Microelectronics

TU Chemnitz: How delicate touches influence wave propagation in crystals

May 6, 2026. A French-German research team consisting of members of the FEMTO-ST Institute of the Université Marie et Louis Pasteur, Besançon, and the Faculties of Electrical Engineering and Information Technology and Natural Sciences and the Research Center for Materials, Architectures and Integration of Nanomembranes (MAIN) at Chemnitz University of Technology has uncovered new insights into the emergence of forbidden frequency ranges in periodic solid-state structures. The study entitled “Contact points open wide band gaps in all two-dimensional Bravais lattices” was published at the end of April 2026 in the physics journal “Physical Review B” and makes a fundamental contribution to understanding the transport properties of electromagnetic waves through regularly arranged materials.

The two-dimensional electromagnetic crystal consists of a 7×7 arrangement of copper tubes (length approx. 20 cm) arranged in a square grid, with the contact lines between the tubes made possible by a specially developed wooden base plate. The arrangement can be seen here in the run-up to transmission measurements between two horn antennas at the Chair of High Frequency Technology and General Electrical Engineering (Prof. Ralf Zichner). These take place in an anechoic

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The work examines the influence of contact points between copper pipes arranged regularly in space as individual scatterers on the propagation of radio waves and thus on the development of forbidden frequency ranges for these waves – so-called band gaps. Using theoretical considerations, numerical simulations and experimental measurements of the scattering on all possible two-dimensional arrangements of the tubes – the so-called Bravais gratings – the researchers show that contact points that occur systematically generate wider band gaps and thus enable broadband filters for the high-frequency waves.

The results prove that precise knowledge of the geometric structure of the scatterers and their exact positioning in relation to each other, especially in the case of contact, enables systematic influencing and control of the band structures and thus helps to tailor the propagation of waves. Especially for applications in electronics and photonics, large, adjustable bandgaps are of crucial importance as they determine the electronic and optical behavior of devices.

The study fits into the current research on the development of geometry effects in functional, two-dimensional membrane materials. It is in line with findings from research work in which the authors have demonstrated a similar effect for sound. It was inspired by work carried out as part of the TUCculture initiative on the stele artwork “Thinking and Perception Model for the Phenomenon of Color” by Dresden artist Stefan Nestler (1998) in front of the lecture hall and seminar building at Chemnitz University of Technology. The artwork is the world’s largest realization of a photonic crystal. By further developing the subject area, the authors are making a positive contribution to basic research in the field of wave physics and providing new impetus for materials research.

Original publication: D. Röhlig, R. Zichner, T. Blaudeck, A. Thränhardt, V. Laude: “Contact points open wide band gaps in all two-dimensional Bravais lattices”, Physical Review B 113, 144391 (2026). URL https://doi.org/10.1103/9ql7-t9rh