Multiple Resonant Modes Research Articles

Wideband bandpass filter based on U-slotted SW-HMSIW cavities

A wideband bandpass filter (BPF) is designed based on U-slotted slow wave half mode substrate integrated waveguide (SW-HMSIW) cavities. Similar to the substrate integrated waveguide (SIW), the SW-HMSIW can also achieve a highpass characteristic while the lateral dimensions can be reduced by about 50%. By etching a U-shape slot on the SW-HMSIW cavity, a multiple-mode resonator (MMR) can be realized, which can achieve a wide passband response and make the overall dimension of the filter much more compact. A wide passband, covering from 6.0 GHz to 10.65 GHz with a FBW about 58.13% is achieved. The measured minimum insertion losses including the losses from SMA connectors are 1.1 dB and return losses are better than 10 dB. Besides, the group delay varies between 0.2 and 0.5 ns within the passband. To validate its practicability, a wideband SW-HMSIW BPF fabricated on a double-layer printed circuit board (PCB) is designed and examined. The proposed filter has a more than 54% size reduction compared to the other designs reported in open literatures. The measured results have a good agreement with the simulated results. The effective size of the fabricated filter is about 27 mm × 8.55 mm.

Circularly slotted flower shaped UWB filtering antenna with high peak gain performance

In this paper two UWB (Ultra Wide Band) antennas and a UWB filter are reported. First antenna is circularly-slotted-flower-shaped (CSFS) patch antenna and second one is CSFS antenna combined with flower-shaped UWB bandpass filter called CSFS UWB filtering antenna. Proposed CSFS antenna achieved improved peak gain at higher UWB band with large bandwidth (up to 12GHz). For further enhancement in frequency characteristic a flower-shaped multiple mode resonator (MMR) filter is combined with CSFS UWB antenna. Designed proposed filter is fabricated and measured. It gives better transmission characteristics over the entire UWB band. The integrated design of filter with UWB antenna is fabricated and measured experimentally. Proposed filtering antenna gives better frequency response and achieved high peak gain 9.8 dBi at 8.8GHz with good out of band rejection capability. The overall performances are presented and compared with other related works. The proposed filtering antenna has advantages of good out of band gain reduction, sharp cut off at both band edges of the UWB passband and omnidirectional radiation pattern in H-plane.

Enhanced Directional Emission from Monolayer WSe2 Integrated onto a Multiresonant Silicon-Based Photonic Structure

Two-dimensional transition-metal dichalcogenides such as WSe2 show great promise as versatile atomic-scale light sources for on-chip applications due to their advanced optoelectronic properties and compatibility with a silicon photonics platform. However, the sub-nanometer thickness of such active materials limits their emission efficiency. Hence, new approaches to simultaneously enhance the emission and control its directionality are required. Here, we demonstrate enhanced and directional emission from a WSe2 monolayer integrated onto a silicon photonic structure. This is achieved by coupling of the WSe2 layer to a multiresonant silicon grating-waveguide structure. The interaction with the multiple resonant modes supported by the structure provides simultaneous excitation and emission enhancement, while the dispersion of the modes further routes the emission into specified directions. In addition, our hybrid structure offers the opportunity for ultrafast emission modulation, owing to the reduced emission...

Low-temperature microwave properties of biaxial YAlO3

Low-loss crystals with defects due to paramagnetic or rare earth impurity ions is a major area of investigation for quantum hybrid systems at both optical and microwave frequencies. In this work we examine the single crystal yttrium aluminium perovskite, YAlO$_3$ using the Whispering Gallery Mode Technique. Multiple resonant microwave modes were measured from room temperature to 20 mK allowing precise characterization of the permittivity tensor at microwave frequencies. We show that it is biaxial and characterize the tensor as a function of temperature with estimated uncertainties below 0.26%. Electron spin resonance spectroscopy was also performed at 20 mK, with new transitions identified with Zero-Field splittings of 16.72 and 9.92 GHz. Spin-photon couplings of order 4.2 and 8.4 MHz were observed for residual levels of concentration, which are stronger than the photon cavity linewidths of 116 kHz but the same order of the linewidths of the discovered spin transitions.

Design of a Compact UWB Filter With High Selectivity and Superwide Stopband

This letter presents a design of compact ultra-wideband bandpass filter (BPF) with high selectivity and superwide stopband. Three resonant modes from the multiple-mode resonator (MMR) based on half-mode substrate integrated waveguide (HMSIW) structure and four resonant modes from a pair of electromagnetic bandgap loaded parallel-coupled lines can constitute a wideband performance. Superwide stopband can be achieved and two transmission zeros are realized on both sides of the passband to improve the filter selectivity. A prototype of the BPF operating from 3.1 to 10.4 GHz with an extremely broad stopband region from 10.7 to 24 GHz and a rejection level of 15 dB is demonstrated in the measured results.

Effects of charges on the localized surface phonon polaritons in dielectric nanoparticles

Recently, there has been a great deal of interest in studying the surface phonon polariton (SPhP) modes in polar dielectrics due to their potential applications in the mid-infrared (MIR) spectral range. However, the effects of charges on the SPhP modes have not been discussed up to now. In fact, exotic electrons and electron–phonon (EPh) interactions widely exist in many nanostructures in practice. Here, we theoretically investigate effects of electrons and EPh interactions on the localized SPhPs in polar dielectric nanoparticles within the framework of Mie theory. Our results show that electrons have different effects on the localized SPhP modes in the nanostructures with different electron affinity. For particles with negative electron affinity, such as the MgO case, exotic electrons only lead to blueshifts of the SPhPs resonances with little effect on the magnitudes of resonance absorptions and electric near-field enhancements. While for particles with positive electron affinity, such as the Al2O3 case, except for blueshifts of the resonances, EPh interactions decrease the resonance absorptions largely, and almost annihilate multiple resonance modes into only one in multi-sphere nanostructures. Also, EPh terms reduce the electric near-fields dramatically to values far less than that of particles with no exotic electrons. Our results are helpful to the applications of polar dielectrics in nanoscale within the MIR spectral range.

Design and experiment of piezoelectric multimodal energy harvester for low frequency vibration

Abstract Most piezoelectric vibration energy harvesters are conventional single-degree-of-freedom (SDOF) systems, and typically perform well at the single resonant mode - which makes the harvesters less efficient for low ambient vibration frequencies. In this work, we have proposed and experimentally validated a piezoelectric multimodal energy harvester having several mechanical degrees of freedom (DOFs). This multi-modal vibration energy harvester has a unique design that helps to obtain multiple resonant mode operation of the harvester at the lower frequency range. The finite element method (FEM) simulation model has been used to predict the mode shapes of the proposed energy harvester at different vibration modes. The experimental results imply that the proposed energy harvester can obtain four peak values in the range of 10–20 Hz, which are concentrated around 10, 14, 16, and 20 Hz respectively. In addition, the piezoceramic material lead zirconate titanate (PZT) has been used as a piezoelectric element that has excellent piezoelectric properties. A prototype multimodal energy harvester with four piezoelectric elements is fabricated, where a single piezoelectric element generated a peak power with a maximum of 249 µW delivered to an optimum load of 55 KΩ at 16 Hz resonant mode under 0.4 g base acceleration. In order to increase the output power and bandwidth, it is always a good idea to use multiple piezoelectric elements in one harvester structure; consequently, four piezoelectric elements of the fabricated prototype are connected in parallel. The device with parallel connected piezoelectric modules generates a peak output power of 740 µW across an equivalent optimum load resistance at 3rd resonant mode (16 Hz), while the device's base is excited at 0.4 g acceleration.

Observation of Nonlinear Harmonic Generation of Bulk Modes in SAW Devices.

Nonlinear generation of harmonics is measured on the wafer level on temperature compensated surface-acoustic-wave resonators on lithium niobate. The second-harmonic response features strong peaks looking like multiple resonant modes. The product of the frequency difference between the successive peaks to the substrate thickness is found to remain almost constant. The results also show that the level of the harmonic signal strongly depends on the roughness of the back side of the substrate. Due to these findings, it was assumed that the signal is due to nonlinear generation of a bulk mode. This assumption is confirmed experimentally by measuring the second-harmonic wave field on the back side of the substrate with an interferometer. Possible nonlinear mechanisms explaining these results are discussed.

Wideband non‐traveling‐wave triple‐mode slotline antenna

Design approach of a novel, triple-mode wideband slotline antenna is proposed and studied. The proposed antenna is realised and implemented by employing the multiple resonant modes within a narrow slotline radiator, rather than utilising the traveling-wave effect. At first, a triple-digit, fork-like microstrip tuning stub is used to excite the first and the second odd-order mode within a slim, 3/2-wavelength slotline radiator. Then, a pair of slotline stubs is introduced near the E-field nulls of the third odd-order mode. By finely tuning the parameters of the microstrip/slotline stubs, the three radiation modes are perturbed and merged to generate a wideband, radiation characteristic with three resonances. Prototype antennas are then fabricated and measured. Finally, the design approach is experimentally validated. It is shown that the proposed antenna's radiation bandwidth has been effectively increased to 33.2% while keeping a single, basic-form narrow slotline radiator with a simple, non-traveling-wave configuration.

Morphology-Controlled Synthesis of Hybrid Nanocrystals via a Selenium-Mediated Strategy with Ligand Shielding Effect: The Case of Dual Plasmonic Au-Cu2-xSe.

Integrating a plasmonic metal and a semiconductor at the nanoscale is of great importance for exploring their optical coupling properties. However, the synthesis and fine structural control of such nanostructures remain challenging. Herein we report the facile aqueous-phase Se-mediated overgrowth of metal selenides onto Au nanocrystals. Taking plasmonic Cu2-xSe as an example, the introduction of a Se template allows deposition of large Cu2-xSe crystalline grains onto Au nanocrystal seeds in various shapes, including spheres, rods, and plates. Moreover, the configuration of Au-Cu2-xSe hybrids can be tuned from core-shell to heterodimer structure by controlling the growth behavior of the Se template. Se overgrowth depends critically on the absorption strength of stabilizers on Au seeds: a strongly absorbing stabilizer inhibits isotropic overgrowth, which is in agreement with molecular dynamics simulations. The resultant Au-Cu2-xSe hybrid nanocrystals possess multiple surface plasmon resonance modes. Finally, our synthetic strategy can be extended to prepare other Au-metal selenide hybrids such as Au-Ag2Se and Au-CdSe with controllable morphologies.

Ultra-broadband Tunable Resonant Light Trapping in a Two-dimensional Randomly Microstructured Plasmonic-photonic Absorber

Recently, techniques involving random patterns have made it possible to control the light trapping of microstructures over broad spectral and angular ranges, which provides a powerful approach for photon management in energy efficiency technologies. Here, we demonstrate a simple method to create a wideband near-unity light absorber by introducing a dense and random pattern of metal-capped monodispersed dielectric microspheres onto an opaque metal film; the absorber works due to the excitation of multiple optical and plasmonic resonant modes. To further expand the absorption bandwidth, two different-sized metal-capped dielectric microspheres were integrated into a densely packed monolayer on a metal back-reflector. This proposed ultra-broadband plasmonic-photonic super absorber demonstrates desirable optical trapping in dielectric region and slight dispersion over a large incident angle range. Without any effort to strictly control the spatial arrangement of the resonant elements, our absorber, which is based on a simple self-assembly process, has the critical merits of high reproducibility and scalability and represents a viable strategy for efficient energy technologies.

Planar photonic crystal based multifunctional sensors.

A planar photonic crystal (PPC) structure capable of simultaneous detection of multiple parameters is presented in this paper. We analytically and numerically demonstrate that the reflection spectrum of the PPC structure exhibits multiple high-Q resonant modes that could respond distinctively to different external perturbations, rendering the PPC sensor superior capabilities for multiparameter sensing. We further demonstrate simultaneous pressure and temperature sensing with a PPC sensor. Other advantages of this device include efficient free-space-to-multimode coupling, high sensitivity, on-chip integration, and wafer-scale fabrications.

On Numerical Simulation Approach for Multiple Resonance Modes in Servo Systems

Mechanical resonance is one of the most pervasive problems in servo control. Closed-loop simulations are requisite when the servo control system with high accuracy is designed. The mathematical model of resonance mode must be considered when the closed-loop simulations of servo systems are done. There will be a big difference between the simulation results and the real actualities of servo systems when the resonance mode is not considered in simulations. Firstly, the mathematical model of resonance mode is introduced in this paper. This model can be perceived as a product of a differentiation element and an oscillating element. Secondly, the second-order differentiation element is proposed to simulate the resonant part and the oscillating element is proposed to simulate the antiresonant part. Thirdly, the simulation approach for two resonance modes in servo systems is proposed. Similarly, this approach can be extended to the simulation of three or even more resonances in servo systems. Finally, two numerical simulation examples are given.

偏振不敏感的九聚物太赫兹超材料

A nonamer metamaterial composed of nine split ring resonators with different orientations was experimentally and numerically researched in terahertz band. The nine split rings were arranged spirally. From the first split ring, the subsequent split rings were rotated anti-clockwise by 40. Generally, the split ring resonator was polarization-dependent. It was found that split rings oligomer, which can produce multiple resonance modes, was polarization-independent owing to the near-field energy coupling. The split rings oligomer composed of polarization-dependent resonators exhibited a polarization-independent effect, which enriched the design idea of traditionally uncoupled metamaterial composed of disperse resonators, and induced a new path for terahertz functional devices, like optical switch, modulator, filter and so on.

Suppression of Parallel Plate Modes Using Edge-Located EBG Structure in High-Speed Power Bus

An edge-located electromagnetic bandgap (EL-EBG) structure using a defected ground structure (DGS) is proposed to suppress resonant modes induced by edge excitation in a two-dimensional planar parallel plate waveguide (PPW). The proposed EL-DGS-EBG PPW significantly mitigates multiple transverse-magnetic (TM) modes in a wideband frequency range corresponding to an EBG stopband. To verify the wideband suppression, test vehicles of a conventional PPW, a PPW with a mushroom-type EBG structure, and an EL-DGS-EBG PPW are fabricated using a commercial process involving printed circuit boards (PCBs). Measurements of the input impedances show that multiple resonant modes of the previous PPWs are significantly excited through an input port located at a PPW edge. In contrast, resonant modes in the EL-DGS-EBG PPW are substantially suppressed over the frequency range of 0.5 GHz to 2 GHz. In addition, we have experimentally demonstrated that the EL-DGS-EBG PPW reduces the radiated emission from -24 dB to -44 dB as compared to the conventional PPW.

Tunable Multiple-Step Plasmonic Bragg Reflectors with Graphene-Based Modulated Grating.

We propose a novel plasmonic Bragg reflector (PBR) based on graphene with multiple-step silicon structure. The monolayer graphene bears locally variable optical properties by modulation of electric fields, and the periodical change of effective refractive index on graphene can be obtained by external bias voltage in the mid-infrared region. Through patterning the PBR units into multiple-step structures, we can decrease the insertion loss and suppress the rippling in transmission spectra. By introducing the defect into the multiple-step PBRs, the multiple resonance modes are formed inside the stopband by increasing the step number. This work may pave the ways for the further development of ultra-compact low-cost hyperspectral sensors in the mid-infrared region.

Microwave Measurement System for Detection of Dielectric Objects in Powders

Detection and removal of undesirable objects is an important issue in many material processing industries. This paper presents a microwave-based measurement technique for detection of dielectric objects in powder materials flowing through metal pipes. A nonintrusive microwave sensor is developed, which uses multiple resonant modes to obtain high sensitivity with respect to permittivity variations inside the pipe. Undesirable objects are detected based on the scattering parameters of the sensor, which are measured using a fast-sampling microwave transmitter and receiver unit. We present a detection algorithm derived from the likelihood-ratio test, which includes a parametric model of the local statistical distribution of the measured scattering parameter data. The model involves a set of Mobius transformations that map the measured scattering parameters to a domain where the data are Gaussian distributed. All unknown parameters in the model are estimated from data using maximum likelihood. Based on measurement results from a gravity-fall experimental setup, we conclude that small dielectric objects can be reliably detected in heterogeneous flows of dielectric powder.

High-selectivity UWB bandpass filter with a notched band using stub-loaded multi-mode resonator

In this paper, a novel type of stub-loaded multiple-mode resonator (MMR) with electrical coupling is developed for exploration of a single band-notch UWB Bandpass Filter (BPF) with high selectivity. Based on even and odd mode theory, five resonant modes, including two odd modes, three even modes, and a notched band can be properly designed to form the UWB passband. The odd-mode resonant frequencies can be controlled by tuning the coupling strength between two open stubs with no impact on the even modes, which provides a high design freedom of the UWB filter. Moreover, a pair of transmission zeros (TZs) can be also generated at either side of the passbands for sharp skirts and a TZ is also created within the passband for interference signal rejection. The simulated and measured results show that a notched band is obtained at 8.0GHz, which can be controlled by arranging the parameters of the MMR, sharp attenuation slops at the lower and upper bands can be simultaneously realized, which validates the proposed design flow well.

Near-field coupling and resonant cavity modes in plasmonic nanorod metamaterials

Plasmonic resonant cavities are capable of confining light at the nanoscale, resulting in both enhanced local electromagnetic fields and lower mode volumes. However, conventional plasmonic resonant cavities possess large Ohmic losses at metal-dielectric interfaces. Plasmonic near-field coupling plays a key role in a design of photonic components based on the resonant cavities because of the possibility to reduce losses. Here, we study the plasmonic near-field coupling in the silver nanorod metamaterials treated as resonant nanostructured optical cavities. Reflectance measurements reveal the existence of multiple resonance modes of the nanorod metamaterials, which is consistent with our theoretical analysis. Furthermore, our numerical simulations show that the electric field at the longitudinal resonances forms standing waves in the nanocavities due to the near-field coupling between the adjacent nanorods, and a new hybrid mode emerges due to a coupling between nanorods and a gold-film substrate. We demonstrate that this coupling can be controlled by changing the gap between the silver nanorod array and gold substrate.

Linear dichroism and optical anisotropy of silver nanoprisms in polymer films

We present optical studies of two different size distributions of silver triangular nanoprisms, one with a dipole resonance at 520 nm and the other with a dipole resonance at 650 nm, placed in different media. Significant wavelength-dependent depolarization of scattered light from the silver nanoprisms suspended in water indicates strong interference of multiple surface plasmon resonant modes in the same particle. We use this depolarization as a probe of light scattering by the nanoprisms in a lipid solution due to the rejection of a polarized background scattering. Also, the silver nanoprisms were embedded in a polyvinyl alcohol polymer matrix and oriented by stretching the polymer/nanoprism nanocomposite films. We observe significantly increased linear dichroism in the region associated with the plasmonic in-plane dipole mode upon stretching. Additionally, there is a weaker linear dichroism in the region associated with out-of-plane modes, which vanish in the extinction spectrum of the stretched nanocomposite film.