Difference between revisions of "Evanescent waves"

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As first proposed by Aero and later refined by Rodal on the NSF forums, this theory proposes the EmDrive's tapered conical design causes a gradient in the electric field generated by the Rf source.  As the EM waves inside the fustrum travel toward the small end, they are attenuated by the constricting geometry, producing evanescent waves that carry momentum.  The device must then move to preserve conservation of momentum.<ref>[http://forum.nasaspaceflight.com/index.php?topic=37642.msg1382031#msg1382031 Forum post by Rodal]</ref>
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Two evanescent wave theories have been proposed at NSF:
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@Aero first proposed that evanescent waves ''leaked'' from the interior of the EM Drive through small gaps and produced an ''external'' evanescent wave near-field.  @Aero studied (with a MEEP 2-D model) the interaction of these evanescent waves with the stainless steel vacuum chamber at NASA Eagleworks.  Upon reading about this theory, Paul March (NASA Eagleworks) reported at NSF conducting a test of the EM Drive outside the stainless steel vacuum chamber that exhibited measured thrust and thus may have nullified this hypothesis (several tests conducted by R. Shawyer and by Prof. Juan Yang may have also been conducted in environments were such interaction may have been nullified).  @Aero also proposed that another hypothesis involving tachyons (hypothetical particles travelling faster than photons) and evanescent.
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Later Rodal and Todd @WarpTech proposed at the NSF forum that the EmDrive's tapered conical design causes a gradient in the electromagnetic field such that one travelling waves (from the RF source) propagating towards the small end of the truncated cone are attenuated by the tapering geometry, producing evanescent waves that carry momentum.  The EM Drive must then accelerate to satisfy conservation of momentum.<ref>[http://forum.nasaspaceflight.com/index.php?topic=37642.msg1382031#msg1382031 Forum post by Rodal]</ref>
  
 
== Status ==
 
== Status ==

Revision as of 14:58, 1 June 2015

Two evanescent wave theories have been proposed at NSF:

@Aero first proposed that evanescent waves leaked from the interior of the EM Drive through small gaps and produced an external evanescent wave near-field. @Aero studied (with a MEEP 2-D model) the interaction of these evanescent waves with the stainless steel vacuum chamber at NASA Eagleworks. Upon reading about this theory, Paul March (NASA Eagleworks) reported at NSF conducting a test of the EM Drive outside the stainless steel vacuum chamber that exhibited measured thrust and thus may have nullified this hypothesis (several tests conducted by R. Shawyer and by Prof. Juan Yang may have also been conducted in environments were such interaction may have been nullified). @Aero also proposed that another hypothesis involving tachyons (hypothetical particles travelling faster than photons) and evanescent.

Later Rodal and Todd @WarpTech proposed at the NSF forum that the EmDrive's tapered conical design causes a gradient in the electromagnetic field such that one travelling waves (from the RF source) propagating towards the small end of the truncated cone are attenuated by the tapering geometry, producing evanescent waves that carry momentum. The EM Drive must then accelerate to satisfy conservation of momentum.[1]

Status

Numerical Analysis

@Aero performed calculations for evanescent waves leaking from the EM Drive and producing an external near-field. He used a two-dimensional MEEP Finite Difference model that modeled the EM Drive as a perfectly flat trapezium. Maxwell's equations were solved in the 2-D domain, thus the transverse electromagnetic vector could only be represented as a scalar. The 2-D model was due to the enormous amount of memory and computer time required by the Finite Difference method, which made a 3-D model in a home PC not practical. The results from the 2-D analysis showed an efficiency rating 2-3 times that of a perfectly collimated photon drive, which is beneath the reported measurements of EM Drive by NASA Eagleworks, Shawyer's SPR and Prof. Juan Yang's team at NWPU.[2]

Utilizing MEEP 2-D model, the conclusion was that due to rapid dropoff at the frustum surface, evanescent waves were of insufficient magnitude to explain the observed thrust.[3]. See details about @aero's MEEP control file.

Relevant Papers

References

  1. ↑ Forum post by Rodal
  2. ↑ Initial calculations by aero.
  3. ↑ this post by @aero on modeled evanescent waves
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