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Ink-jet technology has far wider potential than plain paper printing.
 | It is also possible to build inkjet-like devices for use in applications where the surface to be painted is not paper – bottles, cables and anything which might need date/time, batch number or other information printing. This kind of mechanism is used in factories to stamp batch and date numbers onto goods. |
| Continuous inkjet is a refinement of inkjet technology intended for very high speed operation. A single nozzle emits a fine stream of ink droplets at some speed and carrying a high electric charge. Electrostatic plates steer the ink droplets to the correct place on the paper. This process bears some resemblance to the way cathode ray tubes work, it could be quite fast - but it could also be incredibly messy. |
All sorts of refinements on the inkjet principle can be devised. One might be a machine using pastry or icing sugar as ink to date-stamp pies – or individualise cakes.
The print elements could be large, using solenoid actuators. As mentioned previously, Samsung have a patent on using electromagnets and barr bearings as actuators.
It might be possible to put edible ink into standard Hewlett –Packard style cartridges.
The cartridge could also be mounted in a little cart, on which one of the wheels carries a position encoder – When pushed across any surface the cartridge would print the message.
Inkjet mechanisms construct an image by squirting small blobs of material onto a surface. The same principles can also be used to make three-dimensional objects. Successively printing the same pattern in the same position will build up an object layer by layer. Common inkjet cartridges produce images with resolutions less than 1000/th of an inch, so complex and detailed objects can be made. The technique is already used for manufacture of organic light emitting devices. Complex integrated circuits might be made using organic semiconductors. At a larger scale the same sort of ideas could be applied to resins, or to ceramics and metalswhich can be baked to harden them. In principle anything in liquid form could be handled - concrete or liquid metal.
Printed Circuits. 
Epson have developed a technique for printing multilayer electronic circuits using conductive and insulating inks. Both circuit interconnects and devices like transistors can be printed. New Scientist reports (03 Nov 2004) that the smallest device made by a prototype printer was 20 millimetres square, 200 microns thick and contained 20 layers. Epson believe they will be able to print components of 15 microns, similar in scale to those found in mobile phones and PDAs. Epson estimate that components made by printing might be half the cost of those made by photolithography and significantly less environmentally harmfull. Epson expect to commercialise the system by April 2007.
Gadget Printer.
New Scientist articles 8th Jan 2003 "Gadget printer promises industrial evolution". A team at University of California, Berkeley led by John Canny have developed techniques for printing fully assembled devices in one go. Conducting and semiconducting polymers are printed so that the circuitry a device requires is part of the body. Circuit elements can include transistors, capacitors and inductive coils - and moving parts. Using transparent polymers and plastic light emitters they could even print light bulbs.
The techinques called "flexonics" would do away with conventional printed circuit boards. One downside is that if a flexonic device breaks it is irrepairable. Another is that polymer devices currently switch at speeds about 1% of those for silicon transistors.
Jordan Pollack of Brandeis University reckons "Santa Claus" production machines will be used first for things like light-bulbs, toys and transistor adios. His own interest is in printing robots.
Spray on Display.
Researchers Ghassan Jabbour and Yuka Yoshioka at University of Arizona, Tuscon have used off-the shelf inkjet printer parts to print computer displays and solar cells on a multitude of different surfaces including silicon wafers, glass, plastic and textiles.
The printer cartridges are filled with different organic liquids to form semi-conducting polymers. the printer controls the amount of ink dispensed to within a few picolitres and 25 microns. Adapting the printer software makes it possible to produce circuits. Jabbour estimates it will take five years for the technology to be developed commercially.
The article also mentions Cambridge University spin-off company Plastic Logic.
Stable Conducting Polymer.
New Scientist reports (14th Dec 2002) that Beng Ong of Xerox Research Mississauga has stabilised the polymer polythiophene so it is not attacked by oxygen in the air. The new process was secret because Xerox were applying for a patent but had been named "XPT".
Polythiophene has chain like molecules which allow electrons to pass from one to another. The material can be dissolved and then sprayed onto paper from an inkjet printer. By slightly modifying the material it can be given different electrical properties and make components like transistors. Ong predicts the circuits could cost as little as a few cents per square metre.
Exploding Ink.
Qinetiq has patented a printable explosive fuse. The ink is made of 1 micrometer aluminium particles, 5 micrometer copper oxide particles and epoxy varnish in an alcohol solvent. This material is stable as a liquid but a controlable explosive as a solid. The envisaged use is to print a line or trail in contact with a metal strip at one end and make a large patch of ink at the other so that it forms an electical igniter, fuse and detonator which can easily be re-printed in field conditions. The material could be used for conventional munitions or as a timing element in airbags and fireworks. Qinetiq even suggests that ganging many devices together could make a very finely adjustable miniature rocket engine.
Inkjet Pen.
Silverborook Research has patented a pen which looks like a fountain pen but uses an inkjet mechanism to deliver ink to the page. The pen is about the size of a fountain pen and has a rolling ball at the tip so that it moves smoothly over paper. Ink delivery is by one or more ink nozzles activated by pressure sensitive switches so that greater pressure makes thicker lines. The inkjets are powered by a battery in the pen body. Coloured inks can be used making a multicolour pen.
Inkjet Camera.
Kia Silverbrook has also filed patentents on a digital camera containing a 3-colour 1600 dpi inket printer head and paper. The camera would produce photographs looking like ordinary prints. Rather than re-charge using cartridges Silverbrook suggest the camera be rented.
Printing Smell.
Hewlett Packard has filed for a patent on recording smells with photographs. An expensive version of the idea incorporates a gas chromatography probe to capture the actual smell. A cheaper option is to have a library or menu such as wet dog that the user can choose from. The idea is that inkjet printers will combine chemicals to replicate the smell when they print the picture. (New Scientist, 12th April 2003).
Inkjet heads have several appliactions outside printing - as medical dosing devices for instance.
Chip Cooling.
An unconventional application of inkjet heads is to semiconductor chip cooling. Chandrakant Patel of Hewlett Packard Labs, Palo Alto has experimented with a 512 nozzle inkjet cartridge filled with water. The team found they could cool a hot-plate and by changing the nozzles they could direct the cooling effect, which is potentially useful because processing elements tend to run much hotter than memory. Temperature sensors within a chip could control the direction of spray.
Water might not be the perfect coolant but Patel has designed a waterproof coating for chips. Flourocarbons are less effective at cooling but don't damage the electronics.
The fluid can be condensed in the top of the chip and returned to the inkjet head without needing a pump.
Ken Goodson of Stanford University whose group specialises in chip cooling thinks the idea has some merit. (New Scientist, 17th Aug 2002)
Chip power consumption is typically 70 Watts per square centimetre and has been rising rapidly to become one of the main limitations on performance.
Optical Switching. Link to New Scientist
New Scientist reports that Agilent Technologies and NTT have separately invented optical switches using bubbles.
Optical fiber is used for most long distance networks. Optical fibers work because their refractive index is higher than that or surrounding material.
Existing optical switches tend to be based on micromirrors and it is difficult to align these with fibers. There are also concerns that the moving parts will wear out.
Both Agilent and NTT use a flat substrate criss-crossed by stripes of a material forming a light carrying channel. Where the channels cross the intersection is a fluid containing channel. The fluid has the same refractive index as the stripe material, so light passes uninterupted.
In the Agilent switch a bubble is created by localised heating, the bubble has a low refractive index and the light is reflected instead of transmitted. By operating the device at close to the vapour temperature of the fluid the bubble can be made to form or dissapear in 10 milliseconds according to research manager David Andersen.
NTT uses two heaters to push a bubble from one position to another, forming a bistable switch. No power is needed to maintain the bubble, just to alter its position.
The report is dated April 1st 2000 - but seems true!
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© Graham Huskinson 2010
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