Innovative Materials for Electric Vehicles: Addressing NVH Challenges in a Silent Racing Environment

The advancement of electric vehicle (EV) technology has led to the gradual diminishing of the noise-shielding effects typically provided by traditional internal combustion engines. As a result, electric vehicles are now facing new acoustic challenges, including road noise, high-frequency motor noise, and electromagnetic interference. Concurrently, user expectations for quietness inside the vehicle are increasing. These changes are profoundly reshaping the design concepts of automotive acoustic materials and systems.

In this context, Dow has leveraged its extensive expertise in polymer materials and acoustic engineering to develop a diverse material system. This includes virtual simulation and testing facilities to explore a closed-loop system that encompasses everything from product design to recycling, driving acoustic solutions towards greater efficiency, lighter weight, and sustainability. We will analyze the restructuring of acoustic demands brought about by the transition to electric vehicles, focusing on material research and development, testing capabilities, collaborative innovation, and sustainability strategies, while assessing the evolution of acoustics and materials.

1. The Electrification Trend Drives Acoustic System Transformation

The New Challenges Following the Phase-Out of Internal Combustion Engine Noise

The noise structure of vehicles is undergoing a fundamental change. In traditional gasoline vehicles, the engine is the primary noise source, particularly during acceleration and under heavy load, which masks mid-to-high frequency noises such as road noise and wind noise. However, in electric vehicles, the mechanical sounds from the power system are significantly reduced, making previously masked sound sources more audible. Data shows that in traditional vehicles, noise from the power system can account for 50% of total vehicle noise, whereas in electric vehicles, this figure drops to 15%. Consequently, noise generated from tire-road friction and wind resistance has become more dominant.

This shift presents challenges to traditional acoustic design strategies, which can no longer rely solely on soundproofing the engine compartment. Instead, comprehensive coverage of various vehicle body parts is required, with precise control over different frequency bands of noise. Additionally, electromagnetic noise from the electric drive system—such as sound and vibration interference caused by inverters and high-frequency motors—not only has complex propagation paths but may also interfere with onboard electronic systems, demanding higher shielding performance from materials.

Increased User Expectations Aligned with System Complexity

Today’s electric vehicle consumers expect more than just “noise reduction”; they seek an “optimized sound experience.” This expectation is linked not only to luxury and driving comfort but also directly impacts the accuracy of advanced driver-assistance systems (ADAS) and voice interactions. In scenarios involving assisted or fully autonomous driving, clear communication of voice prompts, passenger interactions, and even subtle alert signals becomes critical, placing refined demands on noise shielding in specific frequency ranges.

The trend towards lightweight electric vehicles means that any additional soundproofing materials must minimize weight to avoid negatively affecting driving range. Furthermore, the increasing integration and platform development in vehicle design require that acoustic systems are not merely treated as “localized enhancements” but must be part of a larger system engineering approach.

2. Systematic Acoustic Solution Pathways

Based on its chemical and materials platform, Dow has developed a diverse acoustic material system that covers multiple frequency bands and adapts to various vehicle body structures. Key breakthroughs include:

• Functional Polyurethane Foam (PU Foam): By controlling the foam pore structure (open/closed cell ratio, pore size distribution) and foam density, the optimization of sound absorption capabilities in the mid-to-low frequency range can be achieved. High-damping foam used in parts like dashboards, carpets, and door panels can convert vibrational sound waves into thermal energy, significantly enhancing quietness in the passenger area.
• Elastomer Materials (such as EPDM, POE): These are used to build sealing systems and acoustic gaskets, balancing sound insulation, waterproofing, and thermal stability, suitable for complex areas like doors and chassis.
• Multilayer Composite Structures: Dow has developed multilayer material combinations with varying acoustic impedance to meet specific sound wave reflection/absorption needs. For instance, combining sound-absorbing materials with sound barriers can achieve superior attenuation performance in the 400Hz-4000Hz range, effectively addressing wind noise and high-frequency motor whine.

This material design approach not only emphasizes the sound absorption capabilities of the materials themselves but also focuses on their coupling characteristics with the vehicle structure, reflecting an evolution from “passive control” to “active tuning.” Globally, Dow has established multiple ISO-standard acoustic laboratories capable of testing acoustic performance at various levels, from single materials to complete vehicle components.

These tests include, but are not limited to:

• Sound absorption coefficient and sound insulation index tests in semi-anechoic chambers;
• Quantitative analysis of sound transmission and reflection rates through material structures using impedance tubes;
• Modeling material sound-induced vibration responses using excitation systems;
• Measurement of reflection and scattering patterns in reverberation chambers to analyze composite materials’ behavior in complex sound fields.

By integrating simulation technologies, Dow can conduct virtual testing and screening of up to 60,000 material combinations, reducing development cycles. Comparing virtual prototypes with real prototypes further enhances the accuracy of modeling tools, providing a reliable database to support subsequent computer-aided engineering (CAE) simulations.

Sustainability strategies focus on the following three areas:

• Closed-loop Material Management: Through physical/chemical recycling processes, production waste and materials from retired vehicles are converted into recycled raw materials. For example, using Dow’s proprietary binder system, cutting waste can be re-bonded to create new materials, reducing raw material consumption.
• Lightweight Design: The developed sound-absorbing foam materials are lighter than traditional soundproofing layers, reducing overall weight by approximately 10-30%, which significantly optimizes vehicle quality and energy efficiency.
• Carbon Footprint Control: During material formulation and production processes, low-carbon materials and green technologies are prioritized to comply with the carbon requirements of supply chains in Europe and the U.S.

This system not only meets regulatory and customer requirements but also provides a replicable pathway for other companies in the supply chain to develop low-carbon acoustic materials. Numerous global automotive original equipment manufacturers (OEMs) and tier-one suppliers have established collaborative R&D relationships, engaging in acoustic planning during the new vehicle platform design phase and participating in acoustic simulations, platform co-development, and material selection:

• Adding dedicated sound-absorbing structures between the battery pack cover and the vehicle floor to control structural noise from the electric drive system;
• Designing sound-absorbing spaces in areas like the front hood and wheel arches to achieve co-modal control of materials and vehicle structure;
• Involvement in acoustic zone delineation for electrified platforms like MEB and PPE, ensuring targeted material usage.

This proactive “pre-installation development” approach is gradually replacing the past reactive strategy of “remedying issues after they arise,” marking a necessary direction for modern automotive acoustic engineering.

Conclusion

The shift to electrification is not only reshaping vehicle power systems but also presenting unprecedented challenges and opportunities for acoustic engineering. In response to more complex noise sources and heightened comfort expectations, traditional solutions are increasingly inadequate. Cross-disciplinary collaboration and systematic thinking are essential. The control of low-frequency road noise demands higher material performance and spatial adaptability, while managing high-frequency electromagnetic noise necessitates deep integration with electronic control systems. Additionally, in the broader context of sustainability, achieving efficient recycling of acoustic materials while maintaining cost balance remains a challenge that the entire industry chain must collectively overcome.