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With this definition, we can expect a smart textile to behave in a manner that
goes well beyond our normal expectations of textiles. Similarly, Tao (2000)
proposes that ‘smart materials and structures can
be defined as the materials
and structures that sense and react to environmental conditions or stimuli, or
respond to, or be activated to perform a function by manual operation or in
a pre-programmed manner’. The implication, therefore, is that three components
may be present in intelligent textiles: a means of detecting changes in the
environment (sensors); a means of responding to that change (actuators);
and controlling units. In a simple analogy to the human body,
the sensors are
our five senses detecting mechanical (touch, hearing), electromagnetic (vision)
and chemical stimuli (taste, smell), while the actuators include (for example)
muscles, sweat glands, and so on. The controlling unit is our brain – allowing
us to process the information and control our response. Clearly some actuation
responses seem to happen automatically (such as sweating in response to
elevated temperature), while others can be consciously processed (such as
deciding to run away when we see a potential threat approaching in the
distance).
It is this author’s preference to identify three categories of intelligent
textiles, according to the type of features they have and the degree of
sophistication of their intelligent response and behaviour.
Similar classifications
have been used by others. The categories are:
1.
Passive intelligent textiles, which are capable of sensing environmental
conditions or stimuli, and can supply that information to another system
(human or technological). These types of sensors often utilise changes
in the electrical properties of conductive fibres as a means of detecting
stimuli. The textile-based strain gauges developed and used by De Rossi
et al. (1999) and CSIRO/IPRI (Munro
et al., 2004)
are good examples
of these. The stimulus is a mechanical deformation, which brings about
a change in the electrical resistance of a conductive fabric. Detection of
changes in the light transmission properties of optical fibres in response
to stimuli has also been demonstrated (Guan
et al., 2000; Tao
et al.,
2000).
2.
Active intelligent textiles would be capable of not only sensing
environmental conditions or other stimuli, but also responding to them
by adapting their properties in some advantageous way.
Shape memory
materials (Vigo, 1997; Marks, 2001) or electro-active actuators (Otero
and Sansiñena, 1998) are examples of these. Sometimes the sensing and
actuation functions cannot be separated, such as in (at a very simple
level) thermo-chromic materials that change colour in response to a
change in temperature. The colour change is an outcome of thermally
induced changes to the molecular structure of the material.
3.
The final category is intelligent textiles that include systems for processing
© 2009 Woodhead Publishing Limited
Advances
in wool technology
310
and/or transmission of data collected by sensor systems. This might be
used to process sensor inputs and control actuator functions. This category
also includes the field known as ‘electronic textiles’ or ‘wearable
electronics’, and includes textile-based electrical devices. The textile-
based control systems developed by Softswitch (
www.softswitch.co.uk)
and Eleksen (
www.eleksen.com)
are examples of these, as are the numerous
heated textile technologies now available.
In this chapter the terms ‘intelligent textile’ and ‘smart textile’ are taken to
be synonyms and are used interchangeably.
13.2.1 ‘Smart’ textiles that are not really smart
To a large degree manufacturers and marketers are
determining the boundaries
of what constitutes a smart textile. In some circumstances this means that
conventional technologies are being re-packaged as ‘smart’, when perhaps a
better definition of them would simply be ‘high performance’. For example
microporous waterproof breathable membranes are sometimes referred to as
smart, because they allow moisture vapour to pass through, while preventing
liquid moisture from penetrating. This occurs because of the size of the
pores in the membrane (vapour
molecules are small, while droplets are
large) and while this is a very useful function, the material cannot be considered
to be smart because it does not sense any environmental change, nor does it
respond to one. If this is a smart textile then so is the fishing net that allows
small fish to escape while trapping big fish! The concept and the method of
manufacturing the
material may be sophisticated, and certainly offering a
level of performance that exceeds that of conventional materials, but there is
no smart behaviour or smart functionality in the textile itself.
Conversely, just because a material responds to an environmental stimulus
it is not automatically smart either. Metal railway lines might respond to an
increase in temperature by expanding in length, resulting in buckled tracks
and derailed trains. This is clearly not a smart response.
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