Types Of Resonant Modes Research Articles

Tunable transmission spectra of acoustic waves through double phononic crystal slabs

Acoustic resonant modes in a slab with a periodic array of holes are analyzed by using three-dimensional finite-difference time-domain method. We show that there exist two different types of resonant modes in this slab: the coupled Stoneley wave resonant modes and the waveguide resonant modes. Both resonant modes can lead to complex resonant line shapes in the transmission spectrum. By using the distinct property of these resonant modes, a tunable phononic crystal structure consisting of coupled phononic crystal slabs is introduced for achieving acoustic filters and sensors.

Resonant modes in continuous metallic grids over ground and related spatial-filtering applications

We use the theory of periodic structures, full-wave electromagnetic, and microwave circuit simulations to explain the resonant modes that propagate in metallic grids having rectangular unit cells constructed over a ground plane. We show that these metallic grids can support two types of resonant modes that have rectangular and hyperbolic isofrequency dispersion contours. By exploiting the spatial dispersion properties of these modes, a microwave 3GHz∕6GHz harmonic splitter and a highly selective 5.8GHz∕6.2GHz diplexer are designed and simulated. Furthermore, we provide experimental results for the diplexer and for the harmonic splitter, synthesized in microstrip technology. The proposed metallic grids utilize continuous unloaded transmission-line segments thus leading to spatial-filtering devices that are easy to fabricate and are scalable to terahertz frequencies and beyond.

Study on Acoustic Absorbers to Suppress Acoustic Resonance in Tube Bundles of Boiler

This paper deals with the acoustic resonance in tube bundles which occurred in actual boiler plants. In-situ measurements revealed that besides the lift-force directional modes, drag-force directional modes which are difficult to suppress, are generated. In order to suppress both types of resonant modes, acoustic absorbers are adopted which are equipped mid-air in the duct. This phenomena is classified as self-exited oscillation and based on the stability criterion, its design method, including the number or placement of absorbers in the duct space for efficient performance, was developed with the use of acoustic FEM. In order to validate this method, scale model test was executed and the same phenomena as those in the actual plant were realized. In the next step acoustic energy absorbers are equipped in the duct and remarkable increase of the critical flow velocity was confirmed. Finally this method was applied to the actual boiler plant and based these results, it was confirmed that the proposed method is the effective countermeasure for the anti-acoustic resonance in heat exchangers.

Characteristics of single defect laser modes in a two-dimensional square lattice photonic crystal slab

Square lattice photonic crystal single defect nanocavity structures are formed in free-standing slab InGaAsP materials emitting near 1.55 μm. Laser operations are achieved from two types of resonant modes, a degenerate dipole mode and a nondegenerate whispering-gallery-like mode. Each laser mode is identified by the measurement of mode shapes, quality factors, and polarization. The threshold absorbed pump power is estimated to be less than 0.2 mW for the whispering gallery mode. It is found, by rate equation analyses, that nonradiative surface recombination, which takes >60% of carrier recombination near threshold, is one of the main limiting factors for the low-threshold operation of photonic crystal single defect lasers.

Spontaneous emission of an excited atom placed near a “left-handed” sphere

The electrodynamical properties of a microsphere made of hypothetical material with a simultaneously negative permittivity and permeability (a “left-handed” (LH) sphere) are considered. It is shown that three types of resonance modes can be excited in such a sphere: the whispering gallery modes, the plasmon oscillations and the new LH surface modes, which have an anomalous behaviour of the resonant curves. The analytical solution of the dispersion equation is found. It is demonstrated that the electric (E1) and magnetic (M1) dipole decay rates of an atom placed near such left-handed sphere suffer a substantial enhancement in the case of resonance with the modes of a sphere.

Mode coupling in superconducting parallel plate resonator in a cavity with outer conductive enclosure

We have carefully studied the mode coupling effect from analysis of the measured microwave scattering parameters of superconducting films using a parallel-plate-resonator technique. Due to its high resolution and simplicity, this technique has been widely employed to identify the quality of high-T/sub c/ superconducting films by measuring the resonance bandwidth, from which the microwave surface resistance is directly derived. To minimize the radiation loss, the resonator is usually housed in a conductive cavity. Using this method, we observe that a number of strong "cavity" modes due to the test enclosure fall around the lowest TM mode of the superconducting resonator and that a strong interaction between these two types of resonant modes occurs when their eigenfrequencies are close, causing a significant distortion or a strong antiresonance for the resonator mode. To describe this effect, a coupled harmonic-oscillator model is proposed. We suggest that the interaction arises from a phase interference or a linear coupling among the individual oscillators. Our model fits very well the observed Fano-type asymmetric or antiresonant features, and thus can be used to extract the intrinsic Q of the superconducting resonator.

The Dielectric Microwave Resonator

Pieces of single crystals of rutile show high Q resonances in the microwave range. A piece about (1/7?)3 has a Q as high as that of a metal-walled cavity at room temperature. Lowering the temperature increases both the Q and the resonant wavelength. Q's of 105 were seen at 4°K. A frequency equation of first- and second-order approximations was derived in terms of the dimensions and the anisotropic dielectric constant, ??, for rectangular parallelepiped resonators. Accurate values of anisotropic ?? were obtained. In the anisotropic medium there are two types of resonant modes, one of which has an outside E field similar to an electric multipole, and the other an outside magnetic field similar to a magnetic multipole. These two types of modes degenerate into one type if the dielectric is isotropic. Resonators were also made of ceramic rutile and strontium titanate, both of which had Q values of thousands. An extremely high unloaded Q, of the order of a million, was seen at 1.4°K on a KRS-5 (ThBr-Thl) single crystal at X band.