A Smart Material is a material that has been engineered to have specific properties.
For the course you need to know about the Smart Materials shown below:
Shape Memory Alloys
Polymer Optical Fibres
Quantum Tunnelling Composite
Electro-luminescent materials produce light when they are connected to an electrical
current. They are available in thin sheets and in cables. Electro-luminescent sheets
are used as the back light of LCD screens and other electronic devices. Some of
the advantages of electro-luminescent materials are:
• Produce a bright and even light source
• Low power (batteries last longer)
• A range of colours are available
• They can be cut to any shape required
Ferrari dashboard with electro-luminescent display
Animated electro-luminescent tshirt
A shape memory alloys are metals that have been engineered to remember its original
shape when cool. They are also known as:
• Smart metal
• Memory alloy
• Muscle wire
A piece of SMA can be bent into any shape like any other type of wire. But, when
it is heated up it will automatically go back to its original state because it has
a memory of its original shape.
Passing a current through a piece of wire causes it to heat up. Therefore if a piece
of SMA is bent out of shape passing a current through it will make it go back to
its original shape.
The diagram to the right shows a SMA formed in the shape of a spring in the factory.
The weight pulls it out of shape but when the battery is connected it heats up and
the spring contracts, lifting the weight up. When the battery is disconnected the
wire cools and the weight stretches the spring out again.
SMA wires and springs can be used in the place of motors where linear movement is
required, it has the advantage that it has less moving parts that can wear out.
A SMA spring being used to lift up a weight
Fibre Optic Cables
Optical Audio Output of a PS3
Optical fibres are thin rods of clear flexible plastic. If a light is shone down
one end of the fibre it is transmitted by internal refraction and comes out of the
opposite end. They are used to transmit signals and data over long and short distances
in the place of electrical cables. Because they rely on light the signals they transmit
are not affected by electrical interference. LEDs are usually used as the light source
and phototransistors are used to detect the light at the receiver.
PS3 consoles have an optical output which allows it to be connected to an amplifier
connected to speakers instead of using the conventional electrical cable. Because
it is and optical interface the quality of the signal is not degraded by interference
and therefore the sound quality is much better.
Optical fibres can also be used in light displays as shown below:
An Optical Fibre Sign
Optical Fibre Clothing
Piezoelectric materials can generate electricity when they are compressed, this is
called the piezoelectric effect. This effect also works the other way around and
can change its shape very slightly when a voltage is applied to it.
A piezoelectric transducer can convert tiny vibrations into an electrical current
. They could be used in security alarms in shops to detect when items have been moved
(just think about what your exam preparation sheet says)!
Piezoelectric transducers are used as the speakers in musical greeting cards.
The circuit above shows how a piezoelectric transducer can be used with a thyristor
to act as a vibration activated alarm. The transducer could be fitted to a shelf
where a valuable item needs protection. When the transducer detects any vibration
it creates a tiny current which flows into the gate of the thyristor, this latches
the thyristor on causing current to flow through the buzzer. The buzzer will only
switch off when the PTB (push to break) switch is pressed which interrupts the current
flowing between the anode and cathode of the thyristor causing it to reset.