
OpenEMS: a free and open electromagnetic field solver - privong
http://openems.de/start/index.php
======
msla
Page is down, but here's the Github repo:

[https://github.com/thliebig/openEMS-
Project](https://github.com/thliebig/openEMS-Project)

~~~
fosco
google cache :
[https://webcache.googleusercontent.com/search?q=cache:OSe8Ov...](https://webcache.googleusercontent.com/search?q=cache:OSe8Ovb1jWEJ:openems.de/+&cd=1&hl=en&ct=clnk&gl=us)

Also :
[http://openems.de/start/index.php?show=home](http://openems.de/start/index.php?show=home)

[connectivity worked initially, it appears the site is being 'HN'ed']

------
cr0sh
Interesting piece of software.

Seems similar (though much more advanced), to a piece of DOS software I
remember floating around various "overunity" forums I used to visit years ago
(I have a secret fascination with such efforts; I know they can't succeed, but
it is interesting to see the lengths and effort people go for to try), though
I don't recall its name.

This software would probably be very useful for designing motors and
generators, and for the DIY crowd in those areas.

~~~
madengr
Motors usually use static field solvers; i.e. E and H field are independent.
This uses FTDT which is more for propagating waves in media.

~~~
ianai
So signal processing?

~~~
WJW
Yes, though these days the term 'signal processing' is usually only used for
operations on the signal in digital form, ie after sampling. Since this works
for the propagation of the signal in analog form, it is more useful for doing
calculations about propagation of signals in waveguides or in a TWT or
something.

------
amelius
It's informative to look at the strengths and weaknesses of the FDTD method on
Wikipedia: [1].

[1] [https://en.wikipedia.org/wiki/Finite-difference_time-
domain_...](https://en.wikipedia.org/wiki/Finite-difference_time-
domain_method#Strengths_of_FDTD_modeling)

------
madengr
Maybe have to try this. Been using commercial EM tools for years. Really boils
down to ease of use; model entry and results post-processing.

~~~
mindviews
What's your take on model accuracy? I ask because my startup has developed a
high-order accurate CEM solver (think MoM full-wave type solvers but every
time you double the mesh density you get a 100x accuracy improvement thanks to
a bunch of algorithmic breakthroughs). But we've also been putting in a lot of
work to make CAD import fast and easy and it's not clear to me what's going to
get people more interested - the technical performance of the solver or the
usability of the GUI. I'd be interested in thoughts on that. Or anyone
interested in getting hands-on, send me an email (see my profile).

~~~
madengr
Have you tried stripline as a benchmark? It's analytic solution for infinite
ground planes, so plotting error vs simulation time (mesh refinement) gives
nice accuracy vs time curves. Jim Rautio did this for Sonnet a few years ago,
and I then used it to benchmark several solvers. Really just to show that 2.5D
solvers gives much better accuracy vs. simulation time than 3D, for planar
problems.

I use AWR (Axiem, Anaylst), CST, and Sonnet. I'm satisfied with accuracy; need
more speed. It's at a point where material and manufacturing tolerances are
more of an issue, so I need to run parameter sweeps, yield analysis, etc. So
multi-threading, GPU acceleration, and distributed computing help that.

Working on a thick patch antenna today. Axiem (2.5D infinite substrate) said
1.57 GHz. Analyst says 1.51 GHz. It actually measured 1.53 GHz. That's a 3%
error on an 8% 12 dB RL bandwidth antenna. Those simulated results are after
mesh convergence, so finer meshing won't help.

So I use 2-3 solvers on a single problem. It's important that the geometry
translation between them be quick and easy. That's where AWR comes into play;
everything plugs into it. 3D solver (modeling) is horrible for pushing
polygons during the design process. 2.5D solvers are awesome for this, but
then you need to sometimes push the geometry to 3D solver.

~~~
noobermin
Going +1 on this. I'm not an engineer, but I'm a plasma physicist who lives
doing Particle-in-Cell sims, so a very different regime and perspective.

Accuracy isn't really at the forefront of our concerns because most EM solvers
since the 70's are good enough in those terms, and going to higher order
methods aren't worth it for us if it is so much slower. What we need is speed.
For me, give me a way to do 50 simulations in a month that are converged
enough that allow me to do a parameter scan over laser phase, focal point,
etc. Allow me to do more 3D simulations. That what I need. The reason is that
for me, plasma is so fuzzy anyway that the nth term error in the expansion
pales in comparison to if laser focuses half a micron off target, which is a
much more common source of error bars in a real experiment.

I imagine it's similar for engineers, our solvers are good enough for most
problems, just make them faster and allow us to do more 3D simulations in
shorter time.

~~~
madengr
I went to a defense oriented EM conference about 25 years ago. One of the
military guys slams a TWT down on the table and says he'll pay $1M to model
this; he was serious. Of course now I can buy CST particle studio. I assume
it's feasible now.

~~~
carapace
(Traveling-wave tube?)

\----

(Edit: What a cool device!! I've just been reading up on them and Wowee! I'm
in the wrong field. No pun intend.)

~~~
madengr
Yep. Any sort of particle & wave interaction; klystrons, TWT, magnetrons, etc.
with nonlinear and thermal effects rolled in. Nasty problems.

------
aluhut
Page seems down from here (Germany).

~~~
amingilani
Here too (Pakistan)

------
gravypod
How does this compare to NEC2?

------
throwaway7645
Is that a common acronym for electromagnetic solvers? It can also deal with
health and the power grid depending on context.

------
cozzyd
anyone have any experience on how it compares to meep ([http://ab-
initio.mit.edu/wiki/index.php/Meep](http://ab-
initio.mit.edu/wiki/index.php/Meep))? I've used meep for a few things but am
not too entrenched that I can't switch...

~~~
thliebig
It uses the same method, but the focus of openEMS is more in RF devices while
Meep is more focused on optics. One important difference is that openEMS
supports graded (inhomogeneous) meshes. You need this since for RF devices
some features are much much smaller than the wavelength, e.g. feeding lines,
and you do not want (or need) a dense mesh everywhere in those cases.
Furthermore openEMS has a small GUI to display the defined structure and mesh
to inspect if your setup is ok.

------
th0ma5
Useful for antenna design, right?

~~~
madengr
Yes, at least for electrically small antennas.

~~~
thliebig
Large antenna arrays a fine too... Just takes longer to simulate of course.

------
nullc
How does it compare to Meep?

