Seawater used to receive terrestrial digital broadcasting signals

Mitsubishi Electric has succeeded in using a column of seawater as an antenna to receive the signals of terrestrial digital broadcasting for the first time in the world.

When seawater being ejected upward with a pump, etc is used as an antenna, electric current flows out to the surface of the sea or under the surface if no measures are taken. For example, at the time of transmission, antenna efficiency (the ratio of power radiating into the space to the input power) lowers.

To address this problem, Mitsubishi Electric developed an “insulating nozzle,” a power supply structure that prevents a high-frequency current from flowing out to the sea and makes the electric current effectively flow between the transceiver and antenna. The insulating nozzle is attached to the outlet of water being ejected. The nozzle prevents the leakage of electric current into the water because its height is 1/4 that of the wavelength of broadcast waves.

The conductivity of seawater is lower than those of metals. Therefore, the diameter of the water column needs to be large, requiring a powerful pump. Mitsubishi Electric used a commercially-available electromagnetic field simulator to calculate the minimum diameter that realizes a high enough antenna efficiency with a commercially-available pump.

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