I have gone for a design which combines the style that the Doctor has used previously with his sonic screwdrivers, and the power of the sonic screwdriver that was made for the 11th Doctor by the TARDIS. I think in terms of style it mainly borrows from the 10th Doctor's sonic, but the combination of the red and gold at front end was for nostalgia, as it reminds me of the 3rd Doctor's sonic.
The main colour is white, with a gold-plated back end and gold-plated claws. The claws are held in place by red connections. When the claws are pushed forward these connections are what bend the claws backward, causing them to open. As the claws are pushed forward the inside is revealed to be a metallic blue. The colours look pretty basic on the attached file but I imagine it would look much better on the finished product. I was originally going to use a blue LED but I think a green one would look like a more powerful light.
The claws at the front end help to direct the sonic vibrations towards specific targets, but when the red button on the handle is pressed it causes the claws to open for a broader range. The emitter is controlled by a button which can be pressed both forwards or backwards. Pressing it forwards would have a normal effect, while pressing it backwards would "reverse the polarity".
Just in case the dimensions aren't clear in the picture:
Length of handle - 100mm
Length of back end - 20mm
Length of front end - 35mm
Diameter - 28mm
Diameter of emitter - 9mm
Diameter of claws when closed - 62mm
There are loads of great entries in this competition so I'll feel slightly threatened, but I believe my design is well thought out so I hope I have a good chance.
Good luck to everyone else who has entered the competition, and to everyone planning on entering.