How it Works
The MicroPower Chip is a new type of semiconductor device for direct energy conversion, similar in operation to thermoelectric devices. Just like thermoelectric devices it converts the heat applied to one of its surfaces directly into electrical energy. Conversely, if electrical energy is applied to the chip, one of its surfaces will dramatically cool.
The chips themselves, five of which are shown next to a dime in the picture on the right, are approximately 2mm² in size, and have very high current densities, on the order of 1,000 A/cm2, so chips as small as the ones in the photo will produce more than 10 Amps.
For a video demonstration of basic thermoelectric technology, please click on video below:
The Power Mode
MicroPower’s embodiment of its patented Power Mode technology is a simple semiconductor device designed to convert heat directly to electricity. This design is based on a combination of solid-state thermoelectric and thermionic principles. Conventional thermoelectric technology, developed in the 19th century, joins two dissimilar metallic or semiconducting plates and adds heat to produce a low-voltage, direct current. The amount of current produced is dependent on the difference in temperature between the hot side of the device, which is collecting the heat, and the cold side, which is being cooled by the air, a heat sink or some other method. The weakness of thermoelectrics are their low efficiency (typically below 5%) at a hot side temperature of about 200°C. Because of this low efficiency and low temperature range, thermoelectric conversion technology is only utilised for applications in which it’s the only viable technology solution, as is the case with deep space or remote terrestrial power generation. Despite these limitations, the global market for thermoelectric systems is currently estimated at $300 million per annum.
The other technology upon which the design of MicroPower’s Power Mode converter is based is called thermionics. The typical thermionic system consists of two parallel conductive surfaces (an emitter and a collector) separated by a vacuum gap. Heating the emitter to a very high temperature causes electrons to boil off, traverse the gap, and be absorbed into the colder collector, where the electrons can be connected to an external load. Although vacuum thermionic devices achieve absolute conversion efficiencies exceeding 20%, the key limitations include prohibitively high manufacturing costs and intimidating operating temperatures (above 1,100°C) thus confining the use of thermionic systems to limited special purposes such as nuclear-powered converters and special military applications.
MicroPower’s devices combine the best aspects of thermoelectrics and thermionics. Operating between 200˚C and 600˚C, MicroPower’s semiconductor technology has demonstrated conversion efficiencies approaching 40% of ideal Carnot Cycle conversion efficiencies with absolute efficiencies of 18% – in other words, thermionic efficiency at a significantly lower temperature range in which many waste heat applications were simply not previously thought viable.
The Cooling Mode
The conversion process is reversible, i.e., applying electrical power transports thermal energy from one side of the device to the other. However, the design elements for Cooling Mode and Power Mode converters differ in order to optimize performance according to application. Design elements required to assemble optimized Cooling Mode devices are common to Power Mode devices so in that sense the design elements have been co-developed and tested. Initial models project higher conversion efficiencies for the Cooling Mode than for Power Mode as a result of this ability to assemble optimized structures from the design elements already developed. Laboratory tests for cooling, at least in some cases, have already yielded cryogenic temperatures (temperatures below negative 150°C). However further work is required to assemble optimum structures consistently from the existing design elements.