Active Shielding Applied to an Electriﬁed Road in a Dynamic Wireless Power Transfer (WPT) System

: An active coil system is proposed to shield the magnetic ﬁeld produced by a dynamic wireless power transfer (WPT) system used to power electric vehicles (EVs) in motion. The considered dynamic WPT is based on an electriﬁed road with many short-track pads. A sophisticated mathematical procedure is developed to optimize the design of the active coils conﬁguration and their excitation. By the proposed approach, the resulting magnetic ﬁeld is compliant with the reference levels (RLs) of the ICNIRP (International Commission on Non-Ionizing Radiation Protection) 2010 Guidelines inside the cabin of EVs and on the side of the electriﬁed road.


Introduction
The future of road transport will be based on a large use of electric vehicles (EVs). Currently, the EVs are equipped with an internal battery that must be periodically charged, mainly using a plug-in connection. At the moment, one of the most critical issues in EVs is given by the battery, which has high cost, great weight, and long charging time. All these weaknesses lead to a reduced autonomy of the EVs. To overcome these difficulties and to increase safety, the idea is to recharge the battery using a wireless connection instead of a plug-in connection. This is made possible by the technology known as wireless power transfer (WPT), based on inductive coupling between a coil mounted on the road surface and a coil mounted on board the EV [1][2][3][4]. The current experimentation is mainly focused on static WPT, i.e., assuming the EV stopped in a parking spot equipped with a charging station [5,6]. There are also some recent studies on dynamic WPT, i.e., assuming the EV in motion [7,8]. It implies that the road must be electrified, i.e., studded by many separate coils (charging pads), or using a long-track coil. In both cases, using dynamic WPT, the EV battery can be automatically recharged during motion, leading to a significant increase of the EV range that can be practically infinite, as in other electrified transports like trains. Furthermore, the size of the onboard battery can be greatly reduced with a consequent reduction in cost and weight for the vehicle, leading to an important improvement of performance and reduction in consumption. A vehicle with infinite range is perfect for the project of an autonomous driving system.
There are several issues for the practical realization of an electrified road. One of these critical aspects is the electromagnetic pollution produced by the currents flowing in the coils of the WPT system that can generate a time-variable magnetic field in the surrounding environment, i.e., in the cars and in the areas nearby the electrified road where people can stay [9][10][11][12]. The victims of the incident

Mathematical Method
A near field WPT system based on magnetic resonant coupling is considered for the dynamic wireless charging of EVs. The magnetic field generated by the WPT inductive coil currents must be confined, or mitigated, in critical areas. The objective of this research is the mitigation of the magnetic field beside the electrified road line in the sidewalk area typically occupied by pedestrians, runners, road workers, etc. The safeguard of this area is committed to ensuring a magnetic field below the limits, i.e., reference levels (RLs) fixed by the ICNIRP (International Commission on Non-Ionizing Radiation Protection) 2010 Guidelines [21], and is obtained by the use of active shielding coils. The equivalent circuit of a two-coil WPT system with an active shielding coil is composed by three circuital meshes representing the WPT primary (or transmitting (Tx)) circuit, the WPT secondary (or receiving (Rx)) circuit, and the active coil circuit, respectively, as shown in Figure 1. The primary circuit is powered by a voltage generator, VG, with an internal resistance, RG, the secondary circuit is terminated on a resistive load, RL, representing the charging circuit of the EV battery, and the active shielding coil is powered by a voltage generator, VA. The equivalent circuit represents a simplified model of the system where all electronic components (inverter, rectifier, etc.) are modeled by simplified analogical devices at resonance. In the circuit R1, R2, and R3 are the series resistances of the Tx, Rx, and active coils, respectively, L1, L2, and L3 are the coil self-inductances, k12, k23, and k13 are the coupling factors among coupled inductors, C1 and C2 are the series compensation capacitors obtained by C1 = 1/(ω 2 L1) and C2= 1/(ω 2 L2) assuming a series-series (SS) compensation topology, and ω = 2πf is the angular frequency, f being the resonance frequency.

Tx circuit
Rx circuit Active coil circuit Figure 1. Equivalent circuit of a 2-coil wireless power transfer (WPT) system and an active shielding coil.
The mesh equations of the equivalent circuit written in matrix form are [15]: 1  1  12  1 2  13  1 3  1  1   12  1 2  2  2  23  2 3  2  2  3   13  1 3  23  2 3  3  3   1 1 0 or in a more compact form as: where [Z] is the impedance matrix. The mesh current vector [I] can be obtained via Equation (2) as: The mesh equations of the equivalent circuit written in matrix form are [15]: or in a more compact form as: where [Z] is the impedance matrix. The mesh current vector [I] can be obtained via Equation (2) as: Energies 2020, 13, 2522 4 of 14 The matrix [Z] is invertible, as the rows of the matrix are linearly independent. Indeed, all main diagonal elements of [Z] are real or complex with positive real parts, while the mutual terms of the matrix [Z] are all purely imaginary. Assuming linearity, the magnetic flux density B x j , y j , z j = B x x j , y j , z j x + B y x j , y j , z j y + B z x j , y j , z j z at the jth generic point x j , y j , z j produced by the m coil currents, I 1 , I 2 , I 3 , can be expressed applying superposition as: where b k,x , b k,y and b k,z are the x, y, z components of the magnetic flux density generated by a unit current flowing in the kth coil, with k = 1, . . . ,m and m = 3 [15]. Equation (4) can be rewritten in matrix form: Let us now consider a cloud of n points. By writing the equation systems Equation (5) for these n points and considering Equation (3), the following matrix form is obtained: x (x n , y n , z n ) b 1y (x n , y n , z n ) b 2y (x n , y n , z n ) b 3,y (x n , y n , z n ) b 1z (x n , y n , z n ) b 2z (x n , y n , z n ) b 3,z (x n , y n , z n ) that can be also written in compact form as: where At each point (x j ,y j ,z j ) with j = 1, . . . ,n of the cloud, the transfer function vector [b k,x (x,y,z) b k,y (x,y,z) b k,z (x,y,z)] T is calculated, taking into account the field produced by the currents flowing into each of the m coils. Manipulating Equation (7) it yields: It should be convenient to use a voltage-controlled voltage source V A = α V G to power the active coil, automatically adapting the shielding field to the incident one which is related to the voltage source V G . Thus, Equation (9) becomes: To determine the parameter α that controls the voltage-controlled voltage source of the active coil, V G is assumed to be initially constant, and then the norm of [g 1 ] + α[g 3 ] is minimized. It should be noted that, if we consider the squared norm of Equation (10), we obtain: where the left-hand side of Equation (11) is a 3n column vector and B(x j , y j , z j ) is a 3-column vector. The summation on the right side of Equation (11) is proportional to the average value of B in the cloud of n points inside the region to be shielded. Minimizing Equation (11) we find the value of α such that the average value of B over the n considered points is minimum. The value of the unknown term α that minimizes Equation (11) can be then obtained applying the pseudoinverse as [15]: In order to deliver the exact same amount of power in both cases (with and without the active shield) the value of the generator voltage V G used in the case without active shield is rescaled by a factor λ: where P out,REQ is the required power from the load, and P out,CALC is the power calculated using the unscaled value of V G . Obviously, being V A = αV G , the voltage-controlled source V A is also rescaled when rescaling V G . The power transfer efficiency η of the system is calculated, taking into account the losses due to the presence of the active coil as: where P in = real (V 1 I 1 ) is the input real power at port 1-1 , P out = real (V 2 I 2 ) is the output real power at port 2-2 , and P act = R 3 |I 3 | 2 is the power used by the active coil, where all electrical quantities are shown in Figure 1.

Method Validation
To validate the proposed method, a simple WPT system was considered. The WPT system was composed of two circular planar stacked coils with a single active shielding coil, as shown in Figure 2. The identical WPT coils had an external radius, r c = 4 cm, and number of turns, N = 10. The separation distance between the primary and the secondary coil was set to d c = 4 cm. The coils were realized with Litz Wire to reduce the losses. The series-series compensation topology was adopted and the capacitors were chosen to reach the resonant condition at the operational frequency of f = 85 kHz. The load of the system was a simple resistor R L = 10 Ω. The active shield was composed in this validation Energies 2020, 13, 2522 6 of 14 test by a semi-annular shaped coil with dimensions: internal radius r si = 15 cm, and external radius r se = 30 cm. The magnetic field was minimized in a cloud of n = 3 × 3 × 3 = 27 equidistant points inside a 5 × 5 × 5 cm 3 cubic region whose center p has distance d p = 40 cm from the vertical axis of the WPT coils.
Energies 2019, xx, x FOR PEER REVIEW 6 of 14 inside a 5 × 5 × 5 cm 3 cubic region whose center p has distance dp = 40 cm from the vertical axis of the WPT coils. The self and mutual inductances and resistances were measured using an LCR meter (Keysight E4980A). They were also calculated as described in [15]. The measured and calculated results are reported in Table 1.
The coil current and voltage were also measured. The WPT system is powered by a full bridge inverter, that amplifies the signal given from a signal generator. The input voltage was adjusted to obtain the fixed output power on the load. The magnetic field produced by the WPT coils in the point p was measured by the field probe described in [22]. The measured and calculated results, in terms of electrical performances and magnetic field, are reported in Table 2 without active shielding [15].
Then, the procedure described in Section 2 for the shielding coil was applied to minimize the field in the region to be shielded, i.e., a cubic region around point p, with dimensions comparable to the size of the magnetic field sensor. At the end of the numerical procedure, the values of module and phase of the shielding current were obtained as |I3| = 0.89 A and φ3 = 197°, respectively, when assuming zero phase for the primary current I1. Finally, the active coil was powered, injecting I3 into the coil by a separate inverter, driven by auxiliary output of the signal generator, to permit a total control of the phase injected to the coil. The system efficiency η, the magnetic flux density B at point p, and the shielding effectiveness (SE = 20 log10 (Bw/o_shield / Bwith_shield)) were obtained with active shielding, as reported in Table 3. The measured and calculated results highlight that a significant field reduction (SE = 18.1 dB) at this frequency leads to a very little decrease of WPT efficiency (only one percentage point). The self and mutual inductances and resistances were measured using an LCR meter (Keysight E4980A). They were also calculated as described in [15]. The measured and calculated results are reported in Table 1. Table 1. Calculated and measured circuit parameters with active shielding. The coil current and voltage were also measured. The WPT system is powered by a full bridge inverter, that amplifies the signal given from a signal generator. The input voltage was adjusted to obtain the fixed output power on the load. The magnetic field produced by the WPT coils in the point p was measured by the field probe described in [22]. The measured and calculated results, in terms of electrical performances and magnetic field, are reported in Table 2 without active shielding [15]. Table 2. Calculated and measured quantities in the validation test without active shielding. Then, the procedure described in Section 2 for the shielding coil was applied to minimize the field in the region to be shielded, i.e., a cubic region around point p, with dimensions comparable to the size of the magnetic field sensor. At the end of the numerical procedure, the values of module and phase of the shielding current were obtained as |I 3 | = 0.89 A and ϕ 3 = 197 • , respectively, when assuming zero phase for the primary current I 1 . Finally, the active coil was powered, injecting I 3 into the coil by a separate inverter, driven by auxiliary output of the signal generator, to permit a total control of the phase injected to the coil. The system efficiency η, the magnetic flux density B at point p, and the shielding effectiveness (SE = 20 log10 (B w/o_shield /B with_shield )) were obtained with active shielding, as reported in Table 3. The measured and calculated results highlight that a significant field reduction (SE = 18.1 dB) at this frequency leads to a very little decrease of WPT efficiency (only one percentage point). Table 3. Calculated and measured quantities in the validation test with active shielding.

Applications
The proposed shielding method is applied to the dynamic WPT system described in [20]. The considered system adopts multiple sequential short-track primary pads that are mounted on the road. For safety and efficiency reasons, the primary coils are activated one at a time, only when the presence of the secondary coil mounted on the car underbody is detected. Thus, this system can be analyzed similarly to a typical static WPT system, considering different positions of the secondary coil along the electrified road. A sketch of the configuration is shown in Figure 3, where just one short-track primary pad is depicted. The vertical distance between primary and secondary coil is set equal to d 12 = 20 cm. The battery load and all the electronics attached to the secondary coil are modeled by a simple equivalent resistor R L = 4 Ω. The planar transmitting coils in the xy plane have a narrow rectangular shape, with the long side parallel to the road direction (x axis) to ensure the transmission of the power for a longer period. The external dimensions of the primary coil are: l tx = 150 cm and w ty = 50 cm. The secondary coil also has a rectangular shape, but in this case the long side is in the y direction, to improve the tolerance to possible lateral misalignment. The dimensions of the secondary coil are: l rx = 50 cm and w rx = 60 cm. On the receiving coil, two ferrite blocks are adopted with rectangular shape of dimensions w fe × l fe = 15 cm × 25 cm and thickness t fe = 0.5 cm. These ferrite blocks are in the pick-up coil design of the Fabric project [20], and they are used to enhance the electrical performances by improving the magnetic field behavior due to the reduction of the reluctance. The primary and secondary coils both have N = 10 turns and are realized with a Litz Wire made of 1260 strands of AWG (American wire gauge) 38 insulated wires, to reduce the power losses. In our simulations we have considered an SUV vehicle. The dimensions of the metallic bodyshell shown in Figure 4 are: length 423 cm, height 144 cm, and width 180 cm. The car body is modeled with aluminum alloy panels having thickness t = 2 mm and electrical conductivity σ = 30 MS/m. performances by improving the magnetic field behavior due to the reduction of the reluctance. The primary and secondary coils both have N = 10 turns and are realized with a Litz Wire made of 1260 strands of AWG (American wire gauge) 38 insulated wires, to reduce the power losses. In our simulations we have considered an SUV vehicle. The dimensions of the metallic bodyshell shown in Figure 4 are: length 423 cm, height 144 cm, and width 180 cm. The car body is modeled with aluminum alloy panels having thickness t = 2 mm and electrical conductivity σ = 30 MS/m.   The active coil configuration was designed following the guideline described in [15] for static WPT systems. The main idea was to design an active coil so that the magnetic flux generated by the active coil cancels (or at least minimizes) the magnetic field generated by the WPT coils. Also, the coupling factor is minimized between the WPT coils and the shielding coil, to avoid a negative impact on the WPT efficiency. To this aim, a simple rectangular coil (in green in Figure 4), mounted on the ground near the primary coil, is adopted and made by the same Litz wire used for the other coils. The dimensions of the active coil are: lsx = 160 cm and wsx = 20 cm. The center of the Cartesian axes (0,0,0) corresponds to the center of the primary coil, while the secondary coil, attached to the vehicle, moves along the x-axis. The shielding coil has been centered in (0, 60, 0) cm in order to reduce the coupling with the WPT coils and in such a way that the secondary coil never overlaps the active coil in case of the coil's lateral misalignment, and also to avoid a pedestrian covering the shielding coil. The lumped parameters are calculated by a procedure described in [23]. To accurately model the resistance of Litz wires, datasheets have been used. The calculated self-inductances and resistances are shown in Table 4, while the mutual coupling coefficients depend on the vehicle position as shown in Table 5. To take into account the movement of the vehicle, three different positions of the secondary coil center are considered with the following coordinates in cm: x1(0, 0, d12), x2(25, 0, d12), x3(50, 0, d12). The lumped inductances and coupling factors were extracted by a numerical procedure based on the solution of the magneto quasi static (MQS) field equations, with a code based on the finite element method (FEM). The field penetration through the vehicle bodyshell was taken into account by transition impedance boundary conditions [24]. The computational domain was discretized by 106033 tetrahedral finite elements with second order interpolation functions.  The active coil configuration was designed following the guideline described in [15] for static WPT systems. The main idea was to design an active coil so that the magnetic flux generated by the active coil cancels (or at least minimizes) the magnetic field generated by the WPT coils. Also, the coupling factor is minimized between the WPT coils and the shielding coil, to avoid a negative impact on the WPT efficiency. To this aim, a simple rectangular coil (in green in Figure 4), mounted on the ground near the primary coil, is adopted and made by the same Litz wire used for the other coils. The dimensions of the active coil are: l sx = 160 cm and w sx = 20 cm. The center of the Cartesian axes (0,0,0) corresponds to the center of the primary coil, while the secondary coil, attached to the vehicle, moves along the x-axis. The shielding coil has been centered in (0, 60, 0) cm in order to reduce the coupling with the WPT coils and in such a way that the secondary coil never overlaps the active coil in case of the coil's lateral misalignment, and also to avoid a pedestrian covering the shielding coil. The lumped parameters are calculated by a procedure described in [23]. To accurately model the resistance of Litz wires, datasheets have been used. The calculated self-inductances and resistances are shown in Table 4, while the mutual coupling coefficients depend on the vehicle position as shown in Table 5. To take into account the movement of the vehicle, three different positions of the secondary coil center are considered with the following coordinates in cm: x 1 (0, 0, d 12 ), x 2 (25, 0, d 12 ), x 3 (50, 0, d 12 ). The lumped inductances and coupling factors were extracted by a numerical procedure based on the solution of the magneto quasi static (MQS) field equations, with a code based on the finite element method (FEM). The field penetration through the vehicle bodyshell was taken into account Energies 2020, 13, 2522 9 of 14 by transition impedance boundary conditions [24]. The computational domain was discretized by 106033 tetrahedral finite elements with second order interpolation functions. The considered region to be shielded is in centimeters {−80 ≤ x ≤ 80, −125 ≤ y ≤ −90, −5 ≤ z ≤ 45} that is discretized in n = 6750 points. In this region, shown in Figure 4 by a green box, the minimization is done on the average value of the norm of B. The constant value of the delivered power is ensured via (13) varying the input voltage. After applying the method described in Section 2, we have calculated the magnetic field without, and with, the active shield. The calculations are performed imposing a constant value of delivered power to the load P out = 10 kW. The rms source voltages and currents flowing through the coils for different positions of the secondary coil center along x axis are reported in Tables 6-8.   As can be seen from the obtained results, the influence of the active shield has a very small influence on the efficiency of the WPT system, with a power loss of about 1%. Then, the attention was focused on the performance in terms of magnetic field reduction. A cylinder with height 180 cm and elliptical base with semi-major axis of 40 cm and semi-minor axis of 20 cm is considered. The elliptical cylinder represents a respect volume. At any point inside this volume the magnetic field must be below the limit fixed by international regulations, which in Europe are mainly the RLs of the ICNIRP 2010 Guidelines. The RL in terms of magnetic flux induction at 85 kHz is equal to 27 µT for the ICNIRP 2010 and equal to 6.25 µT for the ICNIRP 1998 [25], still valid in some countries, due to the not repealed or adjourned European Council Recommendation [26]. Two positions of the respect volume near the EV Energies 2020, 13, 2522 10 of 14 are considered. The vertical cylinder of Figure 5a represents a respect volume for a pedestrian standing near the vehicle, while the horizontal cylinder of Figure 5b represents a respect volume for a pedestrian lying down on the side of the road near the vehicle. The maximum values of magnetic flux induction B inside the vertical and horizontal cylindrical regions (see Figure 5) are shown in Figure 6. A field reduction of more than 50% is observed in both cylindrical regions. These results are very satisfactory. elliptical base with semi-major axis of 40 cm and semi-minor axis of 20 cm is considered. The elliptical cylinder represents a respect volume. At any point inside this volume the magnetic field must be below the limit fixed by international regulations, which in Europe are mainly the RLs of the ICNIRP 2010 Guidelines. The RL in terms of magnetic flux induction at 85 kHz is equal to 27 µT for the ICNIRP 2010 and equal to 6.25 µT for the ICNIRP 1998 [25], still valid in some countries, due to the not repealed or adjourned European Council Recommendation [26]. Two positions of the respect volume near the EV are considered. The vertical cylinder of Figure 5a represents a respect volume for a pedestrian standing near the vehicle, while the horizontal cylinder of Figure 5b represents a respect volume for a pedestrian lying down on the side of the road near the vehicle. The maximum values of magnetic flux induction B inside the vertical and horizontal cylindrical regions (see Figure  5) are shown in Figure 6. A field reduction of more than 50% is observed in both cylindrical regions. These results are very satisfactory.  The maximum value of the magnetic flux induction beside the vehicle has been calculated on an xz plane for three different positions of the secondary coil center along the x-axis (x1 = 0, x2 = 25 cm, x3 = 50 cm) at lateral distances of 10 cm (a), 20 cm (b), and 30 cm (c) from the vehicle body, as shown in Figure 7. These lateral distances correspond to y = −100 cm (a), y = −120 cm (b), and y = −120 cm (c), respectively, for the considered vehicle dimensions. A field reduction between 33% and 39% was obtained. Without active shielding, the field is very close to the ICNIRP 2010 RL of 27µT, while the use of the active coil permits a considerable safety margin at any distance. Around a lateral distance of 30 cm, the magnetic flux induction is also compliant with the ICNIRP 1998 RL of 6.25 µT.   Figure 7. These lateral distances correspond to y = −100 cm (a), y = −120 cm (b), and y = −120 cm (c), respectively, for the considered vehicle dimensions. A field reduction between 33% and 39% was obtained. Without active shielding, the field is very close to the ICNIRP 2010 RL of 27µT, while the use of the active coil permits a considerable safety margin at any distance. Around a lateral distance of 30 cm, the magnetic flux induction is also compliant with the ICNIRP 1998 RL of 6.25 µT. x3 = 50 cm) at lateral distances of 10 cm (a), 20 cm (b), and 30 cm (c) from the vehicle body, as shown in Figure 7. These lateral distances correspond to y = −100 cm (a), y = −120 cm (b), and y = −120 cm (c), respectively, for the considered vehicle dimensions. A field reduction between 33% and 39% was obtained. Without active shielding, the field is very close to the ICNIRP 2010 RL of 27µT, while the use of the active coil permits a considerable safety margin at any distance. Around a lateral distance of 30 cm, the magnetic flux induction is also compliant with the ICNIRP 1998 RL of 6.25 µT.     Inside the vehicle cabin in a xy plane at a distance of 20 cm (z = 50 cm) from the vehicle bottom, we have found that the maximum of the magnetic field norm is marginally lower in the case of active shielding. However, the field level is always below 100 nT, as shown in Figure 11. This means that the active shielding designed to mitigate the field in a region beside the vehicle does not increase the magnetic field inside the cabin. Inside the vehicle cabin in a xy plane at a distance of 20 cm (z = 50 cm) from the vehicle bottom, we have found that the maximum of the magnetic field norm is marginally lower in the case of active shielding. However, the field level is always below 100 nT, as shown in Figure 11. This means that the active shielding designed to mitigate the field in a region beside the vehicle does not increase the magnetic field inside the cabin. Finally, it should be noted that we assume the dynamic behavior of WPT systems as a sequence of static states. To this aim, we considered only three positions for the receiving coil; however, the optimal shielding current can be easily derived for all the positions. Moreover, an automatic shielding current regulator can be realized using the current on both the transmitting and receiving coils as feedback for the regulation, to obtain the optimal shielding efficiency at any instant.

Conclusions
A method to reduce the magnetic field produced by a dynamic power transfer system using active shielding coils is presented. The proposed method allows halving of the magnetic field in proximity of the vehicle. First, the theory of active shielding is explained, and the method to calculate the optimum current to be applied to the active coils is provided, to minimize the field in the most critical areas. Then, an experimental validation of the calculation method is carried out by measurements on a simplified configuration. Finally, the procedure is applied to a dynamic WPT system, based on an electrified road with many short-track pads. Very good results were obtained in terms of field reduction without a significant degradation of the electrical performances. The main obtained results are: the active shielding coils halve the magnetic flux induction beside the electrified road where humans can stay; the field levels are compliant with ICNIRP reference levels; the magnetic field inside the cabin is not increased by the active coils; the losses in the active coils are very limited; and the decrease in the power transfer efficiency is around one percentage point, due to presence of the losses in the active coil. Finally, although not addressed in this paper, the implementation of the active shielding coil technology should be very simple and low-cost. Finally, it should be noted that we assume the dynamic behavior of WPT systems as a sequence of static states. To this aim, we considered only three positions for the receiving coil; however, the optimal shielding current can be easily derived for all the positions. Moreover, an automatic shielding current regulator can be realized using the current on both the transmitting and receiving coils as feedback for the regulation, to obtain the optimal shielding efficiency at any instant.

Conclusions
A method to reduce the magnetic field produced by a dynamic power transfer system using active shielding coils is presented. The proposed method allows halving of the magnetic field in proximity of the vehicle. First, the theory of active shielding is explained, and the method to calculate the optimum current to be applied to the active coils is provided, to minimize the field in the most critical areas. Then, an experimental validation of the calculation method is carried out by measurements on a simplified configuration. Finally, the procedure is applied to a dynamic WPT system, based on an electrified road with many short-track pads. Very good results were obtained in terms of field reduction without a significant degradation of the electrical performances. The main obtained results are: the active shielding coils halve the magnetic flux induction beside the electrified road where humans can stay; the field levels are compliant with ICNIRP reference levels; the magnetic field inside the cabin is not increased by the active coils; the losses in the active coils are very limited; and the decrease in the power transfer efficiency is around one percentage point, due to presence of the losses in the active coil. Finally, although not addressed in this paper, the implementation of the active shielding coil technology should be very simple and low-cost. Funding: This research was funded by the University of L'Aquila, L'Aquila, Italy.

Conflicts of Interest:
The funding sponsors had no role in: the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; and in the decision to publish the results.