Welcome to the ink-jet age
Published: 06 Jan 2006 18:15 GMT
Mention the term ink jet and most people will probably think of printers. Indeed there can be few computer owners who have not possessed one, and although the cartridges can be rather expensive, the printers themselves are cheap and give a high quality full colour print out.
However, when the engineers at HP Laboratories first developed the ink jet back in 1979 printing was far from being their number one application for the new technology. These engineers had visions of using the device in applications as wide ranging as medicine and materials science, but, as so often happens it was the marketing department that decided upon the application, printing would yield bigger profits and take far less development.
So it has come about that ink jet technology is now firmly associated in the minds of most people with printing. But the vision that those engineers had back in 1979, of ink jets being used for a wide range of other applications, was not forgotten.
Simple technology
Innovators are increasingly realising that although an ink jet is a deceptively simple technology — an array of nozzles that moves back and forth depositing tiny droplets of ink onto a sheet of paper — it is the fact that those ink droplets are so precisely measured and placed which means that the range of such a device extends far beyond merely printing on paper.
"Inkjet technology is no longer just being harnessed to print coloured fluid inks, but also functional fluids, for applications such as electronic circuits, displays, fuel cells, RFID tags, live tissue engineering and rapid manufacture." says Rob Harvey, business development manager of inkjet manufacturer Xaar. "Inkjet, and Xaar's solution enables manufacturer's to take a 'product' concept, which utilises functional fluids, and build it rapidly from prototype to one-off manufacture through to quite large volumes, economically and with greatly reduced development time."
Secret versatility
To understand why this is so, we need to look at the basics of ink jet technology. The secret of the ink jet's versatility lies in the ability of manufacturers to drill an array of very small nozzles, just a few micrometers in diameter, in a silicon or composite printhead. The size of the nozzle determines the size of the droplets that can be produced.
Behind each nozzle in the printhead lies a small ink chamber with a connecting channel that allows it to be filled from an ink reservoir. At the other end of the ink chamber from the nozzle lies a piezoelectric crystal that is connected to the ink jet control circuitry. When an electric current bends this piezoelectric crystal it forces the liquid ink down the nozzle at high velocity, and as it comes out of the nozzle it forms a small droplet travelling at speed. Each droplet produced is exactly the same size and travelling at exactly the same velocity.
The ink jet should not therefore be though of as a printer but is a general purpose tool for creating very small precisely measured droplets of liquid.
Over the last twenty years ink jet technology has been greatly refined, the number of nozzles in a head has increased from just 12 to over 3,000 in some industrial devices. Droplet sizes have been reduced to just a couple of micrometers in diameter and the number of droplets that can be produced per second has increased considerably.
Three dimensions
What innovators are realising is that the ink jet allows the engineer to precisely place an exactly measured minute quantity of liquid onto a surface. In a printer the liquid is coloured ink, but it could be anything that comes as a liquid or is suspended within a liquid medium — from suspensions of metal particles to living cells. Similarly in a printer the head is simply moved from side to side and the paper gradually inched up, however, the printhead...
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