Number Of Resonant Frequencies Research Articles

Theoretical analysis of linear oscillations of bubbles in a polydisperse cluster

The dynamics of a single air bubble in an unbounded liquid are significantly different from the dynamics of an individual bubble in clusters due to the hydrodynamic interaction between the bubbles. Studying the mechanism of this interaction is one of the important aspects in the study of the fundamental nature of acoustic and hydrodynamic cavitation. In this work, to analyze small oscillations of bubbles in a spherical cluster near a stable equilibrium position, the mathematical theory of a linear conservative system with several degrees of freedom is applied to explain the mechanism of interaction between bubbles of different sizes. Using this theory, in the general case, it has been proven that the number of resonance frequencies in a polydisperse cluster coincides with the number of fractions. It is shown that in the regions of the main resonance (at low frequencies) bubbles of different fractions oscillate in phase, and in the regions of secondary resonances (at high frequencies) the phases successively change to the opposite, starting with the fraction containing bubbles of the largest radius, and further changing in order of decreasing. Using the example of a two-fraction cluster, it was found that there is an inertial connection between the bubbles, but there is no force connection; when the number of bubbles of one of the fractions is small, the connection between them and the bubbles of the other fraction is weak, while the interaction between them can be strong. An analysis of the energy transfer between bubbles of different fractions showed that the change in the nature of bubbles oscillations in the fraction with a small radius, while the nature of vibration of bubbles in the other fraction does not change, is the result of dynamic damping.

Background Material Identification Using a Soft Robot

Soft robotics is an emerging technology that provides robots with the ability to adapt to the environment and safely interact with it. Here, the ability of these robots to identify the surface of interaction is critical for grasping and locomotion tasks. This paper describes the capability of a four-limb soft robot that can identify background materials through the collection of reflection coefficients using an embedded antenna and machine learning techniques. The material of a soft-limb robot was characterized in terms of the relative permittivity and the loss tangent for the design of an antenna to collect reflection coefficients. A slot antenna was designed and embedded into a soft limb in order to extract five features in reflection coefficients including the resonant frequency, −3 dB bandwidth taken from the lowest S11, the value of the lowest S11, −3 dB bandwidth taken from the highest S11, and the number of resonant frequencies. A soft robot with the embedded antenna was tested on nine different background materials in an attempt to identify surrounding terrain information and a better robotic operation. The tested background materials included concrete, fabric, grass, gravel, metal, mulch, soil, water, and wood. The results showed that the robot was capable of distinguishing among the nine different materials with an average accuracy of 93.3% for the nine background materials using a bagged decision-tree-based ensemble method algorithm.

Design, modeling, and experiment of a multi-bifurcated cantilever piezoelectric energy harvester

A multi-bifurcated cantilever piezoelectric energy harvester (BCPEH) is designed and verified to achieve a wide and adjustable response frequency band. The theoretical model is derived based on the Euler-Bernoulli beam theory and continuity boundary conditions to investigate the dynamic response of the BCPEH. The displacement frequency response function and the voltage frequency response function of the BCPEH are deduced based on the Galerkin method, and the theoretical results of a typical multi-bifurcated cantilever piezoelectric energy harvester, the Y-shaped BCPEH, are verified by the finite element method (FEM) and experiments. In addition, by comparing experimental output power of the Y-shaped BCPEH with that of the traditional cantilever-based piezoelectric energy harvester with the same mass of the bifurcated part at the beam-tip, it demonstrates that the Y-shaped BCPEH has a wider operational frequency band. Moreover, it is found that the Y-shaped BCPEH can be designed with an asymmetric configuration to adjust its response frequency distribution. The number of resonant frequencies and the output power of the asymmetric Y-shaped BCPEH are higher than that of the symmetric Y-shaped BCPEH. And the Y-shaped BCPEH has even better performance than L-shaped BCPEH. This study provides a new design concept for enhanced energy harvester.

Analysis of noise characteristics of a diode generator in a multi-circuit system

In modern microwave electronics, it is extremely important to evaluate the possibility of efficient generation of highly stable oscillation modes and the creation of low-noise generators with a millimeter wavelength range. The purpose of the research was to determine the type of wave for the most effective modes of oscillation and to ensure the operation of various modes in the mode of mutual synchronization, which becomes possible because the real design of generators can include a number of reactive elements that form a number of resonant frequencies in the microwave range. This paper shows how it is possible to provide conditions for generation at a particular frequency and simultaneously obtain high stability of vibrations. The main research methods were: analysis and generalization of literature data and results of our own research on the peculiarities of oscillation generation in a multi-circuit system of a Gann diode generator and conditions under which high frequency stability is established; experimental studies using microwave spectrum analyzers, microwave devices. In this paper, the possible generation frequencies are calculated, the operation modes of the diode generator are studied, and their phase noise is experimentally measured. It is shown that when the generation frequency approaches the cut-off frequency of the waveguide with the help of structural elements or by changing the supply voltage, a mode of mutual synchronization of vibrations at high harmonics occurs using the H102 wave type in a very narrow range of frequency (phase) noise. A generator with a multicircuit resonant system was experimentally studied and a small amount of phase noise was obtained for both types of H101 and H102 waves. At the same time, the best parameters and noise characteristics occurred at the lowest types of vibration types. These results have an experimental novelty, which allows us to hope for the development of constructive solutions that provide the creation of highly stable low-noise generators of millimeter wavelength range with the minimum mass dimensional parameters.

A resonant frequency retrieving method for low Q-factor materials based on resonant ultrasound spectroscopy

Resonant ultrasound spectroscopy (RUS) allows identification of the elastic properties of solid materials vibrating under an ultrasonic excitation from the measurement of their inherent frequencies. Retrieving the resonant frequencies is therefore a key signal processing step in RUS, which is generally addressed using a linear prediction filter. In this study, the Empirical Mode Decomposition (EMD) was proposed to retrieve the inherent resonant frequencies of materials with low Q-factor (quality factor). EMD was used to decompose the frequency response of the tested sample into intrinsic mode functions (IMF). The relevant IMF was selected from which the resonant frequencies could be computed. A bovine cortical bone sample was measured and its resonant frequencies were identified with EMD and with linear prediction for comparison. The elastic constants were also derived using both approaches. The number of resonant frequencies (45) extracted with EMD was larger than the number of frequencies (26) identified using the classical linear prediction approach. In particular, EMD proved to be more effective in detecting resonance in the higher frequency range (i.e., between 235 kHz and 400 kHz), i.e., on the weak excitation side where the spectral amplitude is low. The number of measured frequencies matching with the calculated ones was also larger for EMD (39) compared to linear prediction (17). If these results are confirmed in further studies on more samples, EMD combined with RUS, by improving the extraction of resonant frequencies for low Q-factor materials, may be considered to be useful not only to improve the reliability of the estimation of elastic parameters, but also to extend the application range of RUS.

Vibration testing of vehicle components by fatigue damage spectrum control

Random vibration testing with increased kurtosis introduces high peaks into shaker drive signals to simulate land vehicle vibration more accurately or to shorten duration of fatigue damage testing. For the latter, the kurtosis control method must be able to pass high kurtosis values from the generated shaker vibration into the stress response of the tested component. It was verified and confirmed in the paper that the method of phase manipulation based on the analytical relationship between the IFFT phases and kurtosis was capable of doing so if the resonance frequency of the component is known. However, the fatigue damage spectrum model used for evaluation of time-to-failure considers not just one but a number of resonance frequencies constituting a certain test profile which cannot be simulated by the kurtosis control alone. For this purpose, the phase manipulation method was developed further and verified for operational vibrations of a railway vehicle.

Dual-Band Slim Microstrip Patch Antennas

This paper presents a planar dual-band slim microstrip patch antennas. The antenna comprises four sections: patch and shorting, centered, and offset pins with the overall size of $30\times50$ mm2. It is shown that the centered and offset pins help to improve antenna matching while providing efficient radiation performance. With the aid of shorting pins, lower band operation at 1900 MHz is achieved. Moreover, the higher frequency band is expanded from 3480 to 3570 MHz. Simulations show that at the lower band frequencies, the antenna gain and efficiency are 1.0 dBi and 28%, respectively. On the other hand, at the upper frequency band, the antenna maximum gain is 2.4 dBi, and the efficiency of at least 25% is observed. The numerical simulation shows that the number of resonant frequencies is directly related to the patch width. In order to validate the simulation results, a prototype of the proposed antenna is fabricated and measured. Good agreement has been achieved between the simulation and measurement results.

The approach to the calculation of harmonic oscillations of electroelastic cylinders

The paper presents a new approach to the reduction of harmonic equations of electromechanical axially symmetric oscillations in cylindrical system of coordinates to first order ordinary differential equations based on the Hamiltonian formalism by radial coordinate and difference approximations by axial coordinate. Numerical implementation is executed for cylinders with membranes on ends. Integrating of boundary problem is developed by discrete orthogonalization method. Testing of results and comparison with obtained by other authors and other methods results is done. A study of two-dimensional harmonic oscillations of polarized by thickness piezoceramic cylinders at electric load is developed. The dependence of the oscillations nature from the frequency and resonant frequencies for cylinders of different length are defined. The dynamic characteristics of the electromechanical cylinder state at forced oscillations with a frequency close to the first natural frequency are studied. It is established, that with increasing of cylinder length natural frequencies are reduced and the number of resonant frequencies in the considered frequence range increases.Ref. 12, fig. 2.

A compact CPW‐fed antenna with fractal S‐shaped patches for multiband applications

ABSTRACTWe present the design of a novel compact coplanar waveguide‐fed antenna with fractal s‐shaped patches for multiband applications. The antenna consists of three fractal s‐shaped patches with different lengths. We demonstrate that the number of resonant frequencies is in direct proportion with the number of fractal s‐shaped patches. This is to say that, the number of resonant frequencies in a multiband antenna can be increased by increasing the number of patches. The resonant frequencies can be selected by carefully adjusting the length of the patches. We have designed our antenna to operate at 2.5/5.3/7.1/8.4 GHz. The measurement results show that the proposed antenna has 10 dB impedance bandwidths of 622 MHz (2.322–2.944 GHz), 466 MHz (5.113–5.579 GHz), 121 MHz (6.890–7.011 GHz) and 1080 MHz (8.206–9.286 GHz) to cover all the 2.4 GHz Bluetooth, 5.5 GHz WiMAX, and 2.4/5.2 GHz WLAN bands. The latter two bands of our proposed antenna fall within the X band range which finds vast applications in radar, aircraft, spacecraft and mobile or satellite communication system. The proposed antenna is printed on a single‐layered FR4 substrate, and it occupies a small volume of 17 × 18 × 1.6 mm3. The simulated and measured performance of the antenna confirms its omnidirectional radiation pattern and quad‐band operation. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:541–546, 2017

New Compact Microstrip Patch Antennas: Design and Simulation Results

Objectives: To design new multi-band antennas based on patch resonator with comparative results to each other. Both antennas are compact in size and have high quality responses which can be applied in many handheld and personal communication devices. Methods/Analysis: New microstrip patch antennas based on modified first iteration of Minkowski fractal geometry and applying central small square cut in the main resonator have been presented in this paper with and without inserting corner square patches. Both antennas have designed using single layer and dual feeds to operate as multi frequency devices. The antennas have been modeled and optimized by using the Microwave Office (MWO) simulator based on the method of moments. The projected antennas have been designed using FR4 substrate with a relative dielectric constant of 4.4 and a substrate height of 1.6 mm. Compared with the microstrip patch antenna without inserting corner patches using same main patch resonator dimensions and substrate specifications, the designed antenna with corner patches exhibits more operational frequencies as well as as greater frequency ratios with respect to the first fundamental frequency. Findings: New microstrip antennas based on patch resonator with and without inserting corner patches have been proposed. The first antenna exhibits multi-frequency behavior, where resonances appear to take place at frequencies of 2.49, 3.03and 6.63 GHz, within 2 to 7 GHz frequency range. The second antenna exhibits a higher number of resonant frequencies that appear at 2.14, 2.55, 5.03, 5.81, 5.9 and 6.14 GHz respectively under same previous frequency range. The first three operational frequencies have decreased or shifted by inserting corner square patches due to increased electrical physical dimensions of the second antenna. Also, these corner patches act as EM perturbation elements to stimulate the second antenna with more resonant frequencies within 2-7 GHz frequency sweeping range. Theoretically, there is an important relation between antenna dimensions and guided wavelength. This relation specifies if antenna dimension is less than quarter guided wavelength (λg), then the antenna is impractical because radiation resistance, bandwidth and gain are decreased and therefore the antenna size is enlarged. By the way, the dimensions of Antennas 1and 2 have been found to be (0.259 λg x 0.259 λg) and (0.269 λg x 0.269 λg) respectively according to their fundamental frequencies which are satisfactory. Both antennas have small sizes and high quality responses which can be applied in many handheld and personal communication devices. Novelty/Improvement: In this paper, new multi-band antennas based on patch resonator have been proposed. The proposed resonators have been initiated from the transformed version of the first iteration of Minkowski fractal geometry. These antennas have compact dimensions with good return loss and radiation pattern performances which are desired features to be adopted in many communication devices

A planar multiband Koch snowflake fractal antenna for cognitive radio

This paper of lettering reveals about a modified Koch snowflake fractal multiband antenna for cognitive radio applications. Multiband antennas can be employed for spectrum sensing in cognitive radio. This new microstrip-modified Koch fractal antenna exhibits multiple actions in four dissimilar resonant frequencies at 3.2, 5.2, 6, and 9.5 GHz correspondingly that covers the frequency bands such as S, C, and X bands. Its multiband behavior was analyzed by designing and simulating in ADS EMDS software. Three iterations were carried out to study the performance of modified Koch snowflake fractal antenna. The outer ring and a small rectangular slot in the center of the antenna are used for 50 Ω impedance matching and to increase the number of resonant frequencies. The fractal antenna parameters such as gain, directivity, and its radiation pattern are also analyzed in this paper. The measured results show good agreement with the simulated results.

Magnetoelectric cylindrical layered composite structure with multi-resonance frequencies

A combined ME composite structure is made of several cylindrical layered composites in series or parallel connection. Due to the cylindrical structure, the combined structure does not need more space. The characteristics of multi-resonance frequencies have been studied. Each resonance frequency of the structure can be adjusted by changing the cylinder diameter of the corresponding cylindrical layered composites. The number of resonance frequencies increases as the number of cylindrical layered composites increases. The multi-resonance frequencies behavior makes these cylindrical layered composite structures suitable for applications in multifuctional devices with multi-frequencies operation.

Interaction of a plane electromagnetic wave with a structure consisting of a strip grating, a metamaterial layer, and magnetized plasma: resonance effects and their interpretation

We reduce the boundary-value problem of the diffraction of a plane electromagnetic wave by a structure, which consists of a strip grating, a metamaterial layer, and magnetized plasma, to a system of linear algebraic second-kind equations with the kernel operator. Resonance properties of this structure are studied, and it is found that in the low-frequency range, it has several series of an infinite number of resonance frequencies with condensation points at certain finite frequencies.

A MULTI-WIDEBAND STACKED PATCH ANTENNA WITH PARASITIC RESONATORS AND SWITCHED SLOTS

A compact stacked microstrip patch antenna is proposed based on slot matching concept. Double layers of patches with parasitic resonator elements and substrates are manipulated in a stacked configuration. Slots and switches are integrated to each patch to enhance the antenna applicability for multi-wideband applications. The dimensions of the patches, parasitic elements, slots, and states of the switches and their positions are designed such that the antenna gives different number of resonant frequencies. The proposed antenna is capable to achieve a return loss less than -9.54 dB and voltage standing wave ratio

Free vibration analysis of an eccentric hollow cylinder using exact 3D elasticity theory

The translational addition theorem for cylindrical wave functions in conjunction with the appropriate orthogonal series expansions and the pertinent boundary conditions are employed to develop an exact 3D elasticity solution for free vibrations of a simply (shear diaphragm) supported elastic circular cylinder of finite length with an eccentrically located inner circular cavity. The frequency spectrum plots of the first several eigenfrequencies are presented in a wide range of dimensionless eccentricities for selected length-to-radius and inner–outer radius ratios. Also, a detailed study on the 2D free vibration characteristics of an infinite eccentric cylinder is included. The numerical results describe the imperative influence of cavity eccentricity, mode type, and radii and length ratios on the vibrational characteristics of the hollow cylinder. It is observed that the introduction of bore eccentricity causes not only an increase in the number of resonant frequencies through the splitting of degenerate modes of the unperturbed problem, but also changes the appearance order of natural vibration modes. The accuracy of solutions is checked through appropriate convergence studies, and the validity of results is established with the aid of a commercial finite element package as well as by comparison with the data in the existing literature.

Polarization dependent transmission through asymmetric C-shaped holes

We report that asymmetric c-shaped holes show mode switching between single- and double-resonance frequencies in the terahertz region, when the polarization direction of the incident light is controlled. The number of resonant frequencies is attributed to fundamental shape modes such as circle-, coaxial-, and rectangular-shaped holes activated under each polarization condition. All of these resonant peaks also show a transmission of over 90% with the assistance of the periodically arranged holes. These experimental results are in close agreement with theoretical simulations.

Multiple Resonances in Fluid-Loaded Vibrating Structures

This study deals with spectral analysis of fluid-loaded vibrating structure. It was recently observed in a numerical study on a high order perturbation method under heavy fluid loading that a loaded vibrating plate results, not only in classical frequency shift of in vacuo single resonance (in both real part because of fluid added mass and imaginary part because of energy lost by radiation into fluid), but also in an increase in number of resonance frequencies : as a result of loading, a single in vacuo resonance frequency of structure is transformed into a multiple resonance frequency. Here we show that this phenomenon is said to be a refinement of Sanchez's classical result in their book (Vibration and coupling of continuous systems, Springer-Verlag -1989-, paragraph 9.3) where it was established, using asymptotic analysis, that in case of a light loading conditions the scattering frequencies of a fluid loaded elastic structure (ie resonance frequencies) are nearly real eigenfrequencies of elastic body alone and complex scattering frequencies of fluid with a rigid solid. A theoretical explanation of observed phenomenon of multiple resonance is given using classical results of distribution of zeros of entire functions. It is established that every single in vacuo resonance frequency of a rectangular plate is transformed into an infinite number of resonances when fluid-loading is accounted for.

Paraelectric-Ferroelectric Phase Transitions in Small Spherical Particles

A transition in a spheroidal particle from the paraelectric to the ferroelectric phase as well as dynamic susceptibility are studied without approximation in the paraphase. It is assumed that the surface charge is compensated and the boundary condition for the polarisation is P = 0, i.e. with zero polarisation at the surface of the particle. There is an infinite number of resonance frequencies in the dynamic dielectric function within the quasistatic approximation. The paraphase properties of the dielectric response of the particle are discussed. The transition temperature decreases with decreasing diameter d of the particles inverse quadratically. There exists such a critical diameter that for the particles with the diameter below the critical one the ferroelectric phase is absent. Comparison of the experiment with theoretical results is carried out. Introduction of a dead layer thickness leads to a very good agreement of theory with the experiment for PbTiO 3 and to a good agreement with the experiment for BaTiO 3 .

Elastic Properties of Structural Phases in Shape Memory Alloys Investigated by Resonant Ultrasound Spectroscopy

Elastic constants of solids were, until recently, evaluated predominantly by pulse-echo ultrasonic methods which are based on measuring the speed of ultrasonic waves propagation in solids. Resonant ultrasound spectroscopy (RUS) is a relatively novel method in which all components of elastic tensor are determined from measured resonance frequencies of a freely vibrating specimen. The RUS technique has been employed in this work to investigate temperature dependence of the elastic properties of the parent austenite phase in CuAlNi shape memory alloy single crystals. This phase exhibits very high elastic anisotropy (anisotropy factor A 12) and softening the shear coefficient C0 upon cooling when approaching the Ms transformation temperature. The complications (need for large number of resonant frequencies) emerging when one tries to determine all elastic constants of highly elastically anisotropic materials by the RUS technique are discussed. It is concluded that the shear coefficients C0 and C44, which are the most important for shape memory alloys, are, nevertheless, determined reliably.

Optical Properties of Cometary Dust

AbstractCometary dust is observed in a variety of ways: scattered light, thermal emission, stellar occultations, coma and tail morphology, radar echoes, and meteors associated with comets. To interpret these observations with respect to the physical parameters of the dust (size, shape, and composition) and the properties of the dust-emitting region, the physics of how electromagnetic radiation interacts with small particles must be understood.The interaction between electromagnetic radiation and a small particle depends on the size, shape, and composition of the particle. The composition determines the optical constants of the material. Classically, a solid can be approximated by a collection of bound charges with a number of resonant frequencies. The optical constants (the index of refraction or dielectric constant) are a measure of the ability of the material to vibrate in response to an incoming electromagnetic wave. The laboratory measurement of optical constants is very difficult, and many published optical constants may be in error. Care must also be taken in choosing the optical constants that best represent the assumed composition of the cometary dust.Scattering theory is usually synonymous with Mie theory, although Mie theory pertains only to spherical particles. In many cases, homogeneous spheres may be good approximations of the dust in the coma, but an understanding of the effects of non-sphericity and heterogeneity is essential to determine the limitations of the spherical approximation. A variety of methods exist that, although computationally intensive, do provide insight into shape effects.