Advanced Materials for Electromagnetic Shielding: Fundamentals, Properties, and Applications

By Sabu Thomas

A comprehensive review of the field of materials that shield people and sensitive electronic devices from electromagnetic fields

Advanced Materials for Electromagnetic Shielding offers a thorough review of the most recent advances in the processing and characterization of the electromagnetic shielding materials. In this groundbreaking book, the authors—noted experts in the field—discuss the fundamentals of shielding theory as well as the practice of electromagnetic field measuring techniques and systems. They also explore applications of shielding materials used as absorbers of electromagnetic radiation, or as magnetic shields and explore coverage of new advanced materials for EMI shielding in aerospace applications. In addition, the text contains methods of preparation and applicability of metal foams.

This comprehensive text examines the influence of technology on the micro-and macrostructure of polymers enabling their use in screening technology, technologies of shielding materials based on textiles, and analyses of its effectiveness in screening. The book also details the method of producing nanowires and their applications in EM shielding. This important resource:

• Explores the burgeoning market of electromagnetic shielding materials as we create, depend upon, and are exposed to more electronic devices than ever
• Addresses the most comprehensive issues relating to electromagnetic fields
• Contains information on the manufacturing, characterization methods, and properties of materials used to protect against them  
• Discusses the important characterization techniques compared with one another, thus allowing scientists to select the best approach to a problem

Written for materials scientists, electrical and electronics engineers, physicists, and industrial researchers, Advanced Materials for Electromagnetic Shielding explores all aspects in the area of electromagnetic shielding materials and examines the current state-of-the-art and new challenges in this rapidly growing area.

• Language: English
• Publisher: Wiley
• Release date: Nov 30, 2018
• ISBN: 9781119128632

Book preview

1

EMI Shielding Fundamentals

M. K. Aswathi¹, Ajay V. Rane¹,², A. R. Ajitha1, Sabu Thomas1,3, and Maciej Jaroszewski⁴

¹ International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala, India

² Composite Research Group, Department of Mechanical Engineering, Durban University of Technology, Durban, South Africa

³ School of Chemical Sciences, Mahatma Gandhi University, Kottayam, Kerala, India

⁴ Faculty of Electrical Engineering, Wrocław University of Science and Technology, Wrocław, Poland

1.1 Fundamentals of EMI Shielding Theory

Electromagnetic shielding is process of reducing the dispersion of electromagnetic waves into a desired space by hindering the waves with a shield made of conductive material. The effective performance of electrical instruments or the working of electrical instruments is interrupted, degraded, obstructed, or limited due to the electromagnetic interference (EMI). In a material the main mechanisms for EMI attenuation are reflection, absorption, and multiple reflection [1, 2]. Reflection is the primary mechanism of EMI shielding. For reflection the material must possess mobile charge carriers such as electrons or holes that interact with the electromagnetic radiation. Metals are the most common material for EMI shielding and the available free electrons in metals interact with the electromagnetic waves [3]. If the material is highly conductive the shielding against EM (electromagnetic) waves will occur through the reflection mechanism. However, conductivity is not a condition for EMI shielding but it does enhance the reflection mechanism of an EMI shielding material.

The secondary mechanism for EMI shielding is absorption, which requires the existence of electric or magnetic dipoles to interact with the electromagnetic radiation. It changes with the thickness of the material. Materials that have a high dielectric constant provide electric dipoles and materials with high magnetic permeability provide magnetic dipoles for the EMI shielding by absorption [1].

The third mechanism is multiple reflections, which is the reflections at different surfaces or at the interface of the material. Materials that have large specific internal surfaces or composites with fillers show a multiple reflection mechanism. Generally, multiple‐reflection decreases the total shielding value if the material is thinner than the skin depth and the value can be neglected if the material has a higher thickness than the skin depth. At higher frequencies electromagnetic radiation penetrates only to the near surface region of the electrical conductor. This is known as the skin effect. The intensity of penetration of an electromagnetic wave decreases exponentially with increasing depth of the conductor [4]. The skin depth is the depth of the conductor at which the intensity of the incident field drops in to 1/e of the incident value and is denoted by δ [5]:

equation

Here f is the frequency, μ is the magnetic permeability, and σ the electrical conductivity in Ω−1 m−1. Skin depth is not directly proportional to frequency, magnetic permeability, and conductivity, i.e. skin depth decreases with increase in frequency, magnetic permeability, or electrical conductivity. Owing to this skin effect, a material that contains a conductive filler with a small unit size of filler is more effective for shielding than a filler with a large unit size. The complete cross section of the filler unit can be used only when the unit size of the filler is less than or comparable with the skin depth.

Shielding effectiveness, which is expressed in dB, is the sum of reflection loss, absorption loss, and multiple reflections [6]. When electromagnetic waves strike the surface of an object they undergo reflection, multiple reflection, absorption, and transmission as shown in Figure 1.1. To be a shield against the EM wave, the material should reflect or absorb the electromagnetic wave. Factors determining shielding effectiveness (SE) are classified in Figure 1.2.

Image described by caption and surrounding text.

Figure 1.1 Schematic representation showing mechanism of electromagnetic shielding.

Hierarchy diagram of factors determining shielding effectiveness, including frequency of incident electromagnetic field; shield thickness; and conductivity, permeability, permittivity of shield material.

Figure 1.2 Factors determining shielding effectiveness [7].

Source: Adapted from Gooch 2007.

1.2 Materials for EMI Shielding

Owing to the increasing use of electronic equipment the shielding of other instruments and of human beings from electromagnetic waves is a very serious issue in the present scenario, which is detailed in Chapter 2. The EM waves harmfully affect both the device performance and human beings. Nowadays, a reduction in the use of electronic equipment is not always practical. What we are able to do is to reduce the penetration of EM waves produced from electronic instruments. To decrease the penetration we must use a shield or block the EM waves from the desired surface.

Metals are commonly used for EMI shielding application in the form of thin sheets or sheathing in automotive applications. But, metal is expensive, prone to corrosion, heavy, and the cost of manufacturing processes is also very high, which makes them an undesired choice for electronic application. Conductive polymer nanocomposites have attracted a great deal of academic and industrial interest by considering the cost‐effectiveness, easy processability, and their possible applications in many areas including EMI shielding. Polymer nanocomposites based on CNTs (carbon nanotubes), carbon black (CB), graphene, metal nanoparticles, carbon fibers, foams, and magnetic nanoparticles show good shielding capacity against EM waves. Several groups have studied and reported the EMI shielding effectiveness of different materials and mechanisms behind the EMI shielding ability of those materials. Characterization and requirement for EMI shielding materials are mentioned in the classification chart in Figure 1.3. Chapters 7–14, 16, and 17 describe these materials in detail in accordance to EM shielding.

Hierarchy diagram of characterization and requirements for EMI shielding materials, including shielding effectiveness measurement, electrical conductivity, thermal conductivity, and permeability.

Figure 1.3 Characterization and requirements for EMI shielding materials [8].

Source: Adapted from Tong 2009.

1.3 Mechanism of EM Shielding Materials

Carbon nanotubes, a 1D nanostructure, are rolled up sheets of graphene, made up of a hexagonal lattice of sp² hybridized carbon atoms. Depending upon the number of graphene sheets used to form the cylindrical shape the carbon nanotubes are of different types, namely single walled, double walled, multiwalled. Carbon fibers (CFs) come under 1D carbon nano‐allotropes, having interlocked sheets of graphene. Carbon black is a good filler to enhance the EMI shielding effectiveness of a material; it is produced by the thermal decomposition of hydrocarbons. Carbon black has graphite layers different from that of amorphous carbon. Every carbon atom in the graphite layer forms three covalent bonds with neighboring carbon atoms and the free p‐orbits from each carbon atom overlap to from delocalized π electrons. The presence of these freely moving π electrons make carbon black a good conducting material.

Carbon fiber paper (CFP) and nickel coated carbon fiber paper (NCFP) reinforced epoxy composites show EMI shielding efficiencies of 30 and 35 dB, respectively, in the frequency range 3.22–4.9 GHz for 0.5 mm thick sheets at 8 wt% fiber content. This is due to the increased conductivity shown by the nanocomposites; in addition, both absorption loss and reflection loss contribute to the total EMI shielding but the major contribution is from reflection. The material shows higher electrical conductivity due to the presence of mobile charge carriers. These charge carriers interact with the EM waves, which induces reflection as the major mechanism for the shielding [9].

Carbon black reinforced cement composites show a good EMI shielding value due to the presence of freely moving π‐bond electrons. The shielding effectiveness increased with increase in carbon black content because of the conductive network path and through the reflection mechanism [10].

Carbon black reinforced polyaniline/poloxalene composites can be used as a lightweight EMI shielding material with a shielding effectiveness of 19.2–19.9 dB at 10 wt% CB. The good EMI shielding value obtained is due to the formation of a network between carbon black and the blend system. The interconnected network contributes to the shielding value obtained through reflection as the shielding mechanism [11].

Carbon micro coils (CMCs) are another material used as a filler in making EMI shielding material. The polyurethane composites with CMCs show an increased EMI shielding value that depends on the layer thickness of the material. Hence the mechanism is based on absorption [12].

In the case of multiwalled carbon nanotube (MWCNT)/polypropylene (PP) composites the contribution of absorption loss to the total EMI shielding is higher than reflection so the major mechanism is absorption and reflection is the secondary shielding mechanism [13]. Here, multiple‐reflection is excluded from the discussion because it lowers the overall EMI SE.

Figures 1.4a–c show power balance graphs for different MWCNT/PP composites with various amounts of MWCNT and different plate thickness. The percentage of power blocked by reflection is increased with increase in MWCNT content in all three cases (Figures 1.4a–c), but in the case of 0.34 and 1 mm plates the percentage of absorption initially increases with increasing MWCNT content and then decreases. In the third case (2.8 mm thick plates) the contribution by absorption increases linearly with increasing MWCNT content [13].

Image described by caption and surrounding text.

Figure 1.4 Power balance graph for MWCNT/PP nanocomposite in the X‐band frequency range of plate thickness (a) 0.34, (b) 1, and (c) 2.8 mm [13].

Reproduced with permission of Elsevier.

The EMI shielding effectiveness shown by samples of MWCNT, CNF, and high structure carbon black (HS‐CB) nanoparticles with acrylonitrile–butadiene–styrene (ABS) polymer [14] showed that whatever the nanofiller type the reflection loss was always less than the absorption loss (Figure 1.5a and b). The contribution of absorption loss to total EMI SE is 75%. When the shielding by absorption exceeds 10 dB most of the re‐reflected wave will be absorbed within the shield itself and so multiple reflections were ignored.

Image described by caption and surrounding text.

Figure 1.5 Shielding mechanisms: (a) absorption loss, reflection loss, and total shielding as function of CNF content; (b) power balance as function of CNF content [14].

Reproduced with permission of Elsevier.

The electromagnetic interference shielding effectiveness of lightweight graphene/polystyrene composite [15] is shown in Figure 1.6a and b. The graphs show that the contribution of reflection loss is negligible over the entire frequency range. The composite has a porous structure. This means that power is dissipated as heat rather than reflected back from the composite’s surface, which clearly describes why absorption is the primary mechanism and the secondary mechanism is reflection for such conductive porous composites in the X‐band frequency region.

Image described by caption and surrounding text.

Figure 1.6 Comparison of SEtotal, SEA, and SER for GPS045 (a) and GPS027 (b) in the 8.2–12.4 GHz range [15].

Reproduced with permission of the Royal Society of Chemistry.

The EMI shielding mechanism of PTT/MWCNT composites was studied by resolving the total EMI SE into absorption and reflection loss. Figure 1.7 shows the effect of MWCNT content on absorption and reflection. The graphs shows that with increasing amounts of MWCNT both SEA and SER increased, but the rate of increase of SEA was higher compared to that of SER. At 0.24 vol.% of MWCNT the absorption contribution was 16% but with 4.76 vol.% of MWCNT the absorption contribution increased to 73%. These results show that for PTT/MWCNT composites the primary shielding mechanism is absorption rather than reflection in the observed frequency range [16].

Image described by caption and surrounding text.

Figure 1.7 Graph showing contribution of reflection and absorption loss to total EMI SE in PTT/MWCNT composites [16].

Reproduced with permission of Springer.

The composite fabricated by dip‐coating process using silver nanowire (AgNW)‐coated cellulose papers shows a reflection dominant EMI shielding mechanism. Figure 1.8 shows that there was a rapid increase in the reflectance, R, at three dip‐coating cycles, which means the dominant shielding mechanism changed from absorbance to reflectance around the number of cycles [17].

Image described by caption and surrounding text.

Figure 1.8 Graph showing contribution of reflection, absorption, and transmittance to total EMI shielding of AgNW/cellulose papers and their dependence on electrical conductivity at 1.0 GHz [17].

Reproduced with permission of the American Chemical Society.

An EMI shielding investigation of PET fabric/PPy composite showed that absorption as well as reflection contributes to the total EMI shielding of the composite and that with increasing electrical conductivity the EMI shielding through reflection increased. Figure 1.9 shows that the reflection dominated absorption by considering the total EMI shielding. As shown in Figure 1.9, with decreasing specific volume resistivity shielding effectiveness by reflection increased, and shielding effectiveness by absorption decreased. The increase in reflection mechanism is due to a smaller skin depth of the composite [18].

EMI SE vs. specific volume resistivity vs. reflectance or absorbance displaying descending curves for R and SE and ascending curve for A. Curves for R and A are intersecting.

Figure 1.9 Graph showing contribution of absorbance, reflectance, and total EMI SE of PET fabric/PPy composites with various specific volume resistivities [18].

Reproduced with permission of Elsevier.

Graphene is a single sheet of carbon nanostructure in which the carbon atoms are in sp² hybridization. Graphene is a 2D carbon nanostructure. Graphite is the next member of the graphene family, made by the stacking of graphene monolayers. These layers interact through Van der Waals forces of attraction.

Graphene nanosheets consist of a monolayer or a few monolayers of graphene and act as an EMI shielding material. These carbon forms are made from sp² hybridized carbon atoms, with the edges or deformation sites showing the presence of some sp³ hybridized carbon atoms. Graphene oxide (GO), another two‐dimensional material coming under the graphene family, is formed by the introduction of covalent CO bonds in graphene. These graphene forms also contain delocalized π bond electrons – the presence of these freely moving electrons make them conducting.

Graphene nano‐platelets with polyaniline and poly(3,4‐ethylenedioxythiophene) (PEDOT)/poly(styrene sulfonate) (PSS) with different ratios give paint like layers and act as an EMI shielding material. The contribution of absorption and reflection to the total EMI shielding value depends on the graphene/polyaniline ratios [19].

Graphene nanoplatelets (GNPs) in the insulating polymer matrix ultrahigh molecular weight polyethylene (UHMWPE) form a conductive network, and with 15 wt% filler the material shows 99.95% EMI shielding attenuation. The presence of a conductive path and the calculation using the power balance point out that the material absorbs more radiation than it reflects [20].

Another EMI shielding material obtained from PEDOT coated MWCNT and polyurethane matrix shows EMI shielding effectiveness through the absorption mechanism [21].

This chapter focuses the fundamentals of EMI shielding (reflection, absorption, and multiple reflections). Details on materials used for EMI shielding are given in further chapters of this book. The materials used for EMI shielding are fabricated in the form of an enclosure, i.e. a shielding enclosure. A shielding enclosure is a box or housing or cover providing isolation to the EMI emitter or receiver. This specialized cover is fabricated by considering the requirements for a particular EMI application. The materials covered in this book are fabricated and form part of a shielding enclosure. General principles for designing an enclosure should be followed; the current book deals only with materials for EMI shielding and with advancements in material sciences related to EMI shielding.

References

1 Hu, Q. and Kim, M. (2008). Electromagnetic interference shielding properties of CO2 activated carbon black filled polymer coating materials. Carbon Lett. 9: 298–302.

2 Khan, D., Arora, M., Wahab, M.A., and Saini, P. (2014). Permittivity and electromagnetic interference shielding investigations of activated charcoal loaded acrylic coating compositions. J. Polym. 1–8.

3 Jagatheesan, K., Ramasamy, A., Das, A., and Basu, A. (2014). Electromagnetic shielding behaviour of conductive filler composites and conductive fabrics – a review. Indian J. Fibre Textile Res. 39: 329–342.

4 Lee, B.O. et al. (2002). Influence of aspect ratio and skin effect on EMI shielding of coating materials fabricated with carbon nanofiber / PVDF. J. Mater. Sci. 37: 1839–1843.

5 Chung, D.D.L. (2001). Electromagnetic interference shielding effectiveness of carbon materials. Carbon 39: 279–285.

6 Jose, G. and Padeep, P.V. (2014). Electromagnetic shielding effectiveness and mechanical characteristics of polypropylene based CFRP. Int. J. Theor. Appl. Res. Mech. Eng. 3: 47–53.

7 Gooch, J.W. and Deher, J.K. (2007). Electromagnetic Shielding and Corrosion Protection for Aerospace Vehicles. Springer.

8 Tong, X.C. (2009). Advanced Materials and Design for Electromagnetic Shielding Interference Shielding. CRC Press.

9 Wei, C. et al. (2014). Electromagnetic interference shielding properties of electroless nickel‐coated carbon fiber paper reinforced epoxy composites. J. Wuhan Univ. Technol. ‐ Mater. Sci. Ed. 29: 1165–1169. doi: 10.1007/s11595‐014‐1060‐y.

10 Huang, S., Chen, G., Luo, Q., and Xu, Y. (2011). Electromagnetic shielding effectiveness of carbon black ‐carbon fiber cement based materials. Adv. Mater. Res. 168–170: 1438–1442. doi: 10.4028/www.scientific.net/AMR.168‐170.1438.

11 Kausar, A. (2016). Electromagnetic interference shielding of polyaniline / poloxalene / carbon black composite. Int. J. Mater. Chem. 6: 6–11.

12 Kang, G. and Kim, S. (2014). Electromagnetic wave shielding effectiveness based on carbon microcoil‐polyurethane composites. J. Nanomater. doi: 10.1155/2014/727024.

13 Al‐saleh, M.H. and Sundararaj, U. (2009). Electromagnetic interference shielding mechanisms of CNT / polymer composites. Carbon N. Y. 47: 1738–1746.

14 Al‐saleh, M.H. (2013). EMI shielding effectiveness of carbon based nanostructured polymeric materials: a comparative study. Carbon N. Y. 60: 146–156.

15 Yan, D.‐X., Ren, P.‐G., Pang, H. et al. (2012). Efficient electromagnetic interference shielding of lightweight graphene / polystyrene composite. J. Mater. Chem. 18772–18774. doi: 10.1039/c2jm32692b.

16 Gupta, A. and Choudhary, V. (2011). Electrical conductivity and shielding effectiveness of poly(trimethylene terephthalate)/multiwalled carbon nanotube composites. J. Mater. Sci. 46: 6416–6423.

17 Lee, T., Lee, S., and Jeong, Y.G. (2016). Highly effective electromagnetic interference shielding materials based on silver nanowire / cellulose papers. ACS Appl. Mater. Interfaces 8: 13123–13132. doi: 10.1021/acsami.6b02218.

18 Kim, M.S. et al. (2002). PET fabric/polypyrrole composite with high electrical conductivity for EMI shielding. Synth. Met. 126: 233–239.

19 Drakakis, E., Kymakis, E., Tzagkarakis, G. et al. (2017). Applied surface science a study of the electromagnetic shielding mechanisms in the GHz frequency range of graphene based composite layers. Appl. Surf. Sci. 398: 15–18.

20 Al‐saleh, M.H. (2016). Electrical and electromagnetic interference shielding characteristics of GNP / UHMWPE composites. J. Phys. D Appl. Phys. doi: 10.1088/0022‐3727/49/19/195302.

21 Online, V.A., Dhawan, R., Singh, B.P., and Dhawan, S.K. (2015). RSC Adv. doi: 10.1039/C5RA14105B.

2

EM Noise and Its Impact on Human Health and Safety

Halina Aniołczyk

Nofer Institute of Occupational Medicine, Lodz, Poland

2.1 Introduction

The latest approach to ensure a high level of protection of contemporary humanity as well as electrical and electronic equipment against undesirable emission of electromagnetic fields (EMFs) consists of two aspects: technical standardization of products included in those devices (equipment and installations), which must meet the requirements of the electromagnetic compatibility (EMC), and the bio‐hygienic standards that specify the admissible limits for the EMF emissions to ensure the safety and protection of human health. This is particularly important because in recent years the lifestyle and work of people in many countries have significantly changed as a result of the development of modern telecommunication and data communication systems, especially wireless, which is clearly manifested by the expansion of mobile phone systems, development of computer technology, and the rapid spread of the use of wireless internet. At the same time, progress in medicine has enabled individuals with dysfunctional organs to make use of pacemakers, defibrillators, implants, and inner ear prostheses, neurostimulators of retina (active implants) or artificial joints, surgical clips, stents (passive implants), etc. Such people are more exposed to health hazards due to the impact of the EMF from various devices and systems. The Earth's natural electromagnetic environment is characterized by EMFs related with the phenomena occurring in the atmosphere, and radiation in the vicinity of the surface of the Earth from the Sun and Space (mainly from the center of our Galaxy). Please note the difference between terrestrial natural constant electric and magnetic fields on one hand, and the slow‐ and fast‐varying EMFs on the other. Modern man in the place of life and work is exposed both to the ubiquitous EMFs of natural origin and to EMFs artificially created through conscious global activities of introducing more modern technologies that change the environment. Each piece of electrical and electronic equipment is likely to be a source of electromagnetic disturbances that occur as conducted interference as well as radiated emissions (conducted, in the frequency range up to 30 MHz, and radiated in the frequency range above 30 MHz) that are emitted to the surrounding environment. Operation of the equipment can disturb the operation of other devices, thus becoming a hazard not only to normal functioning of that equipment but also, indirectly, to humans. Some of that equipment is designed specifically for emission of an EMF (for example, all broadcasting equipment). The spectrum of EMFs and radiation covers a very wide frequency range. Figure 2.1 shows the general spectrum classified according to bandwidth. This classification is of significant importance, because the mechanisms according to which EMF affects living organisms, including humans, depend significantly on the frequency. The relevant literature in this field makes a clear distinction between the frequency bands, which are assigned different names (industrial frequencies, radio waves, microwaves, etc.) and introduces a specific terminology to describe the parameters characterizing those fields, measuring the intensity levels of their prevalence in areas accessible to humans, especially in the area of work, and testing the effects of the exposure. In this study, attention has been focused on the field of non‐ionizing radiation, which has a frequency below 8 × 10¹⁴ Hz, that does not cause ionization of the medium that it penetrates (for example, the quantum energy for EMFs with a frequency below 300 GHz is less than 1.25 × 10−3 eV).

Image described by caption and surrounding text.

Figure 2.1 Spectrum of electromagnetic field and radiation.

Currently, the radio‐frequency EMFs most frequently used in practice includes frequencies ranging between 3 kHz and 300 GHz and their regulation and use is governed by the International Telecommunication Union (ITU) [1]. These EMFs are used mainly in sectors such as telecommunication (including broadcasting), wireless communication, radar, radio navigation, meteorology, and global positioning systems (GPS); in industry, mainly for inductive and capacitive heating; in medicine: surgery, physical therapy, diagnostics (EPR spectrometers, magnetic resonance imaging (MRI) systems), for treatment of cancer; and in science.

In Europe, the problems of protection of devices and humans from undesirable or excessive emissions to the working environment is governed by Directives: on EMC, 2014/30/EU [2, 3] and protection, 2013/35/EU [4] and uniform requirements apply to the member countries of the European Union (EU). In the field of protection of the general population against EMFs recommendations from the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) 1998 are used [5] and in EU countries the applicable regulation is the Recommendation 1999/519/EU on the limitation of public exposure to EMFs (0 Hz to 300 GHz) 1999 [6]. Implementation of the Council recommendation is not compulsory and thus the individual countries implement their own protective policies [7]. Compliance with the requirements contained in the above documents enforces a variety of preventive measures, including organizational and technological ones. Screening of equipment, workstations, rooms that require particular protection and even whole buildings or separate areas (architectural shielding) represents one of several intensively developing technological solutions. This chapter discusses the basic impacts of EMFs on human health and safety, taking into account the preamble to the recommendation. This work discusses the basic effects of EMFs on human health with reference to the basis for limiting exposure set forth in ICNIRP 1998, the ICNIRP 2009 update, and taking into account recent literature data [8, 9]. It presents the major and also the most common devices and installations that are sources of EMF emissions, together with the assessment of the level of exposure to occupational and residential hazards experienced by the members of contemporary society. The rules governing the protection of humans from EMFs recommended for use at the international level, in the countries of the European Union, or at the national level (for example, in Poland) differ in the values of exposure limits. The differences mainly result from the adopted philosophy (biological effects or health effects, remote, or short‐term effects). The process of developing international ICNIRP regulations based on the concept of specific absorption rate (SAR) as a measure of exposure to EMFs and the national provisions using Polish regulations as an example to highlight their original, zonal concept of gradation of the level of risk attributable to EMF exposure in the work environment have been briefly outlined. Exposure to EMFs should be monitored and in cases were the allowable limits are exceeded appropriate measures should be undertaken: prevention, such as the monitoring of the health of workers; organizational, such as proper location of EMF sources relative to the workplaces, rotation of workers employed at workplaces with severe EMF exposure, and personal protective equipment as well as monitoring of the levels of EMF intensity; personnel training; technological, such as shielding of EMF sources and workplaces. The issues discussed in this chapter mainly include problems relating to the frequency range of 30 kHz to 100 GHz and emission occurring at undesirable or excessive intensity level is considered here as electromagnetic disturbance (EM noise) subject to the protective provisions. The devices used in the army and in air or naval navigation, which are dominated by the use of radar and the production of pulsed EMFs, are not discussed here.

2.2 Impact of Non‐ionizing EMFs on Humans

The possibility of a detrimental effect on the health and safety of persons exposed to EMFs and the establishment of threshold values for EMF interaction with living organisms in the widest possible spectrum invariably has aroused the interest of researchers since the 1950s (Schwan, Gordon, Johnson et al.) [8–10]. This is due to the problems discussed below. First of all, it is advisable to know the effects of EMF on the human body and then correlate those effects that have already been detected and documented with their causes, mainly the conditions of exposure, such as operating frequency range of the field, its intensity and the effective time of the exposure. It is not easy in a situation where non‐ionizing EMF spectrum covers the frequency range from 0 Hz (static electric and magnetic fields) up to 300 GHz (slow‐ and fast‐changing EMF). So far, it has been established that:

Electrostatic fields interact with living organisms by inducing an electrical charge on the surface of the body, producing current flow inside the body, inducing dipole and orienting permanent dipoles in accordance with the direction of the field.

Static magnetic fields interact with the internal electric currents of the organism, changing the orientation of the structures according to their magnetic properties and affecting spin states of electrons.

Alternating electric, magnetic, and EMF – their direct impact on living organisms depends primarily on the frequency of the field and mainly includes: the phenomenon of feedback from electric fields and magnetic low frequencies and absorption of energy in the tissues, which turns into other types of energy, e.g. heat, especially with fields of the higher frequency range. Overall, health effects resulting from exposure to EMFs include the stimulation of the sense organs, nervous system, and muscles (non‐thermal effects), and those resulting from the heating of body tissues (thermal effects). Such effects may be classified into direct effects associated with the impact of the EMF on the human body (which may be either thermal or non‐thermal) and indirect effects caused by the EMF interacting with items remaining in the field, such as medical devices (medical equipment, whose work can be disturbed) and active devices (pacemakers, defibrillators) and passive implants, etc. whose performance may become impaired.

The high frequency EMFs (>100 kHz) have been divided into four frequency ranges characterized by specific EMF energy absorption characteristics in the human body:

In the frequency range 100 kHz to 20 MHz, energy absorption in the trunk increases with frequency and may reach a significant value in the limbs.

In the range 20–300 MHz, the absorption of energy in the whole body may be considerable due to the so‐called geometric resonance (association between the size of the body or its anatomical parts and the wavelength of the incident EMF), i.e. 450 MHz for the head and 150 MHz for the forearm.

In the range 300 MHz up to approx. 3 GHz, there may occur significant local, non‐uniform absorption and the hot‐spots‐in‐the‐head phenomenon.

In the range above 10 GHz, absorption occurs on the surface of the body [11, 12].

The human body, from the point of view of its interaction with EMFs, is a medium with irregular shapes, varying sizes, and a multi‐layer structure of the tissue showing different dispersive dielectric properties depending on the frequency. Thus, the amount and distribution of EMF energy absorbed by the human body depends on the electrical characteristics of the tissue, the geometry, the frequency, and polarization of the incident EMF. In‐depth theoretical and experimental studies initiated by Johnson and Guy in the 1970s [10] on the distribution and size of the absorbed energy of EMFs in living organisms taking into account the exposure conditions and the characteristics of the incident EMF wave have resulted in the implementation of the concept of SAR as a measure of exposure to EMF.

The values of SAR, both local and whole‐body, depend on a number of environmental parameters, including the distance between the source and the object, the frequency, polarization, grounding, and the EMF reflection [10–12].

The concept of SAR was introduced in 1991 in the IEEE C95.1‐1991 [13] and is now accepted as a dosimetric value, which is a measure of the energy absorbed per unit mass of tissue, expressed in W kg–1. Since then, the SAR values have become one of the main criteria in determining the limits of exposure to EMF. In the international ICNIRP guidelines, the SAR value represents the criterion of basic restrictions [5]. In particular:

For frequencies below 1 kHz, the fundamental criterion for the magnetic field is the density of the current induced in the human body, the threshold value of which required for stimulation of the central nervous system (CNS) or evoking of magnetophosphenes (i.e. flashes of light that are seen when one is subjected to a 20 Hz magnetic field and 50 mV m−1 electric field [14]) is 100 mA m−2.

In the frequency range 100 kHz to 10 MHz, the criteria include both the value of current density, such as to avoid changes in the nervous system, and the value of SAR, such as to avoid heat stress.

In the frequency range 10 MHz to 10 GHz, the criterion is the SAR value independently for the whole body and local exposure, separately for the head, the trunk, and the limbs.

For frequencies above 10 GHz, the penetration depth of the EMF into the tissues is low and so the SAR is not the best parameter for estimating the energy absorbed (absorption phenomenon occurs mainly on the surface of the body). Thus a more correct dosimetric quantity here is the value of the power density of the incident field. For the frequency range, with assumed dominance of the thermal effect, the experimentally determined threshold concentration SAR averaged over the entire body was 4 W kg−1, which, under moderate environmental conditions, after 30 minutes human exposure in the resting posture results in a temperature rise of not more than 1 °C [5]. The impact of EMF on humans and the consequent risk to health should be distinguished from terms such as interaction, biological effect, or the perception of hazard. Recent international rules in the EU are based on well‐documented health effects resulting from current (low frequency) and thermal (high frequency) influences for short‐term exposure. The effects of long‐term exposure are not sufficiently scientifically documented. At the same time, it is suggested that if the absorbed energy does not cause an increase in temperature above the level that the human body itself may compensate by thermoregulatory physiological processes, the observed effects, classified as non‐thermal effects, according to the current state of knowledge, are considered to be a weak biological agent. A review of the world literature by Szmigielski (2007) on clinical research (medical and epidemiological studies on people exposed in the workplace to EMF) shows no evidence of a specific disease attributable to that exposure [15].The influence of high‐frequency EMF is likely, but only for cases of long‐term exposure (>10 years), and with intensities of at least the order of a few W m−2, and a daily dose above 30–40 W m−2 h−1[16]. However, there may be all sorts of disorders and functional changes of physiological systems (CNS, the vegetative regulation, cardiovascular, and so on). These may include non‐specific morbidity symptoms (NSMS) such as headaches, fatigue, insomnia, distraction, etc., symptoms of vegetative neuroses, increased number and frequency of functional changes, such as cardiovascular symptoms developing normally with age and also slightly increased risk of developing certain types of cancer [17]. The current state of knowledge points to the existence of limited evidence of increased risk of certain cancers, including leukemia or brain tumors in a population, as described in the publications of the International Agency for Research on Cancer (IARC) based on literature reports on the effects of neoplasia as a result of chronic exposure to EMFs with low levels of intensity that:

Classify radio frequency electromagnetic fields (RF EMF) as group 2B, which includes factors probably carcinogenic to humans [18];

classify electric and magnetic static extremely low frequency (ELF) fields as the same group 2B of substances possibly carcinogenic to humans [19].

Consequently, some countries have introduced the Principle of Precautionary Approach [20] (for example, Switzerland, Italy) [21, 22], which is a more restrictive recommendation compared to the EU recommendation [6] primarily as far as the protection of the general population is concerned, to national regulations. Our current knowledge on the health effects of long‐term exposure to EMFs is limited. This is mainly due to the lack of relationship between the results of epidemiological studies on populations and experimental animals as well as the lack of a full explanation of mechanisms of EMF effects at that level of the intensity and duration of exposure. Sensational reports on adverse health effects of human exposure to EMFs often result from the application of unfair study protocols or unfair analyses of the study results. This last statement is important from the point of view of protecting the environment and people who are subject to a chronic but poorly controlled exposure to EMFs and confirms that further studies are required [7, 23].

2.3 Overview of Most Common Sources of EMFs in the Occupational and Residential Modern Human Environment

The EMFs produced artificially as a result of human activity occurring both in the workplace and in the residential municipal environment may adversely affect human health. The development of technological civilization, especially the electrification (overhead high voltage power lines) and the dissemination of telecommunications and wireless communications (radio and TV broadcasting stations, radar, radio navigation, base stations, mobile phones) mean that most of the world's population now live in an electromagnetic environment with much higher EMF strengths than existed 100 years ago. Excessive, higher‐than‐natural levels of intensity in the biosphere have become especially evident in low‐frequency areas of non‐ionizing radiation. Currently, this area is expanding to the scope of frequencies above 1 GHz, used primarily in wireless communications and the Internet. Radio lines are already operated at frequencies of 60–90 GHz. Modern science does not fully explain the effects of EMFs on living organisms, particularly in such high‐frequency ranges. A huge amount of equipment and installations producing EMFs, hereafter referred to as sources of EMFs, are characterized by great diversity, which means that discussion of the risks they offer to human health and safety is difficult. Therefore, available data from studies performed at the Institute of Occupational Medicine (NIOM) in Lodz under the leadership of the author of this study are used here, relating to those EMF sources that are most distinctive in terms of technical parameters, high EMF intensities occurring in their vicinity, ubiquitous prevalence, and employees' access to areas where the values of the intensities are close to the maximum admissible intensity (MAI) specified by Polish regulations [24–29].

In addition to power supply lines operated in Europe at 50 Hz and in the USA at 60 Hz, the most widely used are radiofrequency (3 kHz to 300 GHz) EMFs. Particularly intensive sources of EMF are used in sectors such as:

Broadcasting – radio and television broadcasting stations (RTVCS);

communication, including wireless – line‐of‐sight and satellite radio lines, base stations and mobile stations of mobile radiocommunication (dispatcher radiotelephone networks), mobile phone base stations, public security systems, wireless computer networks (WLAN, WiMax);

radiolocation – radar, radio navigation, and meteorological stations (using pulse‐modulated electromagnetic radiation), GPS;

industry – mainly induction heating (furnaces for hardening) and capacitive heating (dielectric welding machines, dielectric dryers);

medicine – surgery (electrosurgical diathermy), physical therapy (short‐wave HF) and micro‐wave (MF) diathermy, diagnostics (EPR spectrometers, MRI equipment), health care (hyperthermia kits and accelerators used in oncology);

science: radio astronomy (space research), laboratories at universities, scientific research institutes, industrial laboratories etc. develop and apply new systems, experimental prototypes of new devices, testing, and checking of a wide range of aspects – from EMF generation through EMF propagation in various physical media to the effects, including biological (research on plants and animals).

The most common equipment and installations generating EMF in the occupational and residential environment are summarized in Table 2.1. This summary refers to Poland, but may serve as a database to illustrate the problems typical for most countries, not just in Europe.

Table 2.1 Most common equipment and installations generating 0 Hz–300 GHz EMF.

Currently, broadcasting is dominated by VHF FM broadcasting systems, where antennas are installed not only on free‐standing towers but also on the roof of tall public buildings and also on the roof of residential buildings. In radio communications, the dominant systems include GSM900, GSM1800, and UMTS900 and UMTS2100 mobile phone base stations, in which not only antennas but also containers with transceiver units are deployed like the VHF FM stations. To ensure their continuous operation, dedicated teams of workers are employed to install or remove, maintain, and repair the antennas.

In health care, the dominant types of such devices include apparatus for electrosurgery and short‐wave (SW) diathermy. These devices are installed indoors, in operation theaters and physical therapy rooms, not always correctly, so there are frequent problems with interference with other equipment due to undesired EMF emissions. Very stringent requirements apply to the installations of MRI, which must be installed in a specially shielded rooms to protect the MRI equipment against EMFs coming in from the environment.

In industry, dominant EMF sources include induction furnaces for steel hardening, capacitive welding machines, and high‐frequency (HF) dryers. They are a source of strong EMF due to improper shielding of the main sources of EMFs, such as inductors and electrodes, and also the HF electric current leads.

Personnel working in close vicinity to such equipment include workers who make, install, test, operate, maintain, repair, and dismantle it; those workers are subject to varying degrees of risk of exposure to EMFs.

In the municipal environment, all people are exposed to EMFs at different frequency ranges, but the extent of that exposure varies depending on the industrialization of the area and population density.

The most important problem is to meet the MAI standards developed by the bodies of researchers, including biologists, physicists, doctors, and engineers, and keep the EMF intensity within the ranges considered to be acceptable for the safety and protection of human health. What are the intensities of EMFs in the real working and living conditions of modern man in the jungle of so many devices and installations producing the EMFs with respect to the MAI provisions? For risk analysis of EMFs, equipment and installations were selected that are found in each country, and EMFs produced by that equipment and installations were assessed with reference to ICNIRP 1998 recommendations and regulations developed and currently valid in Poland; please note that the requirements of the Polish regulations are more stringent than the recommendations of ICNIRP, Directive 2013/35/EU, and Council Recommendation 1999/519/EU.

2.4 Protection Against EMFs in European and International Law

Health, as defined by the World Health Organization (WHO), is a state of complete physical, mental, and social well‐being, and not merely the absence of disease or physical disability.

The problem of protecting people against excessive or unwanted EMF emissions prevailing in their residential and occupational environments is regulated by the relevant law. These regulations are of various importance: the standards, recommendations, directives, decrees, or ordinances. According to the WHO the most important regulations include ICNIRP 1998, 2010 and 2014 [5, 30, 31]. For the frequency range in which the thermal effect was assumed to be dominant, a whole body SAR threshold value of 4 W kg−1 at which the temperature increase is within 1 °C was experimentally determined. Thus, for occupational exposure, the above value with the safety factor of 10, i.e. SAR = 0.4 W kg−1, has been adopted as a criterion of basic restriction for whole‐body exposure. Basic restrictions in the ICNIRP Guidelines are given, depending on the frequency EMF as: limits of density of the current induced in the head and trunk, SAR averaged over the whole body, the local SAR in the head and trunk, and separate local values of SAR in the limbs. Basic criteria according to ICNIRP 1998 for occupational exposure to EMF are presented in Table 2.2. The specified values of SAR are not directly measurable. To enable an assessment of exposure, so‐called reference levels were defined, i.e. values of the electric component of the field, of the magnetic component, magnetic induction, and power density for the equivalent plane wave. The reference levels were determined using the appropriate mathematical models and extrapolating the results of laboratory tests to give the so‐called resonance curve. For the range above 10 GHz, a limit for power density of 50 W m−2 was specified. This value is averaged over any 68/f¹.⁰⁵‐minute period (where f is the frequency in GHz); in other frequency ranges (up to 10 GHz) the averaging time is six minutes for each of any exposure period.

Table 2.2 Basic restriction on current density and SAR for RF EMF (100 kHz–10 GHz).a–g

a f is the frequency in hertz.

b Because of electrical inhomogeneity of the body, current densities should be averaged over a cross‐section of 1 cm² perpendicular to the current direction.

c For frequencies up to 100 kHz, peak current density values can be obtained by multiplying the rms value by √2 (~1.414). For pulses of duration tp the equivalent frequency to apply in the basic restrictions should be calculated as f = 1/(2tp).

d For frequencies up to 100 kHz and for pulsed magnetic fields, the maximum current density associated with the pulses can be calculated from the rise/fall times and the maximum rate of change of magnetic flux density. The induced current density can then be compared with the appropriate basic restriction.

e All SAR values are to be averaged over any six‐minute period.

f Localized SAR averaging mass is any 10 g of contiguous tissue; the maximum SAR so obtained should be the value used for the estimation of exposure.

g For pulses of duration tp the equivalent frequency to apply in the basic restrictions should be calculated as f = 1/(2tp). Additionally, for pulsed exposures in the frequency range 0.3–10 GHz and for localized exposure of the head, in order to limit or avoid auditory effects caused by thermoelastic expansion, an additional basic restriction is recommended. This is that the SA should not exceed 10 mJ kg−1 for workers and 2 mJ kg−1 for the general public, averaged over 10 g tissue.

Exposure limits for the population are five times lower than those accepted for occupational exposure.

ICNIRP recommendations have been adopted by many countries worldwide, including Europe.

In the EU, work has been undertaken on the unification of values limiting the exposure to EMFs in the workplace. In 1989, Directive 89/391/EEC was published on projects aimed at improving health and safety in the work environment [32]. It is general in its character and introduces the obligation for employers to ensure the protection of workers against excessive exposure to harmful physical agents, including EMF. In 2013, the detailed Directive 2013/35/EU was published on the minimum requirements to control risk to the health and safety of workers exposed to EMF; those requirements were to have been implemented for use in all EU member states not later than 1 July 2016 [4].

To limit public exposure to EMF, on 12 July 1999 the European Council recommended exposure limits by an official act [6], which was based on the recommendations of ICNIRP [5]. On a global scale, individual countries implement more stringent limits compared to the ICNIRP guidelines and EU recommendations, particularly with regard to exposure of the population, using the Principle of Precautionary Approach [20]. Table 2.3 shows as an example the diversity of exposure limits for the 1800 MHz frequency [33].

Table 2.3 EMF radiation regulations for mobile towers (1800 MHz) valid in individual countries.

Poland is one of those European countries that has one of the oldest traditions in the implementation of protection from EMFs in the workplace [34]. The first limits on the exposure to EMF were introduced for use in 1961 for the microwave range (frequency range >300 MHz) and they were an adaptation of regulations in the former USSR. They were based on the results of research carried out in the 1950s at the Moscow Institute of the Academy of Medical Sciences under the direction of Gordon (1966) [9]. The concept of protection against the non‐thermal effects, based on clinical and medical studies of workers exposed to EMFs, was used as a criterion for the protection of human health. The Soviet regulations of 1956 specified 0.1 W m−2 per work shift and 10 W m−2 for temporary (short‐term) exposure limited to five minutes per day as the highest allowable power density in the frequency range 300 MHz to 100 GHz. Somewhat earlier, in 1953, limits of exposure to EMFs were implemented in the United States of America, based on the work by Schwan [8]. The concept of the adopted exposure limits was based on the energy balance for a man who performs light work, and was intended to protect people against thermal effects. The highest allowable power density in the frequency range 10 MHz to 100 GHz was assumed to be 100 W m−2 for each period of six minutes of exposure at any time. Since 1972, Poland has introduced successively its own limit values of occupational exposure to EMF. The philosophy behind the Polish exposure limits was based on the original concept of protection zones: hazardous, dangerous, and intermediate. The area outside the protection zones has been assumed to be the safe zone. The criterion of non‐thermal effects has been adopted as the limit for the safe zone, while the criterion of thermal effects with the appropriate safety factor has been adopted as the limit value for the hazardous zone. Thus, for the hazardous zone, limits on the time spent in the zone were introduced, based on the energy load of the human body exposed to the EMF, which was a measure of exposure, while a total ban on staying in the dangerous zone was introduced. Limits of exposure for the general population were introduced for the first time in 1980. Limits of exposure to EMFs in the workplace over the whole frequency range of 0 Hz to 300 GHz were regulated in 2002 [35] and in 2003 for the general population [36]. Figure 2.2 shows a graphical comparison of exposure limits under ICNIRP 1998 and those currently in force in Poland.

Graph displaying descending step curve for Poland (general public) and descending–ascending step curves for Poland (occupational) and ICNIRP (occupational and general public).

Figure 2.2 Comparison of exposure limits set by ICNIRP 1998 and those currently in force in Poland (2002).

There are minor differences between the requirements quoted above in the process of determining the actual values of intensity of the electric (E, V m−1) and magnetic (H, A m−1) fields acting on the worker: averaging (over time) of the measured effective value; maximum acting on the employee (according to ICNIRP); and maximum instantaneous effective value acting in a location corresponding to the axis of a worker body (according to the Polish requirements). Polish regulations are currently being modified because of their necessary harmonization with Directive 2013/35/EU. Work on the harmonization of national legislation with the Directive has continued in the Interdepartmental Committee on the Maximum Admissible Concentrations and Intensities for Agents Harmful to Health in the Working Environment (Expert Group on Electromagnetic Fields) and is due to be completed by the end of June 2016. Table 2.4 shows the limits for public exposure to EMFs in the Polish regulations.

Table 2.4 Permissible levels of electromagnetic fields in the environment under the Polish regulations.

a f – As indicated in the frequency range column.

2.5 Assessment of the Level of EMFs in the Workplaces

An analysis of environmental conditions of workers occupationally exposed to EMFs based on the results of tests and measurements of RF EMF for more than 450 selected pieces of equipment representative of various sectors of the economy in which they are most often used and the values obtained indicated that the intensities adopted for civil protection had been exceeded [29]. Elevated values were recorded for almost 280 devices in radiocommunication, more than 100 devices in health care, 60 devices in industry, and 8 devices in science.

Analyzed parameters characterizing the source of EMF were such as the intensity of the electric field (E) in the vicinity of the device and at employee work space, dimensions of protection zones, and how many times the intensity at employee space is higher than the MAI. The MAI value corresponds to the value separating the intermediate zone from the dangerous zone, where, according to Polish regulations, workers can stay during an eight‐hour working day. A similar analysis was performed according to the ICNIRP 1998, criteria assuming that EMF was present at the employee space for at least six minutes.

The results of the analysis of levels of intensity of the electrical component of the EMFs for selected RF devices used in various sectors of the Polish economy are presented graphically in Figure 2.3.

Highest levels of electric field intensity for workplaces at selected common RF EMF sources used in Poland, displaying clustered bars represent “From the device” (filled) and “At workplace” (unfilled).

Figure 2.3 Highest levels of electric field intensity for workplaces at selected common RF EMF sources used in Poland.

In the broadcasting sector, transmitters and antennas of 50 stations (30 VHF FM radio stations, producing EMF in the frequency range 87.5–108 MHz, and 20 television stations operating 48 television channels in the frequency range 470–862 MHz) were analyzed in detail. The highest measured values of E field strength recorded in the vicinity of 8 VHF FM radio antennas installed on masts erected on the roofs of buildings ranged between 2.5 and 83.0 V m−1 (Me: 5.8 V m−1) at the place of maintenance works, accessible from the roofs of the building, superstructures, or platforms on the poles (with the exception of work done in the immediate vicinity of antennas, at the height of their installation). The ICNIRP was higher by a factor of 1.4–4.2 relative to the MAI. In radio and wire communication, the results of the measurements for 18 radio line (RL) objects were analyzed. In an accessible area of five antennas, the RL measured values were 6.1–44.7 V m−1 (Me: 10.6 V m−1). The quotient exceeds the MAI of 2.2 only in relation to work on platforms near the antenna and do not include activities at the height of the antennas themselves (in the direction of the axis of the main lobe). The ICNIRP limit value was not exceeded.

Land mobile radiocommunication uses vehicle and portable radiotelephones. The detailed analysis covered 11 transportable stations installed in vehicles, and three portable phones used by the security services. Radiotelephone stations were operated at 44 MHz and 144–174 MHz, transmitter power: 25 watts for stations operating in the higher band, 10 W for those operating in the lower frequency band, and 1–5 W for portable phones. The highest values of measured E values inside the 11 vehicles with installed transportable units were 5–76 V m−1 (Me: 23 V m−1) in the immediate vicinity of the installation and 4.3–36.0 V m−1 (Me: 7.5 V m−1) in places occupied by the driver and the worker next to the driver. The ICNIRP limits were not exceeded. The intensity of E field at the driver–radio operator position was up to 1.8‐fold MAI. Highest measured E field intensities in the vicinity of the portable phone antenna were 54–74 V m−1 (Me: 60 V m−1), in the absence of the operator. ICNIRP quotient was up to 1.2‐fold and MAI quotient was over two‐fold. Analysis of the results of tests and measurements of EMFs for extreme working conditions during the assembly, disassembly, and maintenance operations performed in the vicinity of