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Heating and pain sensation produced in human skin by millimeter waves: Comparison to a simple thermal model
Abstract
Cutaneous thresholds for thermal pain were measured in 10 human subjects during 3-s exposures at 94 GHz continuous wave microwave energy at intensities up to approximately 1.8 W cm(-2). During each exposure, the temperature increase at the skin's surface was measured by infrared thermography. The mean (+/- s.e.m.) baseline temperature of the skin was 34.0+/-0.2 degrees C. The threshold for pricking pain was 43.9+/-0.7 degrees C, which corresponded to an increase in surface temperature of approximately 9.9 degrees C (from 34.0 degrees C to 43.9 degrees C). The measured increases in surface temperature were in good agreement with a simple thermal model that accounted for heat conduction and for the penetration depth of the microwave energy into tissue. Taken together, these results support the use of the model for predicting thresholds of thermal pain at other millimeter wave (length) frequencies.
... This is far below the frequency spectra of amplitude modulation waveforms of communications or broadcasting signals. For example, the amplitude modulation waveforms of GSM cellular signals have frequency components at harmonics of 217 Hz [18] and such harmonics would produce very tiny fluctuations in skin temperature compared to the slow rise in skin temperature due to the time-averaged power density. Pulses from devices transmitting at high crest factors (e.g. ...
... The thermal model can be validated with reference to experiments by Walters et al [18],together with data from a more recent but much smaller study by Parker et al. [19] Walters et al. exposed 10 subjects (7 males, 3 females) on their backs to 3-sec 94 GHz pulses with incident power densities ranging from 9-17.5 kW/m 2 , while simultaneously measuring the increase in skin temperature using infrared thermography. Male subjects were shirtless, females wore sports bras. ...
... The study did not record burns or other skin damage in the subjects. Fig. 7 compares experimental and predicted results from [18], with each datapoint representing a single exposure to a single subject. The figures also shows recorded temperature increases from a later, and much smaller study, by Parker et al. [19]. ...
This study examines thermal responses of skin to pulsed millimeter wave (mm-wave) and radiofrequency (RF) radiation. We review limits for pulse uence in the IEEE Std. C95.1-2019 and the 2020 guideline of the International Commission on Nonionizing Radiation Protection (ICNIRP), as well as the recently reaffirmed guidelines of the U.S. Federal Communications Commission (FCC). The focus of the study is on millimeter-wave frequencies (30-300 GHz) where energy is absorbed close to the body surface and intense pulses could potentially cause high temperature gradients at the skin, but the model is extended to lower frequencies as well. The study employs a simple one-dimensional baseline thermal model for skin and Pennes' bioheat equation (BHTE), together with a baseline model for thermal damage to skin based on a standard model. The predicted yemperature increases produced by 3-sec pulses at 94 GHz are consistent with previous experimental results with no adjustable parameters in the model. The few reported data on thermal damage to the skin from pulsed 94 GHz energy are insuf cient to enable a conventional analysis of damage thresholds and the data may be affected by errors in dosimetry. The baseline model suggests that the implicit limits on pulse uence in the present FCC guidelines might allow, in extreme (but in practice unrealistic) cases, transient increases in skin temperature that approach thresholds for thermal pain but which remain well below levels anticipated to cause thermal damage. Limits on pulse fluence in the current IEEE and ICNIRP
exposure guidelines would preclude such effects. Such extreme pulses are far above those that are emitted by wireless and other technologies but may be emitted by some nonlethal weapons systems. FCC's proposed ``device-based time averaging'' rules will restrict thermal transients in skin from mm-wave transmitters to
levels that are roughly an order of magnitude below the slower temperature increases produced by the low frequency
components of the modulation waveform and appear to be excessively conservative. An appendix discusses the applicability of two approximations to the analytical solutions to the bioheat equation that can be used to estimate temperature increases in skin from exposure to mm-waves.
... We briefly review a few papers that motivate us for this study. In [5], cutaneous thresholds for thermal pain were measured in 10 human subjects (3 female and 7 male Caucasian volunteers, 31 -70 years old with an average age of 43.7, military or DoD civilians or contractors). Each subject was tested with 3-second exposures to 94 GHz electromagnetic wave of intensity up to 1.8 W/cm 2 . ...
... The measured surface temperature was in good agreement with a simple one-dimensional thermal model that accounted for heat conduction and for the penetration depth of the electromagnetic energy into tissue. One important observation in [5] was that the skin surface temperature increased roughly by 10˚C after a 3-second exposure to 1.8 W/cm 2 at 94 GHz. ...
... at one test condition, the activation temperature act T can be set to any value in the as the activated volume at reflex according to formula(5). When restricted to data at one test condition, c T z ; it does not allow us to determine act T and c z simultaneously.Non-dimensional temperature profile at reflex, ( ) nd nd reflex T y , for various values of applied power density dep,nd P . ...
... For experimental studies these include, but are not limited to, adequate dosimetry and inclusion of a sham-exposed group. Apart from minor differences in detail and terminology, the IEEE C95.1-2019 standard and ICNIRP (2020) guidelines are similar, both in their rationales and in the limits themselves, which are described at length in the documents themselves and in supporting commentaries (e.g., [7], [8], [45], and [48]). ...
... These calculated temperature increases are well below the ICNIRP's "operational adverse health effect thresholds" and below variations in skin temperature under ordinary environmental conditions. Table 4 [36], [43], [45], [50], [51], [52], [53], [54], [55] summarizes several mm-wave thermal damage studies, indicating the threshold for injury or cutaneous thermal pain in comparison to ICNIRP and IEEE exposure limits. The thresholds reported in the table are for minimally detectable injury or cutaneous thermal pain for specified exposure times and are approximately an order of magnitude above allowable mm-wave exposure limits. ...
This article reviews, at a nontechnical level, the issue of potential health effects of millimeter wave exposure (30-300 GHz) as well as 5G NR exposure in the high band (presently, 24.25-52.6 GHz). MM-wave energy is chiefly absorbed in the top layers of skin. The established hazards from such energy are associated with excessive heating of tissue, including thermal damage to skin and the eye, and thermal pain. Present exposure limits to mm-waves in IEEE Standard C95.1-2019 and ICNIRP (2020) Guidelines are based on numerical modeling of tissue heating and on a limited number of human and animal studies, and appear to be quite conservative with respect to thermal hazards. The existence of many mm-wave bioeffects studies, many reporting biological effects of exposure over a wide range of frequencies and exposure levels but with high risk of bias and other limitations, introduces significant uncertainty in assessing the health effects literature. Health agencies have not identified hazards of 5G high band and mm-wave exposure at “nonthermal” levels below current exposure limits, but all recommend further research. The present authors suggest several lines of needed research, and point to the need to improve the quality of future bioeffects studies.
... There are two potential thermal hazards from millimeter waves: thermal pain and superficial burn. For example, in the 94 GHz exposure with a 1.8 W/cm 2 beam, the thermal pain starts when the surface temperature reaches approximately 44 • C, about 10 • C increase over a typical skin baseline temperature [5]. In contrast, the threshold for burn corresponded to peak temperatures of approximately 60 • C, and required a beam energy fluence (energy delivered per area) 2-3 times higher than that producing thermal pain [6]. ...
... • v act (t), the activated skin volume at time t, is a derived quantity. It is calculated from T (x, y, z, t) using formula (5). v act (t) has dependence on P d (r) via T (x, y, z, t). ...
We assess the skin thermal injury risk in the situation where a test subject is exposed to an electromagnetic beam until the occurrence of flight action. The physical process is modeled as follows. The absorbed electromagnetic power increases the skin temperature. Wherever it is above a temperature threshold, thermal nociceptors are activated and transduce an electrical signal. When the activated skin volume reaches a threshold, the flight signal is initiated. After the delay of human reaction time, the flight action is materialized when the subject moves away or the beam power is turned off. The injury risk is quantified by the thermal damage parameter calculated in the Arrhenius equation. It depends on the beam power density absorbed into the skin, which is not measurable. In addition, the volume threshold for flight initiation is unknown. To circumference these difficulties, we normalize the formulation and write the thermal damage parameter in terms of the occurrence time of flight action, which is reliably observed in exposure tests. This thermal injury formulation provides a viable framework for investigating the effects of model parameters.
... The thermal imaging temperatures in group B was higher than group C at 48 h, and 72 h, implying higher pain and inflammatory response in group B than group C. Likewise group B maintained higher significance up to week 1, group A was also higher than that of group C at this time point. These findings agree with the work of Walters et al. (2000), that reported thresholds for painful cutaneous sensation during stimulation by millimeter wavelength microwaves, together with an analysis of the thermal response of skin in terms of a simple heat conduction model. The significantly high changes in the values of WST within group C and in the comparisons of groups A and B agrees with the findings of Gethin et al. (2021) in their study that reported that normal thermal imaging temperature of wound beds to range between 30.2°C and 33.0°C using the thermographic camera. ...
... Likewise castration in group A dogs characterized with high innervations of the perinium as well as the scrotum, derived from the branches of four nerves, the genitofemoral, pudendal, posterior femoral cutaneous, and ilioinguinal nerves (Garcia and Sajjad, 2019) could suggest why group A had significantly higher values than Group C. Whereas in gastrotomy, the skin of the abdomen is innervated by dorsal and lateral cutaneous branches of spinal nerves T12 through L3 (Bailey et al., 1984) and the Linea alba generally with limited blood supply and innervations. According to Walters et al. (2000), surface temperature increases with pain, however, skin surface temperature has been observed to be higher over organs with high metabolic rates rather than those at rest, as well as over muscles rather than tendons or bones (Wang et al., 2010) (Kanitakis, 2002) and this could explain why significantly higher WST in the otectomy and castrated dogs over those that had gastrotomy. If nociception remains a factor, this could add to the observed lower significant difference in group C than those of Group A and B for the facts that there could be fewer nociception around the Linea alba. ...
Infrared thermography analyzes changes in the surface temperature of the skin and has been used in companion animals to identify inflammatory processes, neoplasia, pain, and neuropathies. This study evaluated and compared surgical wound surface temperatures in Nigerian Indigenous Dogs (NID). Nigerian indigenous dogs are a medium-sized breed that weighs between 8 to 30 kg with moderate hair length, and a mesocephalic cranial index. The dogs were randomly allocated into groups A, B, and C for castration, otectomy, and gastrotomy, respectively. The wound surface temperature (WST) in the NID that underwent gastrotomy were significantly higher particularly at 18-48 h compared with Pre and other sampling periods within the group. It was also found that, at 0 h versus 48 h, 18 h versus 48 h, week 1 versus 18h; 24h; 48h; and 72h showed significant (p < 0.05) differences among NID subjected to gastrotomy (group C). However, the WST of NID subjected to castration and otectomy were significantly higher than that of gastrotomy. At 48 and 72 h, and week 1, the WST of NID in otectomy also known as ear cropping (group B) and castration (group A) were significantly (p < 0.05) higher than that of gastrotomy (Group C). Thermography of the surgical wounds aided postoperative wound management in the NID that underwent castration, otectomy and gastrotomy. Hence, the study suggests that guided WST with the aid of infrared thermography could be deployed as a useful tool to aid post operative wound management.
... In the only animal study that could be located on thermal pain from mm-wave exposures, Xie et al. (2011) inferred thresholds for thermal pain from EEG responses in anesthetized rats exposed to 35 GHz RF energy at power densities between 5-75 kW m −2 for up to 30 s, with exposed areas of skin of 1.8 and 3.6 cm 2 . These authors reported a threshold temperature for thermal pain of 44 o C, corresponding to an increase in skin temperature of 10 o C, which is similar to results of Walters et al. (2000) for humans. ...
... These studies involved exposures to RF energy that exceed the occupational exposure limits by factors ranging from ≈10-40. With one exception (Walters et al., 2000), these results are based on very limited experimental data, in many cases single data points from single human subjects. ...
Two major sets of exposure limits for radiofrequency (RF) radiation, those of the International Commission on Nonionizing Radiation Protection (ICNIRP 2020) and the Institute of Electrical and Electronics Engineers (IEEE C95.1-2019), have recently been revised and updated with significant changes in limits above 6 GHz through the millimeter wave (mm-wave) band (30-300 GHz). This review compares available data on thermal damage and pain from exposure to RF energy above 6 GHz with corresponding data from infrared energy and other heat sources and estimates safety factors that are incorporated in the IEEE and ICNIRP RF exposure limits. The benchmarks for damage are the same as used in ICNIRP IR limits: minimal epithelial damage to cornea and first-degree burn (erythema in skin observable within 48 h after exposure). The data suggest that limiting thermal hazard to skin is cutaneous pain for exposure durations less than ≈20 min and thermal damage for longer exposures. Limitations on available data and thermal models are noted. However, data on RF and IR thermal damage and pain thresholds show that exposures far above current ICNIRP and IEEE limits would be required to produce thermally hazardous effects. This review focuses exclusively on thermal hazards from RF exposures above 6 GHz to skin and the cornea, which are the most exposed tissues in the considered frequency range.
... Studies performed at 60 GHz demonstrated that while the maximum value of the power density and specific absorption rate occurs at the epidermis, up to 60% of the incident power reaches the dermis, and only 10% gets to the hypodermis [10] [11]. Absorption of the MMW energy causes the local temperature of the skin to rise and can activate nociceptors [12] and consequently lead to a sensation of pain [13] [14]. ...
... Combining the procedures outlined in Problems 1, 2 and 3 above, we obtain such a methodology exactly for this purpose. Applied Mathematics Function ( ) , T y t as given in (12) and (13), has the properties below 1) ( ) , T y t y ∂ ∂ is always negative. ...
... Considering the finite penetration depth-experimentally found to vary within the range of 0.05-0.2 mm at 94 GHz, according to figure 4 in Walters et al. [2000]-and a readily occurring transmission coefficient of 0.9 [Samaras and Kuster, 2019], this results in a reduced temperature increase prediction of 1.4-2.8°C. This is in line with the temperature measurements from Walters et al. [2000], which provide a temperature increase of 1.5°C when scaling their experimentally fitted function to a transmission coefficient of 0.9. ...
... mm at 94 GHz, according to figure 4 in Walters et al. [2000]-and a readily occurring transmission coefficient of 0.9 [Samaras and Kuster, 2019], this results in a reduced temperature increase prediction of 1.4-2.8°C. This is in line with the temperature measurements from Walters et al. [2000], which provide a temperature increase of 1.5°C when scaling their experimentally fitted function to a transmission coefficient of 0.9. Even higher transmission coefficients can result from oblique incidence or different skin layer thicknesses [Samaras and Kuster, 2019]. ...
Both the current and newly proposed safety guidelines for local human exposure to millimeter‐wave frequencies aim at restricting the maximum local temperature increase in the skin to prevent tissue damage. In this study, we show that the application of the current and proposed limits for pulsed fields can lead to a temperature increase of 10°C for short pulses and frequencies between 6 and 30 GHz. We also show that the proposed averaging area of 4 cm2, that is greatly reduced compared with the current limits, does not prevent high‐temperature increases in the case of narrow beams. A realistic Gaussian beam profile with a 1 mm radius can result in a temperature increase about 10 times higher than the 0.4°C increase the same averaged power density would produce for a plane wave. In the case of pulsed narrow beams, the values for the time and spatial‐averaged power density allowed by the proposed new guidelines could result in extreme temperature increases.
... For a 94 GHz beam, the penetration depth of electromagnetic wave into the skin tissue is z s = 1/μ = 0.16 mm [7]. As given in (3), the electromagnetic power density passing through depth z decays exponentially in z/z s . ...
We study the temperature evolution in the three-dimensional skin tissue exposed to an electromagnetic beam of millimeter wavelength. The skin absorption coefficient of the beam frequency determines how deep the electromagnetic energy penetrates into the skin tissue, which gives a sub-millimeter penetration depth for a 94 GHz wave. In contrast, in the lateral directions perpendicular to the depth, the beam size is usually much larger than the penetration depth. Based on this separation of length scales, we establish an asymptotic formulation in which each term has separable dependences on the depth coordinate and on the lateral coordinates. We solve it analytically to obtain a two-term asymptotic solution of the temperature distribution in the three-dimensional skin tissue. This closed-form analytical solution provides a practical and accurate way of predicting the temperature. When the beam size is moderately larger than the penetration depth (a ratio of 20), the effect of lateral heat conduction is well captured in the asymptotic solution with maximum error less than 0.0017 in the normalized temperature of magnitude well above 1.
... For a 94 GHz beam, the penetration depth of electromagnetic wave into the skin tissue is z s = 1/µ = 0.16 mm [5]. As given in (3), the electromagnetic power density passing through depth z decays exponentially in z, relative to the penetration depth z s . ...
We study the temperature evolution in the three-dimensional skin tissue exposed to an electromagnetic beam of millimeter wavelength. The skin absorption coefficient at the beam frequency determines how deep the electromagnetic energy penetrates into the skin tissue, which gives a sub-millimeter penetration depth for a 94 GHz wave. In contrast, in the lateral directions perpendicular to the depth, the beam size is usually much larger than the penetration depth. Based on this separation of length scales, we establish a formulation in which each term has separable dependences on the depth coordinate and on the lateral coordinates. We solve the equations in the formulation analytically to obtain a two-term asymptotic solution of the temperature distribution in the three-dimensional skin tissue. This closed-form analytical solution provides a practical and accurate way of predicting the temperature. It is useful when the beam size is moderately larger than the penetration depth. In that situation, the effect of lateral heat conduction is not negligible and is well captured in the asymptotic solution.
... We consider the situation where the skin area of a test subject is exposed to a beam of millimeter wave [10][11][12]. We adopt a model of skin temperature evolution like that in our previous studies [13][14][15]. ...
... At short times, heat transport in skin is typically characterized only by conduction [58]. Below an "effective time" of 15 seconds, Walters et al. showed that surface temperature after heating is nearly independent of blood perfusion [59]. Thus, neglecting convective cooling is a valid assumption. ...
Modern diagnostics is pivoting towards less invasive health monitoring in dermal interstitial fluid, rather than blood or urine. However, the skin's outermost layer, the stratum corneum, makes accessing the fluid more difficult without invasive, needle-based technology. Simple, minimally invasive means for surpassing this hurdle are needed.
To address this problem, a flexible, Band-Aid-like patch for sampling interstitial fluid was developed and tested. This patch uses simple resistive heating elements to thermally porate the stratum corneum, allowing the fluid to exude from the deeper skin tissue without applying external pressure. Fluid is then transported to an on-patch reservoir through self-driving hydrophilic microfluidic channels.
Testing with living, ex-vivo human skin models demonstrated the device's ability to rapidly collect sufficient interstitial fluid for biomarker quantification. Further, finite-element modeling showed that the patch can porate the stratum corneum without raising the skin's temperature to pain-inducing levels in the nerve-laden dermis.
Relying only on simple, commercially scalable fabrication methods, this patch outperforms the collection rate of various microneedle-based patches, painlessly sampling a human bodily fluid without entering the body.
The technology holds potential as a clinical device for an array of biomedical applications, especially with the integration of on-patch testing.
... Below an "effective time" of 15 seconds, researchers showed that surface temperature after heating is nearly independent of blood perfusion [182]. Therefore, given our system's timescale, this assumption was valid. ...
The current medical practice for diagnosing, monitoring, and treating many disease conditions requires biomarker monitoring in bodily fluids, typically blood or urine. Methods for extracting these fluids are often painful, invasive, or time consuming. Therefore, researchers have pivoted to less-invasive testing in interstitial fluid (ISF), the extracellular fluid lying between tissues in the body. The outermost barrier layer of skin, the stratum corneum, makes extracting ISF difficult. Our group has developed a device for thermally generating small pores in the skin to allow ISF to exude for collection and testing. However, to allow its simple fabrication, the prototype device was built on rigid and brittle substrates.
This dissertation details efforts to make such a device flexible. A background to the problem is presented, followed by a proposed solution in the form of a polymer-based patch. The patch ablates small areas of the skin with microfabricated resistive elements, then collects the exuded fluid using microfluidic channels. Polydimethylsiloxane (PDMS), a flexible silicone polymer which makes up the walls of these channels, was chemically modified to induce the channels' self-driven fluid collection without the need for an external pump. The physics behind this modification was explored in detail, and a novel model to describe the behavior was proposed and characterized. Subsequently, a full device consisting of PDMS and Kapton, a flexible polyimide, was fabricated. The device was tested using living, ex-vivo skin models to replicate living human tissue's response to poration. Fluid was collected from these models and tested for biomarkers, demonstrating the device's function and utility. A finite element model was also developed in order to connect the electrical function of the microheating elements to the resulting ablation depth and thermal profiles in the skin.
In all, this device presents a novel solution to biomarker monitoring in an alternative human biofluid. Relying only on simple, commercially-scalable fabrication methods, the patch outperforms multiple technologies from the literature and holds potential as a clinical device for an array of biomedical applications.
... The absorbed energy goes into increasing the skin temperature. Thermal nociceptors in the skin are activated upon the local temperature reaching the activation temperature [7]. The electrical signal produced by nociceptors is proportional to the total number of nociceptors activated [8] [9]. ...
... For applications to skin, q is chosen such that DT < 10 C (typically < 5 C), the threshold for sensation of pain and for compliance with IEC6061-1. 76,78,150 Representative TPS data collected from three materials (water, air, and the skin of the forearm) appear in Fig. 6(b). The results display the expected inverse relationship between DT and the measurement time t. ...
Measurements of the thermal properties of the skin can serve as the basis for a noninvasive, quantitative characterization of dermatological health and physiological status. Applications range from the detection of subtle spatiotemporal changes in skin temperature associated with thermoregulatory processes, to the evaluation of depth-dependent compositional properties and hydration levels, to the assessment of various features of microvascular/macrovascular blood flow. Examples of recent advances for performing such measurements include thin, skin-interfaced systems that enable continuous, real-time monitoring of the intrinsic thermal properties of the skin beyond its superficial layers, with a path to reliable, inexpensive instruments that offer potential for widespread use as diagnostic tools in clinical settings or in the home. This paper reviews the foundational aspects of the latest thermal sensing techniques with applicability to the skin, summarizes the various devices that exploit these concepts, and provides an overview of specific areas of application in the context of skin health. A concluding section presents an outlook on the challenges and prospects for research in this field.
... Therefore, the dT dt t=0 represents the initial temperature slope immediately after the 5G signal is applied. The temperature slope with respect to time is obtained using the nonlinear curve fitting based on the analytical expressions from the one dimensional heat transfer [28]. ...
In this study, an in vitro experimental system is developed for fifth-generation (5G) 3.5 GHz exposures. A radial transmission line (RTL) housed in an incubator can support the single-mode propagation at a 3.5 GHz band. A conical antenna is also placed at the center of an RTL to ensure field symmetries. A 5G signal generator along with a customized power amplifier can create 5G new radio time division duplex (TDD) waveforms. Additionally, a feedback scheme implemented by employing a directional coupler and power meter allows power control to ensure a steady output power. The system is evaluated based on temperature measurements using the initial temperature slope and nonlinear curve fitting to determine the specific absorption rate (SAR) values. Comparing SARs obtained from a “worst-case” signal of a maximum power condition with the values obtained from a “TDD” signal of an actual 5G TDD transmission gives the initial slope ratio of 0.741, which is very similar to the theoretical duty cycle of 0.743. It is also shown that the average output power, water temperature, incubator air temperature, and CO2 density are adequately controlled for appropriate in vitro experiments.
... We consider the situation where a skin area of a test subject is exposed to an electromagnetic beam of millimeter wavelength [5] [6] [7]. We adopt a model similar to the one in our previous studies [3] [4] [8], which we now describe briefly. ...
... On the other hand, the natural background of these waves on The Earth is not high [9], which means that the adaptation resources of biological systems are not developed during evolution to properly protect them from probable damages. From the beginning of the studies of this physical factor effect on biosystems it was maintained that MM EMW have a potential dangerous effect on different tissues of animals -skin [10], cornea [11], nervous system [12], etc. At the present MM EMW are also used in physiotherapeutic procedures, such as treatment of different cancers, cardiovascular diseases, diabetes, ulcers, leucopenia, skin disorders, bronchial asthma and wound healing [13][14][15]. ...
In this work the study of the effect of millimeter range electromagnetic waves (MM EMW) on methyl violet interaction with human serum albumin (HSA) has been carried out, using the UV-denaturation, fluorescence spectroscopy and CD spectroscopy methods. It was revealed that MM EMW irradiation leads to weakening of the stability of HSA and decreasing of interaction force between HSA and methyl violet (MV). It was also shown that MM EMW irradiation by water non-resonant frequency, affecting immediately the structure of HSA, changes its secondary structure, while the irradiation by water-resonant frequency does not invoke structural changes, but weakens the stability more. The last insistence results from the water cluster reconstruction, due to which the structured water affects the conformation of HSA.
... Exposure to millimeter-wave radiofrequency electromagnetic fields (RF-EMF) of sufficient intensity can result in a heat-pain sensation if the absolute tissue temperature reaches or exceeds a threshold of~42-43 o C (Defrin et al. 2006;Walters et al. 2000). This may be especially concerning for brief, high intensity pulses where a painful stimulation may occur before a behavioral response to avoid the stimulus can be initiated. ...
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 oC, 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.
... However, the penetration depth of mm-waves inside the biological tissues is small, so the heating effect is mainly for the skin and eyes. In fact, the biological effects of mm-waves have been investigated in several studies (Erwin and Hurt, 1981;Gandhi and Riazi, 1986;Ryan et al., 2000;Riu et al., 1997;Walters et al., 2000;Kues et al., 1999), albeit not in the context of 5G communications. The studies did not find adverse health impacts for mm-wave exposure with levels below the guidelines (WHO, 2020). ...
The massive deployment of advanced wireless networks is essential to support broadband connectivity, low latency communication, and Internet of Things (IoT) applications. Nevertheless, in the time of coronavirus disease (COVID-19) there is a massive amount of misinformation and uncertainty about the impact of fifth-generation cellular network (5G) networks on human health. In this paper, we investigate the main categories of misinformation regarding 5G, i.e., fake theories, the misconception of 5G features, and open questions that require further research. Then, we propose two novel approaches for the design of ElectroMagnetic Field (EMF)-aware cellular networks that can reduce human exposure to radiofrequency radiation.
... Higher localized heats cause pain and cell damage in human body, however temperatures less than 42 • C may not damage the cells [77]. Experiments conducted on human skin thresholds for thermal pain at 94GHz continuous wave frequencies result in skin surface temperature rises from 34 • C to 43.9 • C. Human skin exposure to RF EMFs cause heat in the skin and gives a threshold temperature of 43 • C for pain [78]. Most of the literature about thermal thresholds of human body due to EMFs show that the temperature thresholds of 41 • C-43 • C beyond which there is likelihood of tissue damages and the severity of damage increases with exposed time [79]- [81]. ...
millimeter (mmWave) frequencies are covering from 30GHz to 300GHz in the electromagnetic spectrum and their uses in various applications like next-generation wireless communication systems (massive 5G telecommunications network), medical devices, airport security and automatic collision avoidance systems are growing vastly in the near future. Therefore, it is important to study the effects of mmWave radiation (non-ionization radiation) on biological systems and biophysical mechanisms. This paper focus on thorough review of nascent literature about current understandings of biological effects and epidemiological studies due to mmWave radiation in human beings. It presents latest guidelines with quantitative electromagnetic field thresholds by considering the realistic exposure scenarios of “general public” and “occupational” who undergo through wireless communication sources in their daily life. It also gives necessary safety measures to be taken while using the emerging mmWave technologies for future generation wireless communication networks.
... We consider the situation where a skin area of the test subject is exposed to a moving beam [4] [5] [6]. We adopt a formulation similar to the one in our previous studies [3] [7]. ...
... Particularly, when a high-powered microwave beam reaches a human subject, it quickly produces an intolerable heating sensation in the skin and compels the subject to withdraw from the beam [3]. ...
... The most extensive studies that were designed explicitly to assess potential hazards of millimeter waves were carried out in the late 1990s to early 2000s by a group at Brooks Air Force Base, TX, and their collaborators at several universities. Many of those studies involved shortterm exposure (seconds to minutes) at levels far above current exposure limits and examined effects such as thresholds for thermal pain in humans (Walters et al. 2000) or corneal burns in rhesus monkeys (Chalfin et al. 2002). The Air Force supported one long-term cancer study using a well-established skin tumor model in mice with negative results (Mason et al. 2001). ...
This COMAR Technical Information Statement (TIS) addresses health and safety issues concerning exposure of the general public to radiofrequency (RF) fields from 5G wireless communications networks, the expansion of which started on a large scale in 2018 to 2019. 5G technology can transmit much greater amounts of data at much higher speeds for a vastly expanded array of applications compared with preceding 2-4G systems; this is due, in part, to using the greater bandwidth available at much higher frequencies than those used by most existing networks. Although the 5G engineering standard may be deployed for operating networks currently using frequencies extending from 100s to 1,000s of MHz, it can also operate in the 10s of GHz where the wavelengths are 10 mm or less, the so-called millimeter wave (MMW) band. Until now, such fields were found in a limited number of applications (e.g., airport scanners, automotive collision avoidance systems, perimeter surveillance radar), but the rapid expansion of 5G will produce a more ubiquitous presence of MMW in the environment. While some 5G signals will originate from small antennas placed on existing base stations, most will be deployed with some key differences relative to typical transmissions from 2-4G base stations. Because MMW do not penetrate foliage and building materials as well as signals at lower frequencies, the networks will require "densification," the installation of many lower power transmitters (often called "small cells" located mainly on buildings and utility poles) to provide for effective indoor coverage. Also, "beamforming" antennas on some 5G systems will transmit one or more signals directed to individual users as they move about, thus limiting exposures to non-users. In this paper, COMAR notes the following perspectives to address concerns expressed about possible health effects of RF field exposure from 5G technology. First, unlike lower frequency fields, MMW do not penetrate beyond the outer skin layers and thus do not expose inner tissues to MMW. Second, current research indicates that overall levels of exposure to RF are unlikely to be significantly altered by 5G, and exposure will continue to originate mostly from the "uplink" signals from one's own device (as they do now). Third, exposure levels in publicly accessible spaces will remain well below exposure limits established by international guideline and standard setting organizations, including ICNIRP and IEEE. Finally, so long as exposures remain below established guidelines, the research results to date do not support a determination that adverse health effects are associated with RF exposures, including those from 5G systems. While it is acknowledged that the scientific literature on MMW biological effect research is more limited than that for lower frequencies, we also note that it is of mixed quality and stress that future research should use appropriate precautions to enhance validity. The authorship of this paper includes a physician/biologist, epidemiologist, engineers, and physical scientists working voluntarily and collaboratively on a consensus basis.
... High-intensity mmWave exposure is found to generate heat sensations in skin, followed by pain if the power intensity is increased. Experiments in Walters et al. (2000) verifies the same. Similar conclusions are expected to hold valid for mmWave frequencies beyond the bands focused in these studies. ...
Beamforming is the central concept that can make millimeter‐wave (mmWave) a viable solution by solving challenges of link‐budget, cost, power, form factor, complexity, regulatory constraint, and so on. Before deployment of mmWave beamforming solution for 5G, and possibly beyond, several fundamental questions need to be answered. Some of them include hardware constraints, performance matrices, realistic propagation channel models including impairments due to obstacles such as body, blockages due to casings, phase noise, a model for spatial‐temporal variations in channels, and advanced MIMO techniques for multi‐carrier and multiuser communications. The site constraints and massive non‐line‐of‐sight transmission within the urban environment are severely questioning the conventional terrestrial low power node deployments that used to work well at low operational frequencies (sub‐6 GHz). In addition to this, in beamforming technology using massive antenna arrays, the coordination of the users and beams at the transmitter and receiver end within a large network are very challenging. In this article, we comprehensively investigate some of the most prominent and best practice solutions that attempted to answer these challenging questions.
... The corresponding physical quantities would be specific (energy) absorption (SA) below 6 GHz [2] and absorbed energy density (AED) above 6 GHz [11]. However, surprisingly, only a few study evaluated the temperature elevation for a pulse or pulse trains with energy concentrated shorter than the averaging time (6 min) [9], [12]. Only approach we can take is to derive the relation computationally. ...
... stun guns or tasers, whose effectiveness depends on individual traits or a physical condition of a man. It has also been proved that there is a safety margin between the time after which a person feels the pain and the quick escape from the striking wave distance, and the time in which the radiation can cause skin burns (Walter, Blick, Johnson, Adair, Foster, 1978). ...
This thesis is about the origin and development of electromagnetic weapons used in policing and military tasks as a non-lethal tool. The electromagnetic weapon was taken into consideration as a military or police means of antipersonnel engagement in the late 1970s. In the 1980s the USA conducted some defense programs towards development of lethal high energy laser weapons, to shoot down ballistic missiles and high-power microwave weapons designed to destroy electronic equipment. This technology was adapted by US Joint Non-Lethal Weapons Directorate (JNLWD) to construct new or adapted non-lethal delivery systems, which could be used in military operations. Until late 1990s several types of electromagnetic weapons were created and taken into account for practical use. The most important were: Active Denial System and electromagnetic pulse generators devices, for example E-bomb, which was probably used against Iraq in 2003 war.
This article reviews considerations related to exposure assessment and biological effects of radiofrequency energy with emphasis on health and safety. The rationale for two major exposure limits is described. Major areas of controversy about health effects of low‐level radiofrequency energy are described, both as related to uncertainties in the scientific data and in large variations in exposure limits around the world.
This article reviews considerations related to exposure assessment and biological effects of radiofrequency energy with emphasis on health and safety. The rationale for two major exposure limits is described. Major areas of controversy about health effects of low‐level radiofrequency energy are described, both as related to uncertainties in the scientific data and in large variations in exposure limits around the world.
The widespread use of Fifth Generation (5G) mobile network systems is driving a significant transformation in the way society uses wireless technology. This phenomenon arises as a consequence of the implementation of contemporary radio transmission systems, exemplified by the utilization of cuttingedge techniques such as millimeter wave beamforming on mobile devices. Understanding the issues regarding human exposure to radiation in the range of this new technology is crucial for device designs to comply with relevant regulatory bodies. This article provides an overview of the topic, with a focus on millimeter wave frequencies, presenting detailed discussions on exposure level assessment and certification procedures based on international standards. In addition to analyzing procedures outlined in international guidelines, a novel and innovative Machine Learning based methodology is introduced to expedite the product certification process to the fullest extent. Measurements were also carried out in a highly advanced setup to evaluate the expressions for calculating spatial-average power density (sPD), the new restriction for frequencies above 6 GHz. Each of the expressions presented in international standards is suitable for specific contexts associated with the field regions where the measurement is performed, necessitating their combined use. In general, this study provides technical support to national regulatory authorities, manufacturers of millimeter wave devices, and dosimetry measurement laboratories, benefiting the entire production chain.
Dominant effect of human exposure to electromagnetic fields in GHz frequency range corresponding to operation of 5G mobile communications systems is tissue heating i.e. local temperature elevation at the body surface, i.e. skin, ear and eyes. For the frequencies below transition frequency of 6GHz specific absorption rate (SAR) is used to quantify the volume heating. On the other hand, the surface heating above 6GHz is quantified via absorbed power density ( S ab ). Once these quantities are determined by means of internal field dosimetry procedures it is possible to determine the local surface temperature increase by solving the bio-heat transfer equation. The present paper deals with the calculation of tissue surface heating due to exposure to millimeter waves. Internal dosimetry is based on the planar tissue model exposed to dipole antenna radiation. Electromagnetic model is based on the analytical solution of Pocklington integro-differential equation while the assessment of tissue surface heating in planar tissue model has been carried by analytically solving a simplified variant of the bio-heat transfer equation. Some illustrative results for power density and temperature elevations will be presented for different antenna parameters.
The application of 28 GHz millimeter-wave is prevalent owing to the global spread of fifth-generation wireless communication systems. Its thermal effect is a dominant factor which potentially causes pain and tissue damage to the body parts exposed to the millimeter waves. However, the threshold of this thermal sensation, that is, the degree of change in skin temperature from the baseline at which the first subjective response to the thermal effects of the millimeter waves occurs, remains unclear. Here, we investigated the thermal sensation threshold and assessed its reliability when exposed to millimeter waves. Twenty healthy adults were exposed to 28 GHz millimeter-wave on their left middle fingertip at five levels of antenna input power: 0.2, 1.1, 1.6, 2.1, and 3.4 W (incident power density: 27–399 mW/cm²). This measurement session was repeated twice on the same day to evaluate the threshold reliability. The intraclass correlation coefficient (ICC) and Bland–Altman analysis were used as proxies for the relative and absolute reliability, respectively. The number of participants who perceived a sensation during the two sessions at each exposure level was also counted as the perception rate. Mean thermal sensation thresholds were within 0.9°C–1.0°C for the 126–399 mW/cm² conditions, while that was 0.2°C for the 27 mW/cm² condition. The ICCs for the threshold at 27 and 126 mW/cm² were interpreted as poor and fair, respectively, while those at higher exposure levels were moderate to substantial. Apart from a proportional bias in the 191 mW/cm² condition, there was no fixed bias. All participants perceived a thermal sensation at 399 mW/cm² in both sessions, and the perception rate gradually decreased with lower exposure levels. Importantly, two-thirds of the participants answered that they felt a thermal sensation in both or one of the sessions at 27 mW/cm², despite the low-temperature increase. These results suggest that the thermal sensation threshold is around 1.0°C, consistent across exposure levels, while its reliability increases with higher exposure levels. Furthermore, the perception of thermal sensation may be inherently ambiguous owing to the nature of human perception.
In this paper, the analysis of exposure reference levels is performed for the case of a half-wavelength dipole antenna positioned in the immediate vicinity of non-planar body parts. The incident power density (IPD) spatially averaged over the spherical and cylindrical surface is computed at the 6-90 GHz range, and subsequently placed in the context of the current international guidelines and standards for limiting exposure to electromagnetic (EM) fields which are defined considering planar computational tissue models. As numerical errors are ubiquitous at such high frequencies, the spatial resolution of EM models needs to be increased which in turn results in increased computational complexity and memory requirements. To alleviate this issue, we hybridise machine learning and traditional scientific computing approaches through differentiable programming paradigm. Findings demonstrate a strong positive effect the curvature of non-planar models has on the spatially averaged IPD with up to 15% larger values compared to the corresponding planar model in considered exposure scenarios.
Given the explosion in both the number of wireless devices and equipment radiating electromagnetic fields ( EMF ) and the growing public concern about it, accurate measurement of electromagnetic exposure and its application are expected to become increasingly important in future wireless communication systems. Indeed, the next generation of wireless networks seeks to provide customers with faster data rates, better quality of service ( QoS ), and reduced latency by increasing the number of access point s ( AP s), i.e. densification, which will increase EMF exposure. Similarly, the proliferation of future linked gadgets, such as the Internet of things ( IoT ) devices, may increase EMF exposure. This chapter provides a detailed assessment of existing methods for measuring EMF exposure in various circumstances, such as during data transmission uplink/downlink, and provides details on the metrics that are most typically used for evaluating EMF exposure in wireless communication. It also determines which metrics are most suited for reducing exposure.
Wireless communication technologies have transformed the way civilizations communicate information. To handle the ever‐increasing number of wireless users, the capacity of wireless communication networks is expected to increase 1,000 times. A portion of this capacity expansion will be made feasible by increasing the number of access points (APs), which will increase the number and kind of electromagnetic field (EMF) exposure sources in the environment. This chapter includes a thorough examination of the potential health risks associated with EMF exposure as well as the impact of this sort of exposure on the general public. This chapter also examines the potential effects of new wireless technologies on EMF exposure and suggests some unique research approaches for mitigating these effects in future wireless communication systems. The influence of mmWave or massive MIMO/beamforming on EMF exposure, for example, has yet to be thoroughly explored and included into the exposure evaluation framework.
In response to the urgent requirement for a high-power millimeter-wave system with small size, low cost, and excellent maneuverability in W-band, a compact high average power sheet beam extended interaction oscillator (SB-EIO) based on periodic cusp magnet (PCM) is designed, fabricated, hot tested and reliability verified. The maximum output power is 10.2 kW at a working duty of 1%. When the duty is increased to 27%, an average power of 2.2 kW is achieved, corresponding to a
pulse and 675 Hz repetition frequency. The device can be repeatedly turned on and off quickly during a 6-minute operating time and the single longest running time exceeds 60 min. The 96.0% transmission rate of the sheet beam (45.5 kV, 2.49 A) is verified. The overall weight of SB-EIO including the magnet and external package is less than 10 kg, which is ideal for equipping movable platforms.
This article presents a technique for the accurate assessment of the spatially averaged incident power density (IPD) on a spherical human head model from 3.5 to 100 GHz. The spatially-averaged IPD is defined either by averaging components of the power density vector normal to an evaluation surface, or by averaging its norm. The electromagnetic exposure assessment is provided for a dipole antenna placed at a separation distance of 2–150 mm from the model. We compare the IPD averaged over a proposed spherical surface with differently positioned planar surfaces. Results show that, for appropriate settings of the ex- posure above 6 GHz, the IPD averaged on a spherical surface is up to 12% larger for the normal definition, while marginally lower for the norm definition. In the worst case scenario, the spatially averaged IPD on a spherical surface is up to about 30% larger regardless of the definition. Comparative analysis between the definitions of the IPD averaged on a spherical model demonstrates that the norm definition yields significantly larger values in the reactive near field at characteristic frequencies, whereby this difference is marginal out of the reactive near field.
A semisolid human-body phantom for simulating the steady-state temperature elevation at the skin surface due to exposure to millimeter waves (MMWs) and quasi-MMWs was developed in this article. The phantom was designed by optimizing the electric constants of a mixed material consisting mainly of water and glycerin. First, the empirical equation of the complex permittivity of the phantom with respect to the composition and frequency was derived from dielectric measurements of phantoms. Then, the phantom composition used to obtain the temperature elevation equivalent to skin exposure were optimized using a computational approach. Here, the phantom composition was optimized at frequencies ranging from 10 to 100 GHz. In addition, we found that a single composition can be used for frequencies from 20 to 100 GHz. This phantom can simulate the temperature elevation due to skin exposure within the variation of the temperature elevation due to the individual differences in human tissue thickness. The developed phantom was validated by thermographic measurement using a horn antenna and an array antenna at 28 and 60 GHz, respectively. The developed phantoms are applicable to the thermal assessment of skin exposure to electromagnetic fields at MMW and quasi-MMW frequencies.
The deployment of the fifth-generation (5G) wireless communication services requires the installation of 5G next-generation Node-B Base Stations (gNBs) over the territory and the wide adoption of 5G User Equipment (UE). In this context, the population is concerned about the potential health risks associated with the Radio Frequency (RF) emissions from 5G equipment, with several communities actively working toward stopping the 5G deployment. To face these concerns, in this work, we analyze the health risks associated with 5G exposure by adopting a new and comprehensive viewpoint, based on the communications engineering perspective. By exploiting our background, we investigate the alleged health effects of 5G exposure and critically review the latest works that are often referenced to support the health concerns from 5G. We then precisely examine the up-to-date metrics, regulations, and assessment of compliance procedures for 5G exposure, by evaluating the latest guidelines from the Institute of Electrical and Electronics Engineers, the International Commission on Non-Ionizing Radiation Protection (ICNIRP), the International Telecommunication Union (ITU), the International Electrotechnical Commission (IEC), and the United States Federal Communications Commission (FCC), as well as the national regulations in more than 220 countries. We also thoroughly analyze the main health risks that are frequently associated with specific 5G features (e.g., multiple-input multiple-output (MIMO), beamforming, cell densification, adoption of millimeter waves, and connection of millions of devices). Finally, we examine the risk mitigation techniques based on communications engineering that can be implemented to reduce the exposure from 5G gNB and UE. Overall, we argue that the widely perceived health risks that are attributed to 5G are not supported by scientific evidence from communications engineering. In addition, we explain how the solutions to minimize the health risks from 5G (including currently unknown effects) are already mature and ready to be implemented. Finally, future works, e.g., aimed at evaluating long-term impacts of 5G exposure, as well as innovative solutions to further reduce the RF emissions, are suggested.
International guidelines/standards for human protection from electromagnetic fields have been revised recently, especially for frequencies above 6 GHz where new wireless communication systems have been deployed. Above this frequency a new physical quantity "absorbed/epithelial power density" has been adopted as a dose metric. Then, the permissible level of external field strength/power density is derived for practical assessment. In addition, a new physical quantity, fluence or absorbed energy density, is introduced for protection from brief pulses (especially for shorter than 10 sec). These limits were explicitly designed to avoid excessive increases in tissue temperature, based on electromagnetic and thermal modeling studies but supported by experimental data where available. This paper reviews the studies on the computational modeling/dosimetry which are related to the revision of the guidelines/standards. The comparisons with experimental data as well as an analytic solution are also been presented. Future research needs and additional comments on the revision will also be mentioned.
We present the design and experiments on a 100-kW level
W
-band gyrotron. The gyrotron was developed as a prototype for an active denial system. We measured a peak output power of 100 kW with 50 kV, 6-A electron beam in 50-
pulses at a repetition rate of 50 Hz. Driven by the long pulse power supplies with 2-A current limited by the specification, the gyrotron operates at the output power of 37 kW with the total efficiency of up to 48% at a collector depression of 18 kV. The gyrotron was also driven in long pulse up to the pulselength of 2 s at the current of 2 A.
International guidelines/standards for human protection from electromagnetic fields have been revised recently, especially for frequencies above 6 GHz where new wireless communication systems have been deployed. Above this frequency a new physical quantity "absorbed/epithelia power density" has been adopted as a dose metric. Then, the permissible level of external field strength/power density is derived for practical assessment. In addition, a new physical quantity, fluence or absorbed energy density, is introduced for protection from brief pulses (especially for shorter than 10 sec). These limits were explicitly designed to avoid excessive increases in tissue temperature, based on electromagnetic and thermal modeling studies but supported by experimental data where available. This paper reviews the studies on the computational modeling/dosimetry which are related to the revision of the guidelines/standards. The comparisons with experimental data as well as an analytic solution are also been presented. Future research needs and additional comments on the revision will also be mentioned.
The currently ongoing deployment if the fifth generation of the wireless communication technology, the 5G technology, has reignited the health debate around the new kind of radiation that will be used/emitted by the 5G devices and networks – the millimeter-waves. The new aspect of the 5G technology, that is of concern to some of the future users, is that both, antennas and devices will be continuously in a very close proximity of the users’ bodies. Skin is the only organ of the human body, besides the eyes, that will be directly exposed to the mm-waves of the 5G technology. However, the whole scientific evidence on the possible effects of millimeter-waves on skin and skin cells, currently consists of only some 99 studies. This clearly indicates that the scientific evidence concerning the possible effects of millimeter-waves on humans is insufficient to devise science-based exposure limits and to develop science-based human health policies. The sufficient research has not been done and, therefore, precautionary measures should be considered for the deployment of the 5G, before the sufficient number of quality research studies will be executed and health risk, or lack of it, scientifically established.
A previous study reported thermal effects resulting from millimeter wave exposures at 35 and 94 GHz on non-human primates, specifically rhesus monkeys' (Macaca mulatta) corneas, but the data exhibited large variations in the observed temperatures and uncertainties in the millimeter wave dosimetry. By incorporating improvements in models and dosimetry, a non-human primate experiment was conducted involving corneal exposures that agreed well with a three-layer, one-dimensional, thermodynamic model to predict the expected surface temperature rise. The new data indicated that the originally reported safety margins for eye exposures were underestimated by 41 ± 20% over the power densities explored. As a result, the expected minimal visible lesion thresholds should be raised to 10.6 ± 1.5 and 7.1 ± 1.0 J cm at 35 and 94 GHz, respectively, provided that the power density is less than 6 W cm for subjects that are unable to blink. If the blink reflex was active, a power density threshold of 20 W cm could be used to protect the eye, although the eyelid could be burned if the exposure was long enough.
The deployment of 5G wireless communication services requires the installation of 5G next-generation Node-B Base Stations (gNBs) over the territory and the wide adoption of 5G User Equipment (UE). In this context, the population is concerned about the potential health risks associated with the Radio Frequency (RF) emissions from 5G equipment, with several communities actively working toward stopping the 5G deployment. To face these concerns, in this work, we analyze the health risks associated with 5G exposure by adopting a new and comprehensive viewpoint, based on the communications engineering perspective. By exploiting our background, we analyze the alleged health effects of 5G exposure and critically review the latest works that are often referenced to support the health concerns from 5G. We then precisely examine the up-to-date metrics, regulations, and assessment of compliance procedures for 5G exposure, by evaluating the latest guidelines from IEEE, ICNIRP, ITU, IEC, and FCC, as well as the national regulations in more than 220 countries. We also thoroughly analyze the main health risks that are frequently associated with specific 5G features (e.g., MIMO, beamforming, cell densification, adoption of millimeter waves, and connection of millions of devices). Finally, we examine the risk mitigation techniques based on communications engineering that can be implemented to reduce the exposure from 5G gNB and UE. Overall, we argue that the widely perceived health risks that are attributed to 5G are not supported by scientific evidence from communications engineering. In addition, we explain how the solutions to minimize the health risks from 5G are already mature and ready to be implemented. Finally, future works, e.g., aimed at evaluating long-term impacts of 5G exposure, as well as innovative solutions to further reduce the RF emissions, are suggested.
Millimeter waves (MMW) are broadband frequencies that have recently been used in several applications in wireless communications, medical devices and nonlethal weapons [i.e., the nonlethal weapon, Active Denial Systems, (ADS) operating at 94–95 GHz, CW]. However, little information is available on their potential effects on humans. These radiofrequencies are absorbed and stopped by the first layer of the skin. In this study, we evaluated the effects of 94 GHz on the gene expression of skin cells. Two rat populations consisting of 17 young animals and 14 adults were subjected to chronic long-term 94 GHz MMW exposure. Each group of animals was divided into exposed and sham subgroups. The two independent exposure experiments were conducted for 5 months with rats exposed 3 h per day for 3 days per week to an incident power density of 10 mW/cm ² , which corresponded to twice the ICNIRP limit of occupational exposure for humans. At the end of the experiment, skin explants were collected and RNA was extracted. Then, the modifications to the whole gene expression profile were analyzed with a gene expression microarray. Without modification of the animal's temperature, long-term chronic 94 GHz-MMW exposure did not significantly modify the gene expression of the skin on either the young or adult rats.
Knowledge of the dielectric properties of biological materials is of importance in solving electromagnetic interaction problems. There is, as yet, no consensus on such data among scientists dealing with these issues. This project is geared towards producing a database of dielectric data based on measurements using recently developed techniques. This has been achieved through measurement over a wide frequency range. The new data were evaluated by comparison with corresponding data from the literature where available. To facilitate the incorporation of the dielectric data in numerical solutions, their frequency dependence was modelled to a spectrum characterised by 4 dispersion regions. The conductivity of tissues below 100 Hz was estimated from the recent measurements mitigated by data from the literature and used to estimate the body and of various body parts.
A monograph which covers "… the traditional concepts of pain, the newer data respecting the phenomenology of pain,… " and an outline of a "… comprehensive theory of pain experience compatible with available information." 505-item bibliography. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
A new adaptive psychophysical method, the step method, is introduced. Simulations show the method to be less biased and more
efficient than constant stimuli or Pentland’s adaptive method for fewer than 40 trials. An experiment using discrimination
of dot number, however, failed to find any differences among the three methods in either bias or efficiency.
A new adaptive psychophysical method, the step method, is introduced. Simulations show the method to be less biased and more efficient than constant stimuli or Pentland's adaptive method for fewer than 40 trials. An experiment using discrimination of dot number, however, failed to find any differences among the three methods in either bias or efficiency.
We measured thresholds for microwave-evoked skin sensations of warmth at frequencies of 2.45, 7.5, 10, 35, and 94 GHz. In the same subjects, thresholds of warmth evoked by infrared radiation (IR) were also measured for comparison. Detection thresholds were measured on the skin in the middle of the back in 15 adult male human subjects at all microwave (MW) frequencies and with IR. Long duration (10-s), large area (327-cm2) stimuli were used to minimize any differential effects of temporal or spatial summation. Sensitivity increased monotonically with frequency throughout the range of microwave frequencies tested. The threshold at 94 GHz (4.5 +/- 0.6 mW/cm2) was more than an order of magnitude less than at 2.45 GHz (63.1 +/- 6.7 mW/cm2), and it was comparable to the threshold for IR (5.34 +/- 1.07 mW/cm2).
Human thresholds for skin sensations of warmth were measured at frequencies from 2.45 to 94 GHz. By solving the one-dimensional bioheat equation, we calculated the temperature increase at the skin surface or at a depth of 175 microm at incident power levels corresponding to the observed thresholds. The thermal analysis suggests that the thresholds correspond to a localized temperature increase of about 0.07 degrees C at and near the surface of the skin. We also found that, even at the highest frequency of irradiation, the depth at which the temperature receptors are located is not a relevant parameter, as long as it is within 0.3 mm of the surface. Over the time range of the simulation, the results of the thermal model are insensitive to blood flow, but sensitive to thermal conduction; and this sensitivity increases strongly with frequency. We conclude with an analysis of the effect of thermal conduction on surface temperature rise, which becomes a dominant factor at microwave frequencies over 10 GHz.
We consider the thermal response times for heating of tissue subject to nonionizing (microwave or infrared) radiation. The analysis is based on a dimensionless form of the bioheat equation. The thermal response is governed by two time constants: one (tau1) pertains to heat convection by blood flow, and is of the order of 20-30 min for physiologically normal perfusion rates; the second (tau2) characterizes heat conduction and varies as the square of a distance that characterizes the spatial extent of the heating. Two idealized cases are examined. The first is a tissue block with an insulated surface, subject to irradiation with an exponentially decreasing specific absorption rate, which models a large surface area of tissue exposed to microwaves. The second is a hemispherical region of tissue exposed at a spatially uniform specific absorption rate, which models localized exposure. In both cases, the steady-state temperature increase can be written as the product of the incident power density and an effective time constant tau(eff), which is defined for each geometry as an appropriate function of tau1 and tau2. In appropriate limits of the ratio of these time constants, the local temperature rise is dominated by conductive or convective heat transport. Predictions of the block model agree well with recent data for the thresholds for perception of warmth or pain from exposure to microwave energy. Using these concepts, we developed a thermal averaging time that might be used in standards for human exposure to microwave radiation, to limit the temperature rise in tissue from radiation by pulsed sources. We compare the ANSI exposure standards for microwaves and infrared laser radiation with respect to the maximal increase in tissue temperature that would be allowed at the maximal permissible exposures. A historical appendix presents the origin of the 6-min averaging time used in the microwave standard.
NOTES AND DISCUSSIONS THE STAIRCASE-METHOD IN PSYCHOPHYSICS A psychophysical method variously referred to as the method of up and downs, 1 the Bekesy audiometric method, 2 or the staircase-method, has come into extensive use in the last few years. The method has several advantages over other more commonly used techniques but it also has some disadvantages. This paper will illustrate the use of the method, will discuss its relative merits and demerits, and will describe a modification which overcomes certain of the disadvantages of the method. The staircase-method is best described by illustrating its use with a specific prob- lem. Suppose the problem is to determine S's absolute, intensive threshold for the sound of a click. The first stimulus that E delivers is a click of some arbitrary intensity. S responds either that he did or did not hear it. If S says 'yes' (he did hear it), the next stimulus is made less intense, and if S says 'no,' the second stimulus is made more intense. If S responds 'yes' to the second stimulus, the third is made less intense, and if he says 'no,' it is made more intense. This procedure is simply continued until some predetermined criterion or 'number of trials' is reached. The results of a series of 30 trials are shown in Fig. 1. The results may be recorded directly on graph-paper; doing so helps E keep the procedure straight. There are a number of ways of determining the intensive value that represents the threshold. The simplest is to compute the mean of the values of a given num- ber of stimuli delivered after the series has reached its final level. This requires an arbitrary decision about when the final level has been reached. The technique, which avoids this difficulty and yields a 50% value, is simply to determine the stimulus above which 50% of the responses are 'yes,'-i.e. in Fig. 1 between 61 and 62 db. Statistical treatment of the results has been discussed by Dixon and Massey, who describe the techniques for determining the means, standard deviations, standard errors, etc., for this type of data.3 The treatments assume, however, that the response to each stimulus is independent of the preceding stimuli and pre- ceding responses. This assumption holds for the examples analyzed, but there is evidence that the assumption does not always hold for human Ss in psychophysical experiments.• The development of techn.iques that take the existing inter-actions into account has not as yet been achieved. W. J. Dixon and F. J. Massey, lnt,.oduction lo Statistical Analysis, 1957, 279· •Georg von Bekesy, A new audiometer, A'la 010-/a,.yngol., 35, 1947, 411-422. •Dixon and Massey, op. cit., 286. • W. S. Verplanck, G. H. Collier, and J. W. Cotton, Nonindependence of succes- sive responses in measurement of the visual threshold, /. exp. Psycho/., 42, 1952, 273-282; Verplanck and Cotton, The dependence of frequencies of seeing on pro- cedural variables: J. Direction and length of series of intensity-ordered stimuli, /. gen. Psycho/., 53, 1955, 37-47; V. L. Senders, Further analysis of response se- quences in the setting of a psychophysical experiment, this JOURNAL, 66, 1 953, 215-229; R. S. Woodworth and Harold Schlosberg, Experimental Psychology, 1954,
A simple and efficient method of estimating points on the psychometric function, and thus of estimating absolute and difference limens, is described. An illustration of the method is given in which sensitivity to inter-aural time differences is measured.
- Blick
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Millimeter-wave exposure system augmentation. Brooks AFB, TX: U S . Air Force Armstrong Laboratory
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