Specific absorption rate (SAR) is a measurement of the amount of radiation absorbed by humans while using a cell phone. Research is currently being done on whether larger SAR measurements correspond to adverse health effects, including higher risks of cancer in humans.
What is specific absorption rate (SAR)?
There is some confusion and misunderstandings behind SAR values for cell phones as well as other devices that have wireless connectivity. Specific absorption provides an accurate measurement for the amount of radio frequency exposure from cell phones which ensures that they are well within safety guidelines set by the FCC.
One would think that having a lower SAR on their cell phone would decrease the amount of radio frequencies a user is going to be exposed to; while this ratio provides an accurate estimate of RF energy exposure, it doesn't necessarily provide adequate information as to the average amount of RF exposure the user will encounter.
The FCC tests and records cell phones' SAR measurements to make sure that the device doesn't exceed a predetermined set exposure level. This is done to ensure that RF energy levels aren't too high for users. Each cell phone manufacturer is required by the FCC to include the worst conditions and most severe operating conditions on all operational frequency bands for the given cell phone.
SAR is a measurement that gives information on a device's RF radiation emission. It is, however, not predictive information; it's only able to measure the radiation present in the conditions in which it is tested. For example, cell phones alternate their operational power for optimal communications and do not operate at maximum power for long periods of time. While SAR should be considered when buying a new cell phone, it cannot ensure that higher exposure to RF will not occur during operation.
SAR measurement equipment. This arm carries a probe that measures the radiation in the human-shaped tub filled with dielectric liquid. Image courtesy of Emitech.
SAR Measurements in Phones
As mentioned above, higher SAR indicates that a device is emitting an increased amount of electromagnetic radiation. Typically, SAR is expressed in units of watts per kilogram (W/kg) in a 1g or 10g section of tissue.
Cell phones can communicate with other devices by sending and receiving signals to local cell sites. A cell site includes an antenna and various electronic communications equipment are placed on top of a radio tower, thus creating a cellular network. These cell networks use RF waves, which is a form of electromagnetic energy that has energy levels between FM (frequency modulation) radio waves and microwaves.
RF waves—like FM radio waves, microwaves, visible light, and infra-red—is non-ionizing radiation. In large enough amounts, non-ionizing radiation can cause harm to tissue. In RF radiation's case, that harm is generally in the form of heating. See the graphic below to see where phones sit on the spectrum of radiation-emitting devices.
An illustration of the electromagnetic spectrum. Image courtesy of the National Cancer Institute.
The RF waves from a cell phone emit from the antenna, which is a part of a device. The RF waves have a maximum amount of energy as soon as they are emitted from the phone. While the antenna is close to the head, the user is more exposed to RF energy and the body tissue closest to the phone absorbs the energy.
Some factors that affect how much RF energy a person is exposed to are:
- The model of phone being used: different phones emit different amounts of energy per gram of body tissue.
- The amount of cell phone traffic in the area: more traffic requires more energy to acquire a decent signal.
- The distance and path to nearest cell site: the further the distance, the higher amount of energy is required to acquire a good signal.
PhonAndroid, a French technology forum and news website, recently released a list of smartphones with their SAR. The Samsung Galaxy Note 7 Edge had the lowest on the list, measuring at 0.264 W/kg.
While there are spotty (pun intended) studies on the risk EM radiation has on humans, it is good to be aware and proactive. There are practices that can mitigate your risk, such as keeping your cell phone away from your heart, hips, genitals, etc. for long periods of time. Another good practice is to keep your phone away from yourself while sleeping at night.
Alternative methods include procuring a radiation-shielding phone case. Pong is a company that manufactures such cases with the goal of minimizing radiation exposure. Pong's president, Shannon Kennedy, stated that the purpose of the case is to redirect the RF energy away from your head. Below is an illustration of the iPhone 3GS without and with the case.
Image courtesy of Pong
In 2009, Wired magazine sat in on a test that showed legitimacy to Pong's claim that their cases reduce exposure to radiation from phone usage. Whether this radiation is actually harmful in the first place is less clear. But it doesn't seem that these cases are hurting anything, at least. Some people may choose a "better safe than sorry" approach.
Waiting for the Science
The long and short of it is that the most recent generation of cellphones has a decreasing measurement of SAR. But there is no evidence to say that this will result in less exposure to radiation overall—nor that said radiation will cause cancer.
The National Toxicology Program released in May of 2016 their initial findings on a long-term study on the effects of cell phone radiation on the health of rats. Until clearer conclusions are found, however, the WHO classifies radiofrequency electromagnetic fields as "Group 2B": "possibly carcinogenic". For more information on the concerns about the carcinogenic effects of cell phone use, visit the National Cancer Institute website.
On the side of device design, it's likely that radiation-resistant phone cases and packaging will be developed sooner than phones that eliminate radiation emissions. Until research shows that higher SAR measurements correspond to higher incidences of cancer, device developers probably won't make radiation minimization a priority. In the meantime, it's good to know that we're a little less vulnerable to the potential risks we take every time we take a call.