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Jensen Li

Publications and source records attributed to Jensen Li.

61 records · Page 4Linked to original sources
arXiv2012

Space-coiling metamaterials with double negativity and conical dispersion

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 experimentally demonstrate an alternative approach for constructing metamaterials with extreme dispersion by simply coiling up space with curled channels. Such a geometric approach has the advantage that the ratio between the wavelength and the lattice constant in achieving a negative or zero index is easily tunable. 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.

cond-mat.mtrl-sci↗
arXiv2011

Bending a periodically layered structure for transformation acoustics

Anisotropic acoustic metamaterials have been proved very useful for their high potential in guiding and manipulating sound energy. In this paper, we further develop the idea by using periodically layered structures for transformational acoustics. Such a simple scheme periodically inserts identically bent solid plates in a background fluid. It forms a metamaterial with high refractive index normal to the curved plates and an index near to one along the plates. We show that the periodically layered structure, combined with transformation approach, can be cut into particular device shapes for acoustic cloaking and illusion.

cond-mat.mtrl-sci↗
arXiv2009

Dielectric Optical Cloak

Invisibility or cloaking has captured human's imagination for many years. With the recent advancement of metamaterials, several theoretical proposals show cloaking of objects is possible, however, so far there is a lack of an experimental demonstration at optical frequencies. Here, we report the first experimental realization of a dielectric optical cloak. The cloak is designed using quasi-conformal mapping to conceal an object that is placed under a curved reflecting surface which imitates the reflection of a flat surface. Our cloak consists only of isotropic dielectric materials which enables broadband and low-loss invisibility at a wavelength range of 1400-1800 nm.

physics.optics↗
arXiv2008

Chiral Negative-Index Metamaterials in Terahertz

Negative index metamaterials (NIMs) give rise to unusual and intriguing properties and phenomena, which may lead to important applications such as superlens, subwavelength cavity and slow light devices. However, the negative refractive index in metamaterials normally requires a stringent condition of simultaneously negative permittivity and negative permeability. A new class of negative index metamaterials - chiral NIMs, have been recently proposed. In contrast to the conventional NIMs, chiral NIMs do not require the above condition, thus presenting a very robust route toward negative refraction. Here we present the first experimental demonstration of a chiral metamaterial exhibiting negative refractive index down to n=-5 at terahertz frequencies, with only a single chiral resonance. The strong chirality present in the structure lifts the degeneracy for the two circularly polarized waves and relieves the double negativity requirement. Chiral NIM are predicted to possess intriguing electromagnetic properties that go beyond the traditional NIMs, such as opposite signs of refractive indices for the two circular polarizations and negative reflection. The realization of terahertz chiral NIMs offers new opportunities for investigations of their novel electromagnetic properties, as well as important terahertz device applications.

physics.optics↗
arXiv2008

Hiding Under the Carpet: a New Strategy for Cloaking

A new type of cloak is discussed: one that gives all cloaked objects the appearance of a flat conducting sheet. It has the advantage that none of the parameters of the cloak is singular and can in fact be made isotropic. It makes broadband cloaking in the optical frequencies one step closer.

physics.optics↗
arXiv2007

Non-local effective medium of metamaterial

In this paper, we investigate the effect of spatial dispersion on a double-lattice metamaterial which has both magnetic and electric response. A numerical scheme based on a dipolar model is developed to extract the non-local effective medium of the metamaterial. We found a structure-induced bianisotropy near the resonance gap even if the artificial particles are free from cross-coupling. A cross-coupled resonance also results from spatial dispersion and it can be understood using a Lorentz frequency dispersion model. The strength of the cross-coupled resonance depends on the microstructure and it is larger at a higher normalized frequency.

cond-mat.mtrl-sci↗