Plant response to microwaves at 2.45 GHz

The solar power satellites (SPS) concept envisions an array of satellites in Earth orbit where they will collect solar energy and beam it to Earth. One transmission method is to use microwaves at 2.45 GHz. It is uncertain what the long-term effects will be of continuous microwave energy illumination of the biosphere. An experiment was done that exposed alfalfa to continuous microwave energy at 2.45 GHz with intensities of 0.5–1.2 mW/cm2. The hypothesis was that plants exposed to microwaves would be no different from those plants not exposed to microwaves. A tray of growing plants was illuminated with microwaves while control plants were grown behind a microwave-opaque shield. Test plants and the control plants were subjected to the same environment otherwise. The experiment was designed so that the only variable to which the test plants were subjected was microwave exposure. Precise, non-destructive measurements were taken weekly of leaf chlorophyll concentration. After 7 weeks the plants were harvested and fresh weight and dry weight were measured. Gross plant variables such as stem length and internodal distance were measured, and overall plant vigor was assessed. In all measured variables there was no difference between the control and the microwave treatment plants.