SPIES won鈥檛 welcome the development of the world鈥檚 first flat-panel cathode
ray tube, because they won鈥檛 find it so easy to sit outside a building and pick
up the signals from a VDU inside. Instead of using 鈥渓eaky鈥� electric coils to
steer an electron beam around a TV screen, IBM鈥檚 new display uses permanent
magnets which give nothing away.
But the new CRT from IBM鈥檚 lab in Greenock, near Glasgow, is not just
designed to deter espionage. It could also mean much cheaper flat-screen TVs.
The new display is put together mechanically from precision-aligned layers. This
is a far less costly process than the one used for flat LCD panels, which are
grown like giant silicon chips. IBM鈥檚 2-centimetre-thick flat-panel screen is
also far more robust.
The display was invented by IBM鈥檚 John Beeteson and Andrew Knox. Knox
recently developed the technology while doing a PhD at Glasgow University. The
flat cathode ray tube is a sealed rectangular box, with a flat cathode plate on
the back, and a slightly curved glass plate at the front
(see Graphic). The
glass is coated with red, green and blue phosphor dots, just as in a normal TV.
But a large permanent magnet plate is sandwiched between the cathode and the
glass, and the magnet itself is peppered with small holes.
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So how does it work? An electrically charged control grid, just behind the
magnet, steers electrons from the cathode into the holes in the magnet. The
intense magnetic field inside the holes makes the electrons spin rapidly,
focusing them into tight beams.
As the electron beams leave the plate perforations and rush towards the
glass, they pass anodes on either side of each hole in the magnet which steer
the electron beam to the correct pixels. When a colour signal is fed to the
anodes on either side of a hole, the beam accelerates straight ahead and hits a
green dot on the glass screen. If one anode is on and the other off, the beam is
slightly deflected to left or right, and hits a red or blue dot.
The pattern of charge on the control grid is continually changed by the video
signal. The pattern and quantity of electrons passing through the magnet create
a monochrome picture on the glass. But when you feed a colour signal to the
anodes, the electron beams then create a full-colour picture on the screen.
The new CRT is essentially a thin rectangular box, which makes it
structurally strong. This means the glass can be thinner, lighter and cheaper
than in conventional screens, which have a deep tube that has to be made of much
thicker glass.
Conventional CRTs use coils to deflect the electron beams, and these leak
electromagnetic radiation. The perforated magnets in the IBM tube only emit
steady magnetism which a spy can鈥檛 turn into a useful signal and the anodes leak
only weak electrostatic fields. Knox says this makes it much harder to eavesdrop
electronically.
But how the emerging technology鈥攔evealed in British patent GB
2353633鈥攚ill be exploited is unclear. Since IBM is not in the highly
specialised business of mass-producing vacuum tubes, the idea is likely to be
licensed to a third party. IBM is currently in talks with an unnamed Far Eastern
consumer electronics company.