<Dd> ρ (\ displaystyle \ rho) is the sample density </Dd> <Dd> V (\ displaystyle V) is the volume of the sample </Dd> <P> SAR measures exposure to fields between 100 kHz and 10 GHz (known as radio waves). 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 . </P> <P> When measuring the SAR due to a mobile phone the phone is placed against a representation of a human head (a "SAR Phantom") 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 . Measurements are made for different positions on both sides of the head and at different frequencies representing the frequency bands at which the device can transmit . Depending on the size and capabilities of the phone, additional testing may also be required to represent usage of the device while placed close to the user's body and / or extremities . Various governments have defined maximum SAR levels for RF energy emitted by mobile devices: </P>

What is mean by sar value in mobile
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