Modeling the interaction between light and a plasmonic nanoantenna, whose critical dimension is of a few nanometers, is complex owing to the “hydrodynamic” motion of free electrons in a metal. Such a hydrodynamic effect inevitably leads to a nonlocal material response, which enables the propagation of longitudinal electromagnetic waves in the material. In this work, within the framework of a Boundary Integral Equation (BIE) and the a Method of Moments (MoM) algorithm, a computational scheme is developed for predicting the interaction of light with three-dimensional nonlocal hydrodynamic metallic nanoparticles of arbitrary shape. The numerical implementation is first demonstrated for the test example of a canonical spherical structure. The calculated results are shown to be in the excellent agreement with the theoretical results obtained with the generalized Mie theory. Additionally, the capability of treating 3D structures of general shapes is demonstrated by gradually deforming the sphere into ellipsoids.

The emergence of space-time modulated metasurface (STMM) as a novel platform for signal modulation holds significant promise for wireless secure communication, particularly within modern information technologies such as Internet of things and the 5th generation and beyond. While previous secure communication methods based on STMM have primarily focused on ensuring information security within both the time and frequency domains, in this study, we introduce a novel code domain modulation scheme in STMM to facilitate wireless secure communications, which is difficult to be detected in both time and frequency domains. The core concept involves synthesizing a smart modulation waveform by using a new code domain so that both secure information transmission and mitigation of jamming are realized. To achieve this, we build a Q-dimensional signal space that has a minimum overlap with the jamming signal space and where orthogonal or quasi-orthogonal basis functions are used for information transmission. Furthermore, this methodology can be readily extended to other abstract signal domains. To exemplify this approach, we implement an STMM and utilize it to transmit the logos of our universities accurately, while eavesdroppers are unable to acquire any useful information through direct identification from the constellation diagrams. This showcases the effectiveness of the proposed secure communication system.

The interaction between light and plasmonic systems with deep‐nanometer characteristics, which is essentially governed by quantum mechanical effects, has been extensively studied by the nonlocal hydrodynamic approach. Several hydrodynamic models, supplemented by additional boundary conditions, have been introduced in order to describe the collective motion of the free electron gas in metals. Four hydrodynamic models, namely the hard wall hydrodynamic model (HW‐HDM), the curl‐free hydrodynamic model, the shear forces hydrodynamic model, and the quantum hydrodynamic model (Q‐HDM), are thoroughly investigated. The investigation studies the mode structure (the natural modes or, in quantum optics, the quasi‐normal modes) of the spherical core–shell topology, which is complemented by the plane wave response from the system. The results of the above hydrodynamic models are also compared with those of the specular reflection method. It is demonstrated that the choice of a particular hydrodynamic model strongly affects the natural frequencies and modes in the mode structure of the topology and thus drastically modifies the simulated fields in the near and far regions. Contrary to HW‐HDM and Q‐HDM, the other two hydrodynamic models fail to predict the particles’ response accurately, showing artifactual mode hybridization.

An innovative wireless power transfer (WPT) system utilizing millimeter wave (mmWave) power for multi-node charging and tracking is presented in this paper. The core concept of the system revolves around the utilization of frequency-dispersive leaky-wave antenna transmitters, enabling passive beam scanning in the far-field without the need for active phased arrays. However, such a system requires a breakthrough in receiving rectenna design at mmWave frequencies, encompassing a wide frequency bandwidth, wide beam width, and high RF-DC conversion efficiency beyond 20 GHz. In this work, we introduce a pioneering mmWave rectenna design achieved through the co-design integration of a magnetoelectric dipole and high-frequency diodes, eliminating the need for complex impedance matching networks at mmWave frequencies. The proposed rectenna operates in the frequency range of 24-34.5 GHz, achieving over 50% RF-DC conversion efficiency for input powers exceeding 15 dBm. Additionally, the rectenna demonstrates improved gain and beamwidth compared to conventional designs, enabling wide-angle reception of frequency-scanning passively beamformed mmWave signals. A practical demonstration of the proposed system showcases simultaneous wireless charging of three nodes, highlighting its notable advantages in terms of mobility, cost-effectiveness, and simplicity over conventional WPT technologies.

In this work, we propose a general boundary integral equation (BIE) approach for solving both the exterior (e.g., scattering) and interior (e.g., guided wave propagation) problems involving general plasmonic waveguiding structures with arbitrary cross-sectional geometries and with a continuous translational symmetry in the direction of wave propagation. In contrast to the field-based approach which deals with the electric and magnetic fields, we employ a potential-based formalism instead, involving vector and scalar potentials, and match them at the media interfaces. The proposed approach can not only handle conventional plasmonic waveguides on the order of a few hundred nanometers, but also those whose critical sizes are a few nanometers and in which the nonlocal hydrodynamic effects need to be accounted for. The BIEs describing the interaction of light with the plasmonic waveguide are solved by the Method of Moments (MoM) algorithm. Two illustrative examples, the first one of which deals with the scattering problem while the second computes the dispersion diagram of a plasmonic cylinder, are considered for both local and nonlocal cases. An excellent agreement is observed between the numerical and theoretical results, with the latter being derived from the generalized Mie theory.