Metallic Waveguide Research Articles

Planar slotted waveguide antenna array for monopulse radar

In monopulse radar, along with mirror and lens antennas, slotted waveguide antenna arrays (SWA) are often used, especially in those cases when it is required to have a flat non-protruding shape and compact dimensions. The design and manufacturing of such antennas have specialties associated with the use of non-standard feeding systems of radiating waveguides, which are considered in this paper as the example of creation of a flat SWA intended for use in a monopulse search and tracking radar. The aim of the article is calculating and modeling a slotted waveguide antenna array based on a hollow metal waveguide with a given level of side lobes and main lobe width of the radiation pattern. The developed SWA contains a radiating and feeding part. The radiating part, with 24 linear resonant waveguide-slot antennas with longitudinal slots on the wide wall of the waveguide, is divided into two subarrays to realize the monopulse mode. Each subarray is fed from the feeding waveguide through slanted slots cut in the wide wall of the waveguide. The antenna design calculation has been carried out in the MathCad, and the modeling has been performed in CAD Ansys HFSS. The energy method has been used to calculate the coordinates of the longitudinal slots on the wide wall of the radiating waveguide as well as the inclined slots on the wide wall of the feeding one. The calculated radiation patterns of the developed antenna array in the E- and H-planes in sum and difference modes have been shown. The paper outlines the methodology for designing a monopulse antenna system using a SWA. The system forms a beam directed perpendicular to the antenna plane. During the design process, the slotted waveguide antenna array based on a hollow waveguide has been modeled and researched to obtain the required characteristics specified in the technical requirements. The proposed approach can be applied to practical antenna design for monopulse radars.

Pure TE and TM modes in the metallic waveguide filled homogeneously with fully anisotropic and lossless medium

AbstractThis letter gives a sufficient condition for the existence of the pure transverse electric (TE) and transverse magnetic (TM) modes in the metallic waveguide filled with a homogeneous, fully anisotropic and lossless medium. The condition is a relation between the permittivity and permeability tensors of the fully anisotropic medium. The theory given in the letter is an extension of the classic electromagnetic waveguide theory. Furthermore, a mixed spectral element method is applied to simulate this type of anisotropic waveguide problem. At last, a numerical experiment shows that the sufficient condition supported in the letter does confirm the existence of the pure TE and TM modes in the anisotropic waveguide.

A Nanosensor Based on Optical Principles for Temperature Detection Using a Gear Ring Model

Based on the characteristics of plasmonic waveguides and resonators, we propose a refractive index (RI) sensor that couples a gear ring with a metal–insulator–metal (MIM) waveguide. Using the finite element method (FEM), we conduct extensive spectral analysis of the sensor’s properties in the near-infrared spectrum. Furthermore, we investigate the structural parameters affecting the refractive index sensing characteristics. This study reveals that the complexity of the ring cavity edge can significantly enhance the sensitivity of the nanosensor. Optimal structural performance parameters are selected when the number of gears is six, resulting in a sensitivity of 3102 nm/RIU and a Figure of Merit (FOM) of 57.4 for the sensing characteristics of the gear ring. It possesses the advantages of small size and high sensitivity. This nanoscale sensor design demonstrates high sensitivity in the field of industrial material temperature detection.

Terahertz metallic waveguide with meta-holes for bidirectional conversion between two-dimensional guided waves and free-space waves

The conversion between guided and free-space waves is crucial for achieving integrated terahertz (THz) communication and signal processing. Herein, a bidirectional conversion mechanism is proposed for bridging two-dimensional (2D) guided waves and free-space waves, which is demonstrated by the wave manipulation of a metallic waveguide with meta-holes (MWMH). Compared with the conventional conversion between one-dimensional guided waves and free-space waves, in the proposed bidirectional conversion process, meta-holes can arbitrarily manipulate the phase of THz waves in higher dimensions, which enables stronger beam-manipulation capability and a higher gain. When used as a transmitting antenna, the MWMH exhibits excellent performance, i.e., a high gain (33.3 dBi), a high radiation efficiency (∼90%), and flexible beam manipulation. When the MWMH is reversely employed as a receiving antenna to obtain the focus of 2D guided waves, it achieves a gain of 27 dB and a focusing efficiency of 50.4%. The measured results for both the transmitting and receiving antennas agree well with the simulation results. The proposed bidirectional conversion mechanism facilitates the development of THz integrated photonic devices and is promising for application in the sixth-generation mobile communication, radar detection, and nondestructive testing.

Terahertz on-chip sensor based on Mach-Zehnder waveguide interferometer for selective recognition of reducing drug

The selective detection of biochemical substances with high sensitivity in the terahertz (THz) band has emerged as a prominent research area, attracting significant attention. Waveguide-on-chip detection of biochemical substances can effectively enhance the interaction between samples and waves, but there is a lack of reports in the THz band. In this work, a dual-channel metallic parallel-plate waveguide (PPWG) is applied to creatively construct a THz Mach-Zehnder interferometer (MZI) sensor for highly sensitive and selective detection of reducing drug on a chip. This sensor exhibits a strong numerical response of 0.75 THz/RIU, allowing for dynamic sensitivity adjustment through mechanically tuning structural parameters, and it is modified through in-situ growth of Prussian blue (PB) to achieve the selective detection of reducing drug. The experiments confirm that the designed sensor-on-chip possesses exceptional detection sensitivity for cysteamine, reaching an impressive maximum sensitivity of 0.09 GHz/nmol and a low limit of detection of 88 nmol. The modified chip exhibits selective detection of cysteamine, demonstrating a maximum response difference of 4.2 times compared to other configurations. Collectively, a pioneer validates the feasibility of the highly sensitive MZI chip in the THz regime and opens up new possibilities for advancing THz biochemical sensing.

A deep learning method for empirical spectral prediction and inverse design of all-optical nonlinear plasmonic ring resonator switches

All-optical plasmonic switches (AOPSs) utilizing surface plasmon polaritons are well-suited for integration into photonic integrated circuits (PICs) and play a crucial role in advancing all-optical signal processing. The current AOPS design methods still rely on trial-and-error or empirical approaches. In contrast, recent deep learning (DL) advances have proven highly effective as computational tools, offering an alternative means to accelerate nanophotonics simulations. This paper proposes an innovative approach utilizing DL for spectrum prediction and inverse design of AOPS. The switches employ circular nonlinear plasmonic ring resonators (NPRRs) composed of interconnected metal–insulator–metal waveguides with a ring resonator. The NPRR switching performance is shown using the nonlinear Kerr effect. The forward model presented in this study demonstrates superior computational efficiency when compared to the finite-difference time-domain method. The model analyzes various structural parameters to predict transmission spectra with a distinctive dip. Inverse modeling enables the prediction of design parameters for desired transmission spectra. This model provides a rapid estimation of design parameters, offering a clear advantage over time-intensive conventional optimization approaches. The loss of prediction for both the forward and inverse models, when compared to simulations, is exceedingly low and on the order of 10−4. The results confirm the suitability of employing DL for forward and inverse design of AOPSs in PICs.

Multiple methods for acoustic emission source location in metal waveguides

Research on sound source location, which is widely used in engineering, is an important topic in acoustic emission (AE) technology. Traditional double-ended location methods have certain limitations, such as sound sources being located between two sensors, a single application scenario and possible time delays. In this study, three theoretically feasible location methods were proposed and experimentally verified based on AE propagation theory to test the accuracy of the AE source location and explore single/double-sensor line location in metal waveguides. The experiments measured the propagation speed of longitudinal and transverse waves in the waveguide and verified the feasibilities of the three acoustic source location methods based on waveform analysis, with waveform matching using the wave range and wave speed differences. The experimental results show a location error of less than 3% for the double-ended and double wave-speed methods and less than 6% for the double-waveguide and reflective-surface types.

Metallic waveguide transmitarrays for dual-band terahertz antennas with high gain and low sidelobe levels

The antenna is an indispensable device in terahertz (THz) wireless communication systems. Owing to the high propagation attenuation of THz waves in atmospheric, THz antennas with high gain and low sidelobe levels (SLLs) are in an urgent need. Here, a metal waveguide transmitarry antenna (MWTA) is proposed to realize high gain and low SLLs at dual THz bands simultaneously. At the frequencies of 0.14 and 0.0972 THz, the peak gains are 32 and 28 dBi, the SLLs are both 21 dB lower than the main lobe, and the 3 dB beamwidths are 4.4° and 5.7°, respectively. As a proof of concept, a prototype with a diameter of 48 mm is fabricated and the measured results are in good agreement with the simulations. The proposed MWTA with high gain and low SLLs at dual THz bands holds great application potential in 6G wireless communication, non-destructive testing, and biomedicine.

Periodic stub implementation with plasmonic waveguide as a slow-wave coupled cavity for optical refractive index sensing

Optical biosensors based on plasmonic nanostructures have attracted great interest due to their ability to detect small refractive index changes with high sensitivity. In this work, a novel plasmonic coupled cavity waveguide is proposed for refractive index sensing applications. The structure consists of a metal–insulator–metal waveguide side coupled to an array of asymmetric H-shape element, designed to provide dual-band resonances. The sharp transmission dips and large field enhancements associated with dual-band resonances can enable sensitive detection of material under test. The resonator array creates a slow light effect to improve light-matter interactions. The structure was simulated using the finite integration technique as the full-wave technique, and the sensitivity and figure of merit were extracted for different ambient refractive indices. The maximum sensitivity of 1774 nm/RIU and high figure of merit of 2 × 104 RIU−1 for the basic model and 1.15 × 105 RIU−1 for the modified model were achieved, demonstrating the potential for high-performance sensing. The unique transmission characteristics also allow for combined spectral shaping and detection over a broad bandwidth. The simple, compact geometry makes the design suitable for on-chip integration. This work demonstrates a promising refractive index sensor based on coupled dual-band resonators in a plasmonic waveguide.

Cold plasma-induced effects on electromagnetic wave scattering in waveguides: a mode-matching analysis

This article presents advancements in an analytical mode-matching technique for studying electromagnetic wave propagation in a parallel-plate metallic rectangular waveguide. This technique involves projecting the solution onto basis functions and solving linear algebraic systems to determine scattering amplitudes. The accuracy of this method is validated via numerical assessments, which involve the reconstruction of matching conditions and conservation laws. The study highlights the impact of geometric and material variations on reflection and transmission phenomena in the waveguide.

Harmonic quantum cascade laser terahertz frequency combs enabled by multilayer graphene top-cavity scatters

Abstract Optical frequency comb synthesizers, operating in the harmonic regime, are metrological sources in which the emitted optical power is concentrated in a few modes, spaced by several multiples of the cavity free spectral range (FSR). This behavior reflects in a large correlation degree and, in principle, in an increased optical power per mode. In miniaturized quantum cascade lasers (QCLs), harmonic frequency combs (HFCs) are hence particularly attracting to explore quantum correlation effects between adjacent harmonic modes, enabled by the inherently large gain media third-order χ (3) Kerr nonlinearity, even if controlled generation of stable HFCs of predefined order, is typically demanding in such electrically pumped sources. Here, we demonstrate stable 2nd order and 3rd order HFC emission in terahertz frequency QCLs by respectively patterning an individual or a couple of equally spaced distributed multilayer graphene absorbers on the top metallic waveguides.

Remote Charging and Degradation Suppression for the Quantum Battery.

The quantum battery (QB) makes use of quantum effects to store and supply energy, which may outperform its classical counterpart. However, there are two challenges in this field. One is that the environment-induced decoherence causes the energy loss and aging of the QB, the other is that the decreasing of the charger-QB coupling strength with increasing their distance makes the charging of the QB become inefficient. Here, we propose a QB scheme to realize a remote charging via coupling the QB and the charger to a rectangular hollow metal waveguide. It is found that an ideal charging is realized as long as two bound states are formed in the energy spectrum of the total system consisting of the QB, the charger, and the electromagnetic environment in the waveguide. Using the constructive role of the decoherence, our QB is immune to the aging. Additionally, without resorting to the direct charger-QB interaction, our scheme works in a way of long-range and wireless-like charging. Effectively overcoming the two challenges, our result supplies an insightful guideline to the practical realization of the QB by reservoir engineering.

Nano Application of Oil Concentration Detection Using Double-Tooth Ring Plasma Sensing

Based on the unique properties of optical Fano resonance and plasmonic-waveguide coupling systems, this paper explores a novel refractive index concentration sensor structure. The sensor structure is composed of a metal–insulator–metal (MIM) waveguide and two identically shaped and sized double-tooth ring couplers (DTR). The performance structure of the nanoscale refractive index sensor with DTR cavity was comprehensively assessed using the finite element method (FEM). Due to the impact of various geometric parameters on the sensing characteristics, including the rotation angles, the widths between the double-tooth rings, and the gaps between the cavity and the waveguide, we identified an optimal novel refractive index sensor structure that boasts the best performance indices. Finally, the DTR cavity sensor achieved a sensitivity of 4137 nm/RIU and Figure of merit (FOM) of 59.1. Given the high complexity and sensitivity of the overall structure, this nanoscale refractive index sensor can be applied to the detection of oil concentration in industrial oil–water mixtures, yielding highly precise results.

Orthogonal mode couplers for plasmonic chip based on metal–insulator–metal waveguide for temperature sensing application

In this work, a plasmonic sensor based on metal–insulator–metal (MIM) waveguide for temperature sensing application is numerically investigated via finite element method (FEM). The resonant cavity filled with PDMS polymer is side-coupled to the MIM bus waveguide. The sensitivity of the proposed device is ~ − 0.44 nm/°C which can be further enhanced to − 0.63 nm/°C by embedding a period array of metallic nanoblocks in the center of the cavity. We comprehend the existence of numerous highly attractive and sensitive plasmonic sensor designs, yet a notable gap exists in the exploration of light coupling mechanisms to these nanoscale waveguides. Consequently, we introduced an attractive approach: orthogonal mode couplers designed for plasmonic chips, which leverage MIM waveguide-based sensors. The optimized transmission of the hybrid system including silicon couplers and MIM waveguide is in the range of − 1.73 dB to − 2.93 dB for a broad wavelength range of 1450–1650 nm. The skillful integration of these couplers not only distinguishes our plasmonic sensor but also positions it as a highly promising solution for an extensive array of sensing applications.

Phosphides‐Based Terahertz Quantum‐Cascade Laser

Due to their high optical phonon energies GaInP/AlGaInP heterostructures are a promising active medium to solve the problem of creating compact semiconductor sources with an operating frequency range of 5.5–7 THz. In this work, the temperature dependences of gain and absorption at 6.4–6.9 THz have been calculated for a GaInP/AlGaInP‐based quantum‐cascade laser (QCL) with two quantum wells in the cascade and a metal–metal waveguide. The dielectric function and mode losses for a 10 μm thick Au–Au waveguide, based on ternary InGaP and quaternary AlGaInP semiconductors, have been investigated in details. A laser structure that provides a mode gain of over 100 cm−1 with a maximum operating temperature about 100 K is proposed. The results of this study open the way to the development of a QCL for operation in a significant part of the GaAs phonon absorption band region, which is inaccessible for existing QCLs.

Energy loss in practical waveguide channel designs

The presence of attenuation of electromagnetic waves in feeder paths leads to a decrease in the efficiency of radio engineering systems, as well as an increase in thermal noise, which reduces the sensitivity of the receiving part of the system. In addition to this, the thermal mode of the path deteriorates, which may be the cause of a decrease in its electrical strength, as well as overheating. For hollow rectangular waveguides, the loss value is determined by the following design characteristics: the internal dimensions of the cross section and the so-called microwave quality of the material in which the ultra-high frequency currents flow. For metallic waveguides microwave quality is characterized, first of all, by intrinsic conductivity and roughness of the inner surface. It should be emphasized that a necessary condition for a full-fledged study of the problem of loss reduction in waveguide devices is the possibility of practical substantiation of the results, specifically – the possibility of conducting measurements of losses in the layout of waveguide devices. However, in many works this issue is not given due attention, and any results of estimation of electrical parameters of conductive layers are not given. The purpose of this work is to study the magnitude of losses in practical designs of waveguide devices. The study is carried out on device layouts, conductive layers of which are made (formed) from common materials of high conductivity with different surface states. This paper presents the results of the study of effective conductivity values of practical waveguide channel designs. The research methodology showed acceptable accuracy (3...5%), and the research results are consistent with previously known data, as well as supplement them. The research results clearly demonstrate that such a widespread concept as the thickness (effective thickness) of the skin layer, obtained by calculation, is of practical importance only for ideal homogeneous materials. In other cases, the depth of occurrence and distribution of microwave current density is difficult to predict, depending on the coating thickness, roughness of the coating and the substrate, as well as on the ratio of their effective conductivities. Most publications on loss reduction in waveguide devices address the issues of surface microroughness. At the same time, in practical designs, attention should be paid to the condition of the surface layer. And it is peculiar not only for galvanic coatings, but also for surfaces obtained by cold deformation. Galvanic silver plating of the inner surface of brass waveguides used to increase electrical conductivity often does not give positive results due to the significant roughness and porosity of the silver coating. While the roughness can be improved (e.g. by mechanical means), reducing the porosity of the deposited metal represents a significant technological challenge.

Effects of spin polarization on the propagation of surface waves on a quantum plasma half-space

The study explores the wave propagation characteristics of surface plasma waves in a semi-bounded plasma, incorporating the influence of spin polarization arising from spin mismatch. The formulated plasma model integrates the density correlation effect via Bohm's potential force, Fermi pressure employing Fermi-Dirac statistics, and the exchange potential. These factors are considered in spin-polarized form and interconnected through the spin polarization index κ. We derive a dispersion relation for surface plasma waves, delineating the propagation features of the configured wave mode. Our findings indicate that an increase in spin polarization among electron populations results in a decrease in the phase velocity of surface plasma waves compared to the usual electron-ion quantum plasma. Moreover, an increase in the exchange potential contributes to a decrease in the phase speed. However, the ratio of plasmon to Fermi energy leads to an increase in the phase velocity of surface plasma waves in a spin-polarized quantum plasma. We provide a comparative analysis of our work with an earlier model based on the gold–air interface, revealing that our model facilitates the propagation of surface plasma waves with higher frequencies across the wave vector. This study highlights the significance of quantum effects for electrostatic surface plasma waves in dense metallic plasmas at room temperature, with implications for signal transmission in metallic waveguides observed in a recent study [Guo et al., “Excitation of graphene magneto-plasmons in terahertz range and giant Kerr rotation,” J. Appl. Phys. 125(1), 013102 (2019)] and some of the references therein.

Fano resonance based on a triangular resonator and its application on nanosensing

Fano resonance sensors based on metal–insulator–metal (MIM) waveguide have potential applications in fields such as biology, chemistry, and the environment. Here, a nanosensor based on Fano resonance in an MIM-based isosceles triangular resonator system is proposed and numerically studied by finite element method. Simulation results show that the Fano peak can be easily tuned by adjusting the scale factor and the refractive index within the resonator. Furthermore, we thoroughly analyze the impact of the apex angle, rotation angle, and vertical displacement of the resonator on the transmission spectrum. Finally, the sensing characteristics of the proposed structure are optimized and analyzed, and a high-performance plasmonic sensor with a sensitivity of 1100[Formula: see text]nm/RIU and the maximum figure of merit of [Formula: see text] is obtained. The distinctive attributes of our suggested structure are applicable in the realization of various integrated components for the development of multifunctional high-performance nanophotonics devices.

Design and analysis of dual‐band plasmonic band pass filter using meandering step impedance resonator

AbstractIn this article, we demonstrated the minimum significant dielectric thickness of silicon dioxide (SiO2) below the diffraction limit for the confinement in the metal–insulator–metal (MIM) waveguide and utilizing this idea, we further exhibited the detail design analysis of dual‐band plasmonic meandering step impedance resonator (MSIR), which can achieve a high quality‐factor compared to a traditional step impedance resonator (SIR). MSIRs have sharper wavelength selectivity compared to SIRs, making them more suitable for applications that require precise wavelength tuning. The tunability of reflection and transmission characteristics with respect to design parameters has been reported. The designed MSIR has demonstrated a good passband response at wavelengths λ = 1414‐nm (E‐band) and 1577‐nm (L‐band) as well as turnability with design parameters. This filter achieved a large frequency spectral range of 139 nm and a high Q factor of ~3 × 104. This work enhances the capability of on‐chip filtering in the plasmonic platform.

Polarization Control of Terahertz Waves Based on Metallic Parallel-Plate Waveguides

Polarization Control of Terahertz Waves Based on Metallic Parallel-Plate Waveguides