Excitation Of Antisymmetric Mode Research Articles

Production of Hydrogen Molecule from Methane Molecule Amplified with Excitation of Anti-Symmetric Modes of Vibration

Some factors, such as pressure and temperature, affect the rate of chemical reactions. In addition, the activation energy barrier must be overcome for the reaction to be initiated. It can be preferred to overcome this barrier by using catalysts and preheating. The catalyst ensures that it obtains the energy to react quickly by transferring it to the reactants. Similarly, the translational, vibrational, and rotational energy levels of reactants can be increased by preheating. According to the kinetic molecular theory of gases, preheating increases the kinetic energies of the gases and the speed of their collision, so the reaction takes place faster. This study theoretically investigates possible reactions of methane that can occur with the effect of only vibrational energy levels. The vibrational excitation of the molecules affects the reaction rates, and the activation barrier is overcome with lower energies. Using laser-based techniques makes the excitation of well-defined vibrational modes possible. This study investigated inelastic collisions of a methane molecule with well-characterized energy levels in infrared spectroscopy with some gases and the vibrational energy transfers that occur in these collisions. The methane molecule is the simplest form of a molecular structure consisting of more than three atoms of hydrogen atoms, which play an essential role in combustion chemistry. It shows that C⸺H stretch excitation increases the reaction rate of methane (CH4) molecules.

Coupled very-high permittivity dielectric resonators for clinical MRI

Dielectric resonators made of high permittivity materials with low losses have been extensively studied for application in magnetic resonance imaging (MRI) and magnetic resonance spectroscopy. They can focus, redistribute, and enhance the radio frequency magnetic field in a controlled way. In this Letter, we investigate coupled very-high permittivity dielectric resonators for clinical bilateral breast MRI. The resonators are tuned to support a TE mode within the frequency of 3 T MRI and implemented as a pair of coaxial hollow cylinders consisting of ceramic rings with extremely high permittivity (ε ∼ 870) and low loss. We study the electromagnetic coupling between two resonators placed in the near field and analyze the impact of symmetric and antisymmetric mode excitation on the sensitivity of the MRI machine. We experimentally verify that the coupling of the mode with symmetric field distribution to the radio frequency body birdcage coil allows us to enhance the receive sensitivity substantially and to decrease the excitation power needed to provide the optimal transmit efficiency, thus making the MRI procedure safer. Our work offers a practical method to realize a simple yet very effective system based on dielectric resonators for bilateral breast imaging.

Compact Plasmonic Structure Induced Mode Excitation and Fano Resonance

Metal-insulator-metal (MIM) waveguide has deep sub-wavelength field confinements, which makes it an important component in many aspects. In MIM structure, both of the symmetric and anti-symmetric modes could be supported. However, the anti-symmetric mode was hardly used in the SPP-based devices due to the critical excitation condition. Here, we demonstrate anti-symmetric mode excitation and Fano resonance in a compact MIM-based plasmonic structure. By changing the position of the output channel, the symmetric mode is suppressed and only anti-symmetric mode is excited. Then, we tune the position of the output channel; anti-symmetric and symmetric mode are both achieved. Furthermore, Fano resonance is realized due to the coupling between anti-symmetric mode and symmetric mode. In addition, we analyze the effects of the parameters of the structure on the transmission spectra, and a plasmonic refractive index sensor with sensitivity about 800 nm/RIU and 1100 nm/RIU based on different waveguide modes is also realized. The proposed structure provides a novel method to achieve anti-symmetric mode excitation, and it has important applications in nanophotonic devices such as filter, sensor, and photoswitch, and has important significance in achieving all-optical on-chip integration.

High-Q Fano resonances via direct excitation of an antisymmetric dark mode.

The engineering of metal-insulator-metal metasurfaces (MSs) displaying sharp spectral features based on Fano-type interference between a symmetric bright mode and an antisymmetric dark mode is reported. The proposed mechanism for direct excitation of antisymmetric mode avoids the necessity of mode hybridization through near-field coupling. Modeling and experimental results bring evidence that such MSs operating in the microwave or terahertz domains provide greater flexibility for Fano resonance engineering and provide strong enhancement of the spectral selectivity factor. It is shown that the occurring Fano resonance interference is related to the broken eigenmode orthogonality in open systems and is independent of hybridization mechanism.

Anti-symmetric mode excitation and seismic response of base-isolated bridges under asynchronous input motion

This paper investigates the effect of asynchronous earthquake ground motion on the transverse response of base-isolated bridges. In this context, the excitation of anti-symmetric modes of vibration under asynchronous input is examined and is statistically correlated with characteristic engineering demand parameters. Different ground motion scenarios are considered for various combinations of soil class, wave propagation velocity and loss of correlation patterns among different support motions, using a spectral representation method to generate m-variate, fully non-stationary, EC8 spectrum-compatible ground motion vector processes. It is shown that in the idealised case of the wave passage effect only, the detrimental effects of asynchronous excitation are concentrated on the very last piers along the direction of the seismic waves. However, when loss of coherency is also taken into account in a more realistic scenario, the impact of spatial variability is significantly more uniformly distributed. Most importantly, the conditional probability of a detrimental increase in an EDP of interest (i.e., pier base bending moments and deck drift) under multi-support excitation given that an anti-symmetric mode is excited is not only uniform but also considerably high. This is a clear evidence that the local increase of seismic demand in the bridge studied is associated with the excitation of the first anti-symmetric mode of vibration.

Excitation of antisymmetric modes and modulated propagation of spin waves in bent magnonic waveguides

Spin-wave propagation in submicron magnonic waveguides, with and without translational-symmetry-broken structural bending, was examined by using micromagnetic simulations. The dispersion relations and mode patterns of spin waves were derived to analyze dynamic excitation in those waveguides. Inclusion of such bending into waveguides is found to be decisive to the appearance of antisymmetric modes. If there is no bending, almost no excitation of antisymmetric modes occurs. The efficient antisymmetric-mode excitation is attributed to the scattering effect of the disordered potential, on the incident symmetric modes, due to structural distortion. Moreover, comparison with a previous study reveals that inhomogeneous static magnetization in the bent area is dispensable for antisymmetric-mode excitation.

Nonlinear Periodic Response of Composite Curved Beam Subjected to Symmetric and Antisymmetric Mode Excitation

The periodic response of cross-ply composite curved beams subjected to harmonic excitation with frequency in the neighborhood of symmetric and antisymmetric linear free vibration modes is investigated. The analysis is carried out using higher-order shear deformation theory based finite element method (FEM). The governing equations are integrated using Newmark’s time marching coupled with shooting technique and arc-length continuation. Shooting method is used to solve the second-order differential equations of motion directly without converting them to the first-order differential equations. This approach is computationally efficient as the banded nature of equations is retained. A detailed study revealed that the response of antisymmetrically excited beams has contribution of higher antisymmetric as well as symmetric modes whereas the response of symmetrically excited beams has the significant participation of the higher symmetric modes except for the excitation in the neighborhood of first symmetric mode. The beam excited in the neighborhood of first symmetric mode has an additional branch corresponding to significant participation of first antisymmetric mode due to two-to-one internal resonance. Furthermore, for the beams excited in the neighborhood of higher modes, the peak response amplitude becomes less than that of the beam excited in the neighborhood of first mode but vibration behavior is drastically different due to the presence of subharmonics and higher harmonics. Two-to-one internal resonance between second antisymmetric mode and first symmetric mode is predicted for the first time.

Studies on Area-controlled Electrostatic Actuation of Small Membrane Reflectors

Membrane mirrors are advantageous in several applications due to their light weight and potential for deployability. Desired optical performance often requires dynamic actuation, however, and electrostatic actuators are frequently employed for this purpose. This paper investigates a variable area/constant voltage method for electrostatic actuation of small circular membrane mirrors designed to meet specified performance requirements for a beam steering and focus/defocus application. The proposed technique involves selective application of a constant voltage to area segments that together make up an electrode pad. The paper shows that a lumped parameter model for this system also has the property of differential flatness (similar to variable voltage/constant area systems), based on which the reference trajectory for membrane deflection can be specified in phase space. The phase space trajectory is derived from the required transient response characteristics (rise time, settling time, etc.). A closed loop system comprised of a controller and an observer is devised using a Lyapunov function-based approach. A `quad cell' beam position finder is used to detect the beam angular deflection and intensity. The overall system is simulated numerically in this paper. The control system is found to provide efficient trajectory tracking for both symmetric and antisymmetric mode excitation. Although the area changes for the proposed system are discrete, the present simulations only consider continuously-variable area actuation.