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November 27, 2007

Of Dipoles and Mobile Displays

foldable paper displayIn my previous article Consciousness, I discussed how dipole phenomenon might help us understand consciousness. Molecules comprise of electrically neutral neutrons in addition to protons, which are positively charged, and electrons which are charged negative. Since the number of electrons and protons are equal, molecules bear no net charge. But the distribution of electrical charges in a molecule is not always symmetrical; charges don't overlap. This inequality leads to what we call dipole moment (here moment means torque or couple, in physics). This is asymmetry in charge is analogous to tiny bar magnets, having north and south poles.

Water for example is a polar molecule and its dipole interactions explain its property of surface tension. When we heat food in a microwave oven, we actually agitate the 'magnet like' water molecules (dipoles) present in the foodstuff, which very rapidly alternate themselves in the rapidly changing microwave frequencies (about 2.5 giga Hertz). Hence the heat!

Now researchers at E Ink Corporation have created a mobile phone display using molecules having dipole moments.Medical biophysics Imagine an egg crate like this as shown in the left. Think of the 'balls' as dipoles and that the left sides of these balls behaving as 'north pole' are colored black; while the right sides as 'south poles' are colored white. This magnetic analogy is appropriate since opposing charges also behave in much the same way. Now, if you were to apply an electrostatic charge to the crate (not the balls), the balls would orient themselves in the direction of the charge. In the process, an image consisting of grayscale halftones will be created.

This display is very very energy efficient, foldable, rollable, can be seen even in bright light and has high contrast. However color technique has to be perfected. Cell phones may be expected to become more energy efficient in the near future.

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