Ferroelectrets (also called piezoelectrets) are relatively young members in the family of piezo‐, pyro‐ and ferroelectric materials. They exhibit ferroic behaviour phenomenologically undistinguishable from that of traditional ferroelectrics, although the materials per se are essentially non‐polar space‐charge electrets with artificial macroscopic dipoles (i.e. internally charged cavities). Since ferroelectrets not only represent a scientific curiosity but also have great application potential, they have attracted tremendous attention from science and industry. The research and development of ferroelectrets has witnessed significant progress in the past few years. New ferroelectrets with large transverse piezoelectric activity, biodegradable ferroelectrets as well as 3‐D printed ferroelectrets are reported. Charging methods of high efficiency are proposed based on better understanding of the physico‐chemical processes during charging. New insights into the piezoelectricity of ferroelectrets are provided. The development of ferroelectret‐based piezoelectric‐magnetic multimodal transducer films opens up new avenues for the research of ferroelectrets. Particularly, more and more novel applications of ferroelectrets in flexible pressure sensors, health monitoring, energy harvesting, air‐coupled ultrasonic non‐destructive testing etc. are reported. Here, these exciting recent advancements in the field of ferroelectret research are reviewed and discussed.
The mode manipulation of Lamb waves plays an important role in damage detection and identification of damage types, location, and size. In this paper, we propose a composite phononic crystal (PC) plate with antisymmetric and symmetric PCs for realizing mode conversion from A0 to S0 mode of Lamb waves. The theoretical analysis, numerical simulations, and experimental validation are introduced and the mode conversion mechanism of the composite PC plate is systematically investigated. The effect of geometrical parameters on band structures of antisymmetric and symmetric PCs is first discussed. Then multi-physics field simulation models are developed and in-plane displacement fields are obtained in numerical simulations, which shows that the mode conversion is enhanced when the period number of the antisymmetric PC decreases and that of symmetric the PC increases. The composite PC plate specimens are fabricated with precision wire cutting technology for experimental measurements and the self-designed polyvinylidene fluoride (PVDF) comb transducer is used to stimulate the Lamb waves. The experimental results are consistent with the numerical simulations, which demonstrate that the proposed composite PC plate can achieve the mode conversion from A0 to S0 mode of Lamb waves. Our proposed structures have applicable values for the mode manipulation of Lamb waves in damage detection.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.