Antiresonance Frequencies Research Articles

Crack identification in beam by antiresonant frequencies

The present paper deals with the concept of antiresonance in multiple cracked beams and application for multi-crack identification. First, governing equations for antiresonant frequency are conducted and used for both computing antiresonant frequencies versus crack parameters and measuring-loading colocation and identifying cracks by measured antiresonant frequencies. Then, a procedure is proposed for crack identification in cantilever beam by antiresonant frequencies based on the so-called crack scanning method. Theoretical development is illustrated by numerical examples.

Modeling and experimental validation of a quantitative bar-type corrosion measuring probe using piezoelectric stack and electromechanical impedance technique

Corrosion coupon method has been widely used to estimate the corrosion rate in multiple industries. However, in this method, the weights of the coupons are measured periodically, which limit the application for on-line monitoring. In this paper, a novel type of quantitative bar-type corrosion measuring probe using piezoelectric stack and electromechanical impedance (EMI) technique was proposed. The probe consists of a piezoelectric stack and a metal bar. The multilayer models were used to derive the solution of the probe in longitudinal vibration mode. Five probe prototypes with designated probe length were fabricated to simulate uniform corrosion induced mass loss and investigate the EMI response with probe length. The relationship between the corrosion induced probe length loss and the first and second resonant and anti-resonant frequencies were analyzed. The measured results agreed well with the theoretical predictions. In addition, the accelerated corrosion tests were also performed to induce corrosion to the probe in a realistic setup and further validate the efficacy of the proposed method. The present study proved the feasibility of using the proposed bar-type corrosion measuring probe to quantitatively assess the corrosion amount by introducing the longitudinal vibration with piezoelectric stack and EMI.

Acoustic characteristics of looped-tube thermoacoustic refrigerators with external and in-built acoustic drivers: A comparative study.

Thermoacoustic refrigerators (TARs) are in the first place acoustic systems. It is indispensable to conduct an acoustic analysis of the entire system before a thermodynamic analysis of the thermoacoustic core. This study focuses on the acoustic characteristics of looped-tube TARs integrated with single (or dual) external (or in-built) acoustic driver(s). System-level acoustic models are established for the looped-tube TARs, and their acoustic performances are discussed and compared. Results show that looped-tube TARs with a single acoustic driver have a standing-wave acoustic field no matter whether the configuration is symmetric or not. The eigenmodes of the TAR are not influenced by the location of the external acoustic driver but are affected by the location of the in-built acoustic driver. New pairs of resonance and anti-resonance frequencies show up for TARs with an asymmetric configuration. Compared with looped-tube TARs with a single external (or in-built) acoustic driver, looped-tube TARs with dual external (or in-built) acoustic drivers have the same (or different) eigenmodes. A standing-wave acoustic field is present inside the loop only when the two acoustic drivers work in in-phase and anti-phase modes. At other phase differences between the two acoustic drivers, the acoustic field inside the loop becomes hybrid, containing both standing- and traveling-wave components. The theoretical methodology and analytical results in this study are valuable in comprehending the acoustic behavior of electrically-driven looped-tube TARs, providing useful guidelines for the active control of acoustic field and heat transport in the thermoacoustic core.

Experimental validation of axially polarized multilayer piezoelectric composite cylindrical transducers with adjustable multifrequency

The axially polarized multilayer piezoelectric composite cylindrical transducers with adjustable multifrequency capability have been proposed by adjusting the external electric resistance and the ratio of piezoelectric layer numbers between the actuator part and the sensor part, which have promising potential in designing the novel cymbal transducer for underwater sound projector and ultrasonic radiator applications. In the previous studies, the multilayer models were established to guide the design of the transducers with arbitrary layer number, and analyzed the dynamic characteristics theoretically. In this work, an experimental study is performed to validate the theoretical models and predictions. Piezoelectric rings with multiple concentric annular electrodes are designed to characterize the multilayer piezoelectric composite cylindrical transducers. The top surface of the piezoelectric rings is divided into two separate parts. One part is covered by multiple concentric annular electrodes, corresponding to the piezoelectric layers, and the other part is uncovered, corresponding to the elastic layers. Four prototypes are fabricated and each consists of four concentric annular electrodes. The impedance spectra are measured by the impedance analyzer to obtain the resonance and anti-resonance frequencies. Effects of two adjusting methods on the dynamic characteristics are evaluated experimentally. The experimental results basically coincide with the theoretical ones. This comprehensive experimental work assures the feasibility of using axially polarized multilayer piezoelectric composite cylindrical transducers with adjustable multifrequencies and confirms the benefit of the developed theoretical models for guiding the fabrication and optimization of this type of transducers.

Analysis of process parameters of hypoeutectoid steel ultrasonic horns with different heat treatment processes

An ultrasonic horn operated at 28 kHz was simulated by finite element analysis. The horns and samples were formed from hypoeutectoid steel containing 0.178 wt% C and 1.3 wt% Cr. They were austenized at 875 °C with a soaking time of 33 min, then quickly water-quenched and oil-quenched. Tempering was performed at different temperatures (200 °C–500 °C) and soaking times (120–240 min). Over the cross-section, the hardness was consistently lower at the center position than at other positions. The maximum (minimum) hardness was achieved after water and oil quenching, tempering at low (high) temperature, and soaking for a short (long) time. Heat treatment decreased the anti-resonance frequency of the ultrasonic horns but increased the mechanical quality factor and the impedance at the anti-resonance frequency. The mechanical quality factor was proportional to both tempering temperature and soaking time. As shown in microstructural images, high mechanical quality was also related to small grain size.

Theoretical and experimental investigations on semi-active quasi-zero-stiffness dynamic vibration absorber

A semi-active quasi-zero-stiffness (QZS) dynamic vibration absorber (DVA) (SAQZS DVA) is proposed to broaden the frequency bandwidth for ultra-low frequency vibration absorption. The SAQZS DVA is constructed by embedding an electromagnetic actively regulatory mechanism (ARM) into a QZS DVA to fulfill tuning capability of vibration absorption. The restoring force and stiffness of the SAQZS DVA are investigated theoretically to demonstrate how the ARM performs by tuning the current in the coils. Then, the complicated expression of the restoring force of the SAQZS DVA is fitted by polynomial approximation, and the frequency-amplitude response is obtained analytically. The results show the SAQZS DVA enables vibration absorption at an ultra-low frequency, and the anti-resonance frequency for vibration absorption can be tuned effectively. Furthermore, the prototype of the SAQZS DVA is built, and the verification experiment is carried out. The results indicate that the anti-resonance frequency for vibration absorption can be tuned from 3. 86 Hz to 4.67 Hz. Moreover, a remarkable reduction in acceleration amplitude can be observed when the anti-resonance frequency is tuned to match the excitation frequency by adjusting the ARM. Consequently, the SAQZS DVA should be a feasible way for vibration absorption tuning in ultra-low frequency range.

Temperature Behavior of SAW Resonators Based on LiNbO₃/Quartz and LiTaO₃/Quartz Substrates.

LiNbO3 (LN) or LiTaO3 (LT) thin plates bonded to quartz are novel types of layered substrates for temperature-compensated surface acoustic wave (TCSAW) devices. In SAW resonators with Al electrodes arranged on LT/quartz and LN/quartz substrates, improved temperature behavior due to opposite signs of temperature coefficients of frequency (TCF) in quartz substrates and LT or LN plates can be combined with high Q -factors if the quartz orientation is optimized. The quartz orientation areas that enabled high Q -factors were deduced from analyzing the quartz anisotropy and the characteristics of shear horizontally (SH) polarized waves were calculated in the optimal orientations as functions of the quartz cut angle and plate thickness. The simulation results illustrated by contour plots of the wave characteristics revealed the presence of zero lines on the plots demonstrating TCFs at resonant (TCFR) and antiresonant (TCFA) frequencies in both layered structures. The strong quartz anisotropy explained anomalous temperature behavior of SAW resonators and the existence of LT/quartz structures with TCFA = TCFR facilitating the design of SAW devices with improved thermal stability in the passband. In the LT/quartz structures, two TCFs vanished simultaneously at certain plate thickness and quartz orientation, while in the LN/quartz zero lines did not intersect but low TCF = -(10-20) ppm/°C combined with electromechanical coupling exceeding 18% were obtained numerically in some structures. The effect of inverting the propagation direction or cut angle in one of the combined materials on the wave characteristics was discussed and numerically estimated.

태양전지 웨이퍼 세정용 초음파 웨이브가이드 설계 제작 및 실험

Until recently, solar energy has been considered as a promising regeneration energy source in the future. Solar cell wafer production involves ingot cutting, cleaning, and packaging processes. In this research, design, fabrication, and testing of a batch-type midsonic for cleaning solar cell wafers were carried out. To reduce the damage compared to conventional systems, we decided to use 400 kHz in a midsonic wave range, and we used far-field to obtain a more regular acoustic pressure. Finite element analysis with Ansys software predicted an anti-resonance frequency of 458 kHz for an ultrasonic waveguide, and the measured result of the fabricated system was 454 kHz with a 0.9% error. Acoustic pressures were measured, and the result confirmed regular and high distributions. Finally, cleaning tests were performed, and a 90% particle removal efficiency (PRE) was achieved at 900 W. Thus, the newly developed midsonic cleaning system can be considered to clean particles on solar cell wafers efficiently while preventing damage.

Finite element simulation and characterization of one-port heterostructured surface acoustic wave resonator

The research work presents the study of a heterostructured surface acoustic wave (SAW) resonator consisting of an interdigital transducer (IDT), lithium niobate (LN), and silicon (Si) substrate. In the proposed structure, Silicon is the base substrate, above it layer of LN is placed then IDT is designed on it. The presented analysis includes the variation of the quality factor and electromechanical coupling coefficient with the change in the width of the piezoelectric layer. The electromechanical coupling coefficient (K 2), quality factor (Q-factor), velocity, resonance, admittance, and anti-resonance frequency have been studied for the thickness of the different layers of LN film. The higher quality factor of one port SAW devices reduces the energy loss and the K 2 of the devices indicates faster energy conversion. The Q-factor and K 2 are found to be depending on the thickness of LN, resonance, and anti-resonance frequency.

Mechanically Modulated Sideband and Squeezing Effects of Membrane Resonators.

We investigate the sideband spectra of a driven nonlinear mode with its eigenfrequency being modulated at a low frequency (<1 kHz). This additional parametric modulation leads to prominent antiresonance line shapes in the sideband spectra, which can be controlled through the vibration state of the driven mode. We also establish a direct connection between the antiresonance frequency and the squeezing of thermal fluctuation in the system. Our Letter not only provides a simple and robust method for squeezing characterization, but also opens a new possibility toward sideband applications.

Lead-Free AE Sensor Based on BZT-BCT Ceramics.

In this study, an acoustic emission (AE) sensor was fabricated using lead-free Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–BCT) ceramics. The acoustic and electromechanical properties of the AE sensor were determined by the shapes of the piezoelectric ceramics. To optimize the AE sensor performance, the shapes of the ceramics were designed according to various diameter/thickness ratios (D/T) = 0.5, 1.0, 1.5, 2.0, 2.5, 3.0. The BZT–BCT ceramic with D/T = 1.0 exhibited excellent values of a piezoelectric charge coefficient (d33), piezoelectric voltage coefficient (g33), and electromechanical coupling factor (kp), which were 370 (pC/N), 11.3 (10−3 Vm/N), and 0.58, respectively. Optimum values of resonant frequency (fr) = 172.724 (kHz), anti-resonant frequency (fa) = 196.067 (kHz), and effective electromechanical coupling factor (keff) = 0.473 were obtained for the manufactured BZT–BCT ceramic with D/T = 1.0. The maximum sensitivity and frequency of the AE sensor made of the BZT–BCT ceramic with a D/T ratio of 1.0 were 65 dB and 30 kHz, respectively.

Are Multiseasonal Forecasts of Atmospheric Rivers Possible?

AbstractAtmospheric rivers (ARs) exert significant socioeconomic impacts in western North America, where 30 of the annual precipitation is determined by ARs that occur in less than 15 of wintertime. ARs are thus beneficial to water supply but can produce extreme precipitation hazards when making landfall. While most prevailing research has focused on the subseasonal (5 weeks) prediction of ARs, only limited efforts have been made for AR forecasts on multiseasonal timescales (3 months) that are crucial for water resource management and disaster preparedness. Through the analysis of reanalysis data and retrospective predictions from a new seasonal‐to‐decadal forecast system, this research shows the existing potential of multiseasonal AR frequency forecasts with predictive skills 9 months in advance. Additional analysis explores the dominant predictability sources and challenges for multiseasonal AR prediction.

백래시비율과 모터입력전압을 고려한 3단 감속 서보시스템의 주파수 분석

This paper proposed the simulation model of the servo system with three-stage reducer and presented the result of frequency analysis of the servo system considering backlash ratios and motor input voltage. By virtue of this work, we realized that if the motor input voltage of the system was large, the influence of each stage backlash ratio could be minimized or removed. Besides, we also found that if the motor input voltage was small, this created an optimal backlash ratio combination which could maximize the anti-resonance and resonance frequency of the servo system. This paper could be useful for determining each stage backlash ratio in designing a three-stage geared servo system with fast response.

Revisiting Piezoelectric Sensor Calibration Methods Using Elastodynamic Body Waves

The application of absolutely calibrated piezoelectric (PZT) sensors is increasingly used to help interpret the information carried by radiated elastic waves of laboratory/in situs acoustic emissions (AEs) in nondestructive evaluation. In this paper, we present the methodology based on the finite element method (FEM) to characterize PZT sensors. The FEM-based modelling tool is used to numerically compute the true Green’s function between a ball impact source and an array of PZT sensors to map active source to theoretical ground motion. Physical-based boundary conditions are adopted to better constrain the problem of body wave propagation, reflection and transmission in/on the elastic medium. The modelling methodology is first validated against the reference approach (generalized ray theory) and is then extended down to 1 kHz where body wave reflection and transmission along different types of boundaries are explored. We find the Green’s functions calculated using physical-based boundaries have distinct differences between commonly employed idealized boundary conditions, especially around the anti-resonant and resonant frequencies. Unlike traditional methods that use singular ball drops, we find that each ball drop is only partially reliable over specific frequency bands. We demonstrate, by adding spectral constraints, that the individual instrumental responses are accurately cropped and linked together over 1 kHz to 1 MHz after which they overlap with little amplitude shift. This study finds that ball impacts with a broad range of diameters as well as the corresponding valid frequency bandwidth, are necessary to characterize broadband PZT sensors from 1 kHz to 1 MHz.

Unit-rank output feedback control for antiresonance assignment in lightweight systems

Antiresonance assignment is an effective approach to vibration absorption in lightweight systems under harmonic excitation. The goal is shifting an antiresonance frequency of a receptance to match the one of the excitation force, for making a system coordinate experiencing no (or very small) forced vibrations. A novel method for antiresonance assignment through active control is proposed and validated in this paper. The method relies on the unit-rank output feedback control technique to shift one antiresonance. The assignment problem is solved for both point and cross-receptances exploiting either collocated or non-collocated control architectures. The gain computation is done analytically, either through the system mass, stiffness and damping matrices, or through the measured receptances. Two method extensions are also proposed. First, the output feedback technique is extended to account for an additional sensor, to perform the simultaneous pole-zero assignment based on the zero non-spillover condition. Second, to allow for larger frequency shifts without reducing too much the stability margins, a passive-active, hybrid strategy is proposed. In the first stage, modification of the inertial and elastic parameters is employed to shift the antiresonance frequency as more as possible; in the second stage, the prescribed antiresonance is exactly assigned by means of active control, with smaller gains compared to active control alone. Experimental validation of the method is proposed through a smart, flexible cantilever beam controlled by a non-collocated pair made by an on-the-shelf piezoelectric actuator and a laser vibrometer.

An adjustable anti-resonance frequency controller for a dual-stage actuation semi-active vibration isolation system

An adjustable anti-resonance frequency controller for a dual-stage actuation semi-active vibration isolation system

Sound absorption of a finite flexible micro-perforated panel absorber back by a rigid air cavity filled with a fibrous porous material

Back by a rigid cavity filled with a layer of porous layer, the sound absorption performance of a micro-perforated panel (MPP) can be enhanced in comparison with other resonance based sound absorbers. In this paper, a theoretical model of a finite flexible MPP back by a rigid air cavity filled with a fibrous porous material is developed to predict normal sound absorption coefficients. Displacements of MPP and sound pressure field in fibrous porous material and acoustic cavity are expressed using a series of modal functions, and the sound absorption coefficients of MPP system are obtained. Additionally, comparison of energy dissipation by MPP and fibrous material is performed to identify effects of a fibrous material on the sound absorption of a MPP. As expected, at anti-resonance frequency of an MPP, the fibrous material provide an alternative energy dissipation mechanism.

A Multi‐Inventory Ensemble Analysis of the Effects of Atmospheric Rivers on Precipitation and Streamflow in the Namgang‐Dam Basin in Korea

AbstractAtmospheric rivers (ARs) are an important concern in regional water management; however, little is known about the AR impacts on hydrology in East Asia (EA). This study analyzes the characteristics of storms, precipitation (P), streamflow (Q), and runoff coefficient (R) in the Namgang‐dam basin in Korea related to ARs for 2000–2013, as well as the sensitivity of the analysis results to AR detection methods, using observed P, Q, and three different AR inventories. The basin experiences 37.3 storms annually, of which 54% are AR storms that provide over 60% of the annual P and Q. The AR (non‐AR) storms are dominant in storm frequency and the storm‐total P and Q for January–July (August–December) with peaks in July (August). The monthly AR frequency varies closely with the seasonal variations in the EA monsoon and the North Pacific storm track which modulate the number of extratropical cyclones. The AR storms produce most of the extreme events; they also generate larger storm‐mean P and Q than the non‐AR storms for all months. The seasonal variations in R are related to the total (AR‐ and non‐AR storms combined) P through the seasonal soil water variations, making the AR effects on R unclear. Considering 95% confidence intervals, the AR storms are distinguished well from the non‐AR storms in storm frequency and the storm‐total and storm‐mean P and Q. The sensitivity to AR inventories is not critical in quantifying the AR‐storm characteristics and their impacts on hydrologic variables except for R.

Optimal design of broadband quasi-perfect sound absorption of composite hybrid porous metamaterial using TLBO algorithm

In this study, the average sound absorption coefficient of a composite hybrid porous metamaterial (CHPM) structure was improved in the frequency range from 0 to 10 kHz by using the teaching–learning-based optimization algorithm when the geometric parameters (Layer spacing and lateral plate length) were regarded as optimization variables. The optimization results revealed that the CHPM exhibited an average sound absorption coefficient of 0.987. Three types of porous materials were used as matrix fillers, and the impedance of CHPM was found to almost perfectly matched with the surrounding air by using lateral plates of different lengths. The porous material suppresses the evanescent wave on the surface of CHPM and raises the sound absorption valley at each anti-resonance frequency, thus the reflection coefficient of the CHPM surface is extremely low. An effective medium model, transfer matrix method, and finite element method were jointly verified. The test results of the acoustic impedance tube proved that the optimized CHPM has a good sound absorption effect up to 1715 Hz. This proposed acoustic structure and optimization method would inspire more design ideas of new-type absorbers in ultra-broadband frequency range, and have potential applications in the field of industrial noise control and the construction of “quiet” cabin design.

Bandgap and vibration transfer characteristics of scissor-like periodic metamaterials

A periodic mass-spring-truss chain based on a scissor-like structure and inertial amplification is proposed to seek for low-frequency vibration attenuation. The resonant and anti-resonant frequencies of a basic element are obtained analytically to explain the resonance and anti-resonance of the periodic chain. The formation of bandgaps is explored, revealing that the vertical movements of the vertices take the input kinetic energy away from the horizontal movement energy. The cut-off frequencies of three models are derived analytically to compare the effect of the inertia amplification, which can reach more than three times the classical mass-spring chain with a small angle. Also, the effect of stiffness amplification is presented when the spring mounted vertically, unlike the classical inertial amplification systems. Thus, the optimal configuration for low-frequency attenuation is obtained, that is, the spring mounted horizontally and the masses mounted at the upper and lower vertices. The chain with mass on the upper and lower vertices has the lowest cut-off frequency, which is 17.7% lower than that of the classical mass-spring chain. A diatomic chain is studied to find lower and wider bandgaps, where the central frequency is 25% lower than the classical mass-spring diatomic chain. The central frequency and width of the new bandgap can be tunable accordingly. The result shows that small angles or low stiffness ratios result in lower bandgaps. Meanwhile, the large angles, big differences of masses, or high stiffness ratios lead to wider bandgaps.