Semcad X Jungfrau Marks the Spot (the Hot Spot)

Now you can predict not only how much radio energy will be absorbed by human tissue but how much hotter the tissue will get

IMAGE: Schmid & Partner Engineering

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Semcad can simulate the radiation pattern around your cellphone—and predict the effect it will have on your brain.

Semcad X Jungfrau is an updated and very attractive program for simulating electromagnetic fields around the sources of radio-frequency (RF) energy. Engineers use such programs to design antennas, study electro­magnetic interference problems, and help bioscientists investigate the possible health risks of exposure to RF fields.

The program uses the finite-difference time-domain (FDTD) method. The user defines the geometry of the problem and puts together the sources of the field, together with objects that might influence it, such as metal conductors. The program then models what happens after the field is turned on by working out just a few cycles of the field at a time over small time increments. At each step it solves the field equations over a grid that covers the region of interest. The FDTD method is now a standard approach for simulating electromagnetic fields at radio frequencies and is employed in several other commercial programs for electro­magnetic field simulation.

The software originated in research at the Swiss Federal Institute of Technology, in Zurich. Now, after several commercial releases, it has evolved into a polished and complete package, with an extensive list of options and features. These include a variety of sophisticated methods to optimize and otherwise tweak calculations, which increase the flexibility of the program at the cost of added complexity.

Semcad’s charming nickname means ”maiden,” and the program’s clear graphical interfaceis indeed very alluring. It makes it easy to design the model to be simulated, and its postprocessor helps visualize the results of the calculations. Semcad can import ­models from several major CAD/CAM programs, as well as a variety of detailed numerical models of the human body.

The program’s latest version offers big gains in computation speed, thanks to a hardware accelerator card that ships with it (by Acceleware, http://www.acceleware.com). The company claims a 10-fold increase in the speed of computations, which I have not attempted to test. With the addition of the accelerator, a user with a late-model desktop computer with a few gigabytes of RAM can run large simulations that, until now, would have required a mainframe computer.

I installed and ran the program without difficulty on a Microsoft Windows XP machine with 3 GB of RAM. The program was easy, even fun to use, at least when it came to setting up and solving simple models. The documentation is clear and visually appealing. An extensive tutorial comes with more than 20 sample problems and an expansive manual. One sample problem, for example, finds the radiation pattern produced in an automobile with a Bluetooth antenna incorporated in its window; another calculates the power absorbed in the human head from a mobile phone. But it takes a lot of time to set up and run complex simulations with Semcad (or any other similar program), and some knowledge of electromagnetics and the FDTD method is necessary to get reliable results.

Schmid & Partner Engineering (http://www.speag.com), in Zurich, which makes the software, also sells the industry standard in equipment for measuring the absorption of RF energy in models of the human body. One of the firm’s founders, Niels Kuster, is a renowned investigator in that field. Unsurprisingly, Semcad has a strong focus on health and safety studies that involve human exposure to RF energy. It even has special features that facilitate such studies.

One of these features, in particular, promises to be influential and useful. In addition to being able to calculate electromagnetic fields induced within the body from a mobile phone, the program can also calculate the resulting temperature increase. Safety guidelines in most of the world are designed to avoid excessive heating of tissue. Conventional electromagnetic simulation programs can calculate only the absorbed power, not the temperature increase in tissue. Incorporating a thermal analysis facility into electromagnetic modeling software is a major step forward.

Competition in this field is intense, however. Remcom (http://www.remcom.com), in State College, Pa., has recently announced an update of a similar product, XFDTD 6.4, which also ships with an accelerator card and can calculate the temperature rise in the body from exposure to RF fields as well.

In addition to its full version, Schmid also sells a ”light” version of Semcad X for less than the cost of most electrical engineering textbooks. This version can nevertheless handle simulations of up to a million cells. More than a decade ago I wrote a review of a hugely expensive FDTD program called Mafia (IEEE Spectrum, December 1995), in which I hoped that competitive pressures would lead to inexpensive FDTD software for engineers with modest budgets. Semcad X Light will fill that function nicely, and perhaps it will help some of our students master this important part of modern EE practice.

In short, Semcad X, in both its versions, is a stellar program, and one that promises to have a major impact in some specialized fields involving the simulation of electromagnetic fields.

About the Author

KENNETH R. FOSTER, an IEEE Fellow, is a professor of bio­engineering at the University of Pennsylvania, in Philadelphia.

To Probe Further

To learn more about research in measuring RF, see ”Measure­ment of Equivalent Power Density and RF Energy Deposition in the Immediate Vicinity of a 24â''GHz Traffic Radar Antenna,” Q. Balzano et al., IEEE Transactions on Electromagnetic Compatibility , May 1995.

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