Speaker
Description
For the investigation of bone conduction mechanisms, cadaveric materials are often used. However, their application is limited by ethical concerns and logistics (specialized laboratories, availability). Furthermore, different preservation methods compromise reproducibility. For our research we adapted the head model developed by Irwansyah et al., aiming to accurately replicate the mechanical impedance ratio between soft tissues and bone by using PETG for the skull and Ecoflex 00-30 silicone for soft tissues. To utilize this head surrogate for contactless, quantitative assessment of the output of photoacoustic bone conduction systems measured by Laser-Doppler-Vibrometry, the light absorption properties of the soft tissues were adjusted using pigments to match those of human skin. When stimulated with a photoacoustic bone conduction hearing device at the mastoid, the measured skin-vibration velocities at the zygomatic arch at frequencies >3000 Hz were within 1 to 6 dB of values obtained from living participants. When stimulated using a conventional B81 bone conduction transducer at the mastoid the measured velocities at 500 Hz, 1000 Hz and 4000 Hz were within 8 dB of values obtained from living participants. Although the model shows a pronounced anti-resonance at 2000 Hz, where velocities deviated by approx. 15 dB from living-subject data, the surrogate reliably replicates a vibratory response under photoacoustic stimulation above 3000 Hz. The origin of the 2000 Hz anti-resonance can likely be attributed to structural simplifications of the surrogate. Future iterations will incorporate layered soft tissue geometries as well as a stiffer skull material and revised skull geometry to better resolve the anti-resonance and extend the validated frequency range.