Designing Magnetic Systems Using CST Studio Suite
Table of contents
Application of Magnetic Systems
Magnetic systems, or systems that make use of magnets and magnetic fields, have a wide range of applications across various industries and fields. Some common applications include medical imaging, electric motors and generators, magnetic separation, magnetic storage, transportation, research instruments such as circulators, magnetic sensors, environmental and geological monitoring, renewable energy technologies, automotive, and consumer electronics such as speakers, headphones, and microphones.
These are just a few examples, and the applications of magnetic systems continue to expand as technology and research advances. In some applications, a homogeneous magnetic field is important, while in other cases, it may not be as critical. The need for a homogeneous magnetic field depends on the specific requirements of the application.
Magnetic field homogeneity
Here are some contexts where magnetic field homogeneity is important:
Medical imaging (MRI): In magnetic resonance imaging (MRI), a highly homogeneous magnetic field is critical to obtaining accurate and clear images of the body’s internal structures. Inhomogeneities in the magnetic field can cause distortions and artifacts in the images.
Nuclear magnetic resonance (NMR) spectroscopy: NMR spectroscopy is used to analyze the molecular composition of substances. A homogeneous magnetic field is essential for precise and consistent measurements of nuclear magnetic resonance frequencies.
Particle accelerators: In particle accelerators such as cyclotrons and synchrotrons, a homogeneous magnetic field is necessary to direct and control the paths of charged particles as they gain energy and are accelerated.
Magnetometry: Magnetic field measurements used in geophysics, environmental monitoring, and scientific research often require a homogeneous field to accurately sense and quantify magnetic properties.
Quantum computing: Some technologies in quantum computing require highly uniform magnetic fields to manipulate and control qubits, the basic units of quantum information.
Precision measurements: Certain precision measurements, such as those involving magnetic susceptibility or magnetic moments, require a homogeneous magnetic field to ensure accurate and repeatable results.
Materials testing: In materials science and materials testing applications, a homogeneous magnetic field may be necessary to study the magnetic properties of materials under controlled conditions.
Research supercollider machine, underground particle accelerator
MRI X-ray scanner machine
Simulating the magnetic system of circulators
Microwave circulators are widely used passive components with diverse applications in test and measurement setups to route signals from sources to the DUT (Device Under Test) and to separate signals coming from the DUT to different test equipment. They are used to protect microwave amplifiers from reflected signals and to prevent damage to the amplifier. This article looks at modeling and simulation of magnetic systems used in microwave circulators. The model of a 3-port circulator from the Component Library of CST Studio Suite is shown in the figure below.
Model of a 3-port circulator from the Component Library of the CST Studio Suite
A suitable design of a magnetic system for a circulator must simultaneously guarantee a homogeneous distribution of the magnetic field in the vertical direction to the magnets and also ensure a negligible magnetic field in the space outside the circulator. Magnetic systems are used in 3-port microwave circulators to magnetize ferrites used for the circulation of the incoming microwave energy. The value of the magnetic field depends on the ferrite material, frequency and bandwidth, and the desired performance parameters of the circulator. This magnetic field is generated using permanent magnets and must be precisely designed while ensuring that its value is homogeneous in the area of the ferrite. This complex task, which includes considerations of magnet arrangement, magnetic materials and magnetic circuit design, is performed using CST Studio Suite.
The magnetic field between two permanent magnets
The magnetic field between two permanent magnets is simulated using CST Studio Suite. The magnets are modeled with their geometry and their remanence. Remanence, also called residual induction or magnetic residue, is a fundamental property of a permanent magnet. Remanence, Br, is usually expressed in units of Tesla (T) or Gauss (G). A higher remanence indicates that the magnet retains more of its magnetization and produces a stronger magnetic field, even without external influence.
Modeling the magnets in CST Studio Suite
Magnets with a diameter of 40cm and a thickness of 5cm were used. These were arranged at a distance of 20cm. The magnetic field in the direction perpendicular to the surface of the magnets (Z-axis) between two permanent magnets is shown in the two following images.
The magnetic field in the XY plane
The magnetic field in the Z direction on a line running in the X direction
The magnetic field between two permanent magnets with yoke
When many magnetic systems operate close to each other, it is important to limit the magnetic fields of each system in its geometry to avoid interference between different magnetic systems. If the magnetic system is covered with magnetic material such as steel, the magnetic field will be limited in the magnetic system, and its strength will be less beyond the magnetic system. These steel parts, also called yoke, are shown here in gray.
Magnetic system with yoke
The comparison of the magnetic field in these two versions is shown in the following figure.
The magnetic field in Z-direction in the middle two magnets with yoke on a line in X-direction
The magnetic field in the XY plane is shown in the following figure between two permanent magnets with yoke.
The magnetic field of magnet and yoke in the XY plane
The additional attachment of the yoke ensures an increase in the magnetic field within the system geometry, as well as a reduction outside the system.
The magnetic field between two permanent magnets with pole shoes
To increase homogeneity, another component made of steel, called the pole shoe, is added to the system. The pole shoe is located between the magnets. The pole shoe is shown in green in the following figure.
Magnet system with yoke and pole piece
As can be seen in Figure 12, the installation of the pole piece leads to a greater homogeneity of the magnetic field within the system boundaries. However, the installation of the pole piece has led to a reduction in the magnetic field strength.
Magnetic field in Z-direction on a line in X-direction in the middle two magnets with yoke and pole piece
The magnetic field in the XY plane is shown in the following figure between two permanent magnets with yoke and pole piece.
The magnetic field of magnets, pole piece, and yoke in the XY plane
The magnetic field between two permanent magnets with side yoke
In the latest version, another component made of steel is added. This part is called the side yoke and is used to reduce the magnetic field outside the magnet system.
Magnet system with yoke, pole piece and side yoke
The magnet system with yoke, side yoke and pole piece has the best homogeneity and at the same time the strength of the magnetic field is greater.
Magnetic field in Z-direction on a line in X-direction, in the middle two magnets with yoke, pole piece and side yoke
The magnetic field of magnets, pole piece, yoke, and side yoke in the XY plane
Designing Magnetic Systems
This blog shows how to design a suitable magnetic field using CST Studio Suite. The magnet system used in microwave circulators generates a magnetic field inside and outside the circulator. This magnetic field must be designed in such a way that a homogeneous magnetic field is generated inside the circulator and a negligible magnetic field is present outside the circulator.
CST Studio Suite simulates magnetic systems using the magnetostatic solver. It is shown that the magnets can be modeled with their magnetic parameters, such as remanence. It is also shown that using a pole piece generates a homogeneous magnetic field inside the circulator. In addition, using a yoke and a side yoke generates an even more homogeneous and stronger magnetic field inside the circulator and also reduces the magnetic field outside the circulator.
