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.

Watch Mike Weldon introducing Acceleware's FDTD solution and it's practical applications:

As I mentioned in my last post, Acceleware has been doing GPU programming for 5+ years now, this makes us veritable seasoned veterans in NVIDIA’s ‘GPU computing ecosystem’. This fact might cause some to wonder why we only officially released the CUDA-based version of our FDTD libraries only a few months ago. The short answer is that it took a long time to port a code base that took 3+ years to build. The more interesting story however are the benefits and results of doing that port to CUDA. This is what I want to focus on in this post.

The foremost two benefits go hand in hand and they are performance and robustness. Before CUDA we were basically hijacking OpenGL, the graphics programming language, to do GPU computing. While this worked, there were many workarounds and kludges that were required to make sure things ran smoothly. We were actually quite proud of what we accomplished in terms of performance, but there was still some left on the table, that OpenGL just couldn’t get to. The other down side was that we didn’t make any friends at NVIDIA when we reported OpenGL computing bugs. “OpenGL isn’t made for computing” they would remind us at each reprise, a fact that couldn’t have been more obvious for our developers, or more painful for me.

For our fourth consecutive year, Acceleware will be exhibiting at the International Microwave Symposium (IMS) held in Boston from June 9th through June 11th.  I’m excited to see many familiar faces and to meet many new ones. We will be showcasing our products including our accelerated FDTD software, clustered solutions, and our linear algebra solvers.
IMS is one of the world’s leading microwave conferences.  We are always impressed by the diversity of industrial and academic applications that exhibit and present during Microwave Week.  Areas of focus vary from military to medical and commercial to academic.  We are excited that we can offer our products to all of these fields to speed up their designs and simulations!
Come by and visit us at Booth #2709! We look forward to showing you our products and talking about ways we can speed up your computions!