Clevertex - Grado Zero Espace Srl

2.1.3.1.2 Stretch sensors
Stretch sensors are predominantly used for sensing and monitoring body parameters, as the textile is
in contact with the skin over a large body area. This means that monitoring can take place at several
locations at the body.
Some examples of body parameters that can be monitors with means of a stretch sensor are:
• Heart rate and ECG,
• Motion: respiration, movement,
• Pressure: blood.
These parameters are measured at the surface or in the upper body layers.
Textile materials composed of fibres form complex networks of conducting parts that make multiple
contacts. During deformation a number of mechanisms take place:
• The number of contact points changes
• Fibres are extended
• Fibre cross-section is decreased
The number of contact points changes drastically at low extension values, where real fibre
deformation rather takes place at higher levels of strain. An increase in number of contact points
reduces the electrical resistance, whereas fibre extension and reduction of cross-section lead to an
increase of the electrical resistance. As a result, the electrical resistance changes due to deformation
in a way that depends mainly on the textile structure.
This gives textile structures piëzo-resistive properties enabling their use as strain or deformation
sensor. From such signals, motion and even position can be extracted. Indirectly, such structures can
be used to estimate the level of pressure exerted by a bandage on the skin which is an important
parameter for instance for prevention of scar formation [24].
We are taking a close look to heart rate measurements. Heart signals are one of the basic parameters
in health care. The heart is basically a muscle that is controlled by the brain though electric impulses.
The body being a vessel filled with aqueous electrolyte, these signals can be detected in all of its
parts. Small metal plates are commonly used to capture these signals while instruments are analysing
the results, extracting the required parameters such as frequency, phases etc..
Several research projects are being conducted that use electro-conductive textile structures instead of
the metal plates.
The Intellitex suit is the name of a prototype suit that was developed by a Flemish consortium of
universities and companies, among them the textile department of Ghent University. It is a biomedical
suit meant for the long term monitoring of heart rate and respiration of children at the hospital. To
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