Human Exposure Analysis to EMFs from 

Ground Assembly of a WPT System during 

the Vehicle’s Non-attendance

Authors

Ahmed Mohamed1, Peter Schrafel2, Andrew Meintz1, Anthony Calabro2

1 Transportation and Hydrogen Systems Center, NREL.

2 Momentum Dynamics.
NREL | 2

Introduction

Description of in-vehicle WPT system.

Vehicle Alignment for wireless charging

Assessment of EMF based on FEA and Measurements 

Results and discussion

Conclusion

Future work
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 Wireless power transfer (WPT) is a technology that could

set human free from the annoying wires.

 WPT technologies:

 IWPT is the most attractive for EV applications. Why?

1. High power transfer capability.

2. Large air-gap (10-25 cm).

3. Maintenance and noise free.

1. Magnetic gear (MGWPT).

2. Acoustic (AWPT).

3. Capacitive (CWPT).

4. Inductive (IWPT).
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4

Dynamic WPT

Quasi-dynamic WPT

Stationary WPT

vehicle pad

ground pad

PPM

https://www.nbcnews.com/mach/mach/futuristic-roads-may-make-recharging-electric-

cars-thing-past-ncna766456
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Introduction

Description of in-vehicle WPT system

Vehicle Alignment for wireless charging

Assessment of EMF based on FEA and measurements 

Results and discussion

Conclusion

Future work
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 Wirelessly Charged NREL’s Shuttle

 Momentum Dynamics WPT system

3φ AC

supply Filter EV

battery 

Primary controller Secondary controller

 

Radio 

munications

 

vehicle pad

ground pad

PPM

o Full electric on-demand

o 16 passenger

o 62.1 kWh battery capacity

o 100 miles range

o 7600 kg curb weight, including VA

o 6.6 kW on-board charger

o 36”x36” symmetrical square pads

o 25 kW maximum power transfer

o 20 (19-21) kHz nominal operating 

frequency
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Introduction

Description of in-vehicle WPT system

Vehicle Alignment for wireless charging

Assessment of EMF based on FEA and Measurements 

Results and discussion

Conclusion

Future work
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http://www.greencarcongress.com/2017/02/20170213-j2954.html
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Introduction

Description of in-vehicle WPT system

Vehicle Alignment for wireless charging

Assessment of EMF based on FEA and measurements 

Results and discussion

Conclusion

Future work
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 3D-FEM for Ground Coil

o Includes material properties (e.g. permeability and 

conductivity).

o Current sources were used for providing the coil 

currents.

o Eddy currents induced in nearby conductors are 

modeled and contribute to the total calculated 

magnetic fields.

o The finite element mesh maximum dimension

varies from 10 mm to 100 mm.

o Dirichlet (Flux Tangential) boundary conditions are

applied to the surrounding area around the model
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 Test Device

o 5 Hz – 100 kHz

o XYZ field measurements

o Built-in spectrum analyzer

o connected to a PC by a fiber optic cable

o dedicated software manages the probe setting, data acquisition

and storage

Low frequency isotropic field probe-analyzer EHP-50D, Narda, Germany

Parameter Value

Span 3-100 kHz

Measurement mode Max RMS over 30 sec.

Hold Maximum Enable

Showing XYZ measurements Enable

Measuring Range Small range

Units B (μT) & E (V/m) https://www.narda-sts.com/en/

http://www.eenewsautomotive.com/news/one-test-system-analysing-electromagneticfields-5-hz-60-ghz
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 Test Set-Up

 Defining coordinates

 Defining a marked safety perimeter

Y-axis

X-axis

GA

× 

× 

× 

× 

× 

× 

× 

× 

× × × × × × 

Z

test region

9"

9"

 Conducting EMF measurements in X, Y, 

and Z directions over and around the 

GA coil.
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 J2954 Standard Exposure Limits (2010 ICNIRP guidelines)

 Human Exposure

o General public

o Occupational Magnetic Field Limit Electric Field Limit

Bpeak (μT) Epeak (V/m)

38.2 (27 RMS) 117 (83 RMS)

38.2 (27 RMS) 117 (83 RMS)

 Basic Restrictions

 Reference Levels

 EMF Standard Limits

Ref. Limits for General Exposure

Ref. Limits for Occupational

Magnetic Field Limit Electric Field Limit

Bpeak (μT) Epeak (V/m)

141.5 (100 RMS) 240.5 (170 RMS)

141.5 (100 RMS) 240.5 (170 RMS)
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Introduction

Description of in-vehicle WPT system

Vehicle Alignment for wireless charging

Assessment of EMF based on FEA and measurements 

Results and discussion

Conclusion

Future work
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 Measured FFT for Magnetic and Electric Felids 

(Height = 6.25” Measured FFT of magnetic fields at 

the center with 2 A coil current ).

Measured FFT of electric fields at the center with 2 A 

coil current (Height = 6.25”).

Y-axis

X-axis

GA

× 

× 

× 

× 

× 

× 

× 

× 

× × × × × × 

Z

test region

9"

9"
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 Measured and Simulated Magnetic Field in XYZ Directions

Measured and simulated maximum RMS value 

of magnetic field along x-axis at 6.25” height.

Measured and simulated maximum RMS value of 

magnetic field along y-axis at 6.25” height.

Y-axis

X-axis

GA

× 

× 

× 

× 

× 

× 

× 

× 

× × × × × × 

Z

test region

9"

9"

Measured and simulated maximum RMS value of 

magnetic field along z-axis at 6.25” height.
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 Measured Electric Field in XYZ Directions

Measured maximum RMS value of electric field along yaxis at 6.25” height.

Measured maximum RMS value of electric field along zaxis at 6.25” height.

Y-axis

X-axis

GA

× 

× 

× 

× 

× 

× 

× 

× 

× × × × × × 

Z

test region

9"

9"
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Introduction

Description of in-vehicle WPT system

Vehicle Alignment for wireless charging

Assessment of EMF based on FEA and measurements 

Results and discussion

Conclusion

Future work
NREL | 19

 The paper presents a methodology to assess the human exposure to EMFs 

from GA during and before alignment.

 Magnetic and electric fields are evaluated while the system is working at low 

power excitation and the vehicle is not present.

 The EMFs are assessed based on both numerical analysis and 

measurements.

 The results show good correlation between experimental and simulated 

results.

 The magnetic field near the surface of the pad is significant and it is 

necessary to be evaluated. 

 For the system under test, both the magnetic and electric fields are within 

the standards limits for human exposure
www.nrel.gov

Ahmed Mohamed

Email: Ahmed.Mohamed@nrel.gov

This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable

Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided

by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Vehicles Technologies Office. The

views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S.

Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S.

Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published

form of this work, or allow others to do so, for U.S. Government purposes.

NREL/PR-5400-72242