1. Field of the Invention
The invention relates generally to devices for directly converting thermal energy to useful electric energy, wherein the invention may also be utilized for directly pumping heat from a colder source to a higher temperature sink. More specifically, the invention relates to a device for utilizing with high efficiency the electric fluctuation energy of small circuits thermally insulated from other small circuits at a different temperature so as to produce useful electric energy. The same device also efficiently pumps heat from lower to higher temperature regions.
2. Description of the Prior Art
Devices for converting thermal energy directly into electric energy have been extensively investigated and the most commonly utilized devices have been the thermionic converters working from high temperature sources and silicon cells utilizing the input thermal energy of solar radiation. The present state-of-the-art has been limited to achieving efficiencies of 15% for thermionic converters and 16% for silicon solar cells. In addition to these limitations on efficiencies, the temperature range over which these devices can work efficiently has been limited to high temperatures in the range of 1400.degree. to 2200.degree. K for the emitter and 500.degree. to 1200.degree. K for the collector of the thermionic converters and to moderate operating temperatures in the range of less than 400.degree. K for the temperature of the silicon solar cells.
The present invention removes these limitations along with providing other improvements in the performance of the direct conversion of thermal energy to electric energy. The thermal converter of this invention eliminates the electron cooling, radiation losses and lead losses of thermionic diode converters and operates reversibly as a heat pump over a wide temperature range. The efficiency for each working temperature range is determined by the physical dimensions of the circuits. The small circuits of this invention yield increased efficiency and power output or heat pump output. The efficiency of the small circuit devices of this invention also improves the efficiency when the input thermal energy is in the form of thermal radiation from a heated source such as solar radiation from the sun which is to be converted to useful power. The Carnot cycle efficiency obtainable from a heat source at solar temperature working with a heat sink at the ambient temperature on earth is over 90%. This invention achieves this efficiency as it is not limited by the heat losses resulting from the diffusion and thermal conduction processes of solar cells. The invention also improves on the efficiency obtainable from the small circuits of the prior art. A typical prior art device is disclosed in U.S. Pat. No. 3,760,257 issued Sept. 18, 1973, which discloses a device used with a directional wide band antenna system to convert radiation energy to useful output power. The improvement of the invention herein over the prior art results generally from minimizing or eliminating the losses resulting from eddy current losses on the receiving antenna surfaces. Also, the efficiency of converting the wide bandwidth radiation such as solar radiation is increased in the instant invention by minimizing or eliminating the losses that occur from impinging stray radiation from other directions and the losses resulting from incompletely utilized voltages from antenna element spacings approaching one wavelength, or from antenna element spacings less than one half wavelength.