About SAR

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Definition

SAR stands for Specific Absorption Rate. SAR is a measure of the rate of energy absorbed by (dissipated in) an incremental mass contained in a volume element of dielectric materials such as biological tissues.

It is also defined as the rate of RF energy absorption per unit mass at a point in an absorbing body.

SAR is usually expressed in terms of watts per kilogram (W/kg) or milliwatts per gram (mW/g).

 

SAR Mathematical Equation

 

SAR-Mathematical-Equation

 

When the human body is exposed to an RF field, the SAR experienced is proportional to the squared value of the electric field strength induced in the body.

 

 

Where:

  • α - Conductivity of the tissue - simulant material (S/m)
  • ρ -Mass density of the tissue – stimulant material (kg/)
  • E - Total RMS electric field strength (V/m)

 

Note: The primary factors that control rate of energy absorption were found to be:

  • The wavelength of the incident field in relations to the dimensions and geometry of the irradiated organism*
  • The orientation of the organism in relation to the polarity of the field vectors
  • The presence of reflecting surfaces
  • Conductive contact made by the organism* with a ground plane

 

* Organism in this case is us

 

SAR FCC Safety Limits

 

Guidelines for human exposure to RF fields are based on SAR thresholds where adverse biological effects may occur.

 

EXPOSURE LIMITS

SAR (W/kg)

General Population / Uncontrolled
Exposure Environment)

Occupational / Controlled
Exposure Environment

Spatial Average
(averaged over the whole body)

0.08

0.4

Spatial Peak
(averaged over any 1g of tissue)

1.60

8.0

Spatial Peak
(hands/wrists/feet ankles averaged
over 10g)

4.0

20.0

 

Notes:

  1. Uncontrolled exposure environments are locations where there is potential exposure of individuals who have no knowledge or control of their potential exposure
  2. Controlled exposure environments are locations where there is potential exposure of individuals who have knowledge of their potential exposure and can exercise control over their exposure.

 

SAR Measurement System

 

SAR-Measurement-SystemFor performing SAR compliance tests a dedicated Dosimetric Assessment System (DASY™) is being used. The DASY4 measurement system we will describe here (manufactured by Schmid & Partner Engineering AG of Zurich, Switzerland) is comprised of the measurement server, robot controller, computer, near-field probe, probe alignment sensor, specific anthropomorphic (SAM) phantom, and various planar phantoms for brain and/or body SAR evaluations.

The robot is a six-axis industrial robot performing precise movements to position the probe to the location (points) of maximum electromagnetic field (EMF). The Cell controller system contain the power supply, robot controller, teach pendant (Joystick), and remote control is used to drive the robot motors. The Staubli robot is connected to the cell controller to allow software manipulation of the robot.

A data acquisition electronic (DAE) circuit performs the signal amplification, signal multiplexing, AD-conversion, offset measurements, mechanical surface detection, collision detection, etc. is connected to the Electro-optical coupler (EOC).

The EOC performs the conversion from the optical into digital electric signal of the DAE and transfers data to the DASY4 measurement server.

The DAE utilizes a highly sensitive electrometer-grade preamplifier with auto-zeroing, a channel and gain-switching multiplexer, a fast 16-bit AD-converter and a command decoder and control logic unit.

Transmission to the DASY4 measurement server is accomplished through as optical downlink for data and status information and an optical uplink for commands and clock lines.

The mechanical probe-mounting device includes two different sensor systems for frontal and sidewise probe contacts. The sensor systems are also used for mechanical surface detection and probe collusion detection.

The robot uses its own controller with a built in VME-bus computer.

 

 

Why is the SAR value not an accurate measure of safety?

 

  • The SAR value is only comparing the isolated heating effect of different phones and does not give an indication that a cell phone is ‘safe.’
  • The power, or heating effect, of the phone is only one of many possible factors impacting cell phone ‘safety.’ Exposures to the radiation from the cell phone at non-heating levels have been linked to many serious biological effects, and the SAR value is not capturing anything about these harmful non-thermal exposures.
  • SAR values are reported to the FCC by the manufacturer and have been known to vary from the reported number by a factor of two across models of the same phone.
  • The SAR value varies with the source of exposure and the person using the phone. For example, if you are in a rural area or in an elevator or a car, where the cell phone uses more power, your brain will get a greater exposure from the higher power required in these instances. Under certain conditions, the SAR value can be 10-100 times higher than reported.
  • Holding the phone in a slightly different way can actually render the worst SAR value phone better than the best SAR value phone.
  • SAR values have been created based on simulations of exposure in a plexiglass head filled with fluid, not a human head, and many scientists consider them to be inaccurate and irrelevant at determining actual biological effects.

One of the worst deficiencies of the SAR value is that it only considers the thermal impact of cell phone usage, and it is very likely that the non-thermal effects of chronic cell phone exposure are more biologically damaging.

Even the FCC acknowledged this concern in their FCC Consumer Facts:

“Some experts think that low frequency magnetic fields rather than RF energy measured by the SAR possibly are responsible for any potential risk associated with wireless devices 

 

References:

 

[1]    Federal Communications Commission. OET Bulletin 65 (Edition 97-01). Supplement C (Edition 01-01). Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields. July 2001.

[2]    Federal Communications Commission. ET Docket 93-62. Guidelines for Evaluating the Environmental   Effects of Radiofrequency Radiation. Aug. 1996.

[3]    ANSI/IEEE C95.1 - 1991. American National Standard safety levels with respect to human exposure to radio frequency electromagnetic fields, 300kHz to 100GHz. New York: IEEE. Aug. 1992.

[4]    Dosimetric Assessment and Radiated Emissions Test Report For the Cell La Vie developed by Wise Eiiviiouineiit Ltd. SAR Tested and Evaluated In Accordance With FCC OET 6 Supplement C: 01-01. EIRP Tested and Evaluated In Accordance With EIA TIA-603. MET Report: EMC28312-SAR. January 20. 2010

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