High-Frequency (HF) electromagnetic (EM) field problems are understood to be problems for which the magnetizing effect of the displacement current cannot be neglected anymore as it is typically done for eddy current problems. Hence, HF problems and especially EM wave propagation problems can only be described and correctly modelled with the full set of Maxwell’s equations and with corresponding numerical techniques.

- Numerical analysis of HF-EM problems:

For the analysis of HF problems beside several commercial numerical software packages also proprietary in-house codes are developed at the institute. Finite Element Method (FEM) based codes as well as Partial Element Equivalent Circuit (PEEC) based codes are available at the IGTE.

- Numerical synthesis of HF components and devices:

Modelling and simulation of HF-EM problems applying FEM based tools typically lead to high computational costs. Therefore, such approaches are impractical for the numerical assisted synthesis of HF components and devices like e.g. antennas. Hence, for such synthesis problems we have developed within the last years an antenna optimization and synthesization framework which utilizes reduced order models such as PEEC or surrogate models for the computation of the forward problem in the numerical optimization process. Frequency domain descriptions and time domain simulation techniques are implemented in the framework. The framework has been utilized very successfully especially for the synthesis of RFID and NFC transponders in the past years.

- Electromagnetic Compatibility:

Beside the described application oriented research activities the HF group at the IGTE also conducts fundamental research on electromagnetic compatibility problems such as shielding, mode conversion as well as fundamental investigations on the detachment of electromagnetic waves from radiating structures and the description of the corresponding field regions.

*Some demonstrative examples are:*

- Equivalent circuit description of the EM-behavior of electrically small loop antennas for RFID and NFC applications.
- Influence of ferrite material and conductive material on the EM-behavior of NFC antennas.
- Standard conform synthesis of NFC loop antennas and antenna matching circuit for contactless payment applications.
- Modelling and numerical computation of coating currents for unbalanced feed symmetric antennas structures.
- Numerical computation of the periodic steady state solution for loop antennas with non-linear resistive loads.

*Distribution of the electric scalar potential for different types of voltage excitations. Left: Symmetrical voltage excitation. Middle and right: Unsymmetrical voltage excitations.*

*PEEC model of close coupled loop antennas for contactless payment applications.*

*Model of a coupled field-circuit problem consisting of two close coupled NFC loop antennas loaded with non-linear electric circuits. The PEEC method is used for modelling the NFC loop antennas.*

*Computed voltage signals at the non-linear electric circuit connected to the NFC loop antenna.*

*Scalar plot of the complex magnitude of the electric field intensitiy obtained from a full wave FEM simulation of an unbalanced feed dipole antenna.*

*3D plot of the reactive near-field of a loop antenna.*