as well as temperature distribution is necessary. This study presents a numerical analysis of specific absorption rate and heat transfer in the heterogeneous human head model exposed to mobile phone radiation. In the heterogeneous human head model, the effects of user age and radiated power on distributions of specific absorption rate and temperature profile within the human head are systematically investigated. This study focuses attention on organs in the human head in order to investigate the effects of mobile phone radiation on the human head. The specific absorption rate and the temperature distribution obtained by numerical solution of electromagnetic wave propagation and unsteady bioheat transfer equation in various tissues in the human head during exposure to mobile phone radiation are presented.

Specific Absorption Rate and Temperature Increase in Human Eye Subjected to Electromagnetic Fields at 900 MHz

Human eye is one of the most sensitive parts of the entire human body when exposed to electromagnetic fields. These electromagnetic fields interact with the human eye and may lead to cause a variety of ocular effects from high intensity radiation. However, the resulting thermo-physiologic response of the human eye to electromagnetic fields is not well understood. In order to gain insight into the phenomena occurring within the human eye with temperature distribution induced by electromagnetic fields, a detailed knowledge of absorbed power distribution as well as temperature distribution is necessary. This study presents a numerical analysis of specific absorption rate (SAR) and heat transfer in the heterogeneous human eye model exposed to electromagnetic fields. In the heterogeneous human eye model, the effect of power density on specific absorption rate and temperature distribution within the human eye is systematically investigated. In particular, the results calculated from a developed heat transfer model, considered natural convection and porous media theory, are compared with the results obtained from a conventional heat transfer model (based on conduction heat transfer). In all cases, the temperatures obtained from the developed heat transfer model have a lower temperature gradient than that of the conventional heat transfer model. The specific absorption rate and the temperature distribution in various parts of the human eye during exposure to electromagnetic fields at 900 MHz, obtained by numerical solution of electromagnetic wave propagation and heat transfer equation, are also presented. The results show that the developed heat transfer model, which is the more accurate way to determine the temperature increase in the human eye due to electromagnetic energy absorption from electromagnetic field exposure.

Specific absorption rate and temperature distributions in human head subjected to mobile phone radiation at different frequencies

This study presents a numerical analysis of specific absorption rate (SAR) and temperature distributions in the realistic human head model exposed to mobile phone radiation at 900 MHz and 1800 MHz. In the realistic human head model, the effects of operating frequency and gap distance between the mobile phone and the human head on distributions of specific absorption rate and temperature profile within the human head are systematically investigated. This study focuses attention on each tissue in the human head in order to investigate the effects of mobile phone radiation on the human head. The SAR and the temperature distribution in various tissues in human head during exposed to mobile phone radiation, obtained by numerical solution of electromagnetic wave propagation and unsteady bioheat transfer equations, are presented. For both frequencies, the highest SAR values are obtained in the region of the skin near the antenna. It is found that the highest SAR values are 0.823 W/kg and 1.187 W/kg for the frequencies of 900 MHz and 1800 MHz, respectively. The SAR values obtained from this study are well below ICNIRP limit for all cases. In addition, it is found that the temperature distributions are not directly proportional to the local SAR values. Moreover, the experimental validation has been carried out by using the infrared camera in order to complement the simulation results.

Head exposure system for a human provocation study to assess the possible influence of UMTS‐like electromagnetic fields on cerebral blood circulation using near‐infrared imaging

A head exposure setup for efficient and precisely defined exposure of human subjects equipped with a near-infrared imaging (NIRI) sensor is presented. In a partially shielded anechoic chamber the subjects were exposed to Universal Mobile Telecommunications System (UMTS)-like electromagnetic fields (EMF) by using a patch antenna at a distance of 4 cm from the head. The non-contact design of the exposure setup enabled NIRI sensors to easily attach to the head. Moreover, different regions of the head were chosen for localised exposure and simultaneous NIRI investigation. The control software enabled the simple adaptation of the test parameters during exploratory testing as well as the performance of controlled, randomised, crossover and double-blind provocation studies. Four different signals with a carrier frequency of 1900 MHz were chosen for the exposure: a simple continuous wave signal and three different UMTS signals. Furthermore, three exposure doses were available: sham, low (spatial peak specific absorption rate (SAR) = 0.18 W/kg averaged over 10 g) and high (spatial peak SAR = 1.8 W/kg averaged over 10 g). The SAR assessment was performed by measurement and simulation. Direct comparison of measurement and numerical results showed good agreement in terms of spatial peak SAR and SAR distribution. The variability analysis of the spatial peak SAR over 10 g was assessed by numerical simulations. Maximal deviations of -22% and +32% from the nominal situation were observed. Compared to other exposure setups, the present setup allows for low exposure uncertainty, combined with high SAR efficiency, easy access for the NIRI sensor and minimal impairment of test subjects.

Numerical Analysis of Specific Absorption Rate and Heat Transfer in the Human Body Exposed to Leakage Electromagnetic Field at 915 MHz and 2450 MHz

In recent years, society has increased utilization of electromagnetic radiation in various applications. This radiation interacts with the human body and may lead to detrimental effects on human health. However, the resulting thermophysiologic response of the human body is not well understood. In order to gain insight into the phenomena occurring within the human body with temperature distribution induced by electromagnetic field, a detailed knowledge of absorbed power distribution is necessary. In this study, the effects of operating frequency and leakage power density on distributions of specific absorption rate and temperature profile within the human body are systematically investigated. This study focuses attention on organs in the human trunk. The specific absorption rate and the temperature distribution in various tissues, obtained by numerical solution of electromagnetic wave propagation coupled with unsteady bioheat transfer problem, are presented.

Analysis of Specific Absorption Rate and Current Density in Biological Tissues Surrounding Energy Transmission Transformer for an Artificial Heart: Using Magnetic Resonance Imaging-based Human Body Model

The transcutaneous energy transmission system used for artificial hearts is a transmission system that uses electromagnetic induction. Use of the TETS improves quality of life and reduces the risk of infection caused by percutaneous connections. This article reports the changes in the electromagnetic effects of TETS that influence a human body when the locations of the air-core coils of the transcutaneous transformer are changed. The specific absorption rate and current density in a model consisting of a human trunk that included 24 different organs are analyzed using an electromagnetic simulator. The air-core coils are located on the pectoralis major muscle near the collarbone in model 1, whereas they are located on the axillary region of the serratus anterior muscle, which overlies the rib in model 2. The maximum current densities in models 1 and 2 are 5.2 A/m(2) and 6.1 A/m(2), respectively. The current density observed in model 2 slightly exceeds the limiting value prescribed by International Commission on Non-Ionizing Radiation Protection (ICNIRP). When the volumes of biological tissues whose current densities exceed the limiting value of current density for general public exposure are compared, the volume in model 2 (156.1 cm(3)) is found to be larger than that in model 1 (93.7 cm(3)). Hence, it is speculated that the presence of the ribs caused an increase in the current density. Therefore, it is concluded that model 1 satisfies the ICNIRP standards.

In vivo13C magnetic resonance spectroscopy of human brain on a clinical 3 T scanner using [2‐13C]glucose infusion and low‐power stochastic decoupling

This study presents the detection of [2-(13)C]glucose metabolism in the carboxylic/amide region in the human brain, and demonstrates that the cerebral metabolism of [2-(13)C]glucose can be studied in human subjects in the presence of severe hardware constraints of widely available 3 T clinical scanners and with low-power stochastic decoupling. In the carboxylic/amide region of human brain, the primary products of (13)C label incorporation from [2-(13)C]glucose into glutamate, glutamine, aspartate, gamma-aminobutyric acid, and N-acetylaspartate were detected. Unlike the commonly used alkanyl region where lipid signals spread over a broad frequency range, the carboxylic carbon signal of lipids was found to be confined to a narrow range centered at 172.5 ppm and present no spectral interference in the absence of lipid suppression. Comparison using phantoms shows that stochastic decoupling is far superior to the commonly used WALTZ sequence at very low decoupling power at 3 T. It was found that glutamine C1 and C5 can be decoupled using stochastic decoupling at 2.2 W, although glutamine protons span a frequency range of approximately 700 Hz. Detailed specific absorption rate analysis was also performed using finite difference time domain numerical simulation.

SA and SAR Analysis for Wearable UWB Body Area Applications

With the rapid progress of electronic and information technology, an expectation for the realization of body area network (BAN) by means of ultra wide band (UWB) techniques has risen. Although the signal from a single UWB device is very low, the energy absorption may increase significantly when many UWB devices are simultaneously adorned to a human body. An analysis method is therefore required from the point of view of biological safety evaluation. In this study, two approaches, one is in the time domain and the other is in the frequency domain, are proposed for the specific energy absorption (SA) and the specific absorption rate (SAR) calculation. It is shown that the two approaches have the same accuracy but the time-domain approach is more straightforward in the numerical analysis. By using the time-domain approach, SA and SAR calculation results are given for multiple UWB pulse exposure to an anatomical human body model under the Federal Communications Commission (FCC) UWB limit.

Numerical specific absorption rate analysis and measurement of a small indoor base station antenna

AbstractA comparison of different compliance rules for a small indoor base station antenna is presented at frequencies 1800, 2140, and 2450 MHz using a computational model. The numerical model of the antenna is validated using measurements of free space electric field values in close proximity of the antenna and specific absorption rate in a flat liquid phantom. Losses of the antenna are approximated using the measured radiation efficiency as a scaling factor between the input and output power of the antenna. The compliance distances are then computed using the reference levels for field values and equivalent power density. Obtained values are compared to the basic restriction limit in the upper torso of an anatomically realistic numerical model of a human body. The results show that in this case the reference level of maximum value of equivalent power density gives conservative compliance distances. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2516–2521, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23726

Energy Transmission Transformer for a Wireless Capsule Endoscope: Analysis of Specific Absorption Rate and Current Density in Biological Tissue

This paper reports on the electromagnetic influences on the analysis of biological tissue surrounding a prototype energy transmission system for a wireless capsule endoscope. Specific absorption rate (SAR) and current density were analyzed by electromagnetic simulator in a model consisting of primary coil and a human trunk including the skin, fat, muscle, small intestine, backbone, and blood. First, electric and magnetic strength in the same conditions as the analytical model were measured and compared to the analytical values to confirm the validity of the analysis. Then, SAR and current density as a function of frequency and output power were analyzed. The validity of the analysis was confirmed by comparing the analytical values with the measured ones. The SAR was below the basic restrictions of the International Commission on Nonionizing Radiation Protection (ICNIRP). At the same time, the results for current density show that the influence on biological tissue was lowest in the 300-400 kHz range, indicating that it was possible to transmit energy safely up to 160 mW. In addition, we confirmed that the current density has decreased by reducing the primary coil's current.

Variability analysis of SAR from 20 MHz to 2.4 GHz for different adult and child models using finite-difference time-domain

This paper deals with the variability of body models used in numerical dosimetry studies. Six adult anthropomorphic voxel models have been collected and used to build 5-, 8- and 12-year-old children using a morphing method respecting anatomical parameters. Finite-difference time-domain calculations of a specific absorption rate (SAR) have been performed for a range of frequencies from 20 MHz to 2.4 GHz for isolated models illuminated by plane waves. A whole-body-averaged SAR is presented as well as the average on specific tissues such as skin, muscles, fat or bones and the average on specific parts of the body such as head, legs, arms or torso. Results point out the variability of adult models. The standard deviation of whole-body-averaged SAR of adult models can reach 40%. All phantoms are exposed to the ICNIRP reference levels. Results show that for adults, compliance with reference levels ensures compliance with basic restrictions, but concerning children models involved in this study, the whole-body-averaged SAR goes over the fundamental safety limits up to 40%.For more information on this article, see medicalphysicsweb.org

Initial Analysis of SAR From a Cell Phone Inside a Vehicle by Numerical Computation

The purpose of this paper is to analyze the influence of the metallic structures of a realistic car body frame on the specific absorption rate (SAR) produced by a cell phone when a complete human body model is placed at different locations inside the vehicle, and to identify the relevant parameters responsible for these changes. The modeling and analysis of the whole system was conducted by means of computer simulations based on the full wave finite-difference time-domain (FDTD) numerical method. The excitation considered was an 835 MHz lambda/2 dipole located as a hands-free communication device or as a hand-held portable system. We compared the SAR at different planes on the human model, placed inside the vehicle with respect to the free space situation. The presence of the car body frame significantly changes the SAR distributions, especially when the dipole is far from the body. Although the results are not conclusive on this point, this change in SAR distribution is not likely to produce an increase above the limits in current guidelines for partial body exposure, but may be significant for whole-body exposure. The most relevant change found was the change in the impedance of the dipole, affecting the radiated power. A complementary result from the electromagnetic computations performed is the change in the electromagnetic field distribution inside a vehicle when human bodies are present. The whole vehicle model has been optimized to provide accurate results for sources placed inside the vehicle, while keeping low requirements for computer storage and simulation time.