Electromagnetic software accelerates ahead
May 26, 2009
Hamish Johnston explains how software born in an accelerator lab is now being used for everything from medical physics to invisibility cloaks
In 1975 Thomas Weiland was a physicist at the Technische Hochschule Darmstadt in Germany when he started working on numerical algorithms. He could not have imagined then that software born out of this first effort would help drive a multi-billion dollar mobile communications boom — and in the process help physicists to design invisibility cloaks.
Indeed, Weiland’s first objective was to solve the eigenvalue problem of arbitrarily shaped and filled wave guides. Weiland — who now runs the Computational Electromagnetics Laboratory at the Technische Universität Darmstadt — solved this problem by inventing the finite integration technique (FIT) for solving Maxwell’s equations.
FIT works by dividing a volume of interest up into a grid and solving an integral form of Maxwell’s equations along edges and on faces of these volumes. The first scientific publication introducing FIT followed in 1977. Since FIT is a very general approach to Maxwell’s equations it was next applied to solve 3D eddy-current problems.
In 1979 Weiland left Darmstadt and worked for two years at the CERN particle-physics lab in Geneva. An important challenge at the time was to understand how the electromagnetic field created by a beam of charged particles interacted with the accelerating radio-frequency cavity itself — the so-called “wakefield effect” — and to work out what influence this had on beam propagation and quality. Weiland then moved on to the University of Hamburg, where he started working on the design of accelerators and on their components, such as cavities — all the time improving and extending FIT.
The resulting code later came to be called MAFIA (an acronym for solving MAxwells Equations using the Finite Integration Algorithm) and it was the first program that allowed accelerator designers to simulate in 3D how particle beams moved through a cavity while under the influence of rf fields from external sources.
Throughout the 1980s Weiland improved and commercialized MAFIA while working at several accelerator labs worldwide. During that time, MAFIA also began to get the attention of companies building equipment that operated at the same radio and microwave frequencies and power levels as the accelerator cavities.
Weiland’s first commercial customer was Siemens, which used MAFIA in different departments — for example in the design of nuclear-magnetic resonance (NMR) devices. However, in this period commercial users remained a small part of the business, with most being research scientists in over 25 countries around the world.
The 1990s saw a boom in mobile communications and the need for software for designing radio-frequency and microwave antennas and other components. In 1992, Weiland therefore founded CST to commercialize MAFIA and focus on the telecoms industry.
In 1996, CST decided to implement the perfect boundary approximation (PBA) — whereby arbitrarilay shaped objects are conformally represented within one mesh cell in contrast to the conventionally used staircase approximation of other transient codes — into its simulation software. Unfortunately, MAFIA could not be easily adapted into a conformal code. In addition the Windows environment offered so many possibilities to improve usability that the decision was taken to build a new program from scratch, this time entirely in-house at CST.
The result was CST’s current flagship product CST MICROWAVE STUDIO (CST MWS), which was first released in 1998. By that time telecoms was dominating CST’s business and CST MWS was aimed squarely at people designing antennas and connectors for mobile phones and base stations.
Since then, the company has launched a series of products that integrate aspects of MAFIA. These fall under the collective banner of the CST STUDIO SUITE and include the CST PARTICLE STUDIO, which was launched in 2005 and is targeted at physicists who design accelerator components — including particle sources, and microwave tubes as well as accelerator cavities.
But the firm’s software is not just restricted to particle physics. Indeed, to encourage the use of its software by academics — and to honour the good work done at universities — CST launched its University Publication Awards in 2003.
For example, medical physicists charged with protecting the health of workers who operate magnetic resonance imaging (MRI) equipment use CST MWS to calculate the electromagnetic field strength inside the human body during a scan. In 2006, Jo Hajnal and colleagues at Imperial College London won an award for using CST’s software to calculate how much electromagnetic radiation is absorbed by a mother and foetus,which is helping practitioners ensure that absorption is kept within current guidelines.
CST MWS is also used by condensed-matter physicists to simulate the electromagnetic properties of nanoelectromechnical systems (NEMS). In 2005, for example, Xiang Zhang of the University of California at Berkeley won an award for developing a new lithography technique for creating nanometer-sized structures. The technique is based on the interference of surface plasmon waves, which are collective excitations of electrons on the surfaces of metals that can be simulated using CST MWS.
CST MWS has also played an important role in the development of “metamaterials” — artificially engineered structures that can be used to make superlenses, invisibility cloaks and other devices that seem to defy the rules of conventional optics. Andrea Alu and Nader Engheta of the University of Pennsylvania won a CST award in 2007 for their use of CST MWS to simulate metamaterial and plasmonic “covers” that could be used to cloak collections of objects by making them transparent to incident radiation.
The previous year Robert Moerland and colleagues at the University of Twente in the Netherlands won an award for their use of CST MWS to design a “near perfect lens” comprising a 20 nm thin metal film. Through a combination of simulations and experimental measurements the team were able to show that such a lens could image features much smaller than the wavelength of the illuminating light — something that a conventional lens cannot do.
And what about the MAFIA code itself? Its latest incarnation MAFIA 4 is still available from CST as an electronic computer-aided design (ECAD) package.
So, the next time someone asks you “what good has come out of particle physics?”, you can point to the latest mobile phone — and who know, maybe in a few years you could mention your invisibility cloak.
About the author
Hamish Johnston is editor of physicsworld.com