Katarzyna Ewa Grabowska

The analysis of attenuation of electromagnetic field by woven structures based on hybrid fancy yarns

In this paper we present an analysis of attenuation by woven structures produced from hybrid yarns. The woven structures have been designed for protection against electromagnetic fields (EMFs). The idea of creating hybrid yarns that may intensively protect against EMFs comes from the analogy discovered between the construction of a fancy bunch yarn and an electric system composed of electro-conductive solenoids on a ferromagnetic material connected in series and then in parallel. The application of hybrid fancy yarn as a weft made of copper as a special effect thread insulated with lacquer and wrapped around a core of steel thread in a textile fabric will enable EMF attenuation as a result of inducing an electromotive force in the special effect thread and magnetizing the core thread. In this way, the designed electric circuit (textile fabric) in the variable primary EMF will be the source of a secondary EMF directed opposite to the direction of the primary field. The fabricated woven structures present electrical and magnetic components of EMF attenuation in some narrow ranges.

Basic Comparison of the Properties of the Loop and Frotte Yarns, Woven and Knitted Fabrics

Abstract Both loop fancy yarns and frotte fancy yarns belong to the group of yarns with continuous effects. The difference between frotte and loop yarn relies on the fact that the loop yarn is constructed with two core yarns and the frotte yarn is constructed with only one core yarn. The differences are evident in the shape of these two types of fancy yarns. These shape differences are the functions of the tensions of component yarns during the twisting process. The shape and construction of the fancy yarn influence its properties. The properties of loop and frotte fancy yarns, woven and knitted fabrics are compared in this article in order to find out the optimal yarn’s and fabric’s production condition to satisfy the final user and maintain low production costs. In terms of economy aspects only, the frotte fancy yarns are believed to be cheaper in production due to lower quantity of components utilize for their production to compare with loop fancy yarns, under conditions of the same settings of ring twisting frame.

Mathematical Basis for Classification of Twisted Multiplied Fancy Yarns

This paper introduces the shape coefficient of fancy yarn as a tool for classifying twisted multiplied fancy yarns. Mathematical functions have been used to describe yarn tensions in the twist zone as a basis for analysis of their variability pattern. On the basis of conducted analyses, characteristic values of the shape coefficient have been identified, according to which twisted multiplied fancy yarns can be classified in an objective way.

Experimental Analysis of the Tensile Properties of Fancy Loop Yarns: Part II

This article compares the tensile properties of real loop fancy yarns produced on a ring twisting machine with the results generated by mathematical models derived in Part I. The theoretical strength of the produced loop yarns was calculated on the basis of input variables of a mathematical model describing tensile strength of loop yarn, with the assumptions of lack of migration of fibers in component yarns and of full migration of fibers and with two assumptions of fiber length distribution in component yarns: trapezoidal and uniform. The test examinations were conducted on four different types of loop fancy yarns, with variable values of the twist of the loop fancy yarns produced on the ring twisting system. Every test was repeated 50 times. It has been found that the results generated by the mathematical model describing tensile strength of a loop yarn are the most consistent with experimental results when we accepted the assumptions of full migration of staple fibers in component yarns and of a trapezoidal distribution of staple fiber lengths in these yarns (a difference of about 5%).

Application of micro-computed tomography (micro-CT) to study unevenness of the structure of yarns

A study was conducted on the structure of a single cotton yarn using micro-computer tomography (micro-CT). This article describes two important parameters determining the unevenness of yarn structure, i.e. the migration of staple fibers and packing density of staple fibers in the yarn cross-section. Relationships were found between the variation of staple fiber migration characteristics and the relationship between yarn durability and twist. For the boundary value, the radius and range of migration are the highest, and the variation coefficient of the fiber migration range is the lowest. The number of fibers in the yarn cross-section decreases with twist. Above the boundary twist value, the number of fibers in the yarn cross-section stabilizes at the value corresponding to the number of fibers in the boundary twist.

Micro-CT supporting structural analysis and modelling of ropes made of natural fibers

This paper describes the modelling of the structure and mechanical parameters of rope components made of natural fibers. Modern X-ray micro-tomography (Micro-CT) was employed to measure the parameters of the internal structure of the multi-component yarns making up rope and utilized as a basic model of twisted rope. The results allowed calculation of the tensions generated in the component yarns and detection of the unevenness of the filling of the component yarns by fibers, which was clearly visible in cross-section. The unevenness of twist measured as a function of distance from the center of the yarn was also detected. The unevenness of fiber distribution in the twisted element decreased its intensity, starting from the surface of the yarn and going deeper into the structure. Migration of the fibers in the frame of the circumference of the component yarns was associated with the mutual slide of single fibers.

Woven Fabrics Containing Hybrid Yarns for Shielding Electromagnetic Radiation

The aim of the study was to verify whether the construction of a specific hybrid yarn containing a ferromagnetic core and electroconductive wire introduced into woven fabric will improve the shielding effectiveness (SE) in comparison with reference fabrics made of the same raw materials but introduced into woven fabrics as plain wefts, not twisted into the hybrid yarn. Hybrid yarn made of electroconductive materials allows the creation of a set of solenoids with a ferromagnetic core made of steel yarn and a solenoid of conductive effect yarns made of copper. The woven fabric made of these yarns placed into an alternating electromagnetic field (EMF) exhibits a phenomenon where an alternating electric voltage is generated between the ends of the copper solenoid, and alternating magnetisation of the ferromagnetic core takes place. Twelve fabrics were produced, nine of which differed in the density with which the hybrid yarns were introduced as wefts, i.e. once every 25×2 tex cotton yarn, every two cotton yarns, and every three cotton yarns, and the remaining three were reference fabrics, without hybrid yarn. It was found that if measured at a frequency of 30 MHz, the fabrics containing hybrid yarns had 60% higher SE than the reference ones.

Mathematical Modeling of Tensile Properties of Fancy Loop Yarns. Theoretical: Part I

To date, the structure and properties of loop fancy yarns with an extended structure have not been sufficiently explored. The aim of this paper is to develop a mathematical model describing the tensile load converted to one unit of linear density for a given yarn strain of a multiplied loop yarn that is the function of density of staple fiber length distribution, degree of fiber migration, slipping length, basic twist of component yarns, yarn twist, tensions stretching single component yarns and friction forces generated in component yarns. The derived mathematical relationships make it possible to objectively control the usable properties of yarns with extended surfaces.

Shielding of electromagnetic radiation by multilayer textile sets

This paper presents the continuation of research on shielding efficiency (SE) of electromagnetic radiation (EMR) by woven fabric made of cotton (warps and wefts) and a hybrid yarn (wefts). This hybrid yarn was made of stainless steel yarn by Bekinox wrapped with an enamelled copper wire from Synflex Elektro GmbH, Germany. The pitch of copper coil on a hybrid yarn equals 3 mm. The wefts were introduced into the fabric in the following order: 1 hybrid yarn, 1 cotton yarn, 1 hybrid yarn, 1 cotton yarn, etc. The construction of this specific fabric was proven to be the most efficient in terms of the hybrid weft construction and the fabric construction to shield EMR among other previously tested fabrics with different weft configuration. The current study proposes to verify the effect of the number of layers of the fabrics and their mutual configuration on the final SE of the multilayered set. Some of the most interesting findings of this study are that increasing the number of layers placed on top of one another with an offset angle of 0° to more than two does not provide a higher SE; however, using three such layers provides an SE of 56 dB, which is over two times higher than that provided by a single layer. Increasing the number of layers of fabric aligned at an angle of 45° provides a higher SE only for a frequency of 30 MHz.