Using compact magnets and 3D-printed rings, scientists have unlocked stronger, more even magnetic fields that could revolutionize MRI and magnetic levitation. Credit: Shutterstock
Two German physicists have unveiled a compact magnet layout that outperforms the famed Halbach array, delivering stronger, more even magnetic fields without bulky superconductors.
Their 3D-printed ring stacks matched analytic predictions and could slash the cost of MRI machines while opening doors for levitation tech and particle accelerators.
Breakthrough in Magnetic Field Generation
Physicists Ingo Rehberg at the University of Bayreuth and Peter Blümler at Johannes Gutenberg University Mainz have unveiled a fresh way to create smooth, uniform magnetic fields using everyday permanent magnets. Their compact setup beats the classic Halbach arrangement, which only works perfectly for magnets of impossible, infinite length.
In real-world, finite sizes, the new design delivers stronger fields and far better uniformity. The breakthrough appears in Physical Review Applied, a leading journal that highlights advances where physics meets engineering, materials science, chemistry, biology, and medicine.
Limitations of Classical Halbach Arrays
Engineers often turn to the Halbach array when they need a tidy, even magnetic field. The idea assumes you can arrange very long magnets in a circle so that their fields blend perfectly at the center. In practice, real magnets are finite. As soon as you shrink the array to a usable size, the magic fades: field strength wobbles from one spot to another, and the setup can no longer claim top performance. Rehberg and Blümler’s optimized three-dimensional arrangement fixes those flaws, giving scientists and engineers a powerful new tool for technologies that demand strong, uniform magnetic fields.
“Focused” magnet system consisting of two stacked rings, each with 16 FeNdB magnet cuboids (side length 20 mm). The inner diameter is 160 mm, and the magnetic field of 20 mT exhibits a homogeneity of approximately 5 per mille over a spherical volume with a diameter of 50 mm. Credit: Peter Blümler
Innovative 3D Magnet Configurations
In their work, Dr. Peter Blümler and Professor Ingo Rehberg present optimal three-dimensional arrangements of very compact magnets, idealized by point dipoles. With a view to possible applications, they investigated, among other things, the optimal orientation of the magnets for two geometries relevant to practical use: a single ring and a stacked double ring. A so-called focused design additionally allows the generation of homogeneous fields outside the magnet plane, for example in an object positioned above the magnets.
For these new arrangements, Rehberg and Blümler developed analytical formulas, which they subsequently validated experimentally. To this end, they constructed magnet arrays from 16 FeNdB cuboids mounted on 3D-printed supports. The resulting magnetic fields were measured and compared with theoretical predictions, revealing excellent agreement. In terms of both magnetic field strength and homogeneity, the new configurations clearly outperform the classical Halbach arrangement as well as its modifications described in the literature.
Real-World Impact and Applications
The new design concepts offer great potential for applications in which strong and homogeneous magnetic fields are required. In conventional magnetic resonance imaging (MRI), for example, powerful superconducting magnets are used to polarize hydrogen nuclei in tissue. These nuclei are then excited by radio waves, generating measurable voltages in detectors surrounding the body. Algorithms use these signals to calculate detailed cross-sectional images that allow physicians to distinguish tissue types based on properties such as density, water or fat content, and diffusion. However, superconducting magnets are technically complex and extremely costly, making this technology hardly available in many parts of the world. For such cases, intensive research is underway to develop alternative methods for generating homogeneous magnetic fields using permanent magnets – a field to which the present study makes a promising contribution. Further potential areas of application include particle accelerators and magnetic levitation systems.
Reference: “Analytic approach to creating homogeneous fields with finite-size magnets” by Ingo Rehberg and Peter Blümler, 11 June 2025, Physical Review Applied.
DOI: 10.1103/9nnk-jytn
