Metamaterials are a group of man-made materials engineered to have special properties not usually found in natural materials, for example, a negative refractive index. Through the precise arrangement of micro-scale structures in repeating patterns, metamaterials can lead to amazing inventions. One of the most attractive applications pertaining to metamaterial is the invisibility cloak, which can hide objects from light waves. However, as a theoretical acoustician, Yun Jing focuses on a less fancy but more practical application of metamaterials: making the world a quieter place.
Jing established his fame in the fields of building and medical acoustics during his Ph.D. and postdoc years in Rensselaer Polytechnic Institute and Harvard Medical School. In 2011, Jing began his career at North Carolina State University as an assistant professor. He was fascinated by the underlying physics of acoustic metamaterials and decided to delve into it.
Needless to say, noise control is essential to our modern life. From airports to city streets to side-by-side residential buildings, almost everything around us can be a potential source of noise and therefore a hazard to health. Conventional noise insulation materials, such as acoustic foams, are generally not efficient enough, especially at low frequencies. They are also deficient in mechanics, which is crucial to various applications like airplanes and automobiles.
In 2015, a breakthrough technology arose from Jing’s lab. He and his colleagues invented a noise control metamaterial that is simultaneously lightweight, strong, and efficiently sound-proof for the first time. The secret lies in a special structure – Jing added a thin layer of membrane inside the core of the widely used honeycomb cell structure, making this affordable material capable of bringing down noise by a factor of 1,000. This invention showed great potential to be used in airplanes, trains, cars, and conference rooms.
Later, Jing further improved the material by removing the very same layer of membrane. Specially designed holes in different sizes were added into the honeycomb cell structure and demonstrated near-perfect sound absorption across a broad-band of wave frequencies. This improvement not only further decreased the density of the material by around 5%, but also eliminated a major hurdle for mass production. In less than 5 years, Jing estimates, this revolutionary metamaterial will be ready for the market.