Fundamental Resonance Frequency Research Articles

Vibration analysis of dynamic mode scanning thermal microscope nanomachining probe

Abstract Here dynamic mode Scanning Thermal Microscope (SThM) nanomachining technique is presented. The hypothesis states that “Excitation on the base can control the depth of nanomachining process by SThM probe”. The mathematical model is determined based on the Euler-Bernoulli beam. Partial differential equation of motion is solved by separating variables for linear equations and assumed modes method for nonlinear equations. Thermal vibrations is associated with a temperature dependent axial force. Constant, linear and quadratic temperature distribution over the probe are investigated while the probe is harmonically excited on the base at its approximated fundamental resonance frequency. The shifted resonance frequencies and amplitude of response in the excited frequency and shifted resonance frequencies are determined. The results indicate that temperature difference shifts the resonance frequencies, and its influence on vibration amplitudes are significant. It is explained that the effect of temperature distribution function is significant on resonance frequencies shift but negligible on amplitudes. It is showed, the amplitude is decreased in all frequencies with increasing the temperature difference. Finally it is demonstrated that with adding a known excitation on the base the depth of nanomachining process can be controlled. It is declared increasing the temperature improves the quality of final nanomachined surface.

A new piezoelectric hollow cylindrical transducer with multiple concentric annular metal fillers

Previous studies have proved that adding proper metal fillers into piezoceramics can enhance their mechanical and dielectric properties. This work will examine a new multiple concentric annular metal filling style in a short piezoelectric hollow cylindrical transducer, and study its radial vibration characteristics. A theoretical model formulated from plane stress condition is proposed to describe this type of transducers, and the reliability of this model is verified by the finite element simulation results. Furthermore, the effects of the important parameters including number, material types and thickness of the filler on the electromechanical characteristics of the transducer are investigated. The results indicate that the metal fillers with greater sound velocity ratio compared with the piezoceramic matrix can increase the fundamental resonance and anti-resonance frequencies. The metal fillers with smaller Young’s modulus can achieve the greater fundamental electromechanical coupling coefficient. These findings obtained are very beneficial for improving the design of piezoelectric cylindrical ultrasonic and underwater sound transducers.

Tuning forks with optimized geometries for quartz-enhanced photoacoustic spectroscopy.

We report on the design, realization, and performance of novel quartz tuning forks (QTFs) optimized for quartz-enhanced photoacoustic spectroscopy (QEPAS). Starting from a QTF geometry designed to provide a fundamental flexural in-plane vibrational mode resonance frequency of ~16 kHz, with a quality factor of 15,000 at atmospheric pressure, two novel geometries have been realized: a QTF with T-shaped prongs and a QTF with prongs having rectangular grooves carved on both surface sides. The QTF with grooves showed the lowest electrical resistance, while the T-shaped prongs QTF provided the best photoacoustic response in terms of signal-to-noise ratio (SNR). When acoustically coupled with a pair of micro-resonator tubes, the T-shaped QTF provides a SNR enhancement of a factor of 60 with respect to the bare QTF, which represents a record value for mid-infrared QEPAS sensing.

Identification of diseases in newborns using advanced acoustic features of cry signals

Our challenge in the current study is to extend research on the cries of newborns for the early diagnosis of different pathologies. This paper proposes a recognition system for healthy and pathological cries using a probabilistic neural network classifier. Two different kinds of features have been used to characterize newborn cry signals: 1) acoustic features such as fundamental frequency glide (F0glide) and resonance frequencies dysregulation (RFsdys); 2) conventional features such as mel-frequency cestrum coefficients.This paper describes the automatic estimation of the proposed characteristics and the performance evaluation of these features in identifying pathological cries. The adopted methods for F0glides and RFsdys estimation are based on the derived function of the F0 contour and the jump "J" of the RFs between two subsequent tunings, respectively. The database used contains 3250 cry samples of full-term and preterm newborns, and includes healthy and pathologic cries.The obtained results indicate the important association between the quantified features and some studied pathologies, and also an improvement in the identification of pathologic cries. The best result obtained is 88.71% for the correct identification of health status of preterm newborns, and 82% for the correct identification of full-term infants with a specific disease. We conclude that using the proposed characteristics improves the diagnosis of pathologies in newborns. Moreover, the method applied in the estimation of these characteristics allows us to extend this study to other uninvestigated pathologies.

Estimation of the Site Effect Using Microtremor Technique at New Akhmim City, Akhmim, Sohag, Egypt

Abstract —Local site effect is a significant aspect of seismic hazards, which often causes amplification of ground motions and results in increase in the damage potential of an earthquake. This article displays an experimental study of microtremors data to investigate the dynamic characteristics of the soil and structures in the desert zone of Akhmim City, east of River Nile, Sohag governorate, Egypt. Because of progressive population growth in the Nile valley and delta regions, the Egyptian Governorate considered increasing the number of new communities, especially in the Sohag district, to improve the living conditions. The study area is one of the new urban areas which was suggested by Egyptian Urban Communities Authority (EUCA). For this purpose, the horizontal to vertical (H/V) spectral ratio was used to provide precious information about the soil properties and its engineering features for foundation purposes. The H/V spectral ratio analyses of ambient noise data at the measurement stations were processed and interpreted using Geopsy Software to calculate the amplification factor and fundamental resonance frequency at each observation point. The results indicate that the resonance frequency ranges between 0.21 and 0.28 Hz at the most of the measurement stations, with some irregularities at stations No. 2 and 4 because of the higher softness of sediments in these locations. Most of lower fundamental frequencies are observed in the southern part of the study area, whereas higher values are observed in the northern part of the study area. The amplification factor ranges between 1.38 and 4.15. Higher values were recorded in the northeastern and southern parts, while lower ones were observed in the northwestern and southwestern parts of the mapped area. It can be concluded that the amplification component increases with increasing softness of the sediments. Interpretation of fundamental frequency distribution map is very significant to estimate the building heights and the number of stories, which was estimated to be 35 to 47.

High performance passive vibration isolation system for optical tables using six-degree-of-freedom viscous damping combined with steel springs.

Mechanical vibrations in buildings are ubiquitous. Such vibrations limit the performance of sensitive instruments used, for example, for high-precision manufacturing, nanofabrication, metrology, medical systems, or microscopy. For improved precision, instruments and optical tables need to be isolated from mechanical vibrations. However, common active or passive vibration isolation systems often perform poorly when low-frequency vibration isolation is required or are expensive. Furthermore, a simple solution such as suspension from common bungee cords may require high ceilings. Here we developed a vibration isolation system that uses steel springs to suspend an optical table from a common-height ceiling. The system was designed for a fundamental resonance frequency of 0.5 Hz. Resonances and vibrations were efficiently damped in all translational and rotational degrees of freedom of the optical table by spheres, which were mounted underneath the table and immersed in a highly viscous silicone oil. Our low-cost, passive system outperformed several state-of-the-art passive and active systems in particular in the frequency range between 1 and 10 Hz. We attribute this performance to a minimal coupling between the degrees of freedom and the truly three dimensional viscous damping combined with a nonlinear hydrodynamic finite-size effect. Furthermore, the system can be adapted to different loads, resonance frequencies, and dimensions. In the long term, the excellent performance of the system will allow high-precision measurements for many different instruments.

Modeling, simulation and experimental research for MEMS cantilevers of complex geometry

The fundamental resonant frequencies for MEMS cantilevers of complex geometry (paddle-shaped rectangular microbeam, homogeneous on a part of length and nonhomogeneous, layered structure to the wider part of the beam) are calculated. A method of analytical calculation using the Mohr-Maxwell theory is proposed for homogeneous microcantilevers, which is then adapted for non-homogeneous structures. The analytical model has been validated by numerical simulation using finite element method (FEM). The experimental validation has been made using laser-Doppler vibrometry (LDV) by scanning with the Polytec MSA-500 system.

Phononic Casimir corrections for Graphene resonator

By calculating a Casimir energy for the acoustic phonons of Graphene, we find some temperature-dependent corrections for the pretension of a Graphene sheet suspended on a trench. We obtain values of the order of few mN/m for these corrections in fully as well as doubly clamped Graphene on a narrow trench with one nanometer width, at room temperature. These values are considerable compared to the experimental values, and can increase the fundamental resonance frequency of the Graphene. The values of these corrections increase by increasing the temperature, and so they can be utilized for tuning the Graphene pretension.

Electrical and acoustic vibroscopic measurements for determining carbon nanotube fiber linear density

Lightweight materials for next-generation electrical and mechanical applications are expected to have significant impacts on aerospace and ground transportation by reducing fuel consumption. Assessing the potential of novel wiring or fibers requires accurate measurement of linear density. The linear densities of fibers are measured by determining the fiber's resonant frequency vibroscopically, which requires complex mechanical equipment for vibrating the fiber. Here, we leverage the electrical conductivity of carbon nanotube (CNT) fibers to induce vibrations by applying an alternating current (AC) to a fiber under a known tension in the presence of a permanent magnetic field, eliminating the need for mechanical actuation. The fiber vibrates at maximum amplitude when the AC frequency matches the fiber's fundamental resonant frequency, creating an audible sound and inducing measurable changes in the fiber electrical properties. Linear density can be calculated accurately from the resonant frequency or the changes in electrical properties in this simplified apparatus during a tensile test.

Biomechanics of the peafowl's crest reveals frequencies tuned to social displays.

Feathers act as vibrotactile sensors that can detect mechanical stimuli during avian flight and tactile navigation, suggesting that they may also detect stimuli during social displays. In this study, we present the first measurements of the biomechanical properties of the feather crests found on the heads of birds, with an emphasis on those from the Indian peafowl (Pavo cristatus). We show that in peafowl these crest feathers are coupled to filoplumes, small feathers known to function as mechanosensors. We also determined that airborne stimuli with the frequencies used during peafowl courtship and social displays couple efficiently via resonance to the vibrational response of their feather crests. Specifically, vibrational measurements showed that although different types of feathers have a wide range of fundamental resonant frequencies, peafowl crests are driven near-optimally by the shaking frequencies used by peacocks performing train-rattling displays. Peafowl crests were also driven to vibrate near resonance in a playback experiment that mimicked the effect of these mechanical sounds in the acoustic very near-field, reproducing the way peafowl displays are experienced at distances ≤ 1.5m in vivo. When peacock wing-shaking courtship behaviour was simulated in the laboratory, the resulting airflow excited measurable vibrations of crest feathers. These results demonstrate that peafowl crests have mechanical properties that allow them to respond to airborne stimuli at the frequencies typical of this species’ social displays. This suggests a new hypothesis that mechanosensory stimuli could complement acoustic and visual perception and/or proprioception of social displays in peafowl and other bird species. We suggest behavioral studies to explore these ideas and their functional implications.

Dielectric-Filled Reentrant Cavity Resonator as a Low-Intensity Proton Beam Diagnostic

Measurement of the proton beam current (0.1–40 nA) at the medical treatment facility PROSCAN at the Paul Scherrer Institut (PSI) is performed with ionization chambers. To mitigate the scattering issues and to preserve the quality of the beam delivered to the patients, a non-interceptive monitor based on the principle of a reentrant cavity resonator has been built. The resonator with a fundamental resonance frequency of 145.7 MHz was matched to the second harmonic of the pulse repetition rate (72.85 MHz) of the beam extracted from the cyclotron. This was realized with the help of ANSYS HFSS (High Frequency Structural Simulator) for network analysis. Both, the pickup position and dielectric thickness were optimized. The prototype was characterized with a stand-alone test bench. There is good agreement between the simulated and measured parameters. The observed deviation in the resonance frequency is attributed to the frequency dependent dielectric loss tangent. Hence, the dielectric had to be resized to tune the resonator to the design resonance frequency. The measured sensitivity performances were in agreement with the expectations. We conclude that the dielectric reentrant cavity resonator is a promising candidate for measuring low proton beam currents in a non-destructive manner.

Empirical estimate of resonance frequency at the Dead Sea basin

We carried out assessments of the fundamental frequencies of the southern Dead Sea basin using records of teleseisms and local earthquakes, obtained by the DESERT2000 (13 events) and DESIRE (40 events) projects that aimed in studying the Dead Sea fault in general and in particular the Dead Sea basin. The observed ground motions are from teleseisms with magnitude larger than 6.5 at distances of 1340–14,800 km, and of local earthquakes in the magnitude range 3.8–4.9 at distances of 90–660 km. We determine the fundamental resonance frequencies of the Dead Sea basin using (1) ratio between the spectra of seismograms recorded on site and those recorded at a reference site and (2) horizontal-to-vertical S-wave spectral ratio. Our results allow dividing the study area into three segments of different lengths: first 22 km (stations JB12–IB13), second 5 km (stations IB15–IB17), and third 45 km (stations IB19–ID27) with fundamental frequencies 0.1, 0.2, and 0.1 Hz, respectively. Amplification factors vary from 2 to 5. Thirteen reference stations are located on rock, at distances of 1–10 km away from the basin, which recorded vibrations in the range of 0.1–0.5 Hz, generated in the Dead Sea basin. We did not find locally induced surface waves, causing significant lengthening of the shaking duration and strong low-frequency amplification. It can be explained by the linear dimensions of the Dead Sea basin, its shape, and the relatively high velocity of shear waves that varies with depth from 800 to 3200 m/s. We use stochastic optimization algorithm to calculate the velocity model, yielding 1-D transfer function matching the observed H/V curves and resonance peaks.

Theoretical and experimental study of gradient-helicoid metamaterial

Resonance based acoustic metamaterials and metasurfaces exhibit outstanding phase modulation capabilities with high transmission coefficient, but it is rather confined to the neighborhood of fundamental or harmonic resonant frequencies. Based on the impedance-matched gradient material, we theoretically and experimentally study a gradient index helicoid metamaterial that can modulate sound wavefront with nearly perfect transmission over a broad bandwidth. Taking advantage of the linear spectral phase shifting, a thin flat metalens is constructed to demonstrate sound focusing with the extraordinary transmission for more than 1/3 octave band. It is anticipated that this engineered material may be used in ultrasonography, ultrasound surgery, and DNA fragmentation. Moreover, with the flexible adjustment of effective parameters, it can be an ideal alternative to the anisotropic inhomogeneous medium and has much better stiffness.

Mode unlocking characteristics of an RF detuned actively mode-locked fiber ring laser

Abstract An actively mode-locked laser (AMLL) is subjected to RF modulation frequency detuning away from its fundamental resonant frequency. The standard theoretical model of mode-locked lasers is extended with perturbative analysis and injection locking theory. The proposed model shows that with increasing detuning, the number of modes with phase-lock decreases. For a mode n , the injection range R n is found to decrease as n − 1 , thus making higher modes more susceptible to unlocking by RF detuning. Experimental verification of these theoretical predictions is obtained by using a custom built Yb 3 + doped fiber based ring AMLL. The AMLL operates at 1064 nm , with a repetition rate of f 0 = 26 . 69 MHz . The unlocking of modes is studied in the electrical domain by varying the RF detuning over a range of ± 13 kHz with a step-size of 130 Hz . The locking limits of a mode decrease as n − 1 as predicted by the theory. The fundamental mode ( n = 1 ) has an injection range of 143 . 4 kHz , with the higher modes, n > 1 , having smaller injection ranges as predicted by the theory.

Can broad-band earthquake site responses be predicted by the ambient noise spectral ratio? Insight from observations at two sedimentary basins

Site-effect assessments performed through earthquake-based approaches, such as the standard spectral ratio (SSR), require good quality records of numerous earthquakes. In contrast, the use of ambient noise appears to be an attractive solution for ease and rapid computation of site responses with sufficient spatial resolution (microzonation), especially in low seismicity areas. Two main approaches are tested here: the horizontal-to-vertical spectral ratio (HVSR) and the noise-based SSR (SSRn). The HVSR uses the relative amplitude of the horizontal and vertical components of the ambient noise. Instead, the SSRn defines the spectral ratio between the seismic noise recorded simultaneously at a site and at a rock reference station, similar to earthquake-based SSR. While the HVSR is currently used in hundreds of site-specific studies, the SSRn approach has been gradually abandoned since the 1990s. In this study, we compare the results obtain from these two approaches with those of earthquake-based SSR. This comparison is carried out for two sedimentary basins, in Provence (southeastern France) and in Argostoli (western Greece). In agreement with the literature, the HVSR does not provide more than the fundamental resonance frequency of the site (f0). The SSRn leads to overestimation of the SSR amplification factors for frequencies higher than the minimal f0 of the basin (f0min). This discrepancy between SSRn and SSR is discussed, and appears to be mainly dependent on the local geological configuration. We thus introduce the hybrid standard spectral ratio (SSRh) approach, which aims to improve upon the SSRn by adding an intermediate station inside the basin for which the SSR is known. This station is used in turn as a local reference inside the basin for the SSRn computation. The SSRh provides site transfer functions very similar to those of the SSR, in a broad frequency range. Based on these results, the SSRn (or SSRh) should be further tested and should receive renewed attention for microzonation inside sedimentary basins.

Site effects observed in the Norcia intermountain basin (Central Italy) exploiting a 20-year monitoring

This work aims to analyse the response to ground shaking of the Norcia intermountain basin (central Italy), where a temporary seismic network (Pilz and Parolai in Norcia basin (Italy) temporary seismic network. GFZ Data Services. https://doi.org/10.14470/8u7554472182 , 2009) was installed from January to May 2009, during the L’Aquila (Mw 6.1) seismic sequence. Here we present the results of the application of various empirical approaches for the evaluation of local site effects, considering hundreds of records relevant to earthquakes in the local magnitude range 3.0–5.4. The site amplification was estimated considering either the standard spectral-ratio (SSRs, Borcherdt in Bull Seismol Soc Am 60:29–61, 1970) or the horizontal to vertical spectral-ratio technique (HVSRs, Lermo and Chavez-Garcia in Bull Seismol Soc Am 83:1501–1506, 1993) techniques, applied to the S-phase and the S-wave coda of selected earthquakes. The results evidence the amplification of both horizontal and vertical components of ground motion at frequencies spanning from about 0.5 Hz, in the deepest part of the basin, to 4 Hz at basin edges. HVSRs show lower amplitudes than SSRs, due to the amplification of the vertical component, highlighting as the single station spectral technique, suitable to estimate the fundamental resonance frequency of the sites, is not able to reliably describe the actual seismic response. Considering the shape of the basin, possible predominant amplification with particular direction are investigated by rotated SSRs that allow to evidence in the central part of the studied area a prevailing amplification of the S-train waves along the 140°N direction. Finally, the generation of surface waves within the basin was investigated by the Multiple Filter Technique analysis (MFT, Dziewonski et al. in Bull Seismol Soc Am 59:427–444, 1969), estimating the backazimuth of the identified surface waves using the method proposed by Baker and Stevens (Geophys Res Lett 31:L09611, 2004. https://doi.org/10.1029/2004GL019510 ). In particular, the favourable conditions for the generation of surface waves inside the basin, have been evaluated by comparing records relevant to earthquakes with different sources and magnitudes recorded in the last twenty-year by the permanent NRC accelerometric station.

A closed-form approach for the resonant frequency analysis of clamped rectangular microplates under distributed electrostatic force

This paper proposes a fast-converged reduced-order model for small vibrations of electrostatically actuated rectangular microplates around their deformed states. On this foundation, one-mode analysis method and thus closed-form analytical expressions are developed for the fundamental resonant frequency analysis. Numerical multi-mode analysis is conducted to investigate the convergence. It is concluded that the one-mode analysis method can give a converged solution, which demonstrates that the proposed model has a faster convergence than previous models where multi modes are needed. The directly calculated resonant frequencies by the closed-form expressions are in good agreement with the numerical results by FEM simulations with less than 5% variation before pull-in. Parametric study shows the closed-form expressions are applicable to the cases in which the thickness is less than 1/20 of the length and width under a nominal length to width ratio of 1∼2.5, and the gap distance is less than or equal to the thickness of the microplate. Additionally, a kind of electrostatic configurations based on multilayer microplates, capacitive micromachined ultrasonic transducers (CMUTs), were used to experimentally validate the closed-form expressions and good agreement was observed.

Design and fabrication of SU-8 CMUT arrays through grayscale lithography

The authors report, for the first time, a simple one-step manufacturing process, without the use of any sacrificial layers, applied for the fabrication of SU-8 ultrasound transducers. Based on grayscale lithography, the method has a high degree of simplicity compared to traditional microfabrication flows. The fabrication of SU-8 CMUT arrays is a case study that validates the application potential of the developed process, its robustness, reproducibility and design predictability. To demonstrate the predictability of the fabrication process, a custom calibration of the SU-8 grayscale lithography has been performed, and the mechanical performance of the CMUT cells has been simulated through FEA tools based on calibration measurement. The dynamical properties of the manufactured SU-8 CMUTs have been experimentally assessed and compared with the simulation results. The CMUT cells have a fundamental resonant frequency at 1.75 MHz, suitable for biomedical imaging; their statistical characterization shows a good match with design simulations with small deviations, indicating acceptable reproducibility, predictability, and robustness. Both mechanical and electrical characterizations show that the proposed grayscale manufacturing technology led to functional CMUT arrays with robust performances. This low-cost, rapid micromanufacturing technique is suitable for any out-of-plane SU-8 based MEMS devices, from pressure sensors to inertial devices and ultrasonic transducer arrays.

Microwave Radar Interferometry as a Cost-Efficient Method of Monitoring the Structural Health of Bridges in New Zealand

The health monitoring of civil infrastructure is becoming more common for investigating actual structural behaviour, allowing early damage detection and helping to protect critical structures. In the New Zealand infrastructural context in particular, the introduction of high-productivity motor vehicles (HPMVs) along with the damage caused by recent earthquakes has resulted in a growing need for verification that bridges are performing as expected. The application of “classical” instruments such as accelerometers and linear variable differential transformers (LVDTs) are very expensive due to high installation costs and the need for a continuous power supply. However, radar interferometry is a promising alternative which can detect structural displacements without directly accessing the bridge, offering not only time and cost savings but also the capability to investigate structures where access is difficult or hazardous. This paper presents a health assessment of a bridge crossing the Rangitata River in New Zealand using this radar technology. Previous surveys of the bridge indicated that it was under capacity for supporting full HPMV loads. The structural performance was assessed by monitoring the maximum vertical mid-span displacements under live traffic conditions. The fundamental resonant frequencies were also measured to confirm the actual support conditions associated with the pier joints.

Compact Multi-Layer Bandpass Filter With Wide Stopband Using Selective Feeding Scheme

This brief presents a new approach for designing compact bandpass filters (BPFs) with harmonic suppression using quarter-wavelength stepped-impedance resonators (SIRs). The voltage-null point of the third harmonic on the SIR is theoretically derived and found for the first time. It is used as the exciting location for the selective feeding line so that the third harmonic cannot be excited and is suppressed successfully in the filter design. Meanwhile, the passband of the BPF operating at the fundamental resonant frequency ( ${f_{ 1 }}$ ) of the SIR can be optimized and obtained by tuning other parameters. By combining the proposed simple technique and the SIR merits, the resultant BPF owns several advantages, such as wide stopband and miniaturization. To demonstrate the feasibility of the proposed idea, two design examples of second-/fourth-order BPFs based on multilayer PCB are designed. In both designs, the third harmonic suppression is larger than 30 dB and the first spurious occurs at a frequency beyond ${7f_{ 1 } }$ . Their simulated and measured results are presented, showing good agreement.