Acoustic seminar | 20 November 2026

Wave propagating in a medium with one or more constitutive parameters vanishing does not accumulate any phase retardation and the medium is the so-called zero-index medium. Such a medium is not mathematically interesting but also bears unusual functionalities, such as wave front engineering, cloaking of objects and wave tunnelling.

In this talk, I will report our progress in realizing three-dimensional (3D) double-zero-index materials for both electromagnetic and acoustic waves. Their intriguing properties, including wave tunneling and cloaking objects, will be discussed. Then I will delve into our recent realization of a 2D double-zero-index material for air borne sound using space-coiling structures. The special features of a space-coiling unit, such as super-anisotropy and degenerate resonance, will also be discussed.

Main paper/arXiv, related to the seminar, and other references

[1] Changqing Xu, et al. Phys. Rev. Lett. 124, 074501 (2020)
[2] Changqing Xu, et al. Phys. Rev. Lett. 127, 123902 (2021)
[3] Changqing Xu, et al. Appl. Phys. Lett. 119, 224102 (2021)
[4] Changqing Xu, et al. Phys. Rev. Appl. 15 054025 (2022)
[5] Keqiang Lyu, et al. Phys. Rev. Appl. 24, 034043 (2025)