Are smart materials intelligent?

In recent years, there have been significant developments in the science and applications of  intelligent, or 'smart', materials.  These can be defined as materials with one or more properties (e.g. mechanical, thermal, optical, or electromagnetic properties) that can be varied in a predictable or controllable way in response to external stimuli, such as, for example, stress, temperature, moisture, pH and electric or magnetic fields. Such materials are now used in a vast number of applications, from photochromic lenses for sunglasses to military and aerospace uses.

Smart structures incorporate smart materials and exhibit one or more of the following features:

• sensors or actuators which are either embedded within a structural material or else bonded to the surface of that material
• control capabilities which permit the behaviour of the material to respond to an external stimulus according to a prescribed functional relationship or control algorithm

A smart structure is thus an integrated system comprising actuators, sensors and a control system.
At a more sophisticated level, smart materials become intelligent when they have the ability to respond intelligently and autonomously to dynamically-changing environmental conditions.

The technologies encompassed by intelligent materials are very diverse and include electrorheological fluids, fibrous materials, ceramics, photonics, microsensors, signal processing, piezoelectrics, dielectric elastomers, biomimetics, shape memory alloys, neural networks, nanotechnology, conducting and chiral polymers, liquid crystals, microactuators, biotechnology and information processing.

Potential applications are similarly widespread and have excited interest in industrial, military, commercial, medical, automotive and aerospace fields. Embedded fibre-optic sensing systems are employed in many engineering disciplines to monitor critical characteristics. Several smart skins programmes have been initiated for both civil and military aircraft. Large space structures are also candidates for the incorporation of smart structural systems because of the variable service conditions in which they operate.

Useful Classification Codes and Controlled Indexing Terms

The wide variety of materials and applications results in intelligent materials cropping up in many parts of the Inspec Classification scheme. The most relevant sections are:

• A8185 Intelligent materials (inc. smart materials)  
• A7760 Piezoelectricity and electrostriction
• B0585 Intelligent materials (engineering materials science) (inc. electrorheological and magnetorheological fluids, smart materials)
• C3240N Intelligent sensors
• C3260N Intelligent actuators
• E1710 Engineering materials
• E2110 Mechanical structures
• E1610 Inspection and quality control
• E1020 Maintenance and reliability

Inspec has a set of controlled terms for intelligent/smart material technology:

• intelligent actuators
• intelligent materials
• intelligent sensors
• intelligent structures  
• intelligent control

Other related areas

There is an extensive range of topics related to intelligent materials/structures. Some of the most useful (and most popular) codes and terms are:

Classification codes

Section A (Physics Abstracts)

• A0670D Sensing and detecting devices
• A4281P Fibre-optic sensors; fibre gyros
• A4660H Electrorheological and magnetorheological fluids

Section B (Electrical and Electronics Abstracts)

• B7230    Sensing devices and transducers
• B7230E  Fibre-optic sensors
• B7630    Avionic systems and aerospace instrumentation

Section C (Computer and Control Abstracts)

• C1340E Self-adjusting systems (inc. adaptive systems)  
• C3120Z Control of other nonelectric variables (inc. vibration control)  
• C3240D Electric transducers and sensing devices
• C3240H Fibre-optic sensors
• C3260B Actuating and final control devices - electric equipment
• C3260Q Electromagnetic actuators
• C3260R Electromechanical actuators
• C3390   Robotics  
• C7420   Computer applications to control engineering

Section E (Manufacturing and Production Engineering)

• E1550   Control technology and theory
• E2160   Micromechanics
• E2200   Mechanical components, systems and devices
• E3030   Construction industry  
• E3644V Mechatronics industry
• E3650C Aerospace industry

The Advanced Materials journal in the Key Abstracts series has one particular chapter covering intelligent materials.

Controlled terms

Other controlled terms which may have some connection with smart materials technology include:

adaptive control
aerospace control
aerospace instrumentation
aerospace materials
aircraft instrumentation
biomimetics
biosensors
carbon fibre reinforced plastics
ceramics
composite materials
condition monitoring
electric sensing devices
electroactive polymer actuators
electromechanical actuators
electrorheology
fault diagnosis
fibre-optic sensors
fibre reinforced composites
flexible structures
magnetostriction
maintenance engineering
mechatronics
micromechanical devices
nanotechnology
nondestructive testing
piezoelectric actuators
piezoelectric materials
piezoelectric transducers
robots
shape memory effects
strain gauges
strain measurement
vibration control

Finally, turning to the question posed by the title "Are Smart Materials Intelligent?", we would probably answer "not yet", but major progress has been made in recent years, with increasingly more complex and sophisticated systems under development.

Inspec will continue to cover the interdisciplinary fields of research to keep you up to date with progress towards this goal.