Which electromagnetic software should I use for my electric/electronic design: Low or high frequency?

Passive components Motors and Generators Solenoids high power Antennas & Radomes
By Ahmed Khebir | 23/11/2021

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 electro-magnetics (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 infra-red, visible light, X-rays and Gamma-rays. 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, X-rays and Gamma-rays instead of electromagnetics. 

Mathematically speaking, the difference between low and high frequency electromagnetics resides in the treatment of the so-called 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 B-H 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
  • Far-field and antenna parameters are sought
  • To compute S-parameters, 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

  • Motors and generators
  • Linear and rotational actuators
  • Relays
  • MEMS
  • Magnetic recording heads
  • Magnetic levitation
  • Solenoids
  • Loud speakers
  • Electromagnetic Brakes and Clutches
  • Alternators
  • Magnetic bearings
  • Permanent magnets
Electro-magnetic behavior
  • Insulation studies
  • Electrostatic discharge
  • Electromagnetic shielding
  • Electromagnetic exposure
  • Electromagnetic levitation
Power electronics
  • Transformers
  • Inverters
  • Converters
  • Bus bars
  • Inductors
High power
  • Coils
  • Sensors
  • NDT, NDE
  • High power
  • High voltage
  • PCBs
  • MRI Magnets
  • Induction heating
  • Bushings
  • Switchgear
  • Cables

Magic Tee, HFWorks

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
  • Antennas
  • Connectors
  • Filters
  • Resonators
  • Couplers
  • Attenuators
  • Terminators
  • Frequency-selective surfaces
  • Band-gap (EBG) structures and meta-materials
  • RF coils for MRI
  • Waveguides
  • Power dividers
  • Multiplexers
  • Power combiners
  • Transitions
  • High Q structures
  • Linear accelerators
  • Signal integrity
  • Power integrity
  • PCBs and IC Packages
  • Chip-Package-Board systems
  • All EMI/EMC structures
  • Simultaneous switch noise (SSN)
  • Simultaneous switching output (SSO)
  • EM field exposure

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