Intrinsic vibration regulation of piezoelectric bone conduction devices: Dynamic damping control via shear-thickening fluids

To address the challenges of uneven frequency response and pronounced resonance peaks in piezoelectric bone conduction devices—particularly at mid-to-high frequencies, which contribute to a perceptually harsh auditory experience—this study proposes a novel dynamic damping control strategy utilizing a shear-thickening fluid (STF). The approach involves encapsulating a nano-SiO2/polyethylene glycol-400-based STF within the piezoelectric transducer assembly, exploiting its intrinsic rheological characteristics: low viscosity under low shear rates and a significant viscosity increase under high shear rates. This enables self-adaptive damping modulation without the need for external control circuits. At low frequencies, the STF behaves as a near-Newtonian fluid, providing stable damping and ensuring efficient mechanical vibration transmission. As frequency increases, rising shear rates induce a progressive enhancement in fluid viscosity, thereby increasing damping and attenuating the mid-to-high-frequency responses. Within resonant frequency bands, large-amplitude vibrations promote the formation of transient particle clusters in the STF, leading to a sharp rise in dynamic viscosity and the loss modulus. This nonlinear, intensity-dependent damping effect effectively suppresses resonance peak amplitudes. Experimental results show that the STF-integrated transducer maintains consistent equivalent sound pressure levels at low frequencies while significantly reducing mid-to-high-frequency gains. The overall frequency response is notably flattened, and subjective evaluations indicate a marked reduction in perceived auditory harshness. Importantly, the proposed method requires no structural modifications to the device or any alterations to the driving circuitry, offering a simple, structurally compatible, and effective solution for optimizing the acoustic performance of piezoelectric bone conduction devices.