Electromagnetic Field Absorption Research Articles

RF coil that minimizes electronic components while enhancing performance for rodent MRI at 7 Tesla.

This study introduces a novel volume coil design that features two slotted end-plates connected by six rungs, resembling the traditional birdcage coil. The end rings are equipped with six evenly distributed circular slots, inspired by Mansfield's cavity resonator theory, which suggests that circular slots can generate a baseline resonant frequency. One notable advantage of this proposed coil design is its reduced reliance on electronic components compared to other volume coils, making it more efficient. Additionally, the dimensions of the coil can be theoretically computed in advance, enhancing its practicality. To evaluate the performance and safety of the coil, electromagnetic field and specific absorption rate simulations were simulated using a cylindrical saline phantom and the finite element method. Furthermore, a transceiver coil prototype optimized for 7 Tesla and driven in quadrature was constructed, enabling whole-body imaging of rats. The resonant frequency of the coil prototype obtained through experimental measurements closely matched the theoretical frequency derived from Mansfield's theory. To validate the coil design, phantom images were acquired to demonstrate its viability and assess its performance. These images also served to validate the magnetic field simulations. The experimental results aligned well with the simulation findings, confirming the reliability of the proposed coil design. Importantly, the prototype coil showcased significant improvements over a similarly-sized birdcage coil, indicating its potential for enhanced performance. The noise figure was lower in the prototype versus the birdcage coil (NFbirdcage-NFslotcage= 0.7). Phantom image data were also used to compute the image SNR, giving SNRslotcage/SNRbirdcage= 34.36/24.34. By proving the feasibility of the coil design through successful rat whole-body imaging, the study provides evidence supporting its potential as a viable option for high-field MRI applications on rodents.

Corrosion and heat-resistant SiCN/C as lightweight fibers for microwave absorption and electromagnetic field shielding in Ku-band

SiCN fibers are usually combined with metals to increase the magnetic loss in electromagnetic field (EMF) shielding, but this results in high weight density, easy corrosion, difficult treatment, and high cost of the material. This study proposes the manufacturing of corrosion and heat-resistant ceramic lightweight fibers containing in-situ synthesized carbon nanostructures (SiCN/C) with excellent EMF shielding in Ku-band (12.4–18 GHz). The samples showed differential trends of EMF shielding effectiveness in terms of reflectance, transmittance, and absorption behavior. Compared to SiCN fibers, the EMF absorption was two times greater when carbon was added to the SiCN matrix. A minimum reflection coefficient (S11) of −12 dB was observed for SiCN/C fibers, meaning a high shielding efficiency with >90 % of the EMF energy shielded. On the other hand, SiCN fibers showed a minimum S11 of −7 dB, resulting in a protection of 80 % against EMF energy. Computational simulations clarified the better features of SiCN/C in electromagnetic shielding compared to SiCN, which was ascribed to enhanced conduction loss derived from conductive free carbon, and dipole and interfacial polarization loss generated by defects. The fibers were resistant to acidic and basic environments and oxidation of up to 600 °C. Moreover, the addition of carbon precursor represented a weight decrease of 17 % for SiCN/C compared to SiCN fibers. This research will afford an alternative solution for the manufacturing of SiCN/C fibers with EMF absorption properties that can be used as lightweight materials in harsh environments.

Photonic approach in stacked slabs having periodic holes for enhancing photocatalytic activities.

Photonic approaches can improve the efficiencies of photo-electrochemical devices towards CO2 reduction and fossil fuel-free societies. In a system consisting of stacked dielectric slabs having periodic holes with each slab coated by photocatalyst layers at both sides, immersed in water, we show that an incident electromagnetic field is effectively confined in the photocatalyst layers, resulting in the enhancement of the photocatalytic activities. In addition, the antireflection effect was engineered by adjusting the distances between the photonic crystal slabs. Numerical results reveal an enhancement factor of 3 for the absorption of electromagnetic fields at the operation frequency in the 3rd band of the dispersion diagram, compared to the bulk photocatalyst. Our system has the feature of periodic holes allowing the movement of reaction products. An analytical model is developed using the revised plane wave method and perturbation theory, which captures the trends observed in numerical results.

Superanomalous skin-effect and enhanced absorption of light scattered on conductive media

Light scattering spectroscopy is a powerful tool for studying various media, but interpretation of its results requires a detailed knowledge of how media excitations are coupled to electromagnetic waves. In electrically conducting media, an accurate description of propagating electromagnetic waves is a non-trivial problem because of non-local light-matter interactions. Among other consequences, the non-locality gives rise to the anomalous (ASE) and superanomalous (SASE) skin effects. As is well known, ASE is related to an increase in the electromagnetic field absorption in the radio frequency domain. This work demonstrates that the Landau damping underlying SASE gives rise to another absorption peak at optical frequencies. In contrast to ASE, SASE suppresses only the longitudinal field component, and this difference results in the strong polarization dependence of the absorption. The mechanism behind the suppression is generic and is observed also in plasma. Neither SASE, nor the corresponding light absorption increase can be described using popular simplified models for the non-local dielectric response.

Development of materials with a multilayer structure of the gradient type based on liquid compositions for the shielding of electromagnetic fields

Nowadays, for shielding and absorption of electromagnetic fields of a wide frequency range, composite materials or solid metal structures are offered and widely used. The article deals with research and development of multilayer protective liquid materials for shielding electric, magnetic and electromagnetic fields of a wide frequency range. A series of liquid shielding mixtures based on standard certified paints and finely dispersed magnetite was produced. Testing of the protective properties of these mixtures was carried out by sequentially applying 2–3 layers of mixtures to the surface, each of which had a certain concentration of the shielding substance. The shielding and reflection coefficients for these multilayer structures are given. It is shown that the advantage of the developed multilayer protective liquid materials lies in obtaining a gradient of electrophysical and magnetic properties of the protective structure with the possibility of calculating dielectric and magnetic permeabilities, taking into account the morphology of the shielding particles. A method of obtaining protective materials of the gradient type, which reduce the influence of electromagnetic fields, is proposed, which is possible for the treatment of surfaces of large areas and complex configurations.

Manipulation of ferroelectric polarization and light absorption in non-noble metal/Aurivillius ferroelectric hybrid to enhance self-driven photodetection by coupling ferro-pyro-phototronic and plasmonic effect

Aurivillius ferroelectrics materials with layer perovskite structure, spontaneous polarization and ferro-pyro-phototronic effect afford a promising avenue for self-powered photodetectors. Nevertheless, poor photo-response caused by weak remanent polarization and low absorption coefficient hinders their further application. Herein, we demonstrate an excellent self-powered photodetector in nanosheets-assembled Bi microspheres array/Nd-doped Bi4Ti3O12 [Bi3.8Nd0.2Ti3O12] nanofibers heterostructured, which can rationally couple between ferroelectric polarization and ferro-pyro-phototronic effect in Aurivillius ferroelectric Bi3.8Nd0.2Ti3O12 and plasmonic effect in non-noble metal Bi. Firstly, an A-site doping with lanthanoid cation Nd3+ and dimension lowering strategy is proposed to improve the ferroelectric properties by reducing the oxygen vacancy concentration and coercive force field of Bi4Ti3O12 nanofibers through electrospinning method. Furthermore, the Bi nanosheets-assembled microspheres array allowing multiple reflection and scattering of incident light is introduced to enhance the local electromagnetic field and light absorption of Bi3.8Nd0.2Ti3O12. Ultimately, the Bi@Bi3.8Nd0.2Ti3O12 with negatively polarized obtains a superior zero-bias photocurrent of -500 nA under 390 nm laser illumination, which is 195.31 and 22.16 times higher than unpolarized Bi4Ti3O12 and Bi3.8Nd0.2Ti3O12, respectively. Simultaneously, an outstanding detectivity (8.11 ×1011 Jones) and fast photoresponse time (57/114 µs) are correspondingly achieved. Our research provides a reliable way to simultaneously realize large ferroelectric polarization and high light absorption for jointly manipulation of electrons and photons in self-powered optoelectronic devices.

High-quality factor mid-infrared absorber based on all-dielectric metasurfaces.

The absorption spectrum of metasurface absorbers can be manipulated by changing structures. However, narrowband performance absorbers with high quality factors (Q-factor) are hard to achieve, mainly for the ohmic loss of metal resonators. Here, we propose an all-dielectric metasurface absorber with narrow absorption linewidth in the mid-infrared range. Magnetic quadrupole resonance is excited in the stacked Ge-Si3N4 nanoarrays with an absorption of 89.6% and a Q-factor of 6120 at 6.612 µm. The separate lossless Ge resonator and lossy Si3N4 layer realize high electromagnetic field gain and absorption, respectively. And the proposed method successfully reduced the intrinsic loss of the absorber, which reduced the absorption beyond the resonant wavelength and improved the absorption efficiency of Si3N4 in the low loss range. Furthermore, the absorption intensity and wavelength can be modulated by adjusting the geometric parameters of the structure. We believe this research has good application prospects in mid-infrared lasers, thermal emitters, gas feature sensing, and spectral detection.

Near Field Radio Frequency Electromagnetic Field Exposure of a Western Honey Bee

It has been suggested that the wireless network evolution to smaller carrier wavelengths (from 2G to 5G) increases radio frequency electromagnetic field (RF-EMF) absorption in western honey bees ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Apis mellifera</i> ). It is unknown whether the radiation performance of antennas is stable when an insect appears in their vicinity. In this research, the absorbed power in a worker honey bee and the influence of the bee’s presence on antennas’ radiation performance are investigated for the newly used frequencies in 5G networks from 6 to 240 GHz. To these aims, numerical simulations using the finite-difference time-domain (FDTD) method were performed, in which a bee model, obtained by micro-CT scanning, was employed. These simulations showed that, in the near field, the absorbed power can increase by a factor of 53 from 6 to 240 GHz. This is a factor of 7 higher than the increase reported in the far-field in previous studies. Furthermore, the simulations revealed that antennas’ radiation efficiency can decrease by up to −40% when a bee appears in the near field. Likewise, it was found that the gain pattern depends on the separation distance between the bee and the antenna with a stronger dependency for higher frequencies.

ЩИТОВИДНАЯ ЖЕЛЕЗА – НОВЫЙ КРИТИЧЕСКИЙ ОРГАН ВОЗДЕЙСТВИЯ ЭЛЕКТРОМАГНИТНЫХ ПОЛЕЙ МОБИЛЬНОЙ СВЯЗИ: ОЦЕНКА ВОЗМОЖНЫХ ПОСЛЕДСТВИЙ ДЛЯ ДЕТЕЙ И ПОДРОСТКОВ

This publication provides an analysis of the studies of Russian and foreign scientists dealing with the problem of studying the effect of electromagnetic fields on the state of the thyroid gland as a new critical organ directly experiencing this type of exposure when using a new generation of mobile communications – smartphones. The review includes an introduction, five sections, and a conclusion.&#x0D; In the section “Distribution of absorbed doses when using mobile phones” studies of the distribution and level of absorption of electromagnetic fields when using mobile communications, including the thyroid gland, are presented. The issues of modelling taking into account the size of the head and the properties of the tissues of children are discussed. “Epidemiological and statistical assessments of thyroid dysfunction” – this section summarizes the data on the incidence of the thyroid gland among the child population in Russia for the period 1990 – 2019. The section “Experimental studies” presents the experimental data of domestic and foreign scientists on morphological and hormonal changes in the thyroid gland of experimental animals when exposed to electromagnetic fields of cellular communication. Biomedical studies of the effects of their impact are described in the section “Changes in the functioning of the thyroid gland in mobile users”. The review is completed by the section “Possible long-term consequences of prolonged exposure to electromagnetic fields on the thyroid gland in mobile communication users”.

VISUALIZATION OF MICROWAVE ABSORPTION OF THE GRAPHITE PERIODICAL STRUCTURE WITH THERMOELASTIC OPTICAL MICROSCOPE

This paper shows a non-destructive visualization of the absorption of microwave filed by a graphite periodic structure. The visualization system was a thermo-elastic optical indicator microscope. The article presents the interaction of the electromagnetic field with graphite cylindrical cells of periodicity and shows the distribution of the electromagnetic field over the graphite cells. Depending on the distance between the periodic structure of graphite and the microwave source, the electromagnetic field distribution and absorption rate were different. The visualization was performed using a microwave signal with a frequency of $11~GHz$ and a maximum power of $35~dBm$.

Modelling the Influence of Electromagnetic Field on the User of a Wearable IoT Device Used in a WSN for Monitoring and Reducing Hazards in the Work Environment.

The aim of this study was to evaluate the absorption in a user’s head of an electromagnetic field (EMF) emitted by the Wi-Fi and/or Bluetooth module of a wearable small Internet of Things (IoT) electronic device (emitting EMF of up to 100 mW), in order to test the hypothesis that EMF has an insignificant influence on humans, and to compare the levels of such EMF absorption in various scenarios when using this device. The modelled EMF source was a meandered inverted-F antenna (MIFA)-type antenna of the ESP32-WROOM-32 radio module used in wearable devices developed within the reported study. To quantify the EMF absorption, the specific energy absorption rate (SAR) values were calculated in a multi-layer ellipsoidal model of the human head (involving skin, fat, skull bones and brain layers). The obtained results show up to 10 times higher values of SAR from the MIFA located in the headband, in comparison to its location on the helmet. Only wearable IoT devices (similar in construction and way of use to the investigated device) emitting at below 3 mW equivalent isotropically radiated power (EIRP) from Wi-Fi/Bluetooth communications modules may be considered environmentally insignificant EMF sources.

Analysis of Electromagnetic Energy Absorption in the Human Body for Mobile Terminals

The human body’s absorption of electromagnetic fields from communication enabled devices has consistently been a research topic for both researchers from universities and companies in the mobile communication industry. The absorption of electromagnetic fields could mainly result in two consequences: (a) antenna radiation efficiency of the device could deteriorate dramatically; and (b) a large amount of the radiated power could be dissipated into the human body, such as the hand, ear, scalp and brain, which is defined and described by Specific Absorption Rate (SAR). A comprehensive analysis of electromagnetic field absorption by the human body has been carried out to explain and answer some of the key questions in this area.

Análisis de capas PML en una región de campo electromagnético utilizando el Método de Diferencias Finitas en el Dominio del Tiempo

The Finite Difference in Time Domain (FDTD) method is currently one of the most used electromagnetism methods in electromagnetic field simulation, however, in order to obtain reliable results from this simulation it is necessary to have optimal boundary conditions. Perfectly Coupled Layers (PML) is characterized by the decomposition of the transversal field to the direction of propagation in its rectangular projections, and the use of both electrical and magnetic conductivity in the numerical layers for the absorption of electromagnetic fields. The PML layers are characterized by values of permittivity, permeability and conductivity that are assigned to each of the equations according to their position in the region. Because it is the same set of equations there is no need to use connection conditions at the junction of the analysis region with the PML absorption region, which provides a natural transition throughout the region. This paper presents the study of the difference between the calculation region with and without PML layers.

In vivo potassium MRI of the human heart.

Potassium ions (K+ ) play a critical role in cardiac electrophysiology, and changes in their concentration reflect pathophysiological processes related to cardiovascular diseases. Here, we investigated the feasibility of in vivo 39 K MRI of the human heart. To achieve this, we developed, evaluated, and applied a 39 K/1 H RF coil, which is tailored for 39 K MRI of human heart at 7.0T. The performance of the 39 K/1 H RF coil was evaluated by electromagnetic field and specific absorption ratio simulations using 2 (male/female) human voxel models. The RF coil was evaluated at the bench and applied in an in vivo proof-of-principle study involving 7 healthy volunteers. The experiments were performed using a 7.0T whole-body MR system in conjunction with a 3D density-adapted projection reconstruction imaging technique. For in vivo 39 K MRI of the human heart, a nominal spatial resolution of 14.5 × 14.5 × 14.5 mm3 within a total scan time of 30 min was achieved. The average SNR within the heart was 9.6 ± 2.4. This work validates the design of a 39 K/1 H RF coil for cardiac MR at 7.0T and demonstrates for the first time in vivo the feasibility of 39 K MRI of the human heart.

Cardiorenal sodium MRI at 7.0 Tesla using a 4/4 channel 1 H/23 Na radiofrequency antenna array.

Cardiorenal syndrome describes disorders of the heart and the kidneys in which a dysfunction of 1 organ induces a dysfunction in the other. This work describes the design, evaluation, and application of a 4/4-channel hydrogen-1/sodium (1 H/23 Na) RF array tailored for cardiorenal MRI at 7.0 Tesla (T) for a better physiometabolic understanding of cardiorenal syndrome. The dual-frequency RF array is composed of a planar posterior section and a modestly curved anterior section, each section consisting of 2 loop elements tailored for 23 Na MR and 2 loopole-type elements customized for 1 H MR. Numerical electromagnetic field and specific absorption rate simulations were carried out. Transmission field ( ) uniformity was optimized and benchmarked against electromagnetic field simulations. An in vivo feasibility study was performed. The proposed array exhibits sufficient RF characteristics, homogeneity, and penetration depth to perform 23 Na MRI of the heart and kidney at 7.0 T. The mean field for sodium in the heart is 7.7 ± 0.8 µT/√kW and in the kidney is 6.9 ± 2.3 µT/√kW. The suitability of the RF array for 23 Na MRI was demonstrated in healthy subjects (acquisition time for 23 Na MRI: 18 min; nominal isotropic spatial resolution: 5 mm [kidney] and 6 mm [heart]). This work provides encouragement for further explorations into densely packed multichannel transceiver arrays tailored for 23 Na MRI of the heart and kidney. Equipped with this technology, the ability to probe sodium concentration in the heart and kidney in vivo using 23 Na MRI stands to make a critical contribution to deciphering the complex interactions between both organs.

Millimeter spatial resolution in vivo sodium MRI of the human eye at 7 T using a dedicated radiofrequency transceiver array.

The aim of this study was to achieve millimeter spatial resolution sodium in vivo MRI of the human eye at 7 T using a dedicated six-channel transceiver array. We present a detailed description of the radiofrequency coil design, along with electromagnetic field and specific absorption ratio simulations, data validation, and in vivo application. Electromagnetic field and specific absorption ratio simulations were performed. Transmit field uniformity was optimized by using a multi-objective genetic algorithm. Transmit field mapping was conducted using a phase-sensitive method. An in vivo feasibility study was carried out with 3-dimensional density-adapted projection reconstruction imaging technique. Measured transmit field distribution agrees well with the one obtained from simulations. The specific absorption ratio simulations confirm that the radiofrequency coil is safe for clinical use. Our radiofrequency coil is light and conforms to an average human head. High spatial resolution (nominal 1.4 and 1.0 mm isotropic) sodium in vivo images of the human eye were acquired within scan times suitable for clinical applications (∼ 10 min). Three most important eye compartments in the context of sodium physiology were clearly delineated in all of the images: the vitreous humor, the aqueous humor, and the lens. Our results provide encouragement for further clinical studies. The implications for research into eye diseases including ocular melanoma, cataract, and glaucoma are discussed. Magn Reson Med 80:672-684, 2018. © 2018 International Society for Magnetic Resonance in Medicine.

Microscopic Origin of Surface-Enhanced Circular Dichroism

Circular dichroism (CD), the difference in absorption of two opposite circularly polarized light sources by chiral molecules, can be significantly enhanced when molecules are adsorbed on the surface of nanostructures. We present a theory based on Poynting’s theorem adapted for chiral media to analyze the surface-enhanced CD of a chiral molecule/nanostructure coupled system. Our theory clarifies the microscopic origin of surface-enhanced CD signals by showing that the enhanced CD has two forms, inherent and induced. The inherent CD is the direct molecular CD that becomes enhanced due to the strongly localized optical helicity density near the nanostructure. The induced CD, previously ignored, derives from asymmetric excitation and absorption of electromagnetic fields inside the nanostructures surrounded by chiral molecules upon the injection of two oppositely circularly polarized light sources. Moreover, it is demonstrated that the induced CD can contribute significantly to the CD signals measured by surfa...

Validation of Numerical Models of Portable Wireless Devices for Near-Field Simulation

The major contribution of the paper is a theoretical proof of the equivalence between two approaches of near-field validation techniques for the numerical models of personal wireless communication devices. The current validation practice is to compare measured and computed electromagnetic field or specific absorption rate distributions. A new validation technique introduced by the authors recently compared measured and computed antenna input-impedance changes while the near field is systematically perturbed by a dielectric control object. The proof of the equivalence is based on two novel formulas derived here: a reaction impedance-change formula, and an error formula that establishes a quantitative relationship between the errors of the impedance changes and the near-field values. The equivalence of the two validation techniques is verified experimentally too by comparing measurements and computations for a planar-inverted F antenna. By performing numerical experiments for two types of printed-circuit board antennas, it is also proved here the first time that the new validation technique is feasible even if the geometric and material properties of the control object are such that the Born approximation can be introduced in the impedance-change formula.

A high-performance light absorber based on a metamaterial nanopyramid array

A high-performance light absorber based on a metamaterial nanopyramid array, which is constructed by alternating aluminum and germanium multilayered thin films, is proposed and numerically studied. The proposed absorber exhibits ultra-flat and nearly 100% absorption performance with the properties of being wide-angle, polarization-insensitive and omnidirectional in the incident waveband ranging from 200nm to 3.6µm. The electromagnetic field and Poynting vector distribution of the nanopyramidal structure are analyzed in detail, and it is found that the electric field is enhanced at the edge of the metal-dielectric taper, while the magnetic field is trapped inside the structure. Moreover, the results show that the electromagnetic field absorption position shifts downward with increased incident wavelength, this is accompanied with an enlarged absorption volume. The nearly perfect absorption of the proposed absorber is attributed to the electric dipole resonance and magnetic polaritons. Properties of ultra-broadband perfect absorption and excellent angle-related performance for the pyramidal structure make it an attractive device in the fields of solar photovoltaic devices and thermal emitters.

Transparent and Flexible Antenna for Wearable Glasses Applications

This paper aims to design, fabricate, and analyze transparent and flexible monopole antennas for an application in wearable glasses. A multilayer electrode film composed of 100-nm-thick indium–zinc–tin oxide (IZTO)/Ag/IZTO (IAI), a type of transparent conducting oxide electrodes, is selected as the conductors of antennas and ground planes of the wearable glasses. The average transparency of the proposed antennas is measured to be 81.1% in the visible wavelength, and the electrical conductivity of the proposed antennas is measured to be 2 000 000 S/m. The proposed antennas are fabricated with physical vapor deposition process in high vacuum. Moreover, nontransparent antennas made of a 40-nm-thick silver (Ag) thin film are designed and fabricated to compare their performances with the transparent IAI antennas. To reduce the electromagnetic field absorption of the human head, we introduced and analyzed three configurations (types A–C) of monopole antennas having different directions of radiation patterns. The fabricated IAI antennas show the average efficiency of 40% and 4-dBi peak gain at 2.4–2.5 GHz. Furthermore, they have a specific absorption rate lower than 1.6 W/kg, which complies with the Federal Communications Commission standard, when the input power is 15 dBm, which is Google Glass’s.