The programmable and digital metamaterials or metasurfaces presented recently have huge potentials in designing real-time-controlled electromagnetic devices. Here, we propose the first transmission-type 2-bit programmable coding metasurface for single-sensor and single- frequency imaging in the microwave frequency. Compared with the existing single-sensor imagers composed of active spatial modulators with their units controlled independently, we introduce randomly programmable metasurface to transform the masks of modulators, in which their rows and columns are controlled simultaneously so that the complexity and cost of the imaging system can be reduced drastically. Different from the single-sensor approach using the frequency agility, the proposed imaging system makes use of variable modulators under single frequency, which can avoid the object dispersion. In order to realize the transmission-type 2-bit programmable metasurface, we propose a two-layer binary coding unit, which is convenient for changing the voltages in rows and columns to switch the diodes in the top and bottom layers, respectively. In our imaging measurements, we generate the random codes by computer to achieve different transmission patterns, which can support enough multiple modes to solve the inverse-scattering problem in the single-sensor imaging. Simple experimental results are presented in the microwave frequency, validating our new single-sensor and single-frequency imaging system.

Scaling devices that can shrink or enlarge an object are designed using transformation optics. The electromagnetic scattering properties of such scaling devices with anisotropic parameters are rigorously analyzed using the eigenmode expansion method. If the radius of the virtual object is smaller than that of the real object, it is a shrinking device with positive material parameters; if the radius of the virtual object is larger than the real one, it is an enlarging device with positive or negative material parameters. Hence, a scaling device can make a dielectric or metallic object look smaller or larger. The rigorous analysis shows that the scattering coefficients of the scaling devices are the same as those of the equivalent virtual objects. When the radius of the virtual object approaches zero, the scaling device will be an invisibility cloak. In such a case, the scattering effect of the scaling device will be sensitive to material parameters of the device.

We propose and design a kind of annular focusing lens based on transformation optics. Based on the method of eigen-mode expansions, closed-form expressions are derived to analyze the proposed annular lens rigorously. We show that the annular lens has excellent focusing property. Even when a barrier (such as a conducting cylinder) exists in the center of the lens, the analytical results demonstrate that the waves are still guided to propagate smoothly and focused on a spot.

We propose an illusion device that transforms a metallic cylinder into a Luneburg lens by using transformation optics. Such a transformed focusing lens guides electromagnetic waves to propagate around the central metallic cylinder smoothly and be focused on one spot, and thus the information of an object behind the obstacle can be transmitted to infinity. In order to realize the required-anisotropic parameters with high permittivity and low permeability, we design embedded split-ring resonators (SRRs) to increase the permittivity of the traditional SRR structures. In experiments, we fabricate and measure the transformed lens, and the tested results agree well with the numerical simulations and theoretical predictions. The proposed transformation lens can mimic some properties of Einstein gravitational lens because their wave propagation behaviors are very similar.

Abstract:The super energy flows generated and transmitted have been investigated in a parallel-plate waveguide, which is filled with air and the anisotropic left-handed materials. Theoretical analysis and numerical simulations show that the propagation modes of the anisotropic super waveguide are consistent with those of the isotropic waveguides [1][2][3]. They also show that the loss of electromagnetic parameters size of waveguide will influence the amplitude of time-average power flows.PACS (2008)