Textile antennas

M Klemm, I Locher, and G Troster, A novel circularly polarized textile antenna for wearable applications , 34 European Microwave Conference (EuMC), 11-14,2004. 

Multilayer fabrics or 3D fabrics are necessary to integrate electronics into textiles. E-textile antennas are multilayer interwoven panels, and each layer depends on the other to work properly. The 3D fabrics are also necessary for nodes and network configurations. 

Top view of 3D woven E-textile antenna is shown in Eigure 9.6. Conductive patch of stainless steel and U-shaped slot are shown at the top. The challenge inherent to many advanced communication and navigation application is achieving wideband operation from a single antenna. One such antenna architecture that is capable of achieving the types of bandwidth required is the slotted patch antenna. This antenna used a thick substrate ( 1.5 cm) and the U-shaped slot to increase the bandwidth. 

Figure 9.6 E-textile antenna (Courtesy of Bally Ribbon Mills).

Figure 9.7 shows a conductive layer of stainless steel on face of lower spacer of E-textile antenna. This E-textile antenna was woven with Quartz fiber spacers, conductive stainless steel, conductive stripline, and conductive patch with Quartz fiber. 

Research (Courtesy of Bally Ribbon Mills) showed that the performance of E-textiles antenna equaled that of antenna produced by conventional methods, whereas the cost and weight were significantly reduced. This technology using textile components and methods allows microwave and ultra-high-frequency antenna. 

These antennas can be used on a variety of projects to realize battlefield wireless anteimas or to incorporate antennas into airframes or vehicles. E-textile antennas could be incorporated into composite structures during the manufacturing process. The use of composite antenna encapsulation allows radar and communications anteimas to be incorporated into airframes and ship hulls in a manner not before possible. This advanced E-textile-based antenna process can find application in the incorporation of antennas and other microwave circuits into UAVs and vehicles. Government and commercial applications of this technology include the incorporation of these wireless antennas into uniforms, truck covers, tents, and seats. They can stitch onto carpets, ceiling tiles, and headliners as well as tapestries and many other textile products that surround us every day. 

Textile antennas are a special class of antennas that are partially or entirely made out of textile materials, in contrast to conventional antennas, which consist of rigid materials. The textiles composing a textile antenna are divided into electrically conductive fabrics, denoted electrotextiles and applied for the radiating and grounding parts, and dielectric materials for the insulating parts of the antenna. 

Finally, communication is realized in a wireless way by means of an integrated wearable textile antenna in combination with a wearable transceiver. Such a kind of wireless communication takes place between the human body and the surrounding environment and is also referred to as body-centric communication. In parallel with textile antennas, this has become a very popular field of research over the last decade [1], with cmcial importance for plenty of applications, ranging from monitoring of vital signs of patients to coordination and monitoring of rescue workers [2], but also in the entertainment sector [3] and in sports [4]. 

Suitable topologies for the realization of wearable textile antennas exhibit a low profile and compact dimensions. Those features are particularly convenient for on-body placement and seamless integration into garments. For this reason, the majority of existing textile antennas are microstrip or patch antennas. 

In this section, a brief overview is given of the fundamental textile antenna parameters, followed by the typical guidelines for the design and analysis of textile antennas (as well as conventional ones). For more in-depth information about this topic, we refer to literature textbooks, such as [12]. 

Usually, the goal of textile antenna design consists in determining the antenna geometry that meets some given design criteria, which are imposed on one or more of the described performance parameters. 

In textile antennas the presence of a ground plane, placed between the radiating element and the wearer s body, is in any case recommended because it acts as an EM shield for the body tissue and thus allows a considerable SAR decrease. 

Challenges and adverse effects related to textile antennas... 

When dealing with wearable textile antennas, several adverse effects, which influence the performance characteristics, often occur. It is very important for the design engineer to be able to efficiently model these effects in order to predict variations in antenna performance. The main adverse effects that are treated in the present literature on textile antennas are briefly summarized as follows. 

The presence of the human body in close proximity to a wearable textile antenna is the most common cause of its performance degradation, since the radiator is integrated into garments and, hence, in close vicinity of the human wearer surface. Typically, wearable antennas are worn in the vicinity of arms, legs, chest, or back of the human... 

Basically, textile antennas can be subdivided into two categories, those having a ground plane (such as patch antennas) and those without (such as UWB dipoles). In the first case, the effect on performance is very small, since the ground plane acts as an electric shield between the radiating elements of the antenna and the human body. 

For textile antennas without a ground plane, the presence of the human body produces substantial effects on the antenna performance because it acts as an absorber for the radiated field and represents an additional loading. This mainly alters the antenna input impedance and efficiency. Radiation patterns also change with respect to the free-space situation the human body acts as a lossy reflector, making the radiation pattern more directional in the off-body direction. An example of such a behavior, on a wearable antenna without ground plane, is shown in Fig. 26.5, where the on-body and free-space horizontal pattern of a wearable UWB monopole antenna on a polyi-mide substrate (realized by the EM group of Ghent University), are compared. 

Antenna bending represents another very important adverse effect to be taken into account when designing and analyzing wearable antennas. Since a textile antenna... 

For wearable systems, including textile antennas, power efficiency represents a crucial matter, especially for the so-called autonomous systems, where the necessary power for the system operation is ideally obtained entirely by means of energy harvesting [16] from the surrounding environment, and no additional power supply is needed. Even in the case of wearable systems equipped with wearable battery units, it is very important to keep power consumption as low as possible. To this aim, several techniques were recently envisaged, by means of innovative textile antennas, such as active antennas as well as the use of multiantenna-processing techniques, such as diversity with multiple wearable antennas. 

In this section, we summarize and describe some of the most recently developed wearable textile antennas. Each of the described antennas possesses features that provide solutions to one or more of the adverse effects and challenges described in the previous section. 

Industrial, scientific, and medical bands are reserved portions of the radio spectrum, defined by the ITU Radio Regulations [23], that are employed in body-centric wireless communication applications and, more in general, for other industrial, medical, and scientific applications. The majority of textile antennas developed to date are intended for operation in some of those ISM bands, especially in the 2.45 GHz, by far the most popular for wearable antennas, and 5.8 GHz bands. The first band represents a good trade-off between antenna dimensions (inversely proportional to fiequency) and path loss (increasing with frequency), whereas the second is more convenient when... 

With respect to other ISM frequency bands, the 5.8 GHz ISM band ([5.725, 5.875] GHz) has received relatively less attention from the research community. Fewer contributors have proposed, to date, wearable textile antennas operating only in the... 

Figure 26.9 Half-diamond dual-band textile antenna protot)fpe.

Wearable textile antennas are particularly convenient for satellite communications. For example, a useful application involves the coordination of activities by a group of rescue workers in operation. Each person may be equipped with a wearable textile system in which a textile antenna connects to a positioning satellite system, such as GPS, Galileo, or the Global Navigation Satellite System (GNSS). By means of such antennas, each rescue worker can acquire information about his/her position, which can be forwarded to the base station that keeps track of the positions and allows optimal coordination of the team s activity. 

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