Engine on a Chip

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Engine on a Chip
The Dream of the Personal Turbine

by	Iddo Genuth

Imagine a millimeter-size personal turbine engine that could meet all your personal electrical needs. That's the vision of MIT researchers, who plan to have an operational prototype by mid-2007. First uses (3-5 years): 10-50 watts for high end laptops and military gadgets.

Originally published on The Future of Things, February 7 2007. Reprinted with permission on KurzweilAI.net February 9, 2007.

After a decade of work, the first millimeter size turbine engine developed by researchers at MIT should become operational by the end of this summer. The new turbine engine will allow the creation of smaller and more powerful batteries than anything currently in existence. It might also serve as the basis for tiny powerful motors with applications ranging from micro UAVs to children's toys. In the more distant future huge arrays of hydrogen fueled millimeter turbine engines could even be the basis for clean, quiet and cost effective power plants.

Turbine engine history

Frank Whittle (Credit: NASA Glenn Research Center)

Turbine engine history goes back to the beginning of the 20^th century. In 1903 the Norwegian inventor Aegidus Elling became the first person to successfully construct a gas turbine engine which produced excess power, reaching 11hp (the Wright brothers Kitty Hawk which flew for the first time that year had 12hp). Several years later Charles Curtis, who invented the Curtis steam engine, filed the first patent application in the U.S. for a gas turbine engine which he was granted in 1914 (but not without some controversy). Four years later, in 1918, General Electric (GE), founded by Edison in the mid 1870s, started work on aircraft engine turbochargers and two decades later on aircraft jet engines on their gas turbine division (now one of the biggest in the world). In 1930 the inventor and Royal Air Force officer Sir Frank Whittle, building on previous work including that of Elling, designed and patented the first gas turbine for jet propulsion. After a neck to neck race to build the first jet powered engine, the German Hans von Ohain, working with the Heinkel Company, became the first to design and test a jet powered aircraft in 1939 beating Whittle which suffered from technical problems with his design.

GE90 engine - the world record holder (Credit: Stanford.edu)

After the war turbine jet engines continued to develop and grow in size and power forming the basis for almost all modern aircraft engines. Holding the world record today is the GE90 series engine which helps power the Boeing 777 Airliner. With 22 blades the engine is over 120 inch (3 meters) tall producing over 115,000lb of thrust (over 127,000lb on a test) this engine is 10,000 more powerful than that used by the Wright brothers one century ago.

Siemens SGT5-8000H 350MW gas turbine schematics (Credit: Siemens)

Enormous gas turbine engines are also used for electrical power production. In a gas turbine (also known as combustion-turbine), hot gases produced from the combustion of natural gas in a high-pressure combustion chamber are passed through the turbine, which spins the generator to produce electricity. Gas turbines are commonly used to serve the peak loads of the electric utility and have grown in size and complexity over the years. Simens' SGT5-8000H advanced gas turbine engine, the alleged world record holder, is a gigantic machine weighing over 440 tons (880,000 pound) and able to reach an output of 340 MW in simple cycle and about twice as much in a combined cycle. The efficiency of the SGT5-8000H is almost 40% and around 60% in combined cycle.

IHI Dynajet 2.6 mini turbine engine (Credit: IHI Aerospace)

Beside airplanes and power plants gas turbine engines have many other uses, ranging from tank engines (gas turbine engine is used in the M1A1 Abrams tank), ship and locomotive engines as well as auxiliary power units. But beside those large scale solutions, new technology has allowed smaller and smaller versions of gas turbines. IHI Aerospace in Japan developed a small portable gas turbine generator called Dynajet 2.6, which produces 2.6 kW and has a total weight of 67 kilograms. A different micro sized gas turbine was developed by researchers at the Swiss Federal Institute of Technology (ETH Zurich). This tiny turbine reached a size of several centimeters producing up to 100 watts of electricity for a period of several days. Pushing the technology even further, researchers at the Massachusetts Institute of Technology developed the building blocks for an even smaller gas turbine engine with a size of about 1 mm which they hope will be fully assembled and functioning before the end of 2007.

ETH micro gas turbine (Credit: ETH Zurich)

Although it might be hard to see the resemblance between a giant like the GE90 and the millimeter scale engine being developed at MIT, they actually have quite a bit in common with each other. A gas turbine, both large and small consists of a compressor, a combustion chamber, and a turbine that is driven by the combustion exhaust and powers the compressor. Upon start-up, fuel is injected at the compressor exit, mixes with air, ignites and escapes in high pressure through the exhaust, spinning the turbine which is used to power the generator producing the electricity.

Producing a millimeter size turbine engine also poses some unique challenges which conventional gas turbines do not face. To understand some of them we need to understand more about the new MIT millimeter turbine engine design.

Going micro

MIT millimeter turbine - same components as a macro sized turbine

The millimeter size turbine engine project in MIT started in the middle of the 1990s when Professor of Aeronautics and Astronautics Alan H. Epstein considered the possibility of creating a personal turbine which will be able to meet all the demands of a modern person's electrical needs, just like a large turbine can meet the electricity demands of a small city.

Millimeter turbine engine - conceptual cross-section

The millimeter turbine has the same components as a macro sized conventional turbine engine, but their size requires an entirely different manufacturing technology. According to Professor Epstein, millimeter sized turbines also have many of the same design considerations as large turbines including basic layout, mechanical stress, oxidation-limit etc. In some respects designing a micro size turbine is simpler than a conventional macro one since the microrotors of the turbine are very stiff, eliminating bending problems which occur on larger rotors. Thermal stress is also not an issue at these sizes as well as maintenance of any kind (you will never fix a micro turbine but simply replace the entire engine).

The millimeter turbine technology is based on semiconductor manufacturing techniques. This enables the fabrication of complex micro parts and assemblies – devices with dimensions in the 1-10,000 micron size range with submicron precision. Such parts are produced with photolithographically-defined features and many can be made simultaneously, offering the promise of low production costs in large-scale production.

Millimeter size turbine engine - Semiconductor manufacturing techniques

The main fabrication processes used in the creation of the millimeter turbine components is etching of photolithographically-defined planar geometries and bonding of multiple wafers. According to Epstein, the usual starting point is a flat wafer of the base material, usually single-crystal silicon. These wafers are typically 0.5 to 1.0 mm thick and 100 to 300 mm in diameter, the larger size representing a more modern technology. Dozens to hundreds of micro sized turbine engines can fit on a single wafer. Ideally, the processing of all the devices on a wafer is carried out in parallel, leading to one of the great advantages of this micromachining approach, low unit cost.

First, the wafers are coated with a light-sensitive photoresist. A high contrast black-and-white pattern defining the geometry is then optically transferred to the resist either by means of a contact exposure with a glass plate containing the pattern (a “mask”), or by direct optical or e-beam writing. The photoresist is then chemically developed as though it was photographic film, baked, and then the exposed areas are removed with a solvent. This leaves bare silicon in the areas to be etched and photoresist-protected silicon elsewhere. The etching process is based on the principle that the bare silicon is etched at a much higher rate, typically 50-100x, than the mask material. Many different options for making masks have been developed, including a wide variety of photoresists and various oxide or metal films. By using several layers of masking material, each sensitive to different solvents, multi-depth structures can be defined. Photoresist on top of SiO2 is one example.

BLEEX exoskeleton (Credit: Berkeley Robotics and Human Engineering Laboratory)

The millimeter size turbine has many possible applications ranging from military to civilian and industrial. The millimeter turbine project in MIT is currently funded by the U.S. military which sees a great potential for this upcoming technology. Anything from small unmanned aerial vehicles (UAVs) to a soldier night scope can be operated by a tiny refuelable turbine powered by a small protected hydrogen fuel cartridge. Another interesting possible use of the millimeter turbine engine is the exoskeleton, a technology currently under development which will enable future soldiers to carry tremendous weights across great distances with little effort. Current exoskeleton prototypes suffer from a range of problems limiting their usefulness. They are big, heavy, cumbersome and restricting as well as very complex and expensive to make. Using millimeter turbine engines to power the exoskeleton can save space, weight, reduce costs and extend the unit operational time. If several millimeter engines could also be used to move the joints of the exoskeleton, and not only be used as a power source for larger motors, they might also potentially allow for a much quieter operation (a disadvantage of most existing exoskeleton systems).

On the commercial market, millimeter engines could also have a large variety of applications ranging from refuelable batteries for consumer products such as laptops, digital cameras and cell phones, to cheap micro engines which could be used for agriculture, Micro-Electro-Mechanical Systems (MEMS), sensors and even toys. Although industrial applications such as power stations made out of large arrays of millimeter size turbine might still be a distant dream due to the low efficiency level of the millimeter engine, It is not inconceivable that in the future more efficient millimeter engines will be able to allow for a competitive alternative to existing power manufacturing technology.

To learn more about the millimeter turbine technology TFOT interviewed Professor Alan Epstein from MIT.

Professor Alan Epstein

Q: When did you start working on the micro gas turbine and what was the initial motivation for the work?

A: Started thinking about it 1995. The motivation was two factors: (1) realizing that since large gas turbine engines can power a city, very small ones could power a person's electrical needs; (2) that MEMS offered an approach to getting the manufacturing costs down a level comparable to the costs per watt of a large engine ($0.3-0.5/WATT).

Q: Did you have a Eureka! Moment during the work?

A: No. Lot's of hard problems (many not foreseen) have been solved by the very hard work of a number of talented people.

Q: What are the components of the micro-turbine engine and how will it work after it will be assembled?

4 mm magnetic motor-generator

A: The components are same as large engine, but the assembly is totally different. The components are etched from solid Si wafers in planes. The wafers are then bonded together to yield a wafer of complete engines. The wafers are then cut apart into individual engines as needed.

Q: What will be the size of the engine (minimum and maximum sizes based on near term lithography technology)?

A: lithographic technology is not the limit, rather etching depth and precision is major constraint on the large size. On the small size end, it is viscous forces in the air which cause the engine performance to rapidly drop off at sizes smaller than about a millimeter.

Q: What sort of performance should we expect from the engine?

A: The best metric is energy per unit weight, about 120-150 w-hr/kg for current commercial Li-ion rechargeable batteries. We expect that 500-700 whr/kg can be accomplished in the near term, rising to 1200-1500 whr/kg in the longer term (for the engine and its fuel supply).

Q: Will the micro-engine be capable of refueling (and how will that be accomplished)?

MIT microengine based battery design

A: Yes. It can readily be refueled. For example, as you do a lighter, or prepackaged fuel cartridges could be used. This is probably a commercial question.

Q: Could you describe the process by which the millimeter engine will be mass produced (what are the different stages/materials) how does it differ (if at all) from existing chip manufacturing techniques?

A: These engines could be manufactured in a fashion similar to that of current electronics chips or automotive sensors, either by new companies or by current chip manufacturers such as Intel or Siemens, or sensor producers such as Bosch or Analog Devices.

Q: What were the major problems you faced on this project? What problems you still face?

A: There have been few easy challenges but the two most difficult problems have been (1) understanding the interaction between manufacturing precision and rotor-bearing performance, and (2) managing the tradeoff between the design requirements (of the thermodynamics, combustion, stress, fluid flow, and electromechanics) with complexity of the manufacturing process. In other words, how to achieve the functionality needed in something simple enough to build. This remains our largest challenge.

Q: In 2003 you were still struggling with putting the pieces of the engine together – where is the research standing at the moment, what are the obstacles you still face, and what do you predict for the next five years?

Cutaway demonstration millimeter gas turbine engine

A: We hope to get the engine producing power by late spring. 1-2 years later, a commercial firm should start bringing it to market which may take 3-5 years.

Q: What will be the first applications of the micro-engine and what will be its price?

A: 10-50 watts for high end laptops and military gadgets (MIT work is sponsored by the US Army). Obviously it must be competitively priced or will not survive long in the market place. Detailed pricing is beyond my competence.

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Mind·X Discussion About This Article:


	fuel economy/global warming issues posted on 02/12/2007 12:34 PM by davetbo	[Top] [Mind·X] [Reply to this post]
This still doesn't _necessarily_ get us away from fossil fuels and global warming issues. Jet airplanes, for example, have notoriously poor fuel efficiency and are a large part of our climate change issues. If they steer this project right from the beginning (toward hydrogen as opposed to fossil fuels) then it will be a positive step for the environment as well.


	Re: fuel economy/global warming issues posted on 02/12/2007 8:19 PM by rowante	[Top] [Mind·X] [Reply to this post]
It should be kept in mind that hydrogen is not an energy source, it is an energy carrier. This technology could be of use to steer us away from fossil fuels if the hydrogen (or other renewable fuel eg ethanol or methanol) is produced using renewable energy systems such as wind, solar PV or biomass. However, new energy storage systems are great but we have the technology now to make the transition from fossil to renewable energy. The problem is not logistics or technics it is entirely political and economic in nature. Fossil/atomic energy industries are monopolistic at worst and oligopolistic at best, their subsidies and entrenched power must be dismantled and liberlized to make way for sustainable and renewable energy systems.


	Re: fuel economy/global warming issues posted on 02/14/2007 3:43 AM by billwerstler	[Top] [Mind·X] [Reply to this post]
Consider this... The solution is economic in nature. We can choose to pay more for products we desire to use to provide our needs. Let us use the marketplace and put our money where our mouths are. Supporting "green" companies, creating your own company, joining any company that fits your ideas of solving your needs in an environmentally sound manner, electing politicians that support your viewpoint, or volunteering your labor to help the transition of energy supplies are a few practical actions I suggest. I cringe when I read that persons want to short-circuit our system of government to speed up the process. Let us make sure that we make the world a better place and not at the expense of our personal right to choose. The marketplace and government that is needed are in place at this very moment. Use what we have and preserve our freedom to do so. Thank you for reading.


	Re: fuel economy/global warming issues posted on 01/23/2009 9:02 PM by shewhowatches	[Top] [Mind·X] [Reply to this post]
I agree with you Hydrogen is the energy carrier. Water is the energy source. I do not believe H2O would give us a perpetual energy due to the elliptical nature of the molecule and its right and left handedness. H3O is promising, but the H4O2 molecule is ideally natured for extraction of 2hydrogen as catalyst, then refusion to maintain the watersource for perpetual fuel. The vertical lift is due to the evaporative properties (fission) of water freeing the hydrogen bound to oxygen, descent would arise as a property of fusion to maintain viscosity or horizontal motion. The craft (beit airborne) would have to have a semipermeable membrane for an exterior, such as polymeric silicates (mica) to interact with atmospheric water. At the micro level you can imagine the atoms bonding creating a lattice to climb. On the macroscale one imagines the light of distant planets and stars magnetically drawing us at speeds beyond any measure of time, as would be noted in light years.


	light of far planets drawing us magnetically posted on 01/24/2009 6:38 AM by Redakteur	[Top] [Mind·X] [Reply to this post]
I agree with you Hydrogen is the energy carrier. Water is the energy source. "Water is the energy source?!" Already wrong! Unless you are speaking of hydroelectric power, or fusion - which I don't think you are - water is definitely not the source, either. Rather, water is merely the source of the FEEDSTOCK, i.e., the thing from which we obtain (at high energy cost, through, e.g., hydrolysis) the energy carrier (i.e, hydrogen.) I do not believe H2O would give us a perpetual energy due to the elliptical nature of the molecule and its right and left handedness. Well, I don't think that any modern-day researchers are hoping to find a "perpetual energy source." But why, pray tell, should the elliptical nature of the H2O molecule preclude its suitability? And why should its right AND left-handedness be an obstacle? (By the way, I have no idea what you mean by "elliptical nature" or "right AND lefthandedness" in this context, but let's assume that those are generally-known terms, and proceed with the explanation as to why they make H2O unsuitable.) On the macroscale one imagines the light of distant planets and stars magnetically drawing us at speeds beyond any measure of time, as would be noted in light years. Oh, sorry, I didn't realize taht you were referring to the well-known fact that the light of distant planets and stars is magnetically drawing us... etc., etc. You obviously have access to some marvelous alien technology which makes all that possible. Carry on. Regards,


	Re: light of far planets drawing us magnetically posted on 01/24/2009 10:01 AM by PredictionBoy	[Top] [Mind·X] [Reply to this post]
Rather, water is merely the source of the FEEDSTOCK, i.e., the thing from which we obtain (at high energy cost, through, e.g., hydrolysis) the energy carrier (i.e, hydrogen.) Hi Redak, hope all is well - You are absolutely correct here - if it was easy to extract raw hydrogen from H20, we would've abandoned oil long ago. The formation of the water molecule, and it's resulting stability, of course represents a deep energy well which is the energy which raw hydrogen promises. You've been missed, don't stay away so long - you're awesome.


	Empiricism Strikes Back posted on 01/24/2009 11:40 AM by Redakteur	[Top] [Mind·X] [Reply to this post]
Hi Redak, hope all is well Things are great! I, likewise, hope that all is well with you. The formation of the water molecule, and it's resulting stability, of course represents a deep energy well which is the energy which raw hydrogen promises. I'm reminded of a certain other poster here who once claimed that H20 was formed at the Earth's core, due to the influx of the solar wind. Heh-heh! You've been missed, don't stay away so long. I just don't seem to get shed of this forum, so I suppose that we'll be seeing each other around in the future. By the way: What actually was the reason for the hiatus of MindExchange? Was there an official explanation? In any event, the pause doesn't seem to have affected things much. Looks like we've got a fresh crop of conspiracy theorists, moonbats, and assorted nuts. Your continued level-headedness, ruthless skepticism, and influence as the inofficial "voice of reason" of MindExchange are much appreciated. Best regards, Redakteur


	Re: Empiricism Strikes Back posted on 01/24/2009 11:43 AM by PredictionBoy	[Top] [Mind·X] [Reply to this post]
What actually was the reason for the hiatus of MindExchange? Was there an official explanation? Nanostuff identified a Javascript security problem with the site.


	Re: light of far planets drawing us magnetically posted on 01/24/2009 10:55 AM by shewhowatches	[Top] [Mind·X] [Reply to this post]
Interesting.........I can accept advice graciously, criticism with an open mind. But assumptions and condemnation regarding what I have said is over the line. Who is talking "alien" technology? I never mentioned it. You are angry. Why? DREAM Fantastic voyage to outer space Traveling beyond the stars. Imaginings of drifting within the planet Mars. Seeing tiny creatures within the minds great head Living beneath the waters taking that first fluid breath. Wandering through the hearts of planeteers Seeking the wisdom of the aged Marveling the lost years.. For I exist as the solar system with scores of dying life Upon I came to mame the soul using water to obscure the true light. Certainly I apopogize if my words somehow insulted you. In a dream I saw the use of water in a craft, imagined the water molecule in a configuration of the cross with 4 hydrogen at each point...H2O was used in comparison. my imaginings took me from the molecule as fuel to the building of the craft and its propulsion system. Using my mind I flew it to the stars. Now does that explain what I said? Gosh, we are the alien. Alien to each other, yet we live on the same planet. Be cautious the response to the words. Look hard and long for the true intent of anothers expression. We all have dreams. "The God's have not revealed to mortals everything from the beginning. But in time as they inquire they find out what is better." Xenophanes Pragmatic science fails to imagine. Unfortunate.


	light-years = units of time?! posted on 01/24/2009 11:32 AM by Redakteur	[Top] [Mind·X] [Reply to this post]
Dear shewhowatches, I sincerely apologize if I offended you! I was merely trying to "have fun with you" - well, actually, I confess that I was teasing you, because I believe that your suppositions (or actually: assertions) are, frankly speaking, ludicrous. I would categorize them as belonging to the realm of pseudo-science, wishful thinking, science-fiction, or fringe physics, on a par with hollow-earth theory, phrenology, etc. You seem like an alright chap. You certainly seem well-spoken, so I suppose that I shouldn't be calling you a "kook." But your statements seemed like pure crackpottery. I really didn't mean to offend you, even though I was attempting to subject you to public ridicule and mockery. By the way, just what did you mean when you said that light-years were a measurement of time? I was under the impression that they are, strictly speaking, a unit of length. Regards, Redakteur


	Re: light-years = units of time?! posted on 01/24/2009 9:39 PM by shewhowatches	[Top] [Mind·X] [Reply to this post]
Redakteur Perhaps we are from the same planet. I am also under the impression lightyears equate units of time. Clearly that was not a question. Nor did I imply agreeing with it. Refer back to the dream. Difficult it was for me to describe my thought traveling in the light. I can say time was not part of the experience. It did not exist. The following poem I wrote to describe feelings and questions stirred by this dream. The experience left an indelible imprint in daily conscious efforts until which time I composed the following giving me closure. TIME AND SPACE L2=EM if; [(cv) (hv) (1/2mv2)] =L2 Equation herein shows factor for the imbalance time cost. Planck's Constant to remind us of the deficit in energy loss. A shift must incorporate the factor of time As dimensions shift insanity will border the line. Time bends light's linear path in curves to spiral reflection amiss Uneven flow projects the shadow of interference or tale of the dark abyss. Man's thought blends reason though his eyes deceive Light bends cloaking the true incidence for reality. To gain knowledge and sense the harmony Earth's sphere is insight to the atomic monopolarity. Light is equal to the harmonic of the frequency and velocity Electromagnetic duality riding parallel in spectral ferocity. Time is the deception as reason finds man With potential energy in need of reprimand. In this, the creation and regeneration of all life Eludes to time's equation the maker of strife. Allow time's treason considering the mass and space The energy is adequate in mirror of the atoms true face. TIME MEASURES THE DEGREE OF DEFICIT IN THE SPEED OF LIGHT. SHADOWS OF CONTAINED REST ENERGY EXPRESS ALL VARIABLES AND ISOLATE THE DIFFERENTIAL. TIME IS EQUAL TO THE CONTAINED REST MASS OBSTRUCTING LIGHT'S POTENTIAL. Any attempt to publicly mock or ridicule me would have no impact. I am not concerned with negative actions as my life experience has already taught me how not to re ACT. We each have our perspectives based on experience...in that is the right for everyone to express those beliefs. shewho....


	Re: Engine on a Chip posted on 02/14/2007 11:22 AM by vonkes	[Top] [Mind·X] [Reply to this post]
Where/what is the high pressure gas source for this 'wafer turbine'? Will it be combustive or catalytic? Where does the exhaust and waste heat go in a battery application? Where/what is the output? Will the wafer process allow magnetic turbine wheels and embedded conductors? What is the bottom scale limit where internal boundary layer drag becomes prohibitive? Where can I find a treatment of these fundamental questions? Thanks.


	Re: Engine on a Chip posted on 02/14/2007 5:35 PM by vonkes	[Top] [Mind·X] [Reply to this post]
Answering some of my questions: http://mtlweb.mit.edu/researchgroups/mems/docs/200 6/mems_88.pdf


	Re: Engine on a Chip posted on 01/22/2009 7:13 PM by tommybillysammy	[Top] [Mind·X] [Reply to this post]
ats fasinating


	Re: Engine on a Chip posted on 01/22/2009 7:26 PM by Big Monkey	[Top] [Mind·X] [Reply to this post]
Microturbines A micro turbine designed for DARPA by M-Dot Also known as: Turbo alternators MicroTurbine (registered trademark of Capstone Turbine Corporation) Turbogenerator (registered tradename of Honeywell Power Systems, Inc.) Microturbines are becoming widespread for distributed power and combined heat and power applications. They are one of the most promising technologies for powering hybrid electric vehicles. They range from hand held units producing less than a kilowatt, to commercial sized systems that produce tens or hundreds of kilowatts. Part of their success is due to advances in electronics, which allows unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows the generator to be integrated with the turbine shaft, and to double as the starter motor. Microturbine systems have many advantages over reciprocating engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. Microturbines also have the advantage of having the majority of their waste heat contained in their relatively high temperature exhaust, whereas the waste heat of recriprocating engines is split between its exhaust and cooling system.[4] However, reciprocating engine generators are quicker to respond to changes in output power requirement and are usually slightly more efficient, although the efficiency of microturbines is increasing. Microturbines also lose more efficiency at low power levels than reciprocating engines. They accept most commercial fuels, such as gasoline, natural gas, propane, diesel, and kerosene as well as renewable fuels such as E85, biodiesel and biogas. Microturbine designs usually consist of a single stage radial compressor, a single stage radial turbine and a recuperator. Recuperators are difficult to design and manufacture because they operate under high pressure and temperature differentials. Exhaust heat can be used for water heating, space heating, drying processes or absorption chillers, which create cold for air conditioning from heat energy instead of electric energy. Typical microturbine efficiencies are 25 to 35%. When in a combined heat and power cogeneration system, efficiencies of greater than 80% are commonly achieved. MIT started its millimeter size turbine engine project in the middle of the 1990s when Professor of Aeronautics and Astronautics Alan H. Epstein considered the possibility of creating a personal turbine which will be able to meet all the demands of a modern person's electrical needs, just like a large turbine can meet the electricity demands of a small city. According to Professor Epstein current commercial Li-ion rechargeable batteries deliver about 120-150 Wh/kg. MIT's millimeter size turbine will deliver 500-700 Wh/kg in the near term, rising to 1200-1500 Wh/kg in the longer term.[5]

Brain Archive

Turbine engine history

Going micro