Transcript 3.2 student presentation on smart materials

What Are Optical Fibres…?
Optical fibres carry digital information in the form of LIGHT through a
glass or plastic fibre. This is achieved by using the principal of
TOTAL INTERNAL REFLECTION to guide the light along the length
of the hair-thin fibre.
The light travels through the CORE
The CLADDING reflects light back into the core
The fibre is protected by the outer plastic BUFFER COATING
How Do They Work…?
These fibres are bundled into OPTICAL CABLES which contain
hundreds or thousands of fibres
The light travels through the core, bouncing off the MIRRORED surface of the CLADDING. The signal does,
however, DETERIORATE over a distance due to IMPURITIES in the core that absorb some of the light. The
purer the core, the further the light can travel.
A TRANSMITTER encodes the information to be sent through the fibre into light signals. The OPTICAL FIBRE
carries the light signals over a distance. An OPTICAL RECEIVER receives and decodes the light signal back into
digital information. The signal may need to be boosted by an OPTICAL REGENERATOR if the signal is travelling
over a large distance.
What Are They Used For…?
Fibre optics are used for… TELECOMMUNICATIONS: transmitting
phone signals, Internet connections and cable TV signals; SENSORS:
hydrophones, detecting temperature and pressure in conditions
unsuitable for other types of sensor and optical gyroscopes;
ENDOSCOPES: these consist of an optical fibre and a lens for medical
uses such as a non-invasive way of seeing inside of patients, and
industrial uses such as seeing inside otherwise hard to see places such
as the insides of jet engines; DECORATIVE APPLICATIONS: such as
Christmas trees
Composites are engineered materials
which contain two or more materials
which have differing properties; when
combined, these materials give rise to a
material with superior physical or
chemical properties than either of its
constituent parts.
Examples of composites are:
•Carbon Fiber
•Plywood
•Fiber Glass
Carbon Fiber is very good example of a composite material as it shows
how carbon fibres in a mesh, suspended in a polymer matrix can give
extremely good strength for a very light material. This makes it an
excellent material to use when strength in a product is desired but weight
needs to be kept to a minimum. Examples of products are things like car
body panels, sports equipment and even musical instruments.
Shape memory alloys, or SMA’s, are metals which have two very unique properties, pseudo-elasticity
and the shape memory effect. Psuedo-elasticity is where a metal has an almost rubber like flexibility,
and its uses include bra underwiring, glasses frames and old mobile phone antennae.
The shape memory effect is a unique ability
of shape memory alloys to be severely
deformed and then returned to their original
shape simply by heating them. The two
phases which occur in shape memory alloys
when they change state through temperature
change are known as ‘Martensite’ and
‘Austenite’. Although a state change occurs,
the metal remains a solid, because the
molecules remain closely packed when they
rearrange. In most shape memory alloys, the
temperature only needs to change about 10°C
for the state change to occur. The austenite
phase is the stronger, high temperature
phase, and the martensite phase is the lower
temperature, more deformable phase.
The most impressive use of shape memory alloys is in
the human body (due to their ‘biocompatibility’). For
example when a bone breaks, the metal, in its martensite
phase can be wrapped around the bone, and as it heats
up, changing shape back into the austenite phase, it
exerts pressure pushing the damaged bone sections
back together.
What Are Piezo-Electrics…?
Certain crystals, such as QUARTZ, produce a VOLTAGE when MECHANICAL
STRESS is applied. This effect is also reversible, so if a voltage is applied to
the crystal it will cause the crystal to deform.
If a POSITIVE voltage causes the crystal to become STRETCHED, a
NEGATIVE voltage will cause it to become COMPRESSED.
+ve
-ve
How Does It Work…?
The piezoelectric crystal is NEUTRAL overall, but contains separated POSITIVE and NEGATIVE electrical
charges, which are symmetrically distributed. When mechanical stress is applied, this disturbs the symmetry of
the electrical charges and this causes a VOLTAGE to be produced.
Piezoelectrics can be used as ACTUATORS to turn an electrical input into a mechanical output, or as SENSORS
to turn a mechanical input into an electrical output.
What Is It Used For…?
Piezo-electricity is used for… SENSORS: such as piezoelectric pickups
on electric guitars, electric drum pads and medical ultrasound
transducers; ACTUATORS: loudspeakers, inkjet printers and
piezoelectric motors; FREQUENCY STANDARD: Quartz clocks and
watches use the natural resonant frequency of Quartz to produce
electrical pulses to maintain precise time keeping; REDUCTION OF
VIBRATIONS: this is a relatively new use of piezoelectrics, and involves
crystals detecting vibrations, turning this into an electrical signal, and
using that information to create another counter vibration so the two
cancel out.
Liquid Crystal Display (LCD):
It is a screen made of monochrome pixels which are
relayed to the viewer either by a reflector or back
light. These displays are very efficient and popular
amongst designers as they require a very small
current to operate thus prolonging battery life. Due to
this LCD screens have replaced LEDs. LCD screens
come in many forms; they are used in TV and PC
displays which is a very complex use for them or
simply just as displays on calculators and other
similar items.
6. Reflective surface to send light back to viewer.
5. Horizontal filter film to block/allow through light.
4. Glass substrate with common electrode film.
3. Twisted nematic liquid crystals.
2. Glass substrate with ITO electrodes- determine light and dark.
1. Vertical filter film to polarize light.