QUANTUM TUNNELING COMPOSITES Submitted by: Name: K Satya Ramesh Branch: ECE, Year: 4th Ph.no.-9291329031, Email: firstname.lastname@example.org College: Kakinada Institute of Engineering & Technology, ABSTRACT 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. Applications 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 graphics 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 force Making 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 resistor. 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.