Electric field distribution in porous piezoelectric materials during polarization

High piezoelectric coupling coefficients enable the harvesting of more energy or increase the sensitivity of sensors which work using the principle of piezoelectricity. These coefficients depend on the material properties, but the manufacturing process can have a significant impact on the resulting overall coefficients. During the manufacturing process, one of the main steps is the process of polarization where a poling electric field aligns the ferroelectric domains in a similar direction in order to create a transversely isotropic material able to generate electric fields or deformations. The degree of polarization depends on multiple factors and it can strongly influence the final piezoelectric coefficients. In this paper, a study on the electric field distribution on the sensitivity of the main piezoelectric and dielectric coefficients to the polarization process is performed, focusing on porous piezoelectric materials. Different inclusion geometries are considered, namely spherical, ellipsoidal and spheres with cracks. The electric field distribution at the micro scale within a representative volume element is modelled to determine the material polarization level using the finite element method. The results show that the electric field distribution is highly dependent on the inclusion geometries and cracks and it has a noticeable impact on the equivalent piezoelectric coefficients. These results are compared with experimental measurements from published literature. Good agreement is found between the ellipsoidal model and the experimental data

Electrical and Piezoelectric Behavior of Polyamide/PZT/CNT Multifunctional Nanocomposites

Three-phase polyamide 11 (PA 11)/lead zirconate titanate (PZT)/carbon nanotubes (CNT) composites are elaborated by extrusion. The influence of inorganic particles on the electrical properties of conductive composites and the influence of conductive particles on the ferroelectric properties of organic/inorganic composites are both studied. Inorganic particles do not modify the establishment of the electrical percolation path of CNTs either regarding the percolation threshold value or the conductivity reached above this insulator–conductive transition. The dielectric permittivity of twophase PA 11/PZT composites is improved with the addition of only 0.2% in volume of CNTs. This three-phase composite could be proposed for actuation, energy harvesting and damping performances enhancement

Impact of ecological factors on the distribution of Vanilla siamensis (Orchidaceae: Vanilloideae) in tropical forest at Khao Soi Dao Wildlife Sanctuary, Chantaburi, Thailand

Some species of the pantropical orchid genus Vanilla are widely used in a variety of industries, including food, pharmaceuticals, cosmetics, tobacco and traditional crafts. Vanilla siamensis Rolfe ex Downie is a leafy vine endemic to Thailand. Ecolog- ical factors affecting the distribution of V. siamensis are still unknown. This study aims to examine the distribution of V. siamensis in natural conditions as well as to investigate the impact of environmental factors on its distribution in forest ecosystems. In order to achieve the proposed objectives, a study was conducted in a tropical moist forest at Khao Soi Dao Wildlife Sanctuary. The plant community and environmental factors where V. siamensis occurs were assessed in two study sites. At each site, two plots (10 m×50 m) were set up near waterfalls (NWA) and in adjacent forest areas (AFA). A total of 66 species of woody plants were recorded in the study plots. Higher values for importance value index (IV) were found for Pterygota alata (Roxb.) R.BR., Diospyros de- fectrix H.R. Fletcher, Strombosia ceylanica Gardner, Alchornea rugosa (Lour.) Mull. Arg., and Diospyros transitoria Bakh. The highest number of tree species, number of individu- als, Shannon diversity index and evenness were found at the NWA compared to the AFA. A total of 19 woody plant species act as support trees of V. siamensis in the plant families Malvaceae, Annonaceae and Achariaceae. The results showed that V. siamensis might pos- sible well adapted in the NWA study zone which contained a higher level of soil moisture content compared to the AFA. All results revealed that the distribution of V. siamensis in the study areas could be impacted by tree hosts. All tree host species have a larger diameter at breast height and thicker and softer bark when compared with non-tree hosts