Theoretical and experimental study on traveling wave propagation characteristics of artificial basilar membrane

The traveling wave phenomenon in the artificial basilar membrane (ABM) plays a crucial role in the frequency selectivity and electromechanical signal generation of cochlear implants. Continuous measurement of traveling wave propagation remains challenging due to its rapid spatial displacement variation and the requirement for biomimetic conditions in liquid environments. To address this, we developed a laser Doppler optical scanning system with high spatiotemporal resolution, combined with a fixation device replicating cochlear boundary constraints, and successfully captured the traveling wave propagation process. The traveling wave characteristics of the ABM, including propagation time, velocity, frequency selectivity, and local resonance, are revealed. Experimental results indicate that fluid-mass loading and coupling effects significantly reduce the resonance frequency from 9.3-15.4 kHz in air to 1.9-4.9 kHz in liquid and decrease the propagation velocity from 199.20 m/s to 61.78 m/s under our typical experimental conditions. By correlating spatial modes and local resonances with theoretical analysis, we observe that as the resonance frequency increases, the traveling wave propagates faster, reducing propagation delay. The quantification of traveling wave propagation characteristics provides a critical theoretical and experimental foundation for improving the tonotopic accuracy and biological fidelity of cochlear implants.