Lowest Resonant Mode Research Articles

Nonlinear regimes of the electron cyclotron drift instability in Vlasov simulations

We report on a novel investigation of the nonlinear regime of the electron cyclotron drift instability using a grid-based Vlasov simulation. It is shown that the instability occurs as a series of cyclotron resonances with the electron beam mode due to the E × B drift. In the nonlinear regime, we observe condensation of fluctuations energy toward the lowest resonance mode and below, i.e., an inverse energy cascade. It is shown that the characteristics of the nonlinear saturation state remain far from the ion-sound regime.

Effect of receptors on the resonant and transient harmonic vibrations of Coronavirus

The paper is concerned with the vibration characteristics of the Coronavirus family. There are some 25–100 receptors, commonly called spikes protruding from the envelope shell of the virus. Spikes, resembling the shape of a hot air balloon, may have a total mass similar to the mass of the lipid bi-layer shell. The lipid proteins of the virus are treated as homogeneous elastic material and the problem is formulated as the interaction of thin elastic shell with discrete masses, modeled as short conical cross-sectional beams. The system is subjected to ultrasonic excitation. Using the methods of structural acoustics, it is shown that the scattered pressure is very small and the pressure on the viral shell is simply the incident pressure. The modal analysis is performed for a bare shell, a single spike, and the spike-decorated shell. The predicted vibration frequencies and modes are shown to compare well with the newly derived closed-form solutions for a single spike and existing analytical solutions for thin shells. The fully nonlinear dynamic simulation of the transient response revealed the true character of the complex interaction between local vibration of spikes and global vibration of the multi-degree-of-freedom system. It was shown that harmonic vibration at or below the lowest resonant modes can excite large amplitude vibration of spikes. The associated maximum principal strain in a spike can reach large values in a fraction of a millisecond. Implications for possible tearing off spikes from the shell are discussed. Another important result is that after a finite number of cycles, the shell buckles and collapses, developing internal contacts and folds with large curvatures and strains exceeding 10%. For the geometry and elastic properties of the SARS-CoV-2 virus, these effects are present in the range of frequencies close to the ones used for medical ultrasound diagnostics.

Omnidirectional low frequency energy harvester for wearable applications

We present an omnidirectional energy harvester with lowest resonance mode at 14.85 Hz. The geometry is designed as a spiral shaped, 500 μm thick PZT lateral bimorph to achieve a low resonance frequency while minimizing the area required. The resonance modes and frequencies of the energy harvester are investigated with COMSOL eigenfrequency study. The resonance modes of translation in x, y, z, and rotation around x, y, and z have resonance frequencies at 23.4, 22.9, 14.9, 34.0, 33.6, and 25.5 Hz, respectively. Multiple resonance modes widen bandwidth and enable harvesting energy from all directions. The energy harvester is mounted inside a 3D printed package that can be worn on a human wrist. The design of the package mimics the approximate size of a typical smartwatch, and the motion from walking is along the most sensitive axes of the harvester. It produces an output of 900 mV peak-to-peak for an optimum load of 1.8 megaohms and provided 0.45 microwatts. The output voltage is high enough to charge a battery through commercial diodes.

MODELING OF RING-SLOT-ELEMENT FLOQUET CELL FOR REFLECTARRAY ANTENNAS

The ring-slot-element cell for reflectarray antennas is investigated. The mathematical model of the unit cell is based on the integral equation that is solved by the moment method with the use of the spectral domain Green’s function. Coaxial-line higher modes expressed in terms of cylindrical functions are used as the basis for magnet-current representation. It is shown that “stricken” frequencies at which resonance modes occur are an inherent part of slot elements. These frequencies are determined by the Green’s function poles. Moreover, the lowest resonance mode may occur in the operating band under certain conditions. Reflection-phase dependencies on the ring-slot size are provided, demonstrating that at “stricken” frequencies the unit cell does not operate properly. Field plots are presented, which show that the resonance-mode field distribution on the ring slot is significantly different from the normal-mode field distribution. It is found that the “stricken” frequencies might be shifted beyond the operating band by means of thorough selection of unit-cell geometric parameters.

Miniaturized dual‐band filter using triple‐folded substrate‐integrated waveguide resonators

AbstractA miniaturized dual‐band filter using novel triple‐folded substrate‐integrated waveguide (TFSIW) resonators is proposed in this paper. The proposed TFSIW is enabled by specially designed folding structures, which leads to significant size reduction. The 2 lowest resonant modes, namely folded TE102 mode and folded TE101 mode in the TFSIW cavity, are utilized to achieve a dual resonance response with a small frequency ratio. To validate the design concept, a dual‐band filter operating at 1.91 and 2.32 GHz is designed, fabricated and characterized. Good agreement has been achieved between the simulation and measurement results. Moreover, the size of the proposed TFSIW resonator has been reduced for 86% compared with the conventional SIW resonator (assuming the same frequency ratio).

Compact circular-patch-based bandpass filter for ultra-wideband wireless communication systems

Ultra-wideband (UWB) is a radio technology that enables low-power-level, short-range, and wide-bandwidth communication, and it has been widely applied in personal area networks, precision geolocation, medical, surveillance, and vehicular radar systems. Since Federal Communications Commission released the unlicensed use of the UWB range (3.1–10.6GHz), a significant attention has been paid to the development of UWB devices, particularly UWB bandpass filters. In this paper, we propose a novel UWB bandpass filter based on circular patch resonator that is grounded by via and perturbed by slits and defected ground structures. The resonator’s behaviour is analysed in detail and it is shown that its specific configuration allows a flexible control of the three lowest resonant modes, which are used to form UWB passband. To demonstrate the potential of the resonator, a UWB filter has been designed, fabricated, and measured. The filter is characterized by the insertion loss lower than 1dB and return loss higher than 17dB within the passband, as well as by very small group delay variation of only 0.07ns. Also, the filter exhibits suppression higher than 19dB up to 30GHz, and very small overall dimensions of only 0.31λg×0.31λg, and thus it outperforms other published UWB filters.

Bio-inspired design of directional leaf-shaped printed monopole antennas for 4G 700 MHz band

In this paper, a biologically inspired design methodology to develop directional leaf-shaped printed monopole antennas (PMA) for applications in the fourth-generation (4G) of mobile telecommunications technology is presented. Bio-inspired in the leaf shapes of a sugar cane plant, compact directional PMA are designed (with partial ground planes and flat rectangular reflectors) to cover the Brazilian 4G 700 MHz regulated band (698–806 MHz), with broadside radiation patterns and maximum directive gain up to 7.7 dBi. Simulated and measured results are presented for the proposed leaf-shaped antenna prototypes, and obtained results are compared with a square PMA. The use of bio-inspired leaf-shaped radiators and flat reflectors provides a fine tuning of ultra-wideband commonly presented by a conventional PMA, and the lowest resonant mode can be adjusted to cover the 700 MHz band. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1529–1533, 2016

Measurement and analysis of the lowest resonant mode of a spherical annular‐sector patch antenna

The cavity model for patch antennas has been used extensively since 1970s. This model gives excellent first-order estimates for the antenna's internal fields near any resonant frequency. Although frequently used for planar geometries, there is no reason why the model cannot be employed for other geometries. This study discusses some of the complexities in selecting the correct pair of linearly independent associated Legendre functions when attempting to employ the cavity model using a spherical annular-sector patch antenna.

Precision control of drying using rhythmic dancing of sessile nanoparticle laden droplets

This work analyses the unique spatio-temporal alteration of the deposition pattern of evaporating nanoparticle laden droplets resting on a hydrophobic surface through targeted low frequency substrate vibrations. External excitation near the lowest resonant mode (n = 2) of the droplet initially de-pins and then subsequently re-pins the droplet edge creating pseudo-hydrophilicity (low contact angle). Vibration subsequently induces droplet shape oscillations (cyclic elongation and flattening) resulting in strong flow recirculation. This strong radially outward liquid flow augments nanoparticle transport, vaporization, and agglomeration near the pinned edge resulting in much reduced drying time under certain characteristic frequency of oscillations. The resultant deposit exhibits a much flatter structure with sharp, defined peripheral wedge topology as compared to natural drying. Such controlled manipulation of transport enables tailoring of structural and topological morphology of the deposits and offers possible routes towards controlling the formation and drying timescales which are crucial for applications ranging from pharmaceutics to surface patterning.

Numerical study of low-frequency waves during harbor resonance

The aim of this paper is to investigate how bound and free long waves and their relative components change with respect to short wavelengths when resonance occurs in a long and narrow rectangular harbor. Long-period oscillations excited by bichromatic primary waves are simulated using the Boussinesq model. A separation procedure is proposed to decompose the low-frequency components inside the harbor into bound and free long waves. For comparison, the non-resonant wave condition is also considered. It shows that the amplitudes of bound and free long waves and their ratio are closely related to the short wavelengths, regardless of whether the harbor is resonant or not. For the given harbor and primary wave frequency ranges studied in this paper, when the harbor is at the lowest resonant mode, the amplitudes of bound long waves are always lower than those of free long waves but tend to be larger than half of the latter when the average short wavelengths are larger than 0.66 times the harbor length. When the harbor is non-resonant and the average short wavelengths are larger than 0.56 times the harbor length, the former is inclined to be larger than the latter.

Small‐size LTE/WWAN coupled‐fed loop antenna with band‐stop matching circuit for tablet computer

AbstractBy combining the use of a coupling feed and a band‐stop matching circuit, the proposed small‐size loop antenna for the tablet computer application can operate at its quarter‐wavelength mode as the lowest resonant mode and provide two wide operating bands (704–960 and 1710–2690 MHz) to cover the eight‐band LTE/WWAN operation (LTE700/GSM850/900 and GSM1800/1900/UMTS/LTE2300/2500 bands).The loop antenna comprises a T‐shape radiating feed, a coupled shorted strip, an antenna ground, and a band‐stop matching circuit on the antenna ground. The antenna's metal pattern includes a printed pattern on a thin FR4 substrate of planar size 10 × 55 mm2 and a metal strip of size 4 × 55 mm2 formed a part of the coupled shorted strip and connected orthogonally to the printed pattern. The antenna's occupied volume and the required length of 55 mm along the top edge of the display ground are both the smallest among the internal LTE/WWAN antenna for the tablet or laptop computers that have been reported for the present. Detailed operating principle of the proposed antenna including the effects of the coupling feed using the T‐shape radiating feed and the band‐stop matching circuit for bandwidth enhancement is discussed. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1189–1193, 2012

A 5 GHz Resonant Cavity for Complex Permittivity Measurements: Design, Test Performances and Application

The theoretical treatment of a cavity resonator consists of solving the Maxwell equations in that cavity, respecting the boundary conditions. The resonance frequencies appear as conditions in the solutions of the differential equation involved and are not significantly affected by the fact that the cavity walls have a finite conductivity. Solutions for rectangular cavities and for the lowest resonant mode, where the probability of mistaking one mode from another is slight, are readily obtained. The measurement of the complex permittivity, ε* = ε´-iε´´, can be made using the small perturbation theory. In this method, the resonance peak frequency and the quality factor of the cavity, with and without a sample, can be used to obtain the complex dielectric permittivity of the material. We measure the shift in the resonant frequency of the cavity, f, caused by the insertion of the sample, which can be related to the real part of the complex permitivitty, ε´, while the change in the inverse of the quality factor of the cavity, (1/Q), gives the imaginary part, ε´´. In this work we report the construction details, the performance tests of the cavity to confirm the possibility of the use of the small perturbation theory, and the application of the technique to measure the complex permittivity of a reinforced plastic.

Generation of sound within a closed cell by an alternating current in a straight wire

The suitability of using a wire carrying an alternating current as a laboratory sound source has been examined. An analysis is outlined in which Joule heating of the wire is assumed to be communicated to the surrounding air, which is enclosed within a chamber having dimensions comparable to the sound wavelength. The predictions are compared with measurements of the sound field set up inside a cylindrical cell (15-cm long × 5.3-cm diam), in response to a biased ac in a straight wire parallel to the cell axis, over a frequency range (3.5–8.5 kHz) which contains the three lowest resonant modes that are independent of the axial coordinate. This acoustic field varies with source wire position according to theoretical predictions for each of these (two azimuthal and one radial) modes. An average electrical source power of 33 mW/cm in ♯40 Nichrome wire results in a maximum sound pressure within the cell of approximately 5 mPa at the 3.9-kHz first azimuthal resonance, which is less than 0.1% of that which should exist if the thermal energy were deposited directly into the air.

Extended analysis of rectangular microstrip resonator antennas

An extended theory on rectangular microstrip resonator antennas is presented using the cavity model. Radiation from all four edges of the open cavity is taken into account as well as dielectric and ohmic losses. For a rectangular microstrip antenna excited in its lowest resonance mode, losses, input conductance, and bandwidth are calculated and plotted versus frequency for some different parameters, showing that bandwidths of up to 15 percent (for a voltage standing-wave ratio (VSWR) of less than two) are possible to achieve in the X band.

Interface waves for a flow-excited cavity in the vicinity of resonance

Using computer-assisted synchronous hot-wire technique, longitudinal velocity profiles of the traveling interface wave have been mapped for a cavity excited in the vicinity of its lowest resonant mode. The shear layer perturbed by the oscillation had approximate two-dimensional symmetry for the apparatus used. Near resonance, the phase of the interface wave at the leading edge is not far from that of the local acoustic particle velocity. Vorticity fluctuations travel at a somewhat irregular pace downstream, requiring about one-half cycle to move from leading to trailing edge. Circulation reaches peak value near the center of the cavity mouth. Maximum transverse displacement amplitude of the interface is roughly equal to the width of the shear layer at midpath. Significance of the measurements for understanding the mechanism of flow-excited cavity resonance are discussed. [Work supported by Naval Ship Systems command, under a GHR contract administered by the Naval Ship Research and Development Center.]

Microwave Resonance Shift Method in Stellarator Plasma Density Measurements

To investigate the trapping efficiency of a hot electron plasma and its confinement in a toroidal magnetic field configuration, a small, adiabatically heated, symmetric stellarator has been constructed. Various diagnostics methods are used to find various plasma parameters: electron density and temperature, confinement time, etc. One technique to find electron density and confinement time is to use the microwave cavity frequency shift method. This method is especially applicable in the case of this stellarator since the size of the stainless steel toroidal container is such that it can support the lowest resonant modes with frequencies about 4GHz. The resonance frequency shift method pertaining to a cylindrical resonator is reviewed and the theory applicable to the toroidal geometry is discussed. The resonant mode structure in a toroidal resonator will be described. It is shown in numerical examples that the presence of plasma will cause a considerable shift in the resonant frequency of the cavity. This frequency shift is directly proportional to plasma density and is also influenced by the magnetic field. The system has been built and is described in some detail. A fundamental transistor oscillator, which can be swept over a 0 to 300MHz bandwidth in the range of 2 to 4GHz, provides the microwave signal. An oscilloscope provides a sweep voltage which is conditioned to control the oscillator frequency. A staircase voltage is generated which is used along with the horizontal sweep to form a raster of 1 to 64 lines on the oscilloscope.

Attenuation in Water-Saturated Marine Sediments between 20 kcps and 40 kcps

Sediment samples were placed in thin-walled cylindrical containers 2 in. in diameter and 5 in. long; these were driven as complaint-walled resonators at their lowest resonant modes. From measures of resonant frequency and mechanical Q, sound speed and attenuation were determined. A variety of natural sea-floor sediments, ranging from deep-sea clays to coarse sands from shallow water, have been studied. Lowest attenuations, 1 db/ft or less, were found in deep-sea clays and fine silts where porosity was greater than 0.75. Sediments of intermediate porosity, 0.75 to 0.45, had attenuations between 1 and about 7 db/ft. Sediments of porosity less than 0.45, which are sands, had attenuations between 2.5 and 4.5 db/ft. On a number of samples more than one resonant mode was obtained, and from these data there is an indication that attenuation increases as the first power of the frequency.