Radio frequency waves range from 3KHz to about 300GHz. RF radiation happens due to electrical oscillations of the E and H field. This emission of radio frequency waves(Electromagnetic waves) from various transmission devices referred as RF radiation.
Antenna is the device used to radiate the RF energy in the form of E-M waves in the air when Antenna impedance becomes equal to the free space impedance(377 Ohm). Figure shows electromagnetic rf radiations from mobile and Cellular tower.
HERP(Hazards of Electromagnetic Radiation to Personnel)
There are numerous applications of microwave signals in medical treatment for human body. But exposure of high microwave power to human bodies are hazardous and will cause skin cancer, headaches,dizziness,cataracts,birth defects in new born childs, increased stress and more diseases.HERP i.e. Hazards of Electromagnetic Radiation to Personnel is caused by thermal effect of radiated RF/Microwave energy.
Microwave energy directed on the body may be scattered,reflected and absorbed depending upon field strength,frequency,dimension of the human body. The absorbed microwave energy produces molecular vibration and converts this energy into heat. This is also referred as microwave heating. Significant energy absorption will occur occur when body size is at least (1/10)th of wavelength of microwave frequency radiated.
RF Radiation Hazard Limits
Various agencies have defined safety limits/standards for RF radiation exposure. IRPA(International Radiation Protection Association) sets the permissible exposure levels for general public. The limits take care of skin depth and specific absorption rate. ANSI developed electromagnetic hazard limit of HERP. Various countries such as USSR,CANADA,US and Sweden has their exposure standards which defines exposure limit with application duration and radio frequency.
As per US navy, personnel should not be exposed to power density above 10 mW/cm2, duration of 0.1 hour and frequency range of 10MHz -100GHz, This limit goes to 100 mW/cm2 when the exposure is not continuous.
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