Radiofrequency Exposure Research Articles

Assessment of morphological criteria for the efficiency of radiofrequency circumferential denervation of the pulmonary artery in the experiment (animals, pigs)

The aim of the study. To assess the influence of radiofrequency circumferential exposure modes on the morphological parameters of the pulmonary artery tissues in animal experiment (pigs).Material and methods. In the experiments, we used outbred pigs divided into 3 groups (4 animals in each). The first experimental group included 188 histological samples of the pulmonary arteries (PA) after radiofrequency circumferential exposure on the PA using an ablator clamp. Two lines of exposure on the PA and two lines of exposure on each PA mouth were performed. Ablation was performed until the target level of tissue impedance between the ablator branches corresponding to the values at transmural damage was reached. The second experimental group included 162 histological samples of the PA after circumferential denervation of pulmonary trunk and both PA mouths. Ablation was completed upon reaching 50 % impedance level relative to the impedance values at transmural damage. The third group (control) included 55 histological samples of PA without radiofrequency exposure. The material obtained was studied using light microscopy, hematoxylin and eosin and van Gieson’s staining, and also by impregnation with silver salts according to S. Ramón y Cajal.Conclusions. Morphological criteria for irreversible destruction of nerve fibers and ganglia of the pulmonary trunk adventitial layer and for PA bifurcation were obtained when using two studied ablation modes. Circumferential PA denervation using subthreshold power of radiofrequency exposure made it possible to avoid irreversible damage to the nerve endings and ganglia of the PA intimal layer and thus to preserve physiological neuroreflectory regulation of the PA and the entire pulmonary circulation. Turning off the cascade of pathological reflexes eliminates the factor of the progression of pulmonary hypertension associated with an increase in peripheral resistance of the pulmonary arterioles precapillary link.

A comparative study of RF heating of deep brain stimulation devices in vertical vs. horizontal MRI systems.

The majority of studies that assess magnetic resonance imaging (MRI) induced radiofrequency (RF) heating of the tissue when active electronic implants are present have been performed in horizontal, closed-bore MRI systems. Vertical, open-bore MRI systems have a 90° rotated magnet and a fundamentally different RF coil geometry, thus generating a substantially different RF field distribution inside the body. Little is known about the RF heating of elongated implants such as deep brain stimulation (DBS) devices in this class of scanners. Here, we conducted the first large-scale experimental study investigating whether RF heating was significantly different in a 1.2 T vertical field MRI scanner (Oasis, Fujifilm Healthcare) compared to a 1.5 T horizontal field MRI scanner (Aera, Siemens Healthineers). A commercial DBS device mimicking 30 realistic patient-derived lead trajectories extracted from postoperative computed tomography images of patients who underwent DBS surgery at our institution was implanted in a multi-material, anthropomorphic phantom. RF heating around the DBS lead was measured during four minutes of high-SAR RF exposure. Additionally, we performed electromagnetic simulations with leads of various internal structures to examine this effect on RF heating. When controlling for RMS B1+, the temperature increase around the DBS lead-tip was significantly lower in the vertical scanner compared to the horizontal scanner (0.33 ± 0.24°C vs. 4.19 ± 2.29°C). Electromagnetic simulations demonstrated up to a 17-fold reduction in the maximum of 0.1g-averaged SAR in the tissue surrounding the lead-tip in the vertical scanner compared to the horizontal scanner. Results were consistent across leads with straight and helical internal wires. Radiofrequency heating and power deposition around the DBS lead-tip were substantially lower in the 1.2 T vertical scanner compared to the 1.5 T horizontal scanner. Simulations with different lead structures suggest that the results may extend to leads from other manufacturers.

Effects of radiofrequency field from 5G communications on the spatial memory and emotionality in mice

ABSTRACT The rapid development of 5G network technology has gained much popularity as well as concerns about its adverse effects. In this study, we investigated the effects of 4.9 GHz (one of working frequencies of 5G communication) radiofrequency (RF) field on emotional behaviours and spatial memory in adult male mice. Open field test (OFT), tail suspension test (TST) and Y maze were used to evaluate anxiety, depression-like behaviour and spatial memory ability, respectively. It was found that the anxiety-like behaviour and spatial memory ability of mice did not change, but the depression-like behaviour was induced in mice after 4.9 GHz RF exposure. In addition, the number of neurons significantly reduced and the level of pyroptosis obviously increased in amygdala rather than hippocampus. These results suggested that 4.9 GHz RF exposure could induce depression-like behaviour, which might be associated with the neuronal pyroptosis in amygdala.

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

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

Carcinogenesis from chronic exposure to radio-frequency radiation.

The past two decades have seen exponential growth in demand for wireless access that has been projected to continue for years to come. Meeting the demand would necessarily bring about greater human exposure to microwave and radiofrequency (RF) radiation. Our knowledge regarding its health effects has increased. Nevertheless, they have become a focal point of current interest and concern. The cellphone and allied wireless communication technologies have demonstrated their direct benefit to people in modern society. However, as for their impact on the radiation health and safety of humans who are unnecessarily subjected to various levels of RF exposure over prolonged durations or even over their lifetime, the jury is still out. Furthermore, there are consistent indications from epidemiological studies and animal investigations that RF exposure is probably carcinogenic to humans. The principle of ALARA-as low as reasonably achievable-ought to be adopted as a strategy for RF health and safety protection.

Assessment of incident power density in different shapes of averaging area for radio-frequency exposure above 6 GHz

Objective. The International Commission on Non-Ionizing Radiation Protection guidelines and IEEE C95.1-2019 standard for human protection from local electromagnetic field exposure above 6 GHz state that absorbed (or epithelial) power density (APD) and incident power density (IPD), averaged over a square area, are internal and external physical quantities, respectively, that set the exposure limit. Per exposure standards, the measurement procedure and evaluation of the IPD have been established in technical standards, where a circular averaging area is recommended only for non-planar surfaces in IEC/IEEE 63195-1 and -2. In this study, the effects of two averaging shapes on the APD and IPD are evaluated computationally to provide new insights from the viewpoint of exposure standards. Approach. The relation between the APD, IPD, and the steady-state temperature rise (heating factor) in rectangular and human models for exposure to a single dipole, dipole arrays, and the Gaussian beams is investigated computationally with finite-difference method. Main results. The maximum differences in the heating factor of the APD and IPD for square and circular averaging areas were 4.1% and 4.4% for the antenna–model distance >5 mm, respectively. These differences appear when the beam pattern on the model surface has an elliptical shape. For an antenna–model distance ≤5 mm and at frequencies ≤15 GHz, the heating factors for square averaging areas were not always conservative to those for circular ones (−7.8% for IPD), where only the antenna feed point are visible before beam formation. Significance. The heating factors of the APD and IPD for a circular averaging area are conservative for near-field exposure of canonical sources for frequencies up to 300 GHz, except for a beam with a significant major-to-minor axis ratio and an angle of 30°–60° to a square averaging area. This tendency would help bridge the gap between exposure and product standards.

An effective edge conductivity for reducing staircasing error in induced electric field computation for low-frequency magnetic field dosimetry

Objective. In the low-frequency exposure (<100 kHz), the induced electric field strength is used as a metric for assessment for human protection. Unlike radio-frequency exposure (>MHz), the computational assessment suffers from staircasing error in biological objects. The international guidelines consider additional reduction factor of 3 when setting the limit. Here we propose a new method to reduce the staircasing error in the skin for low-frequency magnetic field dosimetry of voxelized body models. Approach. We have proposed a new method considering the filling ratio of the skin tissue to the air–skin and skin–fat interfaces to determine an effective conductivity for each voxel edge. The proposed method was applied to voxel head models exposed to a uniform magnetic field at 50 Hz. After validation using layered spherical models with several resolutions, anatomical head models are used for further verification. Main results. A comparison of maximum electric field strengths with analytic solutions in two-layer sphere models suggested that the differences in the proposed approach were less than 5.6%, which was smaller than those without the proposal of 26.7%. The distribution of the skin electric field become smoother using the proposed approach, and the staircasing effects were almost unobservable from the field distributions. Significance. The proposed method suggests vital implications for determining induced electric fields in the skin, which is needed to set the limit for human protection from low-frequency electromagnetic fields. The method would be useful when setting the reduction factor and limit in the exposure guidelines and standard.

It is mandatory to review environmental radiofrequency electromagnetic field measurement protocols and exposure regulations: An opinion article.

It is mandatory to review environmental radiofrequency electromagnetic field measurement protocols and exposure regulations: An opinion article.

Effect of radiofrequency exposure on body temperature: Real-time monitoring in normal rats

Radiofrequency radiation (RFR) can generate heat in living organisms. In this study, we monitored the body temperature of healthy animals during RFR exposure in real time using an implantable iButton data logger. A reverberation chamber system for small animals was used for this radiofrequency (RF) exposure in vivo study. Healthy male Sprague-Dawley rats were divided into two groups: with versus without iButton implantation (n = 20 per group). Each group was further divided into a sham-exposed and RF-exposed group (n = 10 per subgroup). Rats were exposed to a 1,760-MHz long-term evolution (LTE) signal in the reverberation chamber system at a whole-body average specific absorption rate of 0 W/kg (sham-exposed) or 4 W/kg (RF-exposed) for 6 h. The body temperature of iButton-implanted rats was recorded using an intraperitoneally implanted iButton every minute over 6 h of RF exposure, whereas that of non-implanted rats was measured directly using a rectal thermometer immediately before and after the 6-h RF exposure period. The temperature values measured by the two types of thermometers were significantly positively correlated (r = 0.63, P < 0.01, linear regression), and changes in body temperatures recorded in iButton-implanted and non-implanted rats measured using two thermometers after 6 h of RF exposure were maintained within <1°C (P = 0.87, general linear model, followed by univariate model). Similar results were obtained for rectal thermometer measurements (P = 0.12, paired t-test). These results suggest that RF exposure at a whole-body average specific absorption rate of 4 W/kg does not induce significant changes in body temperature in healthy rats over a 6-h RF exposure period.

Measurement of personal radio frequency exposure in Japan: The Hokkaido Study on the Environment and Children's health

The opportunities for exposure to radiofrequency electromagnetic fields (RF-EMF) among children are increasing. Children's exposure to RF-EMF in Japan was recorded using a personal exposure meter (ExpoM-RF), and factors associated with the exposure examined. A total of 101 children, aged 10–15 years old, participated in the prospective birth cohort “Hokkaido study”. RF-EMF data were recorded in the 700 MHz-5.8 GHz frequency range for 3 days. The recorded data were summarized into six groups of frequency bands: downlink from mobile phone base stations (DL), uplink from mobile phones to a base station (UL), Wireless Local Area Network (LAN), terrestrial digital TV broadcasting (digital TV), 2.5 GHz and 3.5 GHz Time Division Duplex (TDD), 1.9 GHz TDD, and total (the summation of power density in all measured frequency bands). A questionnaire was used to document the internet environment (at home) and mobile phone usage. Personal RF-EMF exposure in Japanese children was lower than that reported in studies in Europe. The DL signals from mobile phone base stations were the most significant contributors to total exposure, while Wireless LAN and digital TV were only higher at home. The urban residence was consistently associated with increases in the four groups of frequency bands (DL, UL, digital TV, and TDD). TDD level has several associations with mobile phone usage (calls using mobile phones, video viewing, text message service, and online game). The association between inattention/hyperactivity subscale of the Strengths and Difficulties Questionnaire (SDQ) and higher Wireless LAN exposure at nighttime was also noted. Further studies with additional data will shed light on factors involved in RF-EMF exposure among Japanese children.

Externally Triggered Drug Delivery Techniques Using Micro and Nanoparticles

The need for sustained and better-controlled drug administration has led to development of novel drug delivery systems. The concentration of a drug in blood at any given time depends on the prescribed routine of drug intake. Conventional methods of drug intake do not always maintain the required consistent drug concentration. Controlled drug release mechanisms can help in maintaining drug dosage levels while optimizing therapeutic effects. Microparticles and nanoparticles, initially developed as carriers for vaccines and anticancer drugs, are being used in drug delivery systems for drug targeting, improved release profile and efficiency. The drugs can be encapsulated inside the particles, suspended in or with them. However, release of the drug depends on the type of techniques used to trigger drug delivery. This review outlines the major techniques used for drug delivery applications based on external triggering mechanisms while utilising micro and/or nanoparticles. These techniques include ultrasound, light, radiofrequency, electric and magnetic field exposures. Most of these techniques have largely remained in vitro owing to challenges concerning safety due to exposure levels and penetration of external signals due to human physiology. Considering these aspects of the challenge, microwave based external triggering can be a prospective technology for drug delivery using micro and nanoparticles.

Comparative study between radiofrequency-induced and muscimol-induced inhibition of cultured networks of cortical neuron.

Previous studies have shown that spontaneously active cultured networks of cortical neuron grown planar microelectrode arrays are sensitive to radiofrequency (RF) fields and exhibit an inhibitory response more pronounced as the exposure time and power increase. To better understand the mechanism behind the observed effects, we aimed at identifying similarities and differences between the inhibitory effect of RF fields (continuous wave, 1800 MHz) to the γ-aminobutyric acid type A (GABAA) receptor agonist muscimol (MU). Inhibition of the network bursting activity in response to RF exposure became apparent at an SAR level of 28.6 W/kg and co-occurred with an elevation of the culture medium temperature of ~1°C. Exposure to RF fields preferentially inhibits bursting over spiking activity and exerts fewer constraints on neural network bursting synchrony, differentiating it from a pharmacological inhibition with MU. Network rebound excitation, a phenomenon relying on the intrinsic properties of cortical neurons, was observed following the removal of tonic hyperpolarization after washout of MU but not in response to cessation of RF exposure. This implies that hyperpolarization is not the main driving force mediating the inhibitory effects of RF fields. At the level of single neurons, network inhibition induced by MU and RF fields occurred with reduced action potential (AP) half-width. As changes in AP waveform strongly influence efficacy of synaptic transmission, the narrowing effect on AP seen under RF exposure might contribute to reducing network bursting activity. By pointing only to a partial overlap between the inhibitory hallmarks of these two forms of inhibition, our data suggest that the inhibitory mechanisms of the action of RF fields differ from the ones mediated by the activation of GABAA receptors.

The Effect of Electromagnetic Radiation Transmitted from Routers on Antibiotic Susceptibility of Bacterial Pathogens.

Background: Electromagnetic non-ionizing radiation has both thermal and non-thermal outcomes on biological systems, such as humans, animals, and bacteria.Objective: This study aimed to investigate the effect of non-ionizing radiofrequency radiation, emitted by Wi-Fi routers, on bacterial strains and the modification of their susceptibility to modern antibiotics.Material and Methods: In this case-control paired study, four bacteria were selected, and one colony from each bacterial strain was exposed to Wi-Fi radiation forming the exposure group. Another set of colonies was not exposed to Wi-Fi radiation, forming the control group. Eight different antibiotic disks were set on the bacterial plates, and the inhibition zone was measured every 3 h for each colony.Results: Electromagnetic radiation affects bacterial colonies and their susceptibility to antibiotics. Analysis revealed statistically significant differences, correlated with the bacterial strain, the antibiotic agent, and the time of the exposure, in the inhibition zones, mostly after 6 and 24 h (p-value < 0.05). Conclusion: A correlation was observed between antibiotic susceptibility and non-ionizing radiofrequency exposure. Studying the effects of radiofrequency radiation on prokaryotic organisms could clarify more complicated cell structures and organisms, such as eukaryotic. Further experiments, in vitro and in vivo, could provide more information about these outcomes and cause experts to discuss the current guidelines of exposure limits.

Evaluation of clinical results of combined correction of age-related skin changes using fractional microneedle therapy and platelet-rich plasma activated by autologous thrombin.

Background. Involutive processes in the human body are often accompanied by the only visible manifestation - a change in appearance. Against this background, the search for new treatment methods that will focus on timely and rational correction of age-related skin changes and combine the possibility of complex effects on the mechanisms of skin aging is relevant. Hardware physiotherapy technologies and innovative autologous cellular preparations have a powerful regenerative potential, trigger and support physiological tissue regeneration. Despite the substantial amount of data on combined aesthetic correction protocols, there were only isolated data in the domestic and foreign literature on the combined use of fractional needle radiofrequency therapy and platelet-rich plasma activated by autologous thrombin. This was the basis for this study.&#x0D; Aims. To evaluate the results of a combined method for correcting age-related skin changes based on a combination of hardware fractional needle radiofrequency exposure and injection therapy with platelet-rich plasma activated by autologous thrombin, comparing to monotherapy the same methods.&#x0D; Materials and methods. Fractional microneedle radiofrequency therapy was carried out three times with an interval between procedures of 3 weeks with the use of a high-frequency electrosurgical device Scarlet RF. Therapy with autologous plasma rich in platelets activated by autologous thrombin (PRP therapy) was performed three times with an interval between procedures of 3 weeks without the use of preliminary topical anesthesia. Combination therapy combined the use of the above methods. Regression of clinical signs of skin aging was evaluated according to digital dermatoscopy and regression of the total value of the dermatological index of the quality of life of patients, as well as improvement of qualitative and functional parameters of the skin. A statistical analysis was carried out.&#x0D; Results. A comparative analysis of the influence of various methods of correction of involutive changes in the skin of the face showed that the use of combination therapy provides the development of the most significant clinical effect in relation to all the assessed signs of skin aging. Combination therapy was accompanied by a significant increase in the integral index of microcirculation, regardless of age. The reconstructive effect on the morphological structures of the skin according to ultrasonography also turned out to be significantly higher for the combined method of treatment in comparison with radiofrequency therapy.&#x0D; Conclusions. The combined use of fractional microneedle radiofrequency therapy and PRP therapy provides a more effective and prolonged correction of age-related skin changes compared to the monotherapy.

Poster 110: Depth of Tissue Necrosis Following Footprint Preparation with Arthroscopic Radiofrequency Ablation

Objectives:Successful rotator cuff repair depends upon both secure fixation and biologic integration at the bone-tendon interface. Viable osteocytes and sound bony architecture contribute to the mechanical stability of suture anchor repair constructs. Furthermore, because tendons are hypovascular, preserving the microvasculature of the underlying bone bed is important. To create the bone-tendon interface, shoulder surgeons typically employ three different techniques to clear soft tissue from the footprint prior to rotator cuff repair: mechanical debridement, radiofrequency coagulation, and radiofrequency ablation. Conventional radiofrequency devices use radiofrequency energy to vaporize tissue, often in the setting of tumor resection to kill cancerous tissue. In arthroscopy, bipolar radiofrequency wands capitalize on the saline environment, passing radiofrequency waves through the conductive saline medium creating high energy ions. The result is a plasma field that can gently dissolve tissue with limited heat penetration to the surrounding environment, which is referred to as “coblation.” However, the extent to which this energy penetrates the adjacent tissue, potentially damaging nearby vasculature and osteocytes, is unknown. This study aims to explore the histological depth of tissue necrosis caused by arthroscopic radiofrequency ablation wands in comparison to a mechanical shaver.Methods:6 bovine metacarpal bones were collected one hour after devascularization and submerged in normal saline. Footprints were created by a radiofrequency ablation wand, at both the coagulation and ablation settings, and a mechanical shaver. Preparation was performed at 5 and 15 seconds. After the specimens were processed and prepared as hematoxylin and eosin-stained microscopic slides, each footprint was evaluated microscopically by a fellowship-trained pathologist. Depth of tissue destruction, preservation of periosteum, and osteocyte necrosis were evaluated histologically compared to the control sections for each treatment method.Results:Both the coagulation and ablation settings on the radiofrequency ablation wand were compared to the sections debrided with the mechanical shaver and the control sections. The ablation setting removed significantly more tissue than the coagulation setting at 5 seconds and 15 seconds of energy exposure (0.67 mm vs. 2.3 mm; P = .001 and 1.5 mm vs. 3.58 mm; P = .012) (table 1). While the depth of soft tissue destruction increased with time, the difference between 5 and 15 seconds for either treatment was not significant (0.67 mm vs. 1.5 mm; P = ,088, 2.3 mm vs. 3.58 mm; P = .051). The periosteum was rarely breached by any treatment and was seen to be well preserved in most sections. Osteocytes remained viable in the central area of treatment, and the normal cortical bone architecture was maintained. Compared to the control bone sections (figure 1) there was one section treated with ablation for 15 seconds that showed complete loss of overlying soft tissue in the treatment area and necrotic osteocytes at a depth of 0.5 mm from the treatment area (figure 2, 3).Conclusions:When used appropriately, arthroscopic radiofrequency ablation techniques effectively debride soft tissue from the rotator cuff footprint while preserving the underlying periosteal vasculature and cortical osteocytes. However, our results do show that local tissue destruction increases with degree of radiofrequency energy and exposure time which can lead to necrosis of the underlying tissues including the periosteum, osteocytes, and microvasculature. This has the potential to impair the biologic tendon-to-bone healing as well as the integrity of the mechanical repair construct, which would ultimately lead to failure of the repair. Thus, it is important for surgeons to be cautious while using arthroscopic radiofrequency techniques while preparing tendon footprints.TABLE 1.Depth of Soft Tissue Destruction by Treatment in millimeters (mm)Figure 1.Control, 20X. Histologic section demonstrating normal- periosteum, bony architecture, and viable osteocytes. White arrow: intact periosteum. Black arrow: Viable osteocyte.Figure 2.Ablation 15 seconds, 10X. White arrow: intact periosteum. Black arrow: treatment area with complete loss of periosteumFigure 3.Ablation 15 seconds, 20X. Histologic section demonstrating necrotic osieocytes at a depth of 0.5 mm below the treatment area.j White arrow: zone of necrotic osteocytes. Black arrow: viable osteocyie

Neuronal activity under transcranial radio-frequency stimulation in metal-free rodent brains in-vivo

As the use of Radio Frequency (RF) technologies increases, the impact of RF radiation on neurological function continues to receive attention. Whether RF radiation can modulate ongoing neuronal activity by non-thermal mechanisms has been debated for decades. However, the interactions between radiated energy and metal-based neural probes during experimentation could impact neural activity, making interpretation of the results difficult. To address this problem, we modified a miniature 1-photon Ca2+ imaging device to record interference-free neural activity and compared the results to those acquired using metal-containing silicon probes. We monitored the neuronal activity of awake rodent-brains under RF energy exposure (at 950 MHz) and in sham control paradigms. Spiking activity was reliably affected by RF energy in metal containing systems. However, we did not observe neuronal responses using metal-free optical recordings at induced local electric field strengths up to 230 V/m. Our results suggest that RF exposure higher than levels that are allowed by regulatory limits in real-life scenarios do not affect neuronal activity.

Evidences of the radiofrequency exposure on the antioxidant status, potentially contributing to the inflammatory response and demyelination in rat brain

Present study exhibited the oxidative potential of microwave radiation (MWR) leading to the neurodegeneration in rats. Wistar rats were exposed at 2100 MHz frequency for 4 h/day, 5 days/week/3 months. Animals were exposed at an estimated specific absorption rate (0.453 W/kg) and power density (8.237 µW/m2). After exposure irradiated group was compared with control group. Results indicated that microwave exposure significantly increased the levels of serological triglycerides and cholesterol. Oxidative stress is observed through alteration of glutathione homeostasis followed by activated inflammatory response further confirmed by pro and anti-inflammatory cytokines in the exposed group. Histopathological assessments and electron microscopic observation confirmed a significant change in the myelination pattern and cellular organelles in the brain of exposed animals. Taking everything into account it can be concluded that chronic exposure of 2100-MHz frequency caused oxidative stress, which leads to neural damage and demyelination and may affect neural communication.

Analysis of ICNIRP 2020 Basic Restrictions for Localized Radiofrequency Exposure in the Frequency Range above 6 GHz.

ICNIRP 2020 guidelines have defined a practical temperature elevation threshold for human health effects, namely the operational adverse health effect threshold that forms the basis of the absorbed power and energy density basic restrictions. These basic restrictions for localized exposures at frequencies above 6 GHz were evaluated by comparing numerically computed temperature rise against the target temperature rise of 2.5 o C, which is the operational adverse health effect threshold divided by the occupational safety factor of 2. The numerical model employs the maximum absorbed power and energy density levels allowed by the occupational basic restriction for both pulsed and continuous wave exposures. These analyses were performed considering 3- and 4-tissue layer models and a variety of beam diameters, frequencies, and exposure durations. The smallest beam diameters were based on a study of theoretically achievable beam widths from half-wave resonant dipoles and show the impact of the averaging area on the computed temperature elevation. The results demonstrated that ICNIRP's assumed occupational safety factors in the frequency range above 6 GHz were not sufficiently maintained for all exposure scenarios and particularly for short pulse exposures at frequencies of 30 GHz or higher with small beam diameters. Worst-case tissue temperature elevations were estimated to be as much as 3.6 times higher than ICNIRP's target temperature increases. Consequently, the authors suggest a small modification in the application of the ICNIRP 2020 localized basic restrictions, thereby limiting the worst-case tissue temperature increases to 1.4 times the target value.

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.

Assessment of Radiofrequency Exposure in the Vicinity of School Environments in Crete Island, South Greece

This study aimed to estimate the radiofrequency exposure levels in the vicinity of nursery and primary schools at the northwest part of Crete island in Greece. Moreover, the compliance with the exposure limits, according to Greek legislation, was investigated. A total of 396 in situ frequency-selective and broadband measurements were conducted around 69 schools, classified in urban and suburban environments, in the range of 27–3000 MHz (subdivided in seven frequency bands). The measured value of the electric field strength (V/m) was recorded and, subsequently, the exposure ratio was calculated. Statistical analysis was performed in order to analyze and evaluate the data. In addition, a worst-case scenario was examined by considering the highest measured exposure level around each school. The statistical tests indicated that the mean and median values of the exposure ratio, even in the worst-case scenario, were found well below 1 for all frequency bands. The calculated distributions of the electric field measurements demonstrated that almost 90% of the latter were below 1 V/m, with the majority of values lying in the range of 0.5–1 V/m. The main contributors to the total exposure were the mobile communication frequencies and broadcasting, while the exposure was greater in urban than in suburban environments.