Search

Wireless communication systems are made up of several electronic components, which over the years have been miniaturized and made more flexible, such as batteries, sensors, actuators, data processing units, interconnectors and antennas. In the context of wearable systems, the antennas have been challenging because they are conventionally built on rigid substrates, hindering their efficient and comfortable integration into the garment. Considering the flexibility and dielectric intrinsic properties of textile materials, the development of textile antennas may boost wearability and enlarge the domain of applications of such wireless communication systems, aiming purposes such as tracking and navigation, mobile computing, energy harvesting and storage [1]-[7]. Moreover, wearable antennas and clothing with antennas embedded on them emerge as potential interfaces of the human-technology-environment relationship, enhancing the interaction of the end user with some electronic devices, making them less invasive and more discrete. To obtain good results, wearable antennas have to be thin, lightweight, of easy maintenance, robust, and moreover, must be low cost for manufacturing and commercializing. In this way, planar antennas, the microstrip patch type, have been proposed for garment applications, because this type of antenna presents all these characteristics, and also are adaptable to any surface [2]. The knowledge of the electromagnetic properties of the materials is essential to a good design of the antenna. Many criteria should be considered, as several characteristics of the textile materials directly affect the behavior of the antenna [8]. Specific electrically-conductive textiles are available on the market and have been successfully used in the radiating components. Conventional textile fabrics have been used as substrates. However, little information can be found on the electromagnetic properties of these regular textiles. Indeed, woven, knits and nonwovens are inhomogeneous, highly porous, compressible and easily influenced by the environmental hygrometric conditions, making their electromagnetic characterization difficult [9]. In this context, the main objective of this paper is to present an experimental characterization of the electromagnetic properties of some textile materials, aiming the selection of textiles well suited as dielectric substrates for the development of wearable antennas. The Resonator-Based Experimental Technique was used. It is based on the theory of resonant methods and consists in calculate the electromagnetic parameters of the material under test, at a single frequency, by measuring the shift in frequency and the value of Q-factor of one resonator board with a microstrip patch antenna. The resonant methods generally give higher accuracies than non-resonant ones and do not require a complex sample preparation [10]. Other advantage of this method is that the measured values are not influenced by the condition of some variables, as for example, the type of glue/adhesive sheet, the connector and the manufacturing technique of the probe, which can lead to non-repeatability of the measurements and introduce errors in the final values. In order to understand the influence of some mechanical properties, such as thickness and surface roughness, on the electromagnetic behavior of the textile materials, this paper also correlates the permittivity values (measured with the Resonator-Based Experimental Technique) with the mechanical properties. The thickness and surface roughness of the textile fabrics were measured using the KES -- Kawabata Evaluation System [11]. It was found that materials with higher roughness have higher permittivity values, due to the augmented presence of air in the superficial porosity. To validate the experimental characterization method, the measured permittivity values were considered for the dimensioning of wearable antennas, which performance was further tested. These antennas were designed to resonate around 2.45 GHz covering the Industrial, Scientific and Medical (ISM) band, between 2.4 and 2.45 GHz. This bandwidth also supports the WLAN (Wireless Local Area Network), Bluetooth and SRCS (Short Range Communication Systems 802.15.4) applications. The results of the antennas supported the validation of the method. Therefore, the characterization of the electromagnetic properties of textile materials to apply as dielectric substrates in wearable antennas may be easily performed with the resonator-based experimental technique used in this paper. This technique proved to be an efficient, simple, easy and quick technique to find suitable dielectrics for textile antennas. [ABSTRACT FROM AUTHOR]

In 1999, ICBT-Perfojet has proposed Spunjet, nowadays Perfobond technology. The equipment is designed with an original geometry that lays down the filaments in the spunlaid webs. The major structural innovation of the Perfobond nonwovens is the main orientation angle of the filaments. This innovative structure may represent an advantage in the application of the spunbonded nonwovens. This study focuses on the analysis of the effect of the manufacturing process in the orientation of the filaments. The results from the optical analysis have shown that the conveyor face, which is in contact with the conveyor belt, is more anisotropic than the upper face. The ellipticities a/b of the Perfobond nonwovens range from 1.1 to 1.4. In addition, the filaments that are originally laid down at 45° tend to follow the belt movement. On average, the main orientation of the filaments in around 30° at both sides. It was observed that the Perfobond spunbonded nonwovens present a different organization of the filaments in the two faces, being the conveyor face more anisotropic than the upper one. In the spunbond process, the filaments lay down perpendicularly to the forming head, creating a double layer structure. The conveyor face is mainly formed by the filaments that have laid down in the back of the layout line. The upper face is mainly formed by the filaments that lay down in the front of the layout line on the top of the previous ones. The organization of the filaments in the web depends on the action of the air suction velocity. It enhances the conveyor action and consequently decreases the main orientation angle.

This article presents an abstract of the study Fluid Flow in Spunbonded Nonwovens, presented by Rita Salvado et al at the Fiber Society 2005 Spring Conference in Saint Gallen, Switzerland. This study is focused on the liquid in-plane and the air permeability of polypropylene spunbond that are thin and porous. Their permeability was determined testing four layers of nonwoven carefully aligned and joined together. The regime of flow will depend on the fluid properties, on the porous structure and on the flow velocities. The fluids that were used in this study, hexadecane and air, have very different properties. Moreover, the flow velocities observed during the experiments were also very different. The airflow through the spunbond is an inertial flow.