Batteries: thermoelectric and photoelectric – Thermoelectric – Processes
Reexamination Certificate
1999-07-07
2001-03-27
Gorgos, Kathryn (Department: 1741)
Batteries: thermoelectric and photoelectric
Thermoelectric
Processes
C136S205000, C136S239000, C136S240000, C136S237000
Reexamination Certificate
active
06207887
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to thermoelectric devices and in particular to very small thermoelectric generator devices.
2. Description of the Related Art
The generation of electricity by the application of heat at the junction of two dissimilar materials has been known for 178 years. Thermoelectric modules fabricated from simiconductor materials can convert heat into electricity with efficiencies of up to six percent. Despite efficiencies much lower than some other electric generators, these devices can have many practical applications. Waste heat is generally free; so low efficiencies may not be important. In many remote locations thermoelectric devices may be the most economical means of generating electricity even if a source of heat must be provided. Thermoelectric devices can be made very reliable and very small. Many space vehicles have their instruments powered by thermoelectric devices, which typically use heat produced by radioactive sources such as Pu-238 sources. Small prototype thermoelectric devices using radioactive sources have been produced for the purpose of being implanted in people for providing power for pacemakers. One such example is described in U.S. Pat. Nos. 3,780,425 and 3,781,176. This device was proposed as a thermoelectric battery for a cardiac pacemaker. These patents proposed a method of manufacture that proposed the use of epoxy impregnated paper insulators between thermoelectric elements and the use of a photo-resist method of applying contacts.
The United States acting through NASA and JPL are seeking to develop a small power source for a Mars vehicle. The plan is to utilize an existing off-the-shelf radioactive heat unit (called the 1-Watt RHU) which was developed by the Los Alamos National Laboratory, Los Alamos, N. Mex. The 1-Watt RHU produces 1 Watt of thermal power and is used in space to heat instruments so that they will not freeze. The radioactive element in the 1-Watt RHU is Pu-238, which is a very dangerous material, but many tests have proven that the containment vessel, which contains and protects the Pu-238, is so reliable that it would survive an explosion on lift-off and the maximum possible heating on reentry.
Studies have been conducted to combine existing thermoelectric modules with this heat source to produce about 40 mW of electric power at 5.5 Volts for space uses. No such module exists. In fact, one study concluded that the “prospects . . . [of satisfying these requirements] based on a 1-Watt heat source are not encouraging”. (Schock and Or, Parametric Design Study of “Power Stick” and Its Derivatives, CONF 95011, American Institute of Physics, 1995)
What is needed is a miniature thermoelectric module capable of reliably producing for many years 10's of milliwatt power from a very low power heat source such as a heat source generating heat at a fraction of a Watt to a few Watts.
SUMMARY OF THE INVENTION
The present invention provides a miniature thermoelectric module for generating electric power from low power heat sources in the range of a fraction of a Watt to a few Watts (thermal). The module comprises an array of thermoelectric elements, each element having a cross section of less than 0.001 square inch and a length of at least 0.25 inch. The elements are separated from each other with a polyimide insulator sheet in a checkerboard array. In a preferred embodiment, the modules are fabricated by hot pressing a stack of alternating plates of p and n doped thin plates all separated by thin sheets of a polyimide insulator material to produce a pressed stack of p and n doped layers. The stack is then sliced to produce layered plates which are then stacked with insulating polyimide layers positioned between the layered plates to produce the checkerboard array of p and n thermoelectric elements. Contacts are applied to electrically connect all of the elements. In a preferred embodiment, the contacts are applied by first sputtering a thin layer of gold, then welding gold tabs, and then blasting away the excess sputtered gold. In one preferred embodiment, the contacts connect all of the elements in series. In another preferred embodiment, the elements are connected in a series-parallel circuit to enhance reliability. In a preferred embodiment, the module is utilized in a generation unit with a 1-Watt (thermal) radioactive heat source to produce about 40 mW of electric power at 5.5 Volts which is converted to 12 Volts with a DC to DC converter.
REFERENCES:
patent: 3780425 (1973-12-01), Penn et al.
patent: 3781176 (1973-12-01), Penn et al.
Elsner, N. B., Bass, J. C., Ghmaty, C. C., Morris, Baker, N., and Bass, J. A., Fabrication of Milliwatt Modules, 18th International Conference of Thermoelectrics, Aug. 28-Sep. 2, 1999, pp. 505-508.
Bass John C.
Elsner Norbert B.
Gorgos Kathryn
Hi-2 Technology, Inc.
Parsons Thomas H.
Ross John R.
Ross, III John R.
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