New metamaterial can simultaneously reduce noise and increase ventilation

Metamaterials are engineered artificial materials designed to fabricate devices with properties superior to their constituent materials. By placing orifices within an ultrathin plastic polymer, Wang et al. developed what they call a perforated and constrained acoustic metamaterial (PCAM) that can simultaneously provide fluid ventilation and sound insulation within a specific frequency band.

Each unit cell of PCAM consists of a perforated polyetherimide plate supported by a steel constraint stick. The constraint stick enhances the durability of the cell, and orifices on the stick allow for airflow through the polyetherimide’s perforations. As fluid and sound propagate through PCAM, the orifices produce pressure fluctuations in the fluid and allow some sound waves to travel through while reflecting others. As a result, the perforation ratio of the plates can be fine-tuned for specific applications, as increasing the perforation size will improve PCAM’s ventilation properties but weaken its sound insulation.

According to test results, the <2 mm thick PCAM can block 99% of the noise energy at its peak operating frequency of 430 hertz, and 19% of all noise between 360 and 520 hertz. The peak operating frequency can be easily adjusted without affecting PCAM’s ventilation capabilities by simply changing the thickness of the polyetherimide plates.

“Most of the noise emitted by machines and equipment is concentrated below 500 hertz,” said author Xiaole Wang. “Thus, noise reduction around 400 hertz is suitable as a typical application example.”

The authors note a number of practical applications of PCAM. For example, PCAM can be used to replace the back panel of a refrigerator’s compressor chamber, ensuring normal heat dissipation while reducing the amount of noise generated.

Source: “Ultrathin and durable open metamaterials for simultaneous ventilation and sound reduction,” by Xiaole Wang, Xudong Luo, Bin Yang, and Zhenyu Huang, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5121366 .