Wave propagation across the skull under bone conduction: Dependence on coupling methods.

Tahmine S Farahmandi,Jongwoo Lim,Christof Röösli,Alexander M Huber,Ivo Dobrev,Flurin Pfiffner,Namkeun Kim

doi:10.1121/10.0009676

Abstract

This study is aimed at the quantitative investigation of wave propagation through the skull bone and its dependence on different coupling methods of the bone conduction hearing aid (BCHA). Experiments were conducted on five Thiel embalmed whole head cadaver specimens. An electromagnetic actuator from a commercial BCHA was mounted on a 5-Newton steel headband, at the mastoid, on a percutaneously implanted screw (Baha® Connect), and transcutaneously with a Baha® Attract (Cochlear Limited, Sydney, Australia), at the clinical bone anchored hearing aid (BAHA) location. Surface motion was quantified by sequentially measuring ∼200 points on the skull surface via a three-dimensional laser Doppler vibrometer (3D LDV) system. The experimental procedure was repeated virtually, using a modified LiUHead finite element model (FEM). Both experiential and FEM methods showed an onset of deformations; first near the stimulation area, at 250-500 Hz, which then extended to the inferior ipsilateral skull surface, at 0.5-2 kHz, and spread across the whole skull above 3-4 kHz. Overall, stiffer coupling (Connect versus Headband), applied at a location with lower mechanical stiffness (the BAHA location versus mastoid), led to a faster transition and lower transition frequency to local deformations and wave motion. This behaviour was more evident at the BAHA location, as the mastoid was more agnostic to coupling condition.

Highlights

In many clinical situations, bone conduction hearing aids (BCHA) are an option for many patients with conductive or mixed hearing loss (Hulecki and Small, 2011), as well as single sided deafness (Pfiffner et al, 2011)
This study is aimed at the quantitative investigation of wave propagation through the skull bone and its dependence on different coupling methods of the bone conduction hearing aid (BCHA)
Velocity data from experimental and finite element model (FEM) data were analyzed in two different ways: (1) Frequency distribution of deformation: quantifies the amount of deformation across an area of interest

Summary

Introduction

Bone conduction hearing aids (BCHA) are an option for many patients with conductive or mixed hearing loss (Hulecki and Small, 2011), as well as single sided deafness (Pfiffner et al, 2011). Measurements of vibration and deformation have demonstrated that the skull surface exhibits a complex spatialtemporal response, as seen in dry skulls (Ogura et al.,1979; McKnight et al, 2013), cadaver heads (Dobrev et al, 2017; Dobrev et al, 2020; Hoyer and D€orheide, 1983), and living subjects (McLeod et al, 2018). One of the first FE models (Taschke and Hudde, 2006) was used to understand the BC hearing mechanism, it was limited in its validation, geometry fidelity, and mechanical properties of the components (domains). The BC FEM was furthered by Kim et al (2014); it was limited to only two components (material domains), skull and polyurethane, and was only validated against experiential data without making any further investigations of the fundamentals of BC pathways. Brummund et al (2014) and Brummund et al (2015) and Carillo et al (2020) have developed FEM of the skull bone and ear canal; the geometry was limited to the temporal bone

Objectives

Results

Discussion

Conclusion