Acoustic Measurement System Research Articles

Application of acoustic tomography to reconstruct the horizontal flow velocity field in a shallow river

AbstractA novel acoustic tomographic measurement system capable of resolving sound travel time in extremely shallow rivers is introduced and the results of an extensive field measurements campaign are presented and further discussed. Acoustic pulses were transmitted over a wide frequency band of 20–35 kHz between eight transducers for about a week in a meandering reach of theBāsen River, Hiroshima, Japan. The purpose of the field experiment was validating the concept of acoustic tomography in rivers for visualizing current fields. The particular novelty of the experiment resides in its unusual tomographic features: subbasin scale (100 m × 270 m) and shallowness (0.5–3.0 m) of the physical domain, frequency of the transmitted acoustic signals (central frequency of 30 kHz), and the use of small sampling intervals (105 s). Inverse techniques with no a priori statistical information were used to estimate the depth‐average current velocity components from differential travel times. Zeroth‐order Tikhonov regularization, in conjunction with L‐curve method deployed to stabilize the solution and to determine the weighting factor appearing in the inverse analysis. Concurrent direct environmental measurements were provided in the form of ADCP readings close to the right and left bank. Very good agreement found between along‐channel velocities larger than 0.2 m/s obtained from the two techniques. Inverted quantities were, however, underestimated, perhaps due to vicinity of the ADCPs to the banks and strong effect of river geometry on the readings. In general, comparing the visualized currents with direct nodal measurements illustrate the plausibility of the tomographically reconstructed flow structures.

The effect of air-fuel equivalence ratio change on the vibration components of an internal-combustion engine

Nowadays the automotive industry and the motor development are one of the most dynamically developing industries. One solution to the diagnostic systems providing reliability is the acoustic and vibration measurement system, which can indicate and predict a variety of malfunctions after signal processing. The purpose of this experiment is to analyze the effect of the air-fuel equivalence ratio on the vibration components of an internal-combustion engine (ICE) which is a part of the in question measurement system. In the focus of the experiments are the analysis of the time signal, its spectra, and the power content of the signal. With the increment of the air-fuel ratio the amplitudes of the measured signal and its spectral amplitudes showed a downward trend as the RMS values. In addition, certain frequency components disappeared during the actuation of the ICE with an electromotor, so the characterization of the combustion could be come to the front.

Combined transcranial alternating current stimulation and cTBS: a novel approach for neuroplasticity induction

s / Brain Stimulation 8 (2015) 360e377 369 monitor the motor potentials evoked by motor cortices. Ultrasonic attenuation coefficients of skulls in high frequency were measured and calculated using 3D acoustic intensity measurement system (SN2010, Precision Acoustics). Our results indicate that 5MHz focused ultrasound can efficiently penetrate through skull of mouse and stimulate motor cortex to evoke motor potentials and movement responses, thus allow for more precise stimulation on brain of mouse.

Magnetoacoustic Tomography with Magnetic Induction (MAT-MI) Reconstruction Algorithm Based on Characteristics of Acoustic Transducer

AbstractA MAT-MI reconstruction algorithm was applied to general sound detection systems, and the influence of acoustic transducers on MAT-MI image reconstruction was investigated in this paper. The acoustic intensity measurement system was used to measure the acoustic field, and the data was then used to build the acoustic transducer model by a interpolation method. The model was applied to forward and inverse problems of MAT-MI based on Green’s function and discretization method. In order to verify the algorithm, a simulation was carried out using sphere scan schema and cylinder scan schema. A 3D phantom model was set up based on S-L model in CT, with the help of finite element analysis method and the distribution of the transient electromagnetic field and the eddy currentwere calculated. Simulation and reconstruction results through numerical calculation using MATLAB were obtained. Results show that the algorithm can reconstruct the distribution of acoustic source vector; the correlation coefficients are 98.49% and 94.96%, and can be applied to the general transducer. This study provided a basis for the experimental study of MAT-MI and a precise reconstruction of conductivity distribution.

Sound source influence to the room acoustics quality measurement

Objective parameters of the room acoustics quality are obtained from the impulse response, which is measured using the appropriate PC based acoustic measurement system with two types of loudspeakers. Such measurement gives the impulse response that is the result of measurement of the entire system, which consists of the room and electro acoustics equipment. In order to investigate the real influence of loudspeakers on the measurement results, the research was made in the same measuring conditions. Impulse responses were measured with the same measuring system. Measuring point was selected at the optimum listening position in the room, and all measurements were carried out in the same place. The loudspeakers were placed at the optimum and characteristic positions in the room, and rotated around their axes in order to determine the impact of their position and directivity characteristics on the measurement of objective parameters of room acoustic quality.

Acoustic building infiltration measurement system

Systems and methods of detecting and identifying a leak from a container or building. Acoustic pressure and velocity are measured. Acoustic properties are acquired from the measured values. The acoustic properties are converted to infiltration/leakage information. Nearfield Acoustic Holography (NAH) may be one method to detect the leakages from a container by locating the noise sources.

A Flextensional Transducer Prototype with PVDF Piezoelectric Film

This paper presents a prototype of a new flextensional transducer with PVDF (Polyvinylidene Fluoride) piezoelectric film instead of metallic shell. Resonance frequency, bandwidth, transmitting voltage response, and horizontal directivity of the flextensional transducer with PVDF piezoelectric film were respectively measured by using laser-scanning vibrometer, and underwater acoustic measurement system. Experimental results showed that the new transducer features effectively conversion from longitudinal vibration of piezoelectric stack into radial vibration of PVDF piezoelectric film.

Tests of new in-situ seabed acoustic measurement system in Qingdao

A new in-situ seabed acoustic measurement system is developed for direct in-situ measurement of sediment geoacoustic properties (compressional wave velocity and attenuation). The new in-situ system consists of two parts: the deck control unit and the underwater measurement unit. The underwater measurement unit emits sonic waves that propagate through the seafloor sediment, receives the returning signals, and transmits them to the deck control unit for waveform display and analysis. The entire operation is controlled and monitored in real time by the deck control unit on the research vessel and can provide recording of full waveforms to determine the sound velocity and attenuation. This paper outlines the design of the system, the measurement process, and demonstrates its application in tests carried out on seabed sediment off the Qingdao coast, China. The test results show that the system performed well and rapidly provided accurate in-situ acoustic velocity and attenuation estimates of the seafloor sediment.

Multichannel acoustic control of pneumatic impact machine movement in soil and measurement information processing algorithm

The acoustic data measurement system and processing algorithm are developed to position a pneumatic impact machine in soil. The method is based on recording lag time of entry of acoustic signal generated on interaction between the pneumatic impact machine and soil in the receiver of multichannel measurement system relative to reference signal of the machine. The measurement system and the algorithm have been trialed in full-scale conditions.

Research on Acoustic Properties of Seafloor Sediment with Temperature and Pressure Controlled

The submarine in-situ environmental state was simulated to study the acoustic properties of seafloor sediments of the South China Sea in different temperature and pressure environments in this article with the application of the small-scale acoustic measurement system of seafloor sediments. Some conclusions could be drawn, including: (1) the velocity and center frequency of sound wave propagation of sediment are influenced by temperature more than by water pressure in different depth; (2) with the temperature rising, the sound velocity and the energy dissipation increase while the center frequency of sound wave propagation decreases; and (3) with the seawater pressure rising, the sound velocity varied little within 1% through a depth of 1500 m and the energy dissipation decreases large. So when correcting the laboratory measurement sound speed into the in-situ data, it should be noticed that the influence of temperature differing from the in-situ environment is significant and the influence of water pressure variation may be omitted. The variation of the acoustic attributes of the experimental sample showed greatly nonlinearity when the temperature changes, which might result from a lot of coarse sand and shell remains scattered in the measured sediment sample. Compared to the linear acoustic properties of reconstructed samples with an even structure it is maybe the reason for nonlinear variation of acoustic properties due to the uneven structure. Moreover, the correction method of Hamilton with the sound-speed ratio of sediment to bottom seawater should be used with caution due to the nonlinear variation character.

New insight on the restructuring and breakage of particles during uniaxial confined compression tests on aggregates of petroleum coke

With the aim of modelling the mechanical behaviour of carbon anode paste, compression tests within a rigid mould were performed on different recipes of carbon paste containing 32 to 44wt.% binder. The compression was performed by applying a series of loading/unloading cycles. The maximum load was incrementally increased at each cycle. Test results showed that a softening behaviour occurs after the hardening of the anode paste during compaction cycles. This paper attempts to explain the mechanism of this peculiar behaviour. For comparison, two cokes with different shape factors were used to prepare the paste recipes. It was observed that round particles result in less resistance to local shear stress than do the angular ones. Binder, which consists of coal tar pitch and fine coke particles, acts as a lubricant enhancing the compaction of the paste. The breakage and slippage of particles during loading were monitored using an acoustic measurement system. A creep test, performed on a carbon paste and dry aggregates, corroborates that the time-dependency, or creep, of the paste is mainly governed by the solid skeleton.

High resolution acoustic measurement system and beam pattern reconstruction method for bat echolocation emissions

Measurements of the transmit beam patterns emitted by echolocating bats have previously been limited to cross-sectional planes or averaged over multiple signals using sparse microphone arrays. To date, no high-resolution measurements of individual bat transmit beams have been reported in the literature. Recent studies indicate that bats may change the time-frequency structure of their calls depending on the task, and suggest that their beam patterns are more dynamic than previously thought. To investigate beam pattern dynamics in a variety of bat species, a high-density reconfigurable microphone array was designed and constructed using low-cost ultrasonic microphones and custom electronic circuitry. The planar array is 1.83 m wide by 1.42 m tall with microphones positioned on a 2.54 cm square grid. The system can capture up to 228 channels simultaneously at a 500 kHz sampling rate. Beam patterns are reconstructed in azimuth, elevation, and frequency for visualization and further analysis. Validation of the array measurement system and post-processing functions is shown by reconstructing the beam pattern of a transducer with a fixed circular aperture and comparing the result with a theoretical model. To demonstrate the system in use, transmit beam patterns of the big brown bat, Eptesicus fuscus, are shown.

A quartz-bar megasonic system for nano-pattern cleaning

A quartz-bar megasonic system for cleaning nano-particles with uniform acoustic pressures, was designed and manufactured. The impedance graph of the piezoelectric actuator used in the system was predicted using a finite element method (FEM); this gives the anti-resonance frequency of the piezoelectric actuator alone as 987 kHz, which is the same as the experimentally measured value. The impedance graph of the megasonic system was also analyzed. The predicted anti-resonance frequency of the system was 987 kHz, which agreed well with the measured frequency of 983 kHz. The acoustic pressure distributions of the developed system were examined using an acoustic pressure measurement system. The measured average acoustic pressure and its uniformity were compared with a commercially available product in terms of evaluating the system performance. The average acoustic pressure of the bar-type megasonic system was increased by 89%, while standard deviations of the bar-type megasonic system were decreased by 20%. This implies that the developed bar-type megasonic has an improved capability of particle removal efficiency (PRE) as well as better uniformity of the acoustic pressures.

Acoustic Measurement and Monitoring System for Level of Groundwater

Acoustic Measurement and Monitoring System for Level of Groundwater

Application of Hartmann Acoustic Generator in Source of Underwater Pyrotechnic Combustion

In order to investigate acoustic radiation characteristics of underwater pyrotechnic combustion, Hartmann acoustic generator was applied and its main structural parameters effecting acoustic radiation characteristics were studied by using underwater acoustic measurement system. Experimental studies have shown that, when Hartmann acoustic generator was applied, the sound pressure level of underwater pyrotechnic combustion increased significantly because of the strengthening of turbulence degree. The distance between the nozzle and the resonant cavity is an important factor of affecting acoustic radiation characteristics of Hartmann acoustic generator. When the resonant cavity was placed in the unstable pressure area, it could stimulate strong sound waves. On account of the resistance of the water, the combustion products speed of reaching resonant cavity drooped and the collision strength between the feedback combustion products and the newly generated products reduced. So when the distance was larger, the SPL(sound pressure level) was smaller. The SPL of underwater pyrotechnic combustion increased and the acoustic frequency moved to the low frequency with the depth of resonant cavity increased, which is consistent with the acoustic characteristics of Hartmann acoustic generator applied in air.

Correlations between the in situ acoustic properties and geotechnical parameters of sediments in the Yellow Sea, China

Knowledge about the marine sediment acoustic properties is a key to understanding wave propagation in sediments and is very important for military oceanography and ocean engineering. We developed a hydraulic-drived self-contained in situ sediment acoustic measurement system, and measured for the first time the in situ acoustic properties of sediments on 78 stations in the Yellow Sea, China, by employing this system. The relationships between the in situ measured acoustic properties and the onboard or laboratory determined geotechnical parameters were analyzed. Porosity was found to be the dominant factor in reducing velocity in a quadratic fashion; velocity showed an increment with bulk density and a decrement with mean grain size and clay content both with a nonlinear dependence; acoustic attenuation showed a bell-shaped correlation with porosity and mean grain size but reduced with clay content of the sediments. The attenuation results indicate that intergrain friction rather than viscous interactions between pore fluid and solid grains is the dominant loss mechanism in our marine sediments. The relationships established would be used to predict the geotechnical parameters from in situ measured acoustic properties and vice versa, as well as being an indicator of the seafloor processes, potential gas bubbles hazard and gas hydrates resources or other suitable targets of acoustic surveys.

Acoustic Doppler velocity measurement system using capacitive micromachined ultrasound transducer array technology

This paper describes the design, fabrication, modeling, and characterization of a small (1 cm(2) transducer chip) acoustic Doppler velocity measurement system using microelectromechanical systems capacitive micromachined ultrasound transducer (cMUT) array technology. The cMUT sensor has a 185 kHz resonant frequency to achieve a 13° beam width for a 1 cm aperture. A model for the cMUT and the acoustic system which includes electrical, mechanical, and acoustic components is provided. Furthermore, this paper shows characterization of the cMUT sensor with a variety of testing procedures including Laser Doppler Vibrometry (LDV), beampattern measurement, reflection testing, and velocity testing. LDV measurements demonstrate that the membrane displacement at the center point is 0.4 nm/V(2) at 185 kHz. The maximum range of the sensor is 60 cm (30 cm out and 30 cm back). A velocity sled was constructed and used to demonstrate measureable Doppler shifts at velocities from 0.2 to 1.0 m/s. The Doppler shifts agree well with the expected frequency shifts over this range.

The Analysis and Correction of Time-Delay in the Precise Acoustic Measurement System

The acoustic transducer is a nonlinear system, which will cause a time delay to signals. The system group and phase delay have a large influence on the results in the transmit-time measurement. In order to solve the problem, this paper proposes to use the signal phase difference to eliminate the phase delay, and precisely determine the group delay by the method of experiment. At first, this paper theoretically proves that the group delay of the acoustic measurement system is constant, and the phase delay changes over signal frequency, then it analyzes the influence of group and phase delay on the measuring results and meanwhile puts forward a method to use the multi-frequency signal phase difference to eliminate group delay .Finally, it achieves the group delay through experiments, and there is a good consistency between the experimental results and theoretical analysis.

Design and positional accuracy of straight-path traversing room acoustic measurement system based upon low-cost servo motor and light-weight multi-field microphone

The construction and operation of a straight-path traversing, acoustical microphone-based, measurement system is described. The system was designed to support test room qualification procedures such as prescribed in standards ANSI S12.35-1990 and Annex A of ISO 3745-2003. Major system components include a taut line suspending a sliding microphone carriage drawn by a string attached to a rotating drum. Central to the overall light-weight, low-power, mechanical design is the physically small Bruel & Kjaer 4961 microphone, holder, preamp, and signal cable whose multi-field response characteristic should well support accurate room qualification measurements. The battery-powered drum drive mechanism is built using the servo motor, wheels, and gears from a Lego Mindstorms NXT kit. Precision motor rotation is remotely programmable over the NXT controller’s wireless Bluetooth interface. Commonly available sport fishing tackle composes the majority of the suspension assembly. A software interface library is also d...

Two-Dimension Temperature Field Reconstruction in Furnace by Acoustic Method

Acoustic temperature measurement technology is a new temperature measuring technology which is rising in recent years. This paper discusses a kind of reconstruction method of temperature field based on acoustic pyrometer. First , acoustic sensors has been used to obtain measurement data, and the technique of wavelet has been used to denoise in order to improve the accuracy of measurement , secondly, the least-squares algorithm has been used to reconstruct temperature field. Finally, we work out our own acoustic temperature measurement system and has got the satisfying result using our own acoustic pyrometer to detect two-dimension temperature field in the laboratory.