Recent Developments in the Structure, Properties, and Applications of Ferroelectric Polymers

Much work has been published on the design of ultrasound transducers using piezoelectric ceramics, but a great deal of this work does not apply when using the piezoelectric polymers because of their unique electrical and mechanical properties. The purpose of this paper is to review and present new insight into seven important considerations for the design of active piezoelectric polymer ultrasound transducers: piezoelectric polymer materials selection, transducer construction and packaging requirements, materials characterization and modeling, film thickness and active area design, electroding selection, backing material design, and front protection/matching layer design. Besides reviewing these design considerations, this paper also presents new insight into the design of active piezoelectric polymer ultrasonic transducers. The design and fabrication of an immersible ultrasonic transducer, which has no adhesive layer between the active element and backing layer, is included. The transducer features direct deposition of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer onto an insulated aluminum backing substrate. Pulse-echo tests indicated a minimum insertion loss of 37 dB and -6 dB bandwidth of 9.8 to 22 MHz (71%). The use of polymer wear-protection/quarter-wave matching layers is also discussed. Test results on a P(VDF-TrFE) transducer showed that a Mylar/sup TM/ front layer provided a slight increase in pulse-echo amplitude of 15% (or 1.2 dB) and an increase in -6 dB pulse-echo fractional bandwidth from 86 to 95%. Theoretical derivations are reported for optimizing the active area of the piezoelectric polymer element for maximum power transfer at resonance. These derivations are extended to the special case for a low profile (i.e., thin) shielded transducer. A method for modeling the non-linear loading effects of a commercial pulser-receiver is also included.

Photoacoustic configuration studies were performed to measure the water vapor permeability of the polymeric PVDF transfer membranes with a pore size of 0.45 µm and a thickness of 117 and 119 µm, taking advantage of the characteristic that the polyvinylidene difluoride (PVDF), once polarized by the corona poling, creates a piezoelectric polymer. Polymeric membrane measured polarized as a piezoelectric polymer and an unpolarized ferroelectric polymer. Polarized and non-polarized PVDF membranes were developed for the two experimental photoacoustic detection of permeability tests; the first one was used to measure the humidity of bi-distilled water, and the second one was characterized with artificial tears. The obtained results show that PVDF membrane has different permeability coefficient for water and artificial tears, and at the same time, pores in the tested membranes change sizes depending on the liquid used. The results of the permeability and pore size of the PVDF membranes provide insight into vapor transport mechanisms that may inform the future development of humidity sensors.

The measurement of quality in auditorium acoustics by subjective scaling methods—A review of developments in theory and practice

In this paper a review of the recent developments in the theory of a slowly oscillating low aspect ratio, pointed wing at sonic speed is presented, using the concepts of the parabolic method, the equivalence rule and a iteration method to approximately incorporate the thickness effect in the analysis.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComments upon Recent Developments in Theory of FiltrationB. F. Ruth, R. E. Montonna, and G. H. MontillonCite this: Ind. Eng. Chem. 1931, 23, 7, 850–851Publication Date (Print):July 1, 1931Publication History Published online1 May 2002Published inissue 1 July 1931https://doi.org/10.1021/ie50259a036RIGHTS & PERMISSIONSArticle Views57Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (326 KB) Get e-Alerts

Theories of generation of acoustic and magnetohydrodynamic waves are briefly reviewed with a special emphasis on their applicability to stellar convection zones. Recent developments in these theories and possible directions for future studies are discussed. A new approach allowing to extend the Lighthill-Proudman theory of sound generation to a non-isothermal medium is also presented.

Despite extensive research on piezoelectric polymers since the discovery of piezoelectric poly(vinylidene fluoride) (PVDF) in 1969, the fundamental physics of polymer piezoelectricity has remained elusive. Based on the classic principle of piezoelectricity, polymer piezoelectricity should originate from the polar crystalline phase. Surprisingly, the crystal contribution to the piezoelectric strain coefficient d31 is determined to be less than 10%, primarily owing to the difficulty in changing the molecular bond lengths and bond angles. Instead, >85% contribution is from Poisson's ratio, which is closely related to the oriented amorphous fraction (OAF) in uniaxially stretched films of semicrystalline ferroelectric (FE) polymers. In this perspective, the semicrystalline structure–piezoelectric property relationship is revealed using PVDF‐based FE polymers as a model system. In melt‐processed FE polymers, the OAF is often present and links the crystalline lamellae to the isotropic amorphous fraction. Molecular dynamics simulations demonstrate that the electrostrictive conformation transformation of the OAF chains induces a polarization change upon the application of either a stress (the direct piezoelectric effect) or an electric field (the converse piezoelectric effect). Meanwhile, relaxor‐like secondary crystals in OAF (SCOAF), which are favored to grow in the extended‐chain crystal (ECC) structure, can further enhance the piezoelectricity. However, the ECC structure is difficult to achieve in PVDF homopolymers without high‐pressure crystallization. We have discovered that high‐power ultrasonication can effectively induce SCOAF in PVDF homopolymers to improve its piezoelectric performance. Finally, we envision that the electrostrictive OAF mechanism should also be applicable for other FE polymers such as odd‐numbered nylons and piezoelectric biopolymers.

For many years, the idea of a human with bionic muscles immediately conjures up science fiction images of a TV series superhuman character that was implanted with bionic muscles and portrayed with strength and speed far superior to any normal human. As fantastic as this idea may seem, recent developments in electroactive polymers (EAP) may one day make such bionics possible. Polymers that exhibit large displacement in response to stimulation that is other than electrical signal were known for many years. Initially, EAP received relatively little attention due to their limited actuation capability. However, in the recent years, the view of the EAP materials has changed due to the introduction of effective new materials that significantly surpassed the capability of the widely used piezoelectric polymer, PVDF. As this technology continues to evolve, novel mechanisms that are biologically inspired are expected to emerge. EAP materials can potentially provide actuation with lifelike response and more flexible configurations. While further improvements in performance and robustness are still needed, there already have been several reported successes. In recognition of the need for cooperation in this multidisciplinary field, the author initiated and organized a series of international forums that are leading to a growing number of research and development projects and to great advances in the field. In 1999, he challenged the worldwide science and engineering community of EAP experts to develop a robotic arm that is actuated by artificial muscles to win a wrestling match against a human opponent. In this paper, the field of EAP as artificial muscles will be reviewed covering the state of the art, the challenges and the vision for the progress in future years.

Reviews - Selected papers of Abraham Robinson. Volume 1. Model theory and algebra. Edited and with an introduction by H. J. Keisler. Yale University Press, New Haven and London1979, xxxvii + 694 pp. - George B. Selioman. Biography of Abraham Robinson, pp. xiii–xxxii. - H. J. Keisler. Introduction, pp. xxxiii–xxxvii. - Abraham Robinson. On the application of symbolic logic to algebra, pp. 3–11. A reprint of XVIII 182. - Abraham Robinson. Recent developments in model theory, pp. 12–31. A reprint of XL 269. - Abraham Robinson. On the construction of models, pp. 32–42. A reprint of XL 506. - Abraham Robinson, Metamathematical problems, pp. 43–59. (Reprinted from The journal of symbolic logic, vol. 38 (1973), pp. 500–516.) - Abraham Robinson. Model theory as a framework for algebra, pp. 60–83. (Reprinted from Studies in model theory, edited by M. D. Morley, Studies in mathematics, vol. 8, The Mathematical Association of America, Washington, D.C., 1973, pp. 134–157.) - Abraham Robinson. A result on consistency and its application to the theory of definition, pp. 87–98. A reprint of XXV 174. - Abraham Robinson. Ordered structures and related concepts, pp. 99–104. A reprint of XXV 170. - Volume 47 Issue 1

3R29. Theory of Porous Media: Highlights in Historical Development and Current State. - R de Boer (Inst fur Mechanik, Univ Essen, Fachbereich 10 Bauwesen, Essen, D-45117, Germany). Springer-Verlag, Berlin. 2000. 618 pp. ISBN 3-540-65982-X. $95.00. Reviewed by N Katsube (Dept of Mech Eng, Ohio State Univ, 206 W 18th Ave, Columbus, OH 43210).This book consists of historical and recent development of porous material theory, can be used as a reference book in this area. In the early and classical era, general development of continuum mechanics such as Cauchy's formulation of the stress concept, the development of linear elasticity theory, and the foundation of thermodynamics are summarized. At the end of each chapter, biographical notes of the important contributors are outlined. There the readers could learn about the lives of these prominent researchers, including their characters, and the nature of scholarly debates. The readers can also learn about how the lives of these researchers were influenced by the historical events, and how failure in one event had led to success in another. In the modern era, the emphasis is placed on the porous materials. The historical review includes the controversy between Fillunger and von Terzaghi and the subsequent development of the theory by Biot and others. Further development of elasticity and plasticity theories and a more modern framework of continuum mechanics and mixture theory are also discussed. The current state of porous material theory reflects the author's work as well as the related work developed mostly in Europe. It is based on the assumption that the deformation gradient of the constituent can be separated into the part due to the real material and the part due to the change of the pores in size and shape through a multiplicative decomposition process. In developing constitutive theories, the principle of material objectivity as well as entropy inequality is employed. An extensive development of a porous material theory is presented based on these theoretical frameworks.Theory of Porous Media: Highlights in Historical Development and Current State is a great book to have if you would like to know about the historical development of porous material theory since many of the letters and articles written by the researchers in early days are not available in English. In addition, if you would like to follow the recent development of porous material theory, which is consistent with the above stated assumptions, this book will provide an extensive review. However, the reader should be aware that this is not the only approach available in the area of porous materials. There are a number of different approaches available for the development of constitutive behavior of porous materials. These other approaches are more phenomenologically based and often motivated by experimental observations. The developed models are verified by experimental data and used to solve important practical problems.

Density functional theory (DFT) and multiple scattering theory (MST) have been used extensively for calculations in condensed matter physics of the electronic structure of materials built from atomic species throughout the periodic table. As originally formulated for the muffin-tin model, MST in general gave disappointing results in applications to molecules, which discouraged use of this methodology. Recent developments in so-called ‘full-potential’ MST have removed these muffin-tin constraints while retaining the computational efficiency associated with these methods. Full-potential MST is reviewed here, with emphasis on the theoretical basis of computational methods that are viable for molecules. Several recent developments in the formalism of DFT are reviewed, in particular reference-state DFT, which frees the theory from the constraint that the electronic density in the variational model state must be identical to that of the true ground state, and places DFT in the context of the Fermi liquid theory of Landau. The theory of self-interaction corrections is reexamined from this point of view.

This chapter covers the main features and material examples of the electric field activated electroactive polymers. This class of electroactive polymers (EAPs) is very attractive in performing the energy conversion between the electric and mechanical form and hence can be utilized as both solid-state electromechanical actuators and motion sensors. As will be discussed in the chapter, the electromechanical response in this class of polymers can be linear such as in typical piezoelectric polymers or electrets, or nonlinear such as the electrostrictive polymers and Maxwell stress effect induced response. Most of the piezoelectric polymers under investigation and in commercial use are based on poled ferroelectric polymers including PVDF-based and nylon-based ferroelectric polymers. This chapter will discuss in detail the properties of these ferroelectric polymers. In comparison with the electromechanical responses in inorganic materials, the electromechanical activity in these polymers is relatively low. In order to significantly improve the electromechanical properties in electric field activated EAPs, new avenues or approaches have to be explored. From the basic material consideration, these approaches include the strain change accompanied with the molecular conformation change, due to the polar vector reorientation, and from the Maxwell stress effect in soft polymer elastomers. This chapter will discuss the recent results based on those approaches, which have produced remarkable improvements in terms of the electric-field-induced strain level, elastic energy density, and electromechanical conversion efficiency in the electric field activated EAPs.

<p><span>We experimentally investigated the internal dynamics of stationary mono- and bidisperse granular avalanches in an inclined conveyor belt flume. We used the refractive index matching technique to visualize and obtain information from within the granular bulk. In combination with particle tracking velocimetry and coarse-graining techniques, we were able to calculate continuum particle distributions and velocity fields. The experimental avalanches had distinct flow regions: (i) a convective-bulged front, (ii) a compact-layered tail, and (iii) a breaking size segregation wave structure, serving as a transition between the former two. To describe the dynamics of these regions, we computed local strain rates in the form of its tensor invariants. The invariants varied notably between regions; while the largest values and non-linear distributions were found at the front, linear distributions were observed in the tail. In general, and although that slip was considerable at the base of the flow, time-averaged velocity profiles were found to be well captured by a Bagnold model. Based on recent developments in particle-size segregation theory, we calculated the segregation flux within the bidisperse avalanches. In those experiments, we found that segregation flux was higher at the front than at the back, a fact that was confirmed by the observed recirculation of large particles at the front. All our experimental data show a strong link between rheology and segregation, a result that will provide grounding for new developments in segregation theory.</span></p>

The public and researchers in psychology and the social sciences are largely unaware of the huge resources invested in metrology and standards in science and commerce, for understandable reasons, but with unfortunate consequences. Measurement quality varies widely in fields lacking uniform standards, making it impossible to coordinate local behaviours and decisions in tune with individually observed instrument readings. However, recent developments in reading measurement have effectively instituted metrological traceability methods within elementary and secondary English and Spanish language reading education in the U.S., Canada, Mexico, and Australia. Given established patterns in the history of science, it may be reasonable to expect that widespread routine reproduction of controlled effects expressed in uniform units in the social sciences may lead to significant developments in theory and practice.

Over the last decades, the development of algorithms and tools for the safety verification of hybrid systems has been content of intensive research. Numerous novel ideas have been presented and implemented in different tools. Whereas the majority of these tools offer fixed implementations, only few general libraries have been provided for the development of new verification tools.HyPro is such an example, providing a C++ programming library for the implementation of certain types of reachability analysis algorithms for linear hybrid systems. These algorithms, based on flowpipe construction, need geometric or symbolic representation for state sets of hybrid systems. HyPro offers datatypes for different representations, conversions between them, and efficient algorithms based on these datatypes.Since its release in 2017, HyPro's functionalities have been extended by several implementations. In this paper we give a general introduction to flowpipe-construction-based methods and report on HyPro's functional advances as well as on applications of the library.