Terms Of Specific Absorption Rate Research Articles

On-Body Low-Profile Compact AMC-Integrated Wideband Antenna for Body Area Network Applications

This communication presents a wideband and a low-profile flexible wearable antenna intended to operate at a 2.45 GHz WBAN band. The suggested antenna comprises a CPW-fed monopole antenna backed by an artificial magnetic conductor (AMC) to act as a reflector. The latest AMC-integrated design uses R03003 as a dielectric substrate. The suggested design features an impedance bandwidth of 71.03% (1.87–3.93 GHz) with a gain value of 3.62 dBi and has a compact footprint of 40 × 40 mm2. The incorporation of wideband AMC with a monopole antenna leads to bandwidth enhancement and covers the 3.5 GHz WiMAX band. Simulation and experimental studies provide evidence that in the case of structural deformities and human body loading, the suggested AMC-integrated antenna is stable and shows superior efficiency relative to the traditional monopole antenna. Furthermore, numerical analysis demonstrates that the amount of radiation AMC-integrated antenna decreases tremendously in terms of specific absorption rate for various bodily attachment scenarios. Three body templates with various compositions and forms were used to study the effects of the antenna on bodily attachment. Extensive experiments on human body phantoms and bodily attachment are also conducted and the results are presented. The suggested AMC-integrated design thus confirms a promising contender for portable wearable wireless applications.

Investigating the impact of zinc ion substitution on the rheological properties and hyperthermia potential of cobalt ferrite-based ferrofluids

Zn-substituted cobalt ferrite-based ferrofluids (FFs) were successfully synthesized using a modified co-precipitation method. In this study, we aimed to investigate the heating performance of the synthesized FFs using a resonance coil-based magnetic hyperthermia setup and characterize their viscoelastic behaviour using a magneto rheometer. The crystalline spinel phase with Fd3m (227) symmetry was confirmed through Powder X-ray Diffraction (PXRD. Additionally, Vibrating Sample Magnetometer (VSM) measurements allowed us to analyze the effect of Zn substitution on the room temperature magnetic properties of the FFs. To gain insights into the viscoelastic properties, steady-state rheological measurements were performed. The FFs exhibited non-Newtonian behaviour at low shear rates (<100 s−1) and transitioned to Newtonian fluid behaviour at higher shear rates. Furthermore, we investigated the magneto-viscoelastic behaviour of the FFs across a range of magnetic field strengths (0 to 1 T) using three different fluids. It was observed that the viscosity increased as the field strength increased, which can be attributed to the formation of chain-like structures. The heating efficiency of the FFs was evaluated in terms of Specific Absorption Rate (SAR) using the Initial Slope Method (ISM) and Box Lucas Method (BLM). The SAR values for the FFs exhibited a significant increase with Zn substitution, with the maximum values recorded as 188 ± 8 W/g (ISM) and 212 ± 9 W/g (BLM) for Zn0.4Co0.6Fe2O4, surpassing the SAR value of CoFe2O4 (72 ± 8 W/g, ISM; 92 ± 5 W/g, BLM). To assess biocompatibility, we conducted a cell viability assay using HEK-293 cell lines. The results demonstrated high cell viability (>75%) for Zn0.4Co0.6Fe2O4 at a concentration of 100 µg/ml after a 48-hour incubation period.

Integrated sub-6 GHz and millimeter wave band antenna array modules for 5G smartphone applications

Due to their high-frequency ratios, sub-6-GHz and millimeter-wave bands are becoming crucial for fifth-generation (5G) smartphone applications for achieving beam steering and high gain performance without using additional separate antenna elements. This paper presents compact integrated antenna array modules for simultaneous operation in the 3.5 GHz (sub-6 GHz) and (26 GHz) millimeter-wave frequencies. The proposed integrated single antenna element is composed of a microstrip patch antenna, a low-pass filter, and a meandered line-based antenna. The dimensions of the proposed compact integrated antennas are 0.6363 λg×0.2423λg×0.0147λg. The proposed antenna provides wide bandwidth characteristics in both operating frequencies with a -10 dB bandwidth of 500 MHz and 4.5 GHz in the sub-6 GHz and millimeter-wave bands, respectively. The effects of the smartphone on scattering parameters were analyzed. Further, we have studied the safety of smartphone users in terms of specific absorption rate (SAR) and power density (PD). The SAR and PD of the proposed antenna were found under safety limits. Additionally, the proposed antenna array modules were fabricated on a low-cost FR-4 substrate for validation of the simulation results, and a good agreement was found among them. The proposed antenna array packages are excellent candidates for modern 5G smartphones because they provide excellent features such as wide bandwidth characteristics and high gain with wide beam scanning features, and can integrate 3.5 GHz (sub-6 GHz) and (26 GHz) millimeter-wave bands with a high-frequency gap in a small structure.

Structural, magnetic, and biocompatibility evaluations of chromium substituted barium hexaferrite (Co2–Y) for hyperthermia application

In the present work, chromium-substituted cobalt-based Y-type barium hexaferrite ceramics having a general formula of Ba2Co2Fe12-xCrxO22 (0.0 ≤ x ≤ 0.5) have been studied to evaluate its potential candidacy as an optional replacement for various soft ferrite materials in the field of magnetic hyperthermia. The as-obtained ferrite powders are characterized for structural, magnetic, and morphological properties after being calcined at 1200 °C for 2 h. The structural parameters confirm single-phase nanocrystalline Y-type barium hexaferrite formation within all the samples. The room temperature magnetic parameter, i.e., saturation magnetization (Ms), is found to decrease (from 39.07 to 33.50 emu/g), and the coercive field (Hc) is increased (86.87–281.84 Oe) consistently. Later, oleic acid-coated ferrite samples' heating capability is governed within the applied AC magnetic field (25 mT at a frequency of 114.1 kHz) in terms of specific absorption rate (SAR) using time-dependent temperature performance. The superiority of the sample having the greatest SAR value (84.39 w/g for Ba2Co2Fe11.7Cr0.3O22) is interrelated with the particles' geometry, size distribution, magnetic parameters, and surface chemistry obtained from the XPS analysis. This sample is further analyzed for its biocompatibility performance against the MG-63 cell line; the results indicate that it may be a potential candidate for magnetic hyperthermia due to its significant SAR & ILP value along with better biocompatibility.

CSI-Free Rotary Antenna Beamforming for Massive RF Wireless Energy Transfer

Radio-frequency (RF) wireless energy transfer (WET) is a key technology that may allow seamlessly powering future massive low-energy Internet of Things (IoT) networks. To enable efficient massive WET, channel state information (CSI)-limited/free multiantenna transmit schemes have been recently proposed in the literature. The idea is to reduce/null the energy costs to be paid by energy harvesting (EH) IoT nodes from participating in large-scale time/power-consuming CSI training, but still enable some transmit spatial gains. In this article, we take another step forward by proposing a novel CSI-free rotary antenna beamforming (RAB) WET scheme that outperforms all state-of-the-art CSI-free schemes in a scenario, where a power beacon (PB) equipped with a uniform linear array (ULA) powers a large set of surrounding EH IoT devices. RAB uses a properly designed CSI-free beamformer combined with a continuous or periodic rotation of the ULA at the PB to provide average EH gains that scale as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.85\sqrt {M}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> is the number of PB’s antenna elements. Moreover, a rotation-specific power control mechanism was proposed to: 1) fairly optimize the WET process if devices’ positioning information is available and/or 2) avoid hazards to human health in terms of specific absorption rate (SAR), which is an RF exposure metric that quantifies the absorbed power in a unit mass of human tissue. We show that RAB performance even approaches quickly (or surpasses, for scenarios with a sufficiently large number of EH devices, or when using the proposed power control) the performance of a traditional full-CSI-based transmit scheme, and it is also less sensitive to SAR constraints. Finally, we discuss important practicalities related to RAB such as its robustness against non line-of-sight (LOS) conditions compared to other CSI-free WET schemes, and its generalizability to scenarios where the PB uses other than a ULA topology.

Development of deeply focused microwave lens applicator for efficient hyperthermia treatment

In this paper, a deeply focused microwave lens applicator is investigated for hyperthermia treatment. The lens applicator consists of a double spiral antenna (DSA) and frequency selective surface (FSS) as superstrate. The double spiral structure is designed on the top of the upper substrate (Substrate-1), the slotted ground plane is placed between the upper and lower substrate (Substrate-2), and the microstrip feed line is printed on the bottom of the lower substrate. The overall size of the proposed antenna is 32 × 32 × 3.27 mm3. Moreover, an FSS structure (as superstrate) is designed, which has a size of 64 × 64 mm2 (consists of a 4 × 4 unit cell). The FSS structure behaves as a lens that converts the bidirectional field pattern of DSA into the unidirectional pattern, which improves the focusing ability of the proposed applicator towards the phantom. The lens applicator is simulated with heterogeneous phantom (layers of skin, fat, and muscles), and the performance of the applicator is evaluated in terms of specific absorption rate (SAR), penetration depth (PD), and effective field size (EFS). The lens applicator is fabricated and experimentally validated in the presence of an artificial phantom. The measured results are in close agreement with the simulated one. Further, the performance of the applicator is analyzed for a deeply placed irregular-shaped tumor (at 15 mm from the skin surface). The study of temperature distribution is done, and the peak value of temperature is obtained as 43 °C with 2.5 W of microwave power given to the antenna. The temperature value around the tumor is obtained in the range of 41–45 °C, which is suitable for effective hyperthermia treatment.

Application of Stochastic Dosimetry for assessing the Human RFEMF Exposure in a 5G indoor Scenario.

In recent years the introduction of 5G networks is causing a drastically change of human exposure levels in the radio frequency range. The aim of this paper is on expanding the knowledge on this issue, assessing the exposure levels for a particular case of indoor 5G scenario, where the presence of an Access Point (AP) was simulated. Coupling the traditional deterministic computational method with an innovative stochastic approach, called Polynomial Chaos Kriging, allowed to evaluate the exposure variability of an user considering the 3D beamforming capability of the antenna. The exposure levels, expressed in terms of specific absorption rate (SAR) in specific tissues, showed low values compared to ICNIRP guidelines.

Stoichiometry and Orientation- and Shape-Mediated Switching Field Enhancement of the Heating Properties of Fe3O4 Circular Nanodiscs

The generation of topological magnetic vortex-domain structures in iron-oxide nanomaterials has promising applications in biomedical scenarios, such as heat generators for hyperthermia treatments. In this report we describe alternative kinds of magnetic-vortex nanoparticles, circular ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ nanodiscs (NDs), and dissect their heating properties by in-depth investigation of their shape and size, stoichiometry, orientations, and switching field ``${H}_{S}$'' behaviors, through experiments and theoretical simulation. We find that the stoichiometric NDs show better heating performance than nonstoichiometric materials because of the significant electron hopping between ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Fe}}^{2+}$ ion. The higher heating efficiency (in terms of specific absorption rate, SAR) is observed only for the higher switching field regime, an effect that is associated with the parallel and perpendicular alignment of nanodiscs with respect to low and high ac magnetic field, respectively. A higher SAR of approximately 270 W/g is observed at a higher switching field (approximately 700 Oe) for NDs of diameter 770 nm, which increases by a factor of 4 at a switching field of approximately 360 Oe for NDs of diameter 200 nm. The reported results suggest that the heating efficiency in these systems can be enhanced by controlling the switching field, which is, in turn, tuned by size, shape, and orientation of circular magnetic vortex nanodiscs.

A Planar 2×2 MIMO Antenna Array for 5G Smartphones

Here, a planar 2×2 MIMO configuration for the 5G smartphone has been presented. A single element modified planar tree profile shape (MPTPS) antenna is implemented to investigate the suitability in future 5G communication for different sub-6 GHz spectrum band. The size of the single MPTPS antenna is 40 × 25 mm2. The electronic band gap (EBG) and partial ground plane (PGP) techniques have been utilized to tune this antenna. The antenna works from 2.81 – 7.23 GHz, with a (VSWR < 2) bandwidth of 4.42 GHz that covers all the mid-range sub-6 GHz 5G frequencies. It also has a comparatively good gain of 3.14 dBi, high efficiency of 96% and a bi-directional radiation pattern. The antenna has been implemented in a 145 × 75 mm2 smartphone mainboard with MIMO configuration using polarization diversity. More than -21.1 dB isolation has been found between different ports. A good gain of as high as 6.59 dBi is observed for the MIMO in the band. Also, as MIMO performance, excellent envelope correlation coefficient of less than 0.0029 and minimum diversity gain of 9.9853 has been observed. The investigation has been further stretched by adding a liquid crystal display (LCD) for radiation performance and a hand phantom to assess the performance in terms of specific absorption rate (SAR). It is observed that the SAR value is as low as 0.887641 at 3.5 GHz. This design will motivate the researcher to develop high performance MIMO arrays for 5G smartphones.

Symbiotic thermo-chemotherapy for enhanced HepG2 cancer treatment via magneto-drugs encapsulated polymeric nanocarriers

The existence of cancer and its continuous threat to life demands extensive therapeutic research. Moreover, there has been a drastic increment in newer cancer cases every year around the world, which advocates a unique way of improving cancer treatments. Recently, magnetic fluid hyperthermia (MFH) has received significant attention in cancer nano-therapeutics, and it allows us to be symbiotically utilized with other modalities such as chemotherapy to enhance treatment efficacies. However, numerous challenges must be needed to overcome in clinical hyperthermia scenarios such as higher heat-inducing property & therapeutic efficacy with (i) minimal concentration of therapeutic agents to prevent acute toxicity, and also (ii) tolerable MFH strength & frequency to evade needless side effects on the patients. To address these current challenges, in this work superparamagnetic iron oxide nanoparticles (SPIONs) and dual-drugs (nifedipine (a calcium channel blocker) & curcumin) are co-encapsulated in a step-wise manner inside d-ɑ-tocopheryl polyethylene glycol succinate (TPGS)-stabilized poly(d,l-lactide-co-glycolide) (PLGA-a polymeric nanocarrier) nanoparticles (TP-NPs). Herein, significant attention has been given to balancing both the safety and therapeutic effectiveness by optimizing the concentrations of dual drugs, SPIONs & also nanocarriers (i.e., TP-NPs), and also applied alternating magnetic field (AMF). The SPIONs inside TP-NPs have exhibited improved magneto-thermal effects (i.e., measured in terms of specific absorption rate (SAR) = 62.8–72.0 W/gFe) under an applied AMF. As a result of these improved effects via SPIONs, dual drugs are effectively released (almost ∼90 % in a time-dependent manner) and concentrated highly inside the HepG2 cancer cells. Consequently, the in vitro thermo-chemotherapy studies have shown enhanced inhibition rates (up to 89 %) in the growth of HepG2 cancer cells at a very less concentration (i.e., 0.5 mgFe). The results obtained from the present study are compared with previous reports, which have indicated that magneto-drugs encapsulated polymeric nanocarriers (i.e, TP-NPs) prepared in this work are highly promising in improving the cancer treatment efficacy by producing an extensive symbiotic effect.

A Compact Magnetically Dispersive Surface for Low-Frequency Wireless Power Transfer Applications

We present a compact, magnetically dispersive engineered surface for resonant inductive wireless power transfer (WPT) that significantly enhances the performance of an inductive link, increasing the efficiency and/or working distance. The proposed metasurface measures 6 cm $\times 6$ cm $\times0.1$ cm, achieving a greatly reduced thickness over a 3-D metamaterial, especially relative to the long wavelength at the chosen operating frequency of 5.77 MHz, which is in the range of typical wireless biomedical implants. Such feature is obtained by virtue of an extremely compact connected double-spiral unit cell, which provides high inductance values despite the small size. We prove through numerical simulations that the proposed metasurface considerably lowers the electric field level with respect to traditional two- or three-coil WPT systems, while maintaining the same magnetic field level at the receiver. In addition, we conducted efficiency measurements on a fabricated prototype, confirming the performance of our design. The excellent efficiency enhancement, combined with the resulting low electric field, makes the proposed metasurface an attractive solution for a number of WPT applications, especially where the exposure in terms of specific absorption rate (SAR) is one of the major concerns, such as in biomedical implants and rechargeable devices.

Super Ultrawideband Planar Inverted F Antenna on Paper based Substrate with Low SAR

In this paper, a super ultrawide band planar inverted F antenna (PIFA) has been proposed for wearable applications on a low cost, ecofriendly paper-based substrate. This work is a first and important step towards the progression of conformal flexible antennas for a body area network. The proposed antenna has measured impedance bandwidth of 10.6 GHz, which covers almost all the bands of a wireless body area network i.e. GSM (880-960 MHz), GPS (1565-1585 MHz), DCS (1710-1880 MHz), PCS (1850-1990 MHz), UMTS (1920-2170 MHz), ISM (2.4-2.4835 GHz), WiMAX (3.3-3.8 GHz), HIPERLAN (5.15-5.35 GHz), WLAN (5.725-5.850 GHz) and UWB (3.1-10.6 GHz). Initially, the electrical characteristics of paper are extracted using Cavity Resonator and Transmission line method and then used for the design and fabrication of the proposed antenna. The measured results are in good agreement with the simulated results. This paper also focuses on analysis of the effect of electromagnetic absorption in terms of specific absorption rate for a human arm with frequency exposure at 0.9 GHz, 1.5 GHz, 1.8 GHz, 3.5 GHz, 2.45 GHz, 5.2 GHz and 5.8 GHz and is found to be within the recommended limit by FCC.

RF-induced heating in tissue near bilateral DBS implants during MRI at 1.5 T and 3T: The role of surgical lead management

Access to MRI is limited for patients with deep brain stimulation (DBS) implants due to safety hazards, including radiofrequency (RF) heating of tissue surrounding the leads. Computational models provide an exquisite tool to explore the multi-variate problem of RF heating and help better understand the interaction of electromagnetic fields and biological tissues. This paper presents a computational approach to assess RF-induced heating, in terms of specific absorption rate (SAR) in the tissue, around the tip of bilateral DBS leads during MRI at 64MHz/1.5 T and 127 MHz/3T. Patient-specific realistic lead models were constructed from post-operative CT images of nine patients operated for sub-thalamic nucleus DBS. Finite element method was applied to calculate the SAR at the tip of left and right DBS contact electrodes. Both transmit head coils and transmit body coils were analyzed. We found a substantial difference between the SAR and temperature rise at the tip of right and left DBS leads, with the lead contralateral to the implanted pulse generator (IPG) exhibiting up to 7 times higher SAR in simulations, and up to 10 times higher temperature rise during measurements. The orientation of incident electric field with respect to lead trajectories was explored and a metric to predict local SAR amplification was introduced. Modification of the lead trajectory was shown to substantially reduce the heating in phantom experiments using both conductive wires and commercially available DBS leads. Finally, the surgical feasibility of implementing the modified trajectories was demonstrated in a patient operated for bilateral DBS.

Electrical power to run ventricular assist devices using the Free-range Resonant Electrical Energy Delivery system.

Models of power delivery within an intact organism have been limited to ionizing radiation and, to some extent, sound and magnetic waves for diagnostic purposes. Traditional electrical power delivery within the intact human body relies on implanted batteries that limit the amount and duration of delivered power. The efficiency of current battery technology limits the substantial demands required, such as continuous operation of an implantable artificial heart pump within a human body. The fully implantable, miniaturized, Free-range Resonant Electrical Energy Delivery (FREE-D) system, compatible with any type of ventricular assist device (VAD), has been tested in a swine model (HVAD) for up to 3 hours. Key features of the system, the use of high-quality factor (Q) resonators together with an automatic tuning scheme, were tested over an extended operating range. Temperature changes of implanted components were measured to address safety and regulatory concerns of the FREE-D system in terms of specific absorption rate (SAR). Dynamic power delivery using the adaptive tuning technique kept the system operating at maximum efficiency, dramatically increasing the wireless power transfer within a 1-meter diameter. Temperature rise in the FREE-D system never exceeded the maximum allowable temperature deviation of 2°C (but remained below body temperature) for an implanted device within the trunk of the body at 10 cm (25% efficiency) and 50 cm (20% efficiency), with no failure episodes. The large operating range of FREE-D system extends the use of VAD for nearly all patients without being affected by the depth of the implanted pump. Our in-vivo results with the FREE-D system may offer a new perspective on quality of life for patients supported by implanted device.

Simulating, Modeling, and Sensing Variable Tissues for Wireless Implantable Medical Devices

Wirelessly powered implantable medical devices require efficient power transfer through biological tissue within safety constraints on energy absorption, often in the presence of environmental variability. Accurate modeling of the tissue medium is essential to evaluate the performance and sensitivity of transcutaneous powering systems. Here, we investigate loop and dipole antenna topologies in proximity to simulated tissue models and experimental phantoms, with emphasis on representing heterogeneous tissue with functionally equivalent simplified models, and modeling variability in tissue properties for sensitivity analyses. We first present a modified phantom formulation that provides greater control over frequency-dependent properties. We then show that homogeneous phantoms have limited use at representing input impedance and energy absorption at ultrahigh operating frequency by analyzing each antenna topology in proximity to layered or homogeneous tissue across frequency. We compare loop and dipole antenna topologies in terms of specific absorption rate and impedance, and show that frequency-dependent tissue behavior must be considered even at fixed operating frequencies. Finally, we discuss the dual utility of a transmitting antenna as a resonator to detect changes in tissue properties in addition to powering an implanted device.

EXPOSURE ASSESSMENT OF PORTABLE WIRELESS DEVICES ABOVE 6 GHz.

The emerging 5 G wireless devices working at frequencies above 6 GHz are expected to have antenna arrays formed by dipoles, slots, patches or their combination. At lower frequencies, the accepted criteria for exposure compliance is stated in terms of specific absorption rate. IEEE and ICNIRP are adopting epithelial or transmitted power density (PD through body surface) as the dosimetric reference for frequencies above 6 GHz, which entails the measurement of free space PD. Theoretical and numerical results presented in this article show that it is possible to perform meaningful free space PD assessments at half wave (λ/2) distance from arrays and, with the proper instrumentation, as close as λ/(2π). However, if a dissipative body is placed very close (<λ/2π) to the arrays, its reflection and absorption of RF energy can change the electric currents and charges over the antenna. The relevance of such an effect should be further investigated, for instance by means of experimental analysis including measurements of tissue heating when in the presence of a strong reactive near field.

Volumetric wireless coil based on periodically coupled split-loop resonators for clinical wrist imaging.

Design and characterization of a new inductively driven wireless coil (WLC) for wrist imaging at 1.5 T with high homogeneity operating due to focusing the B1 field of a birdcage body coil. The WLC design has been proposed based on a volumetric self-resonant periodic structure of inductively coupled split-loop resonators with structural capacitance. The WLC was optimized and studied regarding radiofrequency fields and interaction to the birdcage coil (BC) by electromagnetic simulations. The manufactured WLC was characterized by on-bench measurements and in vivo and phantom study in comparison to a standard cable-connected receive-only coil. The WLC placed into BC gave the measured B1+ increase of the latter by 8.6 times for the same accepted power. The phantom and in vivo wrist imaging showed that the BC in receiving with the WLC inside reached equal or higher signal-to-noise ratio than the conventional clinical setup comprising the transmit-only BC and a commercial receive-only flex-coil and created no artifacts. Simulations and on-bench measurements proved safety in terms of specific absorption rate and reflected transmit power. The results showed that the proposed WLC could be an alternative to standard cable-connected receive coils in clinical magnetic resonance imaging. As an example, with no cable connection, the WLC allowed wrist imaging on a 1.5 T clinical machine using a full-body BC for transmitting and receive with the desired signal-to-noise ratio, image quality, and safety.

Uncertainties in the estimation of specific absorption rate during radiofrequency alternating magnetic field induced non-adiabatic heating of ferrofluids

Magnetic fluid hyperthermia (MFH) is becoming a viable cancer treatment methodology where the alternating magnetic field induced heating of magnetic fluid is utilized for ablating the cancerous cells or making them more susceptible to the conventional treatments. The heating efficiency in MFH is quantified in terms of specific absorption rate (SAR), which is defined as the heating power generated per unit mass. In majority of the experimental studies, SAR is evaluated from the temperature rise curves, obtained under non-adiabatic experimental conditions, which is prone to various thermodynamic uncertainties. A proper understanding of the experimental uncertainties and its remedies is a prerequisite for obtaining accurate and reproducible SAR. Here, we study the thermodynamic uncertainties associated with peripheral heating, delayed heating, heat loss from the sample and spatial variation in the temperature profile within the sample. Using first order approximations, an adiabatic reconstruction protocol for the measured temperature rise curves is developed for SAR estimation, which is found to be in good agreement with those obtained from the computationally intense slope corrected method. Our experimental findings clearly show that the peripheral and delayed heating are due to radiation heat transfer from the heating coils and slower response time of the sensor, respectively. Our results suggest that the peripheral heating is linearly proportional to the sample area to volume ratio and coil temperature. It is also observed that peripheral heating decreases in presence of a non-magnetic insulating shielding. The delayed heating is found to contribute up to ~25% uncertainties in SAR values. As the SAR values are very sensitive to the initial slope determination method, explicit mention of the range of linear regression analysis is appropriate to reproduce the results. The effect of sample volume to area ratio on linear heat loss rate is systematically studied and the results are compared using a lumped system thermal model. The various uncertainties involved in SAR estimation are categorized as material uncertainties, thermodynamic uncertainties and parametric uncertainties. The adiabatic reconstruction is found to decrease the uncertainties in SAR measurement by approximately three times. Additionally, a set of experimental guidelines for accurate SAR estimation using adiabatic reconstruction protocol is also recommended. These results warrant a universal experimental and data analysis protocol for SAR measurements during field induced heating of magnetic fluids under non-adiabatic conditions.

Assessment of Fetal Exposure to 4G LTE Tablet in Realistic Scenarios: Effect of Position, Gestational Age, and Frequency

The continuous development of radio frequency (RF) devices used in everyday life highlights the need to conduct appropriate health risk assessment due to RF electromagnetic field (RF-EMF) exposure, especially for the fetal exposure in realistic scenarios. In this study, we used stochastic dosimetry, an approach that combines electromagnetic computational techniques and statistics, to assess the fetal exposure to a fourth-generation Long Term Evolution (4G LTE) tablet in realistic scenarios, assessing the influence of the position of the tablet, the gestational age of the fetus, and the frequency of the emitting antenna. Results showed that the exposure in terms of specific absorption rate (SAR) was within the limits of the ICNIRP 1998 General Public Guidelines in all the considered scenarios. The position of the tablet was very influential for the induced SAR in the fetus, resulting in quartile coefficient of dispersion always higher than 40%. The level of exposure for the later pregnancy was found to be higher than those for the early pregnancy. As to the effect of the emitting frequency of the tablet, we found that the higher the frequency, the lower the induced SAR in the fetus.

Investigations on SAR and Thermal Effects of a Body Wearable Microstrip Antenna

Wearable technology has emerged as a hot topic in contemporary years around the globe and the interest in this sector continues to develop and will dominate in the future as well. This research work presents a microstrip-based multi-band monopole antenna for body wearable wireless devices (WWD) used for various body centric wireless communication applications. The designed antenna works at multi bands resonating at 1.8, 2.4, 5.0 and 8.9 GHz covering wireless and UWB based communication technologies. The electromagnetic (EM) effects of radiation absorption are investigated in terms of specific absorption rate and its biological manifestation as heating effect. EM computations and measurements are used to analyze the biological effects when placed on different sites on the body. Thermal effects for short term exposures and steady state conditions are evaluated using analytical methods. Experimental techniques using infrared thermography has been used for finding out the temperature elevation at three specific regions of the body. Simulated, analytical and experimental results of the heating effect are compared and are in good agreement. Further, the rise in temperature is found to be compliant with international safety regulations.