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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 
  • 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 polymers
  • electrorheology
  • fault diagnosis
  • fibre-optic sensors
  • fibre reinforced composites
  • magnetostriction
  • maintenance engineering
  • mechatronics
  • micromechanical devices
  • non-destructive testing
  • piezoelectric actuators
  • piezoelectric materials
  • piezoelectric transducers
  • robots
  • 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.


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