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Design & Technology

Materials

Smart materials

Smart materials have properties that react to changes in their environment. This means that one of their properties can be changed by an external condition, such as temperature, light, pressure or electricity. This change is reversible and can be repeated many times.

There are a wide range of different smart materials. Each offer different properties that can be changed.

Shape-memory alloys

For most materials, if they are bent out of shape, they stay that way. However, if a part made from a shape-memory alloy (SMA) is bent out of shape, when it is heated above a certain temperature it will return to its original shape.

This property makes it useful for making spectacle frames - they return to their original shape if they are put in hot water after bending them.

SMAs are used as triggers to start the sprinklers in fire alarm systems, controllers for hot water valves in showers or coffee machines and for spectacle frames.

Piezoelectric materials

When a piezoelectric material is squeezed rapidly, it produces a small electrical voltage for a moment. If a voltage is put across the material it makes a tiny change in shape.

Piezoelectric materials are being used for contact sensors for alarm systems and in microphones and headphones.

Quantum-tunnelling composite

Quantum-tunnelling composite (QTC) is a flexible polymer which contains tiny metal particles. It is normally an insulator but if it is squeezed it becomes a conductor.

QTC can be used to make membrane switches like those used on mobile phones, pressure sensors and speed controllers.

Electroluminescent materials

Electroluminescent materials give out light when an electric current is applied to them. Among many possible applications are safety signs and clothing for use at night.

Colour-change materials

Boy measuring his temperature with thermochromic thermometer

Thermochromic materials change colour as the temperature changes. These are used on contact thermometers made from plastic strips and test strips on the side of batteries (where the heat comes from a resistor under the thermochromic film). They are also used as food packaging materials that show you when the product they contain is cooked to the right temperature.

Photochromic materials change colour according to different lighting conditions. They are used for security markers that can only be seen in ultraviolet light.

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