Specific absorption rate
SAR is the abbreviation for the specific absorption rate and a measure of the absorption of electromagnetic fields in a material. It always leads to its heating . The specific absorption rate is expressed as power per mass in units of W / kg .
The specific absorption rate can be calculated from
- the field strength in the tissue:
- the current density in the tissue:
- the temperature increase in the tissue:
- E = electric field strength ([ E ] = V / m ) at a point inside a body to be measured (e.g. measuring phantom).
- J = current density ([ J ] = A / m² ), caused by the magnetic and electric fields. (The limit value of the current density for skilled workers is, for example, 10 mA / m². For normal people, 2 mA / m².)
- ρ = density of the fabric ([ ρ ] = kg / m³ )
- σ = electrical conductivity of the tissue ([σ] = S / m )
- c i = specific heat capacity of the tissue ([ c i ] = J / kg K )
- dT / dt = time derivative of tissue temperature ([ dT / dt ] = K / s )
A SAR value is often given for cell phones . With modern devices, this is approximately between 0.10 and 1.99 W / kg. The lower the SAR value, the less the tissue is heated by the radiation. The recommended upper limit of the World Health Organization is 2.0 W / kg. In the past, the SAR value for mobile phones was determined by manufacturers under inconsistent conditions, which made it unreliable. A European standard ( EN 50361) has existed since autumn 2001 , which precisely defines the measurement conditions. In March 2007, EN 50361 was replaced by EN 62209-1.
A maximum SAR value of 0.5 W / kg when used on the ear and 1.0 W / kg when used on the body is permitted for labeling a mobile phone with the blue angel . A maximum SAR value of 0.8 W / kg is permitted for labeling with the TCO '01 Mobile Phone logo.
The SAR value for mobile phones is given for the maximum transmission power . Due to the power regulation , however, a smaller SAR value usually occurs during operation, which depends on the respective cellular network . In well-developed networks with a high density of transmission masts , the mobile phone usually transmits with significantly lower transmission power than in poorly developed networks. As a result, exposure when making calls is also lower in areas with a high density of transmission towers than in areas with a low density of transmission towers. Staying in vehicles and buildings (especially those made of reinforced concrete ), on the other hand, increases the required transmission power. The power levels of standard GSM mobile phones are between 1 and 2000 mW depending on the reception situation and generate permissible SAR values within this range.
Other technically relevant areas
Other areas where SAR values are relevant:
- Diathermy : deliberate warming of tissue for healing purposes
- dielectric heating : ISM frequencies 13.56 and 27 MHz
- Inductive heating : only at frequencies> 100 kHz Whole-body SAR <0.4 W / kg in the event of occupational exposure; below this frequency limit values apply to the electrical and magnetic field strength based on the current density in the body
- Microwaves : microwave oven , industrial drying and plasma generation
- Transmitting systems: near field and work on it. These include radio transmitters , radar devices , but also HF generators for generating plasma, e.g. B. the high frequency sputtering or the excitation of gas lasers
- List of SAR values for cell phones at the Federal Office for Radiation Protection
- List of SAR values for cell phones
- Introduction and list of SAR values for mobile phones at the Mobile Radio Information Center
- Wannenmacher, Debus, Wenz: Radiation therapy . Springer, 2006, ISBN 3540228128 , p. 178.
- Federal Office for Radiation Protection: SAR values of cell phones ( Memento from May 28, 2015 in the Internet Archive ) (February 19, 2008).
A low SAR value does not yet low radiation ( memento from July 16, 2014 in the Internet Archive ), explanation of the connect radiation
factor connect radiation factor - best list: low- radiation cell phones .