Unit Costs and/or Cost Methods or Inputs: Costs will only be estimated for the electronics portion of the rectenna in this section. That is, the one-half-wave dipole, filters, and rectifier circuit. For a "typical" site in New Mexico, at a latitude of 35°N, the rectenna will be 10 KM x 13.2 KM, or 1.04 x 108 M2. Based on a dipole/rectifier cell area of 53 cm2 corresponding to 2.45 GHz, there will be approximately 190 elements/m2. Assuming quantity production of diodes and rectenna elements in the billions (approximately 20 billion/rectenna) production costs could probably be brought down to approximately $ .03 per rectenna element. Therefore, the cost/m2 is estimated to be $5.70/m2, or for the "typical" rectenna, approximately $595M. Technology Status, Criticality: There are several areas which require either further hardware development or further investigations. a. One of the most critical is the development of a diode which will rectify with high efficiency at low levels of input. There are specific parameters which are involved in the development of this type of diode. These are: (1) A reduced junction area. (2) A change in junction materials. (3) Increase in circuit impedance of the rectenna element. Present studies are being made under a NASA contract to investigate these parameters. These include reducing the diode chip area from 10-4 cm2 to 0.125 x IO"4 cm2, changing the junction material from Gallium Arsenide- Platinum to Gallium Arsenide-Wolfram to lower the barrier voltage, and changing the circuit impedance from 120 ohms to 480 ohms to increase the DC voltage for a given power out. On a scale from 1-5 (1 = low criticality, 5 = high criticality), the development criticality is about 3. b. One of the big questions which the public will be interested in is the biological and ecological effects of large MW power densities reaching the Earth. At the present time there is not too much concern about short-term exposures to these power densities. The present military specification states a limit of 10 mW/cm2 as the maximum level of continuous radiation to which humans may safely be exposed. Even the highest power density is only twice this amount at the very center of the rectenna and the power density drops off fairly rapidly from the center. Because of the concept of the wire mesh back-plane construction of the rectenna the levels underneath the rectenna will be considerably reduced. Other studies on this subject suggest a much lower tolerance level for biological life. In a book by M. S. Tolgskaya and Z. V. Gordon, Pathological Effects of Radio Waves, the authors report microscopic changes
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