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1. Piezoelectric Hydrogels: Hybrid Material Design, Properties, and Biomedical Applications

   https://doi.org/10.1002/smll.202310110  

   Zhang, Chi; Kwon, Sun Hwa; Dong, Lin (February 2024, Small)

   Abstract Hydrogels show great potential in biomedical applications due to their inherent biocompatibility, high water content, and resemblance to the extracellular matrix. However, they lack self‐powering capabilities and often necessitate external stimulation to initiate cell regenerative processes. In contrast, piezoelectric materials offer self‐powering potential but tend to compromise flexibility. To address this, creating a novel hybrid biomaterial of piezoelectric hydrogels (PHs), which combines the advantageous properties of both materials, offers a systematic solution to the challenges faced by these materials when employed separately. Such innovative material system is expected to broaden the horizons of biomedical applications, such as piezocatalytic medicinal and health monitoring applications, showcasing its adaptability by endowing hydrogels with piezoelectric properties. Unique functionalities, like enabling self‐powered capabilities and inducing electrical stimulation that mimics endogenous bioelectricity, can be achieved while retaining hydrogel matrix advantages. Given the limited reported literature on PHs, here recent strategies concerning material design and fabrication, essential properties, and distinctive applications are systematically discussed. The review is concluded by providing perspectives on the remaining challenges and the future outlook for PHs in the biomedical field. As PHs emerge as a rising star, a comprehensive exploration of their potential offers insights into the new hybrid biomaterials. 

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2. Physics-Based Device Models and Progress Review for Active Piezoelectric Semiconductor Devices

   https://doi.org/10.3390/s20143872  

   Oh, Hongseok; Dayeh, Shadi A. (July 2020, Sensors)

   Piezoelectric devices transduce mechanical energy to electrical energy by elastic deformation, which distorts local dipoles in crystalline materials. Amongst electromechanical sensors, piezoelectric devices are advantageous because of their scalability, light weight, low power consumption, and readily built-in amplification and ability for multiplexing, which are essential for wearables, medical devices, and robotics. This paper reviews recent progress in active piezoelectric devices. We classify these piezoelectric devices according to the material dimensionality and present physics-based device models to describe and quantify the piezoelectric response for one-dimensional nanowires, emerging two-dimensional materials, and three-dimensional thin films. Different transduction mechanisms and state-of-the-art devices for each type of material are reviewed. Perspectives on the future applications of active piezoelectric devices are discussed. 

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3. Electric field-induced depolarization of direct current and alternating current poled PMN-PT single crystals

   https://doi.org/10.1063/5.0250172  

   Sun, Jeong-Woo; Xu, Zhengze; Lee, Sang-Goo; Jo, Wook; Jiang, Xiaoning; Ryu, Jong Eun (February 2025, Applied Physics Letters)

   Understanding the depolarization of ferroelectric materials caused by external stimuli is critical for maintaining the aligned polarization states. Although thermal depolarization in poled materials is well established, the mechanisms of electric field-induced depolarization remain largely unexplored. In this study, we investigate the electrical depoling behavior of [001]-oriented rhombohedral Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystals poled using direct current poling (DCP) and alternating current poling (ACP). We reveal that the ACP sample exhibits a lower reverse coercive field than the DCP specimen. We compare the effects of bipolar and unipolar electric fields applied in the reverse poling direction, analyzing the changes in permittivity and piezoelectric resonance. Piezoresponse force microscopy is employed to characterize domain configurations in poled and electrically depoled samples. Our findings suggest that property degradation may arise from the nucleation and growth of domains oriented opposite to the initial arrangement. 

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4. Ultrahigh Piezoelectric Performance through Synergistic Compositional and Microstructural Engineering

   https://doi.org/10.1002/advs.202105715  

   Yan, Yongke; Geng, Liwei_D; Zhu, Li‐Feng; Leng, Haoyang; Li, Xiaotian; Liu, Hairui; Lin, Dabin; Wang, Ke; Wang, Yu_U; Priya, Shashank (March 2022, Advanced Science)

   Abstract Piezoelectric materials enable the conversion of mechanical energy into electrical energy and vice‐versa. Ultrahigh piezoelectricity has been only observed in single crystals. Realization of piezoelectric ceramics with longitudinal piezoelectric constant (d₃₃) close to 2000 pC N^–1, which combines single crystal‐like high properties and ceramic‐like cost effectiveness, large‐scale manufacturing, and machinability will be a milestone in advancement of piezoelectric ceramic materials. Here, guided by phenomenological models and phase‐field simulations that provide conditions for flattening the energy landscape of polarization, a synergistic design strategy is demonstrated that exploits compositionally driven local structural heterogeneity and microstructural grain orientation/texturing to provide record piezoelectricity in ceramics. This strategy is demonstrated on [001]_PC‐textured and Eu³⁺‐doped Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃(PMN‐PT) ceramics that exhibit the highest piezoelectric coefficient (small‐signald₃₃of up to 1950 pC N^–1and large‐signald₃₃* of ≈2100 pm V^–1) among all the reported piezoelectric ceramics. Extensive characterization conducted using high‐resolution microscopy and diffraction techniques in conjunction with the computational models reveals the underlying mechanisms governing the piezoelectric performance. Further, the impact of losses on the electromechanical coupling is identified, which plays major role in suppressing the percentage of piezoelectricity enhancement, and the fundamental understanding of loss in this study sheds light on further enhancement of piezoelectricity. These results on cost‐effective and record performance piezoelectric ceramics will launch a new generation of piezoelectric applications. 

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5. Effects of piezoelectric energy harvesting from a morphing flapping tail on its performance

   https://doi.org/10.1016/j.apenergy.2023.122022  

   Alqaleiby, Hossam; Ayyad, Mahmoud; Hajj, Muhammad R.; Ragab, Saad A.; Zuo, Lei (January 2024, Applied Energy)

   Monitoring fish migration, which can extend over distances of thousands of kilometers, via fish tags is important to maintain healthy fish stocks and pre-serve biodiversity. One constraint of current fish tags is the limited power of their batteries. Attaching a piezoelectric element to an oscillating part of the fish body has been proposed to develop self-powered tags. To determine the functionality and potential of this technology, we present an analysis showing variations of the generated voltage with specific aspects of the tail’s response. We also perform numerical simulations to validate the analysis and determine the effects of attaching a piezoelectric element on performance metrics including thrust generation, propulsive efficiency, and harvested electric power. The tail with the attached piezoelectric element is modeled as a unimorph beam moving at a constant forward speed and excited by sinusoidal pitching at its root. The hydrodynamic loads are calculated using three-dimensional unsteady vor-tex lattice method. These loads are coupled with the equation of motion, which is solved using the finite element method. The implicit finite different scheme is used to discretize the time-dependent generated voltage equation. The analysis shows that the harvested electric power depends on the slope of the trailing edge, a result that is validated with the numerical simulations. The numeri-cal simulations show that, depending on the excitation frequency, attaching a piezoelectric element can increase or decrease the thrust force. The balance of required hydrodynamic power, generated propulsive power and harvested elec-trical power shows that, depending on the excitation frequency, relatively high levels of harvested power can be harvested without a high adverse impact on the hydrodynamic or propulsive power. For a specified frequency of oscillations, the approach and results can be used to identify design parameters where harvested electrical power by a piezoelectric element will have a minimal adverse impact on the hydrodynamic or propulsive power of a swimming fish. 

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