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Composite Materials with Negative Elastic Constants

It is very difficult to shield low frequency sound waves. This is mainly because in order to cause wave scattering or reflection, the usual wisdom is that the size of the scatterers must be on the order of the wavelength. Since low frequency sound has long wavelength, it follows that the shielding materials would have to be either very thick or very soft. However, while thick shielding is generally impractical, very soft materials are by definition structurally weak, and hence would have limitations as to their practical use.

A newly invented composite material possess one or multiple low frequency ranges where the effective elastic constants are negative. The implication of the negative elastic constants is that the elastic waves in those frequency ranges would be unable to propagate in such composite materials, i.e., the waves would be evanescent in nature. In this invention, the elastic constants are negative only within designed frequency ranges. With these novel composites, as long as the low frequency sound falls within the negative elastic constants frequency ranges, it can be very effectively shielded within a thin layer of the material, which can nevertheless be structurally strong.
Technology Benefits
1. Shielding low frequency sound with only a thin layer of the composites
2. Cost effective
Technology Application
- Shielding of low frequency sound
- Fabrication of elastic wave guides
- Elastic wave reflectors
Supplementary Information
Patent Number: US6576333B2
Application Number: US199854532A
Inventor: Sheng, Ping | Xiao, Rongfu | Wen, Weijia | Liu, Zheng You
Priority Date: 3 Apr 1998
Priority Number: US6576333B2
Application Date: 3 Apr 1998
Publication Date: 10 Jun 2003
IPC Current: B29C007060 | G10K0011165
US Class: 428323 | 428327 | 428328 | 428378 | 428403 | 428407
Assignee Applicant: The Hong Kong University of Science & Technology
Title: Composite materials with negative elastic constants
Usefulness: Composite materials with negative elastic constants
Summary: The composite material is used for low frequency sound reflection, absorption or sound insulation. It also used in the fabrication of elastic wave guides and elastic wave reflectors.
Novelty: Composite material for use in low frequency sound reflection, comprises matrix material, zones of soft elastic material and embedded zones of solid, high density and high rigidity material
Sub Category
Chemical/Material Application
Application Date
3 Apr 1998
Application No.
US 09/054532
Patent Information
US 6576333
ID No.
Hong Kong

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