I have decided to devote as much time as I can this year to getting everything done with Fry, including, hopefully, a presentation at a UFO conference. I am single again and my life looks to be stable enough for the next year to make this possible.
I have been over the past week and for the next few weeks, moving the good stuff from the Curvity wiki into WordPress here. It is taking a long time, for example, this page on the design and test phase took something like four hours to move over, in large part, because it had 30meg FLV videos which I had to convert into 1meg animated gifs.
I also have a bunch of other somewhat related improvements, including a subdomain dedicated to tracking authentic Fry originals and offering a place to sell them (not public yet).
I also came up with the translation of Curvity into 中文 – Curvity in Mandarin is now called 凹凸论 (ao1 tu1 lun4) which translates into concave convex theory. I also really like the simple 凹凸 characters which are actually completely legitimate 简体 simplified script and found them by typing “curvaceous” into Pleco (flashcard app). The 论 (lun4) character means theory is also used in 相对论 or Relativity.
Over the next few days or weeks I am going to move all the content from the wiki into this WordPress install and then do away with the Wiki. The original intent for the wiki was to allow other people to add and modify content, but over the seven year life of the wiki, two of which have been public, not a single person has modified or added content to the wiki.
The wikimedia software, compared to WordPress, has always been difficult to work with, from deleting and controlling spam to updating it. Another reason is that I want the uniqueness of Fry’s story to jump out and the
I may actually leave the Wiki running, but just in the background and make this blog the default.
As this blog is now getting some traffic from forums and such, here is an update on where things stand:
The EM Drive duplication research this blog documents, ala “G-Zero” (Wiki) has, for the foreseeable future, ceased because:
NASA has done exactly what I had set out to do (NASA link You can find the NASA paper with a PDF Search)
Before the NASA results had come out, I had stopped because I did not have the resources to complete the experiment properly. After talking with Shawyer directly, I realized that I would need to spend a lot more money to get the machined aluminum copper plated cavity resonating and tested properly.
As for the 440Mhz cavity, it has not been built, only simulated but if anyone wants to donate the funds, I might be persuaded to attempt it.
On a house-keeping note: All the content under the “Research Summary” pages of this site were originally on the now-no-longer-password-protected Curvity wiki. I have pointed those pages to the original source pages on the wiki (which means all the picture links work).
If the whole alien contact thing of Curvity hasn’t turned you off yet and you are curious why on earth I would spend so much time and money trying to duplicate the EM Drive, the answer is here.
If you have any questions contact me at sean at daniel fry dot com.
One of the features of the CST Microwave studio is the ability to use variables and equations instead of hardcoded values for dimensions. The variables can then be swept across a range and, with a robust enough model, simulation can be done at each point.
In this case, I varied the large and small diameter of the cavity and the height to see what affect it had on the frequency of the TE0,1,1 mode. With three variable and three points each, the result was 27 different simulations, i.e. hold the height constant and vary the small diameter across three points, then the large diameter across three points.
CST can also do distributed computation and I had two computer going for two days, one an eight core AMD and the other a six, both with better than 16GBs of memory running three simulations simultaneously.
And the results are.. promising.
The first result was to vary one parameter up to 2cm either side of ideal while holding the other two parameters at ideal values. The results were
Varying the large diameter meant the frequency of TE0,1,1 mode only varied from 445Mhz to 437Mhz.
Varying the small diameter meant the frequency varied by the same amount, 445Mhz to 437Mhz
Varying the height had a larger affect and it wasn’t symmetrical: having a height 2cm too small made the frequency of the TE0,1,1 mode jump to 458Mhz, outside the 70cm Ham radio band. However, 2cm too large and the frequency only fell to ~438Mhz, just a couple Mhz lower than 440Mhz.
Now let us keep the height ideal:
With the small and large diameter 2cms higher than ideal, the TE0,1,1 mode was at ~464Mhz (bad)
With the small and large diameter 2cms lower than ideal, the TE0,1,1 mode was at ~453Mhz (bad)
To conclude – the resonant frequency will stay around the target 440Mhz as long as the height is ideal or less than 2cm larger and the large and small diameters are within 1cm.
I was inspired over the past couple of days to investigate the design and cost of building a Shawyer cavity that resonates in the low end of the UHF band, which ranges from 300Mhz to 3GHz [Wikipedia]. At first, I chose a resonate frequency where the cone could be cut from the remains of a 3’x8′ sheet of copper I have and the cavity, shown below resonates at 600Mhz.
The cavity size is 91.4cm high, 83.4cm for the large diameter end and 50cm for the small diameter end.
The cone rolled out just fits inside of a 3′ by 8′ sheet of standard mill dimension sheet of copper.
As expected, the larger cavity produced a theoretical maximum Q of 104,000!!
The reason for using a lower frequency is that it means less expensive, tunable HAM radio sources and a higher Q. In other words, a cavity with a fixed resonate frequency and without a troublesome tuning mechanism means the source needs to be tunable. (And with an ultra-high Q comes an ultra-narrow bandwidth)
However, 600Mhz is outside the HAM radio spectrum and because I want cheap and easy, modding a UHF rig to transmit at that frequency is too difficult, not to mention the amplifier.
So I flipped the problem around, and simulated a cavity that resonated at 440Mhz right in the middle of the UHF HAM radio spectrum allowable in Canada. My actual process was to take the 600Mhz cavity size and increase it by 1.3636 which is decreased the frequency to 440Mhz (because frequency has an inverse relationship with size). The simulation came out dead on the first run:
A Q of 121,000! (A nice 20% bump from a 600Mhz cavity)
The size is 81.8cm in height, 113.7 cm for the large diameter and 68.2 cm for the small diameter
The simulation was done with a eigenmode JDM solver with 1.2M (million) tetrahedrals using adaptive meshing. (My AMD eight core 8350 just tore through the simulation which still took hours!)
Then I took the measurements from the simulation and figured out how much copper I would need, shown below:
Copper (from ThyssenKrupp) comes in standard sizes, 3’by8′ and 3’by10′ in 12oz or 16oz gauges. What is shown is *half* of the cone rolled out on top of one 3’by10′ sheet with half of a 3’by8′ sheet next to it. With a few extra pieces soldered from the unused edges, the entire shape could be cut with tin snips. To build the entire cone, two of the shown pieces would need to be cut and then soldered together, then formed into the cone.
A 3′ by 10′ copper sheet at 12oz gauge, at today’s prices costs $290 and with the 3′ by 8′ 12oz sheet I already have, I would need two 10′ ones, bringing the cost up to $600. This would not include the top or bottom sections which I would either make from a 3′ by 8′ sheet of 32oz copper I have or from aluminum sheeting (not ideal only because it cannot be soldered to the copper – the conductivity difference shouldn’t matter because it carries hardly any current).
Of course, with 12oz copper, the cavity will likely need an external support structure which I haven’t figured out yet.
Building the cavity would be the first step and with my SignalHound spectrum analyzer good to 4Ghz, I could figure out if the Q is in the right place and high enough.
Then I would need to purchase the Ham radio equipment, two pieces of it pretty exotic, a 1Kw linear amplifier and a isolator that can handle 1kW returned load.
I found a commercial linear amplifier that can be had for $5KUS (pretty good!) from Lunar-Link International. You can also buy a kit and make one yourself starting at $1275US from W6PQL, however, all the connectors, housing and everything else could easily add another grand and I run the risk of messing something up. However, I could modify it by adding a 1KW isolator on the output which would be nice.
The next step is to add a power and measurement probe to the simulation and then do a high-count tetrahedral transient solver simulation. With that result in hand, the next step would be to build the cavity and test it. If the Q was high enough and stable enough (didn’t move because of a flexing cavity), it would then be time to source the HAM equipment and test it for movement – hoohah!
Here is an a final email to summarize where things have ended. As usual, you can find the entire thing on the research blog.
I have moved all of my equipment, including the vacuum chamber out of the University and have stored it. Neil, my engineering friend, who was going to design the magnetron feedback loop has sent me back the network analyzer and the thermal camera. He still has the magnetron, waveguide assembly, power supply and an oscilloscope.
As things stand, there are three phases left in order to get a high Q before any testing can commence:
A working power supply with feedback loop (more below)
The cavity – The cavity needs a couple thousand dollars of alterations (both suggested by Shawyer) to make it resonate with a Q of 50K.
The two then need to be combined and the setup tested for deficiencies (i.e. the coax cable connecting the supply to the cavity may be prone to overheating).
As it turns out, the complicated feedback loop I had dreamed up may not be necessary because, as I have mentioned previously, it sounds like the magnetron gets “pulled” into the right frequency because of the strong resonance of the cavity. How this works exactly, however, is not clear to me and I am not sure if some type of external feedback loop is necessary. From the pictures of Shawyer’s demonstration engine, it would seem to have a computer controlled tuning wall at the back of the cavity. If I had to guess – the feedback loop works like this:
The magnetron is turned on and allowed to warm up, the cavity is then tuned to whatever the magnetron frequency settles on (with the screw actuated tuning plate at the back). The hard thing is that the resonant frequency bandwidth of a cavity with a Q of 50K is a couple Khz wide, but a commercial magnetron can wander up to 30Mhz on either side of a target frequency. Once the frequency of the Magnetron gets close to the resonant frequency of the cavity, it is “pulled” into the right frequency because of a reduction in reflections (??). I am pretty fuzzy on how it works.
Let me tie up a few loose ends mentioned in previous blog entries:
I decided not to go through with becoming a CNC programmer/operator for personal reasons – after talking to my working classmates, I realized I don’t want shift work. Larger shops who can pay more usually run their machines in two shifts, one from 6am to 3 pm and one from 4pm to 12pm. I have too many activities in the evenings to take on that type of lifestyle.
Although I simulated a bunch of simple “test cavities”, I never did get the OK from NAIT to use their CNC machines.
Here is a summary of where the cavity was left:
The unmodified cavity has a TE0,1,4 mode with a Q of 2500, an insertion loss of 2.2dB and a resonant frequency at 2.449Ghz instead of the simulated 2.467Ghz and a Q in the tens of thousands.
I have created a model (v4) with Shawyer’s proprietary modifications and have simulated it with the Eignemode solver which resulted in a Q of 62K at 2.43Ghz. The model doesn’t have probes or optimizations (i.e. moving the tuning plate) and needs to be simulated with the Frequency domain solver.
On the plus side, Shawyer asked me today if I wanted to talk to a “CEO of a Canadian space company” who wants to do a “demonstration test”. As excited as I am by potentially getting paid to do this work, I don’t hold out much hope.
While the project has been winding down over the past year, I have been thinking about what I would have done differently and, I would go the other way with a larger cavity at a lower frequency. It has a number of improvements:
The Q will be higher – as you get into smaller and smaller cavities, the same current gets concentrated onto smaller and smaller cavity walls, making the conductivity of the walls more important. With a larger cavity, the same current gets spread out over a much larger area and even copper or aluminum can make for a fantastic Q.
I would make the tapered part of the cavity out of aluminum sheeting, but the end caps out of copper. As I mention in my blog, simulation of even the 2.45Ghz cavity in Aluminum had little difference because the TE mode works such that circular fields are zero along the walls.
High power HAM radio equipment is readily available and relatively inexpensive compared to high-power 2.45Ghz systems and can pump up to 5000Watts of power.
HAM radio equipment is designed to output finely tuned frequencies with narrow bandwidths, unlike commercial magnetrons which have a large and wandering bandwidth.
Because the Mhz frequency has a longer wave length, it means the tolerances for the cavity are not nearly as tight as the Ghz range, which makes for less expensive cavities.
One downside will be a cavity measured in feet making it difficult to handle.
The Faraday cage at the University is being replaced by a modern RF anechoic chamber.
I signed an NDA with Roger Shawyer and I am now simulating a cavity with the modifications suggested.
Since the last update, I am now two classes away from completing the “CNC Certificate”program at NAIT which means I will start applying for jobs as a “CNC Operator”. With my strong programming background and 3D CAD experience, I plan to quickly transition into CNC programming. In the last class, we cut an inside bore and then an external tapered NPT thread.
I have been looking at local machine shops and have found a bunch I have short listed, both for working at and for building the parts I am currently simulating. Here are few that stand out:
The great news is that all of them are within a twenty minute drive.
As for the cavity, as per the agreement with Shawyer, I can’t say much about the alterations necessary to get a high Q, but now that I have seen them, they all make a lot of sense.
On the simulation front, I tried using a modification of my previous model, but the results haven’t been satisfactory and I am rebuilding it from scratch. The problem is that my previous model used a vacuum as the background material to which was added a thin skinned copper cavity. However, the AKS Eignemode solver then treats the external air as a valid location for modes which are useless. The new model will use a metal background into which an appropriately shaped vacuum will be inserted which means a a simpler model with fewer tetrahedral mesh cells. The mesh cells only need to make up the vacuum and the probes. For example here is one of my test structures from a month ago:
As an aside – I have decided not to build the test structures because, as confirmed by Shawyer, the Q will be too low (as is expected with small cavities at 6Ghz, the tolerances required a very tight and wall heating is high). With the necessary alterations for the 2.4Ghz cavity, the test structures are redundant. The test structures were really plan B if Shawyer decided not to respond. NAIT has also not responded to my request to use their CNC machines, which is where I had planned to build the test structures.
Introduced Roger Shawyer of our work and he is going to run our machined cavity dimensions through his simulation software.
Although my last entry was a number of months ago, a few things have been getting done. I have been enjoying my machinist training immensely and we have been learning how to make “O.D.” cuts or “Outside Dimension” cuts. For example, here was our project from last weekend:
This Saturday we are learning how to cut threads and then in MAC303, we are finally learning how to do ID cuts or inside dimensions.
I have also settled on my first simple test structure, a tube that should resonate in the TE0,1 mode at 6Ghz and have a Q of 25,000.:
It should be easy to create from a 3″ diameter 5″ long aluminum bar I can get from the local Metal Supermarket for $33. The great thing about aluminum is that it is so soft that the inserts (the blade used to cut) for machining have almost negligible wear.
I also decided to cross that PONR or Point Of No Return and contacted Roger Shawyer directly. We had an interesting conversation last week and I have point him to this blog. We talked about the following:
Other universities have tried building cavities but ultimately failed where we have – their simulations don’t match actual results.
Have been one (of few?) to have reproduced results.
Yang Jung group have built actual cavities and have gotten results of 750mN using 3Kw power.
The work has gone black/military and moved to Beijing, no more papers are being published.
Yang Jung was “disappeared” for six months with the implication of instilling dogma.
No one outside of China has seen their cavity, although Shawyer did traveled there and given talks.
They rebuilt commercial simulation software which took 19 months in order to deal with the discontinuities of asymmetrical cavities.
A Big Obvious Enterpris-ING company is the US contractor Shawyer has been working with
Sounds like the trick to powering the cavity at the resonant frequency, is to tune the cavity to the magnetron after it has warmed up, and the because of reflection, the cavity will pull the magnetron frequency and lock it in.
A simply geometry will get the cavity into a Q of thousands, but some type of internal shaping is required to get Qs of tens of thousands and the reason is because of phase continuity or coherence has to be maintained.
It’s been along time since my last update, but I’ve managed to measure the magnetron spectrum output using a Signalhound. I sent an email to Signalhound and this was their reply:
For quick hoppers (FHSS), you will probably need to turn image rejection off to catch the signal. This will speed up the sweep but will also pass the image frequency (21.4 MHz below frequency of interest). If you turn video bandwidth down to 6.5 KHz and RBW to 25 KHz, Power Average mode, then turn on Max Hold, you should be able to capture and measure the signal.
These suggestions pointed me in the right direction to get the Signalhound working the way I wanted. Unfortunately I think the signal is very rapidly changing frequency so the max hold suggestion is the only way to see the signal.
Here is the output after turning the magnetron on for 15 seconds at 100% power:
Here is the output after turning the magnetron on for 20 seconds at 30% power:
The pictures don’t tell the full story here. When the magnetron first turns on you see a peak around 2.465GHz which then slowly moves to the right as the magnetron heats up. Here’s the output after turning the magnetron on for 30 seconds at 100% power:
The flattening of the spectrum suggests that I’m right about the frequency shifting to the left as the magnetron heats up. Here are all 3 waveforms superimposed on each other:
This result makes me think that it’s possible to minimize the frequency drift by cooling the magnetron. The next step is to try the same tests with a water cooled magnetron. Fortunately I have a surplus Astek D13449 under my desk to try once I reverse engineer it (no information is available from the company about it).
Machinist training starting well, simulation results and power supply breakthroughs.
The first machinist class, covering the theoretical material, ended on December 7th and getting %96 in the class means I had fun! For example, we learned how to calculate tapers which will be immensely useful for future cavities. The practical part of the class starts in January and I look forward to it.
Neil has also been busy in Kelowna and came up with some great finds:
He emailed the manufacturer of the Signal Hound and, among other tweaks, learned of “peak hold mode” making it capable of seeing the magnetron’s jumpy signal. This is great news!
If you remember October’s update, we had contacted John Gerling at 2450mhz.com in order to get some specs and schematics for the ASTeX magnetron head which his company repairs. Given he had licensed that technology to ASTeX, he responded that he could not help us, but, Neil managed to find a service bulletin off his website that showed us something interesting – the ASTeX magnetron head uses an electromagnetic!!
Woohoo! We had suspected as much looking at the wires that led into the magnet, but having a diagram means we don’t have to guess.
On the cavity side, I have also been simulating like crazy in order to learn more about how modes are created. I have been working primarily with two types of cavities, a larger circular cavity at 1.5Ghz and another at 5.8Ghz.
Back when I started this research, I was looking for other people who had been working with the TE0,1 mode and found a paper, Energy Storage Cavities at the ALS, (actually a website at the time) written by two summer students at the Lawrence Berkeley National Laboratory. They built a simple round resonating chamber made from some scrap aluminum pipe with a diameter of 33cm and a length of 72cm where the TE0,1,5 mode resonated at 1.5Ghz. They were testing, completely unrelated to the EMdrive, to see if they could use the cavity as a type of energy storage mechanism for tuning purposes on a particle accelerator. Their results are useful because they published the size of cavity and the frequency the got the TE mode at, which I can duplicate with CST.
I have also learned more about CST Microwave Studio, for example, that I can use the Eigenmode solver to find modes! The Eigenmode solver is like a simpler version of the Frequency Domain solver I have been using before, but is perfectly suited for resonating structures. My old work flow use to be:
Build a cavity with ports -> Solved with the Frequency solver over a large frequency range requiring a lot of samples (20 to 40 or more) -> Looked for the resonances on the S parameter chart -> Added field monitors at all the resonances -> Simulated -> Looked for the TE mode -> (and if necessary, re-simulate).
My work flow is now:
Build the cavity with probes but without ports – > Simulate with the Eigenmode solver to find what the resonate frequencies are -> Find the TE modes and their frequencies -> Then add ports -> With a narrow frequency band centred on the TE mode , simulate with the Frequency Domain solver. By using a narrow frequency band, the Frequency domain solver takes much less time and it reduces the guess work, as there can be up to ten or more resonances in a single gigahertz spread.
The Eigenmode solver also shows me what a pure TE0,1 should look like and at what frequency, for example:
But I learned something else, thanks to “ifmicrowavescouldtalk.com” [link], a probe can act as a disturbance and split a mode:
“Now we break the symmetry of the structure with a little cylindrical indentation as shown below. Such a perturbation “splits” the eigenfrequencies of modes 1 and 2 from the original 16.83 GHz to 16.5 GHz and 16.87 GHz, as found by the eigensolver tool.”
Even if the Eigenmode solver shows that a cavity can resonate in a TE0,1 mode, the trick is to add a probe that will actually excite that mode.
I also learned from a powerpoint slide entitled “Introduction to RF Cavities for Accelerators” [PPT Link] by Dr. G Burt at the Lancaster University. When using a loop couple to the B-Field (Magnetic field) probe, as we are, the larger (and deeper) the loop, the lower the coupling. Interestingly, when using a straight probe, the higher the penetration, the stronger the coupling. I had run into this exact situation because when I reduced the size of the cavity to resonate at 5.8Ghz, I didn’t reduce the probe loop size and couldn’t figure out why the TE mode was so messed up. After reducing the size of the probe size in half, it works like a charm (Q of 32K).
I have also been studying the magnetic field configuration around the probe to verify that the reason a shorter loop probe has better coupling is because it properly encircles the magnetic field.
I have also been trying a variety of probe shapes and locations to increase the Q value:
I ordered up more probes mounts for the upcoming future test cavities and got ones that are threaded to make mounting easier:
These are SMA style connectors which are only for measurement of the test probe cavities. I will move back to N-style probe connectors when an actual high powered cavity is built.
On a different front, apparently a “Douglas Eagleson” [Link] also tried to reproduce the EMDrive, but failed. I tried emailing him but it bounced.
Some of the latest discussions on the EMDrive are here which starts in March of 2011 and ended in December 3rd, 2011. Not much of note, except a link (that still works) to the Chinese paper.