Introduction to Radio Frequency Radiation

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Introduction to Radio Frequency Radiation

• Robert Curtis, USDOL/OSHADirectorate of Science,
  Technology and Medicine
• March 2003

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Health Effects and Standards
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Frequency and Wavelength
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Electromagnetic Spectrum
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How RF Transfers
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Specific Absorption Rate

• Measure absorbed power in watts per kg of tissue
• Basis of most RF standards

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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

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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

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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)

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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)

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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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Maximum Permissible Exposure (MPE) for
Occupational (Controlled) Environment
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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.

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Maximum Permissible Exposure (MPE) for Public
(Uncontrolled) Environment
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Maximum Contact Current for Occupational
(Controlled) Environment
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Maximum Contact Current for Public (Uncontrolled)
Environment
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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

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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.

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Microwave Measurement
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Antenna Equations

• Equation

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Microwave Applications
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Cassegrain Antenna
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Radio Frequency Measurement
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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

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FCC Limits for MPE

• Table Notes

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Spatial Average
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Single Roof-Top Antenna,various exposure
locations.
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Single Tower, co-located antenna, on-tower
exposure.
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Radio Frequency Applications

• Communication Transmitters
• Industrial Applications

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RF Safety Programs
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Elements of a Comprehensive RF Protection
Program Role of RF Measurements

• Full Text

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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.

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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.

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RF Protection Program (cont.)

• Assignment of responsibilities, including
  adequate authority and resources to implement and
  enforce the program.

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Notice
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Caution
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Warning
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RF Symbols

• RF energy advisory symbol and RF electric current
  hazard advisory symbol.

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Symbols (cont.)
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Summary of Contact Current