Characteristics of smart materials and systems

DEFINITIONS
We have been liberally using the term ‘smart materials’
without precisely defining what we mean. Creating a precise
definition, however, is surprisingly difficult. The term is
already in wide use, but there is no general agreement
about what it actually means. A quick review of the literature
indicates that terms like ‘smart’ and ‘intelligent’ are used
almost interchangeably by many in relation to materials and
systems, while others draw sharp distinctions about which
qualities or capabilities are implied. NASA defines smart
materials as ‘materials that ‘‘remember’’ configurations and
can conform to them when given a specific stimulus’,3 a
definition that clearly gives an indication as to how NASA
intends to investigate and apply them. A more sweeping
definition comes from the Encyclopedia of Chemical Technology: ‘smart materials and structures are those objects that sense environmental events, process that sensory information,
and then act on the environment’.4 Even though
these two definitions seem to be referring to the same type of
behavior, they are poles apart. The first definition refers to
materials as substances, and as such, we would think of
elements, alloys or even compounds, but all would be
identifiable and quantifiable by their molecular structure.
The second definition refers to materials as a series of actions.
Are they then composite as well as singular, or assemblies of
many materials, or, even further removed from an identifiable
molecular structure, an assembly of many systems?
If we step back and look at the words ‘smart’ and
‘intelligent’ by themselves we may find some cues to help
us begin to conceptualize a working definition of ‘smart
materials’ that would be relevant for designers. ‘Smart’
implies notions of an informed or knowledgeable response,
with associated qualities of alertness and quickness. In
common usage, there is also frequently an association with
shrewdness, connoting an intuitive or intrinsic response.
Intelligent is the ability to acquire knowledge, demonstrate
good judgment and possess quickness in understanding.
Interestingly, these descriptions are fairly suggestive of the
qualities of many of the smart materials that are of interest to
us. Common uses of the term ‘smart materials’ do indeed
suggest materials that have intrinsic or embedded quick
response capabilities, and, while one would not commonly
think about a material as shrewd, the implied notions of
cleverness and discernment in response are not without
interest. The idea of discernment, for example, leads one to
thinking about the inherent power of using smart materials
selectively and strategically. Indeed, this idea of a strategic use
is quite new to architecture, as materials in our field are rarely
thought of as performing in a direct or local role.
Furthermore, selective use hints at a discrete response – a
singular action but not necessarily a singular material.
Underlying, then, the concept of the intelligent and designed
response is a seamless quickness – immediate action for a
specific and transient stimulus.
Does ‘smartness’, then, require special materials and
advanced technologies? Most probably no, as there is nothing
a smart material can do that a conventional system can’t. A
photochromic window that changes its transparency in
relation to the amount of incident solar radiation could be
replaced by a globe thermometer in a feedback control loop
sending signals to a motor that through mechanical linkages
repositions louvers on the surface of the glazing, thus changing the net transparency. Unwieldy, yes, but nevertheless feasible and possible to achieve with commonly used
technology and materials. (Indeed, many buildings currently
use such a system.) So perhaps the most unique aspects of
these materials and technologies are the underlying concepts
that can be gleaned from their behavior.

Whether a molecule, a material, a composite, an assembly, or a system, ‘smart materials and technologies’ will exhibit the following characteristics:

* Immediacy – they respond in real-time.
* Transiency – they respond to more than one environmental state.
* Self-actuation – intelligence is internal to rather than external to the ‘material’.
* Selectivity – their response is discrete and predictable.
* Directness – the response is local to the ‘activating’ event.

It may be this last characteristic, directness, that poses the
greatest challenge to architects. Our building systems are
neither discrete nor direct. Something as apparently simple as
changing the temperature in a room by a few degrees will set
off a Rube Goldberg cascade of processes in the HVAC system,
affecting the operation of equipment throughout the building.
The concept of directness, however, goes beyond making
the HVAC equipment more streamlined and local; we must
also ask fundamental questions about the intended behavior
of the system. The current focus on high-performance
buildings is directed toward improving the operation and
control of these systems. But why do we need these particular
systems to begin with?
The majority of our building systems, whether HVAC,
lighting, or structural, are designed to service the building
and hence are often referred to as ‘building services’.
Excepting laboratories and industrial uses, though, buildings
exist to serve their occupants. Only the human body requires
management of its thermal environment, the building does
not, yet we heat and cool the entire volume. The human eye
perceives a tiny fraction of the light provided in a building,
but lighting standards require constant light levels throughout
the building. If we could begin to think of these
environments at the small scale – what the body needs –
and not at the large scale – the building space – we could
dramatically reduce the energy and material investment of
the large systems while providing better conditions for the
human occupants. When these systems were conceived over
a century ago, there was neither the technology nor the knowledge to address human needs in any manner other than through large indirect systems that provided homogeneous
building conditions. The advent of smart materials now enables the design of direct and discrete environments
for the body, but we have no road map for their application in this important arena.