Double Resonant Structures Research Articles

Resonator-based nanoscale plasmonic sensor made of metal–graphene–insulator interfaces

We present a nanoscale refractive index plasmonic sensor based on Fano resonance. We simulate and numerically analyze a novel double T-shaped resonator structure made of conductor–insulator waveguides. Our simulation results show that two Fano resonance peaks can be achieved by the interference between a broadband mode in the straight waveguide and a narrowband mode in the T-shaped resonator. The shifts of Fano resonance peaks by changing the sample refractive index in the resonator structure facilitates the design of a refractive index sensor. To attain a sensor with high sensitivity and figure of merit we employ different geometrical parameters for the resonator structure and analyze the transmission spectra of the sensor. By optimizing the sensor structural parameters we achieve a maximum sensitivity of 523.5 nm/RIU and figure of merit of 2×105 for the sensor made of metal–insulator waveguide. By employing graphene at the core–cladding boundary of the waveguides we attain a high sensitivity of 662.3 nm/RIU and figure of merit of 6.6×105 compared to the literature. We employ samples with refractive indices ranging from 1.0 to 1.05 to analyze the sensor capabilities and employ blood plasma samples to analyze the applications of our sensor structure as a biosensor. Simple fabrication, compactness and high sensitivity are the main advantages of the proposed sensor structure.

Plasmon-enhanced second harmonic generation of metal nanostructures.

As the most common nonlinear optical process, second harmonic generation (SHG) has important application value in the field of nanophotonics. With the rapid development of metal nanomaterial processing and chemical preparation technology, various structures based on metal nanoparticles have been used to achieve the enhancement and modulation of SHG. In the field of nonlinear optics, plasmonic metal nanostructures have become potential candidates for nonlinear optoelectronic devices because of their highly adjustable physical characteristics. In this article, first, the basic optical principles of SHG and the source of surface symmetry breaking in metal nanoparticles are briefly introduced. Next, the related reports on SHG in metal nanostructures are reviewed from three aspects: the enhancement of SHG efficiency by double resonance structures, the SHG effect based on magnetic resonance and the harmonic energy transfer. Then, the applications of SHG in the sensing, imaging and in situ monitoring of metal nanostructures are summarized. Future opportunities for SHG in composite systems composed of metal nanostructures and two-dimensional materials are also proposed.

Wireless High Temperature Sensing Chipless Tag Based on a Diamond Ring Resonator

A passive wireless sensor is designed for real-time monitoring of a high temperature environment. The sensor is composed of a double diamond split rings resonant structure and an alumina ceramic substrate with a size of 23 × 23 × 0.5 mm3. The alumina ceramic substrate is selected as the temperature sensing material. The principle is that the permittivity of the alumina ceramic changes with the temperature and the resonant frequency of the sensor shifts accordingly. Its permittivity bridges the relation between the temperature and resonant frequency. Therefore, real time temperatures can be measured by monitoring the resonant frequency. The simulation results show that the designed sensor can monitor temperatures in the range 200~1000 °C corresponding to a resonant frequency of 6.79~6.49 GHz with shifting 300 MHz and a sensitivity of 0.375 MHz/°C, and demonstrate the quasi-linear relation between resonant frequency and temperature. The sensor has the advantages of wide temperature range, good sensitivity, low cost and small size, which gives it superiority in high temperature applications.

A double cavity resonant device embedded with porous material and microperforated panel

This research proposed a multi-band sound-absorbing device with a double resonant structure embedded with porous abrasive material and a microperforated panel. Inserting a sound-absorbing material in the Helmholtz resonator’s neck and a microperforated board inside the Helmholtz resonator to form a new sound-absorption structure with two air cavities. We discussed each part’s absorption coefficients to explain the sound absorption parameters and mechanism of the proposed double cavity resonant device (DCRD). For the same content of the air cavity, the sound absorption performance of the DCRD is at least 2.17 times higher than that of the Helmholtz resonance structure. The developed DCRD could almost absorb low-frequency sounds without sacrificing high-frequency performance using the microperforated panel 3. The findings show that the optimization of noise reduction, especially for low-frequency sounds, is possible through a flexible design approach without increasing the structure’s size.

Double elliptical resonator based quadruple band metamaterial absorber for EMI shielding applications in microwave regime

A quadruple band wide angle polarization insensitivity metamaterial absorber based on double elliptical resonator structure for electromagnetic interference (EMI) shielding applications in microwave regime has been considered in this paper. The proposed metamaterial absorber (MA) unit cell comprises of a top metallic resonating patch and a ground copper, both of which are separated by an inexpensive FR-4 substrate with a thickness of 0.0185λ and an electrical size of 0.138λ, at lowest resonance frequency. The proposed MA demonstrates the peak absorption of 97 %, 99.9 %, 99.9 % and 99.6 % at 3.46 GHz, 6.44 GHz, 7.89 GHz and 12.44 GHz, respectively for transverse-electric (TE) mode at normal incidence. The quadruple band absorption mechanism has been understood by the analysis of electromagnetic field with surface current distribution. In addition, the designed MA also exhibits near unity absorption for a polarization and oblique incident angle up to 60° for TE mode. The proposed MA offers greater than 35 dB shielding effectiveness in all bands under both simulated and measured environment. The designed MA has been fabricated and measured to validate the simulation results. The agreement between the measured and simulated results allow for EMI shielding applications in microwave regime.

Interplay of polarizations in a cascade EIT system in the presence of vortex coupling light in 87Rb atomic vapor medium

We investigate both experimentally and theoretically the cascade electromagnetically induced transparency (EIT) in configuration in 87Rb atomic vapor medium in the presence of vortex coupling Laguerre Gaussian (LG) light. We demonstrated Doppler free double resonance EIT structure in cascade configuration and observed transmission spectra for and polarized probe and coupling lights. We demonstrate that the double resonance structure can be identified by two photon transition probabilities and it is found to be and . By considering coupling LG light, several polarization combinations are taken into account, and their effects on amplifying and diminishing the EIT resonances are demonstrated experimentally. In order to understand the polarization effects of vortex coupling light on EIT spectrum in a degenerate multilevel atomic system, a theoretical model is developed by considering a simplified double hut level structure. Semi-classical density matrix analysis is used to understand the dynamics and also to establish the enhancement and reduction of EIT peak height with coupling light polarizations. The impact of two photon transition probabilities, polarization combinations and relative orientations of probe and coupling lights in degenerate multilevel atomic systems leads to modification of EIT resonances significantly. We establish quantitative agreement between our theory and experimental results.

Design and Fabrication of Double-Cavity Resonant Structure toward Low-Frequency Sound Absorption Improvement

Exploring broadband sound-absorption technology is of great significance in acoustics, with wide applications in noise control and sound mitigation. In this work, a multiband sound-absorbing device was proposed with two air cavities. A double resonant structure was constructed by embedding a sound-absorbing material in the Helmholtz resonator’s neck and a microperforated board inside the Helmholtz resonator, respectively. In particular, we systematically discussed the sound absorption coefficient of each assembly unit and shed light on the mechanism and structure-activity relationship of the proposed double-cavity resonant device (DCRD). The results showed that the sound absorption performance of the prepared DCRD was about twice higher than that of the Helmholtz resonance structure under the same air cavity content. Thus, it could greatly improve the absorption ratio of low-frequency sound without sacrificing high-frequency performance with the microperforated plate assistance. Overall, we believe this work provides a new toolbox to enrich the family of resonant sound absorption materials, especially realizing noise reduction optimization of low-frequency sounds through a flexible design approach.

Observation of ionospheric Alfven resonator with double spectral resonance structures at low latitude station, Shillong (dipole L=1.08)

Spectral Resonance Structures (SRS) of Ionospheric Alfven Resonator (IAR) are investigated by analysing the magnetic field data of a high sampling frequency induction coil magnetometer, installed at a low latitude Indian station, Shillong(25.56^circ N, 91.86^circ E, dipole L=1.08 ). One of the distinguishing features of IAR resonance structure observed at this latitude is the excitation of two spectral resonance structures simultaneously, one with a small frequency separation and the other with a large frequency separation of subsequent harmonics. The seasonal variation shows that the occurrence of double SRS is more favoured during winter, where, out of the total IAR events observed during winter, about 47% show clear signatures of double SRS and no double SRS are observed during summer. We have examined the altitudinal variation of refractive index using IRI 2016 model to understand the role of local ionospheric conditions in the formation of double spectral resonance structures. Our study reveals that the excitation of double SRS is related to the E-region to F-region variability of refractive index of the ionosphere. We also report that the double spectral resonance structures at Shillong are always observed only in the {B}_{x} component of the magnetic field variation.Graphical

Electrically enhanced graphene-metal plasmonic antenna for infrared sensing

An optical graphene-metal hybrid antenna geometry, permitting the efficient tuning of plasmon resonance with unity absorption is reported. The total optical absorption and optical field enhancement are accomplished by designing a graphene-metal antenna. The antenna is comprised of gold hexagon radiator with bilayer graphene on the top, functioning as a double plasmonic resonant structure. The tunability of absorption and optical field enhancement is realized by electrical gating. The strong coupling takes place between the gold plasmons and graphene plasmons, resulting in the strong enhancement of optical fields. The proposed design is modeled in CST Microwave Studio and is simulated through FDTD solver. Moreover, the dynamic tuning of the resonance frequency and optical absorption is achieved by increasing the chemical potential of graphene layers through gate voltage. The tuning range of the designed antenna is optimized in a bandwidth starting from 30 THz to 34 THz. Although at 33 THz the antenna meets matching conditions by having high input impedance, low admittance, and almost unity absorption. The functioning bandwidth of the antenna is preferable for plasmonic applications i.e. infrared sensing and imaging, where high absorption and enhanced field characteristics are required.

Dissociative electron attachment to amide bond containing molecules: N-ethylformamide and N-ethylacetamide.

To advance our quest to understand the role of low energy electrons in biomolecular systems, we performed investigations on dissociative electron attachment (DEA) to gas-phase N-ethylformamide (NEF) and N-ethylacetamide (NEA) molecules. Both molecules contain the amide bond, which is the linkage between two consecutive amino acid residues in proteins. Thus, their electron-induced dissociation can imitate the resonant behavior of the DEA process in more complex biostructures. Our experimental results indicate that in these two molecules, the dissociation of the amide bond results in a double resonant structure with peaks at ∼5 eV and 9 eV. We also determined the energy position of resonant states for several negative ions, i.e., the other dissociation products from NEF and NEA. Our predictions of dissociation channels were supported by density functional theory calculations of the corresponding threshold energies. Our results and those previously reported for small amides and peptides imply the fundamental nature for breakage of the amide bond through the DEA process.

Enhanced nonlinear optical responses of graphene in multi-frequency topological edge modes.

We propose a hybrid structure where graphene is inserted to the interface of two one-dimensional photonic crystals (1D PCs). The two PCs are designed to have opposite topological properties, and at the interface, topological edge modes exist. The edge modes exist at both the fundamental frequency (FF) and the third harmonic (TH) frequency. This double resonant structure will enhance the nonlinear responses of graphene greatly, including Kerr nonlinearity and TH generation. We discuss these two kinds of nonlinearities both at terahertz (THz) and near-infrared (NIR) frequencies. The influence of Kerr nonlinearity on the resonant frequencies is considered, when we calculate the TH generation. At THz frequency, low-threshold bistability (about 8MW/cm2) is obtained and the TH generation efficiency of 2.5% is achieved with incident intensity of 10MW/cm2. At NIR frequency, the nonlinear conductivities of graphene are about 7 orders lower. Bistability is unlikely to happen with incident intensity below 1GW/cm2. The TH generation efficiency is only about 5×10-6 with incident intensity of 25MW/cm2. The proposed structure is more suitable to work as a low-threshold saturable absorber at NIR frequency. These results may be helpful both for a better understanding of graphene's nonlinear responses in a double resonant structure and for potential applications in THz nonlinear devices and NIR nanophotonics.

Double Resonant Cavity of Oxides/Metal/Nitrides for Long Wavelength Infrared Sensing

Sub wavelength double resonant cavity structures of oxides/metal/nitrides (OMN) for bolometric detection in the long wavelength infrared (LWIR) range are studied for the first time. An optimized OMN structure allows for a significant enhancement in effective absorbance (50%-70%) with respect to that of the bare film on an amorphous Al2O3 substrate (1-30%) in the LWIR atmospheric transparent window (8-14 μm). Remarkable improvement in the response range and sensitivity have been achieved by designing the double cavity OMN structure, where the bottom cavity originates from the high reflectance between the transition metal oxide film and the Al2O3 substrate, while the silicon nitride film on the top serves as a quarter wavelength anti-reflection cavity centered at about 8 μm. The OMN structured LWIR detector can be realized by cost effective methods of chemical solution deposition (CSD) or radio frequency (RF) sputtering deposition. A detectivity of 0.18-0.2×108 cm·Hz0.5/W@6-10 Hz was achieved by using the O...

Analysis of an ultra miniature capsule antenna for gastrointestinal endoscopy

An efficient miniaturized antenna used in Wireless Capsule Endoscopy is presented. Wireless Capsule Endoscopy is the best option to replace conventional Endoscopic methods. An antenna in this capsule provides definitive electromagnetic performance of the system which is used for inspection of the gastrointestinal tract (GI). The proposed antenna has a Double C-shaped Resonant Structure (DCRS) embedded with the antenna structure. This structure can introduce a strong electric response over any desired frequency and thus metamaterials with negative permittivity can be constructed. The parameters of the metamaterial are extracted to confirm its artificial behavior. The characterization of the miniature antenna is done at 2.45 GHz using coaxial cables and we obtained a simulated gain of −23 dBi and the achieved fractional bandwidth is 20.4%. This paper also explains the method for the calculation of the impedance of the isolated antenna structure without any conventional coaxial cable. This antenna design is well suited for ingestible applications as it is miniaturized and operates in the ISM band.

Lyapunov and reversibility errors for Hamiltonian flows

We discuss the stability of a Hamiltonian system by comparing the standard Lyapunov error (LE) with the forward error (FE) due to a small random perturbation. We introduce also the reversibility error (RE) where the evolution is computed forward up to time t and backwards to t=0 in presence of noise. This procedure has been investigated in the case of symplectic maps, but it turns out that the results are simpler in the case of a noisy flow, in the limit of zero noise amplitude. Indeed the stochastic processes defined by the displacement of the noisy orbit at time t for FE, or at time 0 for RE after the evolution up to time t, satisfy linear Langevin equations, are Gaussian processes, and the errors are just their root mean square deviations. All the errors are expressed in terms of the fundamental matrix L(t) of the tangent flow and can be evaluated numerically using a symplectic integrator. Letting eL(t) be the Lyapunov error and eR(t) be the reversibility error a very simple relation holds eR2(t)=∫0teL2(s)ds. The integral relation is quite natural since the local errors due to a random perturbations accumulate during the evolution whereas for the Lyapunov case the error is introduced only at time zero and propagated. The plot of errors for initial conditions in a Poincaré section reflects the phase portrait, whereas in the action plane it allows to single out the resonance strips. We have applied the method to a 3D Hamiltonian model H=H0(J)+λV(Θ), where analytic estimates can be obtained for the single resonances from perturbation theory. This allows to inspect the double resonance structure where the single resonance strips intersect. We have also considered the Hénon–Heiles Hamiltonian to show numerically the equivalence of the errors apart from a shift of 1/2 in the power law exponent in the case of regular orbits. The reversibility error method (REM), previously introduced as the error due to round off in the symplectic integration, appears to be comparable with RE also for the models considered here.

Double resonant porous structure backed by air cavity for low frequency sound absorption improvement

In this study, multi band sound absorbing structure with double resonant porous structure employing a slit porous medium was proposed. Sound absorbing materials are widely used for noise reduction in various industrial fields. When the thickness of the porous medium increases, better absorption efficiency occurs at low frequency bands. Since the thickness should be small, the noise reduction performance at low frequencies is unacceptable for practical applications. The proposed structure was composed of a slit absorber in helical shape attached to a perforated membrane backed by an air cavity. Its acoustic characteristics were controlled by adjusting the design parameters that are essential for specific noise control applications. To confirm the acoustic characteristics, three samples were made and comparison analysis was performed. Sound absorption coefficients were measured using two-microphone impedance tube to verify the acoustic performance. The proposed structure exhibited better low-frequency sound absorption compared with the results of a conventional porous medium. The measurements showed significant sound absorption improvement at low frequency bands without sacrificing performance in the mid- and high-frequency bands. Acoustic impedance of the DRPS was predicted and compared with the measured results. The sound absorption mechanism was composed of a Helmholtz resonator, a perforated membrane and the effect of the slit porous medium. A parametric study was conducted for achieving optimal sound absorption efficiency.

Structural and Dynamics Characterization of the MerR Family Metalloregulator CueR in its Repression and Activation States

CueR (Cu export regulator) is a metalloregulator protein that "senses" Cu(I) ions with very high affinity, thereby stimulating DNA binding and the transcription activation of two other metalloregulator proteins. The crystal structures of CueR when unbound or bound to DNA and a metal ion are very similar to each other, and the role of CueR and Cu(I) in initiating the transcription has not been fully understood yet. Using double electron-electron resonance (DEER) measurements and structure modeling, weinvestigate the conformational changes that CueR undergoes upon binding Cu(I) and DNA in solution. We observe three distinct conformations, corresponding to apo-CueR, DNA-bound CueR in the absence of Cu(I) (the "repression" state), and CueR-Cu(I)-DNA (the "activation" state). We propose a detailed structural mechanism underlying CueR's regulation of the transcription process. The mechanism explicitly shows the dependence of CueR activity on copper, thereby revealing the important negative feedback mechanism essential for regulating the intracellular copper concentration.

Paramagnetic resonance in spin-polarized disordered Bose-Einstein condensates

We study the pseudo-spin density response of a disordered two-dimensional spin-polarized Bose gas to weak alternating magnetic field, assuming that one of the spin states of the doublet is macroscopically occupied and Bose-condensed while the occupation of the other state remains much smaller. We calculate spatial and temporal dispersions of spin susceptibility of the gas taking into account spin-flip processes due to the transverse-longitudinal splitting, considering microcavity exciton polaritons as a testbed. Further, we use the Bogoliubov theory of weakly-interacting gases and show that the time-dependent magnetic field power absorption exhibits double resonance structure corresponding to two particle spin states (contrast to paramagnetic resonance in regular spin-polarized electron gas). We analyze the widths of these resonances caused by scattering on the disorder and show that, in contrast with the ballistic regime, in the presence of impurities, the polariton scattering on them is twofold: scattering on the impurity potential directly and scattering on the spatially fluctuating condensate density caused by the disorder. As a result, the width of the resonance associated with the Bose-condensed spin state can be surprisingly narrow in comparison with the width of the resonance associated with the non-condensed state.

Liquid state DNP at high magnetic fields: Instrumentation, experimental results and atomistic modelling by molecular dynamics simulations

Dynamic nuclear polarization (DNP) at high magnetic fields has recently become one of the major research areas in magnetic resonance spectroscopy and imaging. Whereas much work has been devoted to experiments where the polarization transfer from the electron spin to the nuclear spin is performed in the solid state, only a few examples exist of experiments where the polarization transfer is performed in the liquid state. Here we describe such experiments at a magnetic field of 9.2 T, corresponding to a nuclear Larmor frequency of 400MHz for proton spins and an excitation frequency of 263GHz for the electron spins. The technical requirements to perform such experiments are discussed in the context of the double resonance structures that we have implemented. The experimental steps that allowed access to the enhancement factors for proton spins of several organic solvents with nitroxide radicals as polarizing agents are described. A computational scheme for calculating the coupling factors from molecular dynamics (MD) simulations is outlined and used to highlight the limitations of the classical models based on translational and rotational motion that are typically employed to quantify the observed coupling factors. The ability of MD simulations to predict enhancements for a variety of radicals and solvent molecules at any magnetic field strength should prove useful in optimizing experimental conditions for DNP in the liquid state.

Implication of Natural Polymorphism in Hinge Region of HIV-1 Protease on Protein Conformations, Local Structures and Backbone Dynamics

HIV-1 protease (PR) serves as an important drug target because its inhibition generates immature non-infectious virions. However, drug-pressure selected mutations, along with natural polymorphisms, can lead to drug resistance to HIV-1 protease inhibitors (PIs), which change the drug binding configuration and equilibrium protease conformational sampling. As was suggested in our previous study, (1) a new protease conformation, curled-open, was identified in constructs carrying natural polymorphisms including E35D, and consequently, these constructs displayed higher protein backbone dynamics compared with wild-type subtype B construct characterized by nuclear magnetic resonance (NMR) spectroscopy. In the present work, we discuss the impact of the single E35D natural polymorphism on generating a minor protease conformation (curled-open), and consequently, influencing the protein structure and dynamics. The combined results from Double electron-electron resonance (DEER), NMR spectroscopy and X-ray crystallography structures provide a possible structural mechanism for altered conformational dynamics.

Nested trampoline resonators for optomechanics

Two major challenges in the development of optomechanical devices are achieving a low mechanical and optical loss rate and vibration isolation from the environment. We address both issues by fabricating trampoline resonators made from low pressure chemical vapor deposition Si3N4 with a distributed Bragg reflector mirror. We design a nested double resonator structure with 80 dB of mechanical isolation from the mounting surface at the inner resonator frequency, and we demonstrate up to 45 dB of isolation at lower frequencies in agreement with the design. We reliably fabricate devices with mechanical quality factors of around 400 000 at room temperature. In addition, these devices were used to form optical cavities with finesse up to 181 000 ± 1000. These promising parameters will enable experiments in the quantum regime with macroscopic mechanical resonators.