THE fragile microwave frequencies that will be used by future generations of
cellphones cannot easily pass through house and office walls. So Roke Manor
Research in Hampshire, part of the Siemens group, has filed patents around the
world on a “smart brick” which can make walls transparent to the signals.
Roke says its main priority is developing new 3G devices, but its researchers
were faced with conflicting requirements. Mobile phones are no longer just
phones, they are use-anywhere, do-everything devices
(91av, 21 October 2000, p 29).
But the higher frequencies allocated to 3G, over 2
gigahertz, are significantly weakened by house and office walls. Today’s GSM
mobiles use 900 megahertz and 1.8 gigahertz.
“We had a brainstorming session and asked ourselves the question: ‘Is there a
better form of building material?'” says Paul Smith, Roke’s director of radio
devices. So Roke research engineer Walter Tuttlebee went away and came up with
the “Bricksat”—a modified brick the same size as a standard house brick,
but hollowed out to contain a low-power wide-band radio amplifier connected to
printed circuit antennas on opposite surfaces of the brick
(see Graphic). The
Bricksat can be powered by the mains, suggests Roke. Or it can be fed from a
rechargeable battery that is trickle-charged by a solar panel that makes
electrical energy from sunlight or the room’s own lighting.
Advertisement
The Bricksat can pass signals in both directions. 3G signals picked up by the
antenna on one brick surface are boosted and rebroadcast by the antenna on the
opposite surface. So signals pass through a solid wall, without losing
strength.
The radio spectrum is now so crowded that the only space available for new
services beyond 3G, which can carry the wide bandwidths needed for mobile
multimedia and Internet access, are at frequencies above 3 gigahertz. The
microchips needed to handle these frequencies—based on gallium arsenide
semiconductors—are now affordable. But as the frequency of radio waves
gets higher, and the wavelength shorter, they behave more like light, travel in
straight lines and are blocked by conventional building materials. Increasing
the power of the transmitter is not an option because the signals then travel
too far, interfering with signals from other base stations.
The new bricks could also be used for very low-power computer networks, such
as the emerging 2.4-gigahertz Bluetooth system, which normally only works in one
room. Although Roke’s patents suggest that the new smart bricks could even be
sold in DIY stores, for people to fit themselves, Paul Smith sees house builders
as the main market. “It would be very easy to build a few bricks into a new
building,” he says.
