Hui Feng Ma

Polarization-independent wide-angle triple-band metamaterial absorber

We report the design, fabrication, and measurement of a microwave triple-band absorber. The compact single unit cell consists of three nested electric closed-ring resonators and a metallic ground plane separated by a dielectric layer. Simulation and experimental results show that the absorber has three distinctive absorption peaks at frequencies 4.06 GHz, 6.73 GHz, and 9.22 GHz with the absorption rates of 0.99, 0.93, and 0.95, respectively. The absorber is valid to a wide range of incident angles for both transverse electric (TE) and transverse magnetic (TM) polarizations. The triple-band absorber is a promising candidate as absorbing elements in scientific and technical applications because of its multiband absorption, polarization insensitivity, and wide-angle response.

Cylindrical-to-plane-wave conversion via embedded optical transformation

We investigate the conversion from cylindrical waves to plane waves in a short range through a metamaterial layer which has a circular shape in the inner outline and a square shape in the outer outline. Based on an embedded optical transformation, analytical formulas of the permittivity and permeability tensors are presented for the metamaterial layer which converts the cylindrical waves to plane waves. The designed conversion materials are validated by full-wave simulations using the finite-element method. The proposed structure can be used either as a four-beam antenna or a compact range for near-field measurement of plane waves.

Dual-band asymmetric transmission of linear polarization in bilayered chiral metamaterial

A bilayered chiral metamaterial is proposed and demonstrated to exhibit dual-band asymmetric transmission of linearly polarized electromagnetic waves in two opposite directions. Simulated and measured results show that the bilayered chiral metamaterial can achieve cross-polarization conversion with an efficiency of over 90% for both y- and x-polarized waves. The proposed metasurface can be regarded as an ultrathin polarization-controlled switch that is easily switched on/off by changing a linearly polarized wave to its orthogonal component.

Three-dimensional broadband and high-directivity lens antenna made of metamaterials

We present the theoretical modeling and prototype demonstration of a three-dimensional broadband, low-loss, dual-polarization, and high-directivity lens antenna using gradient index (GRIN) metamaterials, which is composed of multi-layer microstrip square-ring arrays. The elements of metamaterials, closed square-ring units of variable sizes, are distributed on the planar substrate to satisfy the radial gradient index function and the axial impedance matching layer configuration of the lens. The gradient-index metamaterials are designed to transform the spherical wave-front into the planar wave-front and to minimize the reflection loss. A prototype lens antenna, which consists of a metal conical horn and the gradient-index lens, are simulated, constructed, and measured. The resemblance of simulation and measurement results shows that the prototype lens antenna maintains low return loss and high directivity on the whole X-band (from 8 GHz to 12 GHz). Compared to the traditional horn antenna, the metamaterial...

An ultra-wideband surface plasmonic filter in microwave frequency

We propose an ultra-wideband plasmonic waveguide based on designer surface plasmon polaritons (DSPPs) with double gratings. In such plasmonic metamaterials, the DSPP waves in the region of lower frequencies of the dispersion curve can be tightly confined and hence effectively broaden the operating bandwidth. Based on such features, we design and fabricate a high performance DSPP filter, in which a transducer consisting of microstrip, slotline, and gradient corrugations is employed to feed electromagnetic energies into the plasmonic waveguide with high efficiency. The simulated and measured results on reflection and transmission coefficients in the microwave frequency demonstrate the excellent filtering characteristics such as low loss, wide band, and high square ratio. The high performance DSPP waveguide and filter pave a way to develop advanced plasmonic integrated functional devices and circuits in the microwave and terahertz frequencies.

Ultrathin dual-band surface plasmonic polariton waveguide and frequency splitter in microwave frequencies

We present an ultrathin dual-band plasmonic waveguide and frequency splitter experimentally based on designer surface plasmon polaritons (DSPPs) of planar composite periodic gratings. In such planar plasmonic metamaterials, the electromagnetic wave can be tightly confined around an ultrathin metallic grating, and the propagation of DSPPs strongly depends on the dispersion relation determined by the depth of groove. Based on such features, we design and fabricate an ultrathin composite grating to support two DSPP modes, which exhibit low bending loss in the bending surface plasmon polariton (SPP) waveguide. We further propose an ultrathin SPP frequency splitter by adjusting the groove depths of two branches. The experimental results are in good agreement to the numerical simulations.

Compact-sized and broadband carpet cloak and free-space cloak

Recently, invisible cloaks have attracted much attention due to their exciting property of invisibility, which are based on a solid theory of transformation optics and quasi-conformal mapping. Two kinds of cloaks have been proposed: free-space cloaks, which can render objects in free space invisible to incident radiation, and carpet cloaks (or ground-plane cloaks), which can hide objects under the conducting ground. The first free-space and carpet cloaks were realized in the microwave frequencies using metamaterials. The free-space cloak was composed of resonant metamaterials, and hence had restriction of narrow bandwidth and high loss; the carpet cloak was made of non-resonant metamaterials, which have broad bandwidth and low loss. However, the carpet cloak has a severe restriction of large size compared to the cloaked object. The above restrictions become the bottlenecks to the real applications of free-space and carpet cloaks. Here we report the first experimental demonstration of broadband and low-loss directive free-space cloak and compact-sized carpet cloak based on a recent theoretical study. Both cloaks are realized using non-resonant metamaterials in the microwave frequency, and good invisibility properties have been observed in experiments. This approach represents a major step towards the real applications of invisibility cloaks.

Experiments on high-performance beam-scanning antennas made of gradient-index metamaterials

A planar lens made of gradient index metamaterials can transform cylindrical waves to plane waves, and the beam direction of plane waves is controlled by adjusting the refractive-index distributions of the lens. Based on such properties, we present high-performance beam-scanning antennas experimentally using the gradient-index planar lens and horn antenna. The lens is carefully designed with metamaterials to achieve different refractive indices and good matching of impedance. The near-field distributions of antennas are measured using a two-dimensional near-field microwave scanning apparatus, and the radiation patterns are presented to show the high directivity and low sidelobe.

Illusion media: Generating virtual objects using realizable metamaterials

We propose a class of optical transformation media, illusion media, which render the enclosed object invisible and generate one or more virtual objects as desired. We apply the proposed media to design a microwave device, which transforms an actual object into two virtual objects. Such an illusion device exhibits unusual electromagnetic behavior as verified by full-wave simulations. Different from the published illusion devices which are composed of left-handed materials with simultaneously negative permittivity and permeability, the proposed illusion media have finite and positive permittivity and permeability. Hence the designed device could be realizable using artificial metamaterials.

Shrinking an arbitrary object as one desires using metamaterials

Based on transformation optics, we present a shrinking device, which can transform an arbitrary object virtually into a small-size object with different material parameters as one desires. Such an illusion device will confuse the detectors or the viewers, and hence the real size and material parameters of the enclosed object cannot be perceived. We fabricated and measured a shrinking device by using metamaterials, which works at the nonresonant frequency and has low loss. The device has been validated by both numerical simulations and experiments on circular and square objects. Good shrinking performance has been demonstrated.