It is well established that electric, magnetic and electronic product design from basic principles, i.e., by solving Maxwell’s equations, offers the highest level of accuracy and reduces design iterations and prototyping cost. Most software vendors offer two electromagnetic simulation packages: one tailored for low frequency applications, e.g., EMWorks EMS, ANSYS® Maxwell®, Altair Flux®, and one for high frequency, e.g., EMWorks HFWorks, ANSYS® HFSS®, Altair Feko®. It can be confusing for designers as to which package to use, especially that in some cases both low and high frequency packages maybe used. In this article, we shed some light and give some general guidelines on how to choose the more appropriate package for a given application.
Generally speaking, low frequency electromagnetics (LFE) refers to frequencies from DC to a few MHz or tens of MHz. On the other hand, high frequency electromagnetics (HFE) refers to frequencies from few tens of MHz to hundreds of GHz and even few THz, remaining below infrared, visible light, Xrays and Gammarays. Although all frequencies are part of the same electromagnetic spectrum as shown in Fig. 1, beyond THz frequencies other terms are used, such as light, Xrays and Gammarays instead of electromagnetics.
Mathematically speaking, the difference between low and high frequency electromagnetics resides in the treatment of the socalled Maxwell’s displacement current, which is neglected in LFE while in HFE it is not. The displacement current, or time
varying electric flux density, is responsible for coupling the electric and magnetic fields, which causes the propagation of electromagnetic fields. But why neglect the displacement current in LFE? Because the operation frequency is “relatively”
low which makes the wavelength much larger than the size of the device. You may still ask: how do I know if I should neglect the displacement current and hence use low frequency software? Practically speaking, the nature of the problem,
the frequency of operation and the type of the device should ultimately help you figure that out.
Low frequency software
A low frequency software, such as EMWorks’ EMS, EMWorks 2D, and MotorWizard, usually addresses issues such as the following:
 The device is much smaller than the wavelength, even if the frequency is relative high
 The frequency of operation ranges from DC to a few tens of MHz
 The calculation force and torque are sought
 The dielectric breakdown is of interest
 To deal with cogging torque
 To model coils and permanent magnets
 To compute structural deformation due to electromagnetic force or heat
 To calculate the saturation of the core
 To study power integrity, power supply, and power management
 To compute capacitance, inductance, and resistance
 To study the skin and proximity effects
 To calculate eddy currents and eddy current losses
 To model moving objects such as a rotor in a motor or generator
 To study the effect of BH curves or magnetization curves on the performance of magnetic devices and circuits
High frequency software
A high frequency software, such as EMWorks’ HFWorks, usually addresses issues such as the following:
 The wavelength is smaller or comparable to the device size
 The frequency of operation ranges from few tens of MHz to few hundreds of GHz
 Farfield and antenna parameters are sought
 To compute Sparameters, e.g., insertion loss and return loss
 To calculate the characteristic impedance and propagation constant of transmission lines and guides
 Time Domain Reflectometry (TDR) is of interest
 Crosstalk and distortion are of interest
 To examine the signal integrity of the device
 To approximate the temperature’s rise of an electronic device due to dielectric conductor losses
 Compute the resonant frequency and/or quality factor of a resonator
 To study the fidelity of a high frequency structure
 To obtain the vector frequency response of arbitrary 3D circuit/structure
 To study the EMI/EMC of a structure
 To compute the specific absorption rate (SAR) for biomedical applications
As for the devices and equipment, you should use LFE software to model any of the following:
Type  Example of devices 


Electromechanical 


Electromagnetic behavior 


Power electronics 


High power 

Coaxial cable, HFWorks
A horn antenna, HFWorks
A wire bond, HFWorks
5G wearable device, HFWorks
TDR simulation, HFWorks
As for the devices and equipment, use high frequency to model:
Type  Example of devices 

RF& Microwave 

EDA/Electronics 

EMI/EMC 

If you are still in doubt, please contact us. Our electromagnetic application experts will be glad to help you.