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By Stuart Nicol, APREL Laboratories

Specific absorption rate (SAR) is a measure of the amount of radio frequency (RF) energy absorbed by the body when using a wireless device. The Federal Communications Commission (FCC) and other regulatory bodies have adopted limits for safe exposure to RF energy that are expressed as SAR in W/kg. Several companies have developed SAR measurement systems that manufacturers of wireless products can use to physically test SAR associated with their products. In the process of designing an antenna used to validate one of these measurement systems -- the ALSAS-10U (APREL Laboratories SAR Assessment System), designed and developed by the systems team at APREL Laboratories -- there was a need to develop a simulation model along with rules and application that accurately predicts SAR measurement results to within a few percent without the need for significant prototype development and testing. This makes it possible to address SAR compliance problems in the early phases of the design process when problems can be fixed at a much lower cost because much less money has been invested in physical design changes. This article will explain the challenges that were overcome in the development of this model's rules and application for use.

No negative effects on human health have been demonstrated from the low levels of RF energy produced by cell phones and other wireless devices. But regulatory bodies have determined that the possibility remains that such effects may exist and so they have developed standards for exposure to RF energy. The FCC requires wireless phones to comply with a safety limit of 1.6 watts per kilogram over 1g of tissue (1.6 W/kg) in terms of SAR. Many countries in Europe and elsewhere use similar exposure guidelines developed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). These guidelines are described in standards EN50361 and IEEE 1528, which provide methods for measuring SAR that are nearly universally accepted by regulatory bodies. Several companies have introduced measurement systems that typically focus on the measurement of the electric field since E-field probes have fast time response and sufficient sensitivity for SAR measurements.

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•Case Study: Simulation Of Specific Absorption Rate Measurements Speeds Wireless Design