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What is SAR & What Does it Mean?

Cell Phone Radiation

People are increasingly familiar with the scientific measurement called SAR, which is how cell phone radiation is labeled. But few understand what SAR is, or how it is used in regulations.

SAR (which stands for Specific Absorption Rate) is a measurement of the rate at which electromagnetic radiation energy is absorbed by something (generally, human tissue).

So, when you hear that an iPhone 5 has a SAR of 1.18 watts per kilogram of tissue (W/kg), that is a measurement of how much radiation is absorbed by the human head. This is related to, but is not the same as, the actual EMF emitted by the iPhone itself.

When you hear that an iPhone has a SAR of 1.18 W/kg, it is tempting to think of the EMF emissions from an iPhone as being steady. However, this is not how wireless technology works, and it is not how SAR is utilized by regulators. If you use an EM meter to measure emissions from a device like an iPhone, you will quickly note that the actual radiation levels vary widely, depending on how the device is being used (whether it is making a call, for example, or sending an SMS; how far away the phone is from the towers carrying the data transmissions, etc.). And the amount of that radiation that is absorbed by your body will also vary, depending on how you are holding the device (is it against your head? Or in your hands? How far away from your body is it?).

While actual emissions and rate of absorption of EMF radiation varies widely and unpredictably, regulators have defined a system by which a single SAR value is established for these devices.

(Since so many of you reading this will likely have an iPhone, it is worth noting that the iPhone 5’s official SAR value is premised on holding the iPhone 1/8” away from your body. In fact, Apple’s documentation reads: “Carry iPhone at least 10mm away from your body to ensure exposure levels remain at or below the as-tested levels.”)

Official SAR values for devices like cell phones are determined in a lab, by holding a cell phone up to a dummy head, in several predetermined locations. The lab measures the various levels of radiation absorption in the dummy head. At the end of the experiment, the peak level of radiation absorption is determined, and that becomes the official SAR value for the device.

SAR Dummy
A SAR Testing Dummy Used by the Swiss Office of Public Health

In other words, the official SAR value of an iPhone 5 tells you what the peak level of radiation absorption was, in the lab dummy, under the precise conditions on the day, time and location that the phone was tested.

If you hold the phone in any different manner than it was held against the dummy, the exposure will be different. If you are further from the cell tower than the phone in the lab test, the radiation emitted by the phone will likely be higher than in the test, as more power is used to communicate over longer distances. If you are using your phone in your car or on a train, the emissions will likely be higher, as more power is used as your phone continually seeks new cell towers to relay your call. If you are using a headset and keeping the phone away from your body, the amount of radiation your body absorbs will likely be lower.

I guess the simplest way of stating it is this: The official SAR value of a cell phone is the peak level of radiation absorption measured under arbitrary circumstances that will almost certainly NOT match real life usage conditions.

So, official SAR values may present some sort of useful benchmark for the radiation emissions of different cell phone models, but do not fool yourself into thinking that official SAR values are “accurate”, that your digital devices emit consistent levels of EMF, or that your exposure is actually knowable, unless you take measurements yourself.

 


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2 thoughts on “What is SAR & What Does it Mean?

  1. […] can exceed FCC guidelines. And when these companies, like Apple, perform tests to determine the SAR of their phones, the phones are held away from the test […]

  2. […] or specific absorption rate is the standard by which cell phone EMF emissions are regulated. The maximum legal SAR in the […]

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