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Piezoelectric materials are a class of materials that can generate an electric charge when subjected to mechanical stress, or vice versa. These materials have a wide range of applications, from sensors and actuators to energy-harvesting devices and medical implants. Recently, there has been growing interest in using 3D printing to fabricate piezoelectric materials with complex geometries and tailored properties. Three-dimensional printing allows for the precise control of the material's composition, microstructure, and shape, which can significantly enhance piezoelectric materials' performance. Three-dimensional printing has emerged as a promising technique for fabricating piezoelectric materials with tailored properties and complex geometries. The development of high-performance piezoelectric materials using 3D printing could have significant implications for various applications, including sensors, energy harvesting, and medical devices. In this review paper, 3D printing methods for piezoelectric materials, their advantages and disadvantages, representative piezoelectric ceramics, and examples of 3D printing are presented. Furthermore, the applications utilizing these materials are summarized. [ABSTRACT FROM AUTHOR]

Broadband mechanical energy harvesting implies stable output power over a wide range of source frequency. Here we present a cost-effective solution towards achieving broadband response by designing a magnetically coupled piezoelectric energy harvester array that exhibits a large power density of 243 μW/cm 3  g 2 at natural frequency and bandwidth of more than 30 Hz under 1 g acceleration. The magnetically coupled piezoelectric energy harvester array exhibits dual modes of energy harvesting, responding to both stray magnetic field as well as ambient vibrations, and is found to exhibit the output power density of 36.5 μW/cm 3  Oe 2 at 79.5 Hz under the ambient magnetic field while maintaining the broadband nature. The magnetically coupled piezoelectric energy harvester array was demonstrated to harvest continuous power from a rotary pump vibration, an automobile engine vibration and a parasitic magnetic field surrounding a cable of an electric kettle. These demonstrations suggest that the magnetically coupled piezoelectric energy harvester array could serve the role of a standalone power source for wireless sensor nodes and small electronic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] Acoustic energy harvesting (AEH) has emerged as a promising powering process for the sustainable self-powered operation of wireless sensors in wearable, biomedical, and industrial applications. However, despite the abundance of sound sources in the environment, intrinsically low acoustic energy density still poses a critical challenge; therefore, the development of various sound amplification structures, such as Helmholtz resonators (HRs), phononic crystals, and acoustic metamaterials is required. In this study, we combined two distinct sound amplification mechanisms, Helmholtz resonance and omnidirectional acoustic wave focusing, to generate a sufficiently high power output within an ambient sound environment at practically low frequencies (< 1 kHz). A two-degree-of-freedom model was developed to systematically design a HR integrated with a piezoelectric device (HR-PEH). Subsequently, the HR-PEH was incorporated with a circularly symmetric gradient index phononic crystal (GRIN PnC) structure that enabled omnidirectional sound focusing. Finally, we constructed a coupled acoustic system GRIN-HR-PEH. Analytical modeling and experimental characterization revealed the existence of two distinct dual operating frequencies for power maximization: mechanical and acoustic resonances, which offers design flexibility in coupled AEH systems. As a result, the coupled GRIN-HR-PEH system yielded an output power of up to 4.1 mW under an ambient incident sound pressure of 47 dB, satisfying the power requirements of practical applications. • A gradient-index phononic crystal and Helmholtz coupled structure is proposed as a synergistic sound amplification mechanism. • The hybrid system exhibits omnidirectional acoustic energy focusing and harvesting capabilities. • The proposed system yields a remarkable output power generation of 4.1 mW at a low frequency of 471 Hz. [ABSTRACT FROM AUTHOR]

The energy convergence efficiency (η) and dimensionless figure of merit ( DFOM) of CuO-added ( Na0.5 K0.5) NbO3 ( CNKN) ceramics are larger than those of NKN ceramics because of their large Qm values and small dielectric losses. Moreover, the η and DFOM values of CNKN ceramics are comparable to those of P-5C ceramics, which exhibit the highest η and DFOM. Furthermore, the CNKN harvester exhibits a high power density of 12 mW/cm3 at 93 Hz with a load resistance of 250 kΩ; this is similar to the PZT-based energy harvester, indicating that the CNKN ceramic is a good candidate material for energy harvesters. [ABSTRACT FROM AUTHOR]

[Display omitted] • A hybrid energy harvester, comprising a piezoelectric cantilever mounted on a thermoelectric generator, is proposed to enhance heat dissipation induced by cantilever vibration. • The increased power outputs of thermoelectricity and piezoelectricity are numerically analyzed. • The energy harvesting performance of the hybrid energy harvester is compared with that of a conventional harvester, composed of individually separated energy harvesters, to demonstrate its superiority. • Field tests, including wireless IoT device operation and vehicle engine test, verify that the harvester can operate in unstable conditions where inconsistent environmental vibration or heat pulse exist. Hybrid energy harvesters, using multiple harvesting mechanisms, have been proposed to overcome the limitations of single-mode energy harvesters. However, since the most hybrid harvesters have merely combined the energy generated by each mechanism, they could not synergistically enhance the output beyond a simple additive approach. In particular, although thermoelectric-piezoelectric hybrid energy harvesters have been explored for simultaneously utilizing ambient thermal–mechanical energy flows, the conventional design could not achieve the expected sum of separately harnessed individual energy outputs. Moreover, amplifying thermoelectric efficiency using the actively adjusted thermal energy flows through the piezoelectric beam dynamics has not been reported so far. Here, we propose an advanced design of the hybrid energy harvester that combines piezoelectricity and thermoelectricity, resulting in a higher final power generation. The piezoelectric cantilever beam was adopted to leverage oscillation-induced heat dissipation, which increases temperature gradients, prevents thermal saturation and sustains thermoelectric power generation. Cooling capabilities of thermoelectric generators were investigated with respect to cantilever designs, showing that the trapezoidal (narrow) cantilever design exhibits the highest displacement and heat dissipation. Furthermore, finite-element analysis validates the experimental findings to confirm consistent trends with the measured heat dissipation. The hybrid energy harvesting method achieves a power output of 7.619 mW in the presence of 0.5 g vibrational source, more than 50 % increase compared to the absence of vibration. The amplified thermoelectric-piezoelectric generators demonstrate their synergetic performances in powering IoT sensors and harvesting thermal–mechanical energy flows in automobile engines. This outcome highlights that rationally designed hybrid energy harvesters in considering thermal and vibrational characteristics can significantly boost the power output beyond a simple assembly. [ABSTRACT FROM AUTHOR]

Abstract: (1−x)Pb(Zr0.47Ti0.53)O3–xPb[(Zn0.4Ni0.6)1/3Nb2/3]O3 [(1−x)PZT–xP(ZN)N] ceramics with 0.26≤ x ≤0.31 were sintered at 1100°C, and their energy harvesters were fabricated. All specimens exhibit a similar energy convergence efficiency. However, the transduction coefficient (d 33 × g 33) increased with x, reaching 21.5×10−15 m2/N for the x =0.31specimen; the figure-of-merit of the specimens shows a similar variation. The output energy density of the energy harvester also increased with x, and a high output energy density of 231mW/cm3 was obtained for the harvester fabricated using the x =0.31 specimen, indicating that the d 33 × g 33 value significantly affects the output energy density of the energy harvester. [Copyright &y& Elsevier]