A smart material changes one or more of its properties in a controlled and predictable way when exposed to an external stimulus. Piezoelectric, shape-memory, and photochromic materials respond to different stimuli and can perform useful functions without conventional mechanical controls.
How Smart Materials Respond
The stimulus may be pressure, temperature, light, electricity, or another environmental change. The resulting response is often reversible, allowing the material to act as a sensor, actuator, indicator, or control component.
| Smart material | Stimulus and response | Typical application |
|---|---|---|
| Piezoelectric material | Mechanical pressure or deformation produces an electrical charge. Conversely, an applied voltage can cause a small change in shape. | Pressure sensors, electronic lighters, microphones, and ultrasonic transducers |
| Shape-memory material | Heat causes the material to return to a previously programmed shape after it has been deformed. Shape-memory alloys such as nickel-titanium can therefore act as thermal actuators. | Flexible spectacle frames, medical stents, temperature-controlled valves, and actuators |
| Photochromic material | Exposure to ultraviolet light causes a reversible change in colour because the material's molecular structure temporarily changes. It returns to its original state when the stimulus is removed. | Light-sensitive spectacle lenses, UV indicators, and security markings |
A material is considered smart because its response is inherent to the material rather than produced entirely by a separate mechanical system. This can reduce component count, mass, and complexity while improving responsiveness.
A common misconception is that every advanced or newly developed material is smart. A modern material may have improved properties, but it is only smart if it responds predictably to an external stimulus by changing a property or producing an output.
IB Exam Technique
For A3.1 Material classification and properties, define the material, identify the stimulus, state the response, and link both to a product application. If asked to distinguish the three types, avoid merely listing products: explain the stimulus-response mechanism that makes each material suitable.