http://www.wired.com/gadgetlab/2009/10/cellphone-radiation-testing/Is radiation from cellphones dangerous or not? As consumers become increasingly glued to their phones, researchers, environmental organizations and cellphone industry groups debate this question.
So far, the answer is elusive. But you can find out how much radiation your head is absorbing from any given phone.
In the United States, the Federal Communications Commission sets the acceptable radiation standards for cellphones. As part of the device certification process, all handset makers have to offer a certificate from an independent lab that show how the device rates.
Cetecom is one of those labs. The company, based in Milpitas, California, performs radiation testing on devices like mobile phones, laptops, USB modems and sometimes even ankle monitors used by law enforcement. For each category of devices, the testing process is nearly identical.
Wired.com got a rare peek into the labs when we watched them test the iPhone with and without Pong, a new iPhone case that promises to reduce the amount of radiation hitting your brain by directing it up and away from your head.
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The iPhone is carefully positioned to a model of a human male head such that the antenna is near the jaw.
The effects of the radiation depend on the rate at which energy is absorbed by a mass of tissue, like your head. It is called the specific absorption rate (SAR) and measured in watts per kilogram (W/kg).
Based on a recommendation from industry group IEEE, the FCC limits SAR levels for partial-body exposure (including the head) to up to 1.6 W/kg (watts/kilogram), and whole body exposure to up to 0.08 W/kg. For hands, wrists, feet and ankles, the limit is up to 4 W/kg, averaged over 10 grams of tissue.
In general, the lower the SAR, the better the chances your phone is not a potential health hazard. To test the SAR, a mold in the shape of a human head is filled with a fluid formulated to simulate the electrical properties of the human tissue. This fluid typically is made up of salt, sugar, water and a viscosity additive.
The model for the human head is called SAM (standard anthropomorphic model). The size of the head is based on on the 90th-percentile dimensions of the male head, as determined by a study of U.S. Army personnel in the late 1980s — in other words, it’s a big head. Overall ambient temperature and humidity of the testing chamber is also controlled. In this case, the ambient temperature was at 70.7 degrees Fahrenheit and the relative humidity was 36.1 percent, approximating a beautiful fall day in the San Francisco Bay Area.
The first step in the testing process is to strap a phone (the iPhone in this case) to the head mold. The phone is taped to the mold in a way such that the antenna of the phone is positioned near the jaw. The testing system consists of a computer-controlled probe, a robotic arm, amplifier output that connects to a PC and a cable that connects to a universal radio communication tester.
“You can’t do a test with the phone dialing up AT&T because the signal strength would be all over the place,” says Albert Liu, vice-president of business development at Pong Research.
A radio communications tester is used to transmit a signal at full power to test the iPhone
The iPhone is placed in a simulated call with the radio communication tester, which transmits a signal at full power. Now the robotic probe scans the head, measuring the radio frequency energy that is absorbed at each point. The probe finds the region of the highest RF field and tthe location with the highest absorption rate.
Because brain tissue isn’t flat, SAR measurement in terms of W/kg is averaged over 1 g of tissue.
The robotic probe takes anywhere from 20 minutes to 30 minutes to complete the process. According to the certificate filed with the FCC, Apple’s iPhone 3G S has a maximum SAR of 1.19 W/kg when it’s held at the ear. Our test showed the iPhone 3G to have an SAR of 1.18 W/kg, or just about the same as the official FCC number.
Next up, testing the iPhone with a Pong case. The process is repeated and about 20 minutes later, the results are spewed out at with SAR clocking in at 0.42 W/kg.
In other words, Pong’s claims seem to be legitimate: Its case reduces the amount of radiation going from the iPhone into your head to a third of what it would be without the case. Contrary to what we initially wrote on the Pong case, it does appear to work.
An anechoic chamber is used to test the iPhone's signal strength.
Another test that handset makers often run on their devices is the signal strength test. The test is conducted in a specially constructed chamber called an anechoic chamber. Cetecom has a radio-frequency anechoic chamber where the interior surfaces are covered with radiation-absorbent material.
In this case, the iPhone is strapped to the model with the phone facing the ground. The test measures the effective level of radiated power that the phone emits while in a transmit mode. The burst power or the channel power from the phone is measured. The result is a spherical radiation pattern that yields the Total Radiated Power.
The test takes about 45 minutes including setup and is almost completely automated. A lab technician only needs to position the phone right and make sure the computer spews out the results.
In case of the iPhone, the total radiated power was 12.54 dBm (decibels per milliwatt) and remained almost the same with the Pong case, indicating that the sleeve has no effect on signal strength of the phone.
If you’re not an iPhone user, you can learn more about how much cellphone radiation you’re getting from your phone.
