Friday, June 16, 2017

Bio-electromagnetic simulation with Dr. Tilmann Wittig

Following the success of CST's recent bio-electromagnetic (bio-EM) workshops, we sat down with
Dr. Tilmann Wittig, Principal Engineer and Market Coordinator for bio-EM to share an introduction to this challenging and fascinating subject.

First, what do you do at CST?

I coordinate the “Bio-Electromagnetics” market here at CST. We refer to bio-EM whenever we simulate an EM source like e.g. a mobile phone, an MRI, a hearing aid or a pacemaker inside or nearby biological tissue, which in most cases will be a full or partial human body model. In other cases, we may also use animal models or just simplified homogeneous phantom models, representing a kind of average human tissue.

So, what is so special about simulating an EM problem containing tissues? 

One major reason is that bio-EM is one of the few domains where measurement of electromagnetic fields is mostly not an option since we cannot, or at least don’t want to, put field probes into a living human. From a simulation point of view, we face the special challenge of having “wet” tissues with a high content of water that makes both the permittivity and the material losses quite high. In addition, we typically have to deal with complex shapes and various layers of materials with significantly differing properties. Depending on the type of application, these properties can have a severe impact on the device design and functionality. To make such devices work in the presence of complex human tissue distribution is often a challenge!

What kinds of devices are being simulated?

MRI image: Courtesy of German Cancer Research Center (DKFZ)

We have two categories of devices we deal with: First, are devices we want to penetrate human tissue, that’s, for example, MRI or other imaging, pacemaker simulation, where the pacemaker is implanted, or any kind of implant for which there may be wireless charging. So, in that case, we want to be able to send an EM signal inside the body which is much more challenging than it may appear at first glance since high permittivity materials will reflect large amounts of the electromagnetic waves. The problem gets especially hard if we have several layers of biological tissue with very different permittivity e.g. from the skin, via fat and muscle to bone.

Second, we have devices where we just want to communicate in the presence of the body, like a mobile phone or various Bluetooth or soon IoT devices. With such devices, we’d be happy if nothing went inside the body because this means unwanted losses in the body due to penetration. That increases power assumption and affects the battery lifetime of the device but even worse: the problem is, we aren’t quite sure where that energy is placed and what effects it may cause inside the body. The only simulation can give us a hint how much power we have with a certain body position!
Due to the potential hazard, it is also a governmental requirement, every device that’s intended to work in or around the body needs a certificate of its SAR (Specific Absorption Rate) value. You’ll see what the SAR value is, for example, in the small print on your phone and the lower the value, the
better because less energy is going into your body.

Bio-EM is a challenging domain with a large variety of applications. It is important that a device which is intended to work inside or nearby the body is designed taking into consideration a body model to guarantee functionality in this environment, and that at the same time the power levels inside the body are well controlled. It’s interesting that these two kinds of optimization goals are contradictory. We have some customers who need penetration and they are trying to optimize to maximize the penetration like an MRI, and then we have customers who make mobile communication devices and they are optimizing for minimal penetration. 

Dr. Tilmann Wittig
Stay tuned for part two of this interview, in which Dr. Wittig shares the most interesting medical innovations being developed with the help of bio-electromagnetic simulation.

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