Benefits of CST Hybrid Solver for System Level Electromagnetic Analysis

Electronic products are becoming more and more complex, typically with many systems occupying a very small space. These electronic products operate at certain frequencies and if we want to digitally analyze the electromagnetic (EM) fields of the device itself to optimize design performance and efficiency, the electrical size to simulate is typically reasonable. However, these devices are usually part of a much larger system, creating a much bigger electromagnetic simulation problem when compared to the device by itself in terms of wavelength.

Performing System Level Electromagnetic Analysis

It is possible to solve large scale EM simulations using a computer with enough system memory or with the help of Graphics Processing Units (GPUs). These computers are typically expensive and not everyone has access to them.

Solving large electrical problems using one EM simulation method is usually inefficient because of the large aspect ratio between the smallest feature in the device and the large dimension of the surrounding structure. The simulation time is typically very long for large problems and this leads to long product design cycle, delaying your time to market schedule. This method of solving the problem using one solver is referred to as the brute force method and it is not recommended because not everyone has access to top end computer hardware.

A more efficient way to perform system level EM analysis is to divide the large problem into different domains and solve each domain using the appropriate method. This allows for the most suitable method to be used to solve a particular part in the simulation domain, leading to faster analysis, which in turn shortens your product development cycle. This approach is made possible thanks to the complete solver technology in the SIMULIA CST Studio Suite 3D EM analysis software package.

CST Studio Suite Complete Solver Technology

CST Studio Suite offers complete solver technology to tackle all kinds of engineering problems, with electromagnetic field solvers for applications across the EM spectrum contained within a single user interface. These solvers are numerical techniques used to solve the underlying partial differential equations.

CST Studio Suite breaks down electromagnetic simulation into the following application areas: Microwaves & RF/Optical; EDA/Electronics; EMC/EMI; Particle Dynamics, and Statics/Low Frequency. Problems in each of the application areas can be solved using the appropriate solver.

For microwaves and radio frequency analyses, there are solvers in the time and frequency domain available, depending on the result of interest and the behavior of the model on hand. Typical examples are antennas and connectors. Time domain and frequency domain methods have their pros and cons. These methods exist because they are very efficient in solving certain problems but not others. In CST Studio Suite, the time domain solver includes Finite Integration Technique (FIT) and Transmission Line Matrix method (TLM), the frequency domain solver is based on the Finite Element Method (FEM), the Integral Equation solver is based on the Method of Moment, and the Asymptotic solver is based on shooting and bouncing rays.

If you have questions about what solver to use for your specific application, please contact us at [email protected].

CST Studio Suite Hybrid Solver for EM Simulation

Having access to all the EM solver technologies allows for great flexibility. The results from different solvers can be compared directly if the problem falls in certain category. If the results compare well then one can be confident in the solution. The other major benefit is that you can take advantage of the solvers to help you efficiently obtain a solution.

The example mentioned above is extremely difficult to solve because of the large aspect ratio between the smallest and the largest features in the big problem. Imagine a system with a horn antenna pointing at a dish reflector. The horn has smallest dimension of 20 mm at the feed while the dish antenna is 600 mm wide. At the operating frequency of 5GHz, the dish reflector is 10 wavelengths. This small scale example is used for illustration purposes because it is still practical to be solved on a workstation to make comparisons. Imagine having a system that is hundreds of wavelengths, it becomes impractical or impossible to solve such a large problem using one method.

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This is when the hybrid solver approach becomes useful. The horn antenna can be solved with the time domain solver to extract the field distribution around it. The integral equation solver can be used to get the farfield pattern with the extracted field distribution as excitation.

On the left image below, the horn antenna is solved first using the time domain solver – this is the source project and will be calculated first. The image on the right shows the dish reflector using the previously calculated result from the horn antenna project as excitation to get the system farfield pattern. Depending on the location of the source relative to the overall system, both nearfield source and farfield source can be used as excitation. When using the nearfield source approach, the structure reflection cannot be too strong so that it affects the original source excitation. Also, the farfield source scenario assumes that the source is located in the far zone of the reflector.

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Electromagnetic Simulation Result and Time Comparisons

The problem at hand is not an electrically very large structure and it can be solved with a common laptop machine with an Intel Core i7 9850H CPU. The hexahedron mesh count is about 21 million using the time domain solver without GPU. The total simulation time is 1273 seconds, or 21 minutes and 13 seconds. Three frequency points are used –  4, 4.5 and 5 GHZ – so three farfield patterns are available after the simulation.

The pictures below show the mesh view using the brute force method first and the hybrid solver method second. The time domain solver meshes the entire simulation volume which is why mesh cells extend beyond the structures, in this case the horn antenna and reflector dish. The method of moment approach only needs to discretize the surface of the structure and the reflector dish can be seen represented by triangles.

Click image to enlarge
Click image to enlarge

The farfield result at 5GHz from each method is shown below with the directivity of 22.3 dBi from the brute force method. The hybrid method result shows a 22.2 dBi directivity. The blue box on the right represents the nearfield distribution surrounding the horn antenna and was used as the excitation source for the method of moment solver.

Click image to enlarge
Click image to enlarge

The results compare well at 4 GHz and 4.5 GHz. Since the reflector dish is located in the far zone of the horn antenna operating at these frequencies, the farfield can be used as excitation This further reduces the simulation time compared to using the nearfield source approach. For comparison, the time domain source project with just the horn antenna solving 3 frequency points took 24 seconds, and the method of moment platform project took 23 seconds. This translates into the hybrid solver approach taking a total of 47 seconds compared to the brute force approach using the time domain solver taking 1273 seconds. This means you can get your solution 27 times quicker, as well as have a much lower requirement on your hardware resources.

Hybrid Solver Benefits for Electromagnetic Simulation

Having all electromagnetic solver technologies under one license greatly simplifies the workflow. There is one intuitive environment to learn and solvers can be changed with a couple of mouse clicks. The hybrid solver provides a much lower system resource requirement compared to the brute force method while maintaining result accuracy. This is invaluable because not all large models can be solved with typical workstation machines. Total simulation time is much shorter compared to the brute force method, resulting in a solution that is 27 times faster in our example. This will greatly increase the number of scenarios you can explore in the same amount of time when compared to the brute force method.


Questions?

If you have any questions or would like to learn more about SIMULIA CST Studio Suite solvers, contact us at (954) 442-5400 or submit an online inquiry.