Ryszard Kacprzyk

Piezoelectric properties of non-uniform polymeric structures under static load

ABSTRACT Piezo-electrical properties of structures containing ‘soft’ and ‘hard’ dielectric layers with charge stored on the interfaces are described in the paper. The piezo-activation process of structures containing layers with gas voids by partial discharges is described. The influence of the mechanical properties of the ‘soft’ layer on the piezoelectric parameter d33 value and its dependence on the static pressure p are also discussed. It was found experimentally, that for the fibrous type of ‘soft’ dielectric layer, the dependence of the piezoelectric parameter d33 (p) can be described by the function d33 ÷ p−n, where n ≤ 1.

Dependence of the piezoelectric coefficient d33 on the static pressure for non-uniform polymeric layered structures

The paper presents a model describing dependence of the piezoelectric coefficient d33(p) on the pressure p applied to heterogeneous layered dielectric structures. Previous studies have shown that the d33(p) dependence for such structures may be determined by the pressure dependence of the elasticity modulus Y1(p) of a soft layer. The model is related to an elastic layer comprising a nonwoven, for which the Y1(p) dependence can be described by the deformation of individual fibers being in the mutual contact. Model analysis shows that the d33(p) dependence can be approximated by a power-type function: d33(p) = Ap . The power type of the d33(p) dependency, with power-factor -0.20 < n < -0.12 was confirmed experimentally. Słowa kluczowe: efekt piezoelektryczny, dielektryki niejednorodne.

Energy Stored in the Electric Field Produced by a Charged Fabric with a Conductive Mesh

The aim of the research was to set up a simplified analytical fabric-grounded object model for estimation of the energy stored in the electric field occurring in the space surrounding a charged fabric. A standard spherical electrode was used as the grounded object. Synthetic fabric with regularly spread conductive yarns (in the form of a grid with regular cells) was used as a sample. The model allowed to combine the energy stored in the space of the cell with the geometry of the fabric-object system and the surface charge density. The model led to a power type relation between the energy W and the cell, with a diameter of a, in the form W = K∙ an, n ≈ 3. These results were verified by those obtained from numerical modeling using the COMSOL Multiphysics program. It was found that for a cell with a diameter of 10 to 50 mm, the difference in results was lower than 38%. Based on the results obtained, it can be stated that the model proposed can be used for the design of fabrics (used in ESD protection) with the maximum acceptable stored energy.

Photoconduction in outdoor insulation materials

Most of dielectrics operating in the room temperature region use to exhibit an activation character of electrical conductivity. In case of outdoor insulation, exposed to a strong irradiation by white light and UV (sun-light) one can expect a light-generation of additional concentration of charge carriers in insulating materials. Generation of additional charge carriers leads finally to an increase of surface conduction of the material sample or insulator. In case of insulating system operating in DC fields, potential distribution is determined by resistance distribution. Results of investigation of photo-conduction effect, appearing on dielectrics applied in construction of outdoor insulating systems, were presented in the paper. Investigations of surface resistivity carried out on samples (or insulators) made of glass, ceramics and composite insulators covered by silicon layers confirmed surface resistivity decrease for samples submitted to irradiation by white and UV light. Influence of the investigated phenomenon on the DC breakdown voltage was confirmed for insulator models operating in uniform DC fields.