Activated alumina: Is a high-surface-area, highly porous form of aluminum oxide. It can adsorb gases and liquids without changing its form. It works as a desiccant through adsorption. As air passes through the alumina, the water in the air sticks it and becomes trapped and air that passes through an activated alumina filter is dried out. Even immersed in a liquid.
Silica Gel: Silica gel may also be used to keep the relative humidity inside a high frequency radio or satellite transmission system waveguide as low as possible. Excessive moisture buildup within a waveguide can cause arcing inside the waveguide itself, damaging the power amplifier feeding it. Also, the beads of water that form and condense inside the waveguide change the characteristic impedance and frequency, degrading the signal.