Members and Supervisors

Project members

- Hung Quoc DANG

- Baoqi Zhu

Supervisors

- Professor Christophe Fumeaux [1]

- Dr. Shengjian Jammy Chen [2]

Abstract

Wearable antennas have used in a wide range of applications such as: wireless communications, real-time tracking and wireless medical applications. Those antennas have to be integrated into or mounted on clothing and have the stable antenna performances according to the movement of the body. Different particular applications require different antenna performances include: antenna shape, dimension, resonance frequency, gain, direction and radiation efficiency.

This project primarily examines impacts of shorting strategies on the antenna performances. The different shorting strategies are considered in this study include: full shorting wall and two shorting posts which use flexible textile materials to realize. For each shorting methods, we realized three antenna use shorting with silver fabric wall, shorting eyelets and shorting with embroidered wall.

This project also considers impact of different substrate parameter on antenna performances. There feeding techniques include: microstrip line feed, coaxial-line feed and proximity-couple feed, are also examined.

Studies also design the dual-band textile wearable antennas which are able to operate in two ISM bands: (2.4 – 2.5) GHz and (5.725 – 5.875) GHz. All of three antennas satisfy desired requirements.

Introduction

Motivation

Nowadays, Wearable Technology has been widespread used worldwide. Wearable Technology can be found in many fields of life and business. The applications of Wearable Technology are able to be categorized into three different technologies: Advanced wearable products, AI platforms and Big Data.

Wearable antenna has been become one of the most important part in wireless devices. This type of antenna has been using in many fields such as wearable transmitter and receiver, body-sensor, wireless medical applications.

                                                                                   
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Different particular applications require different antenna performances include: antenna shape, dimension, resonance frequency, gain, direction and radiation efficiency. For antenna designs, shorting is a basic component. By using shorting techniques, we can adjust the antenna performances to adapt to specific requirements.

Currently, there are several popular shorting strategies such as: folded strip, embroidered vias, eyelet and PEC. Nevertheless, the shorting strategies which realized by flexible textile material have not been popular.

This project aims to realize the impact of different shorting strategies which use flexible textile materials on the antenna performances. Base on the knowledge about PIFA antenna and shorting strategies, this project is going to design dual-band textile wearable antennas which can operate in two ISM bands: (2.4 – 2.5) GHz and (5.725 – 5.875) GHz.

Objectives

The overall aim of project is to utilize different shorting strategies which use flexible textile materials for wearable antennas. In order to achieve the overall aims, the project’s process is divided by three specific aims.

The first focus is to understand the impacts of different shorting strategies on the antenna specifications. Those shorting strategies include full shorting wall and two shorting posts.

The second specific aim is to design and realize using full shorting wall. In this project, three types of full shorting wall include: shorting wall with silver fabric, shorting eyelets and shorting with embroidered wall, were realized to achieve particular antenna specifications.

The last but not least, the final optimized antenna designs were fabricated and measured for validation. The measured results show the experimentally differences between those shorting strategies for the antenna performances.

Background

Microstrip antenna

There are a lot of antenna types such as: linear wire antenna, aperture antenna, horn antenna and microwave antenna. Among those antennas, microstrip antenna is the most appropriate for wearable application due to several features [1]:

- Simple to manufacture;

- Low cost;

- Compact, lightweight, low-profile configurations;

- Comfortable to planar or non-planar surfaces;

- Robust when mounted on rigid surfaces;

- Versatile with respect to frequency, polarization, pattern and impedance.

                                                                            
                                                                                                      Microstrip antenna [1]

Wearable antenna

Wearable antennas are the special kind of antenna that can be mounted on the clothing and used for communication purposes [7]. Several important factors need to be considered while designing wearable antennas include: appropriate antenna material, fabrication methods and analysis required for a wearable antenna design [7].

There are several conventional wearable antenna designs which include: planar dipoles, monopoles, and microstrip patches [7]. The popular planar microstrip antenna type is Planar Inverted-F Antenna (PIFA). The construction of the PIFA is shown in Fig. 3. In order to control the impedance bandwidth, we can vary the height of PIFA from the ground (less than 10mm). The feed line distance from the shorted edge of the PIFA is used to control the matching of the antenna [11].

                                                                                              
                                                                                                      Construction of the PIFA

Wearable antennas are designed to work while mounting on clothing. Therefore, there are several specific requirements for this antenna type to work effectively and safely in a body-worn context.

Firstly, wearable antennas have to satisfy SAR standards [7]. This standard has been used to consider the amount of power absorbed by the human body. The SAR limit of IEEE is 1.6W/kg for any 1g of tissue [12].

In addition, due to working in body-worn context, wearable antennas must work effectively in different bending conditions. This requirement is especially important when the antenna is mounted on arm of leg which are rounded parts of the body [7].

Furthermore, the on-body measurements have to be considered while designing wearable antenna [7]. Depend on the particular purpose of antenna, it can be applied on different part on body such as: arm, leg, chest and back. Therefore, it is important to measure the antenna performances at particular body part.

Impacts of different shorting strategies on antenna performances

As mentioned above, the primary purpose of shorting strategies is to miniaturize the patch by creating something similar to electric wall. By using shorting strategies, the antenna dimension is reduced significantly.

While shorting wall is placed, the patch and ground are connected. The patch current goes straight to ground instead of be forced to be zero (without shorting wall). At this time, we only need to use the lower half of the cavity to radiate the same resonance frequency with the full patch antenna, the upper half mode is shorted. The fringing fields are shorted at the shorting wall position. At this time, only the fields near the feeding path are used for radiation. Although this method led to the reduction of antenna gain, all other basic antenna performances are similar to the full patch. The difference in Electric field distribution between the full patch antenna and the antenna using shorting wall is shown as: