Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1798232 times)

Offline seggybop

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@seggybop: Do you speak and read Chinese?
If so, can you translate in English the left-side column in the attached table?

Not too well, but I've got someone here who does. Unfortunately we don't know the exact technical equivalents, but here you go:

Quote
模态 mode

频率 frequency
腔体 cavity
耦合高度 coupling height
计算值 calculated Q value
计算推力 calculated thrust
实验值 experimental Q value
实验推力 experimental thrust
Q值修正系数 Q correction factor
推力理修正系数 thrust correction factor
修正值 revised Q
修正推力 revised thrust

Sure, by all means.  Try asking her what are the dimensions of the EM Drive she tested to get the highest force and force/InputPower ever reported:

very simple question:

Big Base Diameter = m
Small Base Diameter = m
Length (measured perpendicular to the bases) = m

sent.

Online Rodal

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@seggybop: Do you speak and read Chinese?
If so, can you translate in English the left-side column in the attached table?

Not too well, but I've got someone here who does. Unfortunately we don't know the exact technical equivalents, but here you go:

Quote
模态 mode

频率 frequency
腔体 cavity
耦合高度 coupling height
计算值 calculated Q value
计算推力 calculated thrust
实验值 experimental Q value
实验推力 experimental thrust
Q值修正系数 Q correction factor
推力理修正系数 thrust correction factor
修正值 revised Q
修正推力 revised thrust

Sure, by all means.  Try asking her what are the dimensions of the EM Drive she tested to get the highest force and force/InputPower ever reported:

very simple question:

Big Base Diameter = m
Small Base Diameter = m
Length (measured perpendicular to the bases) = m

sent.

Thank you.  That shows that the coupling height used for Yang in 2010 was only 40 mm
and that the experimental Q value was Q=50,000 vs calculated Q =53,036

« Last Edit: 08/03/2015 02:12 AM by Rodal »

Offline dumbo

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Do we still need confirmation from Yang Juan? If so (and considering she apparently does not answer emails), it might be worth giving her a call. As per http://hangtian.nwpu.edu.cn/info/1549/7982.htm her phone number is +86 (0)29-88492421

Do we have any native Chinese speakers here?

Offline rfcavity

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I'd be careful messaging her too much. At that kind of university all of her mails and communications are undoubtedly monitored. One or two messages is enough. If she gets a bunch she might end up getting questioned in a police station.

Offline rfcavity

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Consider it from the opposite point of view, as well. If some researcher at the Naval Research Lab working on some experimental propulsion one day got 20 emails from China, some in Chinese, some in poorly formed English, asking about the details of his one paper he published but left out some details (probably to protect confidentiality), would he ever respond? No, and he'd probably get a few meetings with his superiors about it. In China that kind of meeting might go negative a little quickly...

Offline aero

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Now all we need is for some enterprising member to insert this into this.

模态 mode

频率 frequency
腔体 cavity
耦合高度 coupling height
计算值 calculated Q value
计算推力 calculated thrust
实验值 experimental Q value
实验推力 experimental thrust
Q值修正系数 Q correction factor
推力理修正系数 thrust correction factor
修正值 revised Q
修正推力 revised thrust

and we'll all be able to read it.
Retired, working interesting problems

Offline not_a_physicist

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TheTraveller's post that graphed Shawyer's turnable velocity ( http://forum.nasaspaceflight.com/index.php?topic=37642.msg1411849#msg1411849 ) made me curious to see how that lined up with the "power off" event in the video ( http://www.emdrive.com/fullDMtest188.mpg ). Attached are my results.

To try to be consistent with TheTraveller's data, each 'rotation tick' is half of each line-separated segment on the turntable. There will be a small amount of drift from switching between one of the little black rods rotating around to another. The point's location on the time axis will also jitter a little, since I was only recording times with second resolution.

Offline TheTraveller

     =(3.83170597020751*299792458 m/s)/(Pi*2.45*10^9 1/s)

That value of c used above is for vac and not air.

I use a refractive index of air at STP = 1.000277, giving at c in air of 299,709,438 m/s. Is this the air c value you use in your other calcs or are they also vac c based?

Suggest it would be good for us to use the same air c value. It your air c value is different to the air c value I use, would like to understand how your air c value was derived.
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Offline kwertyops

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Now all we need is for some enterprising member to insert this into this.

...

and we'll all be able to read it.

Offline TheTraveller

Now all we need is for some enterprising member to insert this into this.

模态 mode

频率 frequency
腔体 cavity
耦合高度 coupling height
计算值 calculated Q value
计算推力 calculated thrust
实验值 experimental Q value
实验推力 experimental thrust
Q值修正系数 Q correction factor
推力理修正系数 thrust correction factor
修正值 revised Q
修正推力 revised thrust

and we'll all be able to read it.

Problem with that table is the measured S11 return loss Q of 1,531 was for the real frustum that was used to measure the reported Forces. It needed to be that low so the frustum bandwidth could accept 50% of the magnetrons output bandwidth.

Next question is why did Prof Yang use total magnetron power output instead of the reduced real frustum input power? She knew the frustum's 1,531 Q would only accept 50% of the power. All I can see is she wanted to report lower than actuality Specific Forces.

With a Q of 50,000, almost nothing of the magnetrons power would have made it inside the frustum. Would have been like trying to thread a very fine needle with a piece of rope and only getting one fine thread to fit through.

I suggest that table has very little to do with the frustum Prof Yang used to measure the Force generated.

BTW how does one turn a narrow bandwidth frustum with a Q of 50,000 into one that has a wide bandwidth Q of 1,531? What engineering trick of the frustum dimensions can one use to lower the Q from 50,000 to 1,531?

My guess is you need a bloody big waveguide entrance hole in the side wall of the frustum, with massively increases frustum losses and drops Q into the toilet. But then how did Shawyer get a Q of 45,000 with his waveguide feed Demonstrator EMDrive?

There is is much microwave black magic going on here.
« Last Edit: 08/03/2015 04:04 AM by TheTraveller »
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Offline WarpTech

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Now all we need is for some enterprising member to insert this into this.

模态 mode

频率 frequency
腔体 cavity
耦合高度 coupling height
计算值 calculated Q value
计算推力 calculated thrust
实验值 experimental Q value
实验推力 experimental thrust
Q值修正系数 Q correction factor
推力理修正系数 thrust correction factor
修正值 revised Q
修正推力 revised thrust

and we'll all be able to read it.

Problem with that table is the measured S11 return loss Q of 1,531 was for the real frustum that was used to measure the reported Forces. It needed to be that low so the frustum bandwidth could accept 50% of the magnetrons output bandwidth.

Next question is why did Prof Yang use total magnetron power output instead of the reduced real frustum input power? She knew the frustum's 1,531 Q would only accept 50% of the power. All I can see is she wanted to report lower than actuality Specific Forces.

With a Q of 50,000, almost nothing of the magnetrons power would have made it inside the frustum. Would have been like trying to thread a very fine needle with a piece of rope and only getting one fine thread to fit through.

I suggest that table has very little to do with the frustum Prof Yang used to measure the Force generated.

BTW how does one turn a narrow bandwidth frustum with a Q of 50,000 into one that has a wide bandwidth Q of 1,531? What engineering trick of the frustum dimensions can one use to lower the Q from 50,000 to 1,531?

Probably with a very small coupling height, to filter out the low frequency with her waveguide, and then dump the reflected high frequency waves into an external resistor. What remains in the cavity should be the resonant frequency, with some distortion. No? I'm no expert on this, but it looks like she's using a bandpass filter to tune it.

I think the point here, that was well made today by @Rodal is that, to maximize Q, one must maximize the ratio of volume/surface area. The optimal shape (aside from Aerogels) would be a sphere. After that, a cylinder with spherical ends. After that, a tapered cylinder with spherical ends? The more cylindrical it is, the higher the Q.

Also, per Zeng & Fan's Table 1. The eigenvalues lmn for the spherical waves are much larger at smaller cone angle. In all of the cylindrical theories, the Xmn values multiply the thrust. If the same is true for the lmn values, then for TE01 we have an eigenvalue of 28.7754 for the Z&F cone at pi/24, and only 3.83 for the cylinder approximation.

My opinion at the moment is, Shawyer, McCulloch, @Notsosureofit and myself, who have used cylindrical approximations to simplify the problem, are all the same equation. Each one of us is expressing a different "opinion" on how the physics of a frustrum cavity should behave and what the resulting group and phase velocities should be. Z&F on the other hand, have given us the physics of a tapered waveguide. The problem is Hankel Functions are complicated! Maybe I should do a gofundme, to get help to buy Mathematica or something, but instead I am relying on their graphs and charts and trying to plot the design equations instead of formulating them.
Todd

Offline WarpTech

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...
If you think that's it we have all together :)

SD=0.1492m
BD=0.200m
L=0.240m
f_res(TE012)=~2,4537GHz
angle=6,041deg


with SD 0.15m i get 2,4490GHz
angle=5,946deg

Thank you.  Confirmed:

1) There was no "booboo"

2) Your computer program agrees quite well with my computer program (once again).  TheTraveller's program  is only off by 2%, a difference which I consider to be an utterly negligible difference when we are talking about much larger differences here.  The calculations by TheTraveller are quite acceptable for engineering purposes.
I went over my pen and paper calculations again and it does work out. I feel better in a way.

Shell

Shell,

Despite what Shawyer's equation and all the rest of our theories using cylinders describe, I still think the small cone angle is better but I can't back it up with theory yet. I see why it looks "obvious" that thrust would be increased with shorter length and a larger angle. But like you, I have a gut instinct that is telling me there is more to it than that.

Zeng & Fan do define a cut-off for the tapered waveguide. They say that

Quote
There is no well-defined cutoff wavelength but rather a cutoff radius ( Rc). All modes have a cutoff when β=0 . However, it is interesting to note that the magnitude of the cutoff radius is related to the wavelength and the cone half-angle. At about k*r = 10 , for example, the TE11 reaches cutoff inside the tapered hollow waveguide with cone half-angle θ0 = pi/24 .

If you look at the graphs for alpha and beta, the TE modes have a relatively sharp cut-off value of k*r and just end there. On the other hand, the TM modes get reflected. I think this means that the TE modes have a better impedance match with the small end, where the TM mode cannot transfer all of it's energy, the TE mode can.
Todd

Offline TheTraveller

Atmo and Vac c effects on frustum resonance frequency

Some time ago I did a few calcs, using my spreadsheet, to understand what the effect of using c in atmo and c in vac would have on frustum resonance. This assumes the inside of the frustum was operating in either STP atmo or vac. What I found was interesting:

1) Resonance with STP atmo inside the frustum: 2.450000GHz (c = 299,709,438 m/s)

2) Resonance with vac inside the frustum: 2.450680GHz (c = 299,792,458 m/s)

The difference was the vac resonance was 680kHz higher. So what I hear you ask?

Well assuming the frustum had a Q of 50,000, it's bandwidth would be 49kHz or +- 24.5kHz to each side.

Which would mean a nicely working in atmo, 50,000 Q frustum, being driven by a fixed 2.45GHz external frequency, WOULD NOT generate any significant Force if operated internally at vacuum.

Why?

The 2.45GHz driving freq would be outside the now vac frustum's input bandwidth of +- 24.5kHz at a vac resonant freq of 2.450680GHz.


This finding may help to explain why vac operated frustums experience a very large reduction in Force generation versus operation in atmo. Which is one of the reasons my frustum design is sealed and will maintain a constant 1/2 atmo pressure N2 internal environment when operated in atmo or vac.
« Last Edit: 08/03/2015 05:44 AM by TheTraveller »
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Online A_M_Swallow

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Atmo and Vac c effects on frustum resonance frequency

Some time ago I did a few calcs, using my spreadsheet, to understand what the effect of using c in atmo and c in vac would have on frustum resonance. This assumes the inside of the frustum was operating in either STP atmo or vac. What I found was interesting:

1) Resonance in STP atmo: 2.450000GHz (c = 299,709,438 m/s)

2) Resonance in vac: 2.450680GHz (c = 299,792,458 m/s)

The difference was the vac resonance was 680kHz higher. So what I hear you ask?

Well assuming the frustum had a Q of 50,000, it's bandwidth would be 49kHz or +- 24.5kHz to each side.

Which would mean a nicely working in atmo, 50,000 Q frustum, being driven by a fixed 2.45GHz external frequency, WOULD NOT generate any significant Force if placed in a vacuum.

Why?

The 2.45GHz driving freq would be outside the now vac frustum's input bandwidth of +- 24.5kHz at a vac resonant freq of 2.450680GHz.


This finding may help to explain why vac operated frustums experience a very large reduction in Force generation versus operation in atmo. Which is one of the reasons my frustum design is sealed and will maintain a constant 1/2 atmo pressure N2 internal environment when operated in atmo or vac.


Consequently for use in the field the EM drives either have to be kept in an artificial atmosphere so the manufacture can control the speed of light c or the magnetron needs to change its frequency to track the resonate frequency of the frustum. The tracking needs to be performed with high accuracy since the bandwidth is very small, less than +/- 24.5kHz at 2.45GHz.

Offline TheTraveller

Atmo and Vac c effects on frustum resonance frequency

Some time ago I did a few calcs, using my spreadsheet, to understand what the effect of using c in atmo and c in vac would have on frustum resonance. This assumes the inside of the frustum was operating in either STP atmo or vac. What I found was interesting:

1) Resonance in STP atmo: 2.450000GHz (c = 299,709,438 m/s)

2) Resonance in vac: 2.450680GHz (c = 299,792,458 m/s)

The difference was the vac resonance was 680kHz higher. So what I hear you ask?

Well assuming the frustum had a Q of 50,000, it's bandwidth would be 49kHz or +- 24.5kHz to each side.

Which would mean a nicely working in atmo, 50,000 Q frustum, being driven by a fixed 2.45GHz external frequency, WOULD NOT generate any significant Force if placed in a vacuum.

Why?

The 2.45GHz driving freq would be outside the now vac frustum's input bandwidth of +- 24.5kHz at a vac resonant freq of 2.450680GHz.


This finding may help to explain why vac operated frustums experience a very large reduction in Force generation versus operation in atmo. Which is one of the reasons my frustum design is sealed and will maintain a constant 1/2 atmo pressure N2 internal environment when operated in atmo or vac.


Consequently for use in the field the EM drives either have to be kept in an artificial atmosphere so the manufacture can control the speed of light c or the magnetron needs to change its frequency to track the resonate frequency of the frustum. The tracking needs to be performed with high accuracy since the bandwidth is very small, less than +/- 24.5kHz at 2.45GHz.

Yup. For sure. Even more critical when using a Q in excess of 100k as then the -3dB bandwidth drops to <= +-12kHz.

Best way to track the frustum's resonance frequency is to monitor and auto adjust the freq to obtain the lowest reflected Rf power or the lowest VSWR or the highest S11 return loss dB. Which is what I'm designing my system to do. No need for a 2nd port. The frustum's reflected Rf power tells it all.

BTW good thing my control system can step the frequency in +-1kHz steps and hopefully main freq +-4kHz of ideal real time peak resonant value. Nice.
« Last Edit: 08/03/2015 06:07 AM by TheTraveller »
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Offline demofsky

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Atmo and Vac c effects on frustum resonance frequency

Some time ago I did a few calcs, using my spreadsheet, to understand what the effect of using c in atmo and c in vac would have on frustum resonance. This assumes the inside of the frustum was operating in either STP atmo or vac. What I found was interesting:

1) Resonance in STP atmo: 2.450000GHz (c = 299,709,438 m/s)

2) Resonance in vac: 2.450680GHz (c = 299,792,458 m/s)

The difference was the vac resonance was 680kHz higher. So what I hear you ask?

Well assuming the frustum had a Q of 50,000, it's bandwidth would be 49kHz or +- 24.5kHz to each side.

Which would mean a nicely working in atmo, 50,000 Q frustum, being driven by a fixed 2.45GHz external frequency, WOULD NOT generate any significant Force if placed in a vacuum.

Why?

The 2.45GHz driving freq would be outside the now vac frustum's input bandwidth of +- 24.5kHz at a vac resonant freq of 2.450680GHz.


This finding may help to explain why vac operated frustums experience a very large reduction in Force generation versus operation in atmo. Which is one of the reasons my frustum design is sealed and will maintain a constant 1/2 atmo pressure N2 internal environment when operated in atmo or vac.


Consequently for use in the field the EM drives either have to be kept in an artificial atmosphere so the manufacture can control the speed of light c or the magnetron needs to change its frequency to track the resonate frequency of the frustum. The tracking needs to be performed with high accuracy since the bandwidth is very small, less than +/- 24.5kHz at 2.45GHz.
(Emphasis mine.)

Just to add to this Yang - as Rodal has pointed out many times - mentioned that ionized gas had to be considered as part of understanding EM drives. 

However, there has never been any mention by Shawyer or Yang of specific gases.  TheTraveller is planning to use N2 for corrosion control.  Shell has discussed Sulphur Hexafloride for controlling arcing. Rodal has pointed out that Ammonia gas was used in the first masers.  Finally, water molecules resonate around 2.45 GHz so humid air may have an effect.

Offline TheTraveller

Atmo and Vac c effects on frustum resonance frequency

Some time ago I did a few calcs, using my spreadsheet, to understand what the effect of using c in atmo and c in vac would have on frustum resonance. This assumes the inside of the frustum was operating in either STP atmo or vac. What I found was interesting:

1) Resonance in STP atmo: 2.450000GHz (c = 299,709,438 m/s)

2) Resonance in vac: 2.450680GHz (c = 299,792,458 m/s)

The difference was the vac resonance was 680kHz higher. So what I hear you ask?

Well assuming the frustum had a Q of 50,000, it's bandwidth would be 49kHz or +- 24.5kHz to each side.

Which would mean a nicely working in atmo, 50,000 Q frustum, being driven by a fixed 2.45GHz external frequency, WOULD NOT generate any significant Force if placed in a vacuum.

Why?

The 2.45GHz driving freq would be outside the now vac frustum's input bandwidth of +- 24.5kHz at a vac resonant freq of 2.450680GHz.


This finding may help to explain why vac operated frustums experience a very large reduction in Force generation versus operation in atmo. Which is one of the reasons my frustum design is sealed and will maintain a constant 1/2 atmo pressure N2 internal environment when operated in atmo or vac.


Consequently for use in the field the EM drives either have to be kept in an artificial atmosphere so the manufacture can control the speed of light c or the magnetron needs to change its frequency to track the resonate frequency of the frustum. The tracking needs to be performed with high accuracy since the bandwidth is very small, less than +/- 24.5kHz at 2.45GHz.
(Emphasis mine.)

Just to add to this Yang - as Rodal has pointed out many times - mentioned that ionized gas had to be considered as part of understanding EM drives. 

However, there has never been any mention by Shawyer or Yang of specific gases.  TheTraveller is planning to use N2 for corrosion control.  Shell has discussed Sulphur Hexafloride for controlling arcing. Rodal has pointed out that Ammonia gas was used in the first masers.  Finally, water molecules resonate around 2.45 GHz so humid air may have an effect.

I'm using N2, at 1/2 atmo pressure, to stop oxidation of the highly polished OFC (oxygen free copper) interior surfaces of my frustum. When you are designing to achieve a frustum Q of well over 100k, every little bit helps.
« Last Edit: 08/03/2015 06:14 AM by TheTraveller »
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Online A_M_Swallow

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Well done.

The density of air changes as EM Drives rises above sea level. LEO is not a pure vacuum, the air pressure is just extremely low. Other planets, including Mars, have atmospheres. The amount of water vapour and pollutants varies hourly. These will cause the frustum's resonate frequency to change in flight.

Offline TheTraveller

Well done.

The density of air changes as EM Drives rises above sea level. LEO is not a pure vacuum, the air pressure is just extremely low. Other planets, including Mars, have atmospheres. The amount of water vapour and pollutants varies hourly. These will cause the frustum's resonate frequency to change in flight.

Not if the frustum is sealed.

Simple reliability engineering. Eliminate as many variables as possible to get the most consistent short and long term operational characteristics.

Those you can't eliminate, develop real time compensation systems to adjust for and minimise their effects on short and long term operational characteristics.
« Last Edit: 08/03/2015 06:27 AM by TheTraveller »
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Offline TheTraveller

The SPR Ltd / EMDrive website www.emdrive.com has an update:

Quote
July 2015

A peer reviewed version of the IAC 2014 conference paper is given here: http://authors.elsevier.com/a/1RQaGLWHFbB5c

The link includes a 5 minute audio/slide presentation, updated to include the latest test data from the University of Dresden in Germany.
« Last Edit: 08/03/2015 06:33 AM by TheTraveller »
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