Saturday, October 13, 2007

Water Bottle Antenna

In developing nations there's a problem wiring up the network. Not only is power unstable and often unavailable but also if you happen to have a laptop, it's not very useful without an Internet connection. Lacking a telco backbone, wireless is the route to go.
Btu even Wi-Fi is a real problem due to the scarcity of essentially all involved hardware. As with all engineers, this is the step-mother of invention. In this case, a plastic water bottle is used to make a dielectric resonator antennas (DRAs.) These Liquid dielectrics as can be used effectively at frequencies between 1-4 GHz.
What they're doing at BottleNet is finding bottles with the correct dimensions to use as a waveguide. The diameter of the cylinder largely determines what frequencies the antenna can transmit or receive. This has a mathematical relation to the cylinder's length so calculations must be made to cut it to the correct leg nth. More here.
But plastic can't reflect microwaves right? Well yeah, that's a bit of a problem. But appropriately size-cans are in short supply. So these little geniuses just wrap the puppy in a wire mesh called flyscreen so it has a reflection profile. It has a 1-millimeter weave which in comparison to the wireless frequencies is effectively the same as a solid reflective metal surface.
Mali must be a nation of a million MacGyvers. Here's what you'll need to do this at home for materials and tools. The final product actually functions on par with a typical low-end factory made wireless antenna. Full instructions here.
(1) 1.5 litre bottle of Diago mineral water
(1) Piece of metal woven flyscreen 300 mm x 220 mm
(1) Piece of metal woven flyscreen 100 mm x 100 mm
(1) 31 mm length of 14 or 16AWG wire
(1) Appropriate connector (N-type typically)
Awl or pointy object
A soldering iron and solder
Scissors for cutting mesh
Leather gloves for handling sharp edges of flyscreen