Metasurfaces, the two-dimensional counterpart of metamaterials, have caught great attention thanks to their powerful capabilities on manipulation electromagnetic waves. Recent times seen emergence a variety metasurfaces exhibiting not only countless functionalities, but also reconfigurable response. Additionally, digital or coding revolutionized field by describing device as matrix discrete building block states, thus drawing clear parallelisms with information theory and opening new ways...

Inspired by the information theory, a new concept of re-programmable encrypted graphene-based coding metasurfaces was investigated at terahertz frequencies. A channel-coding function proposed to convolutionally record an arbitrary message onto unrecognizable but recoverable parity beams generated phase-encrypted metasurface. single reflective cell with dual-mode biasing voltages designed act as "0" and "1" meta-atoms, providing broadband opposite reflection phases. By exploiting graphene...

Abstract Here, for the first time, real‐time and broadband manipulation of terahertz (THz) waves are acquired by introducing a multifunctional graphene‐based coding metasurface (GBCM). The designed structure consists subwavelength patterned graphene units whose operational statuses can be dynamically switched between two digital states “0” “1”. By engineering spatial distribution chemical potentials across GBCM, various scattering patterns having single, two, four, numerous reflection beams...

Recent emergence of metasurfaces has enabled the development ultra-thin flat optical components through different wavefront shaping techniques at various wavelengths. However, due to non-adaptive nature conventional metasurfaces, focal point resulting optics needs be fixed design stage, thus severely limiting its reconfigurability and applicability. In this paper, we aim overcome such constraint by presenting a reflective component that can reprogrammed focus terahertz waves desired in...

Abstract As one of the cutting-edge technologies in advanced information science, wave-based cryptography is a prerequisite to enable plethora secure encrypting platforms which can be realized by smart multiplexing techniques together with suitable metasurface holograms (meta-holograms). Here, relying on polarization multiplicity and re-writability computer-generated meta-hologram, fully communication protocol elaborately developed at terahertz spectrum host unique merits for exploring...

In the past few years, analog computing has experienced rapid development but mostly for a single function. Motivated by parallel space-time and miniaturization, we show that reconfigurable graphene-based multilayers offer promising path towards spatiotemporal with integrated functionalities properly engineering both spatial- temporal-frequency responses. This paper employs tunable multilayer to enable signal image processing in space time tuning external bias. first part of paper, propose...

Digital metasurfaces have opened unprecedented ways to accomplish novel electromagnetic devices thanks their simple manipulation of waves. However, the leveraging phase-only or amplitude-only modulation restricted full-functionality control devices. Herein, a digital graphene-based engineering wavefront amplitude and phase are proposed for first time tackle this challenge in terahertz (THz) band. The concept its significance verified using reprogrammable multi-focal meta-lens based on...

Digital Metasurfaces have recently offered tremendous opportunities in real-time manipulation of terahertz (THz) waves programmable ways to reach special applications that cannot be achieved using conventional architectures. Unlike the previous demonstrations at this spectrum, which only exploit spatial modulation, paper, we propose a spatiotemporally modulated graphene-based digital metasurface (STGDM) carry out different missions both space and frequency domains. Applying proper...

The non-Hermitian electro-optic (EO) effect in materials with Berry-curvature dipoles (BDs) is important for applications like terahertz lasing. This study shows that a stack of low-symmetry two-dimensional inside cavity supports nonreciprocal growing mode, which generates an unstable resonance leads to self-sustained oscillations. It also found the chiral nature Berry-dipole gain can control laser's handedness, enhancing design lasers.

A simple and fast model for numerically calculating small-signal gain in serpentine waveguide traveling-wave tubes (TWTs) is described. In the framework of Pierce model, we consider 1-D electron flow along a dispersive single-mode slow wave structure (SWS), accounting space-charge effect. The analytical accounts frequency-dependent phase velocity characteristic impedance obtained using various equivalent circuit models from literature, validated by comparison with full-wave eigenmode...

The interaction between a linear electron beam and guided electromagnetic wave is studied in the contest of exceptional points degeneracy (EPD) supported by such an interactive system. study focuses on case traveling tube (TWT) with realistic helix waveguide slow-wave structure (SWS). formulated analytical model that generalization Pierce model, assuming one-dimensional flow along dispersive single-mode guiding SWS taking into account space-charge effects augmented using phase velocity...

We demonstrate how exceptional points of degeneracy (EPDs) are induced in a single transmission line (TL) directly by applying periodic space-time modulation to the per-unit-length distributed capacitance. In such modulated (STM)-TL, two eigenmodes coalesce into degenerate one, their eigenvalues (wavenumbers) and eigenvectors (voltage-current states) when system approaches EPD condition. The condition is achieved tuning parameter modulation, as spatial or temporal frequency, depth....

We study the rise of exceptional points degeneracy (EPD) in various distinct circuit configurations such as gyrator-based coupled resonators, resonators with PT-symmetry, and a single resonator time-varying component. In particular, we analyze their high sensitivity to changes resistance, capacitance, inductance show resonance frequency perturbations. also investigate stability instability conditions for these configurations; example, effect losses leads instability, it may break symmetry...

Optical wave-based computing has enabled the realization of real-time information processing in both space and time domains. In past few years, analog experienced rapid development but mostly for a single function. Motivated by parallel space-time miniaturization, we show that reconfigurable graphene-based metasurfaces offer promising path towards spatiotemporal with integrated functionalities properly engineering spatial- temporal-frequency responses. This paper employs tunable metasurface...

We present an analytical method to compute the wavenumbers and electric fields of space-charge-wave eigenmodes supported by a two-stream electron beam, consisting solid inner cylindrical stream coaxial outer annular stream, both contained within metallic tunnel. extend model developed Ramo case two streams. The accounts for interaction between streams with presence beam-tunnel wall; it can be used complex associated instability plasma frequency reduction effects in vacuum electronic...

We develop an analytical model for traveling wave tubes (TWTs) amplifiers based on the serpentine waveguide (SW). This is a generalization of Pierce model, assuming one-dimensional electron flow along dispersive slow-wave structure (SWS), with space-charge effects accounted for. The cold parameters, i.e., phase velocity and characteristic impedance, are in equivalent circuit model. use relation between interaction impedance extra correction factor that accounts non-uniform beam-wave over...

Magnetic separators that clean the fluid stream from impurities, protect installations in numerous industries. This paper introduces a graphical user interface (GUI) which proposes an optimized coil separating magnetic particles with radius 1 up to 500 ㎛. High gradient fields are employed arbitrary defined fluidic channel is made of nonmetallic material. The effects parameters studied and adjusted design optimum minimum Ohmic loss. In addition, scheme based on particle movements,...

We demonstrate that a circuit comprising two unstable LC resonators coupled via gyrator supports an exceptional point of degeneracy (EPD) with purely real eigenfrequency. Each the includes either capacitor or inductor negative value, showing imaginary resonance frequency when not to other gyrator. With external perturbation imposed on system, we show analytically response follows square-root dependence perturbation, leading possible sensor applications. Furthermore, effect small losses in...

We investigate how a single resonator with time-modulated component extracts power from an external ambient source. The collected is largely dependent on the precise modulation signal frequency choice. focus absorbed vibration using mechanical and time of damper can make significant difference in amount harvested power, leading to more than 10 times enhancement compared analogous system without modulation. also find that narrow band pair peak dip spectrum occurs because presence exceptional...