Fundamental Resonant Mode Research Articles

Source process of long‐period seismic events at Taal volcano, Philippines: Vapor transportation and condensation in a shallow hydrothermal fissure

We analyzed observations of a swarm of more than 40,000 long‐period (LP) seismic events at Taal volcano, Philippines, in 2010–2011. The event waveforms are strongly correlated to each other, consistent with a fixed source location, and begin with a dilatational first motion. They have a peak frequency around 0.8 Hz and a quality factor Q of 6. Waveform inversion of the events pointed to a tensile crack source dipping 30°–60° at a shallow (100–200 m) depth. A simulation using a fluid‐filled crack model indicated that the complex frequencies of the waveforms are explained by the fundamental longitudinal mode resonance of a vapor‐filled crack 188 m long. A satellite thermal infrared image acquired during the swarm period suggests that the LP events were not accompanied by surface gas releases. We considered a vapor transportation model in which vapor exsolved from magma and rose in a fissure extending to the LP source. This model yielded estimates that 105–107 m3 of magma was involved in the LP swarm and that the temperature of vapor in the LP source crack was around 600 K. We modeled a triggering mechanism of the crack resonance based on sudden condensation of vapor at the crack tip in a cold aquifer. This model explained observed characteristics of the events including the dilatational first motion, the total volumetric change, and the fixed source location.

Compact negative‐epsilon stop‐band structures based on double‐layer chiral inclusions

Here the authors propose to use electrically excited compact chiral resonators in microstrip configurations for realisation of weakly-radiating stop-band transmission lines. The fundamental resonant mode of these resonators can be excited by both electric and magnetic fields applied parallel to the spiral axis. The authors propose to use a racemic arrangement of an equal amount of left- and right-handed chiral particles between the ground plane and the signal strip and orient the particles so that they are excited by the electric field of the microstrip line. The advantage of this configuration (in addition to strong coupling and weak radiation from excited particles) is that the ground plane can be preserved from being etched (continuous ground structure). The other advantage is that the size of negative permittivity lines loaded with chiral particles can be made very small compared to previous implementations based on complementary split-ring resonators. The circuit models with properly extracted parameters accurately describe the behaviour of both negative permittivity and double-negative lines loaded with electrically coupled resonators. This parameter extraction technique is based on the comparison between the simulated (or measured) transmission and reflection characteristics of the host line loaded with such resonators and those obtained from its lumped-element equivalent circuit model.

Novel Surface-Mounted Antenna with a Chip Capacitance Embedded for LTE/WWAN Wireless USB Dongle Applications

In this article, a novel printed antenna is proposed, fabricated, and tested for an ultra-wideband LTE/GSM/UMTS WWAN wireless USB dongle attached to a laptop computer. With a chip capacitance (1.0 pF) embedded to improve the desired impedance matching in the design, a fundamental resonant mode at about 750 MHz is successfully excited to cover LTE700/GSM850/900 operating bands, while the big radiating plate can generate two resonance frequencies to meet the bandwidth of DCS1800/PCS1900/UMTS2100/LTE2300/2500. Owing to its simple structure and configuration, the presented antenna, having an evident compact size of 20 × 19 mm2, can be integrated easily in the USB dongle together with the other functional modules. These measurement results (antenna gain and radiation efficiency are better than 1.3 dBi and 45%, respectively) demonstrate that this antenna achieves a good agreement with those of the simulations as well as good omni-directional characteristics within its operating frequency bands, making it promising for wireless USB dongle mobile communication applications.

Interaction between feedback aeroacoustic and acoustic resonance mechanisms in a cavity flow: a global stability analysis

AbstractWe perform a global stability analysis of a flow over an open cavity, characterized by a Reynolds number, based on the upstream velocity and the cavity length, of $7500$. We compute base flows and unstable global modes of the flow for different Mach numbers ranging from $0$ to $0. 9$. In the incompressible regime ($M= 0$), we show that the flow is subject to global instabilities due to Kelvin–Helmholtz instabilities in the shear layer, which become strengthened by a hydrodynamic pressure feedback. The influence of the boundary-layer thickness and of the length-to-depth ratio of the cavity on these shear-layer modes has been investigated. In the compressible regime ($M\gt 0$), we have shown that all unstable global modes are continuously connected to the incompressible shear-layer modes as $M\rightarrow 0$. These shear-layer modes correspond to the beginning of branches of global modes, whose frequencies evolve (as a function of the Mach number), in accordance with the feedback aeroacoustic mechanism (Rossiter, Tech. Rep. Aero. Res. Counc. R. & M., 1964). We have also identified branches of global modes behaving in agreement with acoustic resonance mechanisms (East, J. Sound Vib., vol. 3, 1966, pp. 277–287; Tam, J. Sound Vib., vol. 49, 1976, pp. 353–364; Koch, AIAA J., vol. 43, 2005, pp. 2342–2349). At the intersections between both types of branches, the growth rate of the global modes is seen to display a local maximum. Along the aeroacoustic feedback branches, the number of vortical structures in the shear layer is kept constant, while the pressure pattern inside the cavity is conserved along the acoustic resonance branches. We show that both the feedback aeroacoustic and acoustic resonance mechanisms are at play over the entire subsonic regime, from $M= 0$ to $M= 0. 9$. At low Mach numbers, we suggest that it is still the feedback aeroacoustic mechanism that selects the frequency, even though the fundamental acoustic resonance mode is also important due to enhancing the response. At higher Mach numbers, we observe that the pressure pattern of the acoustic resonance modes (fundamental acoustic modes, first longitudinal acoustic modes, first longitudinal-depth acoustic modes) inside the cavity determines the directivity of the radiated noise. Links with experimental results are finally discussed.

Light Amplification with Low-Gain Material: Harvesting Harmonic Resonance Modes of Surface Plasmon Polaritons on a Magnetic Meta-Surface

We theoretically show that it is feasible to utilize harmonic resonance modes of surface plasmon polaritons on a magnetic meta-surface for light amplification with low-gain material. The required threshold and optimal gain strength for active layer can be substantially reduced to about one-tenth as compared with those utilizing fundamental resonance modes. The findings provide a simple and practical metamaterial approach for light amplification with most of the existing active media.

Excitation mode characteristics in Bi2212 rectangular mesa structures

The rectangular mesa structure of single crystalline Bi2Sr2CaCu2O8+δ with the dimensions of 64 × 135 × 1.35 μm3 was fabricated by using Ar-ion milling with a metallic mask and focused ion beam. From this mesa, the radiation frequencies of 24.226 cm−1 and 17.296 cm−1 were observed at the different temperatures of 25 K and 40 K, respectively. The change of the radiation frequencies is also obviously reflected in the radiation pattern measurement. The radiation pattern observed at lower temperature seems to have an asymmetric shape and its intensity as a whole is slightly weak. In the higher temperature, however, the radiation intensity increases and the radiation pattern becomes almost symmetric shape. The radiation characteristics observed at higher temperature is well explained by the fundamental cavity resonance mode expected from the width of the mesa. This result may give us not only the suggestion of the existence of the adequate matching condition between the geometrical cavity and the ac Josephson current in the mesa but also the guide for the designing of the high efficiency of the radiation.

FREQUENCY-BASED HARBOR RESPONSE TO INCIDENT TSUNAMI WAVES IN AMERICAN SAMOA

September 29, 2009 Samoa tsunami attacked Pago Pago Harbor, the major harbor in American Samoa. The original tsunami waves were greatly amplified when they propagated into the harbor, causing extensive inundations and thus fatalities and village damages. A frequency-based numerical model developed by Lee and Xing (2010) was utilized to investigate the mechanism of the amplification. The fundamental resonance mode of the harbor was identified as 18-minutes period based on the average water depth; the computed amplification factor, defined as the ratio of responded wave amplitude to incoming wave amplitude, was quite large on the fundamental mode at the interior of the harbor. Tidal gauge measurements of several other tsunami events in Pacific Ocean verified the simulation results and further corroborated the local response due to the topography and bathymetry of the harbor is responsible for the amplification of incoming waves. An unfounded speculation was discussed to interpret the distinguishing frequency distribution of wave spectral density in the Samoa tsunami event.

Ferroresonance suppression in power transformers using chaos theory

The main goal of this paper is the determination of the effect of the metal oxide varistor (MOV) on various ferroresonance modes including fundamental resonance, subharmonic and chaos mode which are generated in electrical power systems. Chaos theory is used for analyzing this effect. Also, the bifurcation, phase plan diagram and time domain simulation are used for this purpose. The proposed power system contains a no-load or lightly loaded power transformer. The magnetization curve of the transformer core is modeled by a single-value two-term polynomial. The core loss is modeled based on the flux of the transformer. The MOV modeled as a nonlinear voltage dependent resistance. The suppression effect of MOV on chaotic ferroresonance in power transformer is studied in this paper. The simulation results confirm that connecting the MOV to the transformer has a considerable suppression effect on ferroresonance phenomena.

Fiber-optic vector vibroscope

A directional vibration sensor based on polarization-controlled cladding-to-core recoupling is demonstrated. A compact structure in which a short section of multi-mode fiber (MMF) stub containing a weakly tilted fiber Bragg grating (TFBG) is spliced to another single-mode fiber without any lateral offset. Multiple core modes of the MMF are coupled at the junction and appear as well defined resonances in reflection from the TFBG. Some of those resonances exhibit a strong polarization and bending dependence. Both the orientation and the amplitude of the vibrations can be determined unambiguously via dual-path power detection of the orthogonal-polarimetric lowest order LP(1n) modes. Meanwhile, the unwanted power fluctuations and temperature perturbations can be referenced out by monitoring the fundamental LP(01) mode resonance.

Shorting Plate Planar Inverted Folded Antenna on LC Substrate for Bluetooth Application

Number of investigations done to reduce the size of the microstrip patch antennas at a fixed operating frequency. In general microstrip antennas are half wavelength structures and are operated at the fundamental resonant mode TM01 or TM10. To reduce the size without disturbing the substrate material permittivity value we are having some special techniques like shorting pin, shorting plate, shorting wall and some other slot models. This paper describes the design and simulation of planar inverted folded antenna with shorting plate model on the liquid crystal substrate material. The present study includes verification of radiation patterns, return loss and field distributions. The operating frequency is chosen 2.4GHz for Bluetooth applications. All the output parameters are simulated using commercial Ansoft-HFSS Software.

Design of Hybrid Patch/Slot Antenna Operating in Induced “TM120 Mode”

An ultralow-profile antenna based on a typical magnetic metamaterial unit cell, i.e., complementary electric resonator (CELC) structure, is introduced in this paper. The antenna behaves with an attractive performance of operating in induced “TM120 mode” as the fundamental resonance mode, which is much lower than TM100 mode. Compared to the reported miniature microstrip antennas based on slotting patch/ground technologies, the proposed antenna shows advantages in terms of low profile, high radiation efficiency, and low cross polarization. According to our investigation, even though the relatively strong backward radiation is accessorily caused due to the inherent complementary meander line (CML) slotting as a drawback for this type antenna, the peak gain in the broadside is much higher than a slot antenna with approximately the same dimensions.

Low-profile tetra wire-patch antenna for automotive applications

A wire-patch antenna operating over the terrestrial trunked radio emergency and public safety standard is presented. It exploits the use of shorting wires to operate below its fundamental cavity resonance mode. Thanks to low-cost, low-profile, solidity, ease of fabrication, and dipole-like radiation pattern properties, it results to be particularly suitable for automotive applications. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1711–1714, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26895

Printed spiral‐slot multimode antenna miniaturization for digital television signal receptions

AbstractA compact printed spiral‐slot multimode antenna operated at its quarter wavelength (λ/4) mode as the fundamental resonant mode for digital television (DTV) signal receptions is presented. To achieve broadband characteristics, the proposed antenna is constructed by embedding the eight different quarter‐wavelength spiral slots on system ground plane and is fed using a 50‐Ω microstrip. The eight spiral slots also generate eight λ/4 resonance modes to cover the DTV reception band (470–862 MHz) throughout the world. Further, the proposed antenna has a simple planar eight‐spiral‐slot structure and occupies a small area of 20 × 20 mm2 only on the system ground plane (20 × 70 mm2). The impedance matching and bandwidth of the proposed antenna are significantly affected by the sheet metal on the signal line. The antenna is able to realize an omnidirectional radiation pattern over the entire frequency band. Further, the measurement results agree with the simulation ones. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1369–1371, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26828

Tuneable electromechanical comb generation

An array of equally spaced oscillations or a comb is created within the bandwidth of the fundamental mode of an electromechanical resonator. This phenomenon utilises 2 continuous-wave (CW) pump excitations that piezoelectrically modulate the tension in the mechanical element and is seeded by a CW harmonic excitation of the first mode i.e., the signal. The resultant comb can be dynamically manipulated via the pumps and signal where the teeth separation can be tuned over 3 orders of magnitude and the comb density can be increased from just 2 teeth to nearly 102.

GaAs-based air-slot photonic crystal nanocavity for optomechanical oscillators.

We theoretically investigate an optomechanical structure consisting of two parallel GaAs membranes with an air-slot type photonic crystal nanocavity. The optical cavity has a quality factor of 4.8 × 106 at 1.52 μm and an extremely small modal volume of 0.015 of a cubic wavelength for the fundamental mode in a vacuum. The localized electric field near the air/dielectric-object boundary provides a large optomechanical coupling factor of ~990 GHz/nm. The fundamental mechanical mode resonance is 95 MHz and a quality factor is 83,800 at room temperature, nearly seven times higher than that for a similar Si-based structure. This high mechanical quality factor of a GaAs-based structure stems from low thermoelastic loss and leads to more effective optical control of nanomechanical oscillators.

Strong Multimode Photonic Microresonator and Nanoparticle Interactions

ABSTRACTWe have demonstrated strong multimode photonic microresonator and nanoparticle interactions by using an integrated micro disk resonator from through port of the laser coupling bus waveguide. In addition to the fundamental resonance mode, disk resonator has higher order resonance modes. The excited higher order mode has a node at the position where the electromagnetic energy of the fundamental mode is close to a maximum. Here we report that a self referencing mechanism can be achieved by simultaneous excitation of both fundamental and 2nd order micro disk optical resonance modes. Additionally, we are able to measure the area around the maximum of the fundamental resonance mode and the node of the higher order mode, which have overlaps in the disk. In this work, we used on chip disk microresonator as the example, as a variety of types of optical microresonators have been investigated; we used nanoparticle to interact with the two optical resonance modes excited by the coupling bus waveguide, where the nanoparticle can be either dielectric materials or metallic materials. The strong photonic microresonator and nanoparticle interactions have variety of applications for optical switches, waveguides and detection. The self-referencing characteristics of the two optical resonance modes have potential to achieve photonic functions independent of external perturbation, such as temperature change.

圆形高斯镜平凹腔腔内外激光场研究

By means of boundary finite-element method,the field distribution and eigenvalue of the fundamental mode of the plano-concave resonator with a Gaussian-reflectivity plane mirror are calculated and discussed.The results show that the radius of the mode increase following the decreasing of the characteristic radius of the Gaussian-reflectivity.The radius of the mode is not affected by the changes of the amplitude-reflectivity of mirror center.The characteristic radius of the Gaussian-reflectivity affect the far field distribution of the laser mode.While its value is small,the far field distribution has the diffraction ring around the main peak.In addition,if light is reflected completely at the center of the Gaussian-reflectivity plane mirror,the changes of the far field distribution is not obvious with the characteristic radius of the Gaussian-reflectivity changing.The mode eigenvalue increases with the characteristic radius of the Gaussian-reflectivity increasing.

Printed Coupled-Fed PIFA for Seven-Band GSM/UMTS/LTE WWAN Mobile Phone

A planar printed PIFA is proposed and fabricated in this work, which is promising for internal mobile applications. In the design, the presented antenna consists of a feeding strip and a coupling strip (which is short-circuited to the system ground by a long shorting strip). By the coupled-fed excitation, the proposed antenna can generate multiple resonant modes at lower and upper bands for seven-band WWAN operation, covering GSM850/900/DCS1800/PCS1900/UMTS2100/LTE2300/2500. In detail, the feeding strip can excite high frequency current distributions on the coupling strip by a coupling gap to generate a fundamental resonant mode at around 800 MHz, while the desired upper resonant modes at about 1850 MHz and 2550 MHz can be achieved by the feeding strip itself. The proposed antenna occupies a size of 15 × 45 mm2 and is easily printed on one surface of a FR4 substrate as system circuit board, which makes it suitable for practical mobile applications. Finally, the simulated and measured results are given, which obtain good agreement and illuminate the reliability of the scheme.

Novel UHF RFID Loop Antenna with Interdigital Coupled Section on Metallic Objects

A small-size printed loop antenna operated at its half guided wavelength (λg /2) mode as the fundamental resonant mode for achieving operation in Taiwan RFID UHF band is presented. The proposed antenna consists of a half guided wavelength loop antenna, inter-digital coupling section and a small U-shaped strip inductance structure. The proposed antenna has a simple structure of comprising shorting via of length about 118 mm to cover the Taiwan RFID UHF bands. Further, the antenna has a simple planar structure and occupies a small area of 30 × 40 mm2 on the system circuit board of the metallic object. This proposed antenna with good matched impedance, compact size, and measured maximum reading range in free-space is about 7.2 m, which can be suitable for RFID applications. Details of the proposed loop are discussed in this paper.

Continuous-wave Yb-doped Sc_2SiO_5 thin-disk laser

We present in this Letter experimental results of a Yb:Sc(2)SiO(5) (Yb:SSO) thin-disk laser. To our knowledge, this is the first lasing demonstration of this crystal in thin-disk configuration reported on to date. Preliminary tests regarding the characterization and the laser operation are presented. Two different resonator configurations, a simple linear multimode cavity, and a fundamental-mode folded resonator providing a double pass in the laser crystal were set up. The gain and the small signal gain of the available Yb:SSO sample were calculated using the experimental results of the multimode resonator. The operation in a fundamental-mode resonator with the double pass in the laser crystal led to 9.4 W of output power with an optical efficiency of 25.4%.