Variable spacing Fast-T1ρ for the analysis of fast relaxing species at low-field.

This review article comprehensively evaluates recent studies investigating the potential effects of electromagnetic fields (EMFs) emitted from various sources on human health. The literature addresses the biological effects of electromagnetic radiation (EMR) originating both from mobile communication systems (mobile phones, base stations, wireless modems) and from low-frequency power transmission lines (50 Hz). Findings indicate that specific absorption rate (SAR) and power density values can exceed international limits under certain conditions; this situation may lead to outcomes such as DNA damage, oxidative stress, neurological disorders, adverse effects on reproductive health, and hearing loss. In addition, many studies have reported symptoms including headaches, sleep disturbances, fatigue, difficulty in concentration, and skin problems. These findings reveal the necessity for further experimental and epidemiological research to understand better the short- and long-term health effects of electromagnetic exposure. In conclusion, scientific investigation of different frequencies and exposure scenarios, comprehensive evaluation of biological effects, and raising public awareness on this issue will contribute to a clearer understanding of the impacts of electromagnetic radiation on health.

For the study, we used four kerosene-based ferrofluid samples containing magnetite nanoparticles stabilized with oleic acid. Starting from the initial sample (A0), the other three samples were obtained by dilution with kerosene. The complex magnetic permeability measurements were performed in the microwave region (0.5–6) GHz, for different H values of the polarizing magnetic field, between (0–115) kA/m. These measurements revealed the ferromagnetic resonance phenomenon for each sample, allowing the determination of the anisotropy field (HA) and the effective anisotropy constant (Keff) of nanoparticles, depending on the volume fraction of particles (φ). At the same time, the measurements allowed the determination of the specific magnetic loss power (pm), effective heating rate (HReff), intrinsic loss power (ILP), and specific absorption rate (SAR) as functions of the frequency (f) and magnetic field (H), of all investigated samples, using newly proposed equations for their calculation. For the first time, this study evaluates the maximum limit of the applied polarizing magnetic field (Hmax ≈ 80 kA/m) and the minimum limit volume fraction of nanoparticles (φmin ≈ 3.5%) at which microwave heating of the ferrofluid remains efficient. At the same time, the results obtained show that the temperature increase of the ferrofluid samples, upon interaction with a microwave field, can be controlled by varying both H and φ, pointing to possible applications in magnetic hyperthermia.

Future 5G wireless systems will have substantial challenges in integrating the sub-6GHz and millimeter-wave (mm-wave) bands due to their massive frequency ratios. This paper proposes a machine learning-optimized compact wearable frequency-reconfigurable antenna for sub-6GHz/mm-wave 5G integration. Fabricated on a flexible Rogers Duroid substrate (27.8 × 14 × 0.508mm3), the antenna initially employs a circular structure resonating at 28GHz. Dual-band operation (3.5GHz and 28GHz) is achieved by etching an H-shaped slot into the rectangular patch. A PIN diode is employed to reconfigure the proposed antenna in the ON and OFF states. In the ON state, the antenna operates at 3.5GHz and 28GHz, achieving measured bandwidths of 25.4% and 73.2%, gains of 3.63 dBi and 5.25 dBi, and radiation efficiencies of 90.5% and 88%, respectively. In the OFF state, the antenna operates at 28GHz, achieving a measured bandwidth of 72.9%, gain of 6.2 dBi, and a radiation efficiency of 89%. Bidirectional E-plane and omnidirectional H-plane radiation patterns are maintained across both bands. At 3.5GHz, the specific absorption rate (SAR) value for 1g and 10g of human tissue is 0.438W/kg and 0.0147W/kg, while at 28GHz, the SAR value is 0.801W/kg and 1.09W/kg, which comply with the FCC and ICNIRP standards. Bending tests (lap, chest, arm) demonstrate stable on-body performance. The antenna's S11 was predicted using a supervised ML regression framework. Among tested algorithms, the decision tree achieved state-of-the-art accuracy (R2: 97.80%) with minimal errors (MAE: 0.72, MSE: 0.28, MSLE: 0.56, RMSLE: 0.81, RMSE: 0.66). The proposed antenna system is suitable for future 5G devices.

Radiofrequency (RF) exposure has been extensively studied for potential health risks. Unlike ionizing radiation, RF fields primarily cause thermal health effects, the only established mechanism of biological harm. Regulatory bodies, including the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the Institute of Electrical and Electronics Engineers (IEEE), set limits to prevent excessive heating. This review examines the relationship between RF exposure, heat generation, and physiological responses, with relevance to civilian and military safety. A narrative review of peer-reviewed literature, regulatory reports, and experimental studies was conducted using PubMed, IEEE Xplore, Google Scholar and Scopus. Emphasis was placed on Specific Absorption Rate (SAR) and Cumulative Equivalent Minutes at 43 °C (CEM43). Studies on thermal effects and exposure scenarios were prioritized; speculative non-thermal mechanisms were excluded. Thermal effects depend on frequency, tissue composition, and environmental conditions. Whole-body SAR limits (≤4 W/kg) generally prevent core temperature increases, but localized heating remains a concern. CEM43 provides a temperature-based metric but is difficult to apply in transient exposures. Penetration depth across NATO frequency bands shows variability because of differences in tissue models and measurement methods. This variability is clinically relevant, as localized heating of the skin, eye, or superficial nerves may occur even when whole-body exposure is within limits. Current guidelines prevent systemic overheating but may not fully address localized risks. Combining SAR and CEM43 with refined penetration depth data could improve risk assessment. Future work should refine dose-response thresholds and methods for detecting and modeling localized heating, especially under military conditions where thermoregulation may be impaired.

ABSTRACT This research presents a wearable radiator with dual‐band and quad‐terminal that is compact and made on polyimide substrate. Dual metallic rings integrated with the feed line create the band notch in between 2.66 and 3.28 GHz and convert the wideband into dual band feature. By taking use of spatial and polarization diversity, the separation level among various terminals is more than 25 dB. A single‐negative (SNG) metamaterial‐based metasurface (MS) reflector‐cum‐absorber surface located just below the radiator reduces the specific absorption rate (SAR) for the 1‐ and 10‐g tissue models by more than 90%, while also increasing the radiator gain to 5.65 and 4.55 dBi. ANSYS HFSS 2023 R2 was used for full‐wave simulations, and a Keysight E5071C VNA in both flat and bending configurations was used for experimental validation. Using a three‐layer human tissue phantom (skin, fat, and muscle) with 1‐ and 10‐g averages, SAR assessment was conducted in accordance with IEEE/IEC 62209‐1 and ICNIRP recommendations. Its performance in two frequency bands, 2.3–2.65 and 3.3–3.65 GHz, is confirmed by measurement findings. All these features make the radiator applicable for WBAN application.

Objective. Quality assurance of hyperthermia applicators can be a cumbersome task. Periodic validation of the fields generated by the applicator is crucial for ensuring proper device performance, but the required measurements are very time-consuming. While most clinics use heating rate as a parameter of interest, consensus exists that spatial variation of the electromagnetic field in three dimensions (3D) would be much more insightful. Unfortunately, such 3D coverage would require measurements at many locations.Approach. To address this challenge, we propose a compressed sensing based methodology that enables accurate E-field and specific absorption rate (SAR) reconstruction from significantly reduced sampling densities. Using a Lucite Cone Applicator (LCA) and a homogeneous tissue-mimicking phantom, E-field measurements were obtained via a robotic scanning system equipped with an isotropic EM field probe (EX3DV4, SPEAG). Field maps were reconstructed using a discrete cosine transform (DCT)-based compressed sensing algorithm and evaluated using peak signal-to-noise ratio (PSNR), structural similarity index (SSIM), and the area under 50\%-iso-field contour overlap error. This error refers to the computational reconstruction accuracy of the compressed sensing algorithm when benchmarked against a densely sampled high-resolution reference scan.Main results. Results demonstrated that accurate field reconstruction can be achieved using only 8\% of the full measurements, reducing acquisition time from 135 minutes to just 11 minutes, while maintaining clinically relevant precision (SSIM = 0.9, PSNR = 27 dB, 50\%-iso-field contour overlap error is within ± 2.5\%).Significance. In this way, the need for extensive measurements is reduced while validation reliability is maintained. This approach delivers a faster solution, enhancing information content while significantly reducing the time required for quality assurance in hyperthermia clinics.

This study presents the design and optimization of a terahertz (THz) microstrip patch antenna enhanced with photonic bandgap (PBG) structures. The antenna is implemented on a Polytetrafluoroethylene (PTFE) substrate with Single-Wall Carbon Nanotube (SWCNT) conductors, leveraging the substrate’s low loss tangent and stable permittivity together with the high conductivity of SWCNTs to improve radiation performance. Key physical parameters, including air gap side, lattice constant, and substrate thickness, were varied using CST simulations to generate a comprehensive dataset. Four machines learning models Linear Regression, K-Nearest Neighbors, Decision Trees, and Neural Networks were trained, with the neural network achieving the best predictive accuracy (R² > 0.94) and very low errors across bandwidth (± 0.05 GHz), gain (± 0.1 dBi), efficiency (< 0.5%), and return loss (0.4 dB). Optimization through a genetic algorithm identified the optimal geometry (Y = 60 μm, D = 80 μm, h = 85 μm), yielding 36.8 GHz bandwidth, 9.4 dBi gain, 93.7% efficiency, and − 26.1 dB return loss. Specific Absorption Rate (SAR) analysis confirmed safety compliance, with a maximum value of 1.4 W/kg under FCC limits. By integrating electromagnetic simulation, machine learning, and evolutionary optimization, the proposed approach provides a faster and more accurate design methodology. Owing to its compactness, efficiency, and material flexibility, the antenna shows strong potential for non-invasive medical imaging, biosensing, and wearable health-monitoring in the THz domain.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-27963-1.

This work investigated the electrical, dielectric, and magnetic properties of ferrofluids containing Fe3O4 nanoparticles and their composites with chitosan (30–100 cP and 100–300 cP), relevant to magnetic hyperthermia. The nanoparticles were synthesized by coprecipitation and characterized using impedance spectroscopy, X-ray diffraction, scanning microscopy with X-ray microanalysis, Mössbauer spectroscopy, and calorimetry. The study showed that the chitosan coating altered the textural properties of Fe3O4, reducing the specific surface area from 76.3 m2/g to 68.9–72.5 m2/g. The zeta potential and particle size showed strong pH dependence. Impedance measurements showed that the conductivity of ferrofluids was frequency- and temperature-dependent, with both metallic and dielectric conductivity observed. The complex dielectric permittivity exhibited Maxwell–Wagner–Sillars interface polarization. Calorimetry revealed that specific absorption rate (SAR) ranged from 11.4 to 23.4 W/g, depending on the chitosan concentration and type, while the chitosan coating reduced SAR by 12–40%. These results confirm that the electrical and dielectric parameters of ferrofluids significantly influence their thermal capabilities, which is important for optimizing magnetic hyperthermia therapy when energy dissipation is considered in bio-heat models.

Over the past decade, sensors for skin cancer detection, with operation at micro- and millimeter-wave frequency range, have been under investigation. Thus, safety concerns related to radiation exposure have become critical, especially for patients with vulnerable skin. Studies to date fell short in detailed safety assessments. Many evaluations rely on a single-tissue model representing a single anatomical site. Moreover, most studies assess safety solely via specific absorption rate (SAR) but omit the temperature-rise analysis induced by radiation exposure. In this work, we investigate two types of surface-wave-based antennas operating in the microwave band. Multilayer tissue models were constructed to emulate nine major body sites. The key safety metrics, including the SAR distribution and temperature increase, were analyzed through full-wave electromagnetic simulations in Ansys HFSS. The results reveal substantial inter-site variability in the metrics, highlighting the necessity of full-body evaluation prior to determining the overall safety measures for the new diagnostic devices. Furthermore, we derive power limits for surface-wave antennas in accordance with U.S. and Canadian safety standards, and verify their conservativeness via temperature analysis. Our findings provide a basis for a comprehensive framework for radiation safety assessment of wearable devices operating in the microwave band.

Ensuring reproducible treatments and therapeutic temperature rises is pivotal for wider clinical application of hyperthermia. We propose afast automated quality assurance (QA) procedure using E‑field measurements for relative specific absorption rate (SAR) applicator characterization, with asimilar workflow to radiotherapy dosimetry. Our procedure was demonstrated for 434 MHz superficial contact flexible microstrip applicators (CFMA) with similar antennas and geometry to the ALBA ON 4000D system. Applicators were placed on aliquid saline phantom. ACartesian robot performed E‑field measurements moving E‑field sensors through the phantom. We analysed the influence of spatial resolution on effective field size (EFS) measurements. Using volume measurements, we established effective penetration depth (EPD) variation across the aperture. We evaluated repeatability, measuring central planes on eight different days. Applicators/phantoms were characterized with flat and curved setups, using standard clinical and more excessive bolus thicknesses. Procedures take ~40 min per setup condition. One-centimetre spatial resolution appears sufficient for QA. EPD showed errors < 5% when determined from high-SAR regions (~80-90% of the maximum). The EFS and EPD variability between different days was < 5%. Increasing EPD and decreasing EFS with increasing curvature was observed when using the clinical bolus thickness, with more homogeneous SAR distributions for curved than for flat setups. Excessive bolus thickness resulted in irregular SAR distributions and larger EFS and EPD variations. The proposed QA procedure is characterized by fast, practical and reproducible measurements that are suitable for efficiently evaluating various setup conditions. This flexible workflow can also be used with other radiative hyperthermia systems.

This paper presents the design and performance evaluation of a compact dual-band implantable antenna (Rx) operating at 1.32 GHz and 2.58 GHz for biomedical applications. The proposed antenna is designed to receive power and data from an external transmitting (Tx) antenna operating at 1.32 GHz. The measured impedance bandwidths of the Rx antenna are 190 MHz (1.23–1.42 GHz) and 230 MHz (2.47–2.70 GHz), covering both the power transfer and data communication bands. The wireless power transfer efficiency, represented by the transmission coefficient (), is observed to be −40 dB at a spacing of 40 mm, where the Rx is located in the far-field region of the Tx. Specific Absorption Rate (SAR) analysis is performed to ensure electromagnetic safety compliance, and the results are within the acceptable exposure limits. The proposed antenna achieves a realized gain of −25 dB at 1.32 GHz and −25.8 dB at 2.58 GHz, demonstrating suitable performance for low-power implantable medical device communication and power transfer systems. The proposed design offers a promising solution for reliable biotelemetry and wireless power transfer in implantable biomedical systems.

We synthesized Co0.5Mn0.25Mg0.25Fe2−xGdxO4 (x = 0.00; 0.04; 0.06) nanoferrites using a sol–gel auto-combustion method and studied their structural, magnetic, and biological properties. XRD with Rietveld refinement confirmed the formation of a pure spinel structure with nanosized crystallites. FTIR and XPS analyses proved the presence of metal–oxygen bonds, mixed oxidation states of Fe and Co, and the successful incorporation of Gd3+. TEM images revealed nanometric particles with homogeneous elemental distribution. Magnetic measurements showed that Gd3+ doping modifies the saturation magnetization (Ms) and coercivity (Hc), with the best performance at x = 0.04 (Ms = 45.7 emu g−1, Hc = 427 Oe). Under an alternating magnetic field, the samples efficiently produced heat in the hyperthermia range, with a specific absorption rate (SAR) of about 34 W g−1 for x = 0.04. In vivo experiments in ethanol-induced liver injury models demonstrated that the x = 0.04 sample improved antioxidant activity (increased SOD and CAT levels) and restored important serum biochemical markers such as albumin, total protein, creatinine, urea, uric acid, and electrolytes. This indicates strong hepatoprotective and nephroprotective effects. Antibacterial studies further showed that the nanoferrites were more effective against Gram-positive bacteria (S. aureus, B. subtilis, B. licheniformis) than Gram-negative ones (E. coli, P. aeruginosa). Overall, our results show that Gd3+ substitution enhances both magnetic and biological properties. The x = 0.04 composition provides the best compromise between magnetic heating efficiency, antioxidant protection, and antibacterial activity, making these nanoferrites promising candidates for biomedical applications such as cancer hyperthermia therapy, antioxidant defense, and infection control.

Microwave imaging, used for breast tumor detection, requires low mutual coupling antennas in a circular array configuration, which can lead to signal degradation and distortion in the resulting images. This study proposes a Printed Monopole Antenna design with a Z-shaped slot Electromagnetic Band Gap (PMA-ZEBG) to minimize mutual coupling in a circular array configuration, resulting in a 13 dB decrease. The PMA-ZEBG is compact, measuring 35 × 40 × 1.524 mm (0.30λ0 × 0.34λ0 × 0.01λ0 at 2.61 GHz), and has a bandwidth of 3.2 GHz (2.61 GHz–5.81 GHz). Simulated Specific Absorption Rate (SAR) values at 20 mm between the breast and the antenna indicate that the antenna is within safe standards for microwave imaging. The S-parameters from the PMA-ZEBG can be used to identify and localize tumor presence by employing the Delay and Sum (DAS) algorithm within the Microwave Radar-based Imaging Toolbox (MERIT). The imaging results obtained using the PMA-ZEBG antenna display a more defined tumor image within the specified area and fewer discernible spots on the periphery.

This study introduces a compact, machine learning (ML)-enhanced dual-band antenna designed specifically for wearable applications within Wireless Body Area Networks (WBANs). Wearable antennas in WBAN applications face challenges such as human body-induced electromagnetic interference, limited bandwidth, and SAR compliance, which hinder the effective performance of conventional designs. This work addresses these issues by employing machine learning (ML) to optimize the antenna design, thereby ensuring enhanced performance and adaptability in dynamic, on-body environments. The antenna is fabricated on a flexible 30 × 48.8 mm² Rogers Duroid 3003™ substrate, and operates efficiently at 2.4 GHz and 5.8 GHz, achieving fractional bandwidths of 9.7% and 7.8%, peak gains of 4.0 dBi and 6.2 dBi, and high radiation efficiencies of 91% and 93%, respectively. The radiation profile shows a bidirectional pattern along the E-plane, while the H-plane maintains nearly uniform radiation in all directions at both frequency bands. Compliance with safety regulations was confirmed through Specific Absorption Rate (SAR) analysis, with values of 1.17 W/kg (1 g) and 0.851 W/kg (10 g) at 2.4 GHz, and 0.813 W/kg (1 g) and 0.267 W/kg (10 g) at 5.8 GHz, all well below the regulatory thresholds set by FCC and ICNIRP. Mechanical flexibility and robustness were validated through testing under bent conditions on various body regions including the chest, arm, and lap, reflecting reliable operation in realistic WBAN use cases. Additionally, antenna resonant frequency was predicted using a supervised ML regression approach. Among the evaluated algorithms, the random forest model provided the best performance with an R² value of 87.70% and low error metrics (MAE: 0.35, MSE: 0.89, MSLE: 0.21, RMSLE: 0.35, RMSE: 0.94). These results confirm the antenna’s reliability, safety, and adaptability for body-worn wireless systems.

Abstract In this article, a circularly polarized dielectric resonator antenna (DRA) array with conformal characteristics and improved specific absorption rate (SAR) has been proposed for X-band applications. The proposed structure has been fed through the corporate feed network which excites a radiating mode inside DRA, i.e., $TE_{1\delta1}$ . This mode has been utilized to enhance the impedance bandwidth which is below −10 dB for both the E- and H-plane so as to meet the requirements of next-generation defense communication and low-cost satellite systems. To generate the axial ratio (AR), the extended off-set feed has been employed to provide the required 90 $^{\circ}$ phase shift. Further, in order to enhance the gain and reduce the SAR, an electromagnetic band gap structure has been used as a reflector. Furthermore, multiple arrays have been introduced to extend the coverage area through beam-forming. The proposed design has been fabricated for the experimental validation. The measured IBW and ARBW is 34.74% and 12.2%, respectively. The gain is 10.1 dBic throughout the band of operation along with the radiation efficiency above 85% in various bending conditions. The SAR is much below the permissible limit of 1.6 W/kg. Thus, the proposed array is compact, and it clearly achieves a smaller footprint, better IBW, ARBW and a low SAR with potential prospect for X-band purposes.

Abstract Body-centric and body-worn applications have gained much more attention due to the emergence of wearable electronics. Antenna designs suitable for body-centric communications have then become a crucial part of any wearable system. This article introduces an ultra-wideband (UWB) antenna with dimensions of 24 × 18 × 0.8 mm 3 , designed using a flexible jean substrate. Using a slotted patch and defected ground, a wide impedance bandwidth of 15 GHz was achieved. A novel multiple input multiple output (MIMO) configuration with extended swastika-shaped connected ground is proposed to improve the reliability in body-centric communication. Frequency selective surface (FSS) is deployed to reduce specific absorption rate (SAR) and also to achieve directional radiation pattern at a specified frequency range to support both on- and off-body communications. A novel approach of corner-connected inter-rotated square rings was used to achieve wideband response. With the proposed FSS, the antenna renders a good peak gain of 9.1 dB, with the efficiency ranging from 72% to 94% in the UWB spectrum. The FSS proposal also helped in bringing down the SAR within the limits. All the MIMO diversity parameters reported remain good enough, ensuring link reliability. Real-time on-body measurements were carried out at various body parts. The path loss obtained while using the proposed antenna is considerably minimal. Satisfactory results were obtained from the time domain analysis carried out, which ensures good pulse similarity and minimum phase variations.

Abstract Presented in this study is a compact, dual-band, and highly flexible inverted slotted triangular-shaped monopole antenna. It is backed with a dual-band artificial magnetic conductor for off-body wireless and low specific absorption rate (SAR) medical applications. The antenna is designed to radiate at 2.45 GHz of the Industrial, Scientific, and Medical-band and achieves dual-band resonance by etching two inverted L-shaped slots off the monopole antenna. By doing so, the antenna operates at 5.2 GHz of the wireless local area network frequency band. In off-body operation, the integrated design achieves gain improvements at both operating frequencies by 6 and 4.9 dBi, respectively, compared to the standalone antenna. In the case of the on-human-body operation scenario, low SAR levels of 0.39 and 0.07 W/kg were realized at both resonant frequencies, respectively. The proposed integrated design was fabricated and tested, where the tested results highly align with the simulated ones in free space and on-body cases. The antenna size is only 39 × 25 mm 2 which is claimed to be an ultra-size. Thus, the presented antenna is claimed to be very competitive in terms of the small size and the achieved antenna parameter results.

PHASE: Personalized Head-based Automatic Simulation for Electromagnetic properties in 7T MRI.

&lt;p&gt;Metamaterials possess the capability to enhance fifth-generation (5G) communication technology. This article proposes an innovative construction of a miniature metamaterial absorber (MMA) with a dramatically improved effective medium ratio (EMR) characterized by utilizing a multi-square split-ring resonator (MSSRR) MMA unit cell specifically designed for operation in the 5G sub-7 GHz and Sub-8 GHz frequency bands. The unit cell of the MMA is designed using a commercially available FR-4 material with εr=4.3, which is cost-effective. The proposed MMA achieves a remarkably high EMR of 9.83, indicating superior compactness and design efficiency. The MMA of interest operates with absorbance peaks of 70.632%, 96.936%, and 79.930% within the frequencies of 3.554 GHz, 4.940 GHz, and 8.335 GHz, respectively. Along with the absorption analysis, our examination also includes E-field, H-field, surface current, and power flow. The expected MMA has proven potential for application in some frequency bands related to 5G, released absorption signal, and specific absorption rate (SAR) assistance.&lt;/p&gt;