Speaker
Description
The work aims to generate audible sound by photoacoustic (PA) excitation of an optically absorbing target, with a future goal to develop a photoacoustics-based bone conduction hearing device. Very few studies have explored photoacoustic bone conduction hearing, existing work either fails to reach clinically relevant hearing levels (i.e. a minimum of 60 dB HL) or requires unsafe power levels. This study aims to estimate achievable hearing levels using skin safe PA excitation power (≤300 mW/cm2) in the near infrared (808 nm). We present experimental measurements on a range of PA targets with high optical absorption, high thermal expansion coefficient and low specific heat capacity. The amplitude of a laser was modulated with sinusoidal tones ranging from 250 Hz to 20 kHz and directed to the targets. Experimental measurements on phantoms like a skull simulator and a healthy human volunteer demonstrated the generation of audible sound in mid to high frequencies, although the observed amplitude was rarely above the hearing threshold. While we show that increasing the laser power increase sound pressure linearly, reaching, i.e., 60 dB HL with this approach would require excitation power on the order of 100 W, which is far beyond safety limits. Therefore, ongoing work focuses on optimizing PA target materials and excitation to improve photoacoustic conversion efficiency to safely achieve relevant sound levels.