August 27th – 30th, 2018 — Chicago, IL, USA 

http://www.ieee-vppc.org/2018

“Enlarging e-mobility network”

In-vehicle Assessment of Human Exposure to EMFs 

from 25-kW WPT System Based on Near-field Analysis

•Ahmed Mohamed1, Andrew Meintz1, Peter Schrafel2, Anthony Calabro2

•1 Transportation and Hydrogen Systems Center, NREL.

•2 Momentum Dynamics.
NREL | 2

Introduction

Description of in-vehicle WPT system.

Near field EMF test methodology and setup

EMF test zones and standard safety limits

Results and discussion

Conclusion

Future work
NREL | 3

 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).
NREL | 

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
NREL | 5

Introduction

Description of in-vehicle WPT system

Near field EMF test methodology and setup

EMF test zones and standard safety limits

Results and discussion

Conclusion

Future work
NREL | 6

 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 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

o 62.1 kWh battery capacity
NREL | 7

Introduction

Description of in-vehicle WPT system

Near field EMF test methodology and setup

EMF test zones and standard safety limits

Results and discussion

Conclusion

Future work
NREL | 8

 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
NREL | 9

 Test Set-Up

240" shuttle

20" 20"

8.5"

driver’s 

seat

36"

36"

76"

Y-axis

X-axis

VA &GA

front

back

test region

Z × P1

6'

6'

6'

6'

 Defining coordinates

o GA reference coordinates for measurements outside the vehicle.

o VA reference coordinates for measurements inside the vehicle.

 Defining a marked safety perimeter

o Establishing a restricted area with a distance > 3m .

o Measuring the EMFs at the perimeter with at full power 

operation.

o Modifying the distance until the fields at the perimeter are 

with-in the recommended safe limits.

o If the fields around the vehicle meet the standard limits, the 

perimeter need to be defined to allow enough test area for 

the workers (6-7 ft around the system).
NREL | 10

 Defining the Worst Operating Condition

For each test region, the worst alignment conditions need to be defined and 

considered during the tests.

Coupler Offset & Gap Max Magnetic Field Max Electric Field

dX dY dZ Location B (μT) Location E (V/m)

+max +max max

+max -max max

-max +max max

-max -max max

o Applying different combinations of misalignments (X, Y, Z, pitch, roll and yaw).

o Measuring the EMFs at few points that represent the worst scenarios.

o Comparing the results to define the worst operating condition. 
NREL | 11

Introduction

Description of in-vehicle WPT system

Near field EMF test methodology and setup

EMF test zones and standard safety limits

Results and discussion

Conclusion

Future work
NREL | 12

 EMF Test Zones (SAE J2954)

o Region I: Under the vehicle

o Region II: Around and above the vehicle

o Region III: Inside the vehicle

“J2954A (WIP) Wireless Power Transfer for Light-Duty Plug-In/ Electric Vehicles and 

Alignment Methodology - SAE International.” 
NREL | 13

 J2954 Standard Exposure Limits (2010 ICNIRP guidelines)

 Human Exposure

o General public

o Occupational 

 IMD Coexistence

Region

Magnetic Field Limit Electric Field Limit

Human Exposure IMD Coexistence (Epeak) (V/m) Bpeak (μT) Hpeak (A/m) Bpeak (μT) Hpeak (A/m)

3 38.2 (27 RMS) 29.7 (21 RMS) 21.2 (15RMS) 16.9 (11.96 RMS) 117 (83 RMS)

2 38.2 (27 RMS) 29.7 (21 RMS) 21.2 (15RMS) 16.9 (11.96 RMS) 117 (83 RMS)

1 red

i) Active or passive access control.

ii) Detection and shutdown.

iii) Meet region 2 EMF limits.

green Meet region 2 EMF limits.

 Basic Restrictions

 Reference Levels

 EMF Standard Limits

Region

Magnetic Field Limit Electric Field Limit

Bpeak (μT) Hpeak (A/m) Epeak (V/m)

3 141.5 (100 RMS) 113.2 (80 RMS) 240.5 (170 RMS)

2 141.5 (100 RMS) 113.2 (80 RMS) 240.5 (170 RMS)

1 red

i) Active or passive access control.

ii) Detection and shutdown.

iii) Meet region 2 EMF limits.

green Meet region 2 EMF limits.

Ref. Limits for General Exposure

Ref. Limits for Occupational
NREL | 14

 Other EMF Standards

 2010 ICNIRP guidelines

 1998 ICNIRP guidelines

 IEEE C.95.1-2014

 IEEE C.95.6

 ACGIH TLV 2017

Ref. Limits for General Exposure & Occupational

standard Magnetic field, Brms (μT) Electric field, Erms (V/m)

general public occupational general public occupational

ICNIRP 2010 27 100 83 170

IEEE C.95.1-2014 

(3 kHz -5 MHz) 205 615 614 1842

ACGIH TLV 2017 (2.5-30) kHz --- 200 --- 1842

“J2954A (WIP) Wireless Power Transfer for Light-Duty Plug-In/ Electric Vehicles and Alignment 

Methodology - SAE International.” 
NREL | 15

Introduction

Description of in-vehicle WPT system

Near field EMF test methodology and setup

EMF test zones and standard safety limits

Results and discussion

Conclusion

Future work
NREL | 16

 Region 2 Test

Measured FFT of magnetic fields at point P1

with full power transfer (Height = 6.25”).

240" shuttle

20" 20"

8.5"

driver’s 

seat

36"

36"

76"

Y-axis

X-axis VA &GA

front

back

test region

Z × P1

6'

6'

6'

6'

Measured FFT of electric fields at point P1

with full power transfer (Height = 6.25”).

X-axis

Y-axis

VA

X-axis

Y-axis

VA

X-axis

Y-axis

VA

X-axis

Y-axis

VA

X-axis

Y-axis

VA

(a) (b) (c)

(d) (e)

Misalignment Max Brms (μT) Max Erms (V/m)

Position I 16.661 1.7414 

Position II 18.380 2.4091

Position III 17.696 2.5345 

Position IV 17.152 1.7147 

Position V 18.526 2.0853 

(a) Position I (ΔX=0, ΔY=0 and Z=9.5”).

(b) Position II (ΔX=-1”, ΔY=-2.5” and Z=9.5”).

(c) Position III (ΔX=-1”, ΔY=2.25” and Z=9.5”).

(d) Position IV (ΔX=1.5”, ΔY=-1” and Z=9.5”).

(e) Position V (ΔX=0, ΔY=-2.25” and Z=9.5”).
NREL | 17

 EMF Test Results around PPM

- (L) means 6.25” from the ground; and 

- (H), means 26.25” from the ground

PPM

cabinet × × 

× 

Front

Pa

Pb Pc

vehicle pad

ground pad

PPM

Test Point Max Brms (μT) Max Erms (V/m)

Pa,L 0.7251 0.1617 

Pb,L 0.3293 0.1469 

Pc,L 0.2375 0.1416 

Pa,H 1.1235 0.1839 

Pb,H 0.5735 0.1125 

Pc,H 0.3472 0.1106 
NREL | 18

 Region 3 Test Results @ (ΔX=0, ΔY=2.25” and Z=9.5”)

 Driver seat test

A

B

C

Test Point Max Brms (μT) Max Erms (V/m)

PA 0.0328 0.0633 

PB 0.0068 0.0380 

PC 1.0362 0.0257 

 Above the VA tests

× × × × × 

× 

× 

× 

× 

× 

× 

× bus 

inside

seat

VA

bus outside Y’-axis

X’-axis

Magnetic field along X’-axis at a height of 

27.25” from the floor of the bus

Magnetic field along Y’-axis at a height of 

6.25” from the floor of the bus
NREL | 19

Introduction

Description of in-vehicle WPT system

Near field EMF test methodology and setup

EMF test zones and standard safety limits

Results and discussion

Conclusion
NREL | 20

 The paper presents a methodology to assess the human exposure to invehicle WPT system.

 Near-field analysis for EMFs due to 25 kW WPT system for medium duty 

electric vehicles is presented.

 The tests are conducted with the WPT system physically installed in a NREL 

electric shuttle.

 Test results around (region 2), inside (region 3) the bus and around the PPM 

cabinet are investigated and compared with the standard reference levels 

2010 ICNIRP.

 The experimental results show that the WPT system under test meets the 

requirements for the human exposure to the EMFs from the WPT system. 
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-5400-71902