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.