Resonance Frequency Spectra Research Articles

A QCM humidity sensors based on GO/Nafion composite films with enhanced sensitivity

A novel humidity sensor was made of quartz crystal microbalance and graphene oxide (GO)/Nafion nanocomposites. The humidity sensing properties of the sensor, such as sensitivity, stability, humidity hysteresis, dynamic response, and recovery, were investigated by monitoring changes in both resonant frequency and impedance spectrum. The results of the investigation showed the introduction of GO in Nafion matrix significantly enhanced sensitivity of the humidity sensors and maintained higher stability. Possible interpretation is that the introduction of GO sheets improves the hydrophilic property and mechanical property of GO/Nafion nanocomposites due to unique properties of GO. Meanwhile, the sensors based on GO/Nafion nanocomposite films exhibited a narrow humidity hysteresis.

Resolving the formation of modern Chladni figures

The resonant spectrum of a thin plate driven with a mechanical oscillator is precisely measured to distinguish modern Chladni figures (CFs) observed at the resonant frequencies from classical CFs observed at the non-resonant frequencies. Experimental results reveal that modern CFs generally display an important characteristic of avoided crossings of nodal lines, whereas the nodal lines of classical CFs form a regular grid. The formation of modern CFs and the resonant frequency spectrum are resolved with a theoretical model that characterizes the interaction between the plate and the driving source into the inhomogeneous Kirchhoff-Love equation. The derived formula for determining resonant frequencies is shown to be exactly identical to the meromorphic function given in singular billiards that deals with the coupling strength on the transition between integrable and chaotic features. The good agreement between experimental results and theoretical predictions verifies the significant role of the strong-coupling effect in the formation of modern CFs. More importantly, it is confirmed that the apparatus for generating modern CFs can be developed to serve as an expedient system for exploring the nodal domains of chaotic wave functions as well as the physics of the strong coupling with a point scatterer.

Anisotropic Elastic Properties of Chiral Sculptured Thin Films at Micro-Scale Evaluated by Resonance Frequency Spectra

Chiral sculptured thin films (STFs) Glancing-angle deposition (GLAD) thin films are nanoengineered to meet the requirements of a variety of applications such as micro filters, sensors, and waveguides due to their unique frequency characteristics which cannot be achieved by conventional solid materials. For the design, it is necessary to understand the elastic properties of STFs. To facilitate this, we report on our newly developed advanced micro-scale vibration testing process. In the testing, specially designed micro-specimens with surface areas of tens by tens of microns are excited using a piezoelectric (PZT) actuator and the resonance frequencies are detected by a laser device in the vertical or lateral directions successfully. The anisotropy elastic modulus of STFs composed of helical nanosprings are identified on the basis of vibration testing. The thin film shows strong characteristic anisotropy that the solid one hardly can attain. The micro-scale testing technique can be extended to other materials and microstructures.

Tuning for Resonances

AbstractDue to a very distinct spectrum of resonant frequencies, the characterization of optical microcavities calls for widely tunable sources of continuous wave laser light, offering suitably narrow linewidths and single‐mode operation over the entire tuning range. This is why external cavity diode lasers, which allow for mode‐hop free wavelength tuning, often over more than a hundred nanometers, have matured to a fundamental tool of the optical microresonator research apparatus.

Anisotropic elastic properties of chiral sculptured thin films at micro-scale evaluated by resonance frequency spectra

Abstract Chiral sculptured thin films (STFs) are nano-engineered to meet the requirements of a variety of applications such as micro filters, sensors, and waveguides due to their unique frequency characteristics which cannot be achieved by conventional solid materials. For the design, it is necessary to understand the elastic properties of STFs. To facilitate this, we developed an advanced micro-scale vibration testing process. In the testing, specially designed micro-specimens with surface areas of tens by tens of microns are excited using a piezoelectric (PZT) actuator and the resonance frequencies are detected by a laser device in the vertical or lateral directions successfully. The anisotropy elastic modulus of STFs composed of helical nano-springs are identified on the basis of vibration testing. The thin film shows strong characteristic anisotropy that the solid one hardly can attain. The micro-scale testing technique can be extended to other materials and microstructures.

Elastic properties of array films at submicron-scale evaluated by resonance frequency spectra

Submicron array films are nano-engineered to meet the requirements of a variety of applications such as micro filters, sensors, and waveguides due to their unique frequency characteristics which cannot be achieved by conventional solid materials. For the design, it is necessary to understand the elastic properties of submicron array films. To facilitate this, we developed an advanced micro-scale vibration testing process. In the testing, specially designed micro-specimens with surface areas of tens by tens of microns are excited using a piezoelectric (PZT) actuator and the resonance frequencies are detected by a laser device in the vertical or lateral directions successfully. The elastic modulus of submicron array films composed of helical nano-springs are identified on the basis of vibration testing.

Linear instability mechanisms leading to optimally efficient locomotion with flexible propulsors

We present the linear stability analysis of experimental measurements obtained from unsteady flexible pitching panels. The analysis establishes the connections among the wake dynamics, propulsor dynamics, and Froude efficiency in flexible unsteady propulsion systems. Efficiency is calculated from direct thrust and power measurements and wake flowfields are obtained using particle image velocimetry. It is found that for flexible propulsors every peak in efficiency occurs when the driving frequency of motion is tuned to a wake resonant frequency, not a structural resonant frequency. Also, there exists an optimal flexibility that globally maximizes the efficiency. The optimal flexibility is the one where a structural resonant frequency is tuned to a wake resonant frequency. The optimally tuned flexible panels demonstrate an efficiency enhancement of 122%–133% as compared to an equivalent rigid panel and there is a broad spectrum of wake resonant frequencies allowing high efficiency swimming over a wide range of operating conditions. At a wake resonant frequency we find that the entrainment of momentum into the time-averaged velocity jet is maximized.

Measurements of junction coupling during water hammer in piping systems

For the analysis of the effects of fluid–structure interaction (FSI) during water hammer in piping systems, a test facility has been designed and constructed. The research objective is to show on the basis of two specific examples that the necessity of considering FSI is strongly dependent on the boundary conditions of the system. Resonance experiments on movable bends in two piping system configurations focused on junction coupling were carried out. These configurations differ in the length of the hydraulic system and in the geometry of the oscillating bend. The displacement of the bend and the pressure inside the pipe were measured for various free oscillating lengths of the bend while the rest of the piping system was restrained. The results are displayed in resonance curves and frequency spectra for the different configurations. In both cases a correlation between the pressure and the displacement spectrum shows a transfer of momentum from the fluid to the structure, but only in the configuration with the long oscillating pipe section can a reaction of the fluid on the motion of the structure be identified. Frequency shifts of the pressure and a splitting of the pressure peak were observed. The time signals confirm that the effects of FSI are most significant in one system configuration which is strongly influenced by the bend geometry. Furthermore a parameter is presented which quantifies the effects of junction coupling based on the geometrical and hydraulic properties of the bend and the system.

Effects of Heating of Deformation Antinode Areas on Amplitude−Frequency Characteristics of an Ultrasonic Vibration System

The problem of steady-state longitudinal oscillations of a rod-like waveguide was solved. As a result, the distribution of internal heat sources was determined and the spatial and time distribution of temperature over the waveguide surface was calculated. The changes in the resonance frequency spectrum of an ultrasonic oscillatory system (USOS) consisting of a piezoelectric transducer and a rod waveguide were measured experimentally. The variations in the resonance frequency spectrum depend on the rod waveguide temperature. The dependence of the elastic modulus and the absorption coefficient on temperature allows the shift in the USOS resonance spectrum caused by heating of the deformation antinode areas during prolonged operation at resonance frequency to be determined.

Nondestructive evaluation of thickness variations for elastic plates by high-overtone bulk acoustic resonance

Based on the resonant frequency spectra of a high-overtone bulk acoustic resonance, a model for nondestructive evaluation of the elastic plate thickness is given. The simulations demonstrate that the thickness deviations of the elastic plates are sensitive to two parameters: the parallel resonance frequencies and the spacing of parallel resonance frequencies (SPRF). At the normal and transition regions of the SPRF curves, the parallel resonance frequencies periodically linearly decrease with the increase of thickness deviations, which is applicable for evaluating the thickness deviations of the plates.

Procedure for identification and analysis of the vibration characteristics and the mode shapes of semi-submersible platforms

The fundamental vibration characteristics and the mode shapes of a semi-submersible platform determine its operation conditions and long-term structural response. The current investigation presents a procedure for identification of the global natural frequencies and the mode shapes of a semi-submersible platform. The purpose is to evaluate the separation in frequency between the semi-submersible’s global natural frequencies and the exciting wave spectrum. Two types of finite element model are developed and compared: a beam element model and a shell element model. The main differences in the models are the level of resolution in the details and the model complexity. It is shown that both the beam element model and the shell element model can be used for the analysis. However, the beam element model is recommended for a first approximate assessment of the fundamental natural frequency and the interval and spectrum of the global resonance frequencies compared with the wave spectrum. The shell element model is recommended when a more thorough analysis is required. In addition, the natural frequencies of the semi-submersible are calculated for free vibrations in air. The fundamental frequency was 1.9 Hz for the beam element model and 1.5 Hz for the shell element model. When the masses corresponding to a submerged structure in operation mode are considered, including the effects of the added mass, the fundamental frequency for the first mode was decreased to 0.7 Hz when using the beam element model, and to 0.6 Hz when using the shell element model. When compared with the world wave spectrum’s highest frequency of 0.29 Hz reported by Det Norske Veritas, it is concluded that the natural frequencies of the semi-submersible are at a sufficient distance from the exciting wave spectrum.

Dual resonance excitation system for the contact mode of atomic force microscopy

We propose an improved system that enables simultaneous excitation and measurements of at least two resonance frequency spectra of a vibrating atomic force microscopy (AFM) cantilever. With the dual resonance excitation system it is not only possible to excite the cantilever vibrations in different frequency ranges but also to control the excitation amplitude for the individual modes. This system can be used to excite the resonance frequencies of a cantilever that is either free of the tip-sample interactions or engaged in contact with the sample surface. The atomic force acoustic microscopy and principally similar methods utilize resonance frequencies of the AFM cantilever vibrating while in contact with the sample surface to determine its local elastic modulus. As such calculation demands values of at least two resonance frequencies, two or three subsequent measurements of the contact resonance spectra are necessary. Our approach shortens the measurement time by a factor of two and limits the influence of the AFM tip wear on the values of the tip-sample contact stiffness. In addition, it allows for in situ observation of processes transpiring within the AFM tip or the sample during non-elastic interaction, such as tip fracture.

Investigation on Resonance Effects of Closely Resonating Nano-Pillars Attached to SAW Resonator

Surface acoustic wave (SAW) sensors form an important class of micro sensors in the microelecto mechanical systems (MEMS) family. Mass loading effect of a sensing medium is one of the prime sensing principles in SAW sensors. Recently we reported mass loading effect of high aspect ratio nano-pillars attached to a SAW resonator. We observed increase in resonance frequency of the SAW resonator in addition to the general mass loading characteristics. We concluded that when the resonance frequency of the pillar is equal to the SAW resonator frequency, the resonance frequency shift caused by mass loading of pillar tends to a negligible value. When such resonating pillars are used as sensing medium in SAW sensors, even a very small change in the dimension of the pillar will offer significant resonance frequency shift. Accordingly, high sensitive SAW sensors can be developed. However in practice it’s quite difficult to manufacture nano-pillars with accurate dimensions such that they resonate with SAW resonator. There is more probability that the pillars may closely resonate with SAW device and offer mass loading. In the present work we have extended our earlier work and performed finite element method (FEM) simulation to study the insight physics of the closely resonating pillars and their effects on acoustic wave propagating on SAW substrate. In this paper we present the discussion on the resonance effects of typical closely resonating pillars on resonance frequency spectrum of the SAW resonator and observations in the pressure wave at the contact surface of the pillar and SAW resonator substrate. It is observed that when the nano-pillars closely resonate with SAW resonator, the pillar oscillations combine with waves propagating in the substrate and introduce beat frequencies. The results and discussion of this paper adds additional information in designing SAW based coupled resonating systems.

교환 바이어스 인위적 준강자성 기준층을 포함한 자기 터널 접합의 강자성 공명

Spin dynamics of magnetic tunnel junctions with free and fixed reference layers is investigated by ferromagnetic resonance micromagnetic simulations. First, in magnetic tunnel junctions with an exchange biased synthetic ferrimagnetic reference layer, a magnetization direction of each layer and the tunneling magnetoresistance are calculated for a DC magnetic field. To investigate the spin exciting modes in magnetic tunnel junctions, we simulate the ferromagnetic resonance frequency spectra with small RF magnetic fields. Exciting modes of the tunneling magnetoresistance calculated by an included angle between free and reference layers is interpreted from those of each layer. Spin exciting modes are different according to a signs of the DC magnetic field. In a negative magnetic field, FMR frequency spectra of free and reference layers are well elucidated by the modified Kittel`s equation. However, in a positive magnetic field, there is no simple analytic solution related to FMR frequency spectra due to the coupled modes. Since ferromagnetic layers in magnetic tunnel junctions are interactive each other, careful considerations of the reference and fixed layer as well as the free layer are required for understanding on the spin dynamics of magnetic tunnel junctions with an exchange biased synthetic ferrimagnetic reference layer.

Analytical solutions for the resonance response of Goupillaud-type elastic media using [formula omitted]-transform methods

The resonance frequency spectrum is first derived for an m-layered Goupillaud-type elastic medium that is subjected to a discrete sinusoidal forcing function that varies harmonically with time at one end and held fixed at the other end. Analytical stress solutions are obtained from a coupled first-order system of difference equations using z-transform methods, where the determinant of the resulting global system matrix in the z-space |Am| is a palindromic polynomial with real coefficients. The zeros of the palindromic polynomial are distinct and are proven to lie on the unit circle for 1≤m≤5 and for certain classes of multilayered designs identified by tridiagonal Toeplitz matrices. An important result is the physical interpretation that all the positive angles, coterminal with the angles corresponding to the zeros of |Am| on the unit circle, represent the resonance frequency spectrum for the discrete model. A sequence of resonance frequencies for the discrete model appears to be universal for all multilayered designs with an odd number of layers, as it is independent of any design parameters.The resonance frequency results for the discrete model are then extended to describe the resonance frequency spectrum for the continuous model, where the forcing function applied at one end of the strip is continuous and varies harmonically with time while the other end is held fixed. The proposed natural frequency spectrum for a free-fixed m-layered Goupillaud-type strip is confirmed by independently solving a simplified form of the frequency equation, obtained after applying a transformation of the spatial variable. Our results suggest that the natural frequency spectrum depends on the layer impedance ratios and it is inversely proportional to the equal wave travel time for each layer.The results are used to identify layered designs with a common frequency spectrum and modify an existing design to obtain a desired frequency spectrum. Other connections are made with previous stress optimization results, the Chebyshev polynomials of the first and second kind, as well as the natural frequencies of a free-fixed non-Goupillaud-type layered strip.

Steering the optical response with asymmetric bowtie 2-color controllers in the visible and near infrared range

We have proposed an asymmetric bowtie 2-color controller and analyzed its resonance frequency spectra and temporal responses. The results show improved optical properties of the asymmetric bowtie 2-color controller as compared to symmetric bowties. The improved optical properties are a broad bandwidth of the plasmonic spectrum consisting of two resonant peaks, a high field enhancement in the gap of the bowtie structure, and a large effective enhancement volume. The system might have applications in the generation of XUV light via high-harmonic generation as well as in ultrabroadband sensors and multicolor optoelectronic filters.

Quantify Resonance Inspection With Finite Element-Based Modal Analyses

Resonance inspection uses the natural acoustic resonances of a part to identify anomalous parts. Modern instrumentation can measure the many resonant frequencies rapidly and accurately. Sophisticated sorting algorithms trained on sets of good and anomalous parts can rapidly and reliably inspect and sort parts. This paper aims at using finite element-based modal analysis to put resonance inspection on a more quantitative basis. A production level automotive steering knuckle is used as the example part for our study. First, the resonance frequency spectra for the knuckle are measured with two different experimental techniques. Next, scanning laser vibrometry is used to determine the mode shape corresponding to each resonance. The material properties including anisotropy are next measured to high accuracy using resonance spectroscopy on cuboids cut from the part. Then, the finite element model of the knuckle is generated by meshing the actual part geometry obtained with computed tomography. The resonance frequencies and mode shapes are next predicted with a natural frequency extraction analysis after an extensive mesh size sensitivity study. The good comparison between the predicted and the experimentally measured resonance spectra indicates that finite element-based modal analyses have the potential to be a powerful tool in shortening the training process and improving the accuracy of the resonance inspection process for a complex production level part. The finite element-based analysis can also provide a means to computationally test the sensitivity of the frequencies to various possible defects such as porosity or oxide inclusions, especially in high stress regions that the part will experience in service.

High-frequency vibrations of piezoelectric plates driven by lateral electric fields

We study coupled face-shear and thickness-twist motions of piezoelectric plates of monoclinic crystals driven by lateral electric fields. The first-order theory of piezoelectric plates is used. Pure thickness modes and propagating waves in unbounded plates as well as vibrations of finite plates are studied. Both free vibrations and electrically forced vibrations are considered. Basic vibration characteristics including resonant frequencies, dispersion relations, frequency spectra and motional capacitance are obtained. Numerical results are presented for AT-cut quartz plates. The results are expected to be useful for the understanding and design of resonant piezoelectric devices using lateral field excitation.

Studies on the shift in the frequency of the first Schumann resonance mode during a solar proton event

The variation of the first Schumann resonance (SR) frequency spectra observed from the recorded data over Kolkata (22.56°N, 88.5°E) during a solar proton event (SPE) on July 14, 2000 has been presented. It shows increase in frequency during X-ray bursts and decrease during the period of occurrence of an SPE. The results from some other locations for the same event are also reported. The severe X-ray bursts recorded just before the proton event exhibit enhancement in frequency of the first mode due to enhancement of ionization in the D-region of the ionosphere. Some attempts are made to explain the observed variation during solar proton events in terms of the perturbations within the Earth–ionosphere waveguide on the basis of two-layer-model.

Effects of Thickness Deviation of Elastic Plates in Multi-Layered Resonance Systems on Frequency Spectra

A model of high-overtone bulk acoustic resonators is used to study the effects of thickness deviation of elastic plates on resonance frequency spectra in planar multi-layered systems. The resonance frequency shifts induced by the thickness deviations of the elastic plates periodically vary with the resonance order, which depends on the acoustic impedance ratios of the elastic plates to piezoelectric patches. Additionally, the center lines of the frequency shift oscillations linearly change with the orders of the resonance modes, and their slopes are sensitive to the thickness deviations of the plates, which can be used to quantitatively evaluate the thickness deviations.