We examine the effectiveness of the ground-plane invisibility cloak generated from quasiconformal mapping of electromagnetic space. This cloak without anisotropy will generally lead to a lateral shift of the scattered wave, whose value is comparable to the height of the cloaked object, making the object detectable. This can be explained by the fact that the corresponding virtual space is thinner and wider than it should be. Ray tracing on a concrete model shows that, for a bump with a maximum height of 0.2 units to be hidden, the lateral shift of a ray with 45° incidence is around 0.15 units.

Lateral Shift Makes a Ground-Plane Cloak Detectable

We present a surface integral equation (SIE) solution for a special class of anisotropic media, whose permittivity and permeability are both symmetric full tensors with the same or multiple values. This kind of media is generated from the invisible cloaking or absorbing material of a perfectly matched layer (PML) design. A new derivation based on the potential functions is presented to obtain the closed-form Green’s function. Detailed and rigorous proofs of some vector identities are given for the first time. Special treatments are detailed to address the singularity of the anisotropic Green’s function for discretizing the SIE. Numerical experiments validate the accuracy, stability, and high efficiency of the proposed solution compared with the analytical solution or the finite element-boundary integral (FE-BI) method. 

Surface Integral Equation Solutions for Electromagnetic Scattering From a Special Class of Anisotropic Media

Based on the theory of transformation optics (TO), a new and simple method for generating multimodal orbital angular momentum (OAM) carrying beams in 3-D space is proposed in this letter. The proposed 3-D arbitrary-way multimodal OAM generator only requires an electric dipole as the source. It consists of a four-way plane waves converter and four multimodal OAM generators. Since this method only requires the operation of radial scaling map, different topological charge modes can be easily obtained by appropriately setting the sizes of the physical geometries.

A Method to Design Arbitrary-Way Multimodal OAM Generator

Based on transformation optics, a simple and efficient strategy to design 3-D electromagnetic and optical devices is proposed. Using this new method, the materials required are isotropic and free of any singularity or zero value as long as the transformed domains in the virtual and physical spaces are finite. Three electromagnetic devices are designed and illustrated to verify this method. In order to avoid using a magnetic material which is a significant barrier in fabrication, the results are also tested when absorbing the magnetic permeability of the transformed material inside the permittivity. This is the first time to guarantee the obtained materials are all isotropic by transformation optics in 3-D problems. Therefore, the proposed method offers great potential in designing novel 3-D electromagnetic and optical devices, which will make these designed 3-D devices easier to fabricate in practical implementations.

The Scaling Transformation Optics With Isotropic Medium

Unmanned-aerial-vehicle (UAV)-aided data collection for Internet of Things applications has attracted increasing attention. This paper investigates motion planning for UAV collecting low-power ground sensor node (SN) data in a dynamic jamming environment. We targeted minimizing the flight energy consumption via optimization of the UAV trajectory while considering the indispensable constraints which cover the collection data demodulation threshold, obstacle avoidance, data collection volume, and motion principle. Firstly, we formulate the UAV-aided data collection problem as an energy consumption minimization problem. To solve this nonconvex optimization problem, we rewrite the original problem by introducing relaxation variables and constructing equivalence constraints to obtain a new relaxation convex problem, which can be solved iteratively using the successive convex approximation (SCA) method. However, SCA is susceptible to initial values, especially in dynamic environments where fixed initial values may lead to a wide range of results, making it difficult to obtain a truly optimal solution to the optimization problem. To solve the initial value problem in dynamic environments, we further propose a communication-flight-corridor(CFC)-based initial path generation method to improve the reliability and convergence speed of the SCA method by constructing reliable communication regions and resilient secure paths in real time. Finally, simulation results validate the performance of the proposed algorithm compared to the benchmark algorithms under different parameter configurations.

https://www.mdpi.com/2079-9292/12/8/1841/pdf?version=1681351618

Motion Planning in UAV-Aided Data Collection with Dynamic Jamming

The invention discloses a novel method for improving broadband OAM directivity, and relates to an artificial electromagnetic device. A three-dimensional zoom transformation optical method is provided,and the novel method for improving broadband OAM directivity comprises the following steps of: respectively segmenting a three-dimensional region before and after transformation according to a solidangle, and respectively applying three-dimensional zoom transformation optics to corresponding sub-regions obtained by segmentation; designing a cylindrical convergent lens, converting a Mongolian yurt-shaped area in a virtual space, calculating material parameters of the cylindrical convergent lens in a physical space, and respectively simulating convergence effects when the filling material of the convergent lens is magnetic and non-magnetic when the convergent lens works at a single frequency point; verifying the convergence effect of the convergent lens working on a broadband; providing afeasible manufacturing method for the designed convergent lens, segmenting the convergent lens to ensure materials of all segmented sections are uniform, then filling the sections with dielectric materials, and verifying convergence characteristics; and arranging the convergent lens above the antenna array generating OAM wave beams, so that the OAM directivity of the broadband can be improved.

Chen Xie

Papers

The Scaling Transformation Optics With Isotropic Medium

Motion Planning in UAV-Aided Data Collection with Dynamic Jamming

Novel method for improving broadband OAM directivity

A Method to Design Arbitrary-Way Multimodal OAM Generator