Difference between revisions of "Generic EM Drive Information"

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(Added information about how frequency, Q, and mode shape bundle together.)
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This is a location for assorted information concerning EM Drives. Likely applies to all current experimental efforts.
 
This is a location for assorted information concerning EM Drives. Likely applies to all current experimental efforts.
  
== Conservation of Energy Violation ==
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== Simulating With MEEP ==
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[[MEEP]] is is a free finite-difference time-domain (FDTD) simulation software package developed at MIT to model electromagnetic systems<ref>[http://ab-initio.mit.edu/wiki/index.php/Meep]</ref>.  A number of people, including @aero, have been using it to simulate the evolution of the fields within the EM Drive.
  
Doctor White has proposed that the EM Drive is capable of producing constant thrust at a constant power output. User frobnicat has shown (in the following text and image) that if this were to be true, then the EM Drive could be utilized as a source of unlimited energy. <ref>[http://forum.nasaspaceflight.com/index.php?topic=37438.msg1369806#msg1369806 frobnicat on using the EM Drive for unlimited energy.]</ref> This of course constitutes a violation of [http://en.wikipedia.org/wiki/Conservation_of_energy Conservation of Energy.]
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== Conservation of Energy and Momentum ==
 
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See [[Energy Conservation]] and [[Momentum Conservation]] for discussions of the implications to these principles.
"As often remarked : for any propellantless device yielding "given constant thrust for given constant power" (ie. a definite thrust/power ratio) there is a velocity relative to a power feedback loop system above which net power surplus can be generated (indefinitely, wear apart).
 
This velocity is simply the inverse of the thrust/power ratio : V (m/s) = power (W) / thrust (N)." -frobnicat <ref>[http://forum.nasaspaceflight.com/index.php?topic=37438.msg1370818#msg1370818 frobnicat explains constant thrust/power feedback loop]</ref>
 
 
 
<img src="http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=29276.0;attach=619549;image" style="width:20%">
 
 
 
On the assumption that the results provided by the various experimenting groups are valid, then one of the following two options as provided by user deltamass<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1370943#msg1370943 deltamass on the Energy Paradox.]</ref> and clarified by user frobnicat <ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1371907#msg1371907 frobnicat on apparent/non-apparent CoE breakage.]</ref> must be true. The options are as follows:
 
 
 
'''Option 1''': Energy is conserved, but there is a preferred rest frame. In essence, the drive has a maximum change in velocity (a decreasing acceleration curve) that it can impart irrespective of its starting velocity. The idea of a preferred rest frame is at odds with [http://en.wikipedia.org/wiki/General_relativity general relativity].
 
 
 
'''Option 2''': An '''apparent''' breach of conservation of energy is possible, where the mechanism by which conservation of energy is maintained is as yet unknown. An example of a possible solution to this problem is that the drive could in some way be emitting [http://en.wikipedia.org/wiki/Tachyon tachyons.]<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1371907#msg1371907 frobnicat on tachyons.]</ref>
 
 
 
Tachyons are fictional particles that can travel faster than the speed of light.  Sending signals faster than light, leads to violations of causality, see: [http://en.wikipedia.org/wiki/Tachyonic_antitelephone Tachyonic Antitelephone.]
 
 
 
Since option 1 leads to a violation of general relativity and option 2 leads to a violation of causality, one concludes that, with constant input power supplied to the EM Drive, the acceleration cannot be constant.  As remarked by  WarpTech the acceleration must decrease with increasing velocity, as per Newton's 2nd law:<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1370683#msg1370683 WarpTech on decreasing acceleration with increasing velocity.]</ref>
 
 
Acceleration = Thrust / Mass = Power / (Mass*Velocity)
 
 
So, for constant input power to the EM Drive (and constant vehicle mass), the vehicle's acceleration must decrease in inverse proportion to the vehicle's velocity.  To achieve constant acceleration, increasing power must be supplied to the EM Drive, in proportion to the increasing velocity.
 
  
 
== Mode Shape ==
 
== Mode Shape ==
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An EM Drive is a cavity resonator that uses the Quality Factor Q to achieve greater response. There is definitely a peak resonant frequency to achieve the highest Q, though besides Q and frequency, mode shape must also be considered. The shape of the electric and magnetic fields inside the cavity at a given frequency.<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319407#msg1319407 Rodal on frequency, Q, and mode shape.]</ref>
 
An EM Drive is a cavity resonator that uses the Quality Factor Q to achieve greater response. There is definitely a peak resonant frequency to achieve the highest Q, though besides Q and frequency, mode shape must also be considered. The shape of the electric and magnetic fields inside the cavity at a given frequency.<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319407#msg1319407 Rodal on frequency, Q, and mode shape.]</ref>
  
The mode-shape to frequency relation is very sensitive to the exact [[Dimensions]] of the cavity. <ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319117#msg1319117 Rodal's post on geometric relations to mode shape.]</ref>
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The natural frequencies (and therefore the mode shapes) of a cavity are sensitive to the [[Experimental Results|dimensions of the cavity]]. <ref>[https://en.wikipedia.org/wiki/Microwave_cavity#Cylindrical_cavity][http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319117#msg1319117 Rodal's post on geometric relations to mode shape.]</ref> A dielectric insert lowers the natural frequency at which a given mode shape takes place.<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319655#msg1319655 Rodal on the dielectric's contribution to mode shape.]</ref>
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Here is a plot of what a few mode shapes '''in a cylindrical cavity''' look like when viewed perpendicular to the circular cross section plane.
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<img src="http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36313.0;attach=632192;image" style="width:15%">
  
 
== References ==
 
== References ==
 
<references />
 
<references />

Latest revision as of 06:34, 13 July 2015

This is a location for assorted information concerning EM Drives. Likely applies to all current experimental efforts.

Simulating With MEEP

MEEP is is a free finite-difference time-domain (FDTD) simulation software package developed at MIT to model electromagnetic systems[1]. A number of people, including @aero, have been using it to simulate the evolution of the fields within the EM Drive.

Conservation of Energy and Momentum

See Energy Conservation and Momentum Conservation for discussions of the implications to these principles.

Mode Shape

See calculations pertaining to the relationship between thrust and mode shape at Notsosureofit's post and Rodal's response.

An EM Drive is a cavity resonator that uses the Quality Factor Q to achieve greater response. There is definitely a peak resonant frequency to achieve the highest Q, though besides Q and frequency, mode shape must also be considered. The shape of the electric and magnetic fields inside the cavity at a given frequency.[2]

The natural frequencies (and therefore the mode shapes) of a cavity are sensitive to the dimensions of the cavity. [3] A dielectric insert lowers the natural frequency at which a given mode shape takes place.[4] Here is a plot of what a few mode shapes in a cylindrical cavity look like when viewed perpendicular to the circular cross section plane.

References