Non-Ionizing Radiation Protection Research Articles

Transient Thermal Responses of Skin to Pulsed Millimeter Waves

This study examines thermal responses of skin to pulsed millimeter wave (mm-wave) and radiofrequency (RF) radiation. We review limits for pulse fluence 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 re-affirmed 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 temperature 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 insufficient 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 fluence 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.

Computational errors of the induced electric field in voxelized and tetrahedral anatomical head models exposed to spatially uniform and localized magnetic fields

At low and intermediate frequencies, the strength of the induced electric field is used as dosimetric quantity for human protection in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. To compute the induced electric field, numerical methods based on anatomically realistic voxel models are commonly used. However, grid-based models introduce staircase approximation errors when curved surfaces are discretized with voxels, particularly in correspondence of boundaries with large differences in electrical conductivity. By contrast, those kind of artefacts are absent in tetrahedral meshes. Here, we investigate the computational errors that affect voxelized and tetrahedral head models when exposed to uniform magnetic fields at 50 Hz, and localized exposure due to transcranial magnetic stimulation. Five subjects were considered, and for each of them four voxel grids and four tetrahedral meshes were reconstructed with different resolutions. The differences in the results were characterized by comparing the induced electric fields computed using those meshes/grids. The results showed modest discrepancies in the overall electric field distributions between the various grids and meshes. However, the peak electric field strengths were erroneous for both tetrahedral and voxel models. Therefore, post-processing techniques are needed to suppress those numerical artefacts. For this purpose, the 99.99th, or lower, percentile of the electric field strength was found to remove the numerical errors. In addition, we found that spatially averaging the electric fields over 2 mm cubical volumes, as described by the ICNIRP, was effective in removing most of the spuriously large electric fields. When spatial averaging was used, relative coarse head models consisting of approximately 1 mm voxels or tetrahedral meshes with 2 mm average side length were sufficient to mitigate the artefacts. Nonetheless, the additional percentile filtering might still be needed to suppress the erroneous values completely.

Human Postural Control Under High Levels of Extremely Low Frequency Magnetic Fields

Background: International agencies such as the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the International Committee on Electromagnetic Safety (ICES) of the Institute of Electrical and Electronics Engineers (IEEE) need further data to set international guidelines to protect workers and the public from potential adverse effects to Extremely Low-Frequency Magnetic Fields (ELF-MF). Interestingly, electromagnetic induction has been hypothesized to impact human vestibular function (i.e. through induced electric fields). To date, a theoretical 4 T/s vestibular threshold was proposed to modulate postural control, but data is lacking above this limit. Objectives: This research aimed to investigate the impact of full head homogeneous ELF-MF stimulations above the 4 T/s threshold on human postural control. Methods: Postural control of twenty healthy participants was analyzed while full head homogeneous ELF-MF stimulations (20 Hz, 60 Hz, and 90 Hz) up to 40 T/s were applied. Velocity, main direction and spatial dispersion of sway were used to investigate postural modulations. Results: Despite a conclusive positive control effect, no significant effects of ELF-MF exposures on velocity, spatial dispersion, and direction of the postural sway were found for our 3 frequency conditions. Conclusions: The homogeneous full head MF stimulations oriented vertically and delivered at high frequencies induced E-fields having a weaker impact than anticipated, possibly because they impacted only a small portion of the vestibular system. This resulted in an absence of effect on postural control outcomes.

Effect of Electrical Conductivity Uncertainty in the Assessment of the Electric Fields Induced in the Brain by Exposure to Uniform Magnetic Fields at 50 Hz

International exposure standard/guidelines establish limits for external electromagnetic field strengths. At low frequencies, these maximum allowable exposure levels are derived from the limits defined for internal electric field strengths which have been set to avoid adverse health effects. In the IEEE International Committee on Electromagnetic Safety standard, the relationship between internal and external fields was obtained through homogeneous elliptical models without considering the dielectric properties of tissues. However, the International Commission on Non-Ionizing Radiation Protection guidelines were established using computational dosimetry on realistic anatomical models. In this case, variability in the electrical conductivity of the tissues represents a major source of uncertainty when deriving allowable external field strengths. Here we characterized this uncertainty by studying the effect of different tissue conductivity values on the variability of the peak electric field strengths induced in the brain of twenty-five individuals exposed to uniform magnetic fields at 50 Hz. Results showed that the maximum electric field strengths computed with new estimations of brain tissue conductivities were significantly lower than those obtained with commonly used values in low-frequency dosimetry. The lower strengths were due to the new brain conductivity values being considerably higher than those usually adopted in dosimetry modeling studies. A sensitivity analysis also revealed that variations in the electrical conductivities of the grey and white matter had a major effect on the peak electric field strengths in the brain. Our findings are intended to lessen dosimetric uncertainty in the evaluation of the electric field strengths due to electrical properties of the biological tissues.

NUMERICAL ANALYSIS OF SAFETY ZONE OF A LARGE FLAT-PLATE BOUNDED-WAVE EMP SIMULATOR.

The safety zone of a large flat-plate bounded-wave electromagnetic pulse simulator was analyzed using the 3D electromagnetic simulation software Computer Simulation Technology. First, the double-limit requirement cited from the GB 8702 for an instantaneous pulse was clarified compared with the International Commission on Non-Ionizing Radiation Protection guidelines. This means that both the amplitude of the time-domain waveforms and all frequency components should be satisfied with the respective exposure limits. Then, the leakage field of a large flat-plate bounded-wave simulator was simulated. After analyzing the peak amplitude of an instantaneous electric field in a certain area, the observation points along six directions were specified, and the corresponding amplitudes were given. Furthermore, it was verified that the time-domain electric field of the critical points was satisfied with the frequency-domain exposure limits. Finally, the safety distances lower than the reference levels were given, and the safety zones corresponding to the three common exposure limits were obtained.

Modeling and Design of Passive Shield to Limit EMF Emission and to Minimize Shield Loss in Unipolar Wireless Charging System for EV

In this paper, a detailed lumped model of the shield is developed, and an optimization method is proposed to minimize the shield loss while suppressing the emission within the standard limit. The electromagnetic emission in a wireless charging system (WCS) is a serious concern for health and safety, especially for medium- and high-power applications, where strong magnetic field propagates through a large air gap. Usually, a flat aluminum plate is used as a shield to suppress the emission outside the charging area. This field emission increases proportionally with the coil ampere turn; therefore, a much higher shield current is required to suppress the additional emission under the limit set by the International Commission on Non-Ionizing Radiation Protection. In this paper, a novel hybrid shield structure is proposed to limit the electromagnetic field (EMF) emission, as well as to minimize the shield loss. The proposed shielding is evaluated on a laboratory prototype of 7-kW WCS designed for electric vehicle application. The experimental result shows that, while suppressing the EMF under the limit, the shield loss has been reduced by 21% compared to the commonly used aluminum shield.

Free Arrangement Wireless Power Transfer System With a Ferrite Transmission Medium and Geometry-Based Performance Improvement

A free arrangement wireless power transfer system with a ferrite transmission medium and geometry-based performance improvement method are introduced here. The proposed system addresses the efficiency collapse caused by misalignment or increased distance between the transmitter and receiver coils, that is, receivers can be located anywhere on the plate-shaped system, which can be applied to a table, wall, or floor to supply electrical power as needed. Despite its high cost, ferrite is advantageous over air as a medium as the latter diminishes the efficiency at a distance or misalignment. Further, ferrite reduces the transmitter volume and number of coil turns, which is useful for practical applications. Skewed-shape coil windings with higher effective mutual inductance than unskewed structures are used in this system to increase power transfer efficiency. The improvements from the ferrite and coil-winding geometry are verified through Ansoft Maxwell v14.0 and MATLAB simulations. Four prototypes of the proposed system are fabricated and validated at 100 kHz. The highest transfer efficiency at the farthest distance, 55 cm, is 17.5% with the 4-cm-skewed ferrite structure, whereas no power is delivered beyond 10 cm in air. Consequently, the proposed system achieves wider power transfer area and better efficiency without additional power and coil windings while the system complies with the guidelines provided by International Commission on Non-ionizing Radiation Protection (ICNIRP) and IEEE for human safety. This article is accompanied by a demonstrating video.

Research on low frequency electromagnetic environment of electric vehicle and human health

In order to study the influence of electromagnetic environment produced by low frequency current in power cables of electric vehicle on driver’s and co-driver’s tissues, especially in the central nervous system (CNS). The distribution of the magnetic induction intensity and the induction electric field intensity in human trunk and CNS of the driver’s and co-driver’s are calculated and analysed. The results are compared with the related standards of International Committee on Non-ionizing Radiation Protection (ICNIRP). The study shows that the induced fields in human trunk and CNS are much smaller than the occupational and public exposure limits defined by ICNIRP. Therefore, the low frequency current would be safe for human health to some extent.

Examination of electric and magnetic fields around high voltage equipment

In the whole territory of the European Union, both public and occupational exposures are controlled by the Council of the EU, itself. These are strict and clear limits based on the latest researches of World Health Organisation and International Agency for Research on Cancer. International Commission on Non-Ionizing Radiation Protection is also an important body to declare exposure limits which vary on the frequency.In Hungary, latest guidelines of EU Council became a national law. As a result of that, the inspection of occupational exposures of both electric and magnetic field became obligatory. A complete risk analysis has to be performed by accredited bodies to examine, calculate, simulate and measure the potential sources of risks; experts from medical field also must be involved to these researches.This paper introduces the practical results of a 3D simulation with finite element method regarding to both electric and magnetic exposures in the surroundings of a high voltage equipment. All the results were validated by on-site measurements, as well. With this technique, E and B field distributions can not only be analyzed, but visualized easily, as well.

Wireless Power Transfer Through Inductive Coupling For Aimds

For the patients with some cardiovascular diseases, implantable devices like implantable cardiac pacemakers and implantable cardioverter defibrillators play a very important role. The life of implantable device is limited by the life of battery and the size of implanted device is dependent on size of battery. More life of battery demands larger battery size. Since these devices are implanted inside the human body, they must be small in size as well as of long battery life. Wireless re-charging of such devices can only be the solution to reduce the size and increase life of AIMDs. Wireless recharging by magnetic resonance coupling in less time is expected and hence this topic is considered for more research to have uninterrupted power supply from battery. Selection of operating frequency for transfer of power wirelessly is of great concern as it requires attention towards certain guidelines as basic restrictions provided by International Commission on non-ionizing Radiation Protection (ICNIRP). With lower frequencies used for power transfer, the efficiency would be less whereas with higher frequencies efficiency would be higher but with the use of higher frequencies for power transfer certain biological issues needs attention like tissue heating. In the technique of wireless power transfer, the transmitting coil is assumed to be outside the body and receiver coil is considered to be inside the human body above the pacemaker shell. The efficiency of power transfer is affected by frequency for power transfer and distance between the two coils.

Development of a Job-Exposure Matrix for Assessment of Occupational Exposure to High-Frequency Electromagnetic Fields (3 kHz-300 GHz).

The aim of this work was to build a job-exposure matrix (JEM) using an international coding system and covering the non-thermal intermediate frequency (IF) (3-100 kHz, named IFELF), thermal IF (100 kHz-10 MHz, named IFRF), and radiofrequency (RF) (>10 MHz) bands. Detailed occupational data were collected in a large population-based case-control study, INTEROCC, with occupations coded into the International Standard Classification of Occupations system 1988 (ISCO88). The subjects' occupational source-based ancillary information was combined with an existing source-exposure matrix and the reference levels of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for occupational exposure to calculate estimates of level (L) of exposure to electric (E) and magnetic (H) fields by ISCO88 code and frequency band as ICNIRP ratios (IFELF) or squared ratios (IFRF and RF). Estimates of exposure probability (P) were obtained by dividing the number of exposed subjects by the total number of subjects available per job title. With 36 011 job histories collected, 468 ISCO88 (four-digit) codes were included in the JEM, of which 62.4% are exposed to RF, IFRF, and/or IFELF. As a reference, P values for RF E-fields ranged from 0.3 to 65.0% with a median of 5.1%. L values for RF E-fields (ICNIRP squared ratio) ranged from 6.94 × 10-11 to 33.97 with a median of 0.61. The methodology used allowed the development of a JEM for high-frequency electromagnetic fields containing exposure estimates for the largest number of occupations to date. Although the validity of this JEM is limited by the small number of available observations for some codes, this JEM may be useful for epidemiological studies and occupational health management programs assessing high-frequency electromagnetic field exposure in occupational settings.

Design of Magnetic Coupler for Wireless Power Transfer

In order to improve the restraint ability of electromagnetic energy in space and improve the coupling efficiency, a magnetic coupler structure with composite magnetic shield is proposed. Firstly, the model is established by using the finite-element simulation software. Then, according to the limit of public exposure to time-varying electromagnetic fields pointed out in ICNIPR (International Commission on Non-Ionizing Radiation Protection) guidelines, the characteristics and spatial magnetic field distribution of magnetic couplers with a single shielding structure, double shielding structure, and composite shielding structure are compared and analyzed. Finally, the experimental results show that the structure of magnetic couplers with a composite magnetic shield has a good effect in strengthening magnetic field concentration and reducing the electromagnetic interference of wireless charging systems to the external environment. It also has the advantages of smaller volume, lighter weight, and lower cost, and can effectively improve the transmission efficiency and enhance the stability of wireless charging systems.

Mobile phone antenna-matching study with different finger positions on an inhomogeneous human model

ABSTRACTThe human head and hand being in the near-field zone of a mobile phone antenna can drastically influence the antenna matching with free space. The goal of the presented research is to study this phenomenon on an inhomogeneous human model for different relative positions and distances of hand and fingers when using a mobile phone. The only safety criteria commonly used to estimate RF exposure impact on humans is the specific absorption rate (SAR). Its limits are determined by the Federal Communication Commission (FCC) in the USA and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) in Europe. The maximal values of SAR for a mobile handset are determined for each model by the manufacturer. In this paper, it is shown that the peak values provided by the manufacturers and their understanding may need refinement. It is almost impossible to consider all parameters, such as the dependence of SAR on antenna communication matching, with a variety of shapes and forms and other details during physical measurements or numerical estimation. The premise for such assumptions is based on the analysis of S11 dependency on the exposure scenario and the fact that the Automatic Gain Control (AGC) increases power when the signal strength at the base station drops.

Impact of Cell-phone on Human Health: A Systematic Review of Literatures

The growth of communication technology in the last two decades has given the world a new look.With the blessings of digital technology, we can now communicate to any parts of the world with just a touch over the screen of our smart phone. Mobile phone hasnow become an indispensable part of our life.But, biological effects of radio-frequency electromagnetic fields (EMF) transmitted by mobile phones are still a matter of public and scientific debate. Countries accross the world are now getting concerned about the impact of mobiles on human health and environment.Radiofrequency waves generated from mobile phones cause potential public health problems. Short-term effects like changes in sleep, heart rate, and blood pressure, and long-term effects like carcinoma (particularly glioma) are well-documented. International Agency for Research on Cancer (IARC) published cancer risks from Radiofrequency(RF) radiation. Human epidemiological studies gave evidence of increased risk for glioma and acoustic neuroma. Further epidemiological, animal and mechanistic studies have strengthened the association. Besides, the carcinogenic effect of non-ionizing radiation emitted from cordless digital devices, numerous health effects have already been claimed to occur. Faced with this context, scientific community and legislative bodies are raising voice for the reduction of RF-EMF exposure to the safe limit for human health and environment. The RF exposure restriction guideline used by many agencies was established in 1998 by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and was based only on established short-term thermal (heating) effects from RF radiation neglecting non-thermal biological effects. The present study is, therefore, intended to review the literatures relating mobile phone and Wi-fito human health in order to make the scientific community updated on the association between mobile phone use and human health.
 Ibrahim Card Med J 2018; 8 (1&2): 53-65

Evaluation of the Magnetic Field Leakage from Two Wireless Power Transfer Systems for EV/PHV Driven Simultaneously

Wireless power transfer for electric and plug-in hybrid vehicles has been developed to facilitate battery charging. In a wireless power transfer system, because the magnetic field leaks to the surroundings of the vehicle, it is important to evaluate the quantitative human exposure. The International Commission on Non-Ionizing Radiation Protection provides guidelines for human exposure assessment. In this study, we evaluate the magnetic field leakage under two parking configurations and current phase differences for two vehicles being simultaneously charged (3.7 kW at 85 kHz per vehicle). The results of the analysis show that the magnetic field leakage is lower than the reference level of the guidelines for all cases and that the leakage could be reduced by controlling the phase difference between the two wireless power transfer systems equally distributed from the single high-frequency power source for each parking configuration.

Magnetic Field during Wireless Charging in an Electric Vehicle According to Standard SAE J2954

The Society of Automotive Engineers (SAE) Recommended Practice (RP) J2954 (November 2017) was recently published to standardize the wireless power transfer (WPT) technology to recharge the battery of an electric vehicle (EV). The SAE J2954 RP establishes criteria for interoperability, electromagnetic compatibility (EMC), electromagnetic field (EMF) safety, etc. The aim of this study was to predict the magnetic field behavior inside and outside an EV during wireless charging using the design criteria of SAE RP J2954. Analyzing the worst case configurations of WPT coils and EV bodyshell by a sophisticated software tool based on the finite element method (FEM) that takes into account the field reflection and refraction of the metal EV bodyshell, it is possible to numerically assess the magnetic field levels in the environment. The investigation was performed considering the worst case configuration—a small city car with a Class 2 WPT system of 7.7 kVA with WPT coils with maximum admissible ground clearance and offset. The results showed that the reference level (RL) of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines in terms of magnetic flux density was exceeded under and beside the EV. To mitigate the magnetic field, the currents flowing through the WPT coils were varied using the inductor-capacitor-capacitor (LCC) compensation instead of the traditional series-series (SS) compensation. The corresponding calculated field was compliant with the 2010 ICNIRP RL and presented a limited exceedance of the 1998 ICNIRP RL. Finally, the influence of the body width on the magnetic field behavior adopting maximum offset was investigated, demonstrating that the magnetic field emission in the environment increased as the ground clearance increased and as the body width decreased.

Global Analysis of Transcriptional Expression in Mice Exposed to Intermediate Frequency Magnetic Fields Utilized for Wireless Power Transfer Systems.

Background: Intermediate frequency magnetic fields (IF-MFs) at around 85 kHz are a component of wireless power transfer systems used for charging electrical vehicles. However, limited data exist on the potential health effects of IF-MFs. We performed a comprehensive analysis of transcriptional expression in mice after IF-MF exposure. Materials and Methods: We developed an IF-MF exposure system to generate a high magnetic flux density (25.3 mT). The system can expose the IF-MF for a mouse whole-body without considering thermal effects. After 10 days (1 h/day) of exposure, a comprehensive expression analysis was performed using microarray data from both the brain and liver. Results: No significant differences in transcriptional expression were detected in the 35,240 probe-sets when controlling the false discovery rate (FDR) under a fold change cutoff >1.5. However, several differential expressions were detected without FDR-adjustment, but these were not confirmed by RT-PCR analysis. Conclusions: To our knowledge, this is the first in vivo study to evaluate the biological effects of IF-MF exposure with an intense magnetic flux density 253 times higher than the occupational restriction level defined by the International Commission on Non-Ionizing Radiation Protection guidelines. However, our findings indicate that transcriptional responses in the living body are not affected under these conditions.

Personal Exposure to Radiofrequency Electromagnetic Fields Among Palestinian Adults.

This work deals with the assessment of personal exposure to radiofrequency electromagnetic fields and the study of temporal and spatial daily variations in a group of 24 adults from the West Bank, Palestine. Exposure was measured using a personal exposure meter EME SPY 140. Mean values of exposure levels from different radiofrequency sources were calculated using both naive and robust regression on order statistics approaches. The total daily exposure from all radiofrequency electromagnetic field sources varied widely among participants depending on their location, the mobile network they use, their activities, and their mode of transportation, ranging from about 0.2 V m to 0.9 V m. The average total daily exposure of all participants was about 0.48 V m. The main contribution to the mean exposure was from WiFi 2G (45%), GSM900 uplink (19%), GSM900 downlink, and FM radiobroadcasting (each by 11%). Other sources including GSM1800, UMTS2100, WiFi 5G, DECT, TETRA, WiMAX, and TV bands all together contributed 14%. During different activities, participants were exposed to the highest exposure level while traveling and to the lowest exposure while they were sleeping. During the day, participants received the highest exposure during the time period from 1600 to 2400 h. Based on thermal effect of radiofrequency electromagnetic fields, all evaluated personal exposures comply with guidelines recommended for the general public by the International Commission on Non-Ionizing Radiation Protection.

Measurement and evaluation of occupational exposure to electromagnetic field in the vicinity of FM/TV broadcast radiation

This paper involves the measurement and evaluation of electromagnetic field exposure levels at Kamarkouh FM/TV transmitter station at Qom province with multiple-frequency sources. Electromagnetic radiation levels were measured at 34 points for 6 min by Strength Meter Probe which is a broadband meter. The measured electromagnetic radiation levels were then compared to the International Commission of Non-Ionizing Radiation Protection standard. In addition, the theoretical electric field strength values at these same 34 points as above were estimated based on a free-space modeling calculation. The measurement results show that the maximum electromagnetic radiation level was 13.45 V/m, and this is far below the International Commission of Non-Ionizing Radiation Protection limits. The analysis of the comparison between calculated and measured electromagnetic radiation levels showed that there were other sources that contributed to increases in the electric field intensity. The source contributions to the total electric field strength were measured in a practical way. It means that by switching of the transmitters, the electric field strength measured in each state. The results showed that FM frequency band sources provided the highest contributions to the overall electromagnetic radiation level.

Radiation Absorbed Dose Rates from Selected Mobile Phone Base Stations in Ibadan, Oyo State, Nigeria

The aim of this study is to measure the radiation dose from Mobile Phone Base Stations relative to human exposure at various locations within Ibadan metropolis, Southwestern Nigeria by measuring the radiation dose at 10 - 100 metres distance away from the randomly selected base stations and compare the results with other studies/recommended exposure limit. A Victoreen radiation survey meter (fluke 451 model) was used to measure the radiation dose. The meter was calibrated with a calibration factor of 1.1 to standardized the values measured with international recommended standards. The average radiation dose reported for the studied area was 9.36, 11.28, 8.73, 10.17, 8.58, 9.80, 7.13, 10.05, 8.14 and 8.81 µSv/hr respectively. The mean value of radiation dose from the study area was 9.21 µSv/hr which is higher than the maximum permissible level of 5.7 µSv/hr recommended by the American Nuclear Society for persons within 0 – 100 m from a mobile phone base station. The values vary according to the distance which shows that the strength of the radiation field is greatest at the source and diminished quickly with distances. Results obtained for the present study showed that radiation emitted at mobile phone base station are at intensities that are thousands of times less than intensities that can produce a heating effect. Hence, the assumption from the results obtained for the present study area is that the radiation exposures from mobile phone base stations impose no health hazard as the limits recommended in the guidelines by International Commission of Non-Ionizing Radiation Protection do not appear to have any known adverse consequence on human health.