Comment on Redmayne, M.; Maisch, D.R. ICNIRP Guidelines' Exposure Assessment Method for 5G Millimetre Wave Radiation May Trigger Adverse Effects. Int. J. Environ. Res. Public Health 2023, 20, 5267.

This article discusses the contention in the commented-upon paper that Brillouin precursors generated by 5G New Radio (5G NR) and other cellular systems are a possible cause of tissue damage at deeper layers of tissue than the power penetration depth of the carrier frequency. The original theory for Brillouin precursors from pulsed radiofrequency signals (RF-EMF) and speculation about their possible health effects dates back to the 1990's and was based on studies of the propagation of very short (nanosecond) ultrawide-bandwidth RF pulses through water. This assumption is not correct for cellular telephone signals due to their narrow bandwidth. The commented-on paper provides no alternative rationale as to why Brillouin effects should cause tissue damage from RF-EMF radiation from cellular and other communications systems. Other inaccuracies in this paper concerning thermal responses of tissue to RF-EMF are also noted.

Dosimetric assessment in the brain for downlink EMF exposure in Korean mobile communication networks.

Because the position and direction of the human body is not fixed in an actual environment, the incidence direction of the electromagnetic field (EMF) from mobile communication base stations, WiFi access points, broadcasting towers, and other far-field sources is arbitrary. To analyze the overall health effects of radio frequency EMF exposure, the dosimetric assessment for such environmental exposures created from an unspecified number of sources in daily life, along with exposures from specific EMF sources, must be quantified. This study is aimed at numerically evaluating the time-averaged specific absorption rate (SAR) of the human brain for environmental EMF exposure in the frequency range of 50-5800 MHz. Whole-body exposure to EMFs that are evenly incident spatially is considered. By comparing the results of several incidence directions and the number of polarizations, an optimal calculation condition has been derived. Finally, based on the results measured in Seoul at the end of 2021, the SAR and daily specific energy absorption (SA) in the brains of both a child and an adult for downlink exposures from 3G to 5G base stations are reported. Comparison results of the daily brain SA for exposure to DL EMF in all 3G to 5G mobile networks and exposure to a 10-min voice call (uplink EMF) using a mobile phone connected to a 4G network show that the SA from the downlinks is much higher than that from the uplinks.

NextGEM: Next-Generation Integrated Sensing and Analytical System for Monitoring and Assessing Radiofrequency Electromagnetic Field Exposure and Health.

The evolution of emerging technologies that use Radio Frequency Electromagnetic Field (RF-EMF) has increased the interest of the scientific community and society regarding the possible adverse effects on human health and the environment. This article provides NextGEM's vision to assure safety for EU citizens when employing existing and future EMF-based telecommunication technologies. This is accomplished by generating relevant knowledge that ascertains appropriate prevention and control/actuation actions regarding RF-EMF exposure in residential, public, and occupational settings. Fulfilling this vision, NextGEM commits to the need for a healthy living and working environment under safe RF-EMF exposure conditions that can be trusted by people and be in line with the regulations and laws developed by public authorities. NextGEM provides a framework for generating health-relevant scientific knowledge and data on new scenarios of exposure to RF-EMF in multiple frequency bands and developing and validating tools for evidence-based risk assessment. Finally, NextGEM's Innovation and Knowledge Hub (NIKH) will offer a standardized way for European regulatory authorities and the scientific community to store and assess project outcomes and provide access to findable, accessible, interoperable, and reusable (FAIR) data.

ICNIRP Guidelines' Exposure Assessment Method for 5G Millimetre Wave Radiation May Trigger Adverse Effects.

The current global roll-out of 5G infrastructure is designed to utilise millimetre wave frequencies (30-300 GHz range) at data transmission rates in the order of gigabits per second (Gbps). This frequency band will be transmitted using beamforming, a new introduction in near-field exposures. The International Commission on Non-Ionising Radiation Protection (ICNIRP) has recently updated their guidelines. We briefly examine whether the new approach of the ICNIRP is satisfactory to prevent heat damage and other adverse bio-effects once millimetre wave 5G is included, and we challenge the use of surface-only exposure assessment for local exposures greater than 6 GHz in part due to possible Brillouin precursor pulse formation. However, this is relevant whether or not Brillouin precursors occur from absorption of either 5G or future G transmissions. Many significant sources conclude there is insufficient research to assure safety even from the heat perspective. To date, there has been no published in vivo, in vitro or epidemiological research using exposures to 5G New Radio beam-formed signals.

Assessment of Inflammation in 3D Reconstructed Human Skin Exposed to Combined Exposure to Ultraviolet and Wi-Fi Radiation.

In the human environment, the increasing exposure to radiofrequency (RF) radiation, especially that emitted by wireless devices, could be absorbed in the body. Recently, mobile and emerging wireless technologies (UMTS, DECT, LTE, and Wi-Fi) have been using higher frequencies than 2G GSM systems (900/1800 MHz), which means that most of the circulating RF currents are absorbed into the skin and the superficial soft tissue. The harmful genotoxic, cytotoxic, and mutagenic effects of solar ultraviolet (UV) radiation on the skin are well-known. This study aimed at investigating whether 2422 MHz (Wi-Fi) RF exposure combined with UV radiation in different sequences has any effect on the inflammation process in the skin. In vitro experiments examined the inflammation process by cytokines (IL-1α, IL-6, IL-8) and MMP-1 enzyme secretion in a 3D full-thickness human skin model. In the first study, UV exposure was immediately followed by RF exposure to measure the potential additive effects, while in the second study, the possible protective phenomenon (i.e., adaptive response) was investigated when adaptive RF exposure was challenged by UV radiation. Our results suggest that 2422 MHz Wi-Fi exposure slightly, not significantly increased cytokine concentrations of the prior UV exposure. We could not detect the adaptive response phenomenon.

Electromagnetic Fields Exposure Assessment in Europe Utilizing Publicly Available Data.

The ever-increasing use of wireless communication systems during the last few decades has raised concerns about the potential health effects of electromagnetic fields (EMFs) on humans. Safety limits and exposure assessment methods were developed and are regularly updated to mitigate health risks. Continuous radiofrequency EMF monitoring networks and in situ measurement campaigns provide useful information about environmental EMF levels and their variations over time and in different microenvironments. In this study, published data from the five largest monitoring networks and from two extensive in situ measurement campaigns in different European countries were gathered and processed. Median electric field values for monitoring networks across different countries lay in the interval of 0.67-1.51 V/m. The median electric field value across different microenvironments, as evaluated from in situ measurements, varied from 0.10 V/m to 1.42 V/m. The differences between networks were identified and mainly attributed to variations in population density. No significant trends in the temporal evolution of EMF levels were observed. The influences of parameters such as population density, type of microenvironment, and height of measurement on EMF levels were investigated.

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.

Three Quarters of a Century of Research on RF Exposure Assessment and Dosimetry-What Have We Learned?

This commentary, by three authors with an aggregate experience of more than a century in technology and health and safety studies concerning radiofrequency (RF) energy, asks what has been learned over the past 75 years of research on radiofrequency and health, focusing on technologies for exposure assessment and dosimetry. Research programs on health and safety of RF exposure began in the 1950s, initially motivated by occupational health concerns for military personnel, and later to address public concerns about exposures to RF energy from environmental sources and near-field exposures from RF transmitting devices such as mobile phones that are used near the body. While this research largely focused on the biological effects of RF energy, it also led to important improvements in exposure assessment and dosimetry. This work in the aggregate has made RF energy one of the best studied potential technological hazards and represents a productive response by large numbers of scientists and engineers, working in many countries and supported by diverse funding agencies, to the ever rapidly evolving uses of the electromagnetic spectrum. This review comments on present needs of the field, which include raising the quality of dosimetry in many RF bioeffects studies and developing improved exposure/dosimetric techniques for the higher microwave frequencies to be used by forthcoming communications technologies. At present, however, the major uncertainties in dosimetric modeling/exposure assessment are likely to be related to the inherent variability in real-world exposures, rather than imprecision in measurement technologies.

Assessment of Human Exposure Levels Due to Mobile Phone Antennas in 5G Networks.

The recent deployment of 5G networks is bringing benefits to the population but it is also raising public concern about human RF-EMF exposure levels. This is particularly relevant considering the next 5G mobile devices, which are placed in close proximity to the subjects. Therefore, the aim of the following paper is focused on expanding the knowledge of the exposure levels in 5G exposure scenarios, specifically for mobile applications, using computational methods. The mobile antenna was designed considering the 5G technology innovations (i.e., mm-wave spectrum, beamforming capability, high gain and wide coverage), resulting in a phased-array antenna with eight elements at the working frequency of 27 GHz. To assess the exposure levels, different types of skin models with different grades of details and layers were considered. Furthermore, not only was the presence of a mobile phone user simulated, but also that of a person in their proximity, who could be hit by the main beam of the phased-array antenna. All the simulations were conducted in Sim4Life platform, where the exposure levels were assessed in terms of absorbed power density averaged over 4 cm2 and 1 cm2, following the ICNIRP guidelines. The results highlighted that the use of the homogeneous skin model led to the absorbed power density peaks being greatly underestimated, with respect to those obtained in multilayer skin models. Furthermore, interestingly, we found that the exposure levels obtained for the person passing nearby were slightly higher than those experienced by the mobile phone user himself. Finally, using the allowed input power for real mobile applications, all the values remained below the limits indicated by the ICNIRP guidelines.

Induced radiofrequency fields in patients undergoing MR examinations: insights for risk assessment.

Purpose. To characterize and quantify the induced radiofrequency (RF) electric (E)-fields andB1+rmsfields in patients undergoing magnetic resonance (MR) examinations; to provide guidance on aspects of RF heating risks for patients with and without implants; and to discuss some strengths and limitations of safety assessments in current ISO, IEC, and ASTM standards to determine the RF heating risks for patients with and without implants.Methods. InducedE-fields andB1+rmsfields during 1.5 T and 3 T MR examinations were numerically estimated for high-resolution patient models of the Virtual Population exposed to ten two-port birdcage RF coils from head to feet imaging landmarks over the full polarization space, as well as in surrogate ASTM phantoms.Results. Worst-caseB1+rmsexposure greater than 3.5µT (1.5 T) and 2µT (3 T) must be considered for all MR examinations at the Normal Operating Mode limit. Representative inducedE-field and specific absorption rate distributions under different clinical scenarios allow quick estimation of clinical factors of high and reduced exposure.B1shimming can cause +6 dB enhancements toE-fields along implant trajectories. The distribution and magnitude of inducedE-fields in the ASTM phantom differ from clinical exposures and are not always conservative for typical implant locations.Conclusions.Field distributions in patient models are condensed, visualized for quick estimation of risks, and compared to those induced in the ASTM phantom. InducedE-fields in patient models can significantly exceed those in the surrogate ASTM phantom in some cases. In the recent 19ε2revision of the ASTM F2182 standard, the major shortcomings of previous versions have been addressed by requiring that the relationship between ASTM test conditions andin vivotangentialE-fields be established, e.g. numerically. With this requirement, the principal methods defined in the ASTM standard for passive implants are reconciled with those of the ISO 10974 standard for active implantable medical devices.

[Comparative morphological assessment of the damaging effects of cold plasma and radio wave energy on the mucous membrane of the lip in the experiment]. / Sravnitel'naya morfologicheskaya otsenka povrezhdayushchego vozdeistviya kholodnoplazmennoi i radiovolnovoi energii na slizistuyu obolochku guby v eksperimente.

The aim of this study was a comparative morphological assessment of changes in the mucous membrane of the lip in the field of radio wave and cold plasma exposure in the experiment. MATERIAL AND METHODS: Experimental animals removed a portion of the mucous membrane of the inner surface of the lip with a Surgitron radio knife (group 1) and an electrode of the Coblator II cold plasma apparatus (observation group 2). Tissue was taken from the edge of the surgical wound as a trapezoidal flap containing mucous and submucous membranes immediately after the incision and 3 weeks after the surgery. Histological sections were prepared, which were stained with hematoxylin and eosin, as well as according to van Gieson. RESULTS: It was found that, both in cases of using a radio knife and a coblator along the edges and in the depth of the wound, coagulation tissue necrosis was observed, which was more evident in group 1 of observations. In addition, after the radio wave exposure, in the areas close to the defect, the epithelial lining was disrupted to one degree or another, which was not observed when using the coblator. After 3 weeks of the experiment, the stratified squamous non-keratinizing epithelium in both groups had a normal histological structure. At the same time, when using the coblator, the lamina propria of the mucous membrane was completely restored, and in cases with the use of a radio knife, sclerotic processes with the formation of scar tissue took place in the lamina propria of the mucous membrane in some areas. CONCLUSIONS: The use of a coblator should be recognized as a more gentle method, since a comparative analysis of histological changes immediately after the incision showed a more intense damaging effect of the radio knife on the surrounding tissues, which in later stages was accompanied by incomplete regeneration (substitution) of the lip mucosa.

Personal Exposure Assessment to Wi-Fi Radiofrequency Electromagnetic Fields in Mexican Microenvironments.

In recent years, personal exposure to Radiofrequency Electromagnetic Fields (RF-EMF) has substantially increased, and most studies about RF-EMF with volunteers have been developed in Europe. To the best of our knowledge, this is the first study carried out in Mexico with personal exposimeters. The main objective was to measure personal exposure to RF-EMF from Wireless Fidelity or wireless Internet connection (Wi-Fi) frequency bands in Tamazunchale, San Luis Potosi, Mexico, to compare results with maximum levels permitted by international recommendations and to find if there are differences in the microenvironments subject to measurements. The study was conducted with 63 volunteers in different microenvironments: home, workplace, outside, schools, travel, and shopping. The mean minimum values registered were 146.5 µW/m2 in travel from the Wi-Fi 2G band and 116.8 µW/m2 at home from the Wi-Fi 5G band, and the maximum values registered were 499.7 µW/m2 and 264.9 µW/m2 at the workplace for the Wi-Fi 2G band and the Wi-Fi 5G band, respectively. In addition, by time period and type of day, minimum values were registered at nighttime, these values being 129.4 µW/m2 and 93.9 µW/m2, and maximum values were registered in the daytime, these values being 303.1 µW/m2 and 168.3 µW/m2 for the Wi-Fi 2G and Wi-Fi 5G bands, respectively. In no case, values exceeded limits established by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Of the study participants (n = 63), a subgroup (n = 35) answered a survey on risk perception. According to these results, the Tamazunchale (Mexico) population is worried about this situation in comparison with several European cities; however, the risk perception changes when they are informed about the results for the study.

Radio-frequency electromagnetic field exposure and contribution of sources in the general population: an organ-specific integrative exposure assessment.

In order to achieve an integrated radio-frequency electromagnetic fields (RF-EMF) dose assessment, detailed information about source-specific exposure duration and output power is needed. We developed an Integrated Exposure Model (IEM) to combine energy absorbed due to use of and exposure to RF-EMF sources and applied it to a sample of the general population to derive population RF-EMF estimates. The IEM used specific absorption rate transfer algorithms to provide RF-EMF daily dose estimates (mJ/kg/day) using source-specific attributes (e.g. output power, distance), personal characteristics and usage patterns. Information was obtained from an international survey performed in four European countries with 1755 participants. We obtained median whole-body and whole-brain doses of 183.7 and 204.4 mJ/kg/day. Main contributors to whole-brain dose were mobile phone near the head for calling (2G networks) and far-field sources, whereas the latter together with multiple other RF-EMF sources were main contributors for whole-body dose. For other anatomical sites, 2G phone calls, mobile data and far-field exposure were important contributors. The IEM provides insight into main contributors to total RF-EMF dose and, applied to an international survey, provides an estimate of population RF-dose. The IEM can be used in future epidemiological studies, risk assessments and exposure reduction strategies.

Radiofrequency electromagnetic field exposure assessment: a pilot study on mobile phone signal strength and transmitted power levels.

In many epidemiological studies mobile phone use has been used as an exposure proxy for radiofrequency electromagnetic field (RF-EMF) exposure. However, RF-EMF exposure assessment from mobile phone use is prone to measurement errors limiting epidemiological research. An often-overlooked aspect is received signal strength levels from base stations and its correlation with mobile phone transmit (Tx) power. The Qualipoc android phone is a tool that provides information on both signal strength and Tx power. The phone produces simultaneous measurements of Received Signal Strength Indicator (RSSI), Reference Signal Received Power (RSRP), Received Signal Code Power (RSCP), and Tx power on the 3G and 4G networks. Measurements taken in the greater Melbourne area found a wide range of signal strength levels. The correlations between multiple signal strength indicators and Tx power were assessed with strong negative correlations found for 3G and 4G data technologies (3G RSSI -0.93, RSCP -0.93; 4G RSSI -0.85, RSRP -0.87). Variations in Tx power over categorical levels of signal strength were quantified and showed large increases in Tx power as signal level decreased. Future epidemiological studies should control for signal strength or factors influencing signal strength to reduce RF-EMF exposure measurement error.

Model of Steady-state Temperature Rise in Multilayer Tissues Due to Narrow-beam Millimeter-wave Radiofrequency Field Exposure.

The assessment of health effects due to localized exposures from radiofrequency fields is facilitated by characterizing the steady-state, surface temperature rise in tissue. A closed-form analytical model was developed that relates the steady-state, surface temperature rise in multilayer planar tissues as a function of the spatial-peak power density and beam dimensions of an incident millimeter wave. Model data was derived from finite-difference solutions of the Pennes bioheat transfer equation for both normal-incidence plane waves and for narrow, circularly symmetric beams with Gaussian intensity distribution on the surface. Monte Carlo techniques were employed by representing tissue layer thicknesses at different body sites as statistical distributions compiled from human data found in the literature. The finite-difference solutions were validated against analytical solutions of the bioheat equation for the plane wave case and against a narrow-beam solution performed using a commercial multiphysics simulation package. In both cases, agreement was within 1-2%. For a given frequency, the resulting analytical model has four input parameters, two of which are deterministic, describing the level of exposure (i.e., the spatial-peak power density and beam width). The remaining two are stochastic quantities, extracted from the Monte Carlo analyses. The analytical model is composed of relatively simple functions that can be programmed in a spreadsheet. Demonstration of the analytical model is provided in two examples: the calculation of spatial-peak power density vs. beam width that produces a predefined maximum steady-state surface temperature, and the performance evaluation of various proposed spatial-averaging areas for the incident power density.

Use of TETRA personal radios and sickness absence in the Airwave Health Monitoring Study of the British police forces.

BACKGROUND: Terrestrial Trunked Radio (TETRA) is used for radiocommunications among the British police forces. OBJECTIVES: To investigate association of personal radio use and sickness absence among police officers and staff from the Airwave Health Monitoring Study. METHODS: Participant-level sickness absence records for 26 forces were linked with personal radio use for 32,102 participants. We used multivariable logistic regression to analyse TETRA usage in year prior to enrolment and sickness absence (lasting more than 7 or 28 consecutive days) in the following year and a zero-inflated negative binomial model for analyses of number of sickness absence episodes of any duration ('spells') over the same period. In secondary analyses, we looked at an extended period of observation among a sub-cohort with linked data over time, using Cox proportional hazards regression. RESULTS: Median personal radio use (year prior to enrolment) was 29.7 min per month (interquartile range 7.5, 64.7) among users. In the year following enrolment there were 25,655 sickness absence spells among 15,248 participants. There were similar risks of sickness absence lasting more than seven days among users and non-users, although among users risk was higher with greater use, odds ratio = 1.04 (95% confidence interval [CI] 1.02 to 1.06) per doubling of radio use. There was no association for sickness absence of more than 28 days. For sickness absence spells, risk was lower among users than non-users (incidence rate ratio = 0.91; 95% CI 0.75 to 1.11), again with higher risk among users for greater radio use. There was no association between radio use and sickness absence in secondary analyses. DISCUSSION: There were similar or lower risks of sickness absence in TETRA radio users compared with non-users. Among users, the higher risk of sickness absence with greater radio use may reflect working pattern differences among police personnel rather than effects of radiofrequency exposure.

On the Assessment of Human Exposure to Electromagnetic Fields Transmitted by 5G NR Base Stations.

The fifth-generation new radio cellular network will be rolled out within the next few years. Several assessment methods of human exposure to electromagnetic fields transmitted by fifth-generation new radio base stations are discussed. Currently no method exists that allows extrapolation to the maximum theoretical exposure. Thus two new extrapolation methods are proposed. A 95th percentile exposure can be derived from the maximum theoretical exposure by an agreed-upon reduction factor if a more realistic exposure assessment is required.

Brain SAR of average male Korean child to adult models for mobile phone exposure assessment.

This paper aims to implement average head models of Korean males and investigate age-related differences in the brain for exposure from radiation from mobile phones. Four male head models composed of a total of 69 structures were developed through a statistical investigation of the anatomical morphology for the age groups of 6, 9, 15 and 20-24 years in age, which are named KR-6, KR-9, KR-15, and KR-22 herein. Three numerical bar phone models with a dual-band built-in antenna were applied to calculate the specific absorption rate (SAR) in the brain; the body lengths of models M avg and M long have the mean value and upper 5th percentile value of commercial bar phone models, respectively, with an antenna at the bottom, whereas M rev has an antenna on top of the phone body, which is the same as in M avg but rotated 180°. The cheek and tilt positions were employed for SAR simulations. As a result, a higher peak spatial-average SAR (psSAR) was observed in the brain for the child groups of KR-6 and KR-9 than for the adult groups of KR-15 and KR-22. In most configurations, the position-averaged psSAR10 g in the child brain was 62% (M long, 835 MHz), 61% (M avg, 835 MHz), 102% (M long, 1850 MHz), 108% (M avg, 1850 MHz), and 125% (M rev, 1850 MHz) higher than in the adult brain. The higher frequency of 1850 MHz showed a wider difference in the brain psSAR between the child and adult groups owing to the shorter penetration depth. When a long phone with an antenna at the bottom operates at a higher frequency, it significantly reduces the brain exposure.

Personal radio use and cancer risks among 48,518 British police officers and staff from the Airwave Health Monitoring Study.

BACKGROUND: Radiofrequency electromagnetic fields (RF-EMF) from mobile phones have been classified as potentially carcinogenic. No study has investigated use of Terrestrial Trunked Radio (TETRA), a source of RF-EMF with wide occupational use, and cancer risks. METHODS: We investigated association of monthly personal radio use and risk of cancer using Cox proportional hazards regression among 48,518 police officers and staff of the Airwave Health Monitoring Study in Great Britain. RESULTS: During median follow-up of 5.9 years, 716 incident cancer cases were identified. Among users, the median of the average monthly duration of use in the year prior to enrolment was 30.5 min (inter-quartile range 8.1, 68.1). Overall, there was no association between personal radio use and risk of all cancers (hazard ratio [HR] = 0.98, 95% confidence interval [CI]: 0.93, 1.03). For head and neck cancers HR = 0.72 (95% CI: 0.30, 1.70) among personal radio users vs non-users, and among users it was 1.06 (95% CI: 0.91, 1.23) per doubling of minutes of personal radio use. CONCLUSIONS: With the limited follow-up to date, we found no evidence of association of personal radio use with cancer risk. Continued follow-up of the cohort is warranted.

EXPOSURE ASSESSMENT OF PORTABLE WIRELESS DEVICES ABOVE 6 GHz.

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