Anomalous acoustic propagation (negative group velocity, negative refraction, etc.) is a type of unique and interesting phenomena. Previously, this type of phenomena has been observed in isotropic plates and circular tubes. Recently, researchers have developed artificial periodic materials with these characteristics to achieve applications such as super-resolution imaging. As a typical two-dimensional periodic structure, honeycomb structures are widely used in aerospace, transportation, and other fields due to their excellent performance. However, research on the acoustic propagation characteristics within honeycomb structures remains insufficient, which somewhat limits their further applications in acoustics and the development of new technologies for detecting their acoustic properties.

Researchers from the Institute of Acoustics of the Chinese Academy of Sciences (IACAS) have discovered that the flexural wave modes of typical nickel-based high-temperature alloy brazed honeycomb structures exhibit negative group velocity (NGV) feature. It is noticed that this feature only appears within the first half of the honeycomb unit area, while the group velocity becomes normal in the second half. Through analysis, it is believed that the NGV feature arises from the repulsion between the skin’s localized resonance modes of different orders within the same family. The researchers further explored the potential applications of this feature in the detection skin-core debonding defects in honeycomb structures. Experimental results indicate that when acoustic waves propagate through the debonding area, the NGV feature disappears; however, away from the debonding area, this feature reappears in the intact area. Therefore, such NGV feature has potential application value in detecting debonding defects of honeycomb structures.

The research was published online in Applied Physics Letter on January 13, 2025.

Figure 1. Schematic of the negative group velocity feature in a honeycomb structure. (Image by IACAS)

Figure 2. Variation of group velocity feature in Intact area - Debonding area – Intact area. (Image by IACAS)

Reference:

Yuan Ye, Liu Bin, Jia Han, Zhang Zhiguo. Observation of uncommon elastic wave group velocity in common honeycomb structure and its potential for debonding detection. Applied Pyhsics Letters, 126, 022202 (2025). DOI: 10.1063/5.0237493.

Contact:

ZHOU Wenjia

Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China

E-mail: media@mail.ioa.ac.cn