1 Department of Electrical Engineering, Technical University of Denmark2 Electromagnetic Systems, Department of Electrical Engineering, Technical University of Denmark3 Department of Mechanical Engineering, Technical University of Denmark
This thesis focuses on the wireless coupling between hearing aids close to a human head. Hearing aids constitute devices withadvanced technology and the wireless communication enables the introduction of a range of completely new functionalities. Such devices are small and the available power is limited, it is therefore important to characterize the wireless link-budget and tounderstand the mechanisms that control propagation of waves inside and outside the head. For this purpose, different approaches have been used. There are two objectives for this thesis. The first objective is to characterize the ear-to-ear wireless communication channel by understanding the mechanisms that control the propagations of the signals and the losses. The second objective isto investigate the properties of magneto-dielectric materials and their potential in antenna miniaturization. There are three approaches to study the ear-to-ear wireless communication link; a theoretical approach models the human head asa sphere that has the electrical properties of the head, a numerical approach implements a more realistic geometry of the head, and an experimental approach measures directly the coupling between the antennas near a real persons or a phantom head imitating the human head’s electrical properties. Each approach has advantages and disadvantages; the analytical approach gives accurate results and is very fast, though it does not treat complex structures. The numerical approach can treat complex structures but is limited by the electrical size of the structures and requires large memory and long processingtime. The experimental approach yields accurate coupling between the antennas but does not provides detailed information about the field distribution. Therefore, we combine all these three approaches to gain some understanding of the ear-to-ear wireless communication channel. A circular patch antenna was used to study the properties of the magneto-dielectric materials. In the thesis, we focused on three properties; efficiency, quality factor and bandwidth of the antenna. An analytical method is used to calculatethe properties of a low-loss circular patch antenna, while a numerical method was used to analyze a highloss circular patch antenna. The low-loss magneto-dielectric materials can potentially be used to miniaturize the size of the antennas, offering higher efficiency and wider bandwidth than the dielectric materials.