Cars that glow in the dark and have far more passenger space, aircraft and submarines that monitor their complete outer surface, military vehicles that destroy missiles that hit them. The common factor here is smart skin.
Dumb skin is inadequate
Today, the shell of a vehicle is dumb: it is no more than packaging made of bent metal, glass and shaped plastic that protects and streamlines the clever stuff inside. However, the space inside is needed for passengers and cargo. Bulky batteries and motors inside vehicles overheat, needing expensive and unreliable cooling - often water cooling.
And we need many more functions such as solar power and external sensing and lighting that cannot be performed efficiently from within the vehicle. For example, the US Department of Defense has a program to develop real time monitoring of the structural integrity of the whole of the outside of its aircraft using smart skin. It envisages doing the same with aircrew.
Many inventions become appropriate
A large number of appropriate technologies are being adopted that can later become smart skin - multilayer, conformal electrics and electronics over wide areas. Flat electric motors and localised suspension and controls in the wheels have been rendered more practicable using thin film and printed technology.
Mechanical linkages and drive trains are eliminated, saving cost and space and improving reliability.
The same can be said of the multilayer printing replacing heavy, expensive copper wire electrics in vehicles and making the bulky, heavy ceiling and dashboard clusters in a car into multilayered laminate, where T-Ink is a leader.
Schreiner already makes printed decals for BMW cars that light when the door is opened and BMW is preparing laminar Automotive Thermoelectric Generators ATEGs that will harvest heat from the engine and exhaust.
Light emitting diodes in car lights have improved lifetime tenfold: now we have laminar conformal LED arrays that use light guides or large numbers of very thin LEDs. Indeed, LEDs only 20 microns thick have been made and the thinnest LCD TVs are LED backlit. The lifetime limitations of printed large area ac electroluminescent and OLED (organic light emitting display) lighting and display are gradually being overcome.
Smart skin performs better than conventional components
Thin film batteries used in electronics can support faster charge and discharge, last longer and work even when a nail is driven through them. Solicore and others have demonstrated this: it contrasts with some bulk lithium-ion traction batteries exploding when penetrated.
Some thin batteries are printed and conformal, with solid state electrolytes and therefore no possibility of leakage. Wider area versions are now being prepared by Planar Energy, The Paper Battery Company and others. Indeed, thin large area batteries have recently been a great success in several pure electric aircraft that have employed conformal thin film photovoltaics to provide the power. Northrop Grumman, Lockheed Martin, AeroVironment and Aurora Flight Sciences each have contracts up to $530 million to make various dirigibles and aircraft based on a laminar coating of photovoltaics for power.
Alternatively, the "molecular switch" printed layer of the University of Texas at Austin potentially mimics the ability of plants to harvest light and convert it to energy. Laminar power could be produced directly from the sun, rather than inefficient power through a plant mediator, such as corn used for biofuels.
Take all this together and we clearly have a route to smart skin on land, sea and air vehicles saving huge amounts of space, cost, weight and energy but also adding many new functions. For example, if the whole truck or aircraft glowed in the dark it would be much easier to identify and avoid. If the whole of the outside of the car generated electricity, it would be at ten times the power generated by the small rigid solar panel on the top of some cars today.
Invisible vehicle skin
We can generate electricity from printed laminate over the windows and lights of a car if the layer is transparent. Laboratories in Taiwan, Japan and elsewhere have demonstrated both inorganic and organic printed photovoltaics that is transparent and others have translucent versions.
This is also important for smart skin on, say the wings and body of an aircraft. We are no longer limited to one optically active layer - the one on the outside.
Already some printed photovoltaics have transparent transistors on the outside for controlling spectral response. Transparent photovoltaics can be layered over transparent light emitting surfaces which are over transparent wide area sensors - all have been demonstrated.
NEC in Japan is developing transparent rechargeable battery layers and many OLED displays are transparent and conveniently work at or near the low DC voltages generated by transparent photovoltaics.
All that makes us think of invisible smart skin that does not detract from the conventional livery and signage on a vehicle, product or package. Some will even be capable of sound - spoken warnings, information and so on. On the other hand, printed and thin film electronics is giving us stretchable electronics, as with an OLED film stretched over a raw egg without breaking it, and costs low enough for some smart skin to be disposable.
Although, at first sight, it may seem bad practice to put the brains and the power of a vehicle on the outside facing any impact, this is not as bad as it sounds. With wet electrolytes being eliminated, the danger from wet chemicals is removed. That applies to some printed Dye Sensitised Solar Cells DSSC, supercapacitors and hybrid supercapacitor-battery constructions called supercabatteries plus laminar batteries themselves. The use of toxic materials is also becoming a thing of the past.
Biomimetics is being brought to bear - just as the human brain has redundancy - duplication for security of service - so we shall have more of the redundancy of power and circuitry typically seen in a military ship or civil aircraft today. Most of these laminar components are much more damage tolerant anyway, just as a bird can still fly with a few feathers missing and a human hand can still have a sense of touch if part of it is out of action.
Missile destroying skin
So what about vehicle skin that disables incoming missiles? A recent European study has shown that "electric armor" can be a cost-effective way of protecting a vehicle against penetrating explosive devices. It follows earlier work in Russia and the USA with a skin of explosive that destroys incoming ordnance.
Traditional thick steel armor plates are replaced by a capacitor layer - two conducting layers separated by an insulating one. When a shaped charge penetrates the smart skin it closes the circuit to discharge the capacitor to diffuse the attack.
The work was carried out by BMT Defence Services in the UK for the European Defence Agency. This recent study looked at relevant work across Europe and its application to the new electric military vehicles which have little or no heat or sound signature for missiles to home in on but must be lightweight to provide adequate range. A generic electric armor system for a 30 tonne vehicle was developed and a roadmap for key technologies.
New armored vehicles for the British Army are likely to include electric armor from the national Defence Science and Technology Laboratory DSTL to address the threat from rocket-propelled grenades. DSTL has already developed a system weighing only two tonnes but with the protective effect of carrying an extra 10-20 tonnes of steel armor, yet reducing the effect of impacts by rocket propelled grenades to almost zero. Clearly we shall hear of more magic made possible by various forms of smart skin on land, sea and air vehicles.
Leading event on the subject
Printed and potentially printed thin film electronics and electrics are now a subject in their own right. The world's leading event on the subject is Printed Electronics Europe 2011 where those providing and using the key enabling technologies for smart skin and other breakthrough applications will be exhibiting, presenting and demonstrating. That includes NanoMas Technologies, intrinsiq, HC Starck and others making printable nano metal and conductive polymer inks that can be annealed without damaging low temperature, low cost substrates. They also use less material.
Global leader in appropriate polymer film,
For more information on this event or to register for a press pass, please contact Cara Harrington at c.harrington@IDTechEx.com.