Intro to Materials

Smart planes intelligent houses shape memory textiles micromachines self-assembling structures color-changingpaint nanosystems. The vocabulary of the material world haschanged dramatically since 1992, when the first smartmaterial emerged commercially in, of all things, snow skis.Defined as highly engineered materials that respond intelli-gently to their environment, smart materials have becomethe go-to answer for the 21st centurys technological needs.NASA is counting on smart materials to spearhead the firstmajor change in aeronautic technology since the develop-ment of hypersonic flight, and the US Defense Departmentenvisions smart materials as the linchpin technology behindthe soldier of the future, who will be equipped witheverything from smart tourniquets to chameleon-like cloth-ing. At the other end of the application spectrum, toys asbasic as Play-Doh and equipment as ubiquitous as laserprinters and automobile airbag controls have already incor-porated numerous examples of this technology during thepast decade. It is the stuff of our future even as it has alreadypercolated into many aspects of our daily lives.

In the sweeping glamorization of smart materials, weoften forget the legacy from which these materials sproutedseemingly so recently and suddenly. Texts from as early as300 BC were the first to document the science of alchemy.1

Metallurgy was by then a well-developed technology prac-ticed by the Greeks and Egyptians, but many philosopherswere concerned that this empirical practice was not governedby a satisfactory scientific theory. Alchemy emerged as thattheory, even though today we routinely think of alchemy ashaving been practiced by late medieval mystics and charla-tans. Throughout most of its lifetime, alchemy was associatedwith the transmutation of metals, but was also substantiallyconcerned with the ability to change the appearance, inparticular the color, of given substances. While we often hearabout the quest for gold, there was an equal amount ofattention devoted to trying to change the colors of variousmetals into purple, the color of royalty. Nineteenth-centurymagic was similarly founded on the desire for something to beother than it is, and one of the most remarkable predecessorsto todays color-changing materials was represented by aningenious assembly known as a blow book. The magician

Materials in architecture and design 1

1 Materials in architecture and design

s Figure 1-1 NASAs vision of a smart planethat will use smart materials to morph inresponse to changing environmental con-ditions. (NASA LARC)

would flip through the pages of the book, demonstrating tothe audience that all the pages were blank. He would thenblow on the pages with his warm breath, and reflip throughthe book, thrilling the audience with the sudden appearanceof images on every page. That the book was composed ofpages alternating between image and blank with carefullyplaced indentions to control which page flipped in relation tothe others makes it no less a conceptual twin to the modernthermochromic material.

What, then, distinguishes smart materials? This book setsout to answer that question in the next eight chapters and,furthermore, to lay the groundwork for the assimilation andexploitation of this technological advancement within thedesign professions. Unlike science-driven professions in whichtechnologies are constantly in flux, many of the designprofessions, and particularly architecture, have seen relativelylittle technological and material change since the 19thcentury. Automobiles are substantially unchanged from theirforebear a century ago, and we still use the building framingsystems developed during the Industrial Revolution. In ourforthcoming exploration of smart materials and new technol-ogies we must be ever-mindful of the unique challengespresented by our field, and cognizant of the fundamentalroots of the barriers to implementation. Architecture height-ens the issues brought about by the adoption of newtechnologies, for in contrast to many other fields in whichthe material choice serves the problem at hand, materialsand architecture have been inextricably linked throughouttheir history.

1.1 Materials and architectureThe relationship between architecture and materials had beenfairly straightforward until the Industrial Revolution. Materialswere chosen either pragmatically for their utility andavailability or they were chosen formally for theirappearance and ornamental qualities. Locally available stoneformed foundations and walls, and high-quality marbles oftenappeared as thin veneers covering the rough construction.Decisions about building and architecture determined thematerial choice, and as such, we can consider the pre-19thcentury use of materials in design to have been subordinate toissues in function and form. Furthermore, materials were notstandardized, so builders and architects were forced to rely onan extrinsic understanding of their properties and perfor-mance. In essence, knowledge of materials was gainedthrough experience and observation. Master builders were

Smart Materials and New Technologies


s Figure 1-2 Wireless body temperature sen-sor will communicate soldiers physical stateto a medics helmet. (Courtesy of ORNL)

those who had acquired that knowledge and the skillsnecessary for working with available materials, often throughdisastrous trial and error.

The role of materials changed dramatically with the adventof the Industrial Revolution. Rather than depending on anintuitive and empirical understanding of material propertiesand performance, architects began to be confronted withengineered materials. Indeed, the history of modern archi-tecture can almost be viewed through the lens of the historyof architectural materials. Beginning in the 19th century withthe widespread introduction of steel, leading to the emer-gence of long-span and high-rise building forms, materialstransitioned from their pre-modern role of being subordinateto architectural needs into a means to expand functionalperformance and open up new formal responses. Theindustrialization of glass-making coupled with developmentsin environmental systems enabled the international style inwhich a transparent architecture could be sited in any climateand in any context. The broad proliferation of curtain wallsystems allowed the disconnection of the facade material fromthe buildings structure and infrastructure, freeing the mate-rial choice from utilitarian functions so that the facade couldbecome a purely formal element. Through advancementsin CAD/CAM (Computer Aided Design/Computer AidedManufacturing) technologies, engineering materials such asaluminum and titanium can now be efficiently and easilyemployed as building skins, allowing an unprecedented rangeof building facades and forms. Materials have progressivelyemerged as providing the most immediately visible and thusmost appropriable manifestation of a buildings representa-tion, both interior and exterior. As a result, todays architectsoften think of materials as part of a design palette from whichmaterials can be chosen and applied as compositional andvisual surfaces.

It is in this spirit that many have approached the use ofsmart materials. Smart materials are often considered to be alogical extension of the trajectory in materials developmenttoward more selective and specialized performance. For manycenturies one had to accept and work with the properties of astandard material such as wood or stone, designing toaccommodate the materials limitations, whereas during the20th century one could begin to select or engineer theproperties of a high performance material to meet aspecifically defined need. Smart materials allow even a furtherspecificity their properties are changeable and thus respon-sive to transient needs. For example, photochromic materialschange their color (the property of spectral transmissivity)



when exposed to light: the more intense the incident light,the darker the surface. This ability to respond to multiplestates rather than being optimized for a single state hasrendered smart materials a seductive addition to the designpalette since buildings are always confronted with changingconditions. As a result, we are beginning to see manyproposals speculating on how smart materials could beginto replace more conventional building materials.

Cost and availability have, on the whole, restricted wide-spread replacement of conventional building materials withsmart materials, but the stages of implementation are tendingto follow the model by which new materials have tradition-ally been introduced into architecture: initially through highlyvisible showpieces (such as thermochromic chair backs andelectrochromic toilet stall doors) and later through highprofile demonstration projects such as Diller and ScofidiosBrasserie Restaurant on the ground floor of Mies van derRohes seminal Seagrams Building. Many architects furtherimagine building surfaces, walls and facades composedentirely of smart materials, perhaps automatically enhancingtheir design from a pedestrian box to an interactive arcade.Indeed, terms like interactivity and transformability havealready become standard parts of the architects vocabularyeven insofar as the necessary materials and technologies arefar beyond the economic and practical reality of most buildingprojects.

Rather than waiting for the cost to come down and for thematerial production to shift from lots weighing pounds tothose weighing tons, we should step back and ask if we areignoring some of the most important characteristics of thesematerials. Architects have conceptually been trying to fitsmart materials into their normative practice alongsideconventional building materials. Smart materials, however,represent a radical departure from the more normativebuilding materials. Whereas standard building materials arestatic in that they are intended to withstand building forces,smart materials are dynamic in that they behave in response toenergy fields. This is an important distinction as our normalmeans of representation in architectural design privileges thestatic material: the plan, section and elevation drawings oforthographic projection fix in location and in view thephysical components of a building. One often designs withthe intention of establishing an image or multiple sequentialimages. With a smart material, however, we should befocusing on what we want it do, not on how we want it tolook. The understanding of smart materials must then reachback further than simply the understanding of material



s Figure 1-3 The heat chair that usesthermochromic paint to provide a markerof where and when the body rested on thesurface. (Courtesy of Juergen Mayer H)

properties; one must also be cognizant of the fundamentalphysics and chemistry of the materials interactions with itssurrounding environment. The purpose of this book is thustwo-fold: the development of a basic familiarity with thecharacteristics that distinguish smart materials from the morecommonly used architectural materials, and speculation intothe potential of these characteristics when deployed inarchitectural design.

1.2 The contemporary designcontext

Orthographic projection in architectural representationinherently privileges the surface. When the three-dimen-sional world is sliced to fit into a two-dimensional represen-tation, the physical objects of a building appear as flatplanes. Regardless of the third dimension of these planes, werecognize that the eventual occupant will rarely see anythingother than the surface planes behind which the structureand systems are hidden. While the common mantra is thatarchitects design space the reality is that architects make(draw) surfaces. This privileging of the surface drives the useof materials in two profound ways. First is that the material isidentified as the surface: the visual understanding ofarchitecture is determined by the visual qualities of thematerial. Second is that because architecture is synonymouswith surface and materials are that surface we essentiallythink of materials as planar. The result is that we tend toconsider materials in large two-dimensional swaths: exteriorcladding, interior sheathing. Many of the materials that wedo not see, such as insulation or vapor barriers, are stillimagined and configured as sheet products. Even materialsthat form the three-dimensional infrastructure of the build-ing, such as structural steel or concrete, can easily berepresented through a two-dimensional picture plane aswe tend to imagine them as continuous or monolithicentities. Most current attempts to implement smart materialsin architectural design maintain the vocabulary of the two-dimensional surface or continuous entity and simply proposesmart materials as replacements or substitutes for moreconventional materials. For example, there have been manyproposals to replace standard curtain wall glazing with anelectrochromic glass that would completely wrap the build-ing facade. The reconsideration of smart material implemen-tation through another paradigm of material deploymenthas yet to fall under scrutiny.



One major constraint that limits our current thinking aboutmaterials is the accepted belief that the spatial envelopebehaves like a boundary. We conceive of a room as acontainer of ambient air and light that is bounded ordifferentiated by its surfaces; we consider the buildingenvelope to demarcate and separate the exterior environmentfrom the interior environment. The presumption that thephysical boundaries are one and the same as the spatialboundaries has led to a focus on highly integrated, multi-functional systems for facades as well as for many interiorpartitions such as ceilings and floors. In 1981, Mike Daviespopularized the term polyvalent wall, which described afacade that could protect from the sun, wind and rain, as wellas provide insulation, ventilation and daylight.2 His image of awall section sandwiching photovoltaic grids, sensor layers,radiating sheets, micropore membranes and weather skins has



s Figure 1-4 Aerogel has a density only three times that of air, but itcan support significant weights and is a superb insulator. Aerogelswere discovered in 1931 but were not explored until the 1970s.(NASA)

influenced many architects and engineers into pursuing thesuper facade as evidenced by the burgeoning use of double-skin systems. This pursuit has also led to a quest for a super-material that can integrate together the many diversefunctions required by the newly complex facade. Aerogelhas emerged as one of these new dream materials forarchitects: it insulates well yet still transmits light, it isextremely lightweight yet can maintain its shape. Manynational energy agencies are counting on aerogel to be alinchpin for their future building energy conservation strate-gies, notwithstanding its prohibitive cost, micro-structuralbrittleness and the problematic of its high insulating value,which is only advantageous for part of the year and can bequite detrimental at other times.

1.3 The phenomenologicalboundary

Missing from many of these efforts is the understanding ofhow boundaries physically behave. The definition of bound-ary that people typically accept is one similar to that offeredby the Oxford English Dictionary: a real or notional linemarking the limits of an area. As such, the boundary is staticand defined, and its requirement for legibility (marking)prescribes that it is a tangible barrier thus a visual artifact.For physicists, however, the boundary is not a thing, but anaction. Environments are understood as energy fields, and theboundary operates as the transitional zone between differentstates of an energy field. As such, it is a place of change as anenvironments energy field transitions from a high-energy tolow-energy state or from one form of energy to another.Boundaries are therefore, by definition, active zones ofmediation rather than of delineation. We cant see them,nor can we draw them as known objects fixed to a location.

Breaking the paradigm of the hegemonic material as visualartifact requires that we invert our thinking; rather thansimply visualizing the end result, we need to imagine thetransformative actions and interactions. What was once a bluewall could be simulated by a web of tiny color-changingpoints that respond to the position of the viewer as well as tothe location of the sun. Large HVAC (heating, ventilating andair conditioning) systems could be replaced with discretelylocated micro-machines that respond directly to the heatexchange of a human body. In addition, by investigating thetransient behavior of the material, we challenge the privile-ging of the static planar surface. The boundary is no longer



delimited by the material surface, instead it may be reconfi-gured as the zone in which change occurs. The image of thebuilding boundary as the demarcation between two differentenvironments defined as single states a homogeneousinterior and an ambient exterior could possibly be replacedby the idea of multiple energy environments fluidly interact-ing with the moving body. Smart materials, with theirtransient behavior and ability to respond to energy stimuli,may eventually enable the selective creation and design of anindividuals sensory experiences.

Are architects in a position or state of development toimplement and exploit this alternative paradigm, or, at thevery least, to rigorously explore it? At this point, the answer ismost probably no, but there are seeds of opportunity fromon-going physical research and glimpses of the future use ofthe technology from other design fields. Advances in physicshave led to a new understanding of physical phenomena,advances in biology and neurology have led to new dis-coveries regarding the human sensory system. Furthermore,smart materials have been comprehensively experimentedwith and rapidly adopted in many other fields finding theirway into products and uses as diverse as toys and automotivecomponents. Our charge is to examine the knowledge gainedin other disciplines, but develop a framework for its applica-tion that is suited to the unique needs and possibilities ofarchitecture.

1.4 Characteristics of smartmaterials and systems

DEFINITIONS

We have been liberally using the term smart materialswithout precisely defining what we mean. Creating a precisedefinition, however, is surprisingly difficult. The term isalready in wide use, but there is no general agreementabout what it actually means. A quick review of the literatureindicates that terms like smart and intelligent are usedalmost interchangeably by many in relation to materials andsystems, while others draw sharp distinctions about whichqualities or capabilities are implied. NASA defines smartmaterials as materials that remember configurations andcan conform to them when given a specific stimulus,3 adefinition that clearly gives an indication as to how NASAintends to investigate and apply them. A more sweepingdefinition comes from the Encyclopedia of Chemical



Technology: smart materials and structures are those objectsthat sense environmental events, process that sensory infor-mation, and then act on the environment.4 Even thoughthese two definitions seem to be referring to the same type ofbehavior, they are poles apart. The first definition refers tomaterials as substances, and as such, we would think ofelements, alloys or even compounds, but all would beidentifiable 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 ofmany materials, or, even further removed from an identifiablemolecular structure, an assembly of many systems?

If we step back and look at the words smart andintelligent by themselves we may find some cues to helpus begin to conceptualize a working definition of smartmaterials that would be relevant for designers. Smartimplies notions of an informed or knowledgeable response,with associated qualities of alertness and quickness. Incommon usage, there is also frequently an association withshrewdness, connoting an intuitive or intrinsic response.Intelligent is the ability to acquire knowledge, demonstrategood judgment and possess quickness in understanding.

Interestingly, these descriptions are fairly suggestive of thequalities of many of the smart materials that are of interest tous. Common uses of the term smart materials do indeedsuggest materials that have intrinsic or embedded quickresponse capabilities, and, while one would not commonlythink about a material as shrewd, the implied notions ofcleverness and discernment in response are not withoutinterest. The idea of discernment, for example, leads one tothinking about the inherent power of using smart materialsselectively and strategically. Indeed, this idea of a strategic useis quite new to architecture, as materials in our field are rarelythought of as performing in a direct or local role.Furthermore, selective use hints at a discrete response asingular action but not necessarily a singular material.Underlying, then, the concept of the intelligent and designedresponse is a seamless quickness immediate action for aspecific and transient stimulus.

Does smartness, then, require special materials andadvanced technologies? Most probably no, as there is nothinga smart material can do that a conventional system cant. Aphotochromic window that changes its transparency inrelation to the amount of incident solar radiation could bereplaced by a globe thermometer in a feedback control loopsending signals to a motor that through mechanical linkagesrepositions louvers on the surface of the glazing, thus



changing the net transparency. Unwieldy, yes, but never-theless feasible and possible to achieve with commonly usedtechnology and materials. (Indeed, many buildings currentlyuse such a system.) So perhaps the most unique aspects ofthese materials and technologies are the underlying conceptsthat can be gleaned from their behavior.

Whether a molecule, a material, a composite, an assembly,or a system, smart materials and technologies will exhibit thefollowing 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 thegreatest challenge to architects. Our building systems areneither discrete nor direct. Something as apparently simple aschanging the temperature in a room by a few degrees will setoff a Rube Goldberg cascade of processes in the HVAC system,affecting the operation of equipment throughout the build-ing. The concept of directness, however, goes beyond makingthe HVAC equipment more streamlined and local; we mustalso ask fundamental questions about the intended behaviorof the system. The current focus on high-performancebuildings is directed toward improving the operation andcontrol of these systems. But why do we need these particularsystems to begin with?

The majority of our building systems, whether HVAC,lighting, or structural, are designed to service the buildingand hence are often referred to as building services.Excepting laboratories and industrial uses, though, buildingsexist to serve their occupants. Only the human body requiresmanagement of its thermal environment, the building doesnot, yet we heat and cool the entire volume. The human eyeperceives a tiny fraction of the light provided in a building,but lighting standards require constant light levels through-out the building. If we could begin to think of theseenvironments at the small scale what the body needs and not at the large scale the building space we coulddramatically reduce the energy and material investment ofthe large systems while providing better conditions for thehuman occupants. When these systems were conceived overa century ago, there was neither the technology nor the



knowledge to address human needs in any manner otherthan through large indirect systems that provided homo-geneous building conditions. The advent of smart materialsnow enables the design of direct and discrete environmentsfor the body, but we have no road map for their applicationin this important arena.

1.5 Moving forwardLong considered as one of the roadblocks in the developmentand application of smart materials is the confusion over whichdiscipline should own and direct the research efforts as wellas oversee applications and performance. Notwithstandingthat the discovery of smart materials is attributed to twochemists (Jacques and Pierre Curie no less!), the disciplines ofmechanical engineering and electrical engineering currentlysplit ownership. Mechanical engineers deal with energystimuli, kinematic (active) behavior and material structure,whereas electrical engineers are responsible for microelec-tronics (a fundamental component of many smart systemsand assemblies), and the operational platform (packaging andcircuitry). Furthermore, electrical engineers have led theefforts toward miniaturization, and as such, much of thefabrication, which for most conventional materials would behoused in mechanical engineering, is instead under theumbrella of electrical engineering.

This alliance has been quite effective in the development ofnew technologies and materials, but has been less so in regardto determining the appropriate applications. As a result, thesmart materials arena is often described as technology pushor, in other words, technologies looking for a problem.Although this is an issue that is often raised in overviewsand discussions of smart materials, it has been somewhatnullified by the rapid evolution and turnover of technologiesin general. Many industries routinely adopt and discardtechnologies as new products are being developed and oldones are upgraded. As soon as knowledge of a new smartmaterial or technology enters the public realm, industries ofall sizes and of all types will begin trying it out, eliminating theround pegs for the square holes. This trial and error ofmatching the technology to a problem may well open upunprecedented opportunities for application that would havegone undetected if the more normative problem firstdevelopmental sequence had occurred. For architecture,however, this reversal is much more problematic.

In most fields, technologies undergo continuous cycles ofevolution and obsolescence as the governing science matures;



as a result, new materials and technologies can be easilyassimilated. In architecture, however, technologies have verylong lifetimes, and many factors other than science determinetheir use and longevity. There is no mechanism by which newadvances can be explored and tested, and the small profitmargin in relation to the large capital investment of construc-tion does not allow for in situ experimentation. Furthermore,buildings last for years 30 on average and many last for acentury or more. In spite of new construction, the yearlyturnover in the building stock is quite low. Anything new mustbe fully verified in some other industry before architects canpragmatically use it, and there must also be a match with aclient who is willing to take the risk of investing in anytechnology that does not have a proven track record.

The adoption of smart materials poses yet anotherdilemma for the field of architecture. Whereas architectschoose the materials for a building, engineers routinelyselect the technologies and design the systems. Smartmaterials are essentially material systems with embeddedtechnological functions, many of which are quite sophisti-cated. Who, then, should make the decisions regarding theiruse? Compounding this dilemma are the technologies at theheart of smart materials; the branches of mechanical andelectrical engineering responsible for overseeing this areahave virtually no connection to or relationship with theengineering of building systems. Not only are smartmaterials a radical departure from the more normativematerials in appearance, but their embedded technologyhas no precedent in the large integrated technologicalsystems that are the standard in buildings.

How can architects and designers begin to explore andexploit these developing technologies and materials, with therecognition that their operating principles are among themost sophisticated of any technologies in use? Althougharchitecture is inherently an interdisciplinary profession, itspractice puts the architect at the center, as the director of theprocess and the key decision-maker. The disciplines that wemust now reach out to, not only mechanical and electricalengineering, but also the biological sciences, have littlecommon ground. There are no overlapping boundaries inknowledge, such as you might find between architecture andurban design, and there is no commonality of problem, suchas you might find between architecture and ecology. Ourknowledge base, our practice arena, and even our languageare split from those in the smart materials domain. Ultimately,our use of these materials will put us into the heady role ofmanipulating the principles of physics.



1.6 Organization of the textThe objectives of this book are thus three-fold. The first is toprovide a primer on smart materials, acquainting architectsand designers with the fundamental features, properties,behaviors and uses of smartmaterials. Of particular importanceis the development of a vocabulary and a descriptive languagethat will enable the architect to enter into the world of thematerial scientist and engineer. The second objective is theframing of these new materials and technologies as behaviorsor actions and not simply as artifacts. We will be describingsmart materials in relation to the stimulus fields that surroundthem. Rather than categorizing materials by application orappearance, we will then categorize them in relation to theiractions and their energy stimulus. Our third objective is thedevelopment of a methodological approach for working withthese materials and technologies. We will successively buildsystems and scenarios as the book progresses, demonstratinghow properties, behaviors, materials and technologies can becombined to create new responses. If these three objectives aremet, the designer will be able to take a more proactive stancein determining the types of materials and systems that shouldbe developed and applied. Furthermore, competency in thefoundations of energy and material composition behavior willeventually allow the architect or designer to think at aconceptual level above that of the material or technology.One of the constants in the field of smart materials is that theyare continuously being updated or replaced. If we understandclasses of behaviors in relation to properties and energy fields,then we will be able to apply that understanding to any newmaterial we may meet in the future.

To pull these objectives together, the overall organizationof the book follows a bipartite system; categories of behaviorwill be established and then will be overlaid with increasingcomponent and system complexity. Chapter 2 serves as theentry into the subject of material properties and materialbehavior, whereas Chapter 3 first posits the frameworkthrough which we will categorize smart materials. We willestablish a basic relationship between material properties,material states and energy that we can use to describe theinteraction of all materials with the environments thermal,luminous and acoustic that surround the human body. Thisbasic relationship forms a construct that allows us to under-stand the fundamental mechanisms of smartness. Theresulting construct will form the basis not only for thecategories, but will also be useful as we discuss potentialcombinations and applications.



Smartness in a material or system is determined by one oftwo mechanisms, which can be applied directly to a singularmaterial, and conceptually to a compound system (althoughindividual components may well have one of the directmechanisms). If the mechanism affects the internal energyof the material by altering either the materials molecularstructure or microstructure then the input results in a propertychange of the material. (The term property is important inthe context of this discussion and will be elaborated uponlater. Briefly, the properties of a material may be eitherintrinsic or extrinsic. Intrinsic properties are dependent on theinternal structure and composition of the material. Manychemical, mechanical, electrical, magnetic and thermalproperties of a material are normally intrinsic to it. Extrinsicproperties are dependent on other factors. The color of amaterial, for example, is dependent on the nature of theexternal incident light as well as the micro-structure of thematerial exposed to the light.) If the mechanism changes theenergy state of the material, but does not alter the materialper se, then the input results in an exchange of energy fromone form to another. A simple way of differentiating betweenthe two mechanisms is that for the property change type(hereafter defined as Type I), the material absorbs the inputenergy and undergoes a change, whereas for the energyexchange type (Type II), the material stays the same but theenergy undergoes a change. We consider both of thesemechanisms to operate directly at the micro-scale, as nonewill affect anything larger than the molecule, and further-more, many of the energy-exchanges take place at the atomiclevel. As such, we cannot see this physical behavior at thescale at which it occurs.

HIGH-PERFORMANCE VERSUS SMART MATERIALS

We will soon begin to use the construct just described tobegin characterizing smart materials, and specifically look atmaterials that change their properties in response to varyingexternal stimuli and those that provide energy transformationfunctions. This construct is specific to smart materials. It doesnot reflect, for example, many extremely exciting and usefulnew materials currently in vogue today. Many of theseinteresting materials, such as composites based on carbonfibers or some of the new radiant mirror films, change neithertheir properties nor provide energy transfer functions; andhence are not smart materials. Rather, they are what mightbest be described as high-performance materials. They often



s Figure 1-5 Radiant color film. The color ofthe transmitted or reflected light dependsupon the vantage point. Observers at dif-ferent places would see different colors (seeChapter 6)

have what might be called selected and designed properties(e.g., extremely high strength or stiffness, or particularreflective properties). These particular properties have beenoptimized via the use of particular internal material structuresor compositions. These optimized properties, however, arestatic. Nevertheless, we will still briefly cover selected highperformance materials later in Chapter 4 because of the waythey interact with more clearly defined smart materials.

TYPE 1 MATERIALS

Based on the general approach described above, smartmaterials may be easily classified in two basic ways. In oneconstruct we will be referring to materials that undergochanges in one or more of their properties chemical,mechanical, electrical, magnetic or thermal in directresponse to a change in the external stimuli associated withthe environment surrounding the material. Changes are directand reversible there is no need for an external controlsystem to cause these changes to occur. A photochromicmaterial, for example, changes its color in response to achange in the amount of ultraviolet radiation on its surface.We will be using the term Type 1 materials to distinguish thisclass of smart materials.

Chapter 4 will discuss these materials in detail. Briefly,some of the more common kinds of Type 1 materials includethe following:

* Thermochromic an input of thermal energy (heat) to thematerial alters its molecular structure. The new molecularstructure has a different spectral reflectivity than does theoriginal structure; as a result, the materials color itsreflected radiation in the visible range of the electro-magnetic spectrum changes.

* Magnetorheological the application of a magnetic field(or for electrorheological an electrical field) causes a



s Figure 1-6 Design experiment: view directional film and radiantcolor film have been used together in this facade study. (NyriabuNyriabu)

change in micro-structural orientation, resulting in achange in viscosity of the fluid.

* Thermotropic an input of thermal energy (or radiation fora phototropic, electricity for electrotropic and so on) to thematerial alters its micro-structure through a phase change.In a different phase, most materials demonstrate differentproperties, including conductivity, transmissivity, volu-metric expansion, and solubility.

* Shape memory an input of thermal energy (which canalso be produced through resistance to an electricalcurrent) alters the microstructure through a crystallinephase change. This change enables multiple shapes inrelationship to the environmental stimulus.



s Figure 1-7 A cloth made by weaving fiber-optic strands that arelighted by light-emitting diodes (LEDs). (Yokiko Koide)

TYPE 2 MATERIALS

A second general class of smart materials is comprised of thosethat transform energy from one form to an output energy inanother form, and again do so directly and reversibly. Thus,an electro-restrictive material transforms electrical energy intoelastic (mechanical) energy which in turn results in a physicalshape change. Changes are again direct and reversible. Wewill be calling these Type 2 materials. Among the materials inthis category are piezoelectrics, thermoelectrics, photo-voltaics, pyroelectrics, photoluminescents and others.

Chapter 4 will also consider these types of materials atlength. The following list briefly summarizes some of the morecommon energy-exchanging smart materials.

* Photovoltaic an input of radiation energy from the visiblespectrum (or the infrared spectrum for a thermo-photo-voltaic) produces an electrical current (the term voltaicrefers more to the material which must be able to providethe voltage potential to sustain the current).

* Thermoelectric an input of electrical current creates atemperature differential on opposite sides of the material.This temperature differential produces a heat engine,essentially a heat pump, allowing thermal energy to betransferred from one junction to the other.

* Piezoelectric an input of elastic energy (strain) producesan electrical current. Most piezoelectrics are bi-directionalin that the inputs can be switched and an applied electricalcurrent will produce a deformation (strain).

* Photoluminescent an input of radiation energy from theultraviolet spectrum (or electrical energy for an electro-luminescent, chemical reaction for a chemoluminescent) isconverted to an output of radiation energy in the visiblespectrum.

* Electrostrictive the application of a current (or a magneticfield for a magnetostrictive) alters the inter-atomic distancethrough polarization. A change in this distance changes theenergy of the molecule, which in this case produces elasticenergy strain. This strain deforms or changes the shape ofthe material.

With Type 2 materials, however, we should be aware thatuse of the term material here can be slightly misleading.Many of the materials in this class are actually made up ofseveral more basic materials that are constituted in a way toprovide a particular type of function. A thermoelectric, forexample, actually consists of multiple layers of different



materials. The resulting assembly is perhaps better describedas a simple device. The term material, however, has stillcome to be associated with these devices largely because ofthe way they are conceptually thought about and used.Application-oriented thinking thus drives use of the termmaterial here.

SMART SENSORS, ACTUATORS AND CONTROLSYSTEMS

Compounding the problematic of terminology, we will seethat many smart materials may also inherently act as sensorsor actuators. In their role as sensors, a smart material respondsto a change in its environment by generating a perceivableresponse. Thus, a thermochromic material could be useddirectly as a device for sensing a change in the temperature ofan environment via its color response capabilities. Othermaterials, such as piezoelectric crystals, could also be used asactuators by passing an electric current through the materialto create a force. Many common sensors and actuators arebased on the use of smart materials.

In the use of Type 2 materials as a sensor or actuator, thereare also different kinds of electronic systems that are integralto the system to amplify, modify, transmit, or interpretgenerated signals. Logic capabilities provided via micro-processors or other computer-based systems are similarlycommon. There are several different types of strategiespossible here. We will return to this topic in Chapter 5.

COMPONENTS AND SYSTEMS

As is common in any design context, basic types of smartmaterials are normally used in conjunction with many othermaterials to produce devices, components, assemblies and/orsystems that serve more complex functions. As was previouslymentioned, external walls in a building, for example, providea range of pragmatic functions (thermal barrier, weatherenclosure, ventilation, etc.) as well as establishing the visualexperience of a building. Single materials cannot respond tothese many demands alone. Thus, we might have a wholeseries of different types of smart walls depending on exactlyhow the wall is constituted, what primary functions it isintended to serve and the degree to which there are externallogic controls.

In addition to constructions that we normally think of ascomponents, we also have whole systems in buildings thatcan be designed to possess some level of smartness. The



systems of concern here include normal environmentalsystems (heating, ventilation and air conditioning; lighting;acoustical) and structural systems. Historically, one of the firstuses of the term smart was in connection with improvedsensor-based monitoring and control systems for controllingthe thermal environment in a building (the Smart House ofthe 1990s). Whether or not this approach is commensuratewith the term smart as it is used today is an interestingquestion, and one that we will return to in Chapter 7. In thatchapter we will consider different kinds of smart systems inuse today.

SMART VS INTELLIGENT ENVIRONMENTS

Fundamentally, the product of architecture and design is acomplete work whether a building or a lamp. Inherent toeach, however, is a stunning complexity in all of its aspects.Here the question is naturally raised of the notion of smartand/or intelligent environments. The term intelligent itself isas problematic as the term smart, yet it surely suggestssomething of a higher level than does smart. We do expectmore out of intelligent systems than we do from smartmaterials. Everyday connotations of the term intelligentwith suggested notions of abilities to understand or compre-hend, or having the power of reflection or reason, could beuseful, and will help us as we examine the current conceptionsof these environments and develop new ones of our own.

One of the more fascinating aspects of todays society ishow techno-speak terms come into existence and assumecurrency without universal agreement about what is actuallymeant. There has been a lot of recent interest in intelligentrooms and intelligent buildings without a clear consensusabout what is actually meant by these terms. The parallelquestion raised of whether common rooms or buildings aredumb is equally interesting, particularly since architects andbuilders have done rather well at responding to societal andcultural needs for millennia. More specific fundamental needshave not been ignored, nor have the wonderful vicissitudes ofhuman desire. So, presumably, something else and morespecific is meant by the terms intelligent rooms or intelli-gent buildings, but what? Here we also engage in anothermeaning conundrum. The phrase smart environments is inwidespread use and has already been employed in this book.What, if anything, is the difference between an environmentor building space that is intelligent and one that is smart?The engineering and computer science worlds often do notdistinguish between the two, presuming that both represent



s Figure 1-8 Current smart room and intel-ligent room paradigms, with a glimpse intothe future (see Chapter 8)

the crowning culmination of technological development that of the fully contained and controlled environment. InChapters 8 and 9, we begin to propose an alternative in whichsystems become smaller and more discrete, freeing our bodiesand our environments from an overarching web of control. Itis perhaps in this arena that architects can have the mostimpact on the trajectory of these advanced materials andtechnologies.

Notes and references

1 All discussion on alchemy in this chapter is from David. C.Lindberg (ed.), Science in the Middle Ages (Chicago: The

University of Chicago Press, 1978). See in particular chapter

11 on the Science of Matter.

2 Davies, M. (1981) A wall for all seasons, RIBA Journal, 88 (2),pp. 5557. The term polyvalent wall, first introduced in this

article, has become synonymous with the advanced facade

and most proposals for smart materials in buildings are based

on the manifestation of this 1981 ideal.

3 http://virtualskies.arc.nasa.gov/research/youDecide/smartMaterials.html.

4 Kroschwitz, J. (ed.) (1992) Encyclopedia of ChemicalTechnology. New York: John Wiley & Sons.



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