Ivo Locher

Design and Characterization of Purely Textile Patch Antennas

In this paper, we present four purely textile patch antennas for Bluetooth applications in wearable computing using the frequency range around 2.4 GHz. The textile materials and the planar antenna shape provide a smooth integration into clothing while preserving the typical properties of textiles. The four antennas differ in the deployed materials and in the antenna polarization, but all of them feature a microstrip line as antenna feed. We have developed a manufacturing process that guarantees unaffected electrical behavior of the individual materials when composed to an antenna. Thus, the conductive textiles possess a sheet resistance of less than 1Omega/squarein order to keep losses at a minimum. The process also satisfies our requirements in terms of accuracy meeting the Bluetooth specifications. Our investigations not only characterize the performance of the antennas in planar shape, but also under defined bending conditions that resemble those of a worn garment. We show that the antennas can withstand clothing bends down to a radius of 37.5 mm without violating specifications

Screen-printed Textile Transmission Lines

Electronic fabrics is an emerging topic in the field of smart textiles. We present transmission lines structures that were screen-printed on fabrics. They featured a sheet resistance of about 0.15 Ω/, while preserving the flexible nature of textiles. We show that the commonly used 50 Ω line impedance could be achieved on these fabric substrates. This technology is predestinated for printing of one-layer structures, such as fabric antennas and their feed lines. Apart from giving the electrical specifications of the transmission lines, we have performed several mechanical tests regarding stability of the printed layer. Eventually, we propose an advanced printing technique as outlook.

Fundamental Building Blocks for Circuits on Textiles

This paper presents the necessary ingredients for a successful realization of electrical circuits on fabrics. We start with the specification of a hybrid fabric as substrate. The discussion of textile transmission lines as well as textile interconnects reveals a flat frequency response up to about 2 GHz and 600 MHz, respectively. The proposed transmission lines feature line impedances in the range of 250 Omega. A novel interposer concept is the key technology to our approach of implementing circuits on textiles. We introduce different variants of this interposer and give formulas to determine their fabric area consumption. The presented technologies allow realization and wiring of circuits on fabrics with signal frequencies up to several hundred megahertz.

Organic field effect transistors for textile applications

In this paper, several issues concerning the development of textiles endowed with electronic functions will be discussed. In particular, issues concerning materials, structures, electronic models, and the mechanical constraints due to textile technologies will be detailed. The idea starts from an already developed organic field-effect transistor that is realized on a flexible film that can be applied, after the assembly, on whatever kind of substrate, in particular, on textiles. This could pave the way to a variety of applications aimed to conjugate the favorable mechanical properties of textiles with the electronic functions of transistors. Furthermore, a possible perspective for the developments of organic sensors based on this structure are described.

A support infrastructure for the smart kindergarten

Continuing progress in microelectronics has allowed the embedding of sensing, processing, and wireless communications capabilities in familiar physical objects. This enables the creation of smart environments, where communication and computation technologies facilitate interactions between people and their surroundings, instead of just person-to-person or person-to-server communication. In a collaborative project underway at the University of California, Los Angeles, called Smart Kindergarten (SmartKG), we are exploring these technologies in a sensor-instrumented environment for early childhood education. Spatially dense but unobtrusive sensors continuously capture interactions among students, teachers, and common classroom objects. The sensors deliver observations wirelessly to a wired infrastructure for analysis and storage. Two crucial building blocks of this environment are Sylph, a sensor middleware infrastructure, and iBadge, a lightweight sensor-instrumented badge worn by students and teachers.

Enabling Technologies for Electrical Circuits on a Woven Monofilament Hybrid Fabric

Electronic Fabrics is an emerging topic in the field of Smart Textiles. This paper discusses potential technologies to embed electronic circuits into fabrics. Our approach focused on a woven fabric with unobtrusively embedded copper wires that guaranteed usual wearing comfort. Manufacturing, electrical, as well as mechanical aspects of our technologies, were addressed. We explain how interconnects and wiring structures were established within the fabric. Wiring structures were specified by DC resistance, frequency response and line impedance Z0. Our measurements revealed flat frequency responses up to 2 GHz and line impedances in the range of 250 Ω for textile transmission lines. Eventually, we showed that our fabric equipped with electronics withstood the tensile stresses and humidity impacts of daily usage. The presented technologies allow realization and wiring of medium-sized electronic circuits on fabrics with signal frequencies up to several 100 MHz.

Wireless, low-cost interface for body area networks

Embedding of electronics in clothing raises the demand for wireless interconnections for short distances. A low-power transmitter-receiver concept of low-complexity is a crucial factor for maintaining low costs and battery life in a distributed on-body sensor network. This paper presents such a transmission system based on inductive coupling giving a locomotion sensor mounted on the boot as example.