Space-coiling metamaterials with double negativity and conical dispersion

Abstract

Metamaterials are effectively homogeneous materials that display extraordinary dispersion. Negative index metamaterials, zero index metamaterials and extremely anisotropic metamaterials are just a few examples. Instead of using locally resonating elements that may cause undesirable absorption, there are huge efforts to seek alternative routes to obtain these unusual properties. Here, we demonstrate an alternative approach for constructing metamaterials with extreme dispersion by simply coiling up space with curled channels. Such a geometric approach also has an advantage that the ratio between the wavelength and the lattice constant in achieving a negative or zero index can be changed in principle. It allows us to construct for the first time an acoustic metamaterial with conical dispersion, leading to a clear demonstration of negative refraction from an acoustic metamaterial with airborne sound. We also design and realize a double-negative metamaterial for microwaves under the same principle.

High transmission acoustic focusing by impedance-matched acoustic meta-surfaces

“…q 0 and c 0 denote the mass density and wave velocity of water. In the literature, various homogenization schemes have been developed to characterize the effective medium properties of structures associated with coiling-up spaces, such as an S-parameter retrieval method 30 and parameter retrieval method. 8,31 Here, we will analytically explore the effective medium properties of the coiling-up space from coupled-mode theory.…”

Air transparent soundproof window

“…The thickness of the window could be very thin if a curved air passage is used. 23 The measurement of the sound transmission loss using small chambers was carried out in accordance with the test standards for large reverberation chambers: ISO 10140:2010 and ASTM E 90:2004. The test facility, called a 'mini-chamber', consists of two adjacent reverberant chambers with a test opening between them in which the test specimen is inserted.…”

Design of double negativity elastic metamaterial

“…Although a number of double negativity (DN) acoustic metamaterials have been investigated [7][8][9][10][11][12][13][14][15], there are few reports in literature on DN elastic metamaterials. Among the elastic metamaterials that have been published, Wang theoretically investigated the mechanism of negative mass and/or negative modulus of lumped mass models [16].…”