Tunable liquid-metal antenna

This image shows the antenna, feed, and reservoir.

Researchers at the North Carolina State University have managed to control liquid metal to create dynamically tunable antenna.

Antennas work by generating an electromagnetic field as current flows into it and conversely capture an oscillating electromagnetic field generating a current. The size of the antenna is crucial to the reception/generation of the electromagnetic field, the rule of thumb being that the antenna "length dimension" should be about half wavelength. As you diverge from this dimension the amount of conversion gets smaller, the antenna loses efficiency.

If you need to capture different frequencies (the frequency, f, multiplied by the wavelength, lambda, is equal to the speed of light, c) you ideally need different sizes of antenna and this is not always practical.  As the strength of the signal (its power) decreases, the efficiency of the antenna gets more and more important.

Hence, it is easy to understand that in areas like Internet of Thing where the power available is often an issue, having a very efficient antenna would be very important.

Here comes the idea of using liquid-metal to create an antenna that can be dynamically resized as need arises. There is plenty of liquid metal around, all metals, provided they are heated over a certain temperature are liquid. Of course you don't want to heat up to a 1,000° iron to have it liquify, you would need too much energy, but you can have mercury that is liquid at ambient temperature. Event better we have other metal composites that are liquid at ambient temperature, like eutectic gallium and indium.
The problem researchers have been faced so far was how to convince the liquid metal to flow in a given direction to acquire the desired shape.

This is what researchers at NCSU have solved. They discovered that oxidation of the gallium and indium changes its surface tension. By applying a small positive voltage they can decrease the surface tension and this makes the liquid-metal flow into a capillary whilst applying a negative voltage increases the surface tension and makes it retract from the capillary duct.  By carefully applying the voltage it is possibile to fill just the right length of the duct et le voilà: you have created an antenna that can change its length on demand.

The quilt required to further the IoT has got another tile.

Author - Roberto Saracco

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