A METAL object has been made to evolve in a similar way to a simple living creature. Siavash Haroun Mahdavi and Peter Bentley at University College London have created an antenna that can optimise its shape to achieve the best reception of a particular radio signal.
The umbrella-shaped antenna is made from a sheet of aluminium foil on a springy metal frame, which is held in shape by 16 wires made of a nickel-titanium alloy called nitinol (see Diagram). Each wire can be made to contract by up to 8 per cent by passing a current through it, so by switching the current on and off it is possible to subtly alter the shape of the dish.
The researchers connected the antenna鈥檚 output to a computer which measured how effective it was at picking up a UHF signal transmitted from the next room. To start with they applied 20 random combinations of on and off states to the 16 wires. For each combination, the signal quality received by the antenna was compared with that of the unaltered dish. Each combination was expressed as a string of 0s and 1s, and given as input to an evolutionary software algorithm.
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The algorithm chose pairs of strings at random, but the strings that corresponded to a combination that produced better reception were weighted so that there was a greater chance that good 鈥済enomes鈥� would be paired up. The algorithm then chopped up the pairs of strings and swapped over chunks to produce two new offspring in new configurations, occasionally flipping some bits at random to imitate mutations, until 20 new configurations were bred.
Mahdavi and Bentley set the evolutionary experiment running overnight in their central London lab. At the end of the process they found that their antenna performed 20 per cent better than the unaltered ones. They say the technique could lead to spacecraft antennae that can reconfigure themselves to reduce transmission noise.
