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QUANTUM TUNNELLING COMPOSITE (QTC) AND PIEZO ELECTRIC MATERIALS

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QUANTUM TUNNELLING MATERIALS

 

Quantum Tunnelling Composite (QTC), is a composite material, composed of a insulating material (a polymer) and particles of a conducting material. The conducting particles, are suspended within the insulator. In normal use, the QTC composite will not conduct electricity. However, when pressure is applied, the conducting particles are pressed together, allowing electricity to flow through them. The electrical current is said to be able to, ‘tunnel’ through the non-conductive material.
QTCs have been developed so that, more current can flow through them, the greater the pressure applied. This is because increased pressure, means less resistance, to the flow of electricity. In the diagram below, the brightness of a light can be controlled, by increasing or decreasing pressure.
 
 
 
 
NO PRESSURE - BULB DOES NOT LIGHT
PRESSURE APPLIED - BULB LIGHTS
 
Practical applications include: Use in flexible keyboards, that rely on the pressure of finger touch. Pressure Sensors used in buildings and structures to detect movement. Touch sensitive flexile computer and mobile device screens. Touch sensitive lighting systems, wearable textiles and alarm systems.
 
 
 
PIEZOELECTRIC MATERIALS
 

When pressure or mechanical stress is applied to a Piezoelectric material, it produces an electrical charge. Piezoelectric materials include naturally formed crystals (quartz), synthetic crystals, piezoelectric polymers, bone, ceramics and some proteins. If an electric charge is put through a piezoelectric material, it will change shape slightly, called ‘converse piezoelectric effect’. This property is one reason why piezeelectric materials are used in speakers, converting electrical signals to sound.

When ‘pressurised’, these materials produce only a very small amount of electricity and once pressure is stoped, the production of electricity stops, as well. Therefore, the practical application of these materials is limited. Another issue, is that some piezoelectric materials are toxic.

 
As pressure is applied to the piezoelectric material an electrical current is produced.
When the piezoelectric material is not under a compressive force, no electricity is produced.
 
 
A piezo speaker, a common component in electronic circuits, is seen below. The piezoelelctric material expands when it conducts an electrical signal and then returns to its normal size, when the signal is absent. This has the effect of vibrating the air in front of it, creating the sound we hear.
 
 
 
One possible future application is in areas such as floors, where there is a high level of footfall (people walking over it). If the floor was constructed from a safe piezoelectric material, in theory, it is possible to produce useable qualities of electricity.
They are currently used in sonar devices, clocks, cigarette lighters, barbecue-grill igniters and speakers (as seen with mobile phone speakers).
 
 
 
The cigarette lighter operates thanks to the piezo component, which when compressed by the switch, creates an ‘electrical’ spark, igniting the gas
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