Domenico De Salvio – domenico.desalvio2@unibo.it
Instagram: @midrashdds
Department of Industrial Engineering (DIN)
University of Bologna
Bologna, Bologna 40136
Italy
Massimo Garai
Department of Industrial Engineering (DIN)
University of Bologna
Bologna, Bologna 40136
Italy
Popular version of 3pNS3 – Metamaterials application on low-height noise barrier for railways: challenges of real-world scenarios
Presented at the 188th ASA Meeting
Read the abstract at https://eppro01.ativ.me//web/index.php?page=IntHtml&project=ASAICA25&id=3870863
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
If you’ve ever lived near a train line, you know the roar of passing cars can be more than annoying — it can hurt your health. A primary source of this noise comes from transportation; among them, railway lines, having a high density in Europe, can be particularly disturbing for nearby residents. The traditional high noise barriers can help, but they aren’t always practical in urban areas. Low-height noise barriers (LHNBs), typically less than 1 meter high, can be a good alternative. These barriers work well because they can be placed very close to the source of the noise, such as where train wheels interact with the rails, as shown in Figure 1.
Figure 1. A low-height noise barrier is placed next to the railway. Image courtesy of Kraiburg Strail®.
However, for these low barriers to work best, their surface needs to be good at absorbing sound (see Figure 2). Here, acoustic metamaterials can play a key role. These artificial structures have unique properties that natural materials lack, enabling them to absorb sound in ways that conventional materials cannot. Their functionality relies on their geometric configuration rather than solely on the raw materials used, enabling them to be made from weather- and dust-resistant materials.
Figure 2. The effectiveness of an LHNB. The colors represent sound pressure level: red indicates the highest noise levels, while blue shows the lowest. On the left, the noise generated by the wheel-rail interaction. In the middle, the effectiveness of a generic LHNB is shown. On the right, the noise reduction achieved by an optimized sound-absorbing LHNB. The less red there is, the more effective the LHNB is.
This study is part of the European project LIFE SILENT and examines the integration of metamaterials into a specific type of LHNB. It employs two types of acoustic resonators designed within the constraints of a real-world scenario: Neck Embedded Helmholtz Resonators (NEHRs) and Fabry-Pérot (FP) channels. Combining these resonators enables the LHNB to mitigate railway noise.
Designing these complex structures requires a thorough process. The optimal geometry of the metamaterial has been studied through a combination of complex simulations and nature-inspired algorithms. Specifically, the geometry was optimized using a computational technique called “particle swarm” inspired by the social behavior of flocks of birds and schools of fish.
Prototypes of the metamaterial units were 3D printed in plastic because of the need for customization and precision (see Figure 3). Once the efficiency of the metamaterial is tested, serial production of the optimized geometry can also be achieved through traditional industrial molding techniques, thus, in real-world scenarios.
Figure 3. Example of 3D printed metamaterial NEHRs (on the left) and FP (on the right), the units that compose the sound-absorbing LHNB surface.
This work demonstrates how metamaterial engineering can be applied to everyday situations. The study tackles practical limitations and constraints, the need for durability against outdoor conditions, and the challenges of manufacturing complex structures. The research outlines the essential steps to transition from a lab idea to a potentially mass-produced solution against noise pollution by developing a focused design, creating physical prototypes, and conducting tests. While recognizing challenges like manufacturing accuracy and the impact of real-world conditions, the project emphasizes that acoustic metamaterials can be designed to be robust and effective for public infrastructure, paving the way for their practical use for a better daily life.
