Specific absorption rate

Specific absorption rate (SAR) is a measure of the rate at which energy is absorbed by the body when exposed to a radio frequency (RF) electromagnetic field; although, it can also refer to absorption of other forms of energy by tissue, including ultrasound.^[1] It is defined as the power absorbed per mass of tissue and has units of watts per kilogram (W/kg).^[2] SAR is usually averaged either over the whole body, or over a small sample volume (typically 1 g or 10 g of tissue). The value cited is then the maximum level measured in the body part studied over the stated volume or mass.

Calculation

SAR can be calculated from the electric field within the tissue as:

{\text{SAR}}=\int _{\textrm {sample}}{\frac {\sigma (\mathbf {r} )|\mathbf {E} (\mathbf {r} )|^{2}}{\rho (\mathbf {r} )}}d\mathbf {r}

where

\sigma

is the sample electrical conductivity

E

is the RMS electric field

\rho

is the sample density

SAR measures exposure to fields between 100 kHz and 10 GHz.^[3] It is commonly used to measure power absorbed from mobile phones and during MRI scans. The value will depend heavily on the geometry of the part of the body that is exposed to the RF energy, and on the exact location and geometry of the RF source. Thus tests must be made with each specific source, such as a mobile phone model, and at the intended position of use. For example, when measuring the SAR due to a mobile phone the phone is placed at the head in a talk position. The SAR value is then measured at the location that has the highest absorption rate in the entire head, which in the case of a mobile phone is often as close to the phone's antenna as possible. Various governments have defined safety limits for exposure to RF energy produced by mobile devices that mainly exposes the head or a limb for the RF energy:

United States: the FCC requires that phones sold have a SAR level at or below 1.6 watts per kilogram (W/kg) taken over a volume containing a mass of 1 gram of tissue.
European Union: CENELEC specify SAR limits within the EU, following IEC standards. For mobile phones, and other such hand-held devices, the SAR limit is 2 W/kg averaged over 10 g of tissue (IEC 62209-1). For Magnetic Resonance Imaging the limits (described in IEC 60601-2-33) are slightly more complicated:

Averaging time	6 minutes
	Whole body SAR	Partial body SAR	Head SAR	Local SAR
Body Region	whole body	exposed body part	head	head	trunk	extremities
Operating Mode ↓	(W/kg)	(W/kg)	(W/kg)	(W/kg)	(W/kg)	(W/kg)
Normal	2	2 - 10 (b)	3.2	10 (c)	10	20
1st Level Controlled	4	4 - 10 (b)	3.2	10 (c)	10	20
2nd Level Controlled	>4	>(4 - 10) (b)	>3.2	>10 (c)	>10	>20
Short term SAR	The SAR limit over any 10 s period shall not exceed three times the stated values

Notes:

(a) Local SAR is determined over a mass of 10 g.

(b) The limit scales dynamically with the ratio "exposed patient mass / patient mass":

NORMAL OPERATING MODE: Partial body SAR = 10 W/kg – (8 W/kg * exposed patient mass / patient mass)
FIRST LEVEL CONTROLLED OPERATING MODE: Partial body SAR = 10 W/kg – (6 W/kg * exposed patient mass / patient mass)

(c) In cases where the orbit is in the field of a small local RF transmit coil, care should be taken to ensure that the temperature rise is limited to 1 °C.

In comparison to the short term, relatively intensive exposures described above, for long term environmental exposure of the general public there is a limit of 0.08 W/kg averaged over the whole body.^[4]

Mobile-phones SAR list

Brand	Model	Operating system	SAR (W/kg)
LG	Optimus 2X	Android	0.545
Lava	C 41		<1.6
HTC	Nexus One	Android	0.37
HTC	Wildfire	Android	0.754
BlackBerry	Torch	BlackBerry OS 6.0	0.91
BlackBerry	Curve 8320	BlackBerry OS 6.0	0.64
BlackBerry	Curve 8310	BlackBerry OS 6.0	0.72
BlackBerry	Curve 8520	BlackBerry OS 6.0	0.57
BlackBerry	Curve 8900	BlackBerry OS 6.0	0.63
BlackBerry	Curve 9300	BlackBerry OS 6.0	1.07
BlackBerry	Curve 9330	BlackBerry OS 6.0	0.96
BlackBerry	Z10	QNX	0.97 / In HotSpot Mode: 1.50
HTC	Surround	Windows Phone 7	0.439
Motorola	Flipside	Android	0.5
Samsung	Blue Earth		0.196
Samsung	Acclaim		0.29
Huawei	Ideos X5	Android	0.34
LG	Quantum	Windows Phone 7	0.35
Samsung	Haven		0.41
Samsung	Evergreen		0.41
HTC	7 Pro (Arrive)	Windows Phone 7	0.418
Samsung	Captivate	Android	0.42
Samsung	Smiley		0.43
Doro	PhoneEasy 410		0.445
Motorola	Devour	Android 1.6	0.45
Motorola	i890		0.45
Kyocera	Neo E1100		0.479
Samsung	Contour		0.49
HTC	Imagio		0.498
Samsung	Flight SGH-A797		0.505
Samsung	SGH-T249		0.51
Samsung	Rugby II SGH-A847(AT&T)		0.52
Nokia	E5	Symbian	0.88
HTC	EVO		1.03
Apple	iPhone 4	iOS 5.1	0.93
Motorola	Bravo		1.59
Motorola	Droid 2 Global	Android	1.58
Sony Ericsson	Satio (Idou)		1.56
Sony Ericsson	Xperia X10 Mini Pro	Android 2.1	1.55
Sony Ericsson	Xperia Active	Android 2.3.4	0.86
Sony Ericsson	Xperia Mini Pro	Android 2.3.4/4.0.4	0.46
Sony Ericsson	Spiro		1.03
Sony Ericsson	Naite		1.22
Kyocera Jax	S1300		1.55
Motorola	i335		1.53
Motorola	Defy	Android	1.52
Motorola	Grasp		1.52
ZTE	Salute		1.52
ZTE	Bade aka sanfransisco		1.35
LG	Rumor 2		1.51
Motorola	Droid	Android	1.49
Sanyo	Vero		1.49
Motorola	Droid 2	Android	1.49
HTC	Desire	Android	1.48
LG	Chocolate Touch		1.47
Karbonn	Talkies K91		0.98
Karbonn	K102		1.397
Karbonn	K444+		0.342
Karbonn	Spy K595		0.511
Karbonn	TnT KT60		1.03
Karbonn	A9	Android 2.3.6	0.68
Karbonn	A18	Android 4.0.3	1.5
Kyocera	Wild Card M1000		1.46
Kyocera	X-tc		1.45
Motorola	i576		1.45
Motorola	Stature i9		1.44
Motorola	Droid X	Android	1.43
Samsung	Galaxy S2	Android 2.3	0.960
Nokia	3310		0.99
HTC	Titan	Windows Phone 7.5	0.3
HTC	HD7	Windows Phone 7	1.15
Nokia	Lumia 800	Windows Phone 7.5	1.27
Nokia	Nokia 114	Symbian Series 40, 6th Edition	1.46
Nokia	Nokia 101	Symbian Series 30	1.28
Samsung	Galaxy S3	Android 4.0	0.48 (head), 1.29 (body/worn)
Samsung	Nexus S	Android	0.58
Samsung	Galaxy Nexus GT-i9250	Android 4.1	0.303
Apple	iPhone 4S	iOS	1.11
SONY	Xperia U	Android	1.22
Micromax	X263		2

References

^ For example see http://asadl.org/jasa/resource/1/jasman/v104/i3/p1705_s1
^ Jianming Jin (1998). Electromagnetic Analysis and Design in Magnetic Resonance Imaging. CRC Press. pp. §5.3.3 pp. 226ff. ISBN 978-0-8493-9693-9.
^ http://www.icnirp.org/documents/emfgdl.pdf
^ http://www.icnirp.org/documents/emfgdl.pdf A whole-body average SAR of 0.4 W/kg has therefore been chosen as the restriction that provides adequate protection for occupational exposure. An additional safety factor of 5 is introduced for exposure of the public, giving an average whole-body SAR limit of 0.08 W/kg.

External links

[1] For example see http://asadl.org/jasa/resource/1/jasman/v104/i3/p1705_s1

[2] Jianming Jin (1998). Electromagnetic Analysis and Design in Magnetic Resonance Imaging. CRC Press. pp. §5.3.3 pp. 226ff. ISBN 978-0-8493-9693-9.

[3] ttp://www.icnirp.org/documents/emfgdl.pdf

[4] ttp://www.icnirp.org/documents/emfgdl.pdf A whole-body average SAR of 0.4 W/kg has therefore been chosen as the restriction that provides adequate protection for occupational exposure. An additional safety factor of 5 is introduced for exposure of the public, giving an average whole-body SAR limit of 0.08 W/kg.

[1]

[2]

[3]

[4]

Calculation

Mobile-phones SAR list

See also

References

External links