Why does fresh plant material block radio waves?

Answer 1

Radio waves can be blocked (reflected) or attenuated (partially reflected or absorbed) by anything that conducts electricity. A thin sheet of aluminum can completely block (reflect) radio waves. They simply cannot penetrate it. Salt water (as in the ocean) permits radio waves to penetrate only a very short distance. Similarly, living plant material contains water and dissolved ions (the plant's "blood" or the plants food, if you want to look at it that way). This makes the plant something of a "conductor" of electricity. Now to the nut inside the shell of this answer. When radio waves (electromagnetic energy) encounter a conductor, something happens. The frequency of the radio waves, their amplitude, and the "nature" of the conductor will result in a varying degree of interaction. What happens is that the radio waves stimulate microcurrents within the conductive material (the foil, the salt water, the plant with its moisture and ions, whatever). This interaction reflects or absorbs the energy (to a greater or lesser degree) of the incoming radio wave. The microcurrents don't destroy plant tissues because the power contained in the radio wave is very low (microvolts per meter, and usually less). Certainly if a plant is "right on top" of an electromagnetic source, it will take some heat from the radiated energy. But as to the effect of "regular" radio waves, the damage is not noticable, and the signal will be damped or attenuated by interaction with the plant.