Is your job like finding a needle in a haystack? …maybe your job IS finding a needle in a haystack. Regardless of whether the tools of your trade are metal detectors, motors, insulators, antennas, magnets, electron microscopes, ion implanters, … the odds are that some of your equipment was designed using the tools provided by Integrated Engineering Software.
For 30 years INTEGRATED has provided multiphysics simulation tools which have been especially popular for electromagnetic design. In the early years INTEGRATED stood out particularly for using the Boundary Element Method, rather than the Finite Element Method. This meant that many problem types that are not appropriate for Finite Elements could only be reasonably approached with INTEGRATED software. A metal detector for finding a needle in a haystack provides an example of such cases.
What are the components that will need to go into a detection system? The proposed detector will consist of a coil which will produce an oscillating magnetic field which will induce current flow in any conductive materials, such as the needle. That will produce a magnetic field 90 degrees out of phase with the field the coil generated. Detecting and measuring the out of phase field will enable detection of the needle. The simulation result shown above depicts the shape of “isosurfaces” where that out of phase field is at specific values. Notice that these isosurfaces essentially point to the needle. Hence a conceivable detection system would have some field probes providing data that could be processed to point to the needle. However, that is much more complex than the standard hand-held wand such as you see in airport security.
One possible method to use with a single hand-held detector is to measure the EMF induced in the original coil. So considering all other materials to be essentially perfect insulators we are left with the minimal considerations being a coil some distance from a needle. Simulation on a computer should save a lot of time building and testing specific proposed design by systematically moving/rotating the coil and showing the detected signal for each configuration. However, this relies on sufficient precision being achieved in reasonable computation time. To solve with Finite Elements it is necessary to draw the coil and needle, assign physical properties to them, then generate a mesh which will enable the magnetic potential in the surrounding space to be mapped, then from the potential it is possible to compute quantities of interest like the magnetic field or induced EMF.
The challenges for Finite Elements in this model include:
- The mesh has to be of finite size. An artificial boundary needs to be created and some kind of artificial condition needs to be put on it and chosen such that it minimize the effect of artificially terminating magnetic flux.
- The coil is much larger than the needle, but there is also some amount of empty space between them. The smaller the mesh grid is the longer the computation time will be. So the mesh needs to be made sparse in some areas and dense in others in a way that still enables the overall solution to be off sufficient quality.
On the right is a cutaway view of a basic Finite Element mesh for the simulation. The empty space mesh is normally not shown because it obscures the geometry. It is shown here to demonstrate the issues mentioned above, which shows why Finite Element users might say “MESH is a 4 Letter Word”.
From such a difficult mesh one still has to computing an out of phase component which is many orders of magnitude smaller than the total field.
The Boundary Element mesh has none of the above problems for this model, as shown below the method has no artificial boundary and no meshing of the empty space. All that is required is independent meshes on the coil and pin.
Over the last 30 years a lot has changed, we’ve introduced more solvers, the solvers themselves have become more sophisticated and computers have become much more powerful. However, the fundamental issues remain the same. Solving a model like this with Finite Elements is like driving a nail into wood with the handle of a screwdriver. It can be done, slowly. INTEGRATED now provides multiple solvers: Boundary Element, Finite Element, Fast Multipole, Fast Fourier Transform, and Finite Difference Time Domain. Many of these have multiple options for configuration to suit specific models types better. We regard our simulation software as your design toolbox. Simulation software with only Finite Elements would be like a toolbox with only a screwdriver. If you’ve been running simulations where it feels like you have the wrong tool, maybe you do. The way to find out is to contact us and try some of our alternative solving options.
