**3. Prevention guidelines and standards**

Magnetic field exposure assessment is a two‐step process: first, one must characterize the magnetic field inside the vehicle (either by estimation or by measurement). The second step involves determining whether the obtained values could be hazardous for the passengers. Both tasks can prove very challenging, and thus any guidance is welcome. In this sense, there are some standards and guidelines that help with the second step. This section is dedicated to these documents.

Concern regarding potentially hazardous consequences of nonionizing EMR started to raise some decades ago, around the 1950s and 1960s, first about radio waves and microwaves, and more recently about low‐intensity fields as well, such as those generated by power lines, cell phones, and Wi‐Fi devices. The effects of nonionizing electromagnetic fields on the human body have been studied for many years already, and the results are conclusive in some cases and inconclusive in others [20–23].

There are other factors that may influence magnetic field exposure in a positive way. For instance, the results presented in Ref. [14] suggest that the car body shell could behave as a minor magnetic shield for some frequencies. Therefore, constructive aspects such as the shape,

It is also convenient to consider which operating points are potentially more hazardous for human health. Under normal operation of the vehicle, power/current peaks will be higher during strong accelerations than during deep regenerative braking. This is due to two main reasons: the passive nature of some of the movement resistances (rolling resistance and aerodynamic drag), which implies that both of them will always oppose movement, and the global energy efficiency of the traction drive. Notice that driving style will heavily impact total magnetic exposure in EVs: the more aggressive the driving style the higher the magnetic fields

Nevertheless, there is another situation which could involve potentially hazardous exposure for passengers, or even for pedestrians that are close to the vehicle: fast charging. As battery technology improves, higher recharge rates are achieved, which obviously imply higher currents, and hence stronger magnetic fields. Nowadays, charge rates of 2–4 C are already usual, with even higher values reachable in the near future [15, 16]. Therefore, magnetic field generation must be studied not only during normal operation of the vehicle but also during fast charging. As a general rule, it is highly advisable to remain outside of the vehicle, and at

Finally, it is important to consider the wide variety of electric vehicles that exit nowadays, and how their different configurations, topologies, and power levels affect magnetic field exposure. Some considerations have already been mentioned in this chapter about vehicle configuration (front‐wheel vs. rear‐wheel traction, for instance; another example would be battery place‐ ment), and also about the power topology (significant differences arise when adding a DC‐DC converter, or when using hybrid energy storage systems that combine batteries and superca‐ pacitors for increased performance [17]). The largest differences, however, appear when considering electric vehicles of different types, such as motorbikes, buses, racing cars, or even electric planes [18, 19]. Magnetic exposure in these other vehicles could be very different when compared to electric cars, depending on the power levels involved and on the distances

Magnetic field exposure assessment is a two‐step process: first, one must characterize the magnetic field inside the vehicle (either by estimation or by measurement). The second step involves determining whether the obtained values could be hazardous for the passengers. Both tasks can prove very challenging, and thus any guidance is welcome. In this sense, there are some standards and guidelines that help with the second step. This section is dedicated to

material, and thickness of the body shell could affect magnetic exposure.

54 Modeling and Simulation for Electric Vehicle Applications

some distance from it, while fast charge is in process.

between the power equipment and the closest passengers.

**3. Prevention guidelines and standards**

within the vehicle.

these documents.

Basically, there are two types of effects that electromagnetic fields can have on biological tissues: short‐term and long‐term effects. Short‐term effects, also known as acute effects, are those that appear instantaneously, or minutes after the beginning of the exposure. In gener‐ al, these effects only take place under fields of considerable intensity, and disappear as ex‐ posure ceases. The biological mechanisms involved in these short‐term effects are relatively well known, as well as the field values (intensity and frequency) that cause them [24–27]. They are usually classified into two main groups: electrostimulant effects and thermal ef‐ fects. The former are caused by the interaction between low‐frequency fields and living mat‐ ter, either by polarization and dipole reorientation produced by electric fields, or due to induced currents generated by magnetic fields (for instance, a strong alternate magnetic field can induce electrical currents capable of stimulating nerves and muscles in an unde‐ sired way). The latter refer to the exchange of energy between fields and tissues, which rises their temperature. These thermal effects are completely negligible for frequencies under 100 kHz, but become relevant at higher frequencies (consider, for the sake of illustration, the operating principle of a microwave oven, whose working frequency is around 2.45 GHz). Electrostimulant effects are instantaneous, while thermal effects have a time constant of mi‐ nutes.

Long‐term effects, on the other hand, are those that could appear after months or years of exposure. Several studies have tried to determine the relationship between long‐term exposure to electromagnetic fields and different pathologies (cancer, neurodegenerative disorders, etc.), without finding conclusive evidence for it. Approximately half of these studies show small correlations, just statistically significant, between long‐term exposure and these illnesses [28]. In any case, the possibility of such relationships made the International Agency for Research on Cancer (IARC) to classify low‐intensity, low‐frequency electromagnetic fields, and also radiofrequency electromagnetic fields, as "possibly carcinogenic to humans (Group 2B)" [24, 25].

Generally speaking, it is extremely difficult to establish direct biological effects caused by long‐ term exposure, and to obtain reproducible results [23]. As a consequence, standards and guidelines to limit human exposure are elaborated based only on well‐known, scientifically proven, short‐term effects (with appropriate safety factors), and therefore long‐term effects are not taken into account. This applies to the two most extended guidelines nowadays, those from the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) and those from the Institute of Electrical and Electronic Engineers (IEEE). Both are briefly described subse‐ quently.

#### **3.1. ICNIRP's guidelines**

The most extended criteria for recommended exposure limit to EMFs were first proposed by the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) in 1998 [22]. These guidelines are based on current scientific evidence, as well as risk analysis performed by the World Health Organization (WHO). They establish protection recommendations considering well‐known mechanisms and appropriate security factors, the latter being due mostly to scientific uncertainty.

Eleven years after their first publication, no new scientific evidence of any adverse effects had been found [29], a reason why a review of the guidelines on limitation to exposure to high‐frequency EMFs (100 kHz to 300 GHz) was considered unnecessary. Nevertheless, con‐ cerning static EMFs and extremely low‐frequency EMFs (1 Hz to 100 kHz), special guide‐ lines were published in 2009 [30] and 2010 [31], respectively, in an attempt to include the results of the main scientific publications during those 11 years. The referred publications not only established recommended exposure limits to EMFs but also include explanations concerning the ways these fields could affect human health. These two guidelines suggest recommended exposure limits (which are defined in terms of in‐body quantities such as electrical fields and induced currents in a given tissue, which complicates exposure assess‐ ment), but they also provide reference levels for the electromagnetic environment (external electrical and magnetic field values). These levels are extremely helpful to assess magnetic field exposure, since the following consideration is usually applied: if the exposure envi‐ ronment complies with the field reference levels, then it can be assumed that the exposure limits are not infringed. Certainly, exceeding these reference levels does not necessarily im‐ ply that the corresponding exposure limits have been breached. In such cases, further anal‐ ysis is required.


Notes: H and B in unperturbed RMS values. In addition, reference levels relating to tissue‐heating effects need to be considered for frequencies above 100 kHz.

**Table 2.** ICNIRP's reference levels for general public exposure to time‐varying magnetic fields.

Regarding exposure limits to EMFs, different considerations arise depending on the person affected. Thus, there is an "occupational exposure," which is applied to those individuals who are exposed to EMFs as a result of performing their regular job activities. There is also a "general public exposure," which refers to the rest of the population. In summary, ICNIRP's reference levels for static magnetic fields are 400 mT for general public (EVs passengers included) and 2 T for occupational public [30], whereas the Earth's magnetic field ranges from 30 to 60 µT, depending on the region on the Earth. Concerning time‐variant fields, the exposure limits to EMFs for "general public" are given in **Table 2** and also in **Figure 3** [31]. Notice that these values correspond to a sinusoidal, single‐frequency, homogeneous magnetic field exposure.

**3.1. ICNIRP's guidelines**

56 Modeling and Simulation for Electric Vehicle Applications

mostly to scientific uncertainty.

ysis is required.

1–8 Hz 3.2 × 104

8–25 Hz 4 × 103

400–3 kHz 6.4 × 104

considered for frequencies above 100 kHz.

The most extended criteria for recommended exposure limit to EMFs were first proposed by the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) in 1998 [22]. These guidelines are based on current scientific evidence, as well as risk analysis performed by the World Health Organization (WHO). They establish protection recommendations considering well‐known mechanisms and appropriate security factors, the latter being due

Eleven years after their first publication, no new scientific evidence of any adverse effects had been found [29], a reason why a review of the guidelines on limitation to exposure to high‐frequency EMFs (100 kHz to 300 GHz) was considered unnecessary. Nevertheless, con‐ cerning static EMFs and extremely low‐frequency EMFs (1 Hz to 100 kHz), special guide‐ lines were published in 2009 [30] and 2010 [31], respectively, in an attempt to include the results of the main scientific publications during those 11 years. The referred publications not only established recommended exposure limits to EMFs but also include explanations concerning the ways these fields could affect human health. These two guidelines suggest recommended exposure limits (which are defined in terms of in‐body quantities such as electrical fields and induced currents in a given tissue, which complicates exposure assess‐ ment), but they also provide reference levels for the electromagnetic environment (external electrical and magnetic field values). These levels are extremely helpful to assess magnetic field exposure, since the following consideration is usually applied: if the exposure envi‐ ronment complies with the field reference levels, then it can be assumed that the exposure limits are not infringed. Certainly, exceeding these reference levels does not necessarily im‐ ply that the corresponding exposure limits have been breached. In such cases, further anal‐

**Frequency (Hz) Magnetic field** *H* **(Am-1) Magnetic flux density** *B* **(T)**

**Table 2.** ICNIRP's reference levels for general public exposure to time‐varying magnetic fields.

25–400 Hz 1.6 × 102 2 × 10‐4

3 kHz to 10 MHz 21 2.7 × 10‐5

/f2 4 × 10‐2/f2

/ f 5 × 10‐3/f

/f 8 × 10‐2/f

Notes: H and B in unperturbed RMS values. In addition, reference levels relating to tissue‐heating effects need to be

Regarding exposure limits to EMFs, different considerations arise depending on the person affected. Thus, there is an "occupational exposure," which is applied to those individuals who are exposed to EMFs as a result of performing their regular job activities. There is also a "general public exposure," which refers to the rest of the population. In summary, ICNIRP's reference levels for static magnetic fields are 400 mT for general public (EVs passengers

**Figure 3.** ICNIRP's reference levels for sinusoidal magnetic field exposure as a function of frequency (up to 10 kHz).

Notice that the above reference levels are not given as a function of time (exposure duration). They are maximum or absolute values that must never be breached. This is consistent with the fact that their corresponding exposure limits have been established based on short‐term effects only. In other words, the above reference levels should guarantee the absence of harmful biological effects in the short term, based on current scientific evidence and in accordance to the experts' consensus‐based criteria.

Regarding multiple frequency sinusoidal exposure, ICNIRP states that all contributions should be considered cumulative, so that the following global limit should be met:

$$\sum\_{j=1\text{ Hz}}^{10\text{ MHz}} \frac{\mathcal{B}\_j}{\mathcal{B}\_{\text{max},j}} \le 1 \tag{1}$$

where is the field magnitude at each given frequency, and max, is the reference level corresponding to that frequency. The expression for the magnetic field is analogous.

In the case of nonsinusoidal exposure, the evaluation procedure consists in performing a frequency analysis to obtain the corresponding harmonic decomposition. After this, all harmonic components must be considered at the same time by means of Eq. (1). This metho‐ dology is simple, but very conservative, given that it assumes that all harmonic components are in phase (worst‐case scenario), which is hardly real. This assumption is so pessimistic that even background noise can result in a breach of ICNIPR's reference levels if enough harmonic components are included in the calculation [32]. Consequently, a second method is recom‐ mended instead for those cases in which the number of harmonic component is considerable [31]. This alternative method consists in weighting the field components with a filter function (inverse Fourier transform) related to the reference levels [33]:

$$\left| \sum\_{i} \frac{B\_{i}}{\mathcal{E} L\_{i}} \cos(2\pi f\_{i} \cdot t + \theta\_{i} + \varphi\_{i}) \right| \le 1 \tag{2}$$

where EL is the reference level corresponding to the *i*th harmonic, whose frequency is , while and are the field amplitude and phase corresponding to that frequency, respectively, is the filter phase (also for that frequency), and is the time. An example of implementation of the above method can be found in [9] and also in [34], in which Eq. (1) yields 99% with respect to ICNIRP's reference levels, while Eq. (2) decreases this result to 19%.

As aforementioned, ICNIRP's values are given for homogeneous exposure with respect to the whole extension of the human body. However, this assumption is not valid when magnetic field sources are close to the people affected, as might occur in an EV. Again, considering a heterogeneous exposure as homogeneous (taking maximum values as average values) results in a conservative approach. Other methods involve spatial averaging [35] or dosimetric analysis [31].

It is also important to clarify that these guidelines are not legally mandatory, and that become legally binding only if a country incorporates them into its own legislation [36]. At present, many countries and organizations have adopted these security limits. For example, the European Commission uses ICNIRP's guidelines to write regulations about EMR emission limits, applicable within the European Union [37]. Most member countries have therefore adopted these regulations, and some of them have even applied more restrictive criteria or have developed measures to legally enforce them.

#### **3.2. IEEE's exposure standard**

This subsection briefly describes the standard IEEE C95.6 [38]. This standard defines exposure levels to protect against adverse effects in humans from exposure to electric and magnetic fields at frequencies from 0 to 3 kHz.

Regarding long‐term exposures to magnetic fields, the most recent reviews considered in the standard are the following: the International Commission on Non‐Ionizing Radiation Protec‐ tion (ICNIRP) [22], the International Agency for Research on Cancer (IARC) [24], the US National Research Council (NRS) [39], the US National Institute of Environmental Health Sciences (NIEHS) [20, 40] the Health Council of the Netherlands [41], the Institution of Electrical Engineers [42], and the Advisory Group on Non‐Ionizing Radiation (AGNIR) of the UK National Radiological Protection Board [43].

Because none of the above reviews concluded that any hazard from long‐term exposure has been confirmed, this standard does not propose limits on exposures that are lower than those necessary to protect against adverse short‐term effects. The purpose of this standard is just to define exposure standards for the frequency regime 0–3 kHz. For pulsed or nonsinusoidal fields, it may be necessary to evaluate an acceptance criterion at frequencies outside this frequency regime by means of a summation from the lowest frequency of the exposure waveform, to a maximum frequency of 5 MHz, as detailed in the standard itself [38].


Notes: *f* is the frequency in Hz; MPEs refer to spatial maximum.

In the case of nonsinusoidal exposure, the evaluation procedure consists in performing a frequency analysis to obtain the corresponding harmonic decomposition. After this, all harmonic components must be considered at the same time by means of Eq. (1). This metho‐ dology is simple, but very conservative, given that it assumes that all harmonic components are in phase (worst‐case scenario), which is hardly real. This assumption is so pessimistic that even background noise can result in a breach of ICNIPR's reference levels if enough harmonic components are included in the calculation [32]. Consequently, a second method is recom‐ mended instead for those cases in which the number of harmonic component is considerable [31]. This alternative method consists in weighting the field components with a filter function

(inverse Fourier transform) related to the reference levels [33]:

58 Modeling and Simulation for Electric Vehicle Applications

where EL

analysis [31].

*i*

*i <sup>B</sup> f t EL* <sup>å</sup> cos(2p

to ICNIRP's reference levels, while Eq. (2) decreases this result to 19%.

have developed measures to legally enforce them.

**3.2. IEEE's exposure standard**

fields at frequencies from 0 to 3 kHz.

*i ii i*

 qj

is the reference level corresponding to the *i*th harmonic, whose frequency is

 and are the field amplitude and phase corresponding to that frequency, respectively, is the filter phase (also for that frequency), and is the time. An example of implementation of the above method can be found in [9] and also in [34], in which Eq. (1) yields 99% with respect

As aforementioned, ICNIRP's values are given for homogeneous exposure with respect to the whole extension of the human body. However, this assumption is not valid when magnetic field sources are close to the people affected, as might occur in an EV. Again, considering a heterogeneous exposure as homogeneous (taking maximum values as average values) results in a conservative approach. Other methods involve spatial averaging [35] or dosimetric

It is also important to clarify that these guidelines are not legally mandatory, and that become legally binding only if a country incorporates them into its own legislation [36]. At present, many countries and organizations have adopted these security limits. For example, the European Commission uses ICNIRP's guidelines to write regulations about EMR emission limits, applicable within the European Union [37]. Most member countries have therefore adopted these regulations, and some of them have even applied more restrictive criteria or

This subsection briefly describes the standard IEEE C95.6 [38]. This standard defines exposure levels to protect against adverse effects in humans from exposure to electric and magnetic

Regarding long‐term exposures to magnetic fields, the most recent reviews considered in the standard are the following: the International Commission on Non‐Ionizing Radiation Protec‐ tion (ICNIRP) [22], the International Agency for Research on Cancer (IARC) [24], the US

×+ + £ 1 (2)

, while

**Table 3.** IEEE's maximum permissible exposure to sinusoidal magnetic fields for general public: head and torso.


**Table 4.** IEEE's maximum permissible exposure to sinusoidal magnetic fields for general public: arms and legs.

In addition to the in situ electric field restrictions collected in the standard, but not discussed in this chapter, the in situ magnetic field below 10 Hz should be restricted to a peak value of 167 mT for the general public and up to 500 mT in a controlled environment. For frequencies above 10 Hz, a basic restriction on the in situ magnetic field is not specified in IEEE's standard. **Table 3** lists maximum permissible magnetic field limits (flux density *B*, and magnetic field strength *H*) corresponding to head and torso exposure for general public. The averaging time for a root‐mean‐square (RMS) measure is 0.2 s for frequencies above 25 Hz. For lower fre‐ quencies, the averaging time is such that at least five cycles are included in the average, but with a maximum of 10 s. In the same way, **Table 4** shows arm and leg exposure limits, also for general public. All these maximum exposure limits are based on avoidance of the following short‐term reactions [38]:


IEEE's maximum permissible exposure values must be understood in the same way as INCIRP's reference levels. In this sense, compliance with **Tables 3** and **4** ensures compliance with the basic restrictions, which are defined in terms of in‐body quantities. However, lack of compliance with these tables does not necessarily imply lack of compliance with the basic restrictions, but rather that it may be necessary to evaluate whether the basic restrictions have been met [38]. For more information, the reader is referred to the standard itself.

The information contained in **Tables 3** and **4** is also shown in **Figure 4** for clarity. Besides, ICNIRP's reference levels for general public are also included in the figure for comparison.

**Figure 4.** IEEE's maximum permissible exposure to sinusoidal magnetic fields as a function of frequency (up to 3 kHz).

#### **4. State of the art**

This section is devoted to a brief overview of recent publications that deal with EMR and magnetic field exposure in EVs. Some main conclusions, drawn for these studies, are sum‐ marized here as well. Related publications, such as those that analyze EMC in electric vehicles or EMR in other applications, are also mentioned.

In general, there are not many publications about magnetic field exposure in electric and hybrid cars. Most works about electromagnetic fields and EVs address problems belonging to the field of EMC. Some examples of such studies can be found in [44–48]. There are certainly several publications that deal with EMFs and its potentially hazardous effects on human health, both from the medical and from the engineering points of view, but for other applications. A review of the medical literature is certainly out of the scope of this chapter, and hence the reader is referred to specialized bibliography such as [23–26, 28] for that purpose. Regarding engineer‐ ing publications, one classical field of study are power lines [49–52], substations, and other transformation centers [49–54]. Most of these works focus on the effects of EMFs on workers (i.e., occupational exposure). Medical equipment in hospitals is another typical example of electromagnetic evaluation, again focusing on the people operating these machines on a daily basis. More recently, some studies have approached electromagnetic exposure from the point of view of general public, for example, in buildings and urban environments [55, 56]. The first studies in vehicles were probably those about electrical trains and trams, and also about conventional ICE‐based cars [57–59].

In general, publications about EVs and EMR can be classified into two main groups: studies that perform measurements in vehicles (experimental approach) and studies that use analytical approximations or numerical simulations, usually based on the finite element method (FEM) (simulation approach). These two groups are treated separately in the following sections.

#### **4.1. Magnetic field measurement in electric vehicles**

**•** Aversive or painful stimulation of sensory or motor neurons.

**•** Cardiac excitation.

**4. State of the art**

within the body, such as in blood flow.

60 Modeling and Simulation for Electric Vehicle Applications

**•** Muscle excitation that may lead to injury while performing potentially hazardous activities.

**•** Adverse effects associated with induced potentials or forces on rapidly moving charges

IEEE's maximum permissible exposure values must be understood in the same way as INCIRP's reference levels. In this sense, compliance with **Tables 3** and **4** ensures compliance with the basic restrictions, which are defined in terms of in‐body quantities. However, lack of compliance with these tables does not necessarily imply lack of compliance with the basic restrictions, but rather that it may be necessary to evaluate whether the basic restrictions have

The information contained in **Tables 3** and **4** is also shown in **Figure 4** for clarity. Besides, ICNIRP's reference levels for general public are also included in the figure for comparison.

**Figure 4.** IEEE's maximum permissible exposure to sinusoidal magnetic fields as a function of frequency (up to 3 kHz).

This section is devoted to a brief overview of recent publications that deal with EMR and magnetic field exposure in EVs. Some main conclusions, drawn for these studies, are sum‐

**•** Excitation of neurons or direct alteration of synaptic activity within the brain.

been met [38]. For more information, the reader is referred to the standard itself.

One of the first publications specifically dedicated to EMR in hybrid and electric cars is the one by *ElectromagneticHealth.org* [60], which focuses on the 2004 Toyota Prius (second gene‐ration). This preliminary study, which was motivated by a press article published in 2008, titled "*Fear, But Few Facts, on Hybrid Risks,*" concludes that it is considerably difficult to perform repetitive and accurate measurements in a moving vehicle without the proper means. The magnetic field values obtained during this study were not high (always below 1 µT), but possibly higher than those found in conventional ICE‐based cars. The rear seats were the most exposed, according to this work. One year later, in 2009, two more studies were published which included measurements in an electric car and in a hybrid bus, respectively, under dynamic driving conditions [13, 61].

The next two noteworthy publications, Ref. [58] from 2010 and Ref. [34] from 2013, describe some issues that should be taken into account when measuring magnetic fields in vehicles. The work in Ref. [58] deals mainly with trains and trams, but hybrid cars are also considered. Previous measurements performed in trains, locomotives, and railway stations by different researchers are summarized in that paper. Average results are provided for each type of vehicle considered in the study: 200 trains and trams (both urban and suburban), and also one hybrid car. Train and tram measurements were taken in varied conditions: weekdays and weekends, day and night, inside and outside. Regarding the hybrid car, different positions (front and rear parts, left and right sides, floor, seat, and head levels) were taken into account. Frequency spectrum ranges from 5 Hz to 100 kHz. Magnetic field values found in the car are low (in the order of a few µT), especially when compared to ICNIRP's reference levels, although it is not clear which method was used to account for multifrequency exposure (see Subsection 3.1). In average, highest magnetic field values were found at the rear left side of the hybrid car. The maximum levels of recorded magnetic field strength are emitted at 12 Hz, which is a very low frequency. About the study published in [34], it provides an example of how to deal with multifrequency exposure in accordance to ICNIRP's recommendations. This work focuses on electric vehicles exclusively, and the magnetic field values obtained are in line with those from [13], around 15–20% of ICNIRP's reference levels. The paper also presents simulation results (see Subsection 4.2).

In 2015, two journal papers were published with measurement results from a wide variety of hybrid and electric cars [9, 10]. Some of their authors participated in the two publications from the previous paragraph. The study in [9] comprises a total of three conventional cars and eight electric vehicles, including some based on fuel cells instead of batteries. Both laboratory measurements and road measurements were taken and compared to INCIRP's reference levels with a wide‐frequency range, up to 10 MHz. The vehicle that showed highest values reached 18% of ICNIRP's levels. Unsurprisingly, the researchers found that magnetic field exposure was higher in EVs than in ICE‐based vehicles in average. However, the position of maximum exposure within each vehicle (front vs. rear part, foot vs. seat level) was different. This position is probably influenced by the configuration and topology of the vehicle, as described in Section 2. The main sources of magnetic field are identified in this study: at frequencies below 1 Hz, hundreds of µT are present (most likely due to battery current). Between a few Hz and 1 kHz, fields up to 2 µT were found, generated by most sources (combustion engine, steering pump, and wheels are mentioned in the paper, but probably fundamental currents in the inverter and in the electrical machine were also responsible). Finally, above 1 kHz, less than 100 nT was measured, and the authors identified the inverter as the only source (which makes sense, since it is the only power electronics device in the traction drive).

The open‐access study in Ref. [10] focuses on diesel, gasoline, and hybrid cars. Up to 10 vehicles are analyzed, and the results are consistent with previous investigations. Results are presented separately for different seats and for different engine types. In general, magnetic field exposure was higher in hybrid cars, and then in gasoline cars. The authors state that magnetic field exposure depends on the operating conditions (speed, acceleration, etc.), which is unsurpris‐ ing.

## **4.2. Magnetic field estimation by numeric simulations**

Other research projects take a different approach and analyze the problem by means of finite element method (FEM) simulations and even analytical approximations. FEM simulations are helpful to better understand the problem, to analyze magnetic field exposure dependence on certain parameters (for instance, by performing sensitivity analysis), and to develop a predic‐ tive methodology. Being able to estimate magnetic field exposure without actually having to perform measurements could prove extremely useful for EV designers. As proposed in Ref. [62], a fully operational estimation tool would allow for optimized predesign even before building the first prototype, thus reducing engineering time and cost.

**Figure 5.** (a) FEM model used in Ref. [64] to estimate the magnetic field generated by one single NiMH battery cell. (b) Hypothetical battery pack belonging to a hypothetical EV analyzed in Ref. [64]. Both figures have been reused with permission.

This is the approach taken in Refs. [63, 64], works that analyze the magnetic field generated by the inverter and by the batteries, respectively, of a hypothetical EV via FEM simulations (**Figure 5**). Simulation results are validated with experimental measurements in both cases, and then they are used to estimate the worst operating points from the point of view of passenger exposure. Similarly, Refs. [14] and [34] contain two examples of how FEM simula‐ tions can be used for estimation and prediction purposes (**Figure 5**).
