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April 2009 Posts
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I spent some time trying to understand relative permittivity, but found the quote below gives a quick summary.
"But, perhaps in honor of Earth Day, EEStor just decided to put out a brief press release boasting a huge achievement, a relative permattivity of over 22,500 for the barium-titanate powders used in its ultracapacitors. For the non-technical, a capacitor’s permittivity helps determine how much charge the device can hold. The baseline permittivity, using vacuum, is one. The number EEStor is claiming (backed by an external scientist) are up to 1,000 times those of industrial capacitors used today"
So this relative-permittivity is pretty amazing compared to commercially available capacitors. BUT, it seems like this is only one property and there are other of serious importance like dielectric loss (self-discharge) that are also needed to make a real capacitor.
Just like any other technology, a number of things must come together to make an acceptable product. But good for EEstor that they have had this success, but it remains to be seen if this translates into a product.
LaterJohn C. Briggs
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I too had never heard of permittivity. I have heard of dielectric constant though. It was something I read about in my radio theory book 33 years ago when I was a budding ham radio operator. So on a hunch I searched for dielectric constant in wikipedia. What I found was that permittivity is the current term for dielectric constant and it refers to the effect that a dielectric, or insulated material between the plates of a capacitor, has in concentrating the electric lines of flux. The name change is due to the muddy interpretation of the term in the past. The dielectric constant, or more accurately permittivity, of the material is a ratio that is determined by the material being used as the actual dielectric over the dielectric constant of a vacuum. http://en.wikipedia.org/wiki/Dielectric_Constant This is not entirely precise but close so I urge you to check the link.
Also check out the chart on the right side of the page. It lists the dielectric constant of a number of materials. The one for barium nitrate is interesting. Here is the constant: 90 nc–1250–10,000. So it varies widely. To give you the scale of this a standard polystyrene capacitor used in consumer electronics has a permittivity 2.4 to 2.7. If Eestor has come up with a dielectric with a constant, or permittivity of 22,500 then they've hit the mother load. In my opinion though that is a very big if. I wonder about charge leakage.
Rick, from the oil capitol of the world, Houston, TX.
Well, well, well! Eestor has finally made its permitivity announcement- it was late, but here it is- but, as some other sites have already pointed out, the announcement is missing any mention of the other details, like a permitivity of 22,500 at what voltage, that would shed some light on the practicality of their ESU. <sigh> The long watch continues;-) Perhaps, hopefully, the attainment of this test will accelerate more information from Eestor. I am so tempted to visit Dick Weir's house in Cedar Park just to ask him! But I guess that might seem a bit stalkerish:-)
And I liked the hampster to battery analogy, John in San Jose- very funny!
There is nothing like Permitivity to make you think "John Briggs where are you"...not to put any pressure on you John.
Paul the truth has no bounds so if you find a bunch of capacitors in Mr Weir's trash then you know he is a scammer.
I have channeled a dead electrical engineer (no he wasn't shocked to death) by posting why he thinks EEstor is out to lunch. I love reading things I can't understand. Memo to EEstor try Fusion.
"Below is a detailed discussion clearly demonstrating the invalidity of EEstor’s claims and targets.
EEstor does not report either a new material, or any data that indicates the ability to store more energy than known titanate dielectrics. EEstor calculates the amount of energy they expect their capacitor to store. A fundamental oversight results in an invalid calculation that is inaccurate by more than a factor of 100! The error is uncomplicated. Simply, energy does not equal ½ CV2 for a capacitor made from a nonlinear dielectric. For all high permittivity ceramics, the dielectric permittivity (K’) decreases markedly with increasing electric field E (dielectric saturation). Energy increases roughly linearly with voltage for these materials, as opposed to with the square of the voltage (ref 2).
Importantly, this is not a case wherein EEstor claims to have made some specific breakthrough regarding this issue. No such breakthrough is reported. There are no energy storage measurements, no permittivity versus field data, and no mention of eliminating or reducing dielectric saturation. Their patent and presentations indicate a complete lack of awareness (or lack of acknowledgment) of this issue. EEstor simply purports to make (or aspires to make) high K barium titanate based material, with a K of 18,000, and ultimately with an incredibly high breakdown strength of up to 300V/um. They then calculate the energy stored as ½ CV2 without comment on the use of this equation.
How large of an error does this cause? Calculated energy density is ½K’E2 when calculated total energy is ½CV2. For K = 18,000, and a field 100 V/um, this invalid calculation gives 800 J/cc. (½K’E2 = (0.5)(8.85×10-12 F/m)(18,000)(1×108 V/m) = 8×108 J/m3 = 800 J/cc). Eight references describing actual studies of energy storage in high permittivity ceramic dielectrics (including barium titanate and BST) are noted below. All of these studies indicate a maximum energy density ranging from about 2 to 12 J/cc, depending on the exact material and the maximum breakdown voltage (which is on the order of 100V/um in most cases). Notably, for the studies involving very high K materials, if the authors had simply calculated energy storage using ½ CV2, as EEstor does, it would have similarly resulted in reported values on the order of 100 times greater than the actual measured values!
Hence there is no basis for concluding EEstor has made any advance in the field, and clear evidence that the sole basis for their claim of unbelievably high energy storage is the simple, invalid calculation. Their aspiration (with no reported results) to triple the breakdown field to 300 V/um in combination with the invalid calculation adds an additional factor of 9, giving an absurd 7200 J/cc (along with all of the corresponding hype and speculation about a new miracle material).
Below are notes regarding the references noted above that clearly substantiate the analysis above (one report of personal measurements, the other seven directly from a Google search on energy storge in ceramic dielectrics). .
1. (My work, unpublished), 1987 – Report to Maxwell Corporation on energy storage potential in high permittivity ceramics. Measurements were made on thin films up to 100V / um on barium titanate and PLZT based dielectrics. K varied as ~ 1/E over much of the voltage range, resulting in an approximately linear increase in energy density with field. Maximum energy storage was 4 – 8 J/cc.
2. Love, Journal of the American Ceramic Society 1990 – Also observed a linear increase in energy with voltage for several classes of high permittivity (up to 12,000) thick film ceramics (barium titanate, PLZT, PMN). Reported up to 5 J/cc at 80 V/um.
3. Triani, et.al, (ANSTO and CSIRO – Australia, 2001 – J. Materials Science and Engineering. They reported 8 – 10 J/cc for PbSr titanate, and noted that the energy densities were similar to those of the best BaSr titanate materials for a given field, but the maximum fields of up to 100V/um (100KV/mm) were superior for the PST.
4. Kaufmann, et.,al, Penn State and Argonne, 1999. DOE Contract Report. They report sputtered BaSr titanate thin films with a K of 500 and a breakdown field of 100 V / um. K decreases to 120, and the energy storage is 11 J/cc. Also reported are data for hot pressed AFE/FE lead zirconate. These had a maximum K of 12,000, and a breakdown strength of 12 V/um, resulting in an energy storage of 3.2 J/cc.
5. Fletcher, et.al, 1996 Journal of Applied Physics D. They report a theoretical analysis based on Devonshire theory of ferroelectrics. Optimal energy density is predicted for materials with Curie Temperatures well below the operating temperatures. Applied to BaSr titanate, the model predicts an energy density of 8 J/cc at 100 V/um. The model was verified in actual materials.
6. Randolf, et. al, (Austria, 1996) – IEEE Annual Report - Studied dielectric energy storage for powders embedded in polymer matrices. They reported using a PbTitanate-PbZnNiobate material with K = 5000, and reported energy densities of 1 – 10 J/cc.
7. Lawless, et. al., Ceramphysics Inc. 1992 report a high permittivity ceramic (K = 8000) for which a maxium energy density of 6 J/cc was observed for samples with optimum breakdown strength.
8. Freim, Nanomaterials Research Corp NASA SBIR Proposal 1998, reports reduced dielectric saturation for nanocrystalline microstructures, and states that “Commercial coarse grain dielectric based ceramic capacitors are ineffective for use in high energy storage and delivery applications since the dielectric’s permittivity decreases sharply when the applied voltage is increased.” They target 5 – 10 J/cc for the proposed new improved materials.
If you aren’t familiar with dielectric saturation, or even if you are and you don’t think back to where ½ CV2 comes from – you miss it. And until you collect information and compare with the calculation, you have no clue it makes a factor of 100 difference in this case. People don’t even realize what EEstor is asserting. If they said, “we are going to use barium titanate based materials, which up until now how only been able to store 8 J/cc, but our barium titanate will store over 1000 J/cc – people would ask themselves how is that possible and what is the basis for that claim.
Then you would find out it’s not just a case of them not providing data or proof of their claims. They don’t even claim to have observed or measured a property indicating their barium titanate would be different. There is nothing left but the calculation. The sole origin for their high numbers is that they simply start with the K of high permittivity modified barium titanate (eg., K = 18,000 not a new achievement), and simply calculate energy = 1/2CV2. Anyone could have done that at any time for any high K material and gotten the same outrageous numbers.
So at that point, one should ask why people get a factor of 100 less when they actually measure it. The answer is well documented and obvious – dielectric saturation. So the only justification for using 1/2CV2 which gives a factor of 100 higher than known and understood measured values, would be if you made a measured observation that you have a fantastic new material that doesn’t saturate at all and stores 100 times the energy.
EEstor has never made any such claim or reported to have made any such observation. They just did the calculation. It’s just a mistake."
It is amazing how smart cut and paste can make you.
The discussion of ultra-capacitors made me interested in the difference between batteries and capacitors. The following link has a good discussion (somewhat technical, but not too technical).
The cool thing is that they discuss a wide range of electrical storage devices including
1) capacitors2) batteries3) heat battery4) spring battery5) flywheel battery6) compressed air7) pumped storage8) magnetic storage9) nuclear battery
If you don't want to read all this, at least scroll to the bottom to see the so-called Ragone plot for different types of "batteries".
This really puts thing in perspective. Capacitors have high power density (quick acceleration/regen) batteries have high energy density (long distances). Also, note the log-scale.
The ideal storage device would have both high power and high energy density. The plot clearly shows no device exists.
Rick, Like you, I have heard of dielectric constant but not "relative static permittivity" which is apparently the modern term to correctly describe this physical property.
But apparently high "relative static permitivity" alone is not enough to make a good storage device.
ThanksJohn C. Briggs
Fred, Good explanation of the problem of creating an ultra capacitor. Basically they are saying that the linear model doesn't work because the property is non-linear.
I used to design voice coil actuators for disk drives. These too have saturation issues. You can get bigger and bigger magnets, but they do not help unless you provide more steel to carry around the magnetic flux. But steel costs money and weight, so you are always running the steel up near its saturation point where it is very non-linear.
This is the reality of magnetic circuits that limit their performance. I am sure ultra-capacitors have similar issues.
Best part - Ryan's scream of frustration. Such angst. So heartfelt.
And yes, Estor sucks for issuing yet another press release that actually says nothing, a permittivity of 22,500 can be achieved with many materials at low enough voltage.
I hesitate to say much on Eestor, especially with the mountain of information that would seem to dismiss their claims. But I still remain cautiously optimistic about them. Cautious in that I would not bet the butter and egg money on them- but optimistic when I consider the principals involved. These are not just some fly-by-night guys making outrageous claims with some new, unheard-of, gain-energy-from-nothing- type of scheme. In fact, since they do not make any earth-shattering claims of new materials or exotic solutions, I think this lends even more credence to what they are trying to do. Also, the two main guys are long-time engineers with a good track record, and other patents. Now, this is not to say that even if (and it is a very big, speculative IF), they do prove the EESU can provide such high power and storage in one device, that it is even doable in the practical world- problems with cost, manufacturing, etc. But I tend to think they are on to some sort of twist in their process that enables a leap in this field.
And if (again, a big IF) they do attain this, I would be willing to bet that at least one key breakthrough comes from their work on Drive Technology and manufacturing. The science is well beyond me, but a cursory look at the Eestor patents and claims seem to echo some of their earlier patents for their Drive company (whose name suddenly escapes me).
Now, if y'all will excuse me, I have put up my rose-colored sunglasses;-)