I. Piezoelectric Materials

Date: 2015-10-07; view: 562.

Valve

Clutch

Tiny iron particle

To deploy the airbag

The force of an impact

Steadily

Dramatically

Acidity

Undergo changes

Collapse

Swell

In the reverse manner

Moisture

External stimuli

Change in a controlled fashion

Vocabulary

Read the text and do the tasks below

Think of examples from nature that are like smart materials, for example, things that can change shape or colour, or repair themselves.

Work with a partner. Choose one of the smart materials in the text. Think of five interesting ways it could be used. Compare your ideas with other students.

Speaking

The text is taken from http://www.cs.ualberta.ca/~database/MEMS/sma_mems/smrt.html

Smart materials are materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields. There are a number of types of smart material, some of which are already common. Some examples are as following:

- Piezoelectric materials are materials that produce a voltage when stress is applied. Since this effect also applies in the reverse manner, a voltage across the sample will produce stress within the sample. Suitably designed structures made from these materials can therefore be made that bend, expand or contract when a voltage is applied.

- Shape memory alloys and shape memory polymers are Thermoresponsive materials where deformation can be induced and recovered through temperature changes.

- Magnetic shape memory alloys are materials that change their shape in response to a significant change in the magnetic field.

- pH-sensitive polymers are materials which swell/collapse when the pH of the surrounding media changes.

- Temperature-responsive polymers are materials which undergo changes upon temperature.

- Halochromic materials are commonly materials that change their colour as a result of changing acidity. One suggested application is for paints that can change colour to indicate corrosion in the metal underneath them. Chromogenic systems change colour in response to electrical, optical or thermal changes. These include electrochromic materials, which change their colour or opacity on the application of a voltage (e.g. liquid crystal displays), thermochromic materials change in color depending on their temperature, and photochromic materials, which change colour in response to light - for example, light sensitive sunglasses that darken when exposed to bright sunlight. Non-Newtonian fluid is a liquid which changes its viscosity in response to an applied shear rate. In other words the liquid will change its viscosity in response to some sort of force or pressure. One good example of this is Oobleck, a fluid that seems to temporarily turn into a solid when a force is applied quickly.^[1] Another good example is Custard, as long as it is starch based.

Science and technology have made amazing developments in the design of electronics and machinery using standard materials, which do not have particularly special properties (i.e. steel, aluminum, gold). Imagine the range of possibilities, which exist for special materials that have properties scientists can manipulate. Some such materials have the ability to change shape or size simply by adding a little bit of heat, or to change from a liquid to a solid almost instantly when near a magnet; these materials are called smart materials.

Smart materials have one or more properties that can be dramatically altered. Most everyday materials have physical properties, which cannot be significantly altered; for example if oil is heated it will become a little thinner, whereas a smart material with variable viscosity may turn from a fluid which flows easily to a solid. A variety of smart materials already exist, and are being researched extensively. These include piezoelectric materials, magneto-rheostatic materials, electro-rheostatic materials, and shape memory alloys. Some everyday items are already incorporating smart materials (coffeepots, cars, the International Space Station, eyeglasses) and the number of applications for them is growing steadily. Each individual type of smart material has a different property which can be significantly altered, such as viscosity, volume, and conductivity. The property that can be altered influences what types of applications the smart material can be used for.

Piezoelectric materials have two unique properties which are interrelated. When a piezoelectric material is deformed, it gives off a small but measurable electrical discharge. Alternately, when an electrical current is passed through a piezoelectric material it experiences a significant increase in size (up to a 4% change in volume)

Piezoelectric materials are most widely used as sensors in different environments. They are often used to measure fluid compositions, fluid density, fluid viscosity, or the force of an impact. An example of a piezoelectric material in everyday life is the airbag sensor in your car. The material senses the force of an impact on the car and sends and electric charge deploying the airbag.