7.6 Smart materials © Nelson Thornes 2011

What is a smart material? A smart material is a material that changes its properties in response to its environment. It can repeat this change again and again. © Nelson Thornes 2011

Shape memory alloy If a part made from a shape memory alloy (SMA) is bent out of shape, when it is heated to a certain temperature it will return to its original shape. SMAs can be used anywhere where temperature changes. For example, they are often used in water heaters or fire alarms. They can be used to make products switch between two shapes or ‘repair damage’, for example, to mend bent spectacle frames or as springs in artificial muscles for robots. © Nelson Thornes 2011

Polymorph Supplied as granules When heated to 62 degrees or above in water they form a ply able solid Useful for forming : handles/grips Complex shapes Prototype patterns for casting or moulding Completing complex assemblies

Smart Grease Smart grease is used to control movement, producing a dampened, slowed down feeling. For example, smart grease is used on volume control knobs and microscope slides.

Piezoelectric material When a voltage is applied to a piezoelectric material, it makes a tiny change in its shape. It works the other way round too – if you change its shape, it will make a small voltage. The change in shape when a voltage is applied can be used to make sound – many small headphones and speakers contain piezoelectric materials. The voltage produced by a change in shape can be used to record sound, as a microphone. © Nelson Thornes 2011

Quantum tunnelling composite Most materials either allow electricity to pass through them or don’t allow it. Normally, quantum tunnelling composite (QTC) does not allow electricity to pass through it. However, when it is squeezed, electricity can pass through it easily. QTC can be used to replace push buttons. For example, it could be used on the keypads of mobile phones and cash machines, or to replace the buttons on computer keyboards. It can also be used to make pressure sensors, for example for alarm systems. © Nelson Thornes 2011

Thermochromic materials Thermochromic materials change colour as the temperature changes. They can be used as a thermometer to give an indication of temperature. On food packaging they can change colour when a product has been cooked to the right temperature. On cups and mugs, they can display a warning if a product is too hot. They can be made to change colour by the heat from an electrical component called a ‘resistor’. This means that they could be used with electrical circuits to provide visual warning signals or indicate that the circuit is working. © Nelson Thornes 2011

Photochromic materials Photochromic materials change their colour in response to changes in light. Photochromic materials are used for the lenses in sunglasses, to make them go darker as the light level increases. Security markers use photochromic dye that can only be seen under ultraviolet light. This provides a mark that police can detect but does not affect the appearance of the item. These materials are also starting to find uses in nail varnish, jewellery and as paints for cars. © Nelson Thornes 2011

Summary A smart material changes its properties in response to its environment. This change is reversible and can be repeated many times. Depending upon the material, the change in properties may be the caused by temperature, or the amount of light, or an electric current, or pressure. The property that changes depends upon the material. For example, it might be the shape or the ability to conduct electricity or the colour. © Nelson Thornes 2011