Study on electromagnetic dosimetry of the power cable in electric vehicle

To calculate the induced fields in the human body of the driver in an electric vehicle, the power cables of the electric vehicle are taken as the electromagnetic exposure source. The finite elements method is used to construct the electromagnetic environment model, which consists of the vehicle body, the power cables, and the driver body. The maximal values of the magnetic flux density inside the driver’s trunk and head are 4.63 μT and 0.12 μT, respectively. The maximal induced electric field intensity values are 670 mV/m and 99.7 mV/m, respectively. All values are below the safety limits of the ICNIRP. The results show that the electromagnetic environment induced by the power cables is safe for the driver. The study could provide a reference for improving electromagnetic exposure standards for electric vehicles.


Introduction
With scientific and technological progress and industrial reform entering a new stage, the proposal of the "dual carbon" goal makes the electric vehicle (EV) become the focus of the automotive industry [1].The EV has many advantages, such as zero emissions, no pollution, low noise, and superior economic benefits, and it has become an important direction for automotive development.
The electric devices of EVs are mainly composed of inverters, converters, high-voltage power harnesses, power battery packs, and other high-power electronic devices [2].During the operation of these electronic devices, complex low-frequency electromagnetic fields (EMF) are generated.It is important to note that prolonged exposure to this magnetic field environment could adversely affect human health [3].Many countries have implemented the guidelines on electromagnetic exposure from the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for human electromagnetic exposure.The ICNIRP establishes the guidelines of electromagnetic radiation for occupational and public exposure with different frequency bands [4].
Li and Zhang [5] studied the effect of electromagnetic fields in a wireless charging environment on humans of different ages and postures when they are in different positions.Bae and Park [6] measured the electromagnetic environment of wired chargers with different charging speeds.Xu et al. [7] conducted a monitoring study and numerical statistical analysis of the low-frequency magnetic field in 20 electric vehicles of different models with different operating conditions.The results indicated that the magnetic field strength in the car is highest during acceleration and deceleration and lowest during idling.Hang et al. [8] proposed a stable node integral numerical model for simulating cable to human radiation.They analyzed the distribution of human-induced current density in the electromagnetic environment induced by the cables.Based on the basic principle of electromagnetic dosimetry, Dong and Lu [9] simulated and analyzed the electromagnetic exposure level of child passengers sitting in different positions in the electromagnetic environment of a DC power cable.Jia et al. [10] studied the complex electromagnetic environment with multiple radiation sources in the electric tractor.
In this study, the exposure source is the power cable in the EV.The Comsol Multiphysics calculates the magnetic flux density (B-field) and induced electric field intensity (E-field) inside the driver's body.The calculated results are compared with ICNIRP limits to assess the levels of electromagnetic radiation.

Calculation Method and Model
When the human is in a low-frequency EMF environment, there will be an induced field in human tissues.The experimental measurement method cannot be used to measure the induced field in living human tissues.Therefore, the induced fields in the living human body could only be calculated by numerical methods based on electromagnetic dosimetry.This study used Comsol Multiphysics, a finite element method, to determine the levels of electromagnetic radiation experienced by drivers near power cables.

Calculation Model
The battery pack is located at the rear of the vehicle, as shown in Figure 1(a), while the inverter is typically placed in the front area.The power cable connects the drive motor and inverter.So, the AC current flowing in the cables of the EV is the exposure source.The EV body size is 5207 mm×2034 mm×1655 mm.The dielectric parameters of human tissues are generally calculated by the Cole-Cole model [11].Table 1 shows the different dielectric properties of eight tissues and organs, such as muscle, heart, lung, liver, kidney, skull, brain white matter, and cerebellum, at a frequency of 100 Hz.

Numerical Method
In this study, the power cable with a working current of 16 A and a working frequency of 100 Hz is used as the exposure source, and the induced field involves the usage of the Magnetic Field Interface Module in Comsol Multiphysics.This boundary issue is regulated by Maxwell's equations, which deal with the distribution of electromagnetic fields.The calculation is carried out as follows: ߘ ή ‫ܦ‬ = ߩ (3) ߘ ή ‫ܤ‬ = 0 (4)

The B-field inside the Driver Body
Figure 3 shows the B-field in the driver's whole body, and the |B|max in the body is about 4.63 ȝT.It satisfied the ICNIRP reference level (RL) for occupational exposure of 1000 ȝT [4].The B-field in the foot area is large, and the B-field in other body parts is weaker than in the foot.The B-field in the vertical profile of the body is shown in Figure 4.The figures show that the closer to the exposure source is, the stronger the B-field is.The B-field in the whole head is shown in Figure 5.The |B|max of the driver's head is 0.12 ȝT.It is also well below the RL of the ICNIRP for occupational exposure [4].Figure 6 shows the B-field in the driver's brain tissue.The B-field is slightly higher on the right brain, which is related to the position of the radiation source.Figure 6.The B-field in the brain.

The E-field inside the Driver Body
The E-field in the whole body is shown in Figure 7.The |E|max is about 670 mV/m, which satisfies the basic restriction (BR) of the ICNIRP for occupational exposure of 800 mV/m [4].The strength of the E-field in the leg is slightly higher and is related to the distance of the radiation source.Figure 8 shows the E-field in the vertical profile of the body, and the E-field is slightly stronger on the right side.
The brain is one of the important tissues of the human.So, the ICNIRP explicitly specified electrical field limits in the CNS of the brain.Figure 9 shows the E-field in the whole head.The strongest E-field in the whole head is about 99.7 mV/m, which remains below the BR for the occupational exposure of 200 mV/m in ICNIRP [4].As shown in Figure 10, in the driver's brain tissue, the E-field value in the white matter is greater than that in the cerebellum.Figure 10.The E-field in the brain.

Conclusion
In this study, we have calculated the induced field in the driver's tissues and organs exposed to electromagnetic radiation from the power cables of the EV.The calculated results indicate that the maximal values of the B-field inside the human body and head are 4.63 ȝT and 0.12 ȝT, respectively.Similarly, the maximal values of the E-field inside the body and head are 670 mV/m and 99.7 mV/m.They are satisfied with the exposure limits specified in the ICNIRP guidelines [4].The calculations reveal that in the electromagnetic exposure of the power cables, the induced fields in the driver's tissues and organs are significantly correlated to the proximity of the exposure source.The closer the distance is, the stronger the field is.In addition, the dielectric properties of various tissues and organs can affect the induced field within the driver's body.The results show that the electromagnetic exposure of the power cables is safe for the driver.Besides, it could also provide a reference for improving electromagnetic exposure standards and electromagnetic exposure safety protection design in EVs.

Figure 1 .Figure 2 .
Figure 1.Model of the PEV.Based on the human anatomical model obtained by high-resolution MRI scanning, as shown in Figure 2(a), the driver's organ and tissue model is constructed.Figure 2(b) shows the human mesh model.

Figure 3 .
Figure 3.The B-field in the whole-body.Figure 4. The B-field in the vertical profile.

Figure 4 .
Figure 3.The B-field in the whole-body.Figure 4. The B-field in the vertical profile.

Figure 5 .
Figure 5.The B-field in the whole-head.Figure 6.The B-field in the brain.

Figure 7 .
Figure 7.The E-field in the whole-body.Figure8.The E-field in the vertical profile.

Figure 8 .
Figure 7.The E-field in the whole-body.Figure8.The E-field in the vertical profile.

Figure 9 .
Figure 9.The E-field in the whole-head.Figure10.The E-field in the brain.

Table 1 .
Dielectric properties of the different tissues and organs (f=100 Hz).