Materials: Smart Materials
Smart Materials
Smart materials are materials whose physical properties change in response to an input or change in the environment, such as electricity, pressure, temperature, or light.
Many products utilize smart materials, often bringing benefits such as increased safety and/or ease of use.
Shape Memory Alloys (SMAs)
One of the most common smart materials is a shape memory alloy (SMA), called nitinol.
When an SMA is heated to a certain temperature (the transition temperature), it will return to its original shape.
Nitinol has a transition temperature of 70 °C, meaning it will return to its original shape if placed in hot water.
The transition temperature can also be dictated by passing an electrical current through the material.
Example: Dental braces made from nitinol wire can be designed to change at body temperature; therefore when the braces are placed in the mouth, the wire maintains a constant tension.
Common Uses for SMAs:
- Response in change in temperature, for example triggers for fire alarm systems, sprinkler systems, hot water valves in showers, industrial greenhouse windows.
- Repair of malformed or damaged products, for example spectacle frames which have been distorted can return to their original shape when heated to the transition temperature.
- A movement response from an electrical signal, for example artificial muscles in robot arms, electric door locks.
Classification of Smart Materials
SMAs, e.g. nitinol
- How it works? Changes shape in response to a change in temperature or electrical input. For example, nitinol wire in dental braces changes length in response to a change in temperature.
- Uses: Dental braces, self-closing windows, aeroplane wing flaps, bioengineering such as stents, bone plates and screws
Thermochromic Pigment
- How it works? Changes colour in response to temperature change.
- Uses: Room thermometers, medical thermometers for children, bath water thermometers, colour change mugs and kettles, food packaging to indicate food is hot to eat or cool for drinks, baby feeding spoons, battery charge indicator strips
Phosphorescent Pigment
- How it works? Absorbs light energy during the day and 're-emits' the light energy when it is dark.
- Uses: Fire exit signs, 'glow in the dark' products such as adhesive stars, masks, night lights, watch hands
Photochromic Pigment
- How it works? Changes colour with light intensity.
- Uses: Welding goggles, reactive spectacle lenses, security markers that show under UV light
Electroluminescent Wire
- How it works? Thin copper wire coated in a phosphorescent material which glows in response to an alternating current.
- Uses: Glow bracelets, interweaving for clothing, home decoration, outdoor decorative lighting
Piezoelectric Material
- How it works? Gives off a small electrical charge when deformed. Increases in size (up to 4 per cent) when an electrical current is passed through it.
- Uses: Airbag sensors in cars, lighters for barbecues, vibration damping in tennis racquets, musical greetings cards, pressure sensors