Textile Antennas for Wearable Application in the 863-870 MHz Frequency Range: Design, Fabrication and Performance Analysis

Wearable systems offer an effective solution to seamlessly integrate functionalities such as sensing, communication, and localization by implementing the components directly on the fabric or on the wearable device itself. This innovative technology is widely used across numerous IoT applications and fields revolutionizing our everyday lives by improving comfort and portability while simplifying implementation and usage. In health care, wearables systems are extensively employed for monitoring patients' vital data and transmitting it through wireless communication technologies. They are also widely used in sports for monitoring athlete performances enabling GPS tracking and navigation assistance. Additionally, in military applications, wearables technology provides secure and reliable communication in the field. These systems seamlessly integrate both the sensing components and the communication system creating a compact, lightweight, and portable solution enhancing the overall usability and practicality of the device. The key element of the wearables system lies in textile antennas. This work aims to present the design and implementation process of two different types of embroidered textile antennas tailored to be integrated into a smart textile system. The proposed antennas include a bow tie textile antenna based on Sierpinsky geometry and a dipole textile antenna both designed to work at 868 MHz. A simulation analysis is conducted using CST to tune the central frequency of both antennas and determine the appropriate dimensions necessary to start the fabrication process. While the CST model provides valuable insights, certain limitations are identified and will be further addressed. During the fabrication process, several challenges emerged, in particular ensuring consistent and reliable conductivity of the conductive thread across the embroidered pattern. Variations in thread properties and stitching techniques strongly impact the resonant frequency and so the antenna's performance. Based on the analysis, two textile antenna models were crafted for easy hand-embroidering onto a substrate for wearable applications and implemented in a body temperature monitoring system with LoRa connectivity. Additionally, a workshop was conducted in Regensburg, Germany where young students successfully embroidered their antennas, showing the accessibility and ease of implementing smart textiles and textile electronics for diverse solutions.