For design engineers, there are multiple alternative automated EMI/EMC tools, including design rule checker that examines whether PCBs (printed circuit boards) are capable of meeting predetermined design rules, quasi-static simulators that can be used to extract parameters of inductance, capacitance and resistance when the dimensions of components are far smaller than operating wavelength, quick calculators that are used to calculate simple applications through computers based on analytic equations, and full-wave numerical simulation techniques. These automated tools can be applied to solve different EMI/EMC problems in different design steps. However, no automated tools are capable of analyzing the overall design and accurately predicting the problems that will take place to system.
PCB design is so complicated that numerous layers and lines are concerned in it. For engineers, it's quite difficult and boring to manually check the routing of each EMI/EMC key network. Automated tools are capable of extracting PCB design from CAD files and reporting positions violating design rules to users. Generally speaking, these software tools can allow users to predetermine design rules as limiting condition and can even create new rules under the condition of available PCB technologies and speed.
PCB rule checkers can be repeatedly applied during the period of PCB design in order to ensure the design without violating important EMC rules. If PCB is only examined in the final design step, modification in accordance with rules will possibly take much time and even can't be implemented. The examination of PCB design during the period of design results in the avoidance of large-scale modification based on EMC rules following.
PCB design rule checker runs at a very large speed and examines the design rules of each PCB. Nevertheless, these tools just simply provide some hint for users and fail to provide instructions according to the order of severity concerning rules breaking. Some newly-presented PCB software checking tools are capable of associating phenomena of rules breaking and reflecting the information about data rate of signals and degree of rules breaking, which is beneficial for designers to eliminate specific occurrence of rules breaking.
Simulation tools are applied to accurately analyze a small part of overall system. No matter how great screen captures suppliers provide, present EMI/EMC modeling tools fail to do "all the work" since modeling can't replace software engineers and it is only one of tools used by EMI/EMC engineers. EMI/EMC engineers are required to determine which design part that is in need of forward analysis and modeling.
Generally speaking, multi-grade model is required to be established on unresolved issues and the simulation result of the model at the last grade supplies input information to the model at the next grade. This method makes model optimized by separately processing the special issue in each part and integrating the results. Therefore, compared with the modeling for one time that is too "pushy", multi-grade simulation is capable of analyzing issues with larger scale. Besides, EMI/EMC engineers need to better understand the problem and modeling technology so as to find out more multi-grade simulation points of division.
a. Quasi-static simulators
Quasi-static simulators are applied to extract parameters of inductance, capacitance and resistance of system components such as electrical parameters of connector. However, the dimension of components has to be far smaller than the wavelength of harmonic wave with the largest frequency. This type of tools is capable of quickly calculating the parameters of equivalent circuit and parameters can be applied in circuit simulators such as SPICE. One of conditions in terms of implementation of quasi-static condition lies in the requirement that modeling object has to be with small electric size. This type of simulation consists of electric field and magnetic coupling without transmission delay of waves, which is because that modeling object has such a small electric size that it fails to cause delay to coupling between electric field and magnetic field. If components fail to meet the requirement of small size, full-wave modeling method has to be applied.
b. Full-wave simulation tools
Different from quasi-static simulators, full-wave simulation tools have no requirement of small electric size to components. Instead, Maxwell's equations are fully solved without simplification and numerous types of styles are available for full-wave electro-magnetic modeling technology. As the best simulation technology, full-wave simulation tools have become the most commonly-used simulation tools of developers and educators while it receives the most argument as well. Lots of full-wave simulation technology is only applied in specific structures and calculation method modification for different problems is so complicated. Some full-wave simulation technology isn't generally applied, requiring deep understanding in terms of electric-magnetic knowledge and modeling technology. Moreover, some are only applied for far field such as the determination of radar section of a military device.
Different full-wave simulation technologies feature advantages in different aspects and the best modeling technology is to find the specific simulation requirement that is suitable for a certain problem. The most pervasive EMI/EMC full-wave simulation modeling technologies include method of moment (MoM), finite difference time domain (FDTD) technology, finite element method (FEM), transmission line matrix (TLM) and partial element equivalent circuit (PEEC) technology. These different full-wave simulation technologies are actually different manifestations of Maxwell's equations. For example, MoM applies integral equation of Maxwell's equations. Conductors/metals are required to be cut into units with small electric sizes (The current on each stage of conductor is supposed to be constant). The current and all the currents on other component units can be calculated through source. As soon as the current on all the conductor units is obtained, the overall generated electric field and/or magnetic field can be calculated at last.
• FDTD: The differential form in Maxwell's equations is applied in FDTD with the adjacent medium to be air and common modeling takes place with the combination of metal and dielectric. The space compatible with simulation objects is divided into volume elements with small electric size. Each volume element is defined by dielectric constant (ε), magnetic conductivity (μ) and conductivity (δ). As the name indicates, FDTD is mainly applied in time domain so model is capable of receiving wide-band response with pulse as excitation function. After the simulation of FDTD, time domain solution can be transformed into frequency domain solution.
• FEM: It is another type of form in Maxwell's equations, whose typical application is frequency solution. Similarly, the air in the model and all the other materials has to be divided into units with small electric sizes. Variational technology is applied by FEM to solve Maxwell's equations.
• TLM: As another form in Maxwell's equations, the typical application lies in time domain solution. Basically, the space area of modeling objects is divided into multiple 3D transmission line nodes on each of which transmission/reflection can be inferred by node impedance. Each unit is compatible with one node.
• PEEC: This technology is the newest full-wave method in the field of EMI/EMC with integral form in Maxwell's equations in which all relationship between unit fields is replaced by circuit relations. The connections between all units are implemented by local mutual inductance and capacitance. Solvers such as SPICE are applied to simulate overall circuits and solution current and voltage parameters are transformed into fields like MoM.
Up to now, simulation tools become so powerful that engineers have to depend on them. However, they fail to replace engineers' basic understanding on electromagnetism and EMI/EMC design. For primary simulation, novice engineers are suggested to take some training and refer to some learning materials to master how to divide overall product/device into multiple simulation modules and explain the simulation result. Finally, they should learn to verify whether the simulation results can correctly reflect modeling objects and ensure compatibility with basic physical theories.