-
#2420 by meberbs on 06 Nov, 2016 15:46
-
Next Big Future picked up one of the papers posted here...
There is nothing new in the Next Big Future article.
I am sorry but NBF has the paper (first link in their article).
I only skimmed the link on their site, and won't discuss specifics until the official release, because we do not know that their link will match the official release. Since it is being referenced in several places as very positive results, I want to mention that it does not look to me like the conclusive proof some were hoping for.
Again, I won't be specific, because my concerns could be addressed (one way or another) by the official version. -
#2421 by Rodal on 06 Nov, 2016 15:46
-
Quote from: rodal
>Cannot self-accelerate as a closed system with a force/powerInput orders of magnitude greater than a perfectly collimated photon rocket.
Shawyer asserts that due to relativistic effects, the system becomes open. Where is the argument against this? I didn't find it in all that stuff you linked to
Also, are you implying an absolutely closed system ( non relativistic and relativistic ) can propel itself with the force of a photon rocket? How?
If the system is open, it has to interact with some external (i.e. existing outside the frustum) fields or objects. One cannot just state it's open without specifying what it's interacting with.
Shawyer needs to now state what are the external fields that make the system "open" instead of closed, and he needs to recognize that there is internal pressure on the conical side walls of a truncated conical cavity even when the cavity has spherical ends and the waves are spherical waves, and he needs to reconsider his free-body force diagrams, among several things. -
#2422 by DnA915 on 06 Nov, 2016 16:18
-
With the performance of the EW Emdrive, we can do a few calculus.
I shall suppose a huge solar array of 1 MW (instead of 200KW)
The thrust is 1.2mN/Kw. So, 1.2N/Mw
I shall suppose a mass of 100T.
I makes a Delta V per day of 1.2*86000/100000=1.032
So, it makes 1.032m/s of Delta V each day. It is not yet enough to get in a reasonable time to mars. A few km/s of total Delta V are needed. It would needs around 2 orders of magnitude higher thrust.
The actual 1.2mN/Kw would be OK only for orbital position keeping or modifying. With the possibility of saving satellites that were sent in the wrong orbits, or of directly launching more satellites in the same launch, some one in the wrong orbit, and sending them to the right orbit after a few mothes or years of continual acceleration. It could also be used to make small ships able to desorbit a big satellite in some years. So, there are already several possible utilities, but not yet for Mars mission. Or only as a secondary thruster for trajectory corrections.
Why are you using such a low mN/kW? 1.2mN is below most experimental results and far below the best reported results. If it were being used in a production propulsion application, especially at this scale, shouldn't we assume near the top specs of the relatively low budget current productions? Based on current top end experiments, wouldn't we be at a couple of order of magnitude higher, closer to the 1N/kW range? -
#2423 by RotoSequence on 06 Nov, 2016 16:20
-
With the performance of the EW Emdrive, we can do a few calculus.
I shall suppose a huge solar array of 1 MW (instead of 200KW)
The thrust is 1.2mN/Kw. So, 1.2N/Mw
I shall suppose a mass of 100T.
I makes a Delta V per day of 1.2*86000/100000=1.032
So, it makes 1.032m/s of Delta V each day. It is not yet enough to get in a reasonable time to mars. A few km/s of total Delta V are needed. It would needs around 2 orders of magnitude higher thrust.
The actual 1.2mN/Kw would be OK only for orbital position keeping or modifying. With the possibility of saving satellites that were sent in the wrong orbits, or of directly launching more satellites in the same launch, some one in the wrong orbit, and sending them to the right orbit after a few mothes or years of continual acceleration. It could also be used to make small ships able to desorbit a big satellite in some years. So, there are already several possible utilities, but not yet for Mars mission. Or only as a secondary thruster for trajectory corrections.
Why are you using such a low mN/kW? 1.2mN is below most experimental results and far below the best reported results. If it were being used in a production propulsion application, especially at this scale, shouldn't we assume near the top specs of the relatively low budget current productions? Based on current top end experiments, wouldn't we be at a couple of order of magnitude higher, closer to the 1N/kW range?
He's using the most detailed vacuum verified results available. Unfortunately, the best presently available results are an order of magnitude below the power efficiency of a Hall Effect Thruster. -
#2424 by zen-in on 06 Nov, 2016 16:40
-
Next Big Future picked up one of the papers posted here...
There is nothing new in the Next Big Future article.
I am sorry but NBF has the paper (first link in their article).
I only skimmed the link on their site, and won't discuss specifics until the official release, because we do not know that their link will match the official release. Since it is being referenced in several places as very positive results, I want to mention that it does not look to me like the conclusive proof some were hoping for.
Again, I won't be specific, because my concerns could be addressed (one way or another) by the official version.
Thanks for pointing out the link to the paper; I missed that when I read the article. I downloaded the paper and skimmed through it. A lot can be learned from the title:
Q-Thruster In-Vacuum Fall 2015 Test Report.pdf
It looks like this paper describes the vacuum tests they did in Nov. 2014. The photos and graphs are the same. All of the "thrust" waveforms show a first order step response (thermal). There may be more error analysis done in this paper. However if the driving force only has first order characteristics it is a thermal effect. Any error analysis that claims otherwise is wrong. I don't believe this is their peer reviewed paper. In 2015 when these results were announced they acknowledged it was inconclusive and the goal was to improve the apparatus/testing so that more definitive results could be seen.
Below is one of the graphs from this paper. We discussed it early 2015 in this forum. I added the blue curve and comments to show how both edges of the "thrust" pulse are very similar to a first order step response. There is no overshoot or ringing as would be seen with a second order response.
-
#2425 by Gilbertdrive on 06 Nov, 2016 16:54
-
I downloaded the paper and skimmed through it. A lot can be learned from the title:
Q-Thruster In-Vacuum Fall 2015 Test Report.pdf
It looks like this paper describes the vacuum tests they did in Nov. 2014. The photos and graphs are the same. All of the "thrust" waveforms show a first order step response (thermal). There may be more error analysis done in this paper. However if the driving force only has first order characteristics it is a thermal effect. Any error analysis that claims otherwise is wrong. I don't believe this is their peer reviewed paper. In 2015 when these results were announced they acknowledged it was inconclusive and the goal was to improve the apparatus/testing so that more definitive results could be seen.
Below is one of the graphs from this paper. We discussed it early 2015 in this forum. I added the blue curve and comments to show how both edges of the "thrust" pulse are very similar to a first order step response. There is no overshoot or ringing as would be seen with a second order response.
At what point are we allowed to discuss here the EW paper that leaked ? Can a moderator tell us ?
Of course I should be very happy if we are allowed, but it is not very clear yet. Any precision should be welcome ! -
#2426 by flux_capacitor on 06 Nov, 2016 17:03
-
At the time of the New Scientist article controversy, Shawyer was not stating (to my recollection) that the system was "open".
Shawyer in his original theory paper (the 2006 version published by New Scientist, please note the linked paper had corrected versions afterwards and is outdated) already talked about the EmDrive being an "open system":Quote from: Roger ShawyerThe second effect is that as the beam velocities are not directly dependent on any velocity of the waveguide, the beam and waveguide form an open system. Thus the reactions at the end plates are not constrained within a closed system of waveguide and beam but are reactions between waveguide and beam, each operating within its own reference frame, in an open system.
He also added on his website:Quote from: Roger ShawyerThe inevitable objection raised, is that the apparently closed system produced by this arrangement cannot result in an output force, but will merely produce strain within the waveguide walls. However, this ignores Einstein’s Special Law of Relativity in which separate frames of reference have to be applied at velocities approaching the speed of light. Thus the system of EM wave and waveguide can be regarded as an open system, with the EM wave and the waveguide having separate frames of reference.
A similar approach is necessary to explain the principle of the laser gyroscope, where open system attitude information is obtained from an apparently closed system device.
But those explanations do not really follow the way you would expect to comply with general relativity. -
#2427 by Rodal on 06 Nov, 2016 17:18
-
At the time of the New Scientist article controversy, Shawyer was not stating (to my recollection) that the system was "open".
Shawyer in his original theory paper (the 2006 version published by New Scientist, please note the linked paper had corrected versions afterwards and is outdated) already talked about the EmDrive being an "open system":Quote from: Roger ShawyerThe second effect is that as the beam velocities are not directly dependent on any velocity of the waveguide, the beam and waveguide form an open system. Thus the reactions at the end plates are not constrained within a closed system of waveguide and beam but are reactions between waveguide and beam, each operating within its own reference frame, in an open system.
He also added on his website:Quote from: Roger ShawyerThe inevitable objection raised, is that the apparently closed system produced by this arrangement cannot result in an output force, but will merely produce strain within the waveguide walls. However, this ignores Einstein’s Special Law of Relativity in which separate frames of reference have to be applied at velocities approaching the speed of light. Thus the system of EM wave and waveguide can be regarded as an open system, with the EM wave and the waveguide having separate frames of reference.
A similar approach is necessary to explain the principle of the laser gyroscope, where open system attitude information is obtained from an apparently closed system device.
But those explanations do not really follow the way you would expect to comply with general relativity.
Thank you for the correction. So I understand now that Shawyer has been claiming that the EM Drive is an open system that can be explained solely due to Special Relativity and Newton's laws.
I still do not at all understand what makes it an open system. Heat Radiation will make it an open system but will not explain a force/InputPower orders of magnitude greater than a perfectly collimated photon rocket.
Co-propagation out of the cavity of some out-of-phase photons as proposed in http://scitation.aip.org/content/aip/journal/adva/6/6/10.1063/1.4953807 will not explain a force/InputPower orders of magnitude greater than a perfectly collimated photon rocket.
Thermal convection of heat will make it an open system with force/InputPower orders of magnitude greater than a perfectly collimated photon rocket, is Shawyer claiming that the EM Drive force/InputPower is purely due to asymmetric thermal convection? Sort of like a very inefficient heater? Thermal convection cannot be used for space flight applications ...or even for efficient applications in our atmosphere
If anybody else can think of what makes it an open system according to Shawyer, please let us know...
PS: I will correct my original post accordingly -
#2428 by WarpTech on 06 Nov, 2016 17:37
-
At the time of the New Scientist article controversy, Shawyer was not stating (to my recollection) that the system was "open".
Shawyer in his original theory paper (the 2006 version published by New Scientist, please note the linked paper had corrected versions afterwards and is outdated) already talked about the EmDrive being an "open system":Quote from: Roger ShawyerThe second effect is that as the beam velocities are not directly dependent on any velocity of the waveguide, the beam and waveguide form an open system. Thus the reactions at the end plates are not constrained within a closed system of waveguide and beam but are reactions between waveguide and beam, each operating within its own reference frame, in an open system.
He also added on his website:Quote from: Roger ShawyerThe inevitable objection raised, is that the apparently closed system produced by this arrangement cannot result in an output force, but will merely produce strain within the waveguide walls. However, this ignores Einstein’s Special Law of Relativity in which separate frames of reference have to be applied at velocities approaching the speed of light. Thus the system of EM wave and waveguide can be regarded as an open system, with the EM wave and the waveguide having separate frames of reference.
A similar approach is necessary to explain the principle of the laser gyroscope, where open system attitude information is obtained from an apparently closed system device.
But those explanations do not really follow the way you would expect to comply with general relativity.
Thank you for the correction. So I understand now that Shawyer has been claiming that the EM Drive is an open system that can be explained solely due to Special Relativity and Newton's laws.
I still do not at all understand what makes it an open system. Heat Radiation will make it an open system but will not explain a force/InputPower orders of magnitude greater than a perfectly collimated photon rocket.
Thermal convection of heat will make it an open system with force/InputPower orders of magnitude greater than a perfectly collimated photon rocket, is Shawyer claiming that the EM Drive force/InputPower is purely due to asymmetric thermal convection? Sort of like a very inefficient heater? Thermal convection cannot be used for space flight applications ...or even for efficient applications in our atmosphere
If anybody else can think of what makes it an open system according to Shawyer, please let us know...
PS: I will correct my original post accordingly
IMO, a "closed system" should be specified as an EmDrive where the Q is infinite and when the MW source is removed, the stored energy remains stored indefinitely. THEN it is a closed system. As long as the stored energy eventually decays to zero, the system is not closed. So those who claim it is a closed system, need to define why it is closed when it is apparent that the Q is not infinite and the stored energy does not stay indefinitely.
-
#2429 by Rodal on 06 Nov, 2016 17:40
-
...
As discussed in my last post, the system is not closed, when considering heat dissipation. The problem is not whether it is an open system under negligibly small forces.
IMO, a "closed system" should be specified as an EmDrive where the Q is infinite and when the MW source is removed, the stored energy remains stored indefinitely. THEN it is a closed system. As long as the stored energy eventually decays to zero, the system is not closed. So those who claim it is a closed system, need to define why it is closed when it is apparent that the Q is not infinite and the stored energy does not stay indefinitely.
The problem is what makes it an open system with a force/InputPower that is orders of magnitude greater than a perfectly collimated photon rocket. The onus of proving that is not on the shoulders of those pointing this out. The responsibility for proving this, is rather on the shoulders of those claiming that this is possible.
So far only a few have attempted to met this challenge, however much their theories can, and have been criticized:
* McCulloch with Unruh waves
* Todd with a modification of Puthoff's formulation for a polarizable QV, now including dissipation
* White with his formulation for a mutable QV
* Notsosureofit postulating gravitation, entropy, and the proposition that dispersion caused by an accelerating frame of reference implied an accelerating frame of reference caused by a dispersive cavity resonator.
* Alexander Trunev and a gravitation theory plus Yang Mills
* Fernando Minotti and a scalar tensor theory of gravity
I am not including Arto Annila because he did not specify how is the force/InputPower from a few few photons escaping the cavity orders of magnitude greater than a perfectly collimated photon rocket.
I am not including Shawyer because he did not address what makes the system open with a force/InputPower orders of magnitude greater than a perfectly collimated photon rocket, and explainable solely on the basis of Special Relativity and Newton's laws. -
#2430 by Star One on 06 Nov, 2016 18:09
-
Next Big Future picked up one of the papers posted here...
There is nothing new in the Next Big Future article.
I am sorry but NBF has the paper (first link in their article).
I only skimmed the link on their site, and won't discuss specifics until the official release, because we do not know that their link will match the official release. Since it is being referenced in several places as very positive results, I want to mention that it does not look to me like the conclusive proof some were hoping for.
Again, I won't be specific, because my concerns could be addressed (one way or another) by the official version.
There appears to be a high degree of scepticism about what was posted before it was also removed elsewhere, so I will be interested to see how much of this scepticism will be answered by the final paper rather than what was leaked. -
#2431 by Bob012345 on 06 Nov, 2016 18:23
-
With the performance of the EW Emdrive, we can do a few calculus.
I shall suppose a huge solar array of 1 MW (instead of 200KW)
The thrust is 1.2mN/Kw. So, 1.2N/Mw
I shall suppose a mass of 100T.
I makes a Delta V per day of 1.2*86000/100000=1.032
So, it makes 1.032m/s of Delta V each day. It is not yet enough to get in a reasonable time to mars. A few km/s of total Delta V are needed. It would needs around 2 orders of magnitude higher thrust.
The actual 1.2mN/Kw would be OK only for orbital position keeping or modifying. With the possibility of saving satellites that were sent in the wrong orbits, or of directly launching more satellites in the same launch, some one in the wrong orbit, and sending them to the right orbit after a few mothes or years of continual acceleration. It could also be used to make small ships able to desorbit a big satellite in some years. So, there are already several possible utilities, but not yet for Mars mission. Or only as a secondary thruster for trajectory corrections.
Why are you using such a low mN/kW? 1.2mN is below most experimental results and far below the best reported results. If it were being used in a production propulsion application, especially at this scale, shouldn't we assume near the top specs of the relatively low budget current productions? Based on current top end experiments, wouldn't we be at a couple of order of magnitude higher, closer to the 1N/kW range?
According to his public statements I heard, Shawyer stated that the NASA experiments are ten years behind the times. He's glad they are testing it but a bit befuddled that they don't seem interested in doing experiments that are current. -
#2432 by Gilbertdrive on 06 Nov, 2016 18:40
-
With the performance of the EW Emdrive, we can do a few calculus.
I shall suppose a huge solar array of 1 MW (instead of 200KW)
The thrust is 1.2mN/Kw. So, 1.2N/Mw
I shall suppose a mass of 100T.
I makes a Delta V per day of 1.2*86000/100000=1.032
So, it makes 1.032m/s of Delta V each day. It is not yet enough to get in a reasonable time to mars. A few km/s of total Delta V are needed. It would needs around 2 orders of magnitude higher thrust.
The actual 1.2mN/Kw would be OK only for orbital position keeping or modifying. With the possibility of saving satellites that were sent in the wrong orbits, or of directly launching more satellites in the same launch, some one in the wrong orbit, and sending them to the right orbit after a few mothes or years of continual acceleration. It could also be used to make small ships able to desorbit a big satellite in some years. So, there are already several possible utilities, but not yet for Mars mission. Or only as a secondary thruster for trajectory corrections.
Why are you using such a low mN/kW? 1.2mN is below most experimental results and far below the best reported results. If it were being used in a production propulsion application, especially at this scale, shouldn't we assume near the top specs of the relatively low budget current productions? Based on current top end experiments, wouldn't we be at a couple of order of magnitude higher, closer to the 1N/kW range?
According to his public statements I heard, Shawyer stated that the NASA experiments are ten years behind the times. He's glad they are testing it but a bit befuddled that they don't seem interested in doing experiments that are current.
As I am bedfulled that Shawyer never managed any on orbit testing after 10 years of development.
My calculus was following a message that started bySo with the news of very good numbers in EW's upcoming paper, my mind goes more towards the application side of things.
That is why I made my calculus with EW results. It was about the good numbers of EW'S paper.
With Shawyer claims about flying cars, there is even no more need for any rocket engine. SSTO should be easy, and go on mars in 2 days.
Flying car needs at least an acceleration of 10m/s to make vertical lift off. Applying the formula 1/2*a*t² and dividing it by 10^9 to get millions of Km
1/2*10*(86000)^2/10^9=36,98 millions of km after one day
So, when the earth and mars are close, one day accelerating and one day decellerating should be enough.
No need for raptor with Shawyer claims. -
#2433 by FattyLumpkin on 06 Nov, 2016 19:32
-
Not even sure why EWL used TM212 instead of TE012 or TE013, not to mention RCs of X2, 3 or 4 larger in size would have "Q"s orders of magnitude greater. Perhaps it's safe to assert that force/Watt should/would also increase..to what extent I do not know, but Sonny did address extrapolations in his Ames talk (as I recall). Additionally, a larger cavity "supposedly" would "handle" more power input. This is why I as aforementioned was ready to go with a bigger build: say x2 or 2.5 times larger. Anyone interested? I'd ask Shell Jamie or Dave to handle the RF and testing, while I'd be responsible for fabrication. FL
-
#2434 by flux_capacitor on 06 Nov, 2016 19:49
-
Not even sure why EWL used TM212 instead of TE012 or TE013, not to mention RCs of X2, 3 or 4 larger in size would have "Q"s orders of magnitude higher. Perhaps it's safe to assert that force/Watt should/would also increase..to what extent I do not know, but Sonny did address extrapolations in his Ames talk (as I recall). Additionally, a larger cavity "supposedly" would "handle" more power input. This is why I aforementioned was ready to go with a bigger build: say x2 or 2.5 times larger. Anyone interested? I'd ask Shell Jamie or Dave to handle the RF and testing, while I'd be responsible for fabrication. FL
Eagleworks used TM212 instead of TE012 despite TE012 showed higher Q and greater specific force, because it was difficult for them to trigger that TE mode and maintain proper resonance while the frustum was undergoing thermal expansion. Also in the Brady frustum, TE012 is too close to other RF modes. So they defaulted to TM212 which is more comfortable to work with.
I'd like to see tests conducted with bigger frustums too. But what kind of RF generator accessible to a DIYer would you recommend to feed such larger resonant cavity with higher power and lower frequency than a 2 kW @ 2.45 GHz magnetron? -
#2435 by X_RaY on 06 Nov, 2016 20:03
-
Not even sure why EWL used TM212 instead of TE012 or TE013, not to mention RCs of X2, 3 or 4 larger in size would have "Q"s orders of magnitude higher. Perhaps it's safe to assert that force/Watt should/would also increase..to what extent I do not know, but Sonny did address extrapolations in his Ames talk (as I recall). Additionally, a larger cavity "supposedly" would "handle" more power input. This is why I aforementioned was ready to go with a bigger build: say x2 or 2.5 times larger. Anyone interested? I'd ask Shell Jamie or Dave to handle the RF and testing, while I'd be responsible for fabrication. FL
Let's consider the first report. There they stated, there are problems to excite TE012 using the existing/ already builded frustum. Therefore TM212 was used. It's quite logic to get straight forward with the existing one because:
1. There is a lot of experience with the existing frustum and they can compare the new results with the older.
2. Calculate, build and explore another frustum with TE012 optimized geometry would cost a lot of time and money.
3. The current tests may used to check(confirm or reject) if it works at all, not to optimize it to higher thrust levels, that may done during future work.
4. A much larger frustum doesn't make it more easy to test the device.
-
#2436 by Monomorphic on 06 Nov, 2016 20:43
-
Not even sure why EWL used TM212 instead of TE012 or TE013, not to mention RCs of X2, 3 or 4 larger in size would have "Q"s orders of magnitude higher. Perhaps it's safe to assert that force/Watt should/would also increase..to what extent I do not know, but Sonny did address extrapolations in his Ames talk (as I recall). Additionally, a larger cavity "supposedly" would "handle" more power input. This is why I aforementioned was ready to go with a bigger build: say x2 or 2.5 times larger. Anyone interested? I'd ask Shell Jamie or Dave to handle the RF and testing, while I'd be responsible for fabrication. FL
Let's consider the first report. There they stated, there are problems to excite TE012 using the existing/ already builded frustum. Therefore TM212 was used. It's quite logic to get straight forward with the existing one because:
1. There is a lot of experience with the existing frustum and they can compare the new results with the older.
2. Calculate, build and explore another frustum with TE012 optimized geometry would cost a lot of time and money.
3. The actual test may used to check(confirm or reject) if it works at all, not to optimize it to high thrust levels, that may done during future work.
4. A much larger frustum doesn't make it more easy to test the device.
What I have seen in simulations with the NASA frustum and others is that the loop antenna mounted on the side wall is not the ideal location to excite TE01x. It can be done, but requires a number of conditions to be just right - and even then can be fleeting. It is far easier to excite TE01x using either a loop antenna or circularizing antenna positioned along the central axis (as seen in Shawyer's recent patent).
As for frustum size, I will probably migrate towards c-band as fabricating cavities that size is much more economical. There is a small hit in Q for going smaller, but that can be made up for elsewhere.
-
#2437 by X_RaY on 06 Nov, 2016 20:55
-
My answer was directed to FL regarding his questions.Not even sure why EWL used TM212 instead of TE012 or TE013, not to mention RCs of X2, 3 or 4 larger in size would have "Q"s orders of magnitude higher. Perhaps it's safe to assert that force/Watt should/would also increase..to what extent I do not know, but Sonny did address extrapolations in his Ames talk (as I recall). Additionally, a larger cavity "supposedly" would "handle" more power input. This is why I aforementioned was ready to go with a bigger build: say x2 or 2.5 times larger. Anyone interested? I'd ask Shell Jamie or Dave to handle the RF and testing, while I'd be responsible for fabrication. FL
Let's consider the first report. There they stated, there are problems to excite TE012 using the existing/ already builded frustum. Therefore TM212 was used. It's quite logic to get straight forward with the existing one because:
1. There is a lot of experience with the existing frustum and they can compare the new results with the older.
2. Calculate, build and explore another frustum with TE012 optimized geometry would cost a lot of time and money.
3. The actual test may used to check(confirm or reject) if it works at all, not to optimize it to high thrust levels, that may done during future work.
4. A much larger frustum doesn't make it more easy to test the device.
What I have seen in simulations with the NASA frustum and others is that the loop antenna mounted on the side wall is not the ideal location to excite TE01x. It can be done, but requires a number of conditions to be just right - and even then can be fleeting. It is far easier to excite TE01x using either a loop antenna or circularizing antenna positioned along the central axis (as seen in Shawyer's recent patent).
As for frustum size, I will probably migrate towards c-band as fabricating cavities that size is much more economical. There is a small hit in Q for going smaller, but that can be made up for elsewhere.
I have years of experience in exciting this kind of mode in real world sensor applications, therefore I am can confirm your statement completely.
-
#2438 by Monomorphic on 06 Nov, 2016 21:08
-
To further illustrate the importance of antenna location when exciting TE01x modes, here are some sims I ran for the hackaday baby emdrive recently tested by Paul Kocyla and Prof. Tajmar in vacuum. Paul K. was kind enough to provide exact cavity dimensions and antenna location shape and size. A sweep of the frequencies tested showed that none of the familiar modes would have been excited.
After switching out the monopole antenna for a loop antenna positioned along the central axis, even with the course sweep, TE013 was seen at 23.75Ghz. This is because that mode persists over a larger frequency range with this antenna configuration.
-
#2439 by WarpTech on 06 Nov, 2016 21:11
-
Not even sure why EWL used TM212 instead of TE012 or TE013, not to mention RCs of X2, 3 or 4 larger in size would have "Q"s orders of magnitude higher. Perhaps it's safe to assert that force/Watt should/would also increase..to what extent I do not know, but Sonny did address extrapolations in his Ames talk (as I recall). Additionally, a larger cavity "supposedly" would "handle" more power input. This is why I aforementioned was ready to go with a bigger build: say x2 or 2.5 times larger. Anyone interested? I'd ask Shell Jamie or Dave to handle the RF and testing, while I'd be responsible for fabrication. FL
Let's consider the first report. There they stated, there are problems to excite TE012 using the existing/ already builded frustum. Therefore TM212 was used. It's quite logic to get straight forward with the existing one because:
1. There is a lot of experience with the existing frustum and they can compare the new results with the older.
2. Calculate, build and explore another frustum with TE012 optimized geometry would cost a lot of time and money.
3. The actual test may used to check(confirm or reject) if it works at all, not to optimize it to high thrust levels, that may done during future work.
4. A much larger frustum doesn't make it more easy to test the device.
What I have seen in simulations with the NASA frustum and others is that the loop antenna mounted on the side wall is not the ideal location to excite TE01x. It can be done, but requires a number of conditions to be just right - and even then can be fleeting. It is far easier to excite TE01x using either a loop antenna or circularizing antenna positioned along the central axis (as seen in Shawyer's recent patent).
As for frustum size, I will probably migrate towards c-band as fabricating cavities that size is much more economical. There is a small hit in Q for going smaller, but that can be made up for elsewhere.
There is a double hit in the stored energy. The energy stored in the cavity will be proportional to;
E ~ P*Q/f
And the reaction counter mass that the frustum is pushing against is ~ E/c2. Therefore, you want to maximize energy storage. Higher frequency will have lower Q and much lower energy storage for the same power input.
