Summary of EM Environment for Medical Devices

1
Summary of EM Environment for Medical Devices

• Maqsood Mohd
• Sverdrup Technology Inc.
• TEAS Group
• Bldg 260
• Eglin Air Force Base, FL
• Maqsood_at_ieee.org

• Robert M. Nelson
• North Dakota State University
• Dept. of Elec. /Cmpter Eng.
• Fargo, ND 58105
• R.M.Nelson_at_ieee.org

2
Why Care About What EM Environment Medical
Devices are Exposed To?

• Many cases have been reported of interference
  effects between various sources of EM fields and
  medical devices 1-3
• Interference between cell phones and/or radios
  and medical devices
• Interference between electrosurgical units (ESUs)
  and medical instrumentation
• National and international agencies have adopted
  policies/regulations regarding the EMC
  performance of medical devices.

3
What Will Be Addressed in This Talk?

• The references for many excellent studies will be
  provided for the interested reader.
• Many studies examining the EM environment of
  medical devices have been conducted in past years
  (e.g., 4-9). This talk will focus on
  highlighting a few recent results, thus giving a
  flavor of the EM Environment for Medical
  Devices.
• Many other articles are referred to in one of
  last years Symposium papers 10.

4
EM Environment for Medical Devices

• Medical devices are found in many places
• In hospitals and clinics
• In ambulances
• In residential areas
• Throughout our society
• This talk will examine recent results of the EM
  environment in a few of these places.

5
EM Environment for Medical Devices

• Studies Undertaken by a Wide Variety of
  Researchers

• FDA
• University of Oklahoma Center for Wireless EMC
• McGill / Concordia Universities
• University of Pennsylvania
• North Dakota State University
• Independent consultants
• Researchers from various hospitals and medical
  organizations
• Folks from all over the world!!!

6
Types of Field Strength Measurements

• Using broadband probes which have a fairly flat
  frequency response over a wide range of
  frequencies (e.g., probes by Holaday Instruments,
  and others).
• Use of these probes provides one value of the
  total electric (or magnetic) field for the
  frequency range of the probe.
• Using frequency-selective antennas along with a
  spectrum analyzer or field strength meter
• Provides a field strength at each specific
  frequency.

7
EM Environment within the Hospital

• Lots of Different Sources of EM Fields

• External Transmitters (AM, FM, TV and other)
• Mobile Transmitters within Hospital
• ESU (Electrosurgical Unit)
• X-ray machines
• CRT and VDT monitors
• Lights
• Lasers
• Other medical equipment (pumps, monitors,
  ventilators, etc.)

8
EM Environment within the Hospital

• From External Transmitters (AM, FM, TV, etc.)
  11-18

• Fields inside hospital depend on many variables
• How far away transmitters are to hospital
• How far receiver is from windows and exterior
  walls
• Electric field strengths can be up significant
  (3.6 to 19.6 V/m in urban environment), but are
  typically lt 0.1 V/m

9
From Transmitters Internal to the Hospital

• ESUs Electric Fields up to 51 V/m and magnetic
  fields up to 56.4 A/m have been recorded
  11-13,17-22

10
Other Internal Transmitters Can Create
Significant Fields within the Hospital (Max.
Values) 11-12, 17-18, 23

• Hyfrecator gt 30 V/m at 0.1 m
• X-ray control 15 V/m at 0.15 m
• Lighting 30 V/m at 0.05 m
• CRTs / VDTs 6 V/m at 0.1 m
• 9 V/m at 2.5 cm
• Computer trans. 6 V/m at 0.15 m
• Televisions 5.5 V/m at 0.3 m
• Monitoring Eq. 2.9 V/m at 0.3 m
• Laser (standby) 1.4 V/m at 0.1 m

11
What About Magnetic Fields from other Local
Sources? (Max. Values) 11-12

• Compressor 50 A/m at 0.05 m
• Lighting 23 A/m at 0.1 m
• Power panel 15.5 A/m at 0.1 m
• Laser (standby) 14.6 A/m at 0.3 m
• Plume extractor 14.3 A/m at 0.3 m
• Vaporizer 11.1 A/m at 0.05 m
• CRTs / VDTs 10.3 A/m at 0.05 m
• Infusion pump 9.4 A/m at 0.05 m

12
What About Those Cell Phones and Walkie
Talkies? (Max. Values) 11-13,17-18, 23-24

• gt 30 V/m at 0.1 m from 4-W, 467 MHz transceiver
  (7 V/m at 1 m)
• 27 V/m at 0.1 m from 0.6 W cell phone (835 MHz
  analog) (5 V/m at 1 m)
• 22 V/m at 0.1 m from 1-W digital cell phone (1.5
  V/m at 1 m)
• 10 V/m at 2 m from 6-W, 467 MHz transceiver
• 3 V/m at 2 m from 0.6 W, 850 MHz cell phone

13
What about Field Strength Vs. Distance?
From Theoretical and Measured Radiated Field
Strengths for a 49.8 MHz Cordless Telephone,
R.Nelson, Tech. Memo. 83-90IN314-01, ATT, Aug.
2, 1983.
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But Not all Medical Devices are Located in
Hospitals What About Other Environments?

• The FDA has conducted a series of measurements of
  the EM environment, including
• In and around ambulances
• In residential homes
• In medical and dental clinics
• Near electronic surveillance systems (EAS)
• and more .

15
In and around Ambulances 25

• E-Fields Outside 1.6 to 18.3 V/m (5 - 90 W
  Tx)

(Photo Courtesy of J. Coletta from FDA/WEAC)
16
In and around Ambulances 25

• E-Fields Inside 0.4 to 22.4 V/m

(Photo Courtesy of J. Coletta from FDA/WEAC)
17
Significant Electric Fields in a Clinic
Environment (Max. Values) 26

• ESU gt 30 V/m at 0.1 m
• Lighting 14.0 V/m at 0.1 m
• VDTs 8.2 V/m at 0.1 m
• Projector 4.6 V/m at 0.1 m
• Televisions 6.2 V/m at 0.1 m
• CAT Scanner 3.0 V/m at 0.1 m
• Ultrasonic scaler 1.5 V/m at 0.1 m
• Dialysis unit 1.1 V/m at 0.1 m

Note Majority of E-fields were lt 3 V/m for
distances gt 0.5 m
18
Significant Magnetic Fields in a Clinic
Environment (Max. Values) 26

• ESU 81.6 A/m at 0.1 m
• Dialysis unit 14.6 A/m at 0.1 m
• Power panel 14.4 A/m at 0.1 m
• CAT Scanner pwr sup 10.5 A/m at 0.1 m
• Ultrasonic cleaner 9.3 A/m at 0.1 m
• Laser power supp. 8.3 A/m at 0.1 m
• Hearing analyzer 7.5 A/m at 0.1 m

Note Majority of H-fields were lt 3 A/m for
distances gt 0.5 m
19
Significant Electric Fields in Residential
Environments (Max. Values) 26

• TV 10.0 V/m at 0.1 m
• Microwave oven 8.2 V/m at 0.1 m
• HEPA air filter 6.0 V/m at 0.1 m
• 26 MHz cordless phone 5.5 V/m at 0.1 m
• VDT (computer) 2.0 V/m at 0.1 m
• 900 MHz cordless phone 1.8 V/m at 0.1 m

Note All E-Fields were lt 3 V/m for distances gt
0.5 m
20
Significant Magnetic Fields in Residential
Environments (Max. Values) 26

• Fan 44 A/m at 0.1 m
• Microwave oven 43.3 A/m at 0.1 m
• Vacuum cleaner 42.0 A/m at 0.1 m
• Electric stove 36.2 A/m at 0.1 m
• HEPA air filter 30.1 A/m at 0.1 m
• Water main pump 22.5 A/m at 0.1 m
• Humidifier 19.3 A/m at 0.1 m

Note Most H-Fields were lt 3 A/m for distances gt
0.5 m
21
What if someone is near an Electronic
Surveillance System (EAS)? 27

• Four types of systems were examined by FDA / WEAC
• Audio Freq. (AF) - CW sinusoid, freq. 218-518 Hz
• Pulsed Magnetic (PM) - Sinusoid of freq. 58-131
  kHz that is pulse modulated at 15 or 60 Hz
• Radio Freq. (RF) - FM signal swept from 8.8 to
  10.2 MHz at a rate of 300 Hz
• Microwave (MW) - CW sinusoid, frequency is
  approximately 1 GHz

22
Significant Fields from EAS 27

• AF System
• Max. H-Fields 587 to 1074 A/m
• PM System
• Max. H-Fields 24.5 to 26.3 A/m
• RF System
• Max. H-Fields 0.2 to 0.5 A/m
• Max. E-Fields 4.8 to 10 V/m
• MW System
• Max. E- Fields 22.1 to 23.8 V/m

Note The smaller values were measured at least
0.2 m from source. The large values were
measured very close to source.
23
Did You Notice a Change in EMI Potential When
Your Lighting System Was Updated? 28

• FDA/WEAC Replaced low-frequency magnetic ballasts
  with high-frequency, energy efficient ballasts
• High freq. (0.5 MHz - 1.5 GHz) E-fields increased
  from approximately 0.58 V/m to gt 30 V/m (at 0.1
  m)
• Low freq. (5 Hz - 2 kHz) H-fields decreased from
  approximately 3.73 A/m to 0.1 A/m (at 0.1 m)
• FDA/WEAC Replaced low-frequency magnetic ballasts
  with energy efficient, low-frequency ballasts
• Low freq. H-fields decreased slightly (4.26 to
  3.96 A/m)
• High freq. E-field increased slightly - (to 0.6
  V/m).

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CONCLUSIONS

• A flavor has been presented of the EM
  environment that medical devices may be exposed
  to.
• Under certain circumstances, medical devices can
  be subjected to fairly high electromagnetic
  fields.
• Diligence is needed to design medical products to
  function properly in their intended
  electromagnetic environment.

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• Special Thanks for Assistance in Preparing this
  talk goes to the following individuals
• John Coletta from the Winchester Engineering and
  Analytical Center (WEAC) of the FDA
• Jeff Silberberg of the Center for Devices and
  Radiological Health of the FDA
• Don Heirman, Associate Director for EMC of the
  University of Oklahoma Center for the Study of
  Wireless EMC
• William Kimmel of Kimmel Gerke Associates

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• Check out the Other Sessions Dealing with Medical
  Issues!!
• Mon. Morn. (EMC Issues in Noninvasive Medical
  Devices Human Body)
• Wed. After. (EM Biological Effects/Safety)
• Thurs. After. (Special Session Potential Med.
  Device Interaction with Popular Sources of EM
  Energy)
• Fri. Morn. (Current EMC Issues in Healthcare)

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