Dec
24
Understanding Digital Quantum Capacitors
December 24, 2009 | 4 Comments
To start, lets get the digital quantum battery misnomer out of the way. What’s being discussed here and other places isn’t about battery building; it’s about a theoretical construction of a nano-sized capacitor. It’s interesting as the storage medium isn’t like a conventional capacitor with the material between the anode and cathode holding the energy. Rather the power is held in a vacuum. Quantum science can be wrenching sometimes . . .
Many will recall the vacuum tube has been around for decades and for most uses was made obsolete by transistors. We tend to think ‘switch’ when vacuum tube comes to mind. But electrical activity in a vacuum has also led to the fusion field where Bussard’s research is getting close to power production. Other electrical devices can be made inside a tube holding a vacuum. Devices can be made filling the tube with gases such as florescent bulbs, or simply installing a filament and burning it with electricity for light and heat.
For better than eighty years it’s been known that a bit of energy can be held in a vacuum when an anode and cathode are present. Too much energy in and they arc, dumping the energy. What’s curious but factual is the smaller the distance between the electrodes; proportionally the more energy can be inserted.
Digital Quantum Battery Layout. Click image for more info.
Thus Alfred W. Hübler and Onyeama Osuagwu at the University of Illinois at Urbana-Champaign have worked out a theory with supporting math and applied materials science that they believe can be built into a capacitor. Using the math, the assertion is such a capacitor could be two to ten times as great for energy density as the very best lithium-ion battery. Their idea would use conventional silicon chip manufacturing to build capacitor sets on chips by the billions or trillions. As the volume for the energy density is a vacuum, the weight will be in the structure, the energy will stay in the tiny vacuum, so the devices could be quite lightweight.
Quantum Capacitor Comparitive Properties Charts. Click image for more info.
Because they are capacitors without a chemical reaction as in a battery the speed of charges and discharges would also be very high. The two main property requirements for energy storage have good answers.
It sounds almost to good to be true, and for years researchers have recognized that nanoscale capacitors exhibit unusually large electric fields, suggesting that the tiny scale of the devices was responsible for preventing energy loss. Hübler says, “people didn’t realize that a large electric field means a large energy density, and could be used for energy storage that would far surpass anything we have today.” Realization is the innovation’s first step here.
The materials science needed is compelling. Hübler says, “If you look at it from a digital electronics perspective–it’s just a flash drive. If you look at it from an electrical engineering perspective, you would say these are miniaturized vacuum tubes like in plasma TVs. If you talk to a physicist, this is a network of capacitors.” Built on silicon chips, the digital part of the moniker comes from the fact that each nano vacuum tube capacitor would be individually addressable, so the devices might be used for memory as well as storing power.
Hübler hasn’t built anything yet. But he points out that in 2005 a group of Korean researchers showed that nano capacitors can be fabricated. Just remember the numbers needed to get to worthwhile scale will be billions and trillions. Not a threatening number, today’s common processors have transistors in the tens of millions now for a few dollars each. And if not over heated, last a very, very long time indeed.
Vacuum nano tubes can hold electric energy without any losses for many years, and can be charged and discharged rapidly. The largest charging-discharging rate is proportional to the ratio between the gap size and the speed of light. They’ll be quick.
The key design parameter is the gap size between the anode and cathode. As noted electrical breakdown in vacuum gaps has been studied or more than 80 years for gap sizes above 200nm. But little is known for certain about vacuum gaps in the nanometer range.
Hübler and Osuagwu show that in reverse bias, the electric field near nano-tip anodes can be orders of magnitudes larger than the breakdown field of conventional capacitors, varactor diodes, and nano plasma tubes. Their premise is the electrodes are spaced at about 10 nanometers (or 100 atoms) apart so the quantum effects ought to suppress the arcing.
With the current glut of chip fabrication worldwide and the technology at 45nm heading to 28nm, and if the concept can be made to work at such needed scale, small electronic devices like cell phones their could be a path for marketing the technology.
Hübler has applied for Defense Advanced Research Projects Agency funding to develop a prototype, but the concept presents significant challenges. The questions about the materials staying together when loaded with power and when working what other phenomena might appear have been raised. It’s a risk, for sure.
Keep in mind, the silicon chip build would have management and telemetry reports ready almost instantly. A thermistor could send out information for charges and discharges. The chips would run with little concern for colder temperatures. It could be a great solution.
But the potential is huge. Once shown to work, it’s going to be an engineering race.
Comments
4 Comments so far
Feedburner
Reddit
Stumbleupon
Does anyone know what might happen in a car crash if all the capacitor-stored electric energy were released suddenly?
JPS
Hi JP,
The answer depends on the fusing or breakers, if the caps are individually fused, it’d be like shorting across the terminals with a screwdriver. A big cap might melt some of the terminal or the driver. The spark, if there is one won’t last long. Down circuits again, should be fused so the combined caps could flow, thus more spark. Depending on the sizes, the circuit fuse will blow or the individual cap fuses would blow. Fused right, not much is going to happen.
A crushed cap, say a terminal goes to the case would offload to the ground of the case which should ground some way to earth. If I were an ER tech, I’d walk up on one with an insulated grounding tool first thing. The volts might not be too high but the amps could be quite substantial spark, like a big DC welder. I’d rather try to handle a set of caps than batteries, no explosions, long term hot or toxic materials, etc. Batteries take more time, nastier chemicals, etc.
Stored electrons seems lots safer than liquid or compressed gas fuels. But that’s just me.
BW
From where did the talk about orders of magnitude better energy densities come?
According to the graph on p.13 in Hubler’s paper, the predicted energy densities range from 0,5 MJ/kilo to 1,5 MJ/kilo.
1 MJ corresponds to 278/Wh. Astonishing for a capacitor but hardly any tenfold improvements in energy density when compared to current battery technology. Even less so when taking into account a container able to keep theese things in the hard vacuum they need to function as forecasted.
I really enjoyed your article, thank you for the useful content.