Wireless Communication for Hearing Instruments

On-body propagation for personal electronic devices, such as hearing instruments, ear buds and smartwatches has been studied at 2.4 and 5.8 GHz. The main purpose was the development of a propagation channel model that can calculate the path gain for any on-body link confguration.

The full-body-propagation model is based on a previously developed earto- ear model. A specific on-body far-field formulation was introduced to the ear-to-ear model, from which the antenna gain and electric field phase can be calculated. It was found that the introduction of the on-body far-field formulation resulted in an increase in the path-gain-calculation accuracy of the model.

The computational efficiency of the ear-to-ear propagation model is demonstrated by a conducted antenna-radiation-pattern-optimization study. The optimal on-body antenna radiation pattern was obtained for different electrical sizes of the antennas. The observed path-gain improvement was eight decibels. Furthermore, the results showed that the optimal radiation pattern focuses the energy in the directions of the highest geodesic ray density.

The full-body-propagation model is developed as an extension of the ear-toear propagation model. A novel approach to the tracing of the geodesic rays is presented. The rays are confined to the mesh surface of the three-dimensional human-body model. An updated energy spreading factor is defined, such that the path gain is not directly dependent on the total number of rays included in the calculations. The performance of the model was evaluated for four ear-topocket on-body links that consist of one ear antenna and four pocket antennas. The modeled path gain was compared with a full-wave reference simulation performed in Ansys HFSS over the frequency bands 2.0-3.0 GHz and 5.0-7.0 GHz. Good agreement was generally found between the model and the reference. The agreement was slightly better for the results at 2.4 GHz compared to 5.8 GHz.

A simple propagation model based on geometrical optics that can handle on-body wave propagation over concave body sections is proposed. The model is tested for a generic cylindrical configuration. The calculated path gain is compared with that of a full-wave reference simulation for different values of curvature, −4.0 to 0.0m⁻¹. Excellent agreement was seen between the modeled and simulated path gain for curvatures below −2.0m⁻¹. Above this value, a caustic of the geometrical optics eld was crossed and the path gain exhibited a singular behavior. On-body antenna characterization by means of practical measurements has been investigated. A novel two-scan method to solve the problem of phase reconstruction from magnitude-only measurements for on-body antennas has been developed and tested. The additional information required to reconstruct the phase is obtained from a two sets of measurements of the antenna under test in two distinct orientations in the measurement coordinate system, dened by the euler angles. The measured magnitudes are compared to a synthetically created radiation pattern through the spherical wave expansion, and the sum of the squared point-wise errors is attempted minimized. The method was tested for a realistic on-body conguration. It was able to accurately retrieve the magnitude, however, it was less eective in terms of the reconstruction of the phase.