Abstract

In this paper is reported the experience gained in the last five years, in the implementation of wearable systems for personalized health care and their evolution in time. Sensing bio clothes for vital signs monitoring and wearable systems for gesture and posture recognition are specifically illustrated, resulting from the EU funded projects: Wealthy and My Heart.

I. INTRODUCTION

In the last few years, monitoring systems based on multifunctional instrumented garments are playing an innovative role in the development of more human oriented monitoring devices. Smart fabrics allow the monitoring of patients over extended period, in a natural contest, in biomedicine, as well as in several health-focused disciplines, such as bio-monitoring, rehabilitation, telemedicine, tele-assistance, ergonomics and sport medicine [1]. The innovation in this field is originated by the development of a new generation of textile sensors, combining electronics and informatics novelties, leading to the integration of multiple, smart functions into textiles based sensing interfaces, aiming to the reduction of any impediment [2].

In this work, it will be report the experiences gained during the last five years in the manufacturing of sensing systems and their evolution in time. The wearable instrumented garments are based on conductive and piezoresistive fabric developed to work as textile sensors, where the mechanical and thermal properties are kept as those of textile materials.

Our research exploited different technologies from flat and circular knitting to woven process, as well as the use of a cut and sew approach to manufacture sensing elastic fabric on which piezoresistive sensors are printed, according to an engineered body map.

II. MATERIALS AND METHODS

A common textile process like flat-knitting technology (Steiger SA4, Switzerland) allows the implementation of fabric where defined yarns are confined into insulated domains, realizing multi-layered structures where the conductive surface is sandwiched between two insulated standard textile surfaces.

Sensors, electrodes and connections can be fully integrated in the fabric and produced in one single step, by combining conductive and non conductive yarns. The electrical properties of fabric are due to the interaction among the fibres inside the yarn and the interaction among the single loops inside the fabric. The whole textile structure has to be considered as a complicate array of electrical impedances [3].

Most sensors that are used for the detection of vital signs and users movements need to be in close contact with the body (like a second skin). The use of seamless knitting dedicated machine (i.e. Santoni SpA5) can provide elastic, adherent, comfortable garments with these inherent properties.

A. Fabric Electrodes realized by flat-knitting technology

The conductive fabric electrodes, used in the frame of Wealthy European project (IST-2001-37778), have been knitted by means of flat knitting machine (Steiger SA4, Switzerland). They have been realized with commercial stainless steel threads twisted around a standard continuous viscose (or cotton) textile yarn [4].

The quality of bioelectrical signals gathered in dynamic condition can be improved by coupling fabric electrodes with a hydrogel membrane, purchased by ST&D Ltd (Belfast, U.K.). The membrane reduces the contact resistance between the skin and the electrode, and increases the stability of the contact with its adhesive properties, without affecting the comfort. The pH of the chosen membrane avoids skin irritation.