RF energy – or radiation – is just another name way of referring to radio waves. According to the FDA, RF
radiation “is one form of electromagnetic energy which consists of waves of electric and magnetic energy
moving together (radiating) through space.” All energy waves are classified based amplitude – the height
of the wave – and frequency – the distance between the waves or their wavelength. As shown in the figure below, radiation is also classified as “ionizing” or “non-ionizing” based on the impact it has when interacting with other matter.
Higher frequency radiation such as X-rays and Gamma rays have the capability to remove an electron
from an atom, breaking them down into smaller parts to create ions. This “ionization” can potentially
break down the molecules comprising the impacted atoms causing damage and interfering with their
proper function. This is why your dentist will drape a lead cover over you when x-raying your teeth. Ionizing
radiation can also break down human DNA strands leading to cancer.
Lower frequency radiation is “non-ionizing”, so when interacting with organic material – such as humans
– the atomic or molecular structures are not altered and the result is simply heat. We use microwaves to
heat our food and infrared heaters to warm our homes. However, long term exposure can still be detrimental.
You would not want to stand next to a microwave oven in use without any EMI shielding enclosing
the device. When it comes to assessing the hazardous impact on humans, the overall dosage of
radiation is not the sole contributor but also the accumulation of radiation over time.
Cell phone radiation level varies from device to device and is measured by the SAR. As stated previously,
the specific absorption rate or SAR is a measure for the energy absorbed by the body when exposed to a
radio frequency (RF) electromagnetic field. A mobile device’s SAR rating is used to estimate the maximum
rate of RF energy absorption by a user’s head and body when using the device.
According to the FCC, SAR testing uses standardized models (a test dummy) of the human head and
body that are filled with liquids that simulate the RF absorption characteristics of different human tissues.
The SAR test dummy is based upon a large adult male (6’2” tall and 220 pounds) called the Specific Anthropomorphic Mannequin, or SAM. 97% of the population is smaller than the SAM model, meaning that
only 3% of cell phone users are represented. In order to determine compliance, each cell phone is tested while operating at its highest power level in all the frequency bands in which it operates, and in various specific positions against the dummy head and body, to simulate the way different users’ typically hold a cell phone, including to each side of the head.
To test cell phones for SAR compliance, the phone is precisely placed in various common positions next
to the head and body, and a robotic probe takes a series of measurements of the electric field at specific
pinpoint locations in a very precise, grid-like pattern within the dummy head and torso. All data for each
phone placement is submitted as a part of the equipment approval test report for final authorization. In
the U.S., the FCC requires that cell phone manufacturers conduct their SAR testing to include the most
severe, worst-case (and highest power) operating conditions for all the frequency bands used in the USA
for that cell phone. The SAR values recorded on the FCC’s authorization and in the cell phone manual to
demonstrate compliance with Commission rules indicate only the highest single measurement taken
for each frequency range that the particular model uses. FCC approval means that the device will never
exceed the maximum levels of consumer RF exposure permitted by federal guidelines, but it does not
indicate the amount of RF exposure consumers experience during normal use of the device.
A recent study by Bundesamt für Strahlenschutz in Germany shows the amount of RF energy emitted
while a cell phone is held close to the ear, by brand and model. While the FCC in the US sets the standard
for phones at 1.6 W/kg. In contrast, the Blue Angel standard in Germany requires that phones have a SAR
of no more than 0.60 W/kg.
Looking for a material that can redirect RF without interfering with cell phone design? Check out our RF shielding materials.