Specific Absorption Rate Assessment Research Articles

Wearable Antennas for Sensor Networks and IoT Applications: Evaluation of SAR and Biological Effects.

In recent years, there has been a rapid development in the wearable industry. The growing number of wearables has led to the demand for new lightweight, flexible wearable antennas. In order to be applicable in IoT wearable devices, the antennas must meet certain electrical, mechanical, manufacturing, and safety requirements (e.g., specific absorption rate (SAR) below worldwide limits). However, the assessment of SAR does not provide information on the mechanisms of interaction between low-intensity electromagnetic fields emitted by wearable antennas and the human body. In this paper, we presented a detailed investigation of the SAR induced in erythrocyte suspensions from a fully textile wearable antenna at realistic (net input power 6.3 mW) and conservative (net input power 450 mW) conditions at 2.41 GHz, as well as results from in vitro experiments on the stability of human erythrocyte membranes at both exposure conditions. The detailed investigation showed that the 1 g average SARs were 0.5758 W/kg and 41.13 W/kg, respectively. Results from the in vitro experiments demonstrated that the short-term (20 min) irradiation of erythrocyte membranes in the reactive near-field of the wearable antenna at 6.3 mW input power had a stabilizing effect. Long-term exposure (120 min) had a destabilizing effect on the erythrocyte membrane.

Specific absorption rate assessment of fifth generation mobile phones with specific anthropomorphic mannequin model and high‐resolution anatomical head model

With the spread and application of the fifth generation (5G) of mobile communication technology, the number of 5G mobile phone users increase rapidly. The traditional safety standard of electromagnetic radiation of mobile phones was set two decades ago, in which a homogeneous specific anthropomorphic mannequin (SAM) head model with standardized size and shape is utilized for specific absorption rate (SAR) evaluation. The SAM model has been proved conservative for SAR evaluation of 2G, 3G and 4G mobile phone antennas. However, it needs to be validated whether it is still suitable for SAR evaluation of 5G mobile phone antennas. A high-resolution anatomical head model with tissues including muscle, skull, cerebrospinal fluid and brain is developed in this paper. The SAR values of three different generation mobile phone antennas are simulated by utilizing both the SAM model and the high-resolution anatomical head model to assess their applicability. Numerical simulations show that the anatomical model may produce a higher SAR value than the SAM model for a 5G mobile phone antenna. So new head model may need to be developed for the SAR evaluation of 5G mobile phone antennas.

Design and SAR assessment of three compact 5G antenna arrays

In this paper three different multi stub antenna arrays at 27–29.5 GHz are designed. The proposed antenna arrays consist of eight single elements. The structure of feeding parts is the same but the radiation elements are different. The feeding network for array is an eight way Wilkinson power divider (WPD). To guarantee the simulation results, one of the proposed structures is fabricated and measured (namely the characteristics of S11, E-, and H-plane patterns) which shows acceptable consistency with measurement results. The simulation results by CST and HFSS show reasonable agreement for reflection coefficient and radiation patterns in the E- and H- planes. The overall size of the proposed antenna in maximum case is 29.5 mm × 52 mm × 0.38 mm (2.8 {{varvec{lambda}}}_{0}× 4.86{{varvec{lambda}}}_{0} × 0.036{{varvec{lambda}}}_{0}). Moreover, for Specific Absorption Rate (SAR) estimation, a three-layer spherical human head model (skin, skull, and the brain) is placed next to the arrays as the exposure source. The simulation results show that the performance of proposed antennas as low-SAR sources makes them ideal candidates for the safe usage and lack of impact of millimeter waves (mmW) on the human health. In all three cases of SAR simulations the value of SAR1g and SAR10g are below the standard limitations.

Integrated Miniature Multiband Antenna Designed for WWD and SAR Assessment for Human Exposure

The article introduces a new, low-cost, integrated, multiband antenna design intended for wristbands and wearable wireless devices (WWD). With a miniaturized planar square-shape sizing 29 × 29 mm2, the antenna can fit easily inside WWDs. The proposed design covers the most used frequency bands such as LTE2300, ISM2400, LTE2600, WiMAX3500, WiMAX5200, and ISM5800 in which the antenna reaches up to −25 dB and 6.9 dBi in terms of S11 and gain, respectively. To evaluate the exposure amenability of design on human body, we studied the specific absorption rate (SAR) of the design in two main use cases: multilayered human wrist model and a SAM (Specific Anthropomorphic Mannequin) head model. In each use case, the SAR results in different positions for all frequencies are compared to FCC standards.

Design of a compact, wideband, and flexible rhombic antenna using CMA for WBAN/WLAN and 5G applications

AbstractThe design of a compact, wideband flexible monopole antenna printed on a flexible Kapton polyimide substrate is presented. The proposed antenna consists of two rhombic elements embedded within a square plane as the radiating element. The wide bandwidth is aimed at alleviating potential performance degradations due to its application in an on‐body environment. The proposed antenna is designed using two main methods: the method of moments with adaptive cross approximation, and the characteristic mode analysis. The antenna operates from 2.038 to 3.745 GHz, indicating a bandwidth of 1.707 GHz (59.03%). Two dominant resonant frequencies are observed at 2.45 and 3.42 GHz, with realized gain of 3 and 5 dBi, and radiation efficiency of 90% and 83%, respectively. Besides that, the genetic algorithm and particle swarm optimization techniques are used to optimize the antenna and its performance validated via measurements. Besides, in free space, its on‐body performance when placed in proximity of a human body phantom is evaluated. Finally, specific absorption rate assessment is performed to ensure the safety of the proposed antenna when operating on human. Results indicate the antenna's suitability for wearable applications to support different wireless standards.

Microdosimetry Using Rhodamine B Within Macro- and Microsystems for Radiofrequency Signals Exposures of Biological Samples

Exposing living cells to a certain level of electromagnetic field (EMF) might induce some biological effects including temperature elevation. In this article, we studied two exposure systems at the macro and microscopic levels, allowing the study of the EMF effect on the biological samples exposed to 1.8-GHz signals. The macrosystem was an open transverse electromagnetic (TEM) cell that served as a dosimetry reference for defining limitations and optimal conditions for the temperature calibration using Rhodamine B (RhodB). The microfluidic microsystem was based on the coplanar waveguide (CPW) electrodes. Temperature measurements are carried out with a fluorooptic probe to extract specific absorption rate (SAR) values that are compared with numerical dosimetry, based on an FDTD method. After calibration, the fluorescence fits well with the temperature variation measured by the probe. To investigate dosimetry at a microscopic level, the fluorescence of the temperature-dependent dye RhodB was measured by fluorescence microscopy within the microfluidic channel or the biological cells. Results evidenced that the technique is applicable for RhodB concentrations higher than 1 μm with a value of 50 μm recommended for reliable experiments. For steady detection and SAR assessments, temperature variations of a few tenths of degrees were required.

Proficiency Testing for Complex Permittivity Measurements of Tissue Equivalent Liquid Used in SAR Assessment

Tissue equivalent liquid plays an important role in specific absorption rate (SAR) assessment. Proficiency tests (PTs) through interlaboratory comparison of dielectric parameters (i.e., dielectric constant and the electrical conductivity of the tissue equivalent liquid) were conducted in 2017 and 2019. We coordinated the PTs performed with traveling samples circulating among the participating laboratories. As one of the most crucial issues in the PT schemes, these samples are described comprehensively, including the realization, the assignment of reference values, and the verification of homogeneity and stability. Fifteen and eleven laboratories participated in the PTs in 2017 and 2019, respectively. In total, 74 measurement results were provided in terms of best estimate and uncertainty. This paper presents and evaluates the performance of all the participating laboratories. Additionally, the measurement results are grouped in terms of the types of measurement probes. The analysis indicates that the measurement results obtained from two most widely used types of probes are compatible.

Global head SAR assessment of MRI-induced temperature change

Purpose: Underestimation of SAR (Specific Absorption Rate) in MRI poses potential risks to patients and in particular individuals with compromised thermoregulation. EU standards imposes a head SAR limit of 3.2 W/kg as SAR effects are negligible at up to 3 W/kg. We developed a phantom and protocol where heating due the RF pulse is measured and verified against scanner displayed SAR.

A deep learning method for image-based subject-specific local SAR assessment.

PurposeLocal specific absorption rate (SAR) cannot be measured and is usually evaluated by offline numerical simulations using generic body models that of course will differ from the patient's anatomy. An additional safety margin is needed to include this intersubject variability. In this work, we present a deep learning–based method for image‐based subject‐specific local SAR assessment. We propose to train a convolutional neural network to learn a “surrogate SAR model” to map the relation between subject‐specific B1+ maps and the corresponding local SAR.MethodOur database of 23 subject‐specific models with an 8–transmit channel body array for prostate imaging at 7 T was used to build 5750 training samples. These synthetic complex B1+ maps and local SAR distributions were used to train a conditional generative adversarial network. Extra penalization for local SAR underestimation errors was included in the loss function. In silico and in vivo validation were performed.ResultsIn silico cross‐validation shows a good qualitative and quantitative match between predicted and ground‐truth local SAR distributions. The peak local SAR estimation error distribution shows a mean overestimation error of 15% with 13% probability of underestimation. The higher accuracy of the proposed method allows the use of less conservative safety factors compared with standard procedures. In vivo validation shows that the method is applicable with realistic measurement data with impressively good qualitative and quantitative agreement to simulations.ConclusionThe proposed deep learning method allows online image‐based subject‐specific local SAR assessment. It greatly reduces the uncertainty in current state‐of‐the‐art SAR assessment methods, reducing the time in the examination protocol by almost 25%.

Assessment of SAR in human body model with the cochlear implant inside a railway vehicle

Abstract This article details simulation and analysis of electromagnetic field distribution within a railway vehicle, with special focus on distribution thereof in human body phantom with a cochlear implant. Research was carried out using modelling of electromagnetic fields based on the Finite Integration Method. Simulations were performed and analysed in cases where passengers were exposed to long-term radiofrequency field stemming from the use of mobile phones during railway transport. Results were evaluated based on the specific absorption rate (SAR) – the measure of electromagnetic energy absorption in the body (in watts per kilogram [W/kg]). Dual band (900 and 1800MHz) PIFA antennas were designed and employed as radio frequency sources. The homogeneous passenger model includes a cochlear implant and dielectric properties are set according to the evaluated frequency band. Results have shown that the calculated maximum values of SAR are higher than those established within the European maximum SAR limit and additionally, the obtained values are higher than values obtained in simulation in open space.

Intersubject specific absorption rate variability analysis through construction of 23 realistic body models for prostate imaging at 7T.

For ultrahigh field (UHF) MRI, the expected local specific absorption rate (SAR) distribution is usually calculated by numerical simulations using a limited number of generic body models and adding a safety margin to take into account intersubject variability. Assessment of this variability with a large model database would be desirable. In this study, a procedure to create such a database with accurate subject-specific models is presented. Using 23 models, intersubject variability is investigated for prostate imaging at 7T with an 8-channel fractionated dipole antenna array with 16 receive loops. From Dixon images of a volunteer acquired at 1.5T with a mockup array in place, an accurate dielectric model is built. Following this procedure, 23 subject-specific models for local SAR assessment at 7T were created enabling an extensive analysis of the intersubject B1+ and peak local SAR variability. For the investigated setup, the maximum possible peak local SAR ranges from 2.6 to 4.6 W/kg for 8 × 1 W input power. The expected peak local SAR values represent a Gaussian distribution W/kg) with realistic prostate-shimmed phase settings and a gamma distribution Γ(24,0.09) with multidimensional radiofrequency pulses. Prostate-shimmed phase settings are similar for all models. Using 1 generic phase setting, average B1+ reduction is 7%. Using only 1 model, the required safety margin for intersubject variability is 1.6 to 1.8. The presented procedure allows for the creation of a customized model database. The results provide valuable insights into B1+ and local SAR variability. Recommended power thresholds per channel are 3.1 W with phase shimming on prostate or 2.6 W for multidimensional pulses.

Specific Absorption Rate Assessment of Multiple Microstrip Patch Antenna Array

Interaction between electromagnetic field (EMF) radiated from multiple antennas and human body is crucial to be explored as multiple antennas are the essential implemented devices to achieve the requirements of the future evolved fifth generation (5G) technology. Thus, this article presents a significant study of the radiated EMF effect from a single, and multiple antennas towards human through the assessment of specific absorption rate (SAR). The single antenna, 1 x 2, 1 x 3 and 1 x 4 arrays of microstrip patch antennas are designed to cover mobile operating frequencies of 0.8, 0.85, 0.9, 1.8, 2.1 and 2.6 GHz. Two types of human head phantoms are implemented in this study, which are specific anthropomorphic mannequin (SAM) and Voxel head model that placed close to single antenna or antenna array to investigate the penetration of EMF towards the human tissue. The single antenna or antenna array is placed with fixed distance of 10 mm from the phantom, which excited by maximum allowable power of 19 dBm in CST Microwave Studio 2016. The effect of the radiated EMF that quantified by SAR parameter, which depicts satisfying results against the established standard limits at averaged 1g and 10g mass of tissues for all designated frequencies that utilized for single and multiple antennas.

Whole-Body Specific Absorption Rate Assessment of Lossy Objects Exposed to a Diffuse Field Inside a Reverberant Environment

In this study, we provide a novel approach for exposure assessment in terms of whole-body average specific absorption rate ( WBSAR ) due to the electromagnetic fields inside reverberant environments. The approach utilizes power balance theory and the lossy object's absorption cross section ( ACS ). We use this to present a noninvasive technique for determining the WBSAR in reflective environments. Measurements were performed inside a reverberation chamber on spherically-shaped phantoms filled with lossy liquids. The approach was verified by performing invasive temperature measurements and showed excellent agreement (within 5%). This approach can be used for human exposure assessment inside reverberant environments since human body ACS has been well studied in the literature. The main advantage of the proposed approach is that it overcomes the need for complex invasive measurements in order to determine WBSAR .

Specific Absorption Rate Assessment on Human Head Due to Radiations by Mobile Phone Antenna

Abstract Development of mobile phone communication infrastructure in the world has promoted which lead public concern over possible health effect exposure to radio frequency electromagnetic energy (RFEME) emanating from mobile phone antenna. The Micro-strip patch antenna plays an important role in electromagnetic energy transmitting and receiving phenomena in mobile phone. This paper makes an effort to assess the mobile radiation exposure effect on 4 years child, 8years child and an adult head model. Hand held device model having micro-strip antenna is used for human interaction. The software simulation performed by Computer simulation technique (CST) software based on Finite difference Time Domain Technique yields specific absorption rate and 3D-thermal distribution on spherical human head.

A New High-Resolution Electromagnetic Human Head Model: A useful resource for a new specific-absorption-rate assessment model

A high-resolution realistic human head model for the human exposure assessment of the specific absorption rate (SAR) is presented in this article. To our best knowledge, this model is the first Chinese electromagnetic (EM) human head model (CMODEL). The model is built using the first Chinese Visible Human (CVH) data set containing 3,640 serial axial anatomical images. In particular, the model has a voxel resolution of 0.16 ? 0.16 ? 0.25 mm3 for the head part and 0.16 ? 0.16 ? 0.5 mm3 for the shoulder part. Such a high-resolution model allows for an accurate simulation of 49 different tissues and organs for the SAR assessment. A numerical investigation concerning the detailed SAR distribution of the standard specific anthropomorphic mannequin (SAM) model, the popular but low-resolution HUGO model, and this CMODEL is conducted and involves exposing the three models to radiation from the same dual-band antenna, and this investigation demonstrates the usefulness of a high-resolution EM human head model. For the sake of comparison, the eye models that are extracted from the CMODEL and HUGO models, which are illuminated by a one-half wavelength dipole antenna, are employed to demonstrate the advantage of the CMODEL for the SAR assessment.

B1-based SAR reconstruction using contrast source inversion\u2013electric properties tomography (CSI-EPT)

Specific absorption rate (SAR) assessment is essential for safety purposes during MR acquisition. Online SAR assessment is not trivial and requires, in addition, knowledge of the electric tissue properties and the electric fields in the human anatomy. In this study, the potential of the recently developed CSI-EPT method to reconstruct SAR distributions is investigated. This method is based on integral representations for the electromagnetic field and attempts to reconstruct the tissue parameters and the electric field strength based on B_{1}^{ + } field data only. Full three-dimensional FDTD simulations using a female pelvis model are used to validate two-dimensional CSI reconstruction results in the central transverse plane of a 3T body coil. Numerical experiments demonstrate that the reconstructed SAR distributions are in good agreement with the SAR distributions as determined via 3D FDTD simulations and show that these distributions can be computed very efficiently in the central transverse plane of a body coil with the two-dimensional approach of CSI-EPT.

In vivo electric conductivity of cervical cancer patients based on maps at 3T MRI

The in vivo electric conductivity (σ) values of tissue are essential for accurate electromagnetic simulations and specific absorption rate (SAR) assessment for applications such as thermal dose computations in hyperthermia. Currently used σ-values are mostly based on ex vivo measurements. In this study the conductivity of human muscle, bladder content and cervical tumors is acquired non-invasively in vivo using MRI.The conductivity of 20 cervical cancer patients was measured with the MR-based electric properties tomography method on a standard 3T MRI system.The average in vivo σ-value of muscle is 14% higher than currently used in human simulation models. The σ-value of bladder content is an order of magnitude higher than the value for bladder wall tissue that is used for the complete bladder in many models. Our findings are confirmed by various in vivo animal studies from the literature. In cervical tumors, the observed average conductivity was 13% higher than the literature value reported for cervical tissue.Considerable deviations were found for the electrical conductivity observed in this study and the commonly used values for SAR assessment, emphasizing the importance of acquiring in vivo conductivity for more accurate SAR assessment in various applications.

Experimental Assessment of Specific Absorption Rate Using Measured Electric Field Strength in Benson Idahosa University and Environs

There has been growing concern in Nigeria and even the world at large that exposure to radiation from base stations and mobile handsets could lead to increased risk of illnesses such as cancer and may adversely affect cognitive functions like concentration and may cause memory loss, headaches, dizziness and epilepsy among others. In the present paper, the Assessment of RF radiation in the far-field from selected mobile base station sites in BIU and environs, Benin City, Nigeria has been carried out using a handheld three-axis radio frequency meter (EMF meter) for measurement of Electric field. The meter is a broad band device for monitoring high frequency radiation in range of 50 MHz to 3.6GHz. It is used in three-axis (isotropic) measurement mode. The electric field strength of RF radiation within a radial distance of the range 0- 100m was measured with the RF meter. The average values of the Specific absorption rate (SAR) for the general public was estimated from the measured electric field strength and the values gotten were compared with International commission on Non-ionizing radiation. Results shows that the values of the SAR for the eighth base stations selected for the study are within the range of 0.00010W/Kg- 0.0012W/Kg. These values are quite lower than the limit by International Commission on Non –ionizing Radiation Protection (ICNIRP) which is 0.08W/Kg for the whole body average SAR. This may indicate that there is no significant health risk for the general public that are always the vicinity of the Far field of the selected base stations for the various mobile service provider the area.

Radio frequency electromagnetic field compliance assessment of multi‐band and MIMO equipped radio base stations

In this paper, different methods for practical numerical radio frequency exposure compliance assessments of radio base station products were investigated. Both multi-band base station antennas and antennas designed for multiple input multiple output (MIMO) transmission schemes were considered. For the multi-band case, various standardized assessment methods were evaluated in terms of resulting compliance distance with respect to the reference levels and basic restrictions of the International Commission on Non-Ionizing Radiation Protection. Both single frequency and multiple frequency (cumulative) compliance distances were determined using numerical simulations for a mobile communication base station antenna transmitting in four frequency bands between 800 and 2600 MHz. The assessments were conducted in terms of root-mean-squared electromagnetic fields, whole-body averaged specific absorption rate (SAR) and peak 10 g averaged SAR. In general, assessments based on peak field strengths were found to be less computationally intensive, but lead to larger compliance distances than spatial averaging of electromagnetic fields used in combination with localized SAR assessments. For adult exposure, the results indicated that even shorter compliance distances were obtained by using assessments based on localized and whole-body SAR. Numerical simulations, using base station products employing MIMO transmission schemes, were performed as well and were in agreement with reference measurements. The applicability of various field combination methods for correlated exposure was investigated, and best estimate methods were proposed. Our results showed that field combining methods generally considered as conservative could be used to efficiently assess compliance boundary dimensions of single- and dual-polarized multicolumn base station antennas with only minor increases in compliance distances.

Multi-sensors SAR system for real-time dosimetry assessment

A multi-sensors test-bench for determining the SAR (Specific Absorption Rate) due to wireless devices emitting in equivalent human tissues is presented. Real-time SAR assessment is proposed considering a spatially distribued multi-probes test-bench. In comparison with a multi-axial robot SAR system, the proposed one does not require any displacement, thus reducing drastically acquisition time, once parallel data acquisition and interpolation techniques are employed for accelerating measurement.