CommunicationsMicrowaves
Microwaves have wavelengths from about 1 mm to 10 m. and frequencies from about 30 MHz to 300 GHz. Microwaves have wavelengths that are greater than Infrared and smaller than Radio and TV waves.
Areas of Applications:
Communications
Navigation
Medical Diathermy
Microwave Ovens
Drying Equipment
Hazards:
Microwaves less than 3 cm are absorbed in the outer skin
3 to 10 cm wavelengths penetrate from 1 mm to 1 cm into the skin
25 to 200 cm wavelengths penetrate to deeper tissue and organs
Human tissue is transparent to microwaves with wavelengths greater than 200 cm.
Absorbed microwaves are converted to heat. Tissue and body temperatures rise, depending on exposure and location exposed.
The greatest danger from microwaves is to the eyes, where they appear to have a cumulative effect on the lens of the eyes, ultimately producing cataracts. Cataracts depend on the frequency, power density, duration of exposure and intervals between exposures.
Microwaves effect the central nervous system.
The performance of some cardiac pacemakers is also affected by microwaves.
A beneficial use of microwaves is diathermy. Localized application of microwaves up to 100mW/cm2 promotes healing in joints and other tissue.
Controls
Limit the exposure
Reduce the frequency
Reduce the wavelength
Reduce the duration of exposure
Increase the distance from the source
Use shielding materials
Protective clothing
Protective eyewear
High power microwave equipment must be grounded to reduce electrical hazards
Access to microwave locations can be protected by interlocks on doors
During servicing, lockout and tagout procedures are required
Microwave Exposure Standards
These standards are given in various publications prepared by different organizations.
OSHA Standard :
This standard limits power density to 10 mW/cm2 for exposures of 0.10 hr or longer.
American Conference of Governmental Industrial Hygienists (ACGIH) Standard:
Threshold limits are given in Table 1.
|
Frequency |
Power Density(mW/cm2) |
|
10KHz-3MHz |
100 |
|
3-30 MHz |
900/f2 |
|
30-100MHz |
1 |
|
100MHz-1GHz |
f/100 |
|
1-300 GHz |
10 |
Table 1. Microwave threshold limit values. (f= frequency in MHz)
FDA Standard:
Standard limit for the amount of microwaves that can leak from an oven during its lifetime is 5 mW/cm2 at approximately 2 in from the oven surface.
Measurement:
Thermal Detector (Measures the intensity of microwave from the temperature increase in a material)
Electrical Detector (Converts microwaves into direct current and measures the intensity of microwave from the increase in the current density)
Reading Materials:
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Back to Table Of ContentsLast Update: February 6, 2000
By: Serdar Z. Elgun
