TM Modes Research Articles

Design and Analysis of Dual-Band Metasurface Filter for Pulse Waves Based on Capacitive Nonlinear Circuits

In this paper, a novel dual-band metasurface filter (MSF) designed for accurately differentiating pulse waves (PWs) and continuous waves (CWs) is proposed, which is based on a complementary cross resonator (CSR) structure adhered on a dielectric substrate integrated with a capacitive nonlinear circuit. The unit cell of the designed dual-band MSF comprises two identical CSR structures: one of the capacitive nonlinear circuits is configured in parallel with a capacitor (C1) within one CSR structure. These structures loaded with nonlinear circuits are fabricated on a dielectric substrate. The simulation outcomes reveal that, for normally incident CWs with an input power of 10 dBm, the transmittance of the designed dual-band MSF reaches as high as 97.1% at 2.0 GHz and 93.9% at 3.45 GHz. In contrast, when it comes to 50 ns short PWs, the transmittance remains consistently below 6% throughout the entire frequency range from 1 GHz to 5 GHz. In addition, the transmittance of the dual-band MSF for normally incident PWs increases significantly as the pulse width widens at the aforementioned two discrete frequencies. The ensuing simulation data corroborates that within the input power range of −15 to 15 dBm, the transmittance difference between CWs and PWs of the dual-band MSF first rises and then falls as the input power increases. Specifically, when the input power is specified as 10 dBm and the angle of oblique incidence ranges from 0° to 60°, in the context of TE and TM modes, the transmittance of CWs exceeds 80% around both 2.0 GHz and 3.45 GHz, while that of PWs remains below 15%. Finally, the effects of resistance and capacitance on the transmittance of the dual-band MSF for the incident PWs and CWs are also studied. The dual-band MSF proposed herein showcases its potential applications in wireless communication as well as in the realm of anti-electromagnetic interference. The electromagnetic (EM) waveform modulation in the frequency band of 1–5 GHz has great development prospects in low-frequency working fields such as radar antennas and EM protection.

Evaluation of the device characteristics of Bi2Sr2CaCu2O8+δ terahertz-wave emitters using wet-etching techniques

Understanding the device characteristics associated with the shape and size of crystal chips is a key requirement for developing high-performance terahertz (THz) wave-emitting devices made of high-temperature superconductor Bi2Sr2CaCu2O8+δ(Bi2212) crystal chips, because these parameters reflect the emission frequency, emission power, self-heating conditions, and impedance matching. Wet-etching techniques are beneficial for creating comparable emitting chips from the same crystal fragment to further understand the above points regarding using Bi2212-crystal chips. Using wet-etching techniques, we prepared rectangular crystal chips with the same area using three different width (w) and length (L) aspect ratios and compared their emission characteristics. The range of the observed emission frequencies tended to be less dependent on the w/L ratio. However, the three samples differed significantly in terms of the excitation modes expected from the w/L ratio. When the aspect ratio approached one, the results indicated a tendency to resonate in the higher excitation modes. The excitation modes along the width of the chip were suppressed by decreasing the w/L ratio owing to the increased resonance frequencies of the transverse magnetic TM(m,0) modes. Although further studies are required, especially in terms of output enhancement, the results obtained herein are expected to aid in producing devices that can operate in the desired excitation mode.

A Low-Cost and Low-Power Consumption-Based Dual-Band Active Antenna for Vehicle Tracking Applications

This paper presents a cost-effective dual-band active antenna solution with low-power requirements, specifically designed for navigation applications utilizing the Indian Constellations (NavIC) and GPS signals. The antenna features a compact single-layer patch with capacitors, designed to operate at the L1 and L5 bands. In this design, the TM10 and TM30 modes are effectively utilized to achieve a dual-band broadside radiation pattern. The locations of the slots, their dimensions, and capacitors are optimized to lower the TM30 mode frequency band along with achieving right-hand circularly polarized (RHCP). The microstrip-printed hybrid resonator diplexer, the RF choke-based bias tee, and the two-stage LNA along with a matching circuit are designed separately and then integrated into a compact 45 mm × 45 mm (0.17λ × 0.17λ) active circuit board size. The routing of DC biasing and RF lines is optimized to minimize cross-talk and ensure that the active circuit remains free from spurious signal generation while enhancing the overall performance in terms of gain and noise figure. The proposed two-stage active circuit exhibits a gain of 44 dB and 42 dB, with corresponding noise figures of 1.67 dB and 1.1 dB at the L1 and L5 band frequencies, respectively. It operates with a power consumption of 85 mW at a supply voltage of 5 V. The integrated active antenna is developed on an FR4 substrate and evaluated with an in-house developed GNSS receiver, demonstrating a measured carrier-to-noise ratio (C/No) exceeding 40 dB-Hz across both frequency bands.

Enhanced high brightness DBR tapered diode laser based on polarization match.

Tapered diode lasers, composed of an index-guided ridge waveguide and a gain-guided tapered amplifier, are affected by polarization mismatch between the ridge and tapered sections. Beam quality deterioration is caused by TM high-order modes generated in the ridge section. Under high current injection, these TM modes are further amplified in the tapered section due to polarization mismatch, leading to a decrease in the laser output brightness. In this paper, a combination of deep etching in the ridge section and compressive stress in the tapered section is employed to obtain a fundamental mode seed source with a high TE degree of polarization (DOP), simultaneously improving the polarization match between the ridge and tapered sections. The fabricated tapered diode laser achieves a beam quality factor of M2(1/e2) = 1.2 at an output power of 11.57 W. The peak electro-optical efficiency is 59.8%, and the maximum output brightness reaches 936 MW·cm-2·sr-1.

A New Dual‐Band Filtering Power Divider Based on a Single Multimode Modified Triangle Patch Resonator

ABSTRACTThis letter proposes a new design of a dual‐band (DB) filtering power divider (FPD) on a single multimode‐modified triangle patch resonator. The proposed design leverages the resonant characteristics of an equilateral triangle patch resonator to exploit the TM10, TM11, TM21, and TM30 resonant modes within a single multimode‐modified triangle patch resonator, enabling the realization of an FPD with DB operation. To achieve two assumed second‐order filtering passbands, a metal via and multiple perturbed slots are introduced, providing flexible control over the resonant mode frequencies. The first passband is formed by the TM10 and TM11 modes, while the second passband is formed by the TM21 and TM30 modes. To ensure in‐band isolation for both passbands, two sets of isolation networks are developed. A prototype is designed, fabricated, and measured to validate the proposed method. The measured results demonstrate excellent agreement with the simulated ones.

A perfect ultra-wideband solar absorber with a multilayer stacked structure of Ti-SiO2-GaAs: structure and outstanding characteristics.

In this paper, we introduce an entirely new solar absorber design-a multi-layer periodic stacked structure. Through coupling effects, this design has perfect ultra-wideband absorption characteristics. The absorber structure is composed of four absorption units with varying cycle lengths, which are cyclically stacked on the surface of the refractory metal Cr. Each cycle encompasses three-layer nanosheets of Ti-SiO2-GaAs. We verify through finite difference time domain method (FDTD) simulations that the absorber achieves an absorption efficiency of 97.8% within the wavelength range of 280 nm to 3000 nm, with an average efficiency of 96.6% under the AM1.5 standard solar spectrum. The absorber can achieve such a remarkable absorption effect because of surface plasmon resonance (SPR) and Fabry-Pérot resonance effects. At 1500 K, this structure exhibits a thermal radiation efficiency of up to 97.83%. Furthermore, the design is not affected by polarization and it is less affected by the incident angle of the light source. These absorption spectra remain consistent regardless of whether it is in the TE or TM mode. Even when the angle of incidence is increased to 60 degrees, the absorption efficiency remains high. Its unique structure and excellent performance characteristics provide higher solar energy efficiency. These outstanding features enable solar absorbers to have broad application potential in improving solar energy efficiency.

Simulation investigation of a Ka-band phase-locked klystron-type coaxial relativistic Cherenkov generator

To achieve coherent power combination of Ka-band high-power microwave (HPM), a phase-locked klystron-type coaxial relativistic Cherenkov generator (PKC-RCG), which combines the advantageous characteristics of weak dimensional sensitivity of RCG and low input power ratio of relativistic triaxial klystron amplifier (TKA), is proposed and investigated in this paper. The PKC-RCG is composed of two parts: a pre-modulation region adapted from TKA and an energy exchange region adapted from RCG. The pre-modulation region is used for initial speed modulation of intense relativistic electron beams (IREB), ensuring that the output frequency is consistent with the input frequency. The energy exchange region is used for deep clustering of the IREB and achieving efficient beam–wave energy conversion. Phase locking of the output HPM is accomplished through phase delivery of the modulated IREB. Specially designed reflectors and cascaded single-gap bunching cavities with active suppression of asymmetric TM mode are employed in the pre-modulation region to suppress energy coupling and achieve a lower input power ratio. Disk-loaded slow-wave structure with smooth inner conductor is employed in the energy exchange region to further decrease the dimensional sensitivity of RCG. By the proposed Ka-band PKC-RCG, an HPM with a power of 550 MW and a frequency of 29.0 GHz is obtained with ohmic loss being taken into account. Moreover, the input power ratio and phase-locking bandwidth of the proposed Ka-band PKC-RCG are −51.4 dB and 30 MHz, respectively.

A Single‐Layer Wideband Differentially‐Fed Dual‐Polarized Filtenna With Low Cross‐Polarization

ABSTRACTIn this paper, a single‐layer differentially‐Fed dual‐polarized filtenna (DFDPF) with low cross‐polarization is developed. The developed DFDPF consists of four shorted driven patches and four triangular parasitic patches. First, each single‐feed driven patch resonates at its TM10 mode (corresponding to the antiphase TM20 mode of the two differentially‐fed patches). Incorporating shorting pins on the driven patches leads to a lower radiation null. Then, the parasitic patches are embedded into the gap between the driven patches to introduce an extra in‐band resonance operating in its TM1/2,1/2 mode, along with an upper radiation null, while the footprint remains unenlarged. This improves operating bandwidth and roll‐off rate on the upper passband edge. Finally, a pair of symbiotic open‐ended l‐shaped stubs are integrated into each driven patch to further enhance the suppression level of the upper stopband. The developed DFDPF was prototyped and measured for experimental verification. Experimental measurements validate the feasibility of the simulation results, demonstrating a wide –10 dB fractional impedance bandwidth of 19.5% and a peak realized gain of 6.6 dBi. In addition, the cross‐polarization level is lower than –40 dB.

A Simple Single‐Layer Wideband Filtenna With Multiple Controllable Radiation Nulls

ABSTRACTIn this letter, a single‐layer wideband filtenna with multiple controllable radiation nulls is presented. The developed filtenna has a very simple structure and is composed with a square substrate integrated waveguide (SIW) cavity, a square patch, and a pair of U‐shaped slots. Notably, the filtenna possesses three radiation nulls that can be tuned by adjusting specific geometrical parameters. To achieve a wide bandwidth and better frequency selectivity, the TM10 mode of the square patch is utilized to couple with the TE210 mode of the square SIW cavity. And a radiation null at upper and lower edge of the passband can be simultaneously obtained because of the effective multipath coupling and the impact of TE110 mode in SIW cavity. An extra in‐band resonance and out‐of‐band radiation null are concurrently introduced by etching a pair of U‐shaped slots at the metal ground plane so as to further expand the bandwidth and enhance the frequency selectivity. To validate the design method, a prototype of the filtenna operating at center frequency of 4.76 GHz was fabricated and measured. The measurement results show an impedance fractional bandwidth of 15.8% (4.38‐5.13 GHz) and a peak realized gain of 6.1dBi.

Six band metamaterial absorber designed on twisted square and swastika-shaped resonator for S, C, X, and Ku band frequency and sensing applications

Abstract A twisted square split ring and swastika resonator (TSSRSR) based six-band polarization-insensitive metamaterial absorber (MMA) with high effective medium ratio (EMR), and excellent absorption is proposed in this study. It can be utilized as an S, C, X, and Ku band frequency absorber and as a sensor at 6.38 GHz (C-band). A swastika geometry-based unique patch has been introduced in the proposed unit cell to achieve high polarization insensitive properties with excellent absorption of 90%, 96.5%, 91.7%, 90.7%, 95.6%, and 91.7% respectively under S, C, X, and Ku band frequency spectrum. The distinctive features of this proposed TSSRSR unit cell are its simple, unique structure with a high EMR value of 8.06, and polarization-insensitive up to 90∘ at 3.72, 6.38, 10.76, 15.28, 18.84, and 21.08 GHz respectively. The designed MMA unit cell is fabricated on a loss FR-4 dielectric substrate with an electrical dimension of 0.124λ 0 × 0.124λ 0 × 0.157λ 0. The angular insensitive properties of the unit cell were also investigated for a maximum angle of 90∘ for TE and TM mode. Moreover, the unit cell and array structure performance exhibits a maximum absorption of > 90%, suitable for sensing and antenna systems. The simulated outcome is verified by experiment with excellent accordance. The suggested MMA is very attractive for refractive index sensing applications due to several features, including its low profile, excellent angular stability, polarization insensitivity, sensitivity, quality factor (Q), figure of merit (FOM), and EMR value.

Multi-Layer Absorber based on Plasmonic Resonances for Photovoltaic Applications at Visible Spectra

This paper introduces a broadband absorber based on a multilayered, double-cylindrical-shaped metamaterial, numerically characterized for its performance. The structure comprises four interacting layers that generate plasmonic resonances. CST microwave simulations were conducted to analyze its absorption characteristics. The results demonstrate that the proposed metamaterial absorber achieves 99% absorption at 847 nm frequency region and 98% absorption in the 500-1200 nm frequency region. Additionally, polarization dependency analysis confirms that the absorber performs as a perfect, polarization-independent absorber across the studied frequency range. It exhibits high absorption in both TE and TM modes and remains unaffected by polarization or variations in the incident angle. Numerical simulations reveal that the absorption performance is driven by a combination of Fabry–Perot resonance effects, localized surface plasmons, and propagating surface plasmons. In summary, the proposed metastructure demonstrates omnidirectional absorption, polarization independence, and wide-angle incident absorption. This design shows significant potential for applications in photodetectors, active optoelectronic devices, and sensors.

Silicon Nitride Spot-Size Converter with Coupling Loss < 1.5 dB for Both Polarizations at 1W Optical Input

Microwave photonics (MWP) applications often require a high optical input power (>100 mW) to achieve an optimal signal-to-noise ratio (SNR). However, conventional silicon spot-size converters (SSCs) are susceptible to high optical power due to the two-photon absorption (TPA) effect. To overcome this, we introduce a silicon nitride (SiN) SSC fabricated on a silicon-on-insulator (SOI) substrate. When coupled to a tapered fiber with a 4.5 μm mode field diameter (MFD), the device exhibits low coupling losses of <0.9 dB for TE modes and <1.4 dB for TM modes at relatively low optical input power. Even at a 1W input power, the additional loss is minimal, at approximately 0.1 dB. The versatility of the SSC is further demonstrated by its ability to efficiently couple to fibers with MFDs of 2.5 μm and 6.5 μm, maintaining coupling losses below 1.5 dB for both polarizations over the entire C-band. This adaptability to different mode diameters makes the SiN SSC a promising candidate for future electro-optic chiplets that integrate heterogeneous materials such as III-V for gain and lithium niobate for modulation with the SiN-on-SOI for all other functions using advanced packaging techniques.

A novel atmospheric microwave plasma source based on circular waveguide with double ridges for nitrogen fixation

Abstract The rectangular tapered waveguide is the most widely used atmospheric microwave plasma source because of its simple structure, reliable performance, and low cost. However, due to the small generated plasma volume and short residence time, this plasma source has low energy efficiency in gas conversion applications such as nitrogen fixation and methane reforming. This paper proposes a novel atmospheric-pressure microwave plasma source based on a circular waveguide to enlarge the plasma volume. Firstly, the microwave working mode in the circular waveguide is analyzed based on the electromagnetic theory. By optimizing the waveguide dimension and loading double metal ridges into the waveguide, the electric field will work in a superposition mode of TE111 and TM010 modes, focus on the discharge area, and reach its maximum intensity there. Secondly, this device is manufactured and used to generate plasma in different conditions. Compared with the rectangular tapered waveguide, this device can generate larger plasmas under the same conditions. Finally, an atmospheric microwave plasma experimental system is built for nitrogen fixation. Measured results show that the proposed device has higher nitrogen fixation production and lower energy cost compared to the rectangular tapered waveguide. Moreover, the proposed device is easy to cascade, thereby it has great potential for promotion in industrial applications.

A flexible lightweight graphene-based all-dielectric metamaterial for broadband microwave absorption

Abstract To meet the demanding requirements of practical microwave absorbers, such as broadband absorption, considerations must encompass thickness, flexibility, surface density, and manufacturing feasibility. However, absorbers that effectively address all of these aspects are currently scarce. This study introduces a novel graphene-based all-dielectric metamaterial absorber (ADMMA) featuring a trap-like structure, inspired by impedance alternation strategy. Leveraging the dielectric dispersion properties of graphene composites, this ADMMA strategically manipulates the effects of Spoof Surface Plasmon Polaritons, standing wave resonance and half-wave dipole resonance, allocating them to distinct frequency bands, thus achieving a thin-layer broadband absorber. Simulation results demonstrate that, under vertical incidence, the ADMMA achieves a -10 dB bandwidth from 8.1 to 23.1 GHz. A 3-mm-thick sample, with a surface density of merely 2.85 Kg/m², is fabricated using a straightforward process, and reflectance test results closely align with simulation outcomes. Furthermore, it exhibits robust stability under oblique incidences for both TE and TM modes. This innovative approach effectively reduces surface density without compromising absorption performances, emphasizing the potential of the ADMMA for practical applications.

Design of a microwave-induced atmospheric-pressure plasma source based on cylindrical resonant cavity TM010 mode

Abstract A microwave-induced low-temperature atmospheric-pressure source based on cylindrical resonant cavity TM010 mode was designed. The microwave power was fed into the cavity from a rectangular waveguide on top of it through a coupling hole. A metal pin with adjustable insertion depth was added to the cavity to tune its resonant frequency. The fed waveguide was connected by a sliding short. By tuning the sliding short, the energy transfer efficiency from the waveguide to the cavity was changed. Experiments showed that it could induce an argon discharge in the resonant cavity at atmospheric pressure with as low as 30 W incident wave power without any extra trigger. The plasma length reached 50 mm when the incident wave power was 200 W. By exciting the argon with an extra ignitor in the feeding waveguide, the length of the plasma plume could be extended to 260 mm when the incident wave power was 800 W. The plasma generated by this device was filamentous for both cases. The emission spectrum proved the uniformity of the plasma along its length. This work will be helpful in providing a new alternative microwave plasma device for waste gas treatment or chemical reactions that require plasma catalysis.

Broadband Thermo-Optic Photonic Switch for TE and TM Modes with Adiabatic Design

Optical power switches are essential components in fiber optic communication systems, requiring minimal losses, a broad operating wavelength range, and high tolerance to fabrication errors for optimal performance. Adiabatic optical power switches inherently meet these criteria and are well suited for manufacturing processes which support large-scale production at low costs. This paper presents the design and simulation of an adiabatic switch with a flat response in the whole 1525–1625 nm wavelength range (C band and L band) for both TE and TM polarizations. The switch is based on the thermo-optic effect induced by local variations in temperature. The impacts of the design parameters, such as the device length and dissipated heat, are analyzed. The simulation results indicate that the switch achieved high efficiency and low insertion losses, highlighting the potential of adiabatic switches for reliable and scalable integration into advanced optical circuits.

Multiple high-Q Brillouin zone folding guided mode resonances in all-dielectric metasurfaces

High quality (Q) factors guided mode resonances (GMRs) are important platform for enhancing light–matter interactions. Conventional GMRs are excited by embedding periodic nanoholes in planar thin films, where the size of the holes determines the Q-factors. These control methods are relatively limited. In this work, we study multiple high-Q band folding GMRs in the near-infrared region and explore their sensing characteristics. By constructing a nanohole dimer metasurface, five band folding ultrahigh-Q GMRs are formed and corresponding high-Q GMRs are obtained by changing the size of one nanohole to break the mirror symmetry of the structure and thus manipulate the energy radiation of the modes. These resonance modes exhibit greater stability in momentum space, and their excitation is not strictly dependent on perpendicularly incident light, which facilitates experimental testing. We fabricate a series of samples to confirm these high-Q GMRs, with experimental Q-factors reaching 5.0 × 103. Next, we investigate the sensing characteristics of these GMRs, and due to the significant differences in their field distributions, TM0 mode has the best sensing performance among the five modes. Here, by spin-coating photoresists on the surface of the devices, we examine their sensing properties. It is proved that the specificity of the eigenfield localization of TM0 mode results in an excellent performance of the sensing properties of this mode, with an experimental sensitivity and figure of merit of 124 nm/RIU and 105, respectively. This work provides a route for the realization of metasurfaces with high Q-factors, which has potential applications in nanophotonics.

Dispersion analysis of grounded dielectric slab coated with double positive (DPS) / double negative (DNG) material

The present work investigates the dispersion characteristics both for TM and TE modes in a grounded dielectric slab coated with double positive (DPS) material and double negative (DNG) material. The outermost dielectric layer is assumed to be free space. By employing proper boundary conditions at interfaces, dispersion relations for the aforementioned structure for both TM and TE modes are derived. Additionally, surface waves at the interface of free space and DPS/DNG coating are investigated. Existence of mode degeneracy for DNG/DPS combination has been discussed based on dispersion analysis.

Behavior of TE and TM propagation modes in nanomaterial graphene using asymmetric slab waveguide

Abstract In this article, the conduction of transverse electric/transverse magnetic (TE/TM) propagation modes in nanomaterial graphene utilization of asymmetric dielectric slab waveguide was studied in terms of their applicability in optical fiber communication. Nano-graphene film was deposited on silica substrate and air cladding. Three layers were exposed to electromagnetic waves with a 1.55 µm wavelength and 1 µm thick nanographene film, silica, and air covering to study the performance and optical properties of graphene nanomaterials. The models were influenced by factors such as attenuation wavenumbers, cut-off frequency, mode number, propagation wavenumbers, skin depth, and angles of total internal reflection. The impact of these parameters was assessed through numerical analysis, revealing significant correlations. The modes generated ten numbers of TE and nine numbers of TM mode dependent upon the structure of nanographene, with low loss propagation wavenumber. As the TE/TM modes increase, the decay wavenumbers of the cladding and substrate parameters diminish. This indicates that the magnetic and electric fields undergo extremely rapid decay beyond the film region, which leads to the skin depth for higher TE/TM modes traveling longer distances in the cladding and substrate than do lower-order modes. Therefore, nanographene exhibits good optical properties due to its low absorption loss. The angles of internal reflection are greater in magnitude than the substrate and cladding key angles. Still, in the tenth TE mode, the internal reflection angles are extremely close to the critical angle as a result of the small substrate decay parameter and the near operating frequency. The tenth TE mode is weakly characterized. The characteristics of TE/TM modes in an asymmetric three-layer slab waveguide structure are realized for various mode orders and various parameters of nanographene material. The field profiles of the TE/TM modes are submitted to comprehend these characteristics.

Efficiency-enhanced TM-mode gyrotron with down-taper interaction structure

Recent advancements have shown that transverse magnetic (TM)-mode gyrotrons are feasible under specific conditions, yet their capabilities remain insufficiently explored. This article systematically investigates a W-band TM11-mode gyrotron within the down-tapered structure(s) to uncover its limitations and underlying physics. 2D interaction-efficiency maps are scanned as functions of the tube's geometrical parameters or beam parameters under magnetic-field tuning. An oversized tube integrated with short two-stage down tapers enhances the output efficiency of the fundamental axial mode and effectively alleviates the axial-mode competition. The peak electron-beam efficiency of the TM11 mode exceeds 50% with an idealized cold beam. The 3D particle-in-cell simulations are utilized to validate the real-time scheme including multiple transverse modes. Incorporating realistic beam spread, the first-harmonic TM11 mode effectively suppresses the second-harmonic and third-harmonic transverse electric modes with a maximum steady output of 130 kW, corresponding to an interaction efficiency of 37%. Complex dynamics regarding the mode-competing and mode-forming processes are revealed and discussed. This study not only facilitates the exploration of TM-mode gyrotrons but also provides insights into the harmonic gyrotron using the axis-encircling electron beam, where TM modes have more chances to be excited and dominate oscillations.