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Introduction to Radio Frequency Radiation

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Introduction to Radio Frequency Radiation Robert Curtis, USDOL/OSHA Directorate of Science, Technology and Medicine March 2003 Health Effects and Standards Frequency ... – PowerPoint PPT presentation

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Title: Introduction to Radio Frequency Radiation


1
Introduction to Radio Frequency Radiation
  • Robert Curtis, USDOL/OSHADirectorate of Science,
    Technology and Medicine
  • March 2003

2
Health Effects and Standards
3
Frequency and Wavelength
4
Electromagnetic Spectrum
5
How RF Transfers
6
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7
Specific Absorption Rate
  • Measure absorbed power in watts per kg of tissue
  • Basis of most RF standards

8
A Quick Review of RFMW Biological Effects (II)
  • Immune (animals only) - T lymphocyte activity
    alteration _at_ 1.4 W/Kg
  • Blood - no consistent results
  • Cancer - No specific animal life span study
    seeking cancer has been done epl' studies of
    radio hams, electrical workers, and physical
    therapists found excess cancer, but other studies
    have not found association

9
A Quick Review of RFMW Biological Effects (III)
  • Neurological (animals only) - Test of blood/brain
    barrier contradictory unreplicated studies with
    AM PM fields show brain metabolism changes _at_
    gt0.02 W/kg 200 591 MHz, but not _at_ 2450 MHz
  • Mutations - Mutations not found in replicated
    studies to date

10
A Quick Review of RFMW Biological Effects (III)
(cont.)
  • Reproduction - (animals only)
  • Temporary make sterility _at_ 5.6 W/kg
  • Testicular changes _at_ 15 W/kg
  • Leutenizing hormone changes _at_ gt2 W/kg
  • Teratology (animals only) - Malformed offspring
    found _at_ 31 W/kg, strong thermal dependance (temp
    gt41C)
  • Thermoscoustic - (Pulsed only)

11
A Quick Review of RFMW Biological Effects (III)
(cont.)
  • Observed in radar operators in WWII as perceived
    clicking sound. Possible cause of neurological,
    central cholinergic, effects observed by James
    Lai _at_ 0.6 W/kg (0.45 W/kg NOEL, brain SAR 2 W/kg
    for effect)

12
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13
Basis of RF Standards
  • Behavioral disruption threshold
  • Limit temperature increase to 1 degrees C
  • 1-4 W/kg SAR
  • 10-fold safety factor

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15
Maximum Permissible Exposure (MPE) for
Occupational (Controlled) Environment
16
Same Basis, but Standards Differ
  • General population vs. Controlled RF Sites
  • Localized exposure limits (spatial averaging)
  • Time averaging
  • Special exclusions, such as low-power devices,
    peak exposures.

17
Maximum Permissible Exposure (MPE) for Public
(Uncontrolled) Environment
18
Maximum Contact Current for Occupational
(Controlled) Environment
19
Maximum Contact Current for Public (Uncontrolled)
Environment
20
RF Exposure Standards are Typically Based on 6
min. TWA
  • Excursions allowed if 6 min time weighted average
    is within limits
  • Up to 30 min intervals used for public exposure
    standards

21
Spatial Averaging
  • ANSI standard is confusing regarding partial-body
    vs. non-uniform exposure.
  • Exception for testes and eyes (See
    interpretation).
  • OSHA standards, based on old ANSI, does not allow
    for spatial averaging.

22
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23
Microwave Measurement
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31
Antenna Equations
  • Equation

32
Microwave Applications
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Cassegrain Antenna
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48
Radio Frequency Measurement
49
Radio-Frequency MeasurementsIEEE c95.1 - 1991
  • gt300 MHz - E or H or S spatial average
  • 100 - 300 MHz - E H spatial average
  • 3 kHz - 100 MHz - E H spatial average
    including current contact current

50
FCC Limits for MPE
  • Table Notes

51
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55
Spatial Average
56
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63
Single Roof-Top Antenna,various exposure
locations.
64
Single Tower, co-located antenna, on-tower
exposure.
65
Radio Frequency Applications
  • Communication Transmitters
  • Industrial Applications

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84
RF Safety Programs
85
Elements of a Comprehensive RF Protection
Program Role of RF Measurements
  • Full Text

86
RF Protection Program
  • Utilization of RF source equipment which meet
    applicable RF standards when new and during its
    lifetime.
  • RF hazard identification and periodic
    surveillance by a competent person.
  • Identification and Control of RF Hazard Areas.
  • Implementation of controls and SOPs to reduce RF
    exposures to levels in compliance with applicable
    guidelines.

87
RF Protection Program (cont.)
  • RF safety and health training to ensure that all
    employees understand the RF hazards and control
    methods used. Employee involvement in the
    structure and operation of the SH Program.
  • Implementation of an appropriate medical
    surveillance program.
  • Periodic (e.g. annual) reviews of the program to
    identify and resolve deficiencies.

88
RF Protection Program (cont.)
  • Assignment of responsibilities, including
    adequate authority and resources to implement and
    enforce the program.

89
Notice
90
Caution
91
Warning
92
RF Symbols
  • RF energy advisory symbol and RF electric current
    hazard advisory symbol.

93
Symbols (cont.)
94
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95
Summary of Contact Current
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