Dominant Resonant Frequency Research Articles

A Case Study Comparing Active Vs. Passive Enablers for Vehicle Interior Noise Reduction

The implementation of enablers on a luxury sport utility vehicle is used to illustrate the development process for reduction of road noise. The vehicle in this case study was launched into production with two tuned mass dampers for reduction of low frequency road noise content which was amplified by frame modes. Additionally, resonators were integrated into the wheels (rims) to address the dominant cavity resonance frequencies. The results of this successful production implementation are illustrated herein. An RNC (road noise cancellation) system was integrated into the case vehicle to assess its performance relative to the passive enablers listed above. This production representative (embedded software solution) RNC system utilized the vehicle's existing audio system for creation of active noise to cancel noise content which was predicted using accelerometers mounted to the vehicle chassis. A comparison of in-vehicle noise indicated a significant reduction at low frequencies (at all seating locations) when utilizing the active noise control solution. These noise improvements are coupled with a vehicle mass reduction of greater than 4 kg, when compared to the passive enabler solution.

The first half-period of pressure heads for frequency response extraction and analysis of waterhammer with fluid–structure interaction

This paper details an efficient procedure to extract and analyze the pipe system characteristics from the pressure and stress waves generated during the first half-period of the water hammer with fluid–structure interaction (FSI). To this end, a new transient signal is generated using the first half-period of pressure heads through verified mathematical and numerical computations in the time domain. Then, the system’s resonant frequencies are extracted from the new transient signal by employing a fast Fourier transform (FFT) algorithm. The extraction procedure is verified using the analytical results from the literature. The analytical relations of the dominant resonant frequencies corresponding to the pressure and stress waves in the new transient signal are also derived to analyze the frequency data captured using the proposed approach. The effects of the stress wave (structural) frequencies are closely investigated, considering several hypothetical case studies. Both major FSI mechanisms during water hammer in a reservoir–pipe–valve​ system, namely Poisson and junction, are taken into account. The results demonstrate that the presented approach can manifest the hydraulic and structural properties of the pipeline system. The main stress wave frequencies result in a considerable increase in the amplitude of the extracted resonant frequencies, whereas a reduction effect is revealed due to the reflected stress wave frequencies. This research is of crucial importance for system identification in pipelines.

Smart hybrid active/semi-active distributed structural acoustic control of thin- and thick-walled piezo-sandwich bimorph spherical shell cloaks

A novel three dimensional underwater smart piezo-sandwich spherical shell cloak is designed and analyzed based on the hybrid active/semi-active distributed structural acoustic control strategy. The sandwich configuration consists of series- or parallel-connected piezoelectric (PZT) bimorph actuator skin layers collocated with a semi-active electro-rheological fluid (ERF) core layer. Two separate coupled elasto-acoustic formulations are systematically developed. The first model is based on the variational principle of structural mechanics and the approximate Kirchhoff-Love thin shell theory while the standard sliding mode control (SMC) scheme is utilized to activate the acoustic scattering extinction capability of the hybrid structure. The second model is built on the exact linear theory of 3D piezoelasticity and the classical state-space transfer matrix approach along with the active damping control (ADC) strategy. Extensive numerical simulations reveal that the best broadband backscattering cancellation performance can effectively be achieved with the smart hybrid active/semi-active bimorph piezo-sandwich spherical shell cloak operating in parallel connection. To quantify the overall cloaking performance of the proposed design, the percentage error (%Err) of the external cloaked field relative to the background incident pressure field is calculated at selected dominant structural resonance frequencies within eight designated frequency bands (regions I to VIII). The remarkable (near-perfect) cloaking performance of the parallel-connected thick-walled hybrid bimorph piezo-sandwich shell (25%shellcloak) is demonstrated in the intermediate to high frequency regions (i.e., below 1.5% error in regions I, and III to VIII). This excellent invisibility performance is somewhat degraded in a narrow low frequency band (i.e., up to 8% error in region II) which is primarily linked to the elasto-acoustic resonances due to the coherent coupling of various types of highly interacting fluid- and shell-borne peripheral waves. On the other hand, the superior cloaking performance of the parallel-connected thin-walled hybrid bimorph piezo-sandwich shell (7%shellcloak) is observed predominantly in the low frequency range (i.e., below 1.5% error in regions I and II), while this exceptional performance is gradually degraded as the incident wave frequency is increased (i.e., up to 6.5% error in regions III to VIII), where partial or directional cancellation of the scattered field mostly occurs. Also, some important practical issues and limitations regarding the experimental implementation of proposed hybrid active/semi-active acoustic cloaking device are briefly discussed.

A Simple Model to Compute the Characteristic Parameters of a Slotted Rectangular Microstrip Patch Antenna

In this study, we developed an analytical model of slot-loaded rectangular microstrip patch antennas based on the simulation results by varying slot parameters. The dominant resonant frequency predicted by such a model is in strong agreement with the experimental results measured at several locations of slot-loaded rectangular microstrip patch antennas. The model enables a reliable and quick computation of the resonant frequency, which generally follows a harmonic behavior that nearly resembles the resonant frequency of a microstrip antenna without a slot, which can be related to a small change in the impedance caused by the slot position. Results showed a good agreement between simulations and measurements for all the slot positions. Mathematical analytic functions to describe the changes in specific characteristic parameters of the slot-loaded rectangular microstrip patch antennas are also included.

A study of vowel nasalization using instantaneous spectra

Nasalization of vowels is a phenomenon where the oral and nasal tracts participate simultaneously in the production of speech. Acoustic coupling of the oral and nasal tracts, together with the glottal activity, results in a complex dynamic production system. The extent of coupling determines the degree of nasalization in vowels. Changes in the instantaneous response of the vocal tract system are used to study the effects of co-articulatory load of nasals on vowels. Dominant resonance frequency (DRF) contour is extracted from the instantaneous response of the system to determine the duration of the vowel nasalization. The extent of coupling determines the relative dominance of the oral and nasal resonances during the open and closed phases of a glottal cycle. Larger coupling leads to more decay of the energy of the oral resonances, and hence the vowel spectra exhibit predominantly the nasal resonances characteristics. Comparison with the existing measures show the effectiveness of the proposed measures for determining vowel nasalization. Segments of vowels in the context of nasal consonants from utterances of both male and female speakers of English are used to illustrate different aspects of this study on vowel nasalization.

Design of a compact, wideband, and flexible rhombic antenna using CMA for WBAN/WLAN and 5G applications

AbstractThe design of a compact, wideband flexible monopole antenna printed on a flexible Kapton polyimide substrate is presented. The proposed antenna consists of two rhombic elements embedded within a square plane as the radiating element. The wide bandwidth is aimed at alleviating potential performance degradations due to its application in an on‐body environment. The proposed antenna is designed using two main methods: the method of moments with adaptive cross approximation, and the characteristic mode analysis. The antenna operates from 2.038 to 3.745 GHz, indicating a bandwidth of 1.707 GHz (59.03%). Two dominant resonant frequencies are observed at 2.45 and 3.42 GHz, with realized gain of 3 and 5 dBi, and radiation efficiency of 90% and 83%, respectively. Besides that, the genetic algorithm and particle swarm optimization techniques are used to optimize the antenna and its performance validated via measurements. Besides, in free space, its on‐body performance when placed in proximity of a human body phantom is evaluated. Finally, specific absorption rate assessment is performed to ensure the safety of the proposed antenna when operating on human. Results indicate the antenna's suitability for wearable applications to support different wireless standards.

Detection of Fricative Landmarks Using Spectral Weighting: A Temporal Approach

Fricatives are characterized by two prime acoustic properties, i.e., having high-frequency spectral concentration and possessing noisy nature. Spectral domain approaches for detecting fricatives employ a time–frequency representation to compute acoustic cues such as band energy ratio, spectral centroid, and dominant resonant frequency. The detection accuracy of these approaches depends on the efficiency of the employed time–frequency representation. An approach that would not require any time–frequency representation for detecting fricatives from speech has been explored in this work. In this study, a time-domain operation is proposed which emphasizes the high-frequency spectral characteristics of fricatives implicitly. The proposed approach aims to scale the spectrum of the speech signal using a scaling function $$k^2$$ , where k is the discrete frequency. The spectral weighting function used in the proposed approach can be approximated as a cascaded temporal difference operation over speech signal. The emphasized regions in spectrally weighted speech signal are quantified to detect fricative regions. Contrasting the spectral domain approaches, the predictability measure-based approach in literature relies on capturing the noisy nature of fricatives. The proposed approach and the predictability measure-based approaches rely on two complementary properties for detecting fricatives, and a combination of these approaches is put forth in this work. The proposed approach has performed better than the state-of-the-art fricative detectors. To study the significance of the proposed evidence, an early fusion between the proposed evidence and the feature-space maximum log-likelihood transform features is explored for developing speech recognition systems.

Assessment of the vibrational resonant frequency of anisotropic black phosphorus nanoribbon

Black phosphorus (BP) has been enjoying popularity in mechanical and optoelectronic devices due to its superior anisotropic puckered structure. However, the vibrational properties of BP remain unexplored which greatly limits its wide applications in resonance-based nano electromechanical system (NEMS) devices. Therefore, in order to design mechanically reliable ultra-sensitive nanosensors, molecular dynamics simulations are utilized to explore the vibrational properties of monolayer BP. We have systematically assessed the effects of the initial actuation amplitude, internal vacancy density and mechanical strain on the vibrational properties of monolayer BP along the armchair and zigzag directions. It is found that the pristine monolayer BP exhibits lower energy disspation and smaller dominant resonant frequency during free vibration along the armchair direction than along the zigzag direction, indicating the anisotropic mechanical vibrational properties of monolayer BP, which further result in anisotropic multimode resonant characteristics in the vibration frequency spectrum. Additionally, the dominant frequency monotonically decreases gradually with increment of the internal vacancy density, while increasing with increment of the initial actuation amplitude and the mechanical strain. The energy dissipation increases gradually with increment of the initial actuation amplitude and internal vacancy density, but decreases under mechanical strain. Overall, these findings provide a fundamental understanding of the resonant properties of monolayer anisotropic BP that sheds light on its applications in micro- or nano-resonator-based devices.

Aeroacoustic Attenuation Performance of a Helmholtz Resonator with a Rigid Baffle Implemented in the Presence of a Grazing Flow

To broaden its’ effective frequency range and to improve its transmission loss performance, a modified design of a Helmholtz resonator is proposed and evaluated by implementing a rigid baffle in its cavity. Comparison is then made between the proposed design and the conventional one by considering a rectangular duct with the resonator implemented in the presence of a mean grazing flow. For this, a linearized 2D Navier-Stokes model in frequency domain is developed. After validated by benchmarking with the available experimental data and our experimental measurements, the model is used to evaluate the effects of (1) the width Lp of the rigid baffle, (2) its implementation location/height Hg, (3) its implementation configurations (i.e., attached to the left sidewall or right sidewall), (4) the grazing mean flow Mu (Mach number), and (5) the neck shape on a noise damping effect. It is shown that as the rigid baffle is attached in the 2 different configurations, the resonant frequencies and the maximum transmission losses cannot be predicted by using the classical theoretical formulation ω2=c2S/VLeff, especially as the grazing Mach number Mu is greater than 0.07, i.e., Mu>0.07. In addition, there is an optimum grazing flow Mach number corresponding to the maximum transmission loss peak, as the width Lp is less than half of the cavity width Dr, i.e., Lp/Dr≤0.5. As the rigid plate width is increased to Lp/Dr=0.75, one additional transmission loss peak at approximately 400 Hz is produced. The generation of the 12 dB transmission loss peak at 400 Hz is shown to attribute to the sound and structure interaction. Finally, varying the neck shape from the conventional one to an arc one leads to the dominant resonant frequency being increased by approximately 20% and so the secondary transmission loss peak by 2-5 dB. The present work proposes and systematically studies an improved design of a Helmholtz resonator with an additional transmission loss peak at a high frequency, besides the dominant peak at a low frequency.

Delineation of the new site of ngempon temple in ngempon village, bergas district, semarang regency using the microtremor method

Ngempon Temple was discovered below the ground level caused by collapsed land in 1952 in Ngempon Village, Bergas Sub-district, Semarang Regency. The HVSR method is used in the three-component microtremor to identify the bedrock response frequency. Additionally, this method can be used to determine the dominant resonance frequency (f0) and the peak value of HVSR (A), which shows the dynamic characteristics of sediments. This study aims to determine the position and types of archaeological objects that are still hidden and make a modeling of the subsurface conditions. The method used in this study is a trapezoidal measurement geometry by measuring spaces within 2 meters. Data retrieval duration is 10 minutes for each point, and the specified frequency sampling is 10 Hz. The H/V curve generated from data processing will result in the frequency value and amplification that will be analyzed and linked to the Ngempon Temple archaeological data. The results obtained from this study indicate the existence of the temple’s fundamental rocks and rock debris model below the surface indicated by the contours of the HVSR spectrum profile. They are an amplification value of 1.3 and the response frequency with a sensitivity of up to 4 Hz from the surface, and an amplification value of 1.3 and the response frequency with a sensitivity of 5.8-10 Hz. The sensitivity to measurements is based on whether the response passes the excavation of BPCB Central Java. If it passes, then the response indicates an anomaly of the fundamental rocks. Vice versa, if the measurement does not pass the object of research, the response only shows the existence of temple rocks fragments. The amplification value and frequency of response shows a difference between the temple rock and the sediments above it.

A Simple Analytical Solution for the Designing of the Birdcage RF Coil Used in NMR Imaging Applications

A novel analytical solution for the designing of the birdcage RF coil has been demonstrated in this paper. A new concept of dominant resonance path has been introduced in this paper which is used to identify the specific closed current loop in the birdcage RF coil which is responsible for the dominant resonance frequency mode. This concept is used to determine the precise numerical values of the lumped capacitance deployed in the legs and/or end-rings of the birdcage RF coil for its proper operation at the desired resonance frequency. The analytical solution presented in this paper has been established by performing the two-port network based equivalent circuit modeling of the birdcage RF coil. The proposed analytical solution uses T-matrix theory and develops a relationship between the input impedance of the birdcage coil and the impedances of its leg and end-ring segments. The proposed analytical solution provides the information about the resonance frequency spectrum of the birdcage RF coil and solves the issue of its interfacing with external circuits without affecting its resonance characteristics. Based upon the proposed analysis and designing strategy presented in this paper, the low pass, high pass and band pass configurations of the birdcage RF coil were successfully implemented with FPCB (Flexible Printed Circuit board) technique for small volume NMR imaging applications at 1.5 T and 3.0 T MRI system. The results obtained for the implemented birdcage coils using the proposed analysis and designing technique are in closed agreement with already established methods.

Electrochromic Behavior and Phase Transformation in Li4+xTi5O12 upon Lithium-Ion Deintercalation/Intercalation.

The impact of phase transformation from spinel-structured Li4Ti5O12 to rocksalt-type Li7Ti5O12 on the electrochromic properties of the material is studied. Thin films of Li4Ti5O12 are deposited on platinum-coated substrates using radio-frequency-ion beam sputtering. In situ and ex situ optical spectroscopy (in reflectance geometry) is performed along with electrochemical characterization. In situ measurements demonstrate the reversible electrochromic behavior of the deposited thin films and the effect of the change of lithium content on the reflectance spectrum. Ex situ measurements quantify the optical constants of thin films for different charge states by modeling the reflectance spectrum with a Clausius-Mossotti relation. The model reveals the presence of one or two dominant resonant frequencies in the case of Li4Ti5O12 or Li7Ti5O12, respectively, in the UV/visible/NIR region of light. The single strong resonance in the case of Li4Ti5O12 is assigned to transition from O 2p to Ti t2g, that is, across the band gap, whereas for the Li7Ti5O12 phase, the two resonances correspond to the electronic transitions from O 2p to empty Ti t2g and from filled Ti t2g to empty Ti eg. The concentration dependence of the derived dielectric constants points out a fast lithium ion transport through the grain boundaries, thereby segregating a conductive lithium-rich phase at the grain boundaries. This increases the electronic conductivity of the thin films in the initial stages of intercalation and explains the debated mechanism of the fast discharge/charge capability of Li4Ti5O12 electrodes.

Experimental and numerical investigation of noise generation due to acoustic resonance in a cavitating valve

In order to study cavitation induced noise generation in a hydraulic system, cavitation is generated at a planar orifice. The sudden condensation (implosion) of vapor results in shock waves which excite the connected hydraulic pipes with pressure fluctuations. The synchronization between the continuous condensation and evaporation process and shock wave reflection can result in a stationary wave with superelevated pressure amplitudes. The fluid-borne sound is transferred through the mechanical structure into the air, where it can be perceived as a distracting whistling noise. A high-speed camera is used to visualize the void volume. Dynamic pressure signals are recorded in the vicinity of the orifice to analyze the pressure pulsation. The operating point is varied, the orifice geometry is changed and the reflection properties of the pipe on the up- and downstream sides are changed too. In addition, CFD (Computational Fluid Dynamics) simulations of the test bench are used to investigate the root cause of the whistling noise. With regards to representative operating points, the numerical results confirm the measured shedding vapor frequency, particularly the pressure pulsation frequency in the pipe and its amplitude. The conjunction of the experimental and numerical investigations provides the following findings: By reducing the discharge pressure, the void volume increases, which leads to a reduction of the resonance frequency of the pipe downstream of the orifice. For large void volumes, the pressure wave reflection at the void volume can be identified in the amplitude spectrum. The whistling noise depends on the history of the flow field. So, the increase and the reduction of the discharge pressure level leads to different whistling ranges. The whistling range decreases with the increasing length of the pipe resonator. Besides that, the order of the dominant resonance frequency increases. The experimental and numerical results indicate that the whistling noise only occurs, when the jet downstream of the orifice and hence the vapor is perpendicular to the sound propagation in the pipe resonator.

A theoretical study for temperature effects on the dominant color in colloidal nano sphere solutions

The effects of the electron temperature on the dominant color in colloidal nano sphere solutions are analytically studied. This system contains ions (as radiators) close to the hot nano plasma spheres (HNPSs). Considering two separate models of the point radiated ions and applying the fluid dynamic equations and suitable Green’s function, the optical resonance of HNPSs is declared. The thermal effects in HNPSs show that a series of optical resonances occur in the system and the dominant resonance frequencies depend on the plasma geometry, electron density, electron temperature. The resonance frequencies in the two different models are exactly identical. Also, a new type of resonance frequency (subsidiary resonance frequencies), resulting in the thermal effects, is seen by considering two radiators beside the HNPS and, in this case, due to the sign of the ion radiators with same strengths, the even or odd modes are excited, separately. In other words, the permissible resonance frequencies in colloidal nano sphere solutions are categorized into two principal types: dominant resonance frequencies and subsidiary resonance frequencies. In addition, the graphs of the scattering patterns and resonance frequencies of this problem are analyzed. All of the resonance frequencies are varied with the temperature so that decreasing the Debye length (temperature) of HNPSs decreases the resonant frequencies and changes the dominant color of the system. Moreover, the dominant color of the system depends on the number of spheres in a colloidal solution including many bodies of nano-spheres with different radii.

Switching performance of bistable membranes activated with integrated piezoelectric thin film transducers

In this paper we report on the fabrication of bistable micro electromechanical systems (MEMS) membranes, which have diameters in the range of 600–800 µm, a total thickness of 3.13 µm and feature integrated low power piezoelectric transducers based on aluminium nitride. To estimate the impact of the membrane asymmetry due to the integrated piezoelectric transducers, an asymmetric constant in the potential energy calculation of the bistable system is introduced, thus enabling a proper theoretical prediction of the membrane behaviour. To switch between the two bistable ground states, rectangular pulses with frequencies in the range of 50–100 kHz and a peak-to-peak voltage of 30 Vpp are applied. Two different actuation schemes were investigated, whereas one shows positive and the other negative pulse amplitudes. With a Laser-Doppler Vibrometer the velocity of the membranes during the bistable switching process is measured and integrated over time to calculate the membrane displacement in the centre. FFT (fast Fourier transform) spectra of an applied broadband white noise signal were determined in both ground states and showed a strongly decreased dominant resonance frequency in the lower ground state. The results also showed, that the asymmetry of the system causes different switching behaviours for each bistable ground state, whereas it requires less energy to switch from the lower to the upper ground state. Furthermore, it was demonstrated that a minimum of two pulses are needed for switching when using positive rectangular pulses of 30 Vpp in contrast to four when applying negative pulses. The pulse frequency causing switching was in the range of 60–110 kHz, strongly depending on the geometry and applied signal scheme. Additionally, a positive voltage offset applied to the pulse signal characteristics resulted in both a wider range of frequencies suitable for switching and in a decrease of the dominant resonance frequency, which is also beneficial for the switching process and indicates the potential for efficient switching of bistable MEMS membranes.

Application of Modal Strain Energy in Dynamical Analysis of Reactor and Primary Loop System

In order to investigate the dynamical contribution of individual component and equipment in system-level models, this study proposed a computational method based on the modal strain energy (MSE). Two engineering case studies applying the MSE method are demonstrated herein. The first study investigates the main reason causing large seismic response change of a prototype reactor coolant system (RCS) surge pipe due to the location change of surge suspension device. The analysis shows that the local dominant mode of the surge pipe is altered by the location change of the suspension. Such change of dominant resonant frequency leads to a significant change at the corresponding frequency of input seismic response spectrum, thereafter affects the dynamical response. The second case study discusses the decoupled strategy of the main steam-pipe from the loop model for separated dynamical analyses. MSE analysis, together with the second decoupling criteria suggested by USNRC SRP 3.7.2, justifies this deed. Modal strain energy (MSE) method proposed in this paper is able to quantify the dynamical contribution of components and equipment from the system-level dynamical analysis models. The computation of MSE only utilizes the system-level model stiffness and mass matrices. No time-domain transient analysis is necessary.

Discrimination of Complex Radar Targets Using the Dominant Poles Determined in the Time and Frequency Domains

In this paper, we present and compare two techniques of discriminating complex objects, using the electromagnetic scattering response in the time and frequency domains. The scattering in the time and frequency domains are computed using the Finite Difference Time Domain (FDTD) method and the Method of Moments (MoM), respectively. The dominant Natural Resonant Frequencies (NRFs) of the objects have been identified, using the Matrix Pencil of Function (MPoF) algorithm from the scattering response in the time domain, and the Vector Fitting (VF) method using the response in the frequency domain. The dominant NRFs in both cases have been identified after thresholding the power contribution of each pole. A “Risk” function using the dominant poles of any two scattering objects is then defined, which aids in quantifying the discrimination. Perfectly Electrically Conducting (PEC) objects with minor variations in their geometric shape have been discriminated using the risk function. It is shown that the techniques described in this paper are effective in discriminating targets. Both approaches, using the time and frequency domain scattering response are found to yield identical results. A single run of the FDTD algorithm is sufficient to compute the electromagnetic response required to determine the dominant natural resonances. Hence, the approach of using the time domain scattering response is computationally efficient. Thus a hybrid approach of computing the resonances from the time domain scattering response and discrimination using the risk function defined, is fast enough to apply to targets of realistic size such as an aircraft at operational radar frequencies.

Assessment of shunted piezoelectric devices for simultaneous noise and vibration reduction: comparison of passive, active and hybrid networks

Structural vibration and noise control of a cavity-backed three-layered smart piezo-coupled rectangular panel system under harmonic or transient loads is achieved by using purely active, passive, and hybrid active/passive piezoelectric shunt networks. Problem formulation is based on the classical lamination plate theory, Maxwell’s equation for piezoelectric materials, linear circuit theory, and wave equation for the enclosed acoustic domain. The orthogonal mode expansions along with the modal coupling theory are employed to obtain the coupled differential equations of the electro-mechanical-acoustic system, which are then put into the convenient state-space form, and subsequently solved numerically in both frequency and time domains. A triple-mode hybrid RLC shunt circuit, in series with an external active voltage source and connected to a single electroded piezoelectric segment, is tuned to the dominant resonance frequencies of the composite structure. The linear quadratic optimal control (LQR) theory is adopted for obtaining the active control gains. The frequency and time domain performances of the passive, active and hybrid multi-modal piezoelectric systems are calculated and discussed in terms of sensor output voltage, local sound pressure, and control effort. It is found that the hybrid control methodology with properly tuned circuit parameters can be an excellent candidate for simultaneous vibration and structure-borne noise control of the cavity-coupled smart panel with decreased control effort. Also, the active control strategy integrated in the hybrid control system is demonstrated to enhance the overall system damping characteristics and improve the control authority at frequencies where the passive shunt network performs weakly. Limiting cases are considered and correctness of the mathematical model is verified by using a commercial finite element software as well as by comparisons with the literature.

End Point Detection Using Speech-Specific Knowledge for Text-Dependent Speaker Verification

This paper proposes a method using speech-specific knowledge to detect the begin and end points of speech under degraded condition. The method is based on vowel-like region (VLR) detection and uses both excitation source and vocal tract system information. Existing method for VLR detection uses excitation source information. Vocal tract system information from dominant resonant frequency is used to eliminate spurious VLRs in background noise. Foreground speech segmentation using excitation and vocal tract system information is carried out to remove spurious VLRs in the background speech region. Better localization of the end points is done using more detailed information about excitation source in terms of glottal activity to detect the sonorant consonants and missed VLRs. To include an unvoiced consonant, obstruent region detection is done at the beginning of the first VLR and at the end of last VLR. Detected begin and end points are evaluated by comparing with manually marked end points as well as by conducting the text-dependent speaker verification experiments. The proposed method performs better than some of the existing techniques.

Nonlinearity in the Dynamic Response of Flexural Ultrasonic Transducers

Recent studies of the electro-mechanical behavior of flexural ultrasonic transducers have shown that their response can be considered as three distinct characteristic regions, the first building towards a steady state, followed by oscillation at the driving frequency in the steady state, before an exponential decay from the steady state at the transducer's dominant resonance frequency, once the driving force is removed. Despite the widespread industrial use of these transducers as ultrasonic proximity sensors, there is little published information on their vibration characteristics under different operating conditions. Flexual transducers are composed of a piezoelectric ceramic disc bonded to the inner surface of a metallic cap, the membrane of which bends in response to the high-frequency ceramic vibrations of the ceramic. Piezoelectric devices can be subject to nonlinear behavior, but there is no reported detail of the nonlinearity in flexural transducers. Experimental investigation through laser Doppler vibrometry shows strong nonlinearity in the vibration response, where resonance frequency reduces with increasing vibration amplitude.