It is a matter of concern for many people that the
carrier waves used by Bluetooth´s transmitters use the same frequency range as
microwave owens (Bluetooth uses 2.402 GHz to 2.480 GHz). What does it feel like
to get in the path of such waves?
Actually, the transmitting power is far too weak to
be noticeable for humans. Moreover, the radiation is not concentrated in a
beam, but dispersed more or less in all directions. When using a wireless phone
or a Bluetooth device, some of the emitted RF energy is absorbed
by the body. The penetration depth is about 1.5 cm at 2450 MHz (about 2.5 cm at
900 MHz), which means that the absorption is very superficial. The main
absorption mechanism is fieldinduced rotation of polar molecules (for example
H2O), which generates heat through molecular "friction".
Heating by means of radio frequencies is possible
over a broad frequency range. This is taken advantage of in microwave ovens at
2450 MHz using very high power levels (up to 1,000,000 times the power used by
Bluetooth devices). However, 2450 MHz is not a resonance
frequency of water. But does exposure to Bluetooth RF emission heat the human
body? No it does not. The output power of a Bluetooth-enabled device is far too
low to cause any detectable temperature increase. Again, in comparison, the
maximum increase from handheld cellular phones is less than 0.1°C.
There is, however, another side to this; some
people are demonstrably over-sensitive to electromagnetic radiations. Long
exposure to strong fields make some individuals so sensitive, after a few
years, that they can no longer be near such fields without considerable
discomfort. Bluetooth fits into a general development pattern where antennas
for GSM-transmission and other sources of electromagnetic radiations become more
and more prevalent in our cities. The future will show whether this is a
healthy development.
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