LiNbO3 films - a low-cost alternative lead-free piezoelectric material for vibrational energy harvesters
Résumé
Lead-free lithium niobate (LiNbO3) piezoelectric transducer is considered as a substitute to lead-based solutions for vibrational energy scavenging applications. Taking into account the much lower dielectric constant of LiNbO3 crystal compared to conventional piezoceramics (for instance PZT), we implement, in a global optimization approach, a thick single crystal film on silicon substrate with optimized clamped capacitance for better impedance-matching conditions. We design a piezoelectric cantilever based on (YXl)/36° LiNbO3 cut, enhancing the output voltage to achieve piezoelectric transducer performance compatible with harvesting device standards. For a cantilever with bending first resonant frequency of 1.14kHz, an output power up to 380μW is achieved, yielding a power density of 8.26μW.mm−2, therefore comparable to lead-based and -free piezoelectric harvesters, while featuring a widely used material with well-established production process (hence lowering the cost for instance). The harvesting capabilities of the device allows starting a sensor node (from zero energy initial conditions) after 9s only and then maintaining the possibility of sending data every 2s (each transmission event consuming approximately 420μJ) under continuous excitation.
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