Exposure assessment methods for wireless power transfer systems

IEC/TR 62905:2018(E) is a Technical Report. It describes general exposure assessment methods for wireless power transfer (WPT) at frequency up to 10 MHz considering thermal and stimulus effects. Exposure assessment procedures and experimental results are shown as examples such as electric vehicles (EVs) and mobile devices.
Keywords: Exposure Assessment, Wireless Power Transfer (WPT), Human Exposure

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Status
Published
Publication Date
05-Feb-2018
Current Stage
PPUB - Publication issued
Start Date
06-Feb-2018
Completion Date
06-Feb-2018
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IEC TR 62905
Edition 1.0 2018-02
TECHNICAL
REPORT
colour
inside
Exposure assessment methods for wireless power transfer systems
IEC TR 62905:2018-02(en)
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IEC TR 62905
Edition 1.0 2018-02
TECHNICAL
REPORT
colour
inside
Exposure assessment methods for wireless power transfer systems
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20 ISBN 978-2-8322-5350-2

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 62905:2018 © IEC 2018
CONTENTS

FOREWORD ........................................................................................................................... 7

INTRODUCTION ..................................................................................................................... 9

1 Scope ............................................................................................................................ 10

2 Normative references .................................................................................................... 10

3 Terms and definitions .................................................................................................... 10

4 Symbols and abbreviations ............................................................................................ 12

4.1 Physical quantities ................................................................................................ 12

4.2 Constants ............................................................................................................. 12

4.3 Abbreviations ........................................................................................................ 12

5 Overview of WPT systems ............................................................................................. 13

5.1 General ................................................................................................................. 13

5.2 WPT systems whose frequency range is less than 100 kHz .................................. 13

5.3 WPT systems whose frequency range is from 100 kHz to 10 MHz ......................... 17

6 Basic assessment methods ........................................................................................... 20

6.1 General ................................................................................................................. 20

6.2 Basic assessment methods considering direct effect ............................................. 20

6.2.1 General ......................................................................................................... 20

6.2.2 Evaluation based on transmit power or current .............................................. 21

6.2.3 Evaluation of incident fields against reference levels ..................................... 21

6.2.4 Evaluation of incident fields against basic restrictions .................................... 21

6.2.5 Evaluation of induced E-field and SAR against basic restrictions ................... 22

6.2.6 Assessment procedure .................................................................................. 23

6.3 Basic assessment method considering indirect effect ............................................ 23

Annex A (informative) WPT systems whose frequency range is over 10 MHz ....................... 25

Annex B (informative) International exposure guidelines ...................................................... 27

B.1 ICNIRP guidelines................................................................................................. 27

B.2 IEEE standards ..................................................................................................... 30

Annex C (informative) Assessment methods ........................................................................ 33

C.1 Exclusion based on transmit power or current ....................................................... 33

C.2 Measurement of incident electromagnetic fields .................................................... 34

C.2.1 Equipment for electric field measurement ...................................................... 34

C.2.2 Equipment for magnetic field measurement ................................................... 34

C.2.3 Measurement method .................................................................................... 35

C.3 Coupling factor ..................................................................................................... 36

C.4 Generic gradient source model ............................................................................. 37

C.5 Induced E-field or SAR ......................................................................................... 40

C.5.1 Measurement ................................................................................................. 40

C.5.2 Calculation .................................................................................................... 41

C.6 Contact current ..................................................................................................... 43

C.6.1 Equipment ..................................................................................................... 43

C.6.2 Measurements ............................................................................................... 45

Annex D (informative) Case studies ..................................................................................... 46

D.1 WPT system for EV ............................................................................................... 46

D.1.1 General ......................................................................................................... 46

D.1.2 Assessment procedures for WPT system for EV ............................................ 47

D.2 Experimental assessment results for EV ............................................................... 58

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IEC TR 62905:2018 © IEC 2018 – 3 –

D.2.1 General ......................................................................................................... 58

D.2.2 Electromagnetic field measurement results .................................................... 58

D.2.3 Contact current measurement ........................................................................ 60

D.3 WPT system for mobile devices ............................................................................ 61

D.3.1 General ......................................................................................................... 61

D.3.2 Assessment procedures for WPT system for mobile ....................................... 62

Annex E (informative) Numerical and experimental studies .................................................. 64

E.1 Exposure evaluation of WPT for EV ...................................................................... 64

E.1.1 Research in Japan ......................................................................................... 64

E.1.2 Research in Korea ......................................................................................... 68

E.2 Exposure evaluation of WPT for mobile device...................................................... 72

E.2.1 WPT system in 140 kHz band ........................................................................ 72

E.2.2 WPT systems in MHz band ............................................................................ 74

E.3 Coupling factor ..................................................................................................... 79

E.3.1 WPT system for EV ....................................................................................... 79

E.3.2 WPT system for mobile device ....................................................................... 82

E.3.3 Evaluation example of CF and GGSM using a cylinder model ........................ 83

E.4 SAR measurement ................................................................................................ 87

E.5 Contact current ..................................................................................................... 89

E.5.1 WPT system for EV ....................................................................................... 89

E.5.2 WPT systems for mobile (MHz) ...................................................................... 90

Annex F (informative) Medical implants ................................................................................ 92

F.1 Background........................................................................................................... 92

F.2 Medical implant enhancement factor ..................................................................... 92

F.3 Numerical evaluation of medical implant enhancement factor ................................ 97

F.3.1 General ......................................................................................................... 97

F.3.2 Numerical setup ............................................................................................. 97

Bibliography .......................................................................................................................... 99

Figure 1 – Wireless power kitchen appliances [1] .................................................................. 13

(WPT kitchen island of apartment) ........................................................................................ 14

Figure 2 – Use cases of the LCD and semiconductor product lines and kitchen WPT

systems [1] ........................................................................................................................... 14

Figure 3 – Example of a WPT system for EV/PHEV [1] ......................................................... 15

Figure 4 – Example of an online electric vehicle [1] ............................................................... 16

Figure 5 – Technical characteristics of an online electric vehicle [1] ...................................... 16

Figure 6 – Example magnetic induction WPT system block diagram [1] ................................. 18

Figure 7 – Example magnetic resonance WPT system block diagram [1] .............................. 18

Figure 8 – Capacitive coupling WPT system block diagram [1] .............................................. 19

Figure 9 – Typical structure of the capacitive coupling system [1] ......................................... 19

Figure 10 – Flowchart of assessment procedure considering the direct effect ....................... 23

Figure 11 – Two exposure situations for ungrounded and grounded metal objects ................ 24

Figure 12 – Flowchart of assessment procedures for indirect effects ..................................... 24

Figure C.1 – Frequency characteristics of impedance of adult male and IEC equivalent

circuit .................................................................................................................................... 44

Figure C.2 – IEC equivalent circuit ........................................................................................ 44

Figure C.3 – Example of contact current measurement equipment ........................................ 44

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– 4 – IEC TR 62905:2018 © IEC 2018

Figure D.1 – Example for areas of protection, for ground mounted systems [37] ................... 47

Figure D.2 – Area 3 measurement position [37] .................................................................... 48

Figure D.3 – Area 4 measurement position [37] .................................................................... 48

Figure D.4 – Assessment flow of Part 1 ................................................................................ 51

Figure D.5 – Assessment flow of Part 2 ................................................................................ 55

Figure D.6 – Assessment flow of Part 3 ................................................................................ 56

Figure D.7 – Example measurement layout for Area 3 surrounding area of vehicle ............... 59

Figure D.8 – Example measurement layout for Area 4 car interior ......................................... 60

Figure D.9 – Contact current meters used in the measurement ............................................. 60

Figure D.10 – Measurement of contact current ...................................................................... 61

Figure E.1 – Geometry of vehicle model ............................................................................... 64

Figure E.2 – Measured and simulated magnetic field strength leaked from wireless

power system in an electric vehicle [46] ................................................................................ 65

Figure E.3 – Distance dependence of peak induced electric field strength in human

body model ........................................................................................................................... 65

Figure E.4 – Analysis of induced electric field strength in the human body for different

human positions relative to the vehicle [41] ........................................................................... 66

Figure E.5 – Relationship between the maximum induced electric field in the human

body and the magnetic field strength [41] .............................................................................. 67

Figure E.6 – The induced electric field distributions in a human body model lying on

the ground with his right arm stretched [48] .......................................................................... 68

Figure E.7 – EMF human exposure condition from the power line and pickup coils of

OLEV system ........................................................................................................................ 69

Figure E.8 – The model in the field generated by OLEV ........................................................ 70

Figure E.9 – The calculated magnetic field distributions at each distance from OLEV ........... 71

Figure E.10 – Photograph of magnetic field measurement for transmitting and receiving

pads of wireless charging system.......................................................................................... 72

Figure E.11 – Measurement results of magnetic field value for two cases of low voltage

output (case 1) and high voltage output (case 2) ................................................................... 72

Figure E.12 – Transmitting and receiving coils, and magnetic sheet ...................................... 73

Figure E.13 – Simulated magnetic field strength distribution (Charging (a) xy plane,

(b) yz plane; Standby model (c) xy plane, (d) yz plane) and measured value (Charging

(e) xy plane, (f) yz plane; Standby mode (g) xy plane, (h) yz plane) ...................................... 73

Figure E.14 – Position of human body and coil (left), exposure point in chest (right) ............. 74

Figure E.15 – Realistic human body model and system position............................................ 75

Figure E.16 – Position of the human body model: (a) the human body is moved in the

horizontal direction, (b) the coils are moved in vertical direction............................................ 76

Figure E.17 – Peak of 10 g average SAR moved in (a) horizontal direction, (b) vertical

direction ................................................................................................................................ 76

Figure E.18 – Peaks of 10 g average SAR ............................................................................ 77

Figure E.19 – Wireless power transfer system configurations ................................................ 78

Figure E.20 – Electric field and magnetic field distributions around the coil when an

input power is 1 W ................................................................................................................ 78

Figure E.21 – Exposure conditions for WPT system .............................................................. 78

Figure E.22 – Top and bird’s-eye views of (a) solenoid type and (b) circular spiral type

coupling coils, and (c) geometry of electric vehicle with a wireless power transfer

system [13] ........................................................................................................................... 81

Figure E.23 – A numerical model of dielectric cylinder used in the calculation....................... 83

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IEC TR 62905:2018 © IEC 2018 – 5 –

Figure E.24 – Distribution of induced electric field strength inside the cylinder in the

vicinity of a one-turn loop with 1 A current ............................................................................ 85

Figure E.25 – A two-line current model ................................................................................. 85

Figure E.26 – Decay profile of incident magnetic field for each component ........................... 86

Figure E.27 – Profile of incident magnetic field for G = 13 (left) and 80 (right) ..................... 86

Figure E.28 – Distribution of induced electric field for x-, y-, and z-components of the

incident magnetic field profiles generated by GGSM ............................................................. 86

Figure E.29 – Solenoid-type WPT system (left) and flat-spiral-type WPT system (right)

used for SAR measurement .................................................................................................. 88

Figure E.30 – SAR distribution in a liquid phantom, calculated by MoM (above) and

measured by the developed measurement system (below) .................................................... 88

Figure E.31 – Two conditions of contact current measurement .............................................. 89

Figure E.32 – Contact currents with ungrounded condition .................................................... 90

Figure E.33 – Contact currents with grounded condition........................................................ 90

Figure E.34 – Contact current with ungrounded metal ........................................................... 91

Figure E.35 – Contact current with grounded metal ............................................................... 91

Figure F.1 – Model of the insulated perfectly conducting wire with non-insulated bare

tips used as generic implantable medical device ................................................................... 94

Figure F.2 – pSAR (W/kg) at the lead tip as a function of frequency in the range
0,1g

100 kHz to 10 MHz for each lead length (100 mm, 200 mm, 500 mm and 800 mm) ............... 96

Figure F.3 – Induced E-field tangential to the implant, embedded in the homogeneous

tissue, in the absence of the implant, to reach ICNIRP2010 BRs in the frequency range

10 kHz to 10 MHz and as a function of the lead length, when the implant is present ............. 97

Table 1 – Summary of application, technology and specification of WPT systems

whose frequency range is less than 100 kHz......................................................................... 17

Table 2 – WPT systems whose frequency range is from 100 kHz to 10 MHz ......................... 20

Table A.1 – Classification of WPT applications ..................................................................... 26

Table A.2 – Characteristics of beam WPT applications ......................................................... 26

Table B.1 – Basic restrictions up to 10 GHz of ICNIRP1998 .................................................. 27

Table B.2 – Basic restrictions of ICNIRP2010 ....................................................................... 28

Table B.3 – Reference levels for electric and magnetic fields (unperturbed rms values)

of ICNIRP1998 ...................................................................................................................... 29

Table B.4 – Reference levels for electric and magnetic fields (unperturbed rms values)

of ICNIRP2010 ...................................................................................................................... 29

Table B.5 – Reference levels for contact currents of ICNIRP1998 and ICNIRP2010 .............. 30

Table B.6 – Basic restrictions up to 5 MHz of IEEE C95.6 and IEEE C95.1 ........................... 30

Table B.7 – Basic restrictions between 100 kHz and 3 GHz of IEEE C95.1 ........................... 31

Table B.8 – Magnetic field MPE up to 5 MHz of IEEE C95.1 and IEEE C95.6........................ 31

Table B.9 – Electric field MPE for whole-body exposure up to 100 kHz of IEEE C95.1

and IEEE C95.6 .................................................................................................................... 31

Table B.10 – MPE for electric and magnetic field over 100 kHz for whole-body

exposure of IEEE C95.1 and IEEE C95.6 .............................................................................. 32

Table B.11 – Contact current MPE of IEEE C95.1 and IEEE C95.6 ....................................... 32

Table C.1 – Basic restrictions regarding SAR (unit is W/kg) .................................................. 33

Table C.2 – Possible exclusion power level regarding local SAR........................................... 34

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– 6 – IEC TR 62905:2018 © IEC 2018

Table C.3 – Coupling transformation matrix to estimate induced E-field for compliance

with ICNIRP 2010 ................................................................................................................. 38

Table C.4 – Coupling transformation matrix to estimate induced current density for

compliance with ICNIRP 1998 ............................................................................................... 38

Table C.5 – Coupling transformation matrix to estimate induced E-field for compliance

with IEEE 2005 ..................................................................................................................... 39

Table C.6 – Coupling transformation matrix to estimate SAR (pSAR and wbSAR)
10g

for compliance with ICNIRP 1998 and IEEE 2005 ................................................................. 39

Table C.7 – Dielectric properties of the tissue equivalent liquid defined in IEC 62209-2 ........ 40

Table C.8 – Dielectric properties of the tissue equivalent NaCl solution ................................ 40

Table C.9 – Human models and source models .................................................................... 42

Table C.10 – Computational methods ................................................................................... 43

Table C.11 – SAR evaluation method based on numerical simulation.................................... 43

Table D.1 – Uncertainty of H-field measurements for WPT systems in Area 3 ....................... 52

Table D.2 – Numerical uncertainty of the exposure of anatomical human models to

WPT systems for EV ............................................................................................................. 53

Table D.3 – Uncertainty of EMF measurements for WPT systems in Area 4 .......................... 54

Table D.4 – Uncertainty of contact current measurements .................................................... 57

Table D.5 – ICNIRP2010 guideline at 85 kHz ........................................................................ 58

Table D.6 – Specification of DUT .......................................................................................... 58

Table D.7 – Measured incident H-fields and E-fields of Area 3 .............................................. 59

Table D.8 – Measured incident H-fields and E-fields of Area 4 .............................................. 59

Table D.9 – Measurement results of contact current [mA] ..................................................... 61

Table E.1 – Estimated permissible power for WPT system for EV ......................................... 68

Table E.2 – Local SAR and induced electric field in in a human body on the chest surface ... 74

Table E.3 – Simulated result of local SAR and whole-body average SAR by Nagoya

Institute of Technology (NITech) / NTT DOCOMO and NICT (input power is 40 W) ............... 79

Table E.4 – Dimensions of WPT systems for electric vehicles considered by different

groups [13] ........................................................................................................................... 81

Table E.5 – Coupling factor for internal electric field of WPT systems for EV [13] ................. 82

Table E.6 – Coupling factor for peak 10 g SAR for WPT systems at 6,78 MHz

(implemented on the desk) [13] ............................................................................................. 83

Table E.7 – Coupling factor for internal electric field for WPT systems at 6,78 MHz

(implemented on the desk) [13] ............................................................................................. 83

Table E.8 – NICT and IT’IS results of induced electric field and local peak 10 g

average SAR in the dielectric cylinder using GGSM .............................................................. 87

Table E.9 – Experimental and numerical results of spatial peak 10 g average SAR

(input power = 10 W) ............................................................................................................ 88

Table F.1 – Preliminary medical implant enhancement factors for nerve stimulation up

to 10 MHz ............................................................................................................................. 93

Table F.2 – Preliminary medical implant enhancement factors for tissue heating up to

10 MHz (∆T) .......................................................................................................................... 93

Table F.3 – Dielectric and thermal properties assigned to the muscle tissue and to the

generic implants ................................................................................................................... 94

Table F.4 – Induced E-field in the homogeneous tissue without the implant to reach J-

BR of ICNIRP 1998 ............................................................................................................... 95

Table F.5 – Induced E-field in the homogeneous tissue without the implant to reach

SAR-BR of ICNIRP 1998 and IEEE 2005 for f ≥ 100 kHz ....................................................... 95

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IEC TR 62905:2018 © IEC 2018 – 7 –
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