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Submitted by:
Name: K Satya Ramesh
Branch: ECE, Year: 4th,
College: Kakinada Institute of Engineering & Technology,
Quantum Physics in Design and Technology
Despite increasingly rapid advances in technology, rarely do we see the
emergence of an entirely new material. Quantum tunneling composite (QTC for
short) is a very recent creation.
Quantum tunnelling composites (or QTCs) are composite materials of metals
and non-conducting elastomeric binder, used as pressure sensors. They are
made using quantum tunnelling: without pressure, the conductive elements are
too far apart to conduct electricity; when pressure is applied, they move closer
and electrons can tunnel through the insulator. The effect is far more
pronounced than would be expected from classical (non-quantum) effects alone,
as classical electrical resistance is linear (proportional to distance), while
quantum tunnelling is exponential with decreasing distance, allowing the
resistance to change by a factor of up to 1012 between pressured and
unpressured states.
QTC has been implemented within c to make “smart”, touchable membrane control
panels to control electronic devices within the clothing, e.g. mp3 players or mobile
phones. Its rigidity makes use in Arctic/Antarctic exploration or spacesuits equipments.
However, eventually, due to the low cost and a better electric protection of QTC, this
technology will become available to the general user widely in future.
What does it do?
QTC comes in the form of sheet, ‘pills’ and cable. QTC sheet can be
used to make very low cost touch switches that can be placed on the
case of products. QTC ‘pills’ can be used to produce low cost
force/pressure sensors whose resistance varies with the applied force.
How does it operate?
Quantum tunnelling composite is a recently developed ‘smart’ material that exhibits
extraordinary electrical properties. In its normal state it is an insulator, but when it is
compressed it conducts. The material owes its unusual properties (and its name) to a
strange phenomenon of quantum mechanics which mean that electrons are able to
‘tunnel’ through some materials i.e. conduct, if their physical structure is slightly
changed (by pressure).
QTC sheet
The main application of QTC sheet in schools is in making low cost touch switches.
QTC sheet consists of three layers:
a thin layer of (light grey) QTC
a conductor, and
a (white) plastic insulator
To make up a simple switch on the case of an electronic product, self adhesive
copper track can be trapped under screw heads and the screws connected to the
electronic circuit.
The copper track can then be stuck onto the product surface so that the two sides of
the switch come to the required switch position. A small piece of QTC sheet (cut from
the larger sheet in which it is supplied) with the white plastic side on top is used
for the switch, held in position by sellotape.
Only stick the tape over one side of the QTC sheet, not on the area where there is a
gap between the copper tracks; sticking it over the entire sheet can create pressure on
the switch and make it close all the time.
Graphics can be added on top of the switch, but should not be stuck directly onto the
QTC sheet because again this can ‘press’ the switch. A thin sheet of foam can be
placed over the QTC switch and the graphics stuck onto the foam. This prevents the
graphics from pressing the switch
The QTC sheet switch is included in the circuit in the usual way. A pull-down resistor
(R1) of about 3k3 is suitable. The value of this resistor is not critical. If a larger value is
used the switch becomes more sensitive (operates with lower force). The value of 3k3
gives a switch that only requires moderate force and is not triggered by light pressure
e.g. from the weight of the foam sheet over the switch.
The resistance of the QTC sheet switch when moderate pressure is applied is around 1 – 2k.
QTC ‘pills’
Unlike QTC sheet (which switches quite quickly
between a high and low resistance), QTC pills are
pressure sensitive variable resistors.
They can be used as input sensors in electronic
systems and the signal from them can go to
analogue processing units (such as PICs with
analogue to digital converters or amplifiers) to
produce a system that responds to weight or force.
One way to arrange for contact between the pill
and the electronic circuit is to use a pair of self
adhesive copper tracks, with the QTC ‘pill’
sandwiched between them (it is not necessary to
remove the glue).
QTC pills are more expensive than QTC sheet and
so QTC sheet is a better choice if all that is needed
is a simple touch switch.
To represent a QTC pill in a circuit simulation on a computer, use a variable resistor.
Possible applications
QTC sheet can be used to produce:
low cost touch switches
switches that can be placed on the surface of products and decorated with
QTC pills can be used to produce:
input sensors that respond to force or weight
devices that can control quite high currents, allowing motor speed control using
QTC sheet switches can be incorporated into the product design for the case, creating
adaptable membrane switches. It is best to protect them with a thin foam cover to which
graphics can be applied.
When using QTC sheet to make touch switches, it is important to make sure that:
the QTC sheet is placed with the grey side (the QTC material) next to the copper
track and the white side (the insulating plastic layer) away from the copper track
the stick-on copper track is in good electrical contact with the electronic circuit.
Just sticking it onto a terminal or copper track on the circuit does not give reliable
electrical contact. It is important to trap the stick-on copper track under a screw
head or a hexagonal metal spacer.
Extra stuff ?
Instead of carbon, QTC contains tiny metal particles, but it does NOT work by
percolation since the particles remain insulated by the plastic. Instead, electrons pass
through the insulation by a process called quantum tunnelling - hence the name of the
material. To explain this effect, we have to appeal to quantum theory and think of the
electrons as waves. In classical physics, the electrons cannot pass through an insulation
barrier, but according to quantum theory a wave can - and this is what happens in QTC.
To some extent we have to suspend belief, because the world seen through quantum
theory appears so much at odds with its common sense counterpart. (Another way of
describing the quantum tunnelling effect is to say that a probability exists of electrons at
point A - one side of the insulation barrier - appearing at point B - the other side. This is
all very weird - but demonstrably true.)
Applications of QTC
Since its discovery, QTC has passed quickly from a laboratory curiosity into a
commercial product poised to revolutionize product design. It has already been used to
make smart garments that can be wired directly to electronic products such as an iPod.
It is also being retro-fitted, for example, within conventional switches to eliminate arcing
and electrical noise. However, the material is so new that the commercial world is only
just waking up to the vast number of new possibilities and applications. These include
advanced membrane panel switches, speed controllers and sensors. When QTC is
heated or comes into contact with reactive materials, its dimensions change slightly to
bring about a measurable change in resistance. Because of this property, it can even
sense small concentrations of organic molecules in liquid or gas form.
QTC in design and technology
In design and technology QTC has some immediate uses, and it is highly appealing to
think that schools will be working at the same time as industry to explore as yet
unknown practical applications.
The magic of QTC can be demonstrated simply with a tiny square of QTC (called a pill)
and an electric motor. If the pill is placed on a conductor - say a ruler - and touched
with a probe to complete the circuit, the motor will not run. When the pill is compressed,
the motor starts up. Squeeze very hard and it will run at top speed. If you apply varying
pressure the motor speeds up or down since the QTC functions as an infinitely variable
Example applications of QTC using pills
1. A QTC pill bridges the gap between
two pieces of self-adhesive aluminium
foil laid near the ‘hinge’ of a piece of
folded card or plastic sheet. When the
card above the pill is pressed, it acts
either as an on/off press switch or a
variable resistor. Many other card/pill
configurations are possible including
warning switches and alarms.
2. Controlled and sustained pressure on the QTC pill via a screw or lever system turns it
into a potentially useful variable resistor for heavier currents. In this context, the
alternative is an expensive wire-wound resistor with a rating above 1 watt.
3. Three QTC pills placed between a pair of metal plates provide the basis for a weighing
machine. The greater the load, the smaller the measured resistance. The resistance
change can be read directly from a meter or fed to a PC with interpretative software.
4. If three pills are placed on separate self-adhesive foil strips on a card or plastic disk and
overlaid with a metal plate, the weighing machine becomes a 2D joystick. Apply pressure
evenly and all three pills ‘turn on’. Apply more pressure to one side and the resistances
change accordingly. The example shown will control the movement and direction of a twomotor buggy or robot - with a third ‘channel’ for a light, buzzer etc.
5. Movement or force sensors become possible when one or more QTC pills are placed
between a relatively large mass and a ‘reference’ surface. The example shown is a
simply braking indicator consisting of a metal mass able to slide within a plastic tube. If
the tube is moving and suddenly slowed down, the mass will exert pressure on a QTC
pill and change its resistance.
Conclusion: Few materials as exotic as QTC have reached the classroom so quickly.
This technology will help to build safer and reliable electronic goods.