Wisconsin Alumni Research Foundation


UW-Madison Prof. Chu Ma has developed a new type of acoustic functional material that can be assembled as wall panels to achieve indoor sound shaping functions. These include holographic sound enhancement and canceling, acoustic reflected wave steering, focusing and propagating/surface wave conversion. Applications may include home and car audio systems, construction noise control and more.


The sound in a room is a complicated product of waves reflected and scattered off the ceiling, walls and other objects. Changing how those waves interfere with each other offers a way to control a noisy environment and make selected locations much quieter. To precisely control soundwave propagation in a room, scientists have developed acoustic ‘metamaterials’ (generally defined as materials that exhibit properties not found in nature) whose surfaces have mechanical properties designed to reflect, transmit or delay sound waves so that waves manipulated by one part of the material interfere with those manipulated by another part.

However, constructing such metamaterial reflectors can be difficult, and the resulting metamaterial may have a relatively narrow band response, meaning that they work only over a very limited range of frequencies. Both of these drawbacks can limit the use of metamaterials for important commercial applications in the control of audio and other signals.


Prof. Ma’s versatile system provides a simple toolkit for fabricating metamaterial surfaces requiring only two components that can be mixed and matched to achieve the desired sound shaping. It features a pair of reflectors each having a frequency-dependent phase shifting of a reflected waveform but, together, providing a constant phase difference. The new metamaterials are much easier to fabricate and assemble than previous designs. Versatile and easy to manufacture, this technology is suitable for sound isolation in common volumes such as car interiors


The need to control noise and sound in a variety of environments has given rise to a market worth more than $13 billion globally in 2020. This technology differs fundamentally from most available solutions, which cannot be tuned to change performance. In the current market, “other” technologies outside of the mainstream already generate >$230 million in revenues globally. The construction and automotive industries are likely to be the biggest adopters.

Principal Investigator

Learn more about Chu Ma, a 2021 WARF Innovation Award nominee. The annual prize recognizes outstanding disclosures with potential high impact and broad benefit to humankind.


Qin, Zifu, Xiaohan Liu, and Chu Ma. “Acoustic Wave Reflection Control Based on Broadband Differential Phase Shifters.” Frontiers in Mechanical Engineering (2021): 83. https://doi.org/10.3389/FMECH.2021.703019

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