SEMCAD workshop hosted by Dymstec and sponsored by SPEAG and Acceleware, October 2010

Last week I traveled to Seoul, Korea to take part in various customer events organized by NVIDIA and Dymstec, a distributor of Acceleware technology in Korea. The trip was organized along with one of our partners in EM simulation, SPEAG from Zurich. It was my first actual visit to Korea, as many times before I have transited through the airports at Kimpo and Incheon, but never have been able to experience the non-airport version of Korea. I was highly impressed by what Seoul offers in terms of a dynamic and technically advanced city. For example, the GPS systems in cars are equipped with 3D fly-through views and receive multiple inputs of information from traffic to ETAs. Another interesting feature of the GPS systems is the ability to watch live TV though I was wondering about the sanity of that as several cars passed me the baseball game playing on the dash. From a general economic activity point of view, I must have seen at least 200 building cranes during the six day visit creating new forests of office towers and condo buildings.

SAR, Cell Phones, and San Francisco

An interesting article (http://www.theglobeandmail.com/news/technology/san-francisco-passes-cell...) came across my desk this week. It talks about a recent vote in by the Board of Supervisors in San Francisco requiring that cell phone retailers post the specific absorption rate (SAR) for all cellular handsets that they sell. The article caught my attention because many cell phone manufactures use our FDTD libraries to model the electromagnetic field strengths, which are used to calculate SAR as a post processing step.

What is SAR?

SAR is a measure of the amount of power that is absorbed by a human body tissue in Watts/kg, averaged over a 1 gram or 10 gram mass of tissue. The FCC and other national government organizations are responsible for defining the safety limits for normal use.

How do you Measure SAR?

Because it is impractical (and inhumane) to insert a probe into someone’s head while they are using a cell phone, we rely on models to determine how much power the human body is absorbing. Since the absorption rate is highly dependent on the position of the cell phone antenna designers will run hundreds, thousands, or even tens of thousands of simulations to determine the SAR value for a given phone.

The other way to measure the SAR value is to create a physical model of the human head and use probes to measure the value. Ideally, simulations match the model results. Major discrepancies need to be resolved before the phone is sent to manufacturing.

Is Lower Better?

Sure. But if the value is too low, your phone will start dropping calls. Typically, antenna designers will work to minimize SAR while maximizing signal strength from the antenna.