1. Frustum Design Campaign
By Kurt Zeller and Brian Kraft
The EM Drive phenomenon has primarily been demonstrated using frustum shaped
cavities. Therefore many attempts were made to design such a cavity however none
were actually constructed. Preliminary design iterations consisted of warped copper
sheet metal, however DIY attempts posted to the NASA Space Forum revealed that
this design may not always be successful. Furthermore, a thin-skinned copper frustum
will have much more thermal warping occur during full power operation which will
dramatically degrade the resonance over time. A new cavity design was investigated
which could be made much thicker by turning it on a lathe from a solid slug of 6061
Aluminum. This cavity could also be made to a much higher precision than any sheet
metal warping. In addition, mounting a waveguide and heavy magnetron on a thicker
cavity would be much easier. Finally, spherical end caps could be made to further
improve the quality of resonance. The designs included in this document are not the
final dimensions as they are currently being refined to improve the reflection
coefficient.
Introduction
Paul March from NASA Eagleworks create their resonant cavity using thin copper sheet metal
and soldering flat end caps on. However, the resonant mode achieved was a TM211 which has been
deemed far from ideal to generate thrust. Other Forum users followed suit and created their own
copper sheet metal cavities. However, at this time frustum resonance simulations in the community
were underdeveloped and appropriate dimensions were difficult to determine. Later, many users
started using programs such as EMPro, FEKO and COMSOL to determine their own dimensions for the
TE013 resonance. This mode was chosen by Roger Shawyer, the inventor of the EM Drive, because of its
high quality. It is also believed that a transverse electric mode is more suitable to thrusting due to its
ability to move charged particles. However, there is little evidence that any one mode is better than
another except the quality of resonance.
Preliminary Designs
The first designs we pursued were entirely based on dimensions from outside sources, more
specifically Phil Wilson (aka TheTraveler). The only empirical evidence supporting these dimensions
came from Iulian Berca of Romania, who hastily made a thin sheet metal copper cavity and mounted a
magnetron directly on the side of it (seen in Figure 1). Although his results indicated an anomalous
force, the entire experiment was somewhat doubtful due to the techniques used. One of the major
complaints was that his cavity would appear to 'thrust' for only a short duration of time which was

2. explained by a shift from resonance. As any resonant cavity heats up it will thermally expand and,
depending on the frequency, may warp to an extent that the resonant mode is no longer supported. As
we saw from the microwave oven temperature testing, a magnetron will heat up to 90 degrees Celsius
in the span of ten second, leading to severe thermal buckling for a cavity made of thin sheet metal.
Figure 1. Iulian Berca third EM Drive test setup [1]
We decided that our cavity should resist thermal warping more than Iulian's cavity, therefore we
chose to purchase a much thicker 0.048 inch copper plate using the funds granted by the Aero SFC.
However, it was decided that precise EM Pro simulations would be necessary before the copper was
turned into any cavity so that we did not make any mistakes in the antenna placement. Because we
were inexperienced in EM Pro at the beginning of the summer of 2015, the decision was made to pursue
a tunable symmetric cavity that could be adjusted for resonance using the VNA. Although a tunable
frustum was considered, it was deemed more difficult and less controllable. The cylinder also had the
advantage of having relatively simple analytical calculations which could be used to determine the cavity
length required to produce the required mode.
The initial design seen in Figure 2 were done on the side and quickly abandoned as the cylinder
became more demanding. Because Iulian's cavity had thermal warping issues, it was desired to have the
magnetron not heat up as much (improve power reflection) and not distribute its heat to the cavity as
easily. Dimensions to excite the TE011 mode were determined as seen in Figure 3 and 4 and animations
can be found on Kurt's YouTube channel [2]. These simulations were run with both a plane wave
excitation and a coaxial cable input to simulate the magnetron. Unfortunately one major downside of
this design is that it is not easily hung as a pendulum which is required for our thrust measurement
technique.

3. Figure 2. Preliminary frustum designs
Figure 3. Frustum simulations using a plane wave excitation in EM Pro [2]

4. Figure 4. Frustum simulations using a coaxial cable in EM Pro [2]
Later Designs
After the summer experiment was complete I had a great deal of time to think about what
would make the ideal EM Drive. Seeing the VNA resonance sweeps sensitive to the touch made me think
that the cavity should be created with at least 0.005 inches of precision on all internal surfaces.
Unfortunately this entirely rules out sheet metal warping as a manufacturing method unless specialized
machinery were used. It was also desired that the cavity resist thermal buckling and therefore should be
as thick as possible. Finally, the cavity would ideally have spherical end plates because of Shawyer's
claims that they would improve the quality of resonance.
After consulting with Michael Fisher, an experienced machinist with more than 30 year
experience in the orthopedic industry, it was decided that the ideal frustum would be made from a
single, solid slug of aluminum. This raw metal could be purchased for about $500-$750 and could be
used to make all three pieces: a frustum, a bottom, and a top cap. These three could all be turned
independently on a auto lathe in order to produce the accuracy desired. Many EM Pro simulations were
utilized in order to find the optimal dimensions of all components seen in Figures 5 and 6. Many
iterations of this design were made and the final engineering drawings of this frustum can be found in
Appendix R.

6. Final Designs
After going back to Iulian Berca's dimensions, it was evident that a very high quality mode was available
at magnetron frequencies. Figure __ shows the reflection coefficient for a number of simulations which
indicates that a very low reflection coefficient can be achieved using a monopole antenna. The
visualization of the lowest (purple) resonance is pictured in Figure ___.

7. Although this is clearly not the TE013 mode Shawyer recommends, it certainly seems to have potential
to provide verify the EM Drive effect. Not only has one DIY experimenter claimed successful results with
these dimensions using a magnetron, but this resonance is further verified using EM Pro with monopole

8. simulation. Our current plans are to use the copper plate purchased to recreate Iulian's design during
Spring quarter.
References
1. Iulian Berca EM Drive:
http://www.masinaelectrica.com/emdrive-independent-test/
2. Kurt Zeller's YouTube channel
https://www.youtube.com/channel/UCDIeLRPy9437eZLgpyjKBGg