By using a phased electromagnetic dipole array to model a moving charged particle, we experimentally verified a reversed Cherenkov radiation in the left-handed media in the frequency range from 8.1 to 9.5 GHz. Our results demonstrate the feasibility of new types of particle detectors and radiation generators. DOI: 10.1103/PhysRevLett.103.194801 PACS numbers: 41.60.Bq, 41.20.Jb In 1934, Cherenkov discovered experimentally the coherent radiation when some media were bombarded by fast-moving electron beams [1]. Frank and Tamm established the theory of Cherenkov radiation (CR) in the framework of classical electrodynamics in 1937 [2]. The theory shows that CR will radiate only when the speed of the charge is larger than the speed of light in the medium. Since then, CR has been widely applied in high-energy physics. One of the important applications is Cherenkov counters, which are used to determine various properties of a charged particle such as its velocity, charge, direction of motion, and energy. These properties are important in the identification of different particles. The discovery of antiproton [3] is a good example of the application of CR, as well as the discovery of the J particle [4], in which Chen designed the six large Cherenkov counters.In conventional media, the radiation angle of CR c , which is the angle between the direction of wave propagation and charge velocity, is always between 0 and 90 . Thus, the charged particle will interfere with the detection of the forward radiated waves. In 1968, Veselago predicted the abnormal reversed Cherenkov radiation in the lefthanded metamaterials (LHMs) with simultaneously negative permittivity and permeability [5], allowing the backward emitted wave to be easily separable from the emitting particles. More theoretical frameworks have been proposed since then [6]. The first experimental attempt using a beam of charged particles with metamaterials was carried out in a waveguide [7]. Although the result cannot be decisively concluded as a backward CR, the observation of the transmission peak in the left-handed band is an indirect observation of the wakefield generation [7]. In short, experimental verification of backward CR is still very rare. The lack of LHMs for transverse magnetic (TM) polarized waves has been one of the main obstacles. Because of the rotational symmetry of the cylindrical configuration for CR, the experimental verification of the reversed CR requires metamaterials for transversely magnetic polarized waves, which requires negative permeability along the direction and negative permittivities along the and z directions. Since Pendry et al. first showed that the metallic rod arrays [8] and the split-ring resonators (SRRs) [9] exhibited negative permittivity and negative permeability, respectively, most of the LHMs realized so far have been for transverse electric (TE) polarized waves [10], which is not suitable for backward CR detection. The second reason is that the radiation power of CR increases with its frequency; therefore, the optical ...

We experimentally demonstrated an alternative approach of invisibility cloaking that can combine technical advantages of all current major cloaking strategies in a unified manner and thus can solve bottlenecks of individual strategies. A broadband cylindrical invisibility cloak in free space is designed based on scattering cancellation (the approach of previous plasmonic cloaking), and implemented with anisotropic metamaterials (a fundamental property of singular-transformation cloaks). Particularly, nonsuperluminal propagation of electromagnetic waves, a superior advantage of non-Euclidian-transformation cloaks constructed with complex branch cuts, is inherited in this design, and thus is the reason of its relatively broad bandwidth. This demonstration provides the possibility for future practical implementation of cloaking devices at large scales in free space.

The coordinate transformation by using form-invariant transformations of Maxwell equations has led to an approach for designing devices with anisotropic metamaterial. In this paper, we present the design methodology for a low profile planar focusing antenna based on the transformation of a parabolic antenna. The electromagnetic behavior of the planar antenna is simulated by a two-dimensional finite element method and the results show that the planar antenna has the same performances as the parabolic antenna. The coordinate transformation technology provides an alternative design method to the conventional antennas.

We apply coordinate transformations in the design of waveguides with bent geometry to reduce reflection at the incident port. It was found that in the case of metallic waveguides, by applying the transformation to the medium inside a right-angle bent waveguide, low reflection can be obtained. For the case of dielectric waveguides, this can also be done by applying the same transformation to the bent region containing both the dielectric core and its claddings. Our proposed technique provides an alternative method for designing bent waveguides with low insertion loss.