Specific Absorption Rate Measurements Research Articles

Textile Antenna with Dual Bands and SAR Measurements for Wearable Communication

A novel dual-wideband textile antenna designed for wearable applications is introduced in this study. Embedding antennas into wearable devices requires a detailed analysis of the specific absorption rate (SAR) to ensure safety. To achieve this, SAR values were meticulously simulated and evaluated within a human voxel model, considering various body regions such as the left/right head and the abdominal region. The proposed antenna is a monopole design utilizing denim textile as the substrate material. The characterization of the denim textile substrate is carried out using two different methods. The first analysis included a DAC (Dielectric Assessment Kit), while a ring resonator technique was employed for the second examination. Operating within the frequency bands of (58.06%) 2.2–4 GHz and (61.43) 5.3–10 GHz, the antenna demonstrated flexibility in its dual-wideband capabilities. Extensive simulations and tests were conducted to assess the performance of the antenna in both flat and bent configurations. The SAR results obtained from these tests indicate that the antenna complies with safety standard limits when integrated with the human voxel model. This validation underscores the potential of the proposed antenna for seamless integration into wearable applications, offering a promising solution for future developments in this domain.

Electromagnetic Field Pollution Level Measurement for Mobile Phone Networks at Cihan University-Erbil

The health effects by impact of radio-frequency (RF) electromagnetic fields (EMF) have become of increasing concern. We conducted a Specific Absorption Rate (SAR) study and measurements of wireless and mobile phone networks to evaluate the hazard of RF radiation limit. Our measurements have been carried out at different locations on the campus of Cihan University – Erbil. The RF strength level measurement of a base station on site was done by using spectrum analyzer with a dipole antenna and Electro Magnetic Field detector (EMF) application in the handsets for mobile networks, then comparing our measurements with the international slandered SAR’s levels.

Dipolar and anisotropy effect on dextran coated Cu doped ferrite for magnetic hyperthermia applications

The dipolar interaction and magnetic anisotropy effect are the key parameters to tune the self-heating effect of magnetic nanoparticles (MNPs). In this paper, we investigate the impact of Cu2+ doped Fe3O4 and dextran coated nanoparticles (CuxFe3-xO4 with x = 0.15, 0.31, and 0.47) on thermal properties using specific absorption rate measurements (SAR). We look into the prospect of using dipolar and anisotropy effects to increase or decrease the heat released by magnetic nanoparticles, potentially boosting hyperthermia applications. Magnetic nanoparticles with an average particle size of 12–20 nm were observed via TEM. The influence of Cu2+ doping on the structural and magnetic properties of the samples was studied using a vibrating sample magnetometer (VSM). The effective anisotropy calculated for x = 0.15 and x = 0.47 were 5.5 and 4.4 j/m3 respectively. It was shown that increasing the copper doping reduced the effective anisotropy, lowering the SAR values. The SAR value obtained for x = 0.15 and dex-x = 0.15 were 787 and 591 W/g respectively. The uncoated CuxFe3-xO4 nanoparticles achieved hyperthermia temperatures (42–48 °C) much faster than the dextran-coated samples. Eventually temperature can be adjusted to the desired hyperthermia temperature range by altering the sample and Cu2+ concentration. The dextran coating has been shown to dramatically reduce SAR values while still assisting in magnetic hyperthermia temperature regulation. The study also demonstrated that the dipolar interaction influenced the Néel relaxation mechanism which was important in the heat generation mechanism of the MNPs

Towards the Standardization of Photothermal Measurements of Iron Oxide Nanoparticles in Two Biological Windows.

A systematic study on laser-induced heating carried out in two biological windows (800 nm and 1053 nm) for Fe3O4 nanoparticles in water suspension showed evidence of the strong dependence of the specific absorption rate (SAR) on extrinsic parameters such as the vessel volume or laser spot size. The results show that a minimum of 100 μL must be used in order to obtain vessel-size-independent SARs. In addition, at a constant intensity but different laser powers and spot size ratios, the SARs can differ by a three-fold factor, showing that the laser power and irradiated area strongly affect the heating curves for both wavelengths. The infrared molecular absorber IRA 980B was characterized under the same experimental conditions, and the results confirm the universality of the SARs' dependence on these extrinsic parameters. Based on these results, we propose using solutions of IRA 980B as a standard probe for SAR measurements and employing the ratio SARiron oxide/SARIRA 980B to compare different measurements performed in different laboratories. This measurement standardization allows us to extract more accurate information about the heating performance of different nanoparticles.

Application of biocompatible and ultrastable superparamagnetic iron(III) oxide nanoparticles doped with magnesium for efficient magnetic fluid hyperthermia in lung cancer cells.

Magnetic fluid hyperthermia (MFH) is a promising therapeutic strategy that targets malignant tissues by heating to 40-43 °C using magnetic nanoparticles (MNPs) subjected to an alternating magnetic field (AMF). In this study, novel magnetic iron(III) oxide nanoparticles doped with magnesium (Mg0.1-γ-Fe2O3(mPEG-silane)0.5) were synthesized, and their structural, chemical, and magnetic properties were analyzed using the following techniques: Fourier-transform infrared spectroscopy, Raman spectroscopy, vibrating magnetometer analysis, powder X-ray diffraction, inductively coupled plasma mass spectrometry, scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The as-synthesized MNPs were used as water ferrofluids for MFH under an AMF in two calorimetric setups, namely phantom and lung cancer cell (A549) models. The as-synthesized MNPs were hexagonal or rhombohedral shaped, with an average size of 27 nm. They showed a typical soft ferromagnetic behavior based on the hysteresis profile, with a magnetic saturation of 70 emu g-1 and remnant magnetization of 1.6 emu g-1. In phantom studies, the ferrofluid (3.0 mg mL-1) exposed to an AMF (18.3 kA m-1, 110.1 kHz) heated up extremely quickly, reaching more than 90 °C in the first 10 min of magnetization. In cell studies, the ferrofluid (0.25 mg mL-1) under an AMF (16.7 kA m-1, 110.1 kHz) showed a slight increase in temperature within the first 12 min, reaching a peak of ca. 43-45 °C, which was stable up to the end of the AMF exposure (45 min). Under these conditions, a pronounced cytotoxic effect on the lung cancer cells was observed (viability ca. 15-20%). No such deleterious effects were observed when the cells were treated with MNPs only without an AMF. Specific absorption rate (SAR) measurements were performed using three mathematical approaches, namely the initial slope method, the corrected slope method, and the Box-Lucas method, which ranged from ca. 429 to 596 W g-1 for phantom and cell studies. Iron(III) oxide MNPs doped with magnesium were found to be candidates for MFH in lung cancer treatments.

Specific Absorption Rate Measurement Method for Exposure Assessment and Conformity Evaluation of 2.45 GHz RF Wireless Power Transfer System

Specific Absorption Rate Measurement Method for Exposure Assessment and Conformity Evaluation of 2.45 GHz RF Wireless Power Transfer System

Differential method for determining the specific absorption rate coefficient of electromagnetic energy for a liquid phantom

The wide use of small-sized wearable electronic devices in various practical human activities makes it relevant to measure the proportion of electromagnetic energy absorbed by the human body. One of the most important parameters that determines it is the specific absorption rate. In this article we propose a method for determining this coefficient for a liquid phantom, with the use of computer simulation and experimental measurement of the microstrip patch antenna parameters.The antenna is located on an elliptical cylinder and operates in the medical body area network. The method is based on measuring the rise in temperature of the liquid phantom exposed to electromagnetic waves generated by a microstrip antenna over a given time. Homogeneous liquid phantom was created by changing the percentage of salt and sugar in 250 g of water, skin phantom – by changing the percentage of water in 200 g of glycerol. The proposed specific absorption rate measurement method eliminates the need to purchase an expensive set of dielectric probes, which demonstrates its cost-effectiveness. The obtained results of experimental measurements are in good agreement with the results of the performed computer simulation.

Multiuser MIMO Uplink Transmission With Electromagnetic Exposure Constraints: Spectral Efficiency and Energy Efficiency Tradeoff

Along with the relentless development of wireless communications, the electromagnetic (EM) radiation emitted by wireless devices has gradually turned into a significant concern of the public. A growing number of government departments and communication regulatory agencies require that EM radiation be limited to a suitable level with the measurement of specific absorption rate (SAR). Meanwhile, both spectral efficiency (SE) and energy efficiency (EE) are key indicators of wireless transmission systems, so that they generally need to be considered at the same time. To this end, we investigate the resource efficiency (RE), which characterizes the weighted sum of SE and EE, in uplink multiuser multiple-input multiple-output (MIMO) transmission with EM constraints. We first simplify the RE calculation by applying its deterministic equivalents (DEs) and deal with the objective function by the quadratic transform algorithm. Then, a modified RE maximization water-filling algorithm is proposed for the precoder design at the users. Numerical results indicate the superior performance of the EM aware RE oriented transmission scheme.

Multichannel power electronics and magnetic nanoparticles for selective thermal magnetogenetics

Objective. We present a combination of a power electronics system and magnetic nanoparticles that enable frequency-multiplexed magnetothermal-neurostimulation with rapid channel switching between three independent channels spanning a wide frequency range. Approach. The electronics system generates alternating magnetic field spanning 50 kHz to 5 MHz in the same coil by combining silicon (Si) and gallium-nitride (GaN) transistors to resolve the high spread of coil impedance and current required throughout the wide bandwidth. The system drives a liquid-cooled field coil via capacitor banks, forming three series resonance channels which are multiplexed using high-voltage contactors. We characterized the system by the output channels’ frequencies, field strength, and switching time, as well as the system’s overall operation stability. Using different frequency–amplitude combinations of the magnetic field to target specific magnetic nanoparticles with different coercivity, we demonstrate actuation of iron oxide nanoparticles in all three channels, including a novel nanoparticle composition responding to magnetic fields in the megahertz range. Main results. The system achieved the desired target field strengths for three frequency channels, with switching speed between channels on the order of milliseconds. Specific absorption rate measurements and infrared thermal imaging performed with three types of magnetic nanoparticles demonstrated selective heating and validated the system’s intended use. Significance. The system uses a hybrid of Si and GaN transistors in bridge configuration instead of conventional amplifier circuit concepts to drive the magnetic field coil and contactors for fast switching between different capacitor banks. Series-resonance circuits ensure a high output quality while keeping the system efficient. This approach could significantly improve the speed and flexibility of frequency-multiplexed nanoparticle actuation, such as magnetogenetic neurostimulation, and thus provide the technical means for selective stimulation below the magnetic field’s fundamental spatial focality limits.

Design and analysis of circular microstrip patch probe array for precise specific absorption rate measurement at quad-band

AbstractThis paper distinguishes the design and analysis of 3 × 2 circular microstrip patch probe array for specific absorption rate (SAR) measurement at quad-band. This novel approach consists of FR4 substrate radial dimension of 88 mm and it has six circular array elements with a radius of 17 mm; out of these six elements, three array elements are having rectangular slots with dimensions of 1.8 × 1.5 × 1.5 mm3. The array elements are coupled with six probes which have a dimension of 100 mm with a 2.5 mm tip radius; these six probes are embedded into a tissue-equivalent liquid-filled human head mannequin. In this mannequin, instantaneous SAR at any six positions has been investigated. The proposed design resonates at 1.8, 2.1, 2.4, and 2.5 GHz with a return loss of −11.53, −15.90, −15.73, and −25.49 dB. The circular microstrip probe array is fed by a 50 Ohm coaxial feed. In addition, the 3D human head model analysis is also presented. The precisely estimated SAR values are 0.135, 0.108, 0.167, and 0.244 W/kg at 1 g of tissue. For the traceable measurements, each source of uncertainty budget has been estimated.

A Multi-Frequency 3D Printed Hand Phantom for Electromagnetic Measurements.

It has been shown that the presence of a hand holding a wireless handset (cell phone) can influence antenna efficiency and the measurement of specific absorption rate (SAR) and electromagnetic compatibility. Head phantoms, used in handset compliance testing to estimate SAR in the head, have achieved low cost and multi-frequency use. Head phantoms typically consist of a thin plastic shell, open on the top, holding a tissue simulating fluid. The specific simulant fluid used is determined by the radio frequency of the test. IEC 62209-1 has recipes, using safe nontoxic materials, for all the required frequency bands. Thus, head phantoms can be reused at different frequencies simply by changing the tissue simulating fluid. However, standards have not adopted the use of hand phantoms because SAR limits in limbs are less restrictive than the head, the tissue depth in a hand is insufficient to make accurate measurements with current electric field probes, and the cost of a solid hand phantom is limited to a single frequency band. Our goal was to determine whether 3D printing techniques would allow the construction of a hand phantom with the same utility as existing head phantoms. We developed this phantom based on computer simulations to determine how much human anatomy needed to be included in the phantom to obtain results consistent with actual use. Electric field scans of a handset alone, and held by the hand phantom, were performed. Comparison of handset scans using the phantom and human subjects was planned, but not performed due to Covid-19 restrictions and subsequent changes in priorities. We feel a fluid-filled 3D printed hand phantom is viable and practical. The 3D print files are available on GitHub.

Measurement and Calculation of SAR Due to 900 MHz Electromagnetic Waves

Purpose: The widespread use of mobile phones and Base Transceiver Stations (BTSs) has generated public concern about exposure to Electromagnetic (EM) waves. In this study, the electric field intensity and Specific Absorption Rate (SAR) in the emergency, general hospitalization, radiology, and laboratory departments of four hospitals in Arak (Iran) are reported. Materials and Methods: Electric field strength in the 900 MHz frequency band was obtained using a TES 592 radiometer. Then, SAR induced in the brain, skin, fat and bone tissues were calculated based on equations and the obtained values were compared with the thresholds recommended by the International Commissions. Results: The obtained results showed that the electric field’s mean value was 1.334 V/m which is almost 2.7% of the threshold introduced by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and 2.6% of the threshold adopted by the Institute of Electrical and Electronics Engineers (IEEE). The highest SAR value was 1.6 W/kg for the skin, which is lower than the threshold values presented by ICNIRP (2 W/kg) and IEEE (1.6 W/kg). Conclusion: The findings of the present work show that for both quantities in Arak hospitals the SAR values are less than the thresholds announced by IEEE and ICNIRP committees. To deal with the concerns of the community that is generally caused by a lack of awareness, the executions of educational and public awareness programs are recommended.

Low-profile high impedance surface on magneto-dielectric nanocomposite for wideband absorption of mobile phone radiation

An electrically thin (0.024𝜆0) high-impedance surface (HIS) on a magneto-dielectric nanocomposite (NC) is presented as an external shield for wideband absorption of mobile phone radiation. Characterization of the NC and numerical design and analysis of the miniaturized HIS unit cell on NC (0.088𝜆0 × 0.088𝜆0) are presented over 0.85–6 GHz, where 𝜆0 is the free space wavelength at the absorber resonant frequency. The absorber performance is assessed using a mobile phone handset at 0.9 and 1.8 GHz Global System for Mobile Communications (GSM) frequencies and 2.4 GHz Wireless Fidelity (WiFi) frequency. Handset specific absorption rate (SAR) measurements with the absorber recorded in head phantom indicated 83, 48 and 71% reduction in peak SAR at 0.9, 1.8 and 2.4 GHz, respectively without significantly affecting the handset radiation characteristics in free space. Simulation results of human head model with the hand showed SAR reduction of 69, 24 and 65% at 0.9, 1.8 and 2.4 GHz, respectively for 1 g SAR. It is concluded that the proposed absorber could be used to lower handset SAR levels and shield mobile communication signals over 0.85–6 GHz.

Design analysis and validation of coaxial probe for tissue dielectric properties evaluation used in specific absorption rate measurement

ABSTRACT This study distinguishes the design and analysis of a coaxial probe for measurement of biological body dielectric properties, in this measurement estimating the human tissue-equivalent liquid (TEL) permittivity and conductivity, to monitor and maintain the international standards for specific absorption rate (SAR) evaluation over the frequency band of 800 MHz-5 GHz. In addition, deionized (DI) water and ethanediol dielectric properties have been evaluated and the designed probe results compared to the commercial Dielectric Assessment kit (DAK) 3.5 probe. The obtained results are in good agreement with each other, moreover, the SAR calculation and each source of uncertainty budget analysis are estimated. Therefore, this fabricated probe may be suitable for liquid dielectric properties measurement.

Assessment of Indoor-Outdoor Wi-Fi Radiation on Human Body and its Precise SAR Measurement

There has been a lot of awareness concern about the health hazards of RF electromagnetic radiation on the human body, the radiofrequency electromagnetic field (RF-EMF) exposure assessment needs attention. This paper reports experimentally measured electromagnetic radiation emission from public place Wi-Fi devices. Indoor and outdoor measurements are done at different geographic locations in India. For the indoor assessment, the experiment was carried out in the national physical laboratory (NPL) New Delhi for 1-4 antennas Wi-Fi routers at a distance of 0-10-meter range are taken into consideration. The power density and electrical intensity were measured using a spectrum analyzer with isotropic E-field probe TSEMF-B1. For the outdoor measurements, four different Delhi metro stations Wi-fi devices at a distance of 20-meter range towards the train coach and below the Wi-fi routers have been considered. In this experiment, we used an instrument is Narda NBM-550 E-field probe for electric field and radiated power density estimation. In addition, the human whole body 3D model has been simulated in a free space environment, the measured outcome of indoor-outdoor electromagnetic radiation and specific absorption rate (SAR) is compared with the ICNIRP, FCC guideline limits at 2.45-5.87 GHz and precise SAR has been evaluated.

Internal Electric Field Reconstruction and SAR Estimation of In-Body Antenna Using Inverse Equivalent Current Method

In this article, we reconstruct the internal electric field due to a dipole antenna embedded in a dielectric phantom for developing a noninvasive specific absorption rate (SAR) measurement system. The reconstruction method is based on the surface equivalent theorem and boundary conditions, which relate the external field radiated from the embedded antenna to equivalent electromagnetic surface currents on the human body. The electric field data sampled at spatial points on a surface enclosing the phantom are used in the inverse calculation. All field integrals are discretized and numerically solved to obtain the electromagnetic currents on the phantom's surface. The internal electric field distribution and SAR value in a phantom can be calculated from the reconstructed surface currents if the electric properties of the phantom are known. The validity of the method was demonstrated numerically and experimentally using a dipole antenna embedded in the lossy rectangular phantom, which has a dielectric constant close to human skin tissue at 2.5 GHz. Comparison with forward numerical simulations has shown that the surface current and electric field distribution can be predicted with great precision. Carefully performing the experiments using a self-made phantom validated our numerical demonstration and provided satisfactory reconstruction results.

SAR measurement for different antenna configurations

Specific Absorption Rate (SAR) is a measure of radiation absorbed by the human body. SAR is expressed either as an average value of SAR in a cell of 1 gram or an average value in a cell of 10 grams. The aim of the paper is to study the average SAR value in human head due to the usage of mobile phones. The SAR values are measured and studied using a simulation software. In addition to calculating the SAR value, four different antenna configurations were designed with quarter-wave antennas to obtain the optimal design that has the least SAR value. The Specific Anthropomorphic Mannequin (SAM) phantom was used to simulate the human head and the simulation software was used to design the antennas and mobile phone.

Measurement and evaluation of specific absorption rate and temperature elevation caused by an artificial hip joint during MRI scanning

A primary safety concern in a magnetic resonance imaging environment is heating of metallic implants by absorbing radiofrequency (RF) energy during MRI scanning. Experimental measurement in conjunction with computational modeling was used to evaluate the risk of biological tissue injury from the RF heating of artificial hip joints by obtaining both specific absorption rate (SAR) and temperature elevation at 1.5 T and 3 T MRI systems. Simulation result showed that high SAR and high temperature appeared near both head and tail sections of the artificial hip joints. For five different 1.5 T and 3 T MRI systems, measured temperature location showed that high temperature rises occurred near both head and tail regions of the metallic hip joints. Measured SAR value of 24.6 W/kg and the high temperature rise (= 4.22 °C) occurred in the tail region of the hip joint at 1.5 T, which was higher than the limits for temperature required by the international electrotechnical commission 60601-2-33. We have demonstrated the feasibility of evaluating RF heating of metallic hip joints during MRI scans.

Influence of medium viscosity on the heating power and the high-frequency magnetic properties of nanobeads containing magnetic nanoparticles

Magnetic nanoparticles placed in a high frequency alternating magnetic field release heat. This phenomenon can be used to heat and kill cancerous cells, the so-called magnetic hyperthermia treatment. Our study focuses on the influence of the medium viscosity on the heating power of magnetic nanobeads (MNBs) containing superparamagnetic nanoparticles. The specific absorption rate (SAR) of two types of MNBs differing by their size was determined by measuring the area of their high-frequency hysteresis loops. Three different behaviors are observed as viscosity rises: (i) SAR first drops to a minimum value for both MNB sizes; (ii) interestingly, and only for smaller MNBs, after going through a minimum, SAR increases again towards a steady value; (iii) for larger MNBs, SAR remains constant after reaching its minimum value. The physical origin of these different behaviors is interpreted, the key ingredient to explain them being the magnetic interactions, the possibility of the bead to form chains, and their possibility to physically rotate under the influence of the magnetic field. Finally these results lead to questioning the representativeness of SAR measurements in water for nanoparticles intended for biological applications, in which the medium viscosity is very different from the one of water.

Effect of surface functionalization on the heating efficiency of magnetite nanoclusters for hyperthermia application

Here we report the effect of surface functionalization on Fe3O4 assembled nanoclusters with biopolymers, like chitosan and dextran using the solvo-thermal route. XRD analyses confirmed the formation of cubic spinel structure with crystallite sizes ranging from 11 to 14 nm. HRTEM analyses revealed the formation of spherical nanoclusters. Magnetic measurements demonstrate the typical ferromagnetic behavior with saturation magnetization (Ms) up to 71.048, 69.829 and 68.228 Am2Kg−1 for Fe3O4 (FO), chitosan coated Fe3O4 (CFO) and dextran coated Fe3O4 (DFO) respectively at room temperature. Negligible coercivity (Hc) and remenance (Mr) at room temperature implies nearly superparamagnetic behavior. Field cooled (FC) and Zero field cooled (ZFC) measurements of magnetization at an applied field of 100 Oe resulting in the blocking temperature above room temperature for all the samples. Induction heating ability of the samples under alternating magnetic field were studied by means of specific absorption rate measurements (SAR). It is shown that the surface functionalization significantly enhanced the SAR value up to 40% i.e., from 144.08 W/g for FO to 233.28 W/g for DFO at 1 mg/ml concentration. The study also concluded that the dipolar interactions are solely responsible for self-heating behavior of the nanoparticles. It was observed that by changing the sample concentration and different coatings, the final temperature can be tuned to the intended therapeutic (hyperthermia) temperature range (40–44 °C). The in vitro cytocompatibility test resulted in cell viability of more than 90%, which proved that the prepared nanomaterials are promising for the hyperthermia applications.