First produced in 1996, the Quantum Tunneling Composite (QTC) is a composite material made from micron-sized particles conductive filler particles combined with a non-conducting elastomeric binder, typically silicone rubber. The unique method of combining these raw materials results in a composite which exhibits significantly different electrical properties when compared with any other electrically conductive material. Hence it is a flexible polymer that exhibits extraordinary electrical properties as illustrated in Figure . QTC usually comes in the form of pills or sheet. QTC pills are just tiny little pieces of the material. The sheets are composed of one layer of QTC, one layer of a conductive material, and a third layer of a plastic insulator. While QTC sheets switch quickly between high and low resistances, QTC pills are pressure sensitive variable resistors.
QTC is used as a pressure sensor; in its normal state it is a perfect insulator, but when compressed it becomes a more or less perfect conductor and able to pass very high currents. It utilizes quantum tunneling: 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 tunneling is exponential with decreasing distance, allowing the resistance to change by a factor of up to 1012 between pressured and unpressured states as shown in Figure .
QTC has the unique ability to smoothly change from an electrical insulator to a metal-like conductor when placed
under pressure. While in an unstressed state the QTC material is a near-perfect insulator; with any form of deformation the material starts to conduct and with sufficient pressure metallic conductivity levels can be achieved. This property can be utilized to convert pressure or force into an electrical signal as illustrated in Figure .
QTC can be tailored to suit different force, pressure or touch sensing applications – from sensing feather-light or finger operation to heavy pressure applications. Figure above shows various application examples of sensing capabilities of QTC material.
QTC has been implemented within clothing to make “smart”, touchable membrane control panels to control electronic devices within the clothing, e.g. mp3 players or mobile phones. This allows equipment to be operated without removing clothing layers or opening fastenings and makes standard equipment usable in extreme weather or environmental conditions such as Arctic/Antarctic exploration or spacesuits. However, eventually, due to the low cost of QTC, this technology will become available to the general user