A compounding strategy to boost the transduction coefficient in KNN-based piezoelectric composite ceramics for ultrasonic energy harvesting

Abstract

Piezoelectric ultrasonic energy harvesters (PUEHs), an emerging technology that utilizes ultrasonic excitation, have been integrated into various wireless power systems for functional applications. However, most of the current PUEHs use lead-based piezoelectric materials that are harmful to human health and the environment. Additionally, the energy transduction coefficient (d₃₃ × g₃₃) is a key factor in obtaining high-performance PUEHs, yet it is difficult to obtain both a high piezoelectric coefficient (d₃₃) and high piezoelectric voltage constant (g₃₃). Herein, we present a composite strategy of effectively compounding two precursor powders of (K,Na)NbO₃-based ceramics to modulate the piezoelectric coefficient and dielectric constant, thereby boosting d₃₃ × g₃₃ for optimizing ultrasonic energy harvesting. Benefiting from the evolution of overall polarization fluctuations in the composite system, the lead-free composites exhibit an enhanced d₃₃ × g₃₃ value of 10 260 × 10⁻¹⁵ m² N⁻¹, superior to those of most lead-free ceramics and even some lead-based ones. The composites were further manufactured into PUEHs, with ultrasound-induced adjustable outputs of up to ∼16 Vpp, a voltage efficiency of ∼10%, and an instantaneous power of ∼42 mW. The electricity generated by the PUEHs can directly light up a commercial LED array and can be stored in capacitors, showing great potential for being wireless power sources for next-generation micro-electronic equipment.