Articulatory movements influence electromagnetic wave transmission through the vocal tract

TL;DR

This paper validates a finite element model of electromagnetic wave transmission through the human head during vowel pronunciation, enhancing understanding for silent speech interface development.

Contribution

It introduces a validated numerical model of electromagnetic propagation in the human head during speech, linking articulatory configurations to transmission characteristics.

Findings

Good qualitative agreement between simulations and measurements across subjects.

Transmission patterns are consistent for the same vowels, despite individual differences.

Electric field exhibits Mie scattering patterns within 1-6 GHz frequency range.

Abstract

This study experimentally validates a numerical model of electromagnetic propagation through the human head during the pronunciation of different vowels, with the goal of improving our understanding of the underlying physical phenomena. A realistic finite element model was created from magnetic resonance images acquired while pronouncing the vowels /a/, /i/, and /u/. The model was validated against scattering matrix measurements obtained from two subjects whose geometries were modeled. Despite several potential sources of discrepancy, the simulations and measurements showed good qualitative agreement, confirming the validity of the approach. Similar transmission coefficient patterns were observed across subjects for the same vowels. Within the investigated frequency range of (1-6 GHz), the electric field exhibited a Mie scattering pattern. Local minima and maxima in the transmission coefficient, characterizing different articulatory configurations, were correlated with local variations in the electric field amplitude. The transmission coefficient's shape results from an interplay between resonance patterns and antenna placement, while the degree of mouth opening influences the shape of scattering modes. Although technically challenging, this numerical approach proved effective for studying electromagnetic propagation in the human head. The resulting robust numerical model and improved understanding of the underlying physics are expected to facilitate the development of radio-frequency-based silent speech interfaces.