Página 1 dos resultados de 13 itens digitais encontrados em 0.007 segundos

Identification of Elastic, Dielectric, and Piezoelectric Constants in Piezoceramic Disks

Alvarez, Nicolas Leonardo Pérez; Andrade, Marco Aurélio Brizzotti; Buiochi, Flávio; Adamowski, Julio Cezar
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
49.21918%
Three-dimensional modeling of piezoelectric devices requires a precise knowledge of piezoelectric material parameters. The commonly used piezoelectric materials belong to the 6mm symmetry class, which have ten independent constants. In this work, a methodology to obtain precise material constants over a wide frequency band through finite element analysis of a piezoceramic disk is presented. Given an experimental electrical impedance curve and a first estimate for the piezoelectric material properties, the objective is to find the material properties that minimize the difference between the electrical impedance calculated by the finite element method and that obtained experimentally by an electrical impedance analyzer. The methodology consists of four basic steps: experimental measurement, identification of vibration modes and their sensitivity to material constants, a preliminary identification algorithm, and final refinement of the material constants using an optimization algorithm. The application of the methodology is exemplified using a hard lead zirconate titanate piezoceramic. The same methodology is applied to a soft piezoceramic. The errors in the identification of each parameter are statistically estimated in both cases, and are less than 0.6% for elastic constants...

Matrix Method for Acoustic Levitation Simulation

Andrade, Marco Aurélio Brizzotti; Alvarez, Nicolas Leonardo Pérez; Buiochi, Flávio; Adamowski, Julio Cezar
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
38.911157%
A matrix method is presented for simulating acoustic levitators. A typical acoustic levitator consists of an ultrasonic transducer and a reflector. The matrix method is used to determine the potential for acoustic radiation force that acts on a small sphere in the standing wave field produced by the levitator. The method is based on the Rayleigh integral and it takes into account the multiple reflections that occur between the transducer and the reflector. The potential for acoustic radiation force obtained by the matrix method is validated by comparing the matrix method results with those obtained by the finite element method when using an axisymmetric model of a single-axis acoustic levitator. After validation, the method is applied in the simulation of a noncontact manipulation system consisting of two 37.9-kHz Langevin-type transducers and a plane reflector. The manipulation system allows control of the horizontal position of a small levitated sphere from -6 mm to 6 mm, which is done by changing the phase difference between the two transducers. The horizontal position of the sphere predicted by the matrix method agrees with the horizontal positions measured experimentally with a charge-coupled device camera. The main advantage of the matrix method is that it allows simulation of non-symmetric acoustic levitators without requiring much computational effort.; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq); Petrobras/Agencia Nacional do Petroleo (ANP)

Ultrasonic Viscosity Measurement Using the Shear-Wave Reflection Coefficient with a Novel Signal Processing Technique

FRANCO, Ediguer E.; ADAMOWSKI, Julio C.; BUIOCHI, Flavio
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
38.925178%
Real-time viscosity measurement remains a necessity for highly automated industry. To resolve this problem, many studies have been carried out using an ultrasonic shear wave reflectance method. This method is based on the determination of the complex reflection coefficient`s magnitude and phase at the solid-liquid interface. Although magnitude is a stable quantity and its measurement is relatively simple and precise, phase measurement is a difficult task because of strong temperature dependence. A simplified method that uses only the magnitude of the reflection coefficient and that is valid under the Newtonian regimen has been proposed by some authors, but the obtained viscosity values do not match conventional viscometry measurements. In this work, a mode conversion measurement cell was used to measure glycerin viscosity as a function of temperature (15 to 25 degrees C) and corn syrup-water mixtures as a function of concentration (70 to 100 wt% of corn syrup). Tests were carried out at 1 MHz. A novel signal processing technique that calculates the reflection coefficient magnitude in a frequency band, instead of a single frequency, was studied. The effects of the bandwidth on magnitude and viscosity were analyzed and the results were compared with the values predicted by the Newtonian liquid model. The frequency band technique improved the magnitude results. The obtained viscosity values came close to those measured by the rotational viscometer with percentage errors up to 14%...

Computational Method to Determine Reflected Ultrasonic Signals From Arbitrary-Geometry Targets

BUIOCHI, Flavio; BUIOCHI, Elaine B.; FORMIGONI, Paulo O.; ADAMOWSKI, Julio C.
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
38.921802%
A computational method based on the impulse response and on the discrete representation computational concept is proposed for the determination of the echo responses from arbitrary-geometry targets. It is supposed that each point of the transducer aperture can be considered as a source radiating hemispherical waves to the reflector. The local interaction with each of the hemispherical waves at the reflector surface can be modeled as a plane wave impinging on a planar surface, using the respective reflection coefficient. The method is valid for all field regions and can be performed for any excitation waveform radiated from an arbitrary acoustic aperture. The effects of target geometry, position, and material on both the amplitude and the shape of the echo response are studied. The model is compared with experimental results obtained using broadband transducers together with plane and cylindrical concave rectangular reflectors (aluminum, brass, and acrylic), as well as a circular cavity placed on a plane surface, in a water medium. The method can predict the measured echoes accurately. This paper shows an improved approach of the method, considering the reflection coefficient for all incident hemispherical waves arriving at each point of the target surface.; FAPESP; CNPq; ANP; Petrobras

Finite Element Analysis and Optimization of a Single-Axis Acoustic Levitator

Andrade, Marco Aurélio Brizzotti; BUIOCHI, Flavio; Adamowski, Julio Cezar
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
59.555146%
A finite element analysis and a parametric optimization of single-axis acoustic levitators are presented. The finite element method is used to simulate a levitator consisting of a Langevin ultrasonic transducer with a plane radiating surface and a plane reflector. The transducer electrical impedance, the transducer face displacement, and the acoustic radiation potential that acts on small spheres are determined by the finite element method. The numerical electrical impedance is compared with that acquired experimentally by an impedance analyzer, and the predicted displacement is compared with that obtained by a fiber-optic vibration sensor. The numerical acoustic radiation potential is verified experimentally by placing small spheres in the levitator. The same procedure is used to optimize a levitator consisting of a curved reflector and a concave-faced transducer. The numerical results show that the acoustic radiation force in the new levitator is enhanced 604 times compared with the levitator consisting of a plane transducer and a plane reflector. The optimized levitator is able to levitate 3, 2.5-mm diameter steel spheres with a power consumption of only 0.9 W.; CNPq; CAPES; Petrobras/ANP

Viscosity measurement of Newtonian liquids using the complex reflection coefficient

FRANCO, Ediguer E.; ADAMOWSKI, Julio C.; HIGUTI, Ricardo T.; BUIOCHI, Flavio
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
38.92782%
This work presents the implementation of the ultrasonic shear reflectance method for viscosity measurement of Newtonian liquids using wave mode conversion from longitudinal to shear waves and vice versa. The method is based on the measurement of the complex reflection coefficient (magnitude and phase) at a solid-liquid interface. The implemented measurement cell is composed of an ultrasonic transducer, a water buffer, an aluminum prism, a PMMA buffer rod, and a sample chamber. Viscosity measurements were made in the range from 1 to 3.5 MHz for olive oil and for automotive oils (SAE 40, 90, and 250) at 15 and 22.5 degrees C, respectively. Moreover, olive oil and corn oil measurements were conducted in the range from 15 to 30 degrees C at 3.5 and 2.25 MHz, respectively. The ultrasonic measurements, in the case of the less viscous liquids, agree with the results provided by a rotational viscometer, showing Newtonian behavior. In the case of the more viscous liquids, a significant difference was obtained, showing a clear non-Newtonian behavior that cannot be described by the Kelvin-Voigt model.; Brazilian government institutions Fundacao de Anaparo a Pesquisa do Estado de Sao Paulo (FAPESP); Coordenacao de A perfeicoamento de Pessoal de Nivel Superior (Capes); Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq/Finep)

Using Reverberation to Improve Range and Elevation Discrimination for Small Array Sound Source Localization

RIBEIRO, Flavio; ZHANG, Cha; FLORENCIO, Dinei A.; BA, Demba Elimane
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
49.373447%
Sound source localization (SSL) is an essential task in many applications involving speech capture and enhancement. As such, speaker localization with microphone arrays has received significant research attention. Nevertheless, existing SSL algorithms for small arrays still have two significant limitations: lack of range resolution, and accuracy degradation with increasing reverberation. The latter is natural and expected, given that strong reflections can have amplitudes similar to that of the direct signal, but different directions of arrival. Therefore, correctly modeling the room and compensating for the reflections should reduce the degradation due to reverberation. In this paper, we show a stronger result. If modeled correctly, early reflections can be used to provide more information about the source location than would have been available in an anechoic scenario. The modeling not only compensates for the reverberation, but also significantly increases resolution for range and elevation. Thus, we show that under certain conditions and limitations, reverberation can be used to improve SSL performance. Prior attempts to compensate for reverberation tried to model the room impulse response (RIR). However, RIRs change quickly with speaker position...

Vibro-Acoustography Beam Formation with Reconfigurable Arrays

Kamimura, Hermes A. S.; Urban, Matthew W.; Carneiro, Antonio Adilton Oliveira; Fatemi, Mostafa; Alizad, Azra
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC; PISCATAWAY Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC; PISCATAWAY
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
38.93169%
In this work, we present a numerical study of the use of reconfigurable arrays (RCA) for vibro-acoustography (VA) beam formation. A parametric study of the aperture selection, number of channels, number of elements, focal distance, and steering parameters is presented to show the feasibility and evaluate the performance of VA imaging based on RCA. The transducer aperture was based on two concentric arrays driven by two continuous-wave or toneburst signals at slightly different frequencies. The mathematical model considers a homogeneous, isotropic, inviscid medium. The point-spread function of the system is calculated based on angular spectrum methods using the Fresnel approximation for rectangular sources. Simulations considering arrays with 50 x 50 to 200 x 200 elements with number of channels varying in the range of 32 to 128 are evaluated to identify the best configuration for VA. Advantages of two-dimensional and RCA arrays and aspects related to clinical importance of the RCA implementation in VA, such as spatial resolution, image frame rate, and commercial machine implementation, are discussed. It is concluded that RCA transducers can produce spatial resolution similar to confocal transducers and steering is possible in the elevational and azimuthal planes. Optimal settings for number of elements...

Perception of musical intervals : evidence for the central origin of the pitch of complex tones

Fonte: MIT Research Laboratory of Electronics Publicador: MIT Research Laboratory of Electronics
Formato: iv, 75 p.; 7020996 bytes; application/pdf
Português
Relevância na Pesquisa
39.02671%
[by] Adrianus J.M. Houtsma and Julius L. Goldstein.; Based on a Ph.D. thesis in the Dept. of Electrical Engineering, 1971, by A.J.M. Houtsma.; Bibliography: p. 71-75.

Shipboard electronics thermoacoustic cooler

Ballister, Stephen C.; McKelvey, Dennis J.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
39.519658%
A thermoacoustic refrigerator that was optimized for preservation of biological samples in space, was modified for use as a cooler for the CV-2095 shipboard radar electronics rack. The thermoacoustic cooler was tested in the laboratory and demonstrated at sea aboard USS DEYO (DD-989). In the laboratory, using a calibrated heat load, the data acquisition system was able to account for the total energy balance to within 4%. At the highest operating power aboard ship, 226.6 Watts of acoustic power was used to provide 419 Walls of useful cooling power, corresponding to a coefficient of performance of 1.85. Taking into account the 53.9% electroacoustic efficiency of the loudspeakers, the Shipboard Electronics ThermoAcoustic Cooler (SETAC) provided one Watt of cooling for each Watt of electrical power input.

Structure-based modeling of head -related transfer functions towards interactive customization of binaural sound systems

Gupta, Navarun
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
79.05462%
One of the most popular techniques for creating spatialized virtual sounds is based on the use of Head-Related Transfer Functions (HRTFs). HRTFs are signal processing models that represent the modifications undergone by the acoustic signal as it travels from a sound source to each of the listener's eardrums. These modifications are due to the interaction of the acoustic waves with the listener's torso, shoulders, head and pinnae, or outer ears. As such, HRTFs are somewhat different for each listener. For a listener to perceive synthesized 3-D sound cues correctly, the synthesized cues must be similar to the listener's own HRTFs. ^ One can measure individual HRTFs using specialized recording systems, however, these systems are prohibitively expensive and restrict the portability of the 3-D sound system. HRTF-based systems also face several computational challenges. This dissertation presents an alternative method for the synthesis of binaural spatialized sounds. The sound entering the pinna undergoes several reflective, diffractive and resonant phenomena, which determine the HRTF. Using signal processing tools, such as Prony's signal modeling method, an appropriate set of time delays and a resonant frequency were used to approximate the measured Head-Related Impulse Responses (HRIRs). Statistical analysis was used to find out empirical equations describing how the reflections and resonances are determined by the shape and size of the pinna features obtained from 3D images of 15 experimental subjects modeled in the project. These equations were used to yield “Model HRTFs” that can create elevation effects. ^ Listening tests conducted on 10 subjects show that these model HRTFs are 5% more effective than generic HRTFs when it comes to localizing sounds in the frontal plane. The number of reversals (perception of sound source above the horizontal plane when actually it is below the plane and vice versa) was also reduced by 5.7%...

Transthoracic cardiac ultrasonic stimulation induces a negative chronotropic effect

Buiochi, Elaine Belassiano; Miller, Rita J.; Hartman, Emily; Buiochi, Flávio; Bassani, Rosana Almada; Costa, Eduardo Tavares; O'Brien, William D., Jr.
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC; PISCATAWAY Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC; PISCATAWAY
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
38.921802%
The objective of this study is to investigate cardiac bioeffects resulting from ultrasonic stimulation using a specific set of acoustical parameters. Ten Sprague-Dawley rats were anesthetized and exposed to 1-MHz ultrasound pulses of 3-MPa peak rarefactional pressure and approximately 1% duty factor. The pulse repetition frequency started slightly above the heart rate and was decreased by 1 Hz every 10 s, for a total exposure duration of 30 s. The control group was composed of five rats. Two-way analysis of variance for repeated measures and Bonferroni post hoc tests were used to compare heart rate and ejection fraction, which was used as an index of myocardial contractility. It was demonstrated for the first time that transthoracic ultrasound has the potential to decrease the heart rate by similar to 20%. The negative chronotropic effect lasted for at least 15 min after ultrasound exposure and there was no apparent gross damage to the cardiac tissue.; National Institutes of Health (NIH); National Institutes of Health (NIH) [R37 EB002641, S10 RR027884]; Sao Paulo Research Foundation (FAPESP) [06/60032-0]; Sao Paulo Research Foundation (FAPESP)

Waveguide Invariant Active Sonar Target Detection and Depth Classification in Shallow Water

Goldhahn, Ryan
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2010 Português
Relevância na Pesquisa
69.30794%

Reverberation and clutter are two of the principle obstacles to active sonar target detection in shallow water. Diffuse seabed backscatter can obscure low energy target returns, while clutter discretes, specific features of the sea floor, produce temporally compact returns which may be mistaken for targets of interest. Detecting weak targets in the presence of reverberation and discriminating water column targets from bottom clutter are thus critical to good performance in active sonar. Both problems are addressed in this thesis using the time-frequency interference pattern described by a constant known as the waveguide invariant which summarizes in a scalar parameter the dispersive properties of the ocean environment.

Conventional active sonar detection involves constant false alarm rate (CFAR) normalization of the reverberation return which does not account for the frequency-selective fading in a wideband pulse caused by multipath propagation. An alternative to conventional reverberation estimation is presented, motivated by striations observed in time-frequency analysis of active sonar data. A mathematical model for these reverberation striations is derived using waveguide invariant theory. This model is then used to motivate waveguide invariant reverberation estimation which involves averaging the time-frequency spectrum along these striations. An evaluation of this reverberation estimate using real Mediterranean data is given and its use in a generalized likelihood ratio test (GLRT) based CFAR detector is demonstrated. CFAR detection using waveguide invariant reverberation estimates is shown to outperform conventional cell-averaged and frequency-invariant CFAR detection methods in shallow water environments producing strong reverberation returns which exhibit the described striations. Results are presented on simulated and real Mediterranean data from the SCARAB98 experiment.

The ability to discriminate between water column targets and clutter discretes is vital to maintaining low false alarm rates in active sonar. Moreover...