4,237 research outputs found
Microengineered ferroelectret materials for energy harvesting
No full textFerroelectrets are thin films of polymer foams which usually store charges in their internal voids and present a strong piezoelectric property after electrical charging. Ferroelectrets exhibit the similar piezoelectric properties, but the mechanism leading to those properties is completely different: in ferroelectrets, the properties is a result of deformation of charged voids, whereas piezoelectric materials rely on ion displacement in a lattice. For ferroelectrets, the interior voids contain opposite polarity charges on the top and bottom void surfaces and each void can be regarded as a dipole. When a ferroelectret material is compressed or expanded in its thickness direction, the dipole moments inside change in magnitude which leads to the changing of the compensation charge on the surface electrodes. Due to its outstanding piezoelectricity and material properties, ferroelectrets are widely utilized as functional materials in electromechanical sensors and actuators. Compared with piezoelectric materials, ferroelectret materials have several advantages. First, they have a very prominent piezoelectric effect and their piezoelectric coefficient is several times higher than that of traditional piezoelectric materials. Secondly, their production cost is relatively low. Again, most ferroelectrets are mainly composed of non-toxic materials, which do not cause environmental pollution. In addition, a ferroelectret film is light, thin and very soft; it can be made into different shapes and sizes, according to need. Finally, the unique acoustic impedance of ferroelectret materials makes it more useful in areas such as ultrasonic waves and underwater acoustic wave detection. Therefore, ferroelectret materials show great potential in vibration energy harvesting applications. Energy harvesting technology refers to collecting the energy from surroundings into electricity then supplying power to the system. The working principle of the piezoelectric vibration energy harvester is based on the piezoelectric effect of the piezoelectric materials. Under the action of the external vibration force, the piezoelectric layer in the device generates stress and strain, an electrical signal is formed. The piezoelectric energy harvester has the advantages of simple structure, long-life, high-energy density, and compatibility with the MEMS process. Polydimethylsiloxane (PDMS) has been demonstrated in the fabrication of ferroelectrets with controlled void layouts and geometries rather than the random voids associated with foams. Its primary advantages include low cost, fast simple fabrication and high levels of flexibility. However, PDMS is not a stable electret material and the surface charge stability on the void surfaces of the PDMS is poor, causing the effective piezoelectric coefficient of most samples to fall below 10 pC/N in one month, therefore some approaches are necessary to extend the charge stability of the PDMS ferroelectrets or find a novel ferroelectret material suitable for achieving a high level of activity over a large period of time. This report first focuses on some basic definitions and the background related to ferroelectret; This project also tries to use mathematical approach and simulation analysis to find an optimal cellular ferroelectret geometry structure with a high level of piezoelectric activity. This report presents approaches to enhance the surface charge density and stability of a PDMS based ferroelectret device by adding Polytetrafluoroethylene (PTFE) to the PDMS. This report also illustrates a new approach to obtain PDMS ferroelectret with random voids by using mechanical stirring to create cavities
Recent Developments and Future Directions in Flow Visualization: Experiments and Techniques
No full textFlow visualization has long been a critical tool for understanding complex fluid dynamics in both natural and engineered systems [...
A new approach for obtaining PDMS ferroelectrets with random voids
No full textMost previous work regarding to Polydimethylsiloxane (PDMS) ferroelectret was fabricated with controlled void layouts rather than the random voids. This paper illustrates a new way for obtaining Polydimethylsiloxane (PDMS) ferroelectret with random voids by using the bubbles created by reaction between liquid PDMS and curing agent. A mathematic model is illustrated to explore the connection between structure and piezoelectricity. The fabricating process is present and related test is measured. The piezoelectric coefficient d 33 of this PDMS ferroelectret is about 206 pC/N. The maximal peak voltages measured for this PDMS ferroelectret was about 4 V under the force of 300N
Supplemental Material - Wear failure mechanism analysis of self-lubricating fabric composites at high temperature
No full textSupplemental Material for Wear failure mechanism analysis of self-lubricating fabric composites at high temperature by Mingming Yu, Min Zhang, Lin Fang, Musu Ren, Lei Liang, Wang Xie and Pibo Ma in Journal of Industrial Textiles</p
Relating quantitative soil structure metrics to saturated hydraulic conductivity
No full textSoil structure affects saturated hydraulic conductivity (Ks) by creating highly conductive macropores that preferentially transmit soil water. In this study, we explore the relationship between Ks and macropores in an Oxyaquic Vertic Argiudoll in northeastern Kansas. Macropores were quantified from an excavation wall using multistripe laser triangulation (MLT) scanning. Soil water contents were measured at four depths within a soil lysimeter installed within 2 meters of the MLT-scanned soil profile and adjacent to an Ameriflux tower monitoring precipitation, air temperature, and solar radiation. Selected hydraulic properties of soil horizons within the lysimeter were optimized to water content data using a Markov chain Monte Carlo technique in combination with the mobile-immobile water (MIM) model in HYDRUS-1D. Estimates of Ks varied between 4198 cm d-1 in the A horizon and 0.6 cm d-1 in a 2Btss2 horizon with strongly expressed wedge structure. Approximately 87% of the variation in Ks was explained by the geometric mean of the widths of pores quantified with the MLT technique and modified by the coefficient of extensibility (COLE). The use of COLE allows the widths of the macropores obtained at dry conditions to be approximated at saturation. Two models that predict Ks from either texture or water retention data resulted in Ks estimates that were similar to each other, but significantly lower than Ks values predicted with MIM in horizons where structural pores dominate water flow. This technique shows a great deal of promise in better understanding and predicting the relationship of soil structure to water flow.Peer reviewe
An experimental investigation of aerodynamic and aeroacoustic performance of a wind turbine airfoil with trailing edge serrations
No full textTrailing edge (TE) serrations are widely used as an effective passive control method to reduce the turbulent TE noise from wind turbine blades. Other than the acoustic effects, the aerodynamic performance of serrations is also an important issue that should be considered, since it determines the power output of the blade. To this end, the far-field sound pressure level, flow field, and aerodynamic force of the serrated airfoil were measured in an anechoic wind tunnel, and the lift increase and noise reduction effects of the TE serrations were comprehensively evaluated. The result showed that the presence of TE serrations could achieve noise reduction by about 2 dB at the low-to-moderate frequency range at small angles of attack, and meanwhile it could suppress the fluctuation of aerodynamic forces. In addition, the proper orthogonal decomposition method was deployed to decompose the wake flow into various vortex structures with different portions of turbulent kinetic energy so as to reveal the noise reduction mechanism of the serrated TE. The result suggested that TE serrations could effectively inhibit large-scale vortex structures that shed from the boundary layer on the suction side, thereby achieving noise reduction around the vortex shedding frequency
sj-pdf-1-imr-10.1177_03000605231173828 - Supplemental material for Unilateral chronic angle-closure glaucoma in a pediatric patient with neurofibromatosis: a case report
No full textSupplemental material, sj-pdf-1-imr-10.1177_03000605231173828 for Unilateral chronic angle-closure glaucoma in a pediatric patient with neurofibromatosis: a case report by Mingming Jiang, Jing Zhang, Xiaomei Wan, Yichao Ding and Feijia Xie in Journal of International Medical Research</p
Efficient characterization of mechanical nonlinearity in triaxially braided composites by a novel unit cell
No full textA range of nonlinear factors were investigated based on a novel unit cell model with a reduced domain to characterize the mechanical nonlinearity exhibited by braided composites in this study. These factors include geometric nonlinearity, nonlinear shear behaviour, plasticity within the matrix and transverse fibre direction, as well as failure and damage evolution. This novel size-reduced unit cell for braided composites, based on non-orthogonal translational symmetry principles, has been developed to streamline the analysis and tackle convergence challenges. This novel size-reduced unit cell is formulated by leveraging geometric features, as well as the symmetry and anti-symmetry of relative displacement boundary conditions. In order to evaluate the efficacy of these unit cells in characterizing elastic and strength properties, a benchmark study was conducted. The results demonstrate that the novel size-reduced unit cell has the ability to reliably predict the stiffness and strength responses of the 2D3A braided composite at the mesoscale. The unit cell's predictions, which include nonlinear stress–strain curves, modulus, and strength, exhibit a robust analytical performance and a satisfactory agreement with experimental results.</p
A randomly structured composite PDMS/PTFE ferroelectret soft smart material
No full textPolydimethylsiloxane (PDMS) based ferroelectrets are an attractive material for the fabrication of human-based applications given their soft and compliant mechanical properties. The typical fabrication approach is to exploit specifically engineered void geometries fabricated by moulding and bonding layers together. Charge instability can be addressed by the addition of polytetrafluoroethylene (PTFE) particles but this prevents the bonding of PDMS films. This paper illustrates a new approach to obtaining PDMS ferroelectret with random voids by promoting and trapping bubbles to create cavities within a PDMS film. A mathematical model is presented to explore the connection between the percentage of trapped bubbles in the PDMS and the equivalentpiezoelectric coefficient, d33e. The process is compatible with the addition of PTFE powder to the PDMS formulation and a ratio of PTFE to PDMS of 1:3 by weight was found to increase performance achieving an initial d33e of 384 pC/N which reached a steady state value of 186 pC/N measured after 2 months after poling. The energy harvesting potential of the random void PDMS/PTFE ferroelectret was explored by cyclically compressing with a force of 300 N applied at 1 Hz. The output of the ferroelectret was found to charge a 10μF capacitor to 0.26 V after 40 seconds. The ferroelectret's performance as a pressure sensor from 0 to 300 N was explored, and the optimum formulation achieved a sensitivity of 25.2 mV/N, a nonlinearity of 4%, and hysteresis of 4.2%, demonstrating a considerable improvement over the pure PDMS ferroelectret
sj-docx-2-ict-10.1177_15347354221105485 – Supplemental material for Milk and Egg Are Risk Factors for Adverse Effects of Capecitabine-Based Chemotherapy in Chinese Colorectal Cancer Patients
No full textSupplemental material, sj-docx-2-ict-10.1177_15347354221105485 for Milk and Egg Are Risk Factors for Adverse Effects of Capecitabine-Based Chemotherapy in Chinese Colorectal Cancer Patients by Jinrong Xu, Zeshuai Lin, Jiani Chen, Jian Zhang, Wanqing Li, Rui Zhang, Jin Xing, Zhihuan Ye, Xiaoping Liu, Qianmin Gao, Xintao Chen, Jingwen Zhai, Houshan Yao, Mingming Li and Hua Wei in Integrative Cancer Therapies</p
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