Energy harvesting is a promising technology that powers the electronic devices via scavenging the ambient energy. Piezoelectric energy harvesters have attracted considerable interest for their high conversion efficiency and easy fabrication in minimized sensors and transducers. To improve the output capability of energy harvesters, properties of piezoelectric materials is an influential factor, but the potential of the material is less likely to be fully exploited without an optimized configuration. In this paper, an optimization strategy for PVDF-based cantilever-type energy harvesters is proposed to achieve the highest output power density with the given frequency and acceleration of the vibration source. It is shown that the maximum power output density only depends on the maximum allowable stress of the beam and the working frequency of the device, and these two factors can be obtained by adjusting the geometry of piezoelectric layers. The strategy is validated by coupled finite-element-circuit simulation and a practical device. The fabricated device within a volume of 13.1 mm3 shows an output power of 112.8 μW which is comparable to that of the best-performing piezoceramic-based energy harvesters within the similar volume reported so far.

Energy harvesting is an appealing technology that makes use of the ambient energy which is otherwise wasted. Piezoelectric materials directly convert the elastic energy to the electric energy, and thus have a great advantage in scavenging vibrational energy for simplicity in device structure with relatively high power density. This paper provides an overview on the research of piezoelectric materials in energy harvesting in recent decades, from basics of piezoelectricity and working principle of energy harvesting with piezoelectric materials, to the progress of development of high-performance piezoelectrics including ceramics, single crystals and polymers, then to experimental attempts on the device fabrication and optimization, finally to perspective applications of piezoelectric energy harvesting (PEH). The criteria for selection of materials for PEH applications are introduced. Not only the figure of merit but also maximum allowable stress of materials are taken into account in the evaluation of their potential in achieving high energy density and output power density. The influence of the device configuration on the performance is also acknowledged and discussed. The magnitude and distribution of induced stress in the piezoelectric unit upon excitation by the vibration source play an important role in determining the output power density and can be tuned via proper design of device configuration without changing its resonant frequency. Approaches to address the issue of frequency match accompanying with the resonant mode are illustrated with literature examples. Usage of PEH devices can be extended to a variety of vibration sources in everyday life as well as in nature. Some appealing applications of PEH, such as in implantable and wearable devices, are reviewed. energy harvesting, ferroelectric materials, piezoelectricity, figure of merit, applications Citation:Song J D, Wang J. Ferroelectric materials for vibrational energy harvesting.

Pb(Zr1−x Hf x )O3 (x = 0, 0.1, 0.2, 0.5, 1) films were fabricated on Pt/Ti/SiO2/Si substrates using a chemical solution deposition process in this study. The effect of the Zr/Hf ratio on energy-storage performance was evaluated based on the measurement of P–E hysteresis loops. It is shown that the maximum polarization and the recoverable energy density decrease with the increase of the Hf concentration. The energy efficiency of the Hf-contained films is close to each other but higher than the PbZrO3 film. As a result, the Pb(Zr0.9Hf0.1)O3 film achieved in this work exhibited the highest recoverable energy density of 11.3 J cm−3 and a larger energy efficiency of 55% at 800 kV cm−1, exceeding those of either PbZrO3 or PbHfO3 single-component film. This enhancement was related with the size and homogeneity of the crystal grains.

Piezoelectric energy harvesters are expected to power trillions of miniaturized sensors. We theoretically analyze nanogenerators with aligned piezoelectric nanorods using formulaic solutions and finite-element simulation using COMSOL Multiphysics in order to explore the possibility of achieving excellent output performance. It is shown that for the same piezoelectric materials, using a rod-shaped unit will increase the piezoelectric constant d 33 by 33% compared with using a film, owing to less substrate clamping. In addition, when normal force is applied, the stress is concentrated in the nanorods. Therefore, in the case of applying normal force, the aligned nanorod array can generate an output power one or more orders of magnitude higher than films within the same volume. This type of nanogenerator will play an important role in the integration with miniaturized sensors in the off-resonant mode.