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Arthur T Knackerbracket has found the following story:

"If you want to hide something in solid media, this is different," [professor Guoliang] Huang said. "In solid media, the wave is more complicated than the radar wave because in solid media we not only have a compression wave but we also have a shear wave. In civil engineering, we deal with earthquakes—seismic waves, which have longitudinal and shear waves, and most of the damage is cause by the shear wave."

Huang said there is no natural material that satisfies the long-standing problem of transformation-invariance, wherein non-standard properties are needed after certain transformations. He said the ultimate purpose of his research is to model, design and fabricate materials that will fill in this "behavioral gap." The new class of cloaking or polar materials his team created is composed of a functionally graded lattice embedded in an isotropic continuum background. The layers were 3-D printed and manually assembled.

"We experimentally and numerically investigated the characteristics of the proposed cloak and found very good cloaking performance under both tension and shear loadings," Huang wrote in his paper, one of two research papers Huang and his team had published by the Physical Review of Letters on the subject of polar materials.

[...] "The results that the University of Missouri team has recently published are encouraging," said Dr. Dan Cole, program manager, Army Research Office, an element of the U.S. Army Combat Capabilities Development Command's Army Research Laboratory. "This research could lead to new strategies for steering mechanical waves away from critical regions in solid objects, which could enable novel capabilities in soldier protection and maneuvers."

Journal Reference
Xianchen Xu, Chen Wang, Wan Shou, et al. Physical Realization of Elastic Cloaking with a Polar Material, Physical Review Letters (DOI: 10.1103/PhysRevLett.124.114301)

Original Submission