Specific Absorption Rate Levels Research Articles

Evaluation of neonatal outcomes according to the specific absorption rate values of phones used during pregnancy.

The aim was to compare neonatal outcomes according to cell phone specific absorption rate (SAR) levels and daily time spent on cell phones by pregnant women. Women who gave birth at Konya City Hospital between September 2020 and February 2021 were included in this retrospective study. Gestational ages, birth weight, birth length, head circumference, sex, 5-minute APGAR scores, neonate postpartum resuscitation requirement, delivery type, the model of phone used by the pregnant women, and the average time spent on the phone during a day were recorded. To determine the relation between the SAR values of the phones used and delivering a small for gestational age (SGA) baby, receiver operating characteristic curve analysis was performed. In total 1495 pregnant women were included. The rate of delivering a SGA fetus was significantly higher in women who used phones with higher SAR values (p=0.001). The cut-off value for the SAR level was 1.23 W/kg with 69.3% sensitivity and 73.0% specificity (area under the curve: 0.685; 95% confidence interval: 0.643-0.726). No correlation was found between time spent on the phone and SGA birth rate. Although both phone SAR values and time spent on the phone were higher in the symmetrical SGA group compared to the asymmetrical SGA group, the difference was not significant (p>0.05). Although the women who had preterm delivery had higher phone SAR values and had spent more time on the phone compared to those who had term deliveries, the difference was again not significant (p>0.05). As the SAR values of cell phones used during pregnancy increased, there was a trend towards delivering a SGA baby.

Local SAR management strategies to use two-channel RF shimming for fetal MRI at 3 T.

This study evaluates the imaging performance of two-channel RF-shimming for fetal MRI at 3 T using four different local specific absorption rate (SAR) management strategies. Due to the ambiguity of safe local SAR levels for fetal MRI, local SAR limits for RF shimming were determined based on either each individual's own SAR levels in standard imaging mode (CP mode) or the maximum SAR level observed across seven pregnant body models in CP mode. Local SAR was constrained either indirectly by further constraining the whole-body SAR (wbSAR) or directly by using subject-specific local SAR models. Each strategy was evaluated by the improvement of the transmit field efficiency (average |B1 + |) and nonuniformity (|B1 + | variation) inside the fetus compared with CP mode for the same wbSAR. Constraining wbSAR when using RF shimming decreases B1 + efficiency inside the fetus compared with CP mode (by 12%-30% on average), making it inefficient for SAR management. Using subject-specific models with SAR limits based on each individual's own CP mode SAR value, B1 + efficiency and nonuniformity are improved on average by 6% and 13% across seven pregnant models. In contrast, using SAR limits based on maximum CP mode SAR values across seven models, B1 + efficiency and nonuniformity are improved by 13% and 25%, compared with the best achievable improvement without SAR constraints: 15% and 26%. Two-channel RF-shimming can safely and significantly improve the transmit field inside the fetus when subject-specific models are used with local SAR limits based on maximum CP mode SAR levels in the pregnant population.

Sex-dependent impact of perinatal 5G electromagnetic field exposure in the adolescent rat behavior.

The fifth generation (5G) network is currently being worldwide spread out, raising questions about the potential impact of this new technology, particularly on immature organisms. The current study aimed to investigate the effects of daily 5G electromagnetic field (EMF) perinatal exposure on the neurodevelopment of rats. The exposure level was set to the limit of whole-body public exposure defined by the International Commission on Non-Ionizing Radiation Protection. The mother rat specific absorption rate (SAR) was 0.07 W/kg for 22 h/day at 3500 MHz continuous wave from gestational day (GD) 8 to post-natal day (PND) 21. Clinical observations were performed on weight, length, sex ratio, number of pups per litter, and number of stillborn in sham and EMF-exposed groups (n = 7). The age of pinna ear detachment, incisor eruption, and eye opening were recorded. Behavior was assessed on righting, gripping, and negative geotaxis reflexes at PND 3 or 7 and on stereotyped and horizontal movements in the open field at PND 43. Our results indicated that both male and female pups showed delayed incisor eruption in the EMF-exposed group compared to the sham group (+ 1 day). Regarding activity in the open field, adolescent females showed less stereotyped movements (- 70%), while adolescent males showed more stereotyped movements (+ 50%) compared to the sham-exposed adolescent rats. Thus, the present study suggested that perinatal exposure to 5G at SAR level below reglementary threshold led to perturbations in the descendants seen in juveniles and adolescents.

Influence of patient head definition on induced E-fields during MR examination.

Radiofrequency (RF) exposure during MR examination is limited by IEC 60601-2-33 to prevent thermal hazards to patients. These limits are also the basis to derive the maximum induced field for the demonstration of MR safety of implants per ISO/TS 10974 (2018). One limit is the head-averaged specific absorption rate (SAR), for which the head extent is defined differently by MR and implant vendors. The purpose of this technical note is to inform MR safety stakeholders on the sensitivity of safety evaluations due to different head extent definitions. RF distributions from the validated MRIxViP exposure libraries of 12 high-resolution human anatomical models were scaled to the normative SAR limits for different definitions of the head extent to compare the corresponding induced SAR and electric (E-)field levels. The definitions of the head extent used by major implant vendors and defined in ISO/TS 10974 (2018) are larger than those introduced in IEC 60601-2-33 (2022), resulting in lower RF head exposure by up to 2.4 dB (factor 1.7). Other proposed definitions of the head result in intermediate values. The different head extents result in different maximum RF exposures affecting the risk assessment by up to a factor of 1.7. The results of this study can be used to estimate the additional uncertainty in safety assessments. Future revisions of MR standards should eliminate this inconsistency.

In vitro exposure of neuronal networks to the 5G-3.5 GHz signal.

The current deployment of the fifth generation (5G) of wireless communications raises new questions about the potential health effects of exposure to radiofrequency (RF) fields. So far, most of the established biological effects of RF have been known to be caused by heating. We previously reported inhibition of the spontaneous electrical activity of neuronal networks in vitro when exposed to 1.8 GHz signals at specific absorption rates (SAR) well above the guidelines. The present study aimed to assess the effects of RF fields at 3.5 GHz, one of the frequencies related to 5G, on neuronal activity in-vitro. Potential differences in the effects elicited by continuous-wave (CW) and 5G-modulated signals were also investigated. Spontaneous activity of neuronal cultures from embryonic cortices was recorded using 60-electrode multi-electrode arrays (MEAs) between 17 and 27 days in vitro. The neuronal cultures were subjected to 15 min RF exposures at SAR of 1, 3, and 28 W/kg. At SAR close to the guidelines (1 and 3 W/kg), we found no conclusive evidence that 3.5 GHz RF exposure impacts the activity of neurons in vitro. On the contrary, CW and 5G-modulated signals elicited a clear decrease in bursting and total firing rates during RF exposure at high SAR levels (28 W/kg). Our experimental findings extend our previous results, showing that RF, at 1.8 to 3.5 GHz, inhibits the electrical activity of neurons in vitro at levels above environmental standards.

The effect of exposure to radiofrequency LTE signal and coexposure to mitomycin-C in Chinese hamster lung fibroblast V79 cells.

This study aims to investigate the cellular effects of radiofrequency exposure, 1950 MHz, long-term evolution (LTE) signal, administered alone and in combination with mitomycin-C (MMC), a well-known cytotoxic agent. Chinese hamster lung fibroblast (V79) cells were exposed/sham exposed in a waveguide-based system under strictly controlled conditions of both electromagnetic and environmental parameters, at specific absorption rate (SAR) of 0.3 and 1.25 W/kg. Chromosomal damage (micronuclei formation), oxidative stress (reactive oxygen species [ROS] formation), and cell cycle progression were analyzed after exposure and coexposure. No differences between exposed samples and sham-controls were detected following radiofrequency exposure alone, for all the experimental conditions tested and biological endpoints investigated. When radiofrequency exposure was followed by MMC treatment, 3 h pre-exposure did not modify MMC-induced micronuclei. Pre-exposure of 20 h at 0.3 W/kg did not modify the number of micronuclei induced by MMC, while 1.25 W/kg resulted in a significant reduction of MMC-induced damage. Absence of effects was also detected when CW was used, at both SAR levels. MMC-induced ROS formation resulted significantly decreased at both SAR levels investigated, while cell proliferation and cell cycle progression were not affected by coexposures. The results here reported provide no evidence of direct effects of 1950 MHz, LTE signal. Moreover, they further support our previous findings on the capability of radiofrequency pre-exposure to induce protection from a subsequent toxic treatment, and the key role of the modulated signals and the experimental conditions adopted in eliciting the effect.

Deep learning-based local SAR prediction using B1 maps and structural MRI of the head for parallel transmission at 7 T.

To predict subject-specific local specific absorption rate (SAR) distributions of the human head for parallel transmission (pTx) systems at 7 T. Electromagnetic energy deposition in tissues is nonuniform at 7 T, and interference patterns due to individual channels of pTx systems may result in increased local SAR values, which can only be estimated with very high safety margins. We proposed, designed, and demonstrated a multichannel 3D convolutional neural network (CNN) architecture to predict local SAR maps as well as peak-spatial SAR (ps-SAR) levels. We hypothesized that utilizing a three-channel 3D CNN, in which each channel is fed by a map, a phase-reversed map, and an MR image, would improve prediction accuracies and decrease uncertainties in the predictions. We generated 10 new head-neck body models, along with 389 3D pTx MRI data having different RF shim settings, with their B1 and local SAR maps to support efforts in this field. The proposed three-channel 3D CNN predicted ps-SAR10g levels with an average overestimation error of 20%, which was better than the virtual observation points-based estimation error (i.e., 152% average overestimation). The proposed method decreased prediction uncertainties over 20% (i.e., 22.5%-17.7%) compared to other methods. A safety factor of 1.20 would be enough to avoid underestimations for the dataset generated in this work. Multichannel 3D CNN networks can be promising in predicting local SAR values and perform predictions within a second, making them clinically useful as an alternative to virtual observation points-based methods.

A monopole antenna with cotton fabric material for wearable applications

A monopole antenna operated at 2.45 GHz and embedded with artificial magnetic conductor (AMC) for wearable communication systems is investigated in this article. The proposed antenna is composed of a metalized loop radiator with a coplanar waveguide microstrip feedline which is affixed on a cotton fabric material substrate. As well, a cotton-based AMC surface is utilized to eliminate the body’s absorbed radiation and enhance the gain of the antenna. It is composed of 5 × 5 array unit cells etched with I-shaped slots. Using this configuration, simulations show that the specific absorption rate (SAR) level was significantly reduced. Considering flat and rounded body parts, it was found that the SAR values averaged over 10 g at a distance of 1 mm away from the tissues model were only 0.18 W/kg and 0.371 W/kg, respectively. Additionally, the antenna gain was improved up to 7.2 dBi with an average radiation efficiency of 72%. Detailed analysis with experimental measurements of the cotton-based antenna for different operation scenarios is introduced. The measured data show a good correlation with the electromagnetic simulation results.

Embroidered Annular Elliptical E-Textile Antenna Sensor for Knee Effusion Diagnosis

This article presents the design of a wearable textile antenna sensor for knee effusion diagnosis application. According to human anatomy, effusion is the collection of synovial fluid in a specific anatomic space. Knee effusion, often known as water on the knee, is a condition in which excess fluid collects around the knee joint. The antenna sensing patch region is embroidered using an automated computerized embroidery machine, while the design parameters were optimized using machine learning (ML) algorithms, including deep neural network (DNN). For the best fit on a knee joint, an annular elliptical structure of electronic textile (E-textile) antenna sensor is developed. Pure silver-coated highly conductive thread with improved flexibility is used for embroidering the patchwork in order to enhance the feasibility of the proposed device. The fabricated antenna sensor has the operating resonance frequency at 2.19 GHz and performs diagnosis based on the concept of reflection coefficient parameter. Furthermore, the specific absorption rate (SAR) level of a proposed sensor device is being evaluated on the knee joint and has been kept below the safety limit value of 1.6 W/kg averaged over 1 g of tissue model.

Synthesis, structure, hyperthermia behavior and magnetic properties of Mn–Zn particles prepared by a new method of ball-milling and heating

This paper has focused upon the synthesis, structure, hyperthermia and magnetic properties of the Mn–Zn particles prepared by a new combined ball milling and heating process. Normally, it is required that the partial pressure in the final sintering be controlled by the Mn–Zn ferrite preparation, yet in the current method the ferrite has been obtained with a nearly high purity. The nanocrystalline Mn1-xZnxFe2O4 (x = 0.25, 0.5 and 0.75) powders were characterized using the X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), Raman spectrometer (RS), Fourier-transform infrared spectrometer (FTIR), vibrating sample magnetometer (VSM) and specific absorption rate (SAR). The FTIR and Raman data confirmed the result of the XRD data and the presence of spinel structure. The zinc content affected the band lengths, cation distributions and particle sizes. The structural results revealed that as the Zn concentration increases, the particle size decreases and the other cations tend to go to the octahedral sites. The results demonstrated that the highest level of SAR corresponds to the efficient and non-toxic Mn0.75Zn0.25Fe2O4 due to the suitable particle size and noticeable saturation magnetization.

The HL-60 human promyelocytic cell line constitutes an effective in vitro model for evaluating toxicity, oxidative stress and necrosis/apoptosis after exposure to black carbon particles and 2.45 GHz radio frequency

The cellular and molecular mechanisms by which atmospheric pollution from particulate matter and/or electromagnetic fields (EMFs) may prove harmful to human health have not been extensively researched. We analyzed whether the combined action of EMFs and black carbon (BC) particles induced cell damage and a pro-apoptotic response in the HL-60 promyelocytic cell line when exposed to 2.45 GHz radio frequency (RF) radiation in a gigahertz transverse electromagnetic (GTEM) chamber at sub-thermal specific absorption rate (SAR) levels. RF and BC induced moderately significant levels of cell damage in the first 8 or 24 h for all exposure times/doses and much greater damage after 48 h irradiation and the higher dose of BC. We observed a clear antiproliferative effect that increased with RF exposure time and BC dose. Oxidative stress or ROS production increased with time (24 or 48 h of radiation), BC dose and the combination of both. Significant differences between the proportion of damaged and healthy cells were observed in all groups. Both radiation and BC participated separately and jointly in triggering necrosis and apoptosis in a programmed way. Oxidative-antioxidant action activated mitochondrial anti-apoptotic BCL2a gene expression after 24 h irradiation and exposure to BC. After irradiation of the cells for 48 h, expression of FASR cell death receptors was activated, precipitating the onset of pro-apoptotic phenomena and expression and intracellular activity of caspase-3 in the mitochondrial pathways, all of which can lead to cell death. Our results indicate that the interaction between BC and RF modifies the immune response in the human promyelocytic cell line and that these cells had two fates mediated by different pathways: necrosis and mitochondria-caspase dependent apoptosis. The findings may be important in regard to antimicrobial, inflammatory and autoimmune responses in humans.

The effects of RF coils and SAR supervision strategies forclinically applicable nonselective parallel-transmit pulses at 7T.

To investigate the effects of using different parallel-transmit (pTx) head coils and specific absorption rate (SAR) supervision strategies on pTx pulse design for ultrahigh-field MRI using a 3D-MPRAGE sequence. The PTx universal pulses (UPs) and fast online-customized (FOCUS) pulses were designed with pre-acquired data sets (B0 , B1 + maps, specific absorption rate [SAR] supervision data) from two different 8 transmit/32 receive head coils on two 7T whole-body MR systems. For one coil, the SAR supervision model consisted of per-channel RF power limits. In the other coil, SAR estimations were done with both per-channel RF power limits as well as virtual observation points (VOPs) derived from electromagnetic field (EMF) simulations using three virtual human body models at three different positions. All pulses were made for nonselective excitation and inversion and evaluated on 132 B0 , B1 + , and SAR supervision datasets obtained with one coil and 12 from the other. At both sites, 3 subjects were examined using MPRAGE sequences that used UP/FOCUS pulses generated for both coils. For some subjects, the UPs underperformed when simulated on a different coil from which they were derived, whereas FOCUS pulses still showed acceptable performance in that case. FOCUS inversion pulses outperformed adiabatic pulses when scaled to the same local SAR level. For the self-built coil, the use of VOPs showed reliable overestimation compared with the ground-truth EMF simulations, predicting about 52% lower local SAR for inversion pulses compared with per-channel power limits. FOCUS inversion pulses offer a low-SAR alternative to adiabatic pulses and benefit from using EMF-based VOPs for SAR estimation.

Wideband Monopole Eight-Element MIMO Antenna for 5G Mobile Terminal

An eight-element wideband multiple-input multiple-output (MIMO) antenna for the fifth-generation (5G) mobile terminal is proposed. The antenna elements are placed along both long side edges of the mobile terminal with a profile of 6 mm. The proposed monopole-inspired antenna element shows a good impedance match, isolation, and diversity parameter across a very wide bandwidth of 78 % (3.2-7.3 GHz), and it can cover the 5G NR n77/n78/n79/n96, LTE 46, and WLAN 5 GHz bands. The result shows that the MIMO antenna can offer inter-element isolation better than 12 dB, envelope correlation coefficient (ECC) below 0.069, and a peak channel capacity of 42.7 bps/Hz across the desired 5G bands. The specific absorption rate (SAR) analysis of the proposed MIMO antenna with a human head has exhibited SAR levels (0.41 W/Kg and 0.33 W/Kg at two resonating frequencies 3.9 GHz and 5.8 GHz, respectively) much lower than the Federal Communications Commission (FCC) permissible limit (1.6 W/Kg over 1 gram tissue).

Proposed Safety Guidelines for Patient Assistants in an Open MRI Environment.

The wide-open side of an open magnetic resonance imaging (MRI) system allows a patient to easily contact the patient assistant during MRI scans. A wide-open-shaped magnet is highly effective when interventional procedures are necessary. Patient assistants can provide comfort by holding a part of the patient's body. Because current regulations or guidelines are concerned with only patient radio frequency (RF) safety, investigations on the safety of patient assistants exposed to high-magnetic field MRI (up to 1.2 T) are required. In this study, five different poses of patient assistants were numerically simulated at a 1.2 T open MRI system to determine the impact of poses on the RF exposure level. The 10-g averaged specific absorption rate (SAR) levels were analyzed for the poses of each patient assistant wearing gloves. Compared with the patient, up to 29.8% of the patient SAR was observed in the patient assistant. When the patient assistant wore latex gloves, a 63.7% reduction in the 10-g averaged SAR level was observed, which could be a remedy to minimize possible RF hazards. To prevent possible RF hazards during MRI scans, certain clauses regarding the patient assistant's poses or wearing gloves must be added to the existing MRI screening forms.

Solar Cell Integrated Wearable Patch Antenna on Artificial Magnetic Conductor for On-Body and In-Body Communications

This paper presents a patch antenna on a jeans textile with an artificial magnetic conductor (AMC) structure stacked on a solar cell for wearable applications in the Industrial, Scientific, and Medical (ISM) band. Meanwhile, the loading of the AMC reflector increases the radiation efficiency and antenna gain and also results in a reduction in specific absorption rate levels. As examination cases, two textile antenna designs loaded on 7 × 8 patches of AMC plane with the ground plane of both fully copper conductor and partially copper aided with solar cells were fabricated and tested, presenting a strong agreement between simulation and measurement. Its measured impedance bandwidth is 13.79% (2.16 GHz–2.48 GHz) with good return loss and voltage standing wave ratio features in the operating band where it is being used. Besides being a source of electricity, the silicon solar cells are also used as a radio frequency ground plane for the AMC plane. They can produce363.08 mW.

Parallel transmission 2D RARE imaging at 7T with transmit field inhomogeneity mitigation and local SAR control

PurposeWe develop and test a parallel transmit (pTx) pulse design framework to mitigate transmit field inhomogeneity with control of local specific absorption rate (SAR) in 2D rapid acquisition with relaxation enhancement (RARE) imaging at 7T. MethodsWe design large flip angle RF pulses with explicit local SAR constraints by numerical simulation of the Bloch equations. Parallel computation and analytical expressions for the Jacobian and the Hessian matrices are employed to reduce pulse design time. The refocusing-excitation “spokes” pulse pairs are designed to satisfy the Carr-Purcell-Meiboom-Gill (CPMG) condition using a combined magnitude least squares-least squares approach. ResultsIn a simulated dataset, the proposed approach reduced peak local SAR by up to 56% for the same level of refocusing uniformity error and reduced refocusing uniformity error by up to 59% (from 32% to 7%) for the same level of peak local SAR compared to the circularly polarized birdcage mode of the pTx array. Using explicit local SAR constraints also reduced peak local SAR by up to 46% compared to an RF peak power constrained design. The excitation and refocusing uniformity error were reduced from 20%–33% to 4%–6% in single slice phantom experiments. Phantom experiments demonstrated good agreement between the simulated excitation and refocusing uniformity profiles and experimental image shading. ConclusionPTx-designed excitation and refocusing CPMG pulse pairs can mitigate transmit field inhomogeneity in the 2D RARE sequence. Moreover, local SAR can be decreased significantly using pTx, potentially leading to better slice coverage, enabling larger flip angles or faster imaging.

In Vivo Functional Ultrasound (fUS) Real-Time Imaging and Dosimetry of Mice Brain Under Radiofrequency Exposure.

This study aims to analyze in real-time the potential modifications induced by low-level continuous-wave and Global System for Mobile Communications radiofrequency (RF) exposure at 1.8 GHz on brain activation in anesthetized mice. A specific in vivo experimental setup consisting of a dipole antenna for the local exposure of the brain was fully characterized. A unique neuroimaging technique based on a functional ultrasound (fUS) probe was used to observe the areas of mice brain activation simultaneously to the RF exposure with unprecedented spatial and temporal resolution (~100 μm, 1 ms) following manual whisker stimulation using a brush. Numerical and experimental dosimetry was carried out to characterize the exposure and to guarantee the validity of the biological results. Our results show that the fUS probe can be efficiently used during in vivo exposure without interference with the dipole. In addition, we conclude that exposure to brain-averaged specific absorption rate levels of 2 and 6 W/kg does not introduce significant changes in the time course of the evoked fUS response in the left barrel field cortex. The proposed technique represents a valuable instrument for providing new insights into the possible effects induced on brain activation under RF exposure. For the first time, brain activity under mobile phone exposure was evaluated in vivo with fUS imaging, paving the way for more realistic exposure configurations, i.e.awake mice and new signals such as the 5 G networks. © 2022 Bioelectromagnetics Society.

Ultra-wide band flexible antenna applicable for dual-band on-body communications

AbstractIn this article, an ultra-wideband printed flexible monopole antenna is proposed for indoor wireless communications. A flexible Rogers RO3003 is used as a substrate, and its performance is estimated for a flat state and when subject to bending along the y-axis. A 2.45 and 5.8 GHz dual-band textile artificial magnetic conductor (AMC) surface consisting of a 4 × 4 unit-cell array was integrated into antenna design with optimum separation distance to extend its potential applications to wearable on-body communications. The specific absorption rate (SAR) levels were numerically investigated using the Hugo human voxel model at both frequencies to evaluate the on-body safety level. Detailed analysis is presented for antenna designs of flat and bent states in free space and on the human body. The proposed UWB flexible antenna has the size of 41 × 38 × 0.25 mm (0.33λ0 × 0.31λ0 × 0.002λ0 at 2.45 GHz). It was added at a distance of 3 mm above a textile AMC surface of 99 × 99 mm. The integrated model is fabricated and experimentally characterized. Measured data and numerical results show that the impedance matching and radiation characteristics are slightly affected by introducing the bending and human body loading. With these remarkable features, the integrated model can be utilized for wireless indoor and wearable applications.

Performance evaluation of compact FSS‐integrated flexible monopole antenna for body area communication applications

SummaryThis article presents a compact wearable antenna integrated with a novel frequency selective surface (FSS) made of textile materials. The antenna can be applied in wearable health monitoring applications aimed at the 2.45‐GHz Industrial Scientific and Medical (ISM) band. An array of 4 × 4 octagonal slot‐shaped FSS (106 × 106 mm2) superstrate enhances the performance of the modified Koch curve planar monopole antenna (44.85 × 39 mm2). The Jeans substrate prototype with the overall dimensions of 1.128λ0 × 1.128λ0 × 0.319λ0 covers the bandwidth of 2.45‐GHz ISM band from 2.24 to 2.76 GHz (S11 ≤ −10 dB). The band rejection and reflective nature of the proposed FSS suppress the back radiation and improves the antenna's gain by −20 dB and 6.3 dBi, respectively. The specific absorption rate (SAR) level is reduced to 0.445 W/kg from 24.995 W/kg with a higher reduction rate of 98.21%. Many literature reports produced higher gain and lower SAR but exhibited reduced efficiency when the antenna is placed near the human body. The wearable antenna's frequency response tends to vary under bending conditions for narrowband antennas. Wide‐band monopole antennas produce omnidirectional radiation pattern which tends to affect human body tissues. So stable polarization‐insensitive FSS is placed behind the antenna to enhance the antenna's gain and avoid back radiation. The proposed antenna exhibits stable performance under bending conditions with fractional bandwidth of 22.2%, gain of 8.83 dBi, and produces a better efficiency of 91.30% when the antenna is positioned in the vicinity with human body models. The experimental validation shows that the proposed antenna is a promising candidate for wireless body area networks.

An Efficient and Compact Monopole Antenna Backed With Square Loop EBG Structure for Medical Wireless Body Area Network Applications

AbstractIn this paper, a compact, low‐profile, and simple monopole antenna is presented that is operated at the frequency of 2.4 GHz in industrial scientific medical band. The monopole antenna is based on the simple rectangular microstrip patch with a rotated T‐shaped slot. Furthermore, a 2 × 2 electromagnetic band‐gap (EBG) array is used in this design to act as an isolator between the antenna and the human body, which additionally increases the performance of the proposed antenna. The final design has an overall size of only 0.9λg × 0.9λg × 0.034λg (60 × 60 × 2.3 mm3) where λg is the guided‐wavelength with respect to RO4003 substrate at the resonant frequency of 2.4 GHz. This can make the structure a good candidate for wireless body area network applications. A prototype of the designed EBG‐based antenna is fabricated over a widely available RO4003 substrate. The measurement results show a gain of 6.52 dBi, a front to back ratio of 12.12 dB, and a total efficiency of 79.87% around the resonant frequency. Furthermore, numerical studies are conducted to evaluate the specific absorption rate (SAR) of the proposed design, which shows by introducing the EBG structure, more than 96% reduction in SAR level is obtained. All simulations are carried out by CST microwave studio software.