Our Research in Electromagnetic Fields

Research activities in the area of Electromagnetic Fields is largely focused on expanding existing and developing new and innovative computational methods in electromagnetics (EM) both in the time and frequency domain. Our overall objective is to analyze real-world problems in electromagnetic engineering to support our close collaboration with external experimentalists, as well as our own activities addressing today's and future challenges in the design of microwaves, millimeter waves and terahertz devices, circuits and systems.

A fundamental understanding of EM phenomena on the macro, micro and nanoscale is critical in all areas of electromagnetic compatibility including industrial microwaves, biomedical use of electromagnetics including health care applications, the development of radically new sensing principles based on innovative electromagnetic structures and the design of RF and optical sub-systems for sensing, identification and communication. Our group is involved in many of the above activities at the leading edge and has earned international recognition for its significant contributions.

Since 2001 we have also been organizing EMC Zurich, a major international symposium, which is widely recognized as the most important conference in the field of electromagnetic compatibility.

Research Directions
Since the Electromagnetic Fields Group has become rather large, it is subdivided into five topical groups with different focus but strongly overlapping interests:

1. Optical Nanostructures and Plasmonics
2. Computational Electromagnetics
3. EMC, Metrology and Antennas
4. Electromagnetics in Medicine and Biology
5. Microwave Systems

The main foci of these topical groups are:

Development and application of numerical methods for computational EM and optics combined with numerical
optimization; design of antenna structures for radio frequencies, microwaves, and optics; metamaterials for
applications from 50 Hz up to optical frequencies, including industrial applications such as microwave oven sealing,
electrosmog protection, radar absorption, anti-reflective coatings, and infrared protection; LTCC RF front ends for
WLAN and Radio over Fiber applications; microwave and millimeter wave measurement techniques; metrology; EMC; sensors for medicine and biology, including SNOM and plasmonic sensors.

Coordinator: Prof. Dr. Christian Hafner

Nanoscale structures exhibit phenomena which can have very interesting applications at optical frequencies such as optical bandgaps, slow wave propagation, strong field enhancement based on plasmonic effects, optical nano jets, etc. These effects open new avenues to manipulate light. Well-known structures are photonic crystals, plasmonic waveguides, optical antennas, metamaterials, and scanning nearfield optical microscopes.

The behaviour of these phenomena caused by resonances or strongly coupled resonances, makes the numerical simulationof functional structures indispensable but computationally very demanding. Therefore, we are not only applying existing software but also developing new and computationally efficient numerical methods for the analysis of such structures. For example, we work on semi-analytic methodssuch as the multiple multipole program (MMP), the method of auxiliary sources (MAS), rigorous coupled wave analysis (RCWA), method of moments (MoM), finite difference time-domain (FDTD), finite elements (FEM) in time and frequency domain.

Numerical Optimization: To find an optimum configuration for functional nano structures many geometric parameters must be analyzed until a reasonable design is obtained. Due to a lack of design rules for optical nanostructures, we also develop and apply powerful numerical optimizers that are combined with our field solvers as well as with commercial software. From this, we obtain optimally performing nanostructures such as sharp bends in photonic crystal waveguides and in conventional optical waveguides (assisted by small local photonic crystals) with low reflection and radiation, photonic crystal power dividers, etc.

Metamaterials: The codes we develop are not restricted to optical frequencies and optical nano structures. Furthermore metamaterials are frequently manufactured at much larger scales as “proof of concept”. Therefore, we also apply our software to microwave and even low frequency applications such as metamaterials for “electrosmog” protection.

Plasmonics: Currently, plasmonic effects are highly attractive for focusing the light on very small, sub-wavelength areas. We intensively study such effects towards practical applications such as various ultra-small optical waveguide configurations for short distance interconnects, optical nanoantennas, scanning nearfield optical microscopes, and biological sensors.

Coordinator: Dr. Christian Engström

The continuous advancement of microwave circuits and electromagnetic devices towards increased functionality and performance requires simultaneous development of modeling tools that are able to keep up with the growing level of sophistication. Commercial EM simulation programs available today provide powerful design tools, however no single numerical method provides a universal solution and commercial codes often fail to accurately simulate high-end problems found in cutting-edge research. Therefore, research in computational EM is still essential to keep up with the increasing complexity of devices throughout the EM spectrum.

In this area we are working on discontinuous Galerkin methods (DG-FEM), which combine the high accuracy of high order Finite Element Methods (so called hp-FEM) but satisfy the equation in a sense closer to the Finite-Volume method (FVM). DG-FEM is a natural choice for wave-dominated problems with several advantages compared with standard FEM including explicit time stepping and easier coupling to other methods. The Finite-Volume method was the focus in the past and the in-house FVM-code has been applied to many structures, in particular spiral antennas and dielectric resonator antennas. The development of a discontinuous Galerkin code with high-order shape functions enables us to handle many challenging problems in computational EM.

Another promising method in computational EM is the least-square finite element method (LSFEM) which is a finite element method in the Rayleigh-Ritz setting and hence corresponds to minimization of a quadratic functional. Our current work includes an over-determined LSFEM.

We are also working on a Meshless Method in the Time-Domain. The basic idea of the method is to solve the governing differential equations on localized points with a given "radius of influence" rather than in a predefined polyhedral mesh. The advantage is an exceptional geometrical flexibility, since existing points can be moved or new points can be added to refine selectively the discretization. The combination of electromagnetic effects with other physical models appears promising in this framework.

Coordinator: Dr. Jan Hesselbarth

Whereas Antennas tend to define the form factor of a wireless system, the (primarily analogue) RF front-end is the main responsible for power consumption. Given a specific system requirement, the co-design of antenna and front-end will eventually lead to an optimum solution with respect to both size and energy efficiency. We developed know-how in several areas required for complete optimization of microwave front-ends, including antennas, filters, transceiver electronics, and packaging.

Our antenna research covers the HF to millimeter-wave frequency range. The in-house capabilities include various simulation tools, a prototyping workshop, and a measurement chamber operational up to 110 GHz.

Transceivers have been developed recently for 35 GHz radiometer applications (see picture) and for 5 GHz optically fed multilayer ceramic (LTCC) modules. We also applied LTCC to K-band and 60 GHz passive components, such as filters and beamforming networks.

Ongoing research covers body-mounted antennas, tuneable filters, and UWB transceivers for sensor networks.

Coordinator:  Dr. Pascal Leuchtmann

The design of microwave systems often includes computationally very demanding components and subsystems and requires understanding of complex physical processes of wave propagation in diverse environments and
wave interaction with intricate geometries. A combination of engineering expertise and a solid understanding of physics in general and electromagnetics in particular is required for this type of advanced applications.

Metrology: The task of reliably measuring electrical quantities at millimeter- and submillimeter-wave frequencies can be extremely challenging. Advanced metrology necessitates highly-accurate reference standards. The respective design methods for calibration tools necessitate state-of-the-art simulation techniques as well as careful erroranalysis techniques such as advanced statistical approaches. Our direct cooperation with national metrology laboratories and leading manufacturers of measurement equipment, cables and connectors is fruitful for all participants.

Electromagnetic compatibility (EMC): Unlike most engineering disciplines, EMC does not apply electromagnetic waves to achieving a direct purpose; rather it endeavors to inhibit undesired effects of electromagnetic interactions. More often than not, the interactions are second-order effects, making them even more challenging to identify and tackle. One of our current projects, in cooperation with a major industrial partner, addresses the sealing of high-power microwave energy, where a metamaterial-based technology was developed and is in the process of worldwide patenting.

Coordinator: Dr. Jürg Fröhlich

Since 2005 the ‘Group for Electromagnetics in Medicine and Biology’ is extending the research at the Laboratory towards applications of electromagnetic and optical principles in medical technology as well as biomedical research. In close collaboration with academia and industry different projects have been set up covering various topics including impedance spectroscopy, optical spectroscopy, magnetic resonance technology, wireless technologies for health care as well as risk assessment of electromagnetic fields.

Within these projects numerical simulations and experimental evaluations using specific model systems are applied in order to support the understanding of underlying principles relevant for specific technologies in the area of biomedical research. Results support the identification of further research opportunities as well as the development of industrial prototypes.

There is a strong trend towards non-invasive techniques for diagnosis in medicine in order to continuously monitoring vital parameters or to routinely record different parameters for treatment planning purposes. There, the entire
electromagnetic spectrum is of interest ranging from lowfrequency applications up to optics.

One technique of increasing interest is the impedance spectroscopy for the determination of changes in specific constituents via the changes in dielectric properties of tissues. The most prominent example is the application for noninvasive glucose monitoring. In order to gain an increased understanding of the causes for dielectric changes within tissue studying the processes on the cellular level is required. New methods and devices developed within the area of biotechnology allow for single cell analysis of different physical properties whilst changing the biological environment. In order to understand the measured results, appropriate dielectric models will be developed.

Another area in medical technology requiring electromagnetic expertise is Magnetic Resonance Imaging. Controlling the RF interactions between the instrument and the imaging subject is pivotal to high-field MRI. It is at the heart of both the safety and the performance of the emerging technology. Therefore the ability of accurately modelling the electromagnetic behavior will form an important step forward in ongoing, largescale efforts to render ultra-high-field MRI routinely applicable in biomedical research and, ultimately, in medical applications. Progress in modelling RF arrays interacting with biological samples will be relevant not only for the specific task of array design. It is also intended to support future efforts to monitor the safety of high-field MRI exams on a patient-by-patient basis.

The development of highly reliable wireless technologies in health care and the risk assessment of wireless technologies go hand in hand in order to gain a high as possible acceptance by health professionals and the public. On one hand the electromagnetic behavior of wireless technologies in the harsh electromagnetic environment have to be taken into account, on the other hand the increasing concern on potential effects on human health has to be addressed. One project therefore deals with the analysis and the design issues regarding the development of wireless patient body area networks. Different projects include the potential effects of electromagnetic fields on microbiological structures and contributions to other studies in the area of epidemiological assessment of health symptoms.

  See also