Investigation of Implantable Medical Device EMI Due to Radio Waves from RFID reader/writers

Document No JAISA-CRF0700101

Investigation of Implantable Medical Device EMI Due to Radio Waves from

RFID reader/writers

Japan Automatic Identification Systems Association, Japan

Wireless Technology & EMC Research Lab.Graduate School of Information Science and Technology,

Hokkaido University, Japan.

This document is update of:WG4 SG5 March 2006 Kyoto meetingWG4 SG5 July 2006 Vancouver meetingWG4 SG3 August 2006 Paris meeting

Wireless Technologies & EMC Research Lab. Document No JAISA-CRF0700101

Contents

Objectives

Electromagnetic interference (EMI) experiments

Measurement system for electromagnetic field (EMF) distribution

Examples of numerical analysis of electric fields of antennas

Conclusions and future works


ObjectivesPrecise EMI assessment on implantable medical devices

Develop EMI estimation method: computer simulation

Contribute to the study of countermeasures

EMI experiments

Measurement of EMF distributions Numerical analysis

Radio wave from RFID Field strength

Mechanisms

EMI characteristics due to RFID reader/writers onimplantable cardiac pacemakers / implantable cardioverter-defibrillators (ICD)

Validity

EstimationThreshold level


EMI experiments

Number of implantable medical devices Number of RFID reader/writer antennas

73

ICDs

2720200613102005

TotalPacemakersFiscal year

Breakdown of EMI experiments

EMI with different operating modes and functions – pacing/sensing polarity, single/dual chamber mode, and antitachycardia functions are examined.

EMI tests of RFID reader/writers operated at the frequency bands –125 kHz, HF (13.56 MHz) , UHF (950 MHz) , and 2.45 GHz are carried out.

02

UHF

22

2.45 GHz

214

HF

27420061042005

Total125 kHz

Fiscal year


Configuration of the experimental system

Oscilloscope

Chart recorderPacemaker / ICD

Human body model

Function generator(Cardiac pulse)

Antenna Controller

Interferencedistance

1.8 w/v %saline

Oscilloscope & Chart Recorder

Function Generator

RFID reader/writer

Cardiac pacemaker

34 cm

36 cmLead wire

Ventricular electrode Atrial electrode

Saline solution(NaCl 0.18 w/v %)

RFID reader/writer

antenna

Human body model

Interference distance


Overview of the test system

Human torso phantom

Two-axis measurement platform

Chart recorder ECG signal generator/detector

Oscilloscope

RFID reader/writer antenna

x-axis direction

y-axis direction


EMI test results: FY2005

Affected Rate: 14% (107 / 768 modes)

0-4 cm5-9 cm 10-14

cm 15-19cm 20 cm-

Maximum1.0 mV

2.4 mV5.6 mV

Minimum

0

20

40

60

80

100

Affe

cted

mod

es (C

umul

ativ

e gr

aph)

Maximum interference distance （cm） Sensitivity of pacemakers and ICDs

Maximum interference distance: 15 cm

Affected Rate: 3% (26 / 768 modes)Maximum interference distance: 11 cm

Maximum sensitivity

Minimum sensitivity

Maximum1.0 mV2.4 mV5.6 mVMinimum

The results of FY2006 and FY2005 show no significant differences. Statistical processing of EMI characteristics will be carried out.


Measurement of EMF distributions

To determine threshold EMF level and mechanism causing EMI, boththe electric and magnetic field distributions of RFID reader/writer antennas are measured.

Obtained data is also used to check the validity of the numerical analysis results.

Purposes of EMF distribution measurements

The relationship between EMI occurrence probability and EMF distributions are investigated by using measured results.

EMI characteristics obtained by test experiments EMF distributions or strength

EMF strength obtained by numerical analysis EMI estimation


Measurement system configurations Automatic EMF measurement system is developed.

RFID reader/writer antenna ControllerSpectrum analyzer or computer

Electric or magnetic field probe

RFID reader/writer antenna

Magnetic field probe

y-axis

z-axis

x-axis

Automatic field positioner

Spectrum analyzerComputer


-100 -50 0 50 100

100

50

0

-50

-100

Example of measured EMF distributions

zy

x

RFID reader/writerantenna

Magnetic field

The relationship between EMI occurrence probability and EMF distributions are now under investigation.

-100 -50 0 50 1000

-50

-100

-150

-200

Magnetic field distributions of a handheld-type HF antenna

3D magnetic field distributions(Measurement interval: 1cm)

xy-plane (z = 0 cm) xz-plane (y = 0 cm)

2D magnetic field distributions(Measurement interval: 1cm)

Unit: mmUnit: mm


Numerical analysisBreakdown of numerical analysis

To develop a numerical EMI estimation methodology, we have constructed analysis model and conducted fundamental numerical analyses.

Antennas operating in the UHF and 2.45 GHz are suitable for employed numerical analysis method (FDTD method), however, 125 kHz and HF requires further investigation.


Examples of analysis results

Analytical model

The human body model and UHF standard dipole antenna

A 2.45GHz RFID reader/writer antenna

Calculated electric fields(perpendicular to the antenna feed point)

Analytical model Calculated electric fields(surface of the phantom)

Current distributions on the antenna


Conclusions and future worksConclusions

Future works

Detailed experiments to assess the EMI due to RFID reader/writers on implantable medical devices were conducted.

EMF distributions were measured precisely.

Statistical processing of EMI test results of FY2005 and FY2006.

Investigate electromagnetic conditions such as waveform and intermittent period to reduce EMI on implantable medical devices.

Investigate applicability of super computer to develop numerical EMI estimation method.

Fundamental investigations of a numerical analyses methodology were carried out.


Notification of RFID

Gate Type RFID Others RFID For controlled areas RFID

JAISA will provide the design of above signs to NB of ISO/IEC JTC1/SC31, P-Members and O-Members.You can change the trade mark.


Results of 125 kHz RFID reader/writers

0-4 cm 5-9 cm 10-14cm 15-19

cm 20 cm-

Maximum1.0 mV

2.4 mV5.6 mV

Minimum

0

20

40

60

80

100

Affe

cted

mod

es (C

umul

ativ

e gr

aph)

Maximum interference distance （cm）


Maximum interference distance of EMI: 15 cm

Number of antennas: 4

Specifications: ISO/IEC 18000-2

Total test modes: 320 modes

Affected modes: 103 modesAffected rate: 32 %

Communication distance: 0 - 28 cm

Conditions for 125 kHz RFID reader/writers

Results

About 30 % of test mode results due to magnetic field from antennas.

Sensitivity of pacemakers and ICDs


Results of HF RFID reader/writers

0-4 cm 5-9 cm 10-14cm 15-19

cm 20 cm-

Maximum1.0 mV

2.4 mV5.6 mV

Minimum

0

20

40

60

80

100

Affe

cted

mod

es (C

umul

ativ

e gr

aph)



Maximum interference distance of EMI: 5 cm


Specifications: ISO/IEC 18000-3


Affected modes: 4 modesAffected rate: 3 %


Conditions for HF RFID reader/writers

Results

EMI is reduced with magnetic field strength lower than the 125 kHz.

Input power (maximum): 4 W



Results of UHF RFID reader/writers


Specifications: EPC Class 1 Generation 2


Affected modes: 0 modeAffected rate: 0 %


Conditions for UHF RFID reader/writers

Results

EMI not detected during the experiments although UHF RFID reader/writers provide greater communication distance than

those using lower frequency bands.

Input power (maximum): 1 W


Results of 2.45 GHz RFID reader/writers


Specifications: ARIB STD-T81 / RCR STD-1


Affected modes: 0 modeAffected rate: 0 %


Conditions for 2.45 GHz RFID reader/writers

Results

No EMI detected for RFID reader/writer using the UHF and 2.45 GHz. Small input powers generate relatively low field strengths even in the

near field region of the antenna.

Input power (maximum): 300 mW


Summary of all frequency

Affected Rate:3 % (26 / 768 modes)Maximum interference distance: 11 cm

Maximum sensitivity

Minimum sensitivity0-4 cm 5-9 cm 10-14

cm 15-19cm 20 cm-

Maximum1.0 mV

2.4 mV5.6 mV

Minimum

0

20

40

60

80

100

Affe

cted

mod

es (C

umul

ativ

e gr

aph)


Maximum interference distance: 15 cm



Affected rate: 14 % (107 / 768 modes)

Conditions of EMI experiments

Results

As radio waves from lower frequency band RFID reader/writers have time-varying envelope curves or varying magnetic fields due to antenna motion,

the probability of EMI occurrence is high.




Configuration of experimental test system

Controller orComputer

Distance: x


Saline solution(0.18 w/v %)

Torso phantom

Pacemaker or ICD

Lead wireElectrode

Chart recorderNEC San-ei RT3608

> 2 kΩECG signal generatorFunction generator

OscilloscopeYOKOGAWA DL9240L

The test system is based upon proposed one for estimation of EMI due to mobile phones.

We referred AAMI Standard PC69 and EMI test experiments reported by the Ministry of Internal Affairs and Communications of Japan.

Maximum interference distances are measured in centimeters.


Maximum interference distance

Human body


Maximum interference distance

Maximum interference distance refers to the distance which causes EMI to disappear.

The human body is assumed to face an RFID reader/writer antenna.


The human torso phantom

Cardiac pacemaker

34 cm

36 cmLead wire

Ventricular electrode Atrial electrode

Saline solution(NaCl 0.18 w/v %)

The human torso phantom is based upon Irnich’s flat torso phantom model.

Both atrial and ventricular electrodes enable us to separate each chambers’signal by more than 20 dB.

This phantom allows us to examine EMI with low interference by another chambers’ signal.

This construction of a human torso phantom is confirmed to give more conservative results for EMI estimations.


PM/ICD operating mode and EMI test mode

EMI test mode

Pacemakers and ICDs operating mode VVI mode - the Ventricle chamber is paced, the Ventricle chamber is sensed,

and the response to sensing is Inhibited. AAI mode - the Atrium chamber is paced, the Atrium chamber is sensed,

and the response to sensing is Inhibited.

Sensing/pacing polarity

Unipolar mode – a metal housing of pacemakers and a tip electrode of lead wire.

Bipolar mode – a tip electrode and ring electrode located at the end of coaxial lead wire.

Inhibition test – Test mode with no ECG signal is injected. Pacing pulse is inhibited due to intermittent sensing of external noise or radio waves.

Asynchronous test – Test mode with ECG signal is injected. Pacing pulse is generated by noise reversion function of pacemakers triggered by the noise.


Procedure of the test experimentsStart

(4) Recode ECG signal and measurement of maximum interference distance

End

(2) 125 kHz or HF (13.56 MHz)RFID reader/writer

(3) Exposure test (Inhibition / Asynchronous)With varying antenna position

(1) Set PM / ICD parameters.Sensitivity: maximum, Refractory: minimum

Operating mode: VVI or AAI, Polarity: Unipolar / Bipolar

(2) UHF (950 MHz) or 2.45 GHzRFID reader/writer

(3) Exposure test (Inhibition / Asynchronous)With fixed antenna position

Step down sensitivityYes

NoChange operating mode and polarity

EMI occurs?

Complete test with respect to all conditions


Examples of affected ECG signal

Normal ECG signal Affected ECG signal

Inhibition of pacing pulses

Asynchronous pacing pulses

Inhibition test: pacing pulses are inhibited or pulse interval are changed

Asynchronous test: asynchronous pacing pulses are generated

Normal ECG signal Affected ECG signal


EMI occurrence mechanism

• Low frequency bands– Direct conducted current– Alternating magnetic field

• Electromotive force by following Faraday’s low

– High voltage electric field

• High frequency bands– Nonlinear characteristics of pacemaker’s input circuit– Envelop curve of signal are detected by the circuit


EMI test mode for pacemakers

• Inhibition– Test mode with no injected ECG signal.– As the strength of the EMI increases, the effects is

usually inhibition due to intermittent sensing of the EMI by the pacemaker.

• Asynchronous– Test mode with injected ECG signal.– At the high strength, noise may be sensed

continuously, which can trigger a noise reversion mode, which is generally asynchronous pacing.


EMI test mode for ICDs

• False positive mode– Test mode with no injected ECG signal– Defibrillation functions are triggered by the EMI.

• False negative mode – Test mode with injected ECG signal which is same as

defibrillation ECG– Defibrillation functions are disabled by the EMI.


PM/ICD sensing/pacing polarity

• Pacemaker's two electrode– A different electrode and an indifferent electrode

• Sensing/pacing signal is carried by– Unipolar: “a metal housing of pacemakers” and “a tip

electrode of lead wire”

– Bipolar: “a tip electrode and ring electrode with located at the end of coaxial lead wire”


Block diagram of a pacemaker sense amplifier

“Block diagram of a pacemaker sense amplifier showing the main functional elements of a typical atrial or ventricular sense amplifier.”

K. A. Ellenbogen, G. N. Kay, C, -P, Lau, and B. L. Wilkoff, Clinical Cardiac Pacing, Defibrillation, and Resynchronization Therapy, 3RD EDITION. Pennsylvania: Saunders, 2007.

Figure 7-3


Sense amplifier sensitivity

“Sense amplifier sensitivity versus frequency plots. Signals above the threshold (or sensitivity) line are sensed as P waves or R waves. Signals below the sensitivity line are not sensed. Frequencies of typical signals are superimposed on the plot.”K. A. Ellenbogen, G. N. Kay, C, -P, Lau, and B. L. Wilkoff, Clinical Cardiac Pacing, Defibrillation, and Resynchronization Therapy, 3RD EDITION. Pennsylvania: Saunders, 2007.

Figure 7-6


Filtered ventricular EGM


“A. Unfiltered ventricular EGM. Note the prominent T wave. B. The same EGM after filtering by a pacemaker sense amplifier. Filtering has greatly reduced the amplitude of the T wave.”

Figure 7-4


Spectrum of filtered EGM

“Fast Fourier Transform (FFT) showing frequency content of unfiltered and filtered ventricular EGMs. Top, spectrum of an unfiltered EGM. Note the frequency content in the 2 to 10 Hz range, caused by T waves; also note the frequency content between 1-and 40 Hz, caused by R waves. Bottom, Spectrum of filtered EGM. The frequency content from 2 to 10 Hz is removed by filtering.”


Figure 7-5


Tested RFID reader/writer in FY2006 1 of 2

1 WCWHF (13.56MHz)Handheld18

1 WCWHF (13.56MHz)Stationary17


-CW125 kHzStationary2


-CWHF (13.56MHz)Handheld13


-4 Hz with 0.10 duty factorHF (13.56MHz)Handheld9

-4 Hz with 0.10 duty factorHF (13.56MHz)Handheld11

Handheld

Handheld

Handheld

Handheld

Gate

Stationary

Stationary

Stationary

Stationary

Type

HF (13.56MHz)

HF (13.56MHz)

HF (13.56MHz)

HF (13.56MHz)

HF (13.56MHz)

HF (13.56MHz)

125 kHz

125 kHz

125 kHz

Carrier frequency

-

-

-

-

1 W

4 W

-

-

-

Input power

CW12

2.86 Hz with 0.57 duty factor8

CW3

CW1


CW5

CW10

CW4


Intermittent periodRFID No.


Tested RFID reader/writer in FY2006 2 of 2

200 mW-2.45 GHzStationary27

300 mWCWHF (13.56MHz)Stationary20

Stationary

Gate

Handheld

Stationary

Stationary

Stationary

Stationary

Type

2.45 GHz

HF (13.56MHz)

HF (13.56MHz)

HF (13.56MHz)

HF (13.56MHz)

HF (13.56MHz)

HF (13.56MHz)

Carrier frequency

300 mW

4 W

-

300 mW

300 mW

300 mW

300 mW

Input power

-26

CW21

CW19

CW24

CW23

CW22

50 Hz with 0.50 duty factor25

Intermittent periodRFID No.

Investigation of Implantable Medical Device EMI Due to Radio Waves from RFID reader/writers

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