Replicating human scalp properties for enhanced accuracy in the testing of bone conduction hearing devices

Abstract

This thesis investigates and develops an artificial human scalp replica for use in bone conduction hearing device testing, with the goal of improving the accuracy and reliability of bone conduction hearing device evaluations. The work was motivated by Cochlear Bone Anchored Solution’s need to enhance their existing head simulator, which previously lacked a component mimicking the mechanical properties of human scalp tissue. To achieve this, a wide range of silicone-based scalp materials were evaluated using three primary performance metrics: mechanical point impedance, attenuation and acoustic feedback. All measurements were conducted using a standardized measurement setup involving Cochlear’s HeadSim1 simulator. Additionally, a market investigation was conducted to collect new mechanical point impedance reference data from 19 human subjects under identical conditions to ensure comparability with the artificial materials. Multiple types of artificial scalps, including Ecoflex and FS10 variants, in-house crafted silicones, and molded custom shapes, were assessed through repeated measurements to ensure consistency and minimize errors. The findings reveal that Ecoflex0010, particularly the adaption developed in this thesis, best replicates human scalp properties. It demonstrates the lowest mean absolute error (MAE) in mechanical point impedance and attenuation combined, and performs well within acceptable ranges for acoustic feedback compared to clinical reference data. The aim of this study was fully achieved: a validated, usable artificial scalp that improves the fidelity of bone conduction hearing device testing was identified. The broader implication is an enhancement in preclinical evaluation tools for bone conduction hearing devices, leading to more reliable data and potentially reducing the need for clinical testing iterations. This contributes to better design decisions, increased patient safety, and faster innovation cycles in the field of bone conduction hearing device technology.