Absorptive common-mode filter for transmission lines
The technology is based on constructive modifications of electrical conductors, in which the conductor structure is adapted for selective damping of common-mode currents.
Challenge
Power electronics comprises, among other things, the conversion of electrical energy using switching elements. Rapid switching operations can cause conducted interference, which can be mitigated with suitable materials and by switching inductance and capacity. Effective coating of the inner conductor, which is often made of copper, can reduce conduction losses. Incorporating metal alloys between the inner and outer conductors can reduce differential-mode interference. Differential-mode interference can be mitigated by addressing the skin and proximity effects. However, the efficient filtering of common-mode interferences and a simultaneous perpetuation of differential-mode paths and signals can be challenging.
Our Solution
The present invention describes special layers of ferromagnetic or ferritic materials (e.g. iron alloys, ferrites) that are selectively placed in the regions of a conductor where common-mode currents concentrate, while the differential-mode path remains virtually unchanged. By deliberately exploiting the skin and proximity effects, the common-mode current is forced into regions with higher ohmic and/or magnetic losses and thus effectively attenuated within the conductor instead of being filtered only at the conductor end. Hence, common-mode currents experience increased frequency-dependent losses (absorption effect), while differential-mode currents are largely routed to areas with lower losses. The variants include tailored two-conductor arrangements, coaxially arranged conductors and printed circuit board structures.
Figure 1: Modification of two-conductor transmission line arrangements for common-mode filtering.
Figure 2: Filter configuration for common-mode signals on an unbalanced electrical line with two coaxially arranged current-carrying conductors.
Advantages
- Integrated common-mode filter functionality without additional components
- Frequency-selective action
- Maintaining the push-pull signal quality
- Reduced space requirements, weight and costs
Applications
- Power electronics and drive technology
- High-speed data transmission lines
- Differential high-speed interfaces
- EMC-optimized cable and connection systems
- Circuit board systems with integrated common-mode damping
Development Status
Proof-of-Concept successfully shown via computer simulations. Experimental evaluation planned.
Patent Status
European patent application filed.
Patent holder: Ostfalia University of Applied Sciences (Wolfenbüttel, Germany)
Contact
Dr. Mirza Mackovic
Patent & Innovation Manager Technology
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Tel.: +49 551 30724 153
Reference: CPA-2580-FHBW
Published: January 1, 2026.
Tags: Mess- und Analysetechnik, Physik und Technik & Software
