Acoustic Measurement Method Research Articles

Investigation of Acoustic Field Calculation and Measurement Method for Air-coupled Ultrasonic Transducer

The field characteristic of an air-coupled planar ultrasonic transducer was investigated using the spatial impulse response of transducer transmitting aperture,which is based on the assumption of linear sound theory.The impulse response of arbitrary point in field space is calculation by the summation of spherical wave from all of the small area on the transmitting aperture.Attenuation is one of important factor impacting acoustical field distribution for the air-coupled ultrasonic transducer,and which increases with the frequency,a frequency-dependent attenuation function is considered in the field calculation of frequency domain,and then the pressure distribution is obtained by convolution integral of the impulse response with excitation impulse.Compared field measurement experiments are implemented using a multiple-axis scanning system and a miniature aperture detector.The results of theoretic analysis and that of experiment are in a good agreement.Finally,the effects of the receiving aperture size are also considered in sound field measurements,the results indicate that because of the low efficiency and interface loss in air couple,a compromise between resolution and signal to noise ratio(SNR) should be taken into account to choose the receiving aperture size.And a smaller aperture could improve the measuring resolution on condition that the receiving amplification coefficient and the SNR are valid.

An airborne monochromatic acoustic method to measure the hydraulic characteristics of shallow water flows.

Discussed is a new acoustic method to measure the dynamic surface characteristics of open channel flows and hence infer various flow parameters. Hydraulic laboratory tests suggest a relationship between the surface shape and the flow’s internal structure and hydraulic boundary conditions. This work investigates acoustic scattering of a monochromatic ultrasonic wave by a dynamically rough air‐water interface and analyzes the effects of the water surface pattern on the recorded directivity of the scattered acoustic intensity field and its relation to the spatial correlation function for the dynamically rough interface. Temporal analysis of the acoustic intensity scattered by a dynamically rough interface is also used to relate the first and second statistical moments to the fluctuations in the amplitude and phase of the reflected acoustic field. This acoustic measurement method would ultimately allow for remote monitoring of real channel flows and evaluation of flow parameters such as flow rate, depth, turb...

Acoustic evaluation of a contemporary church based on in situ measurements of reverberation time, definition, and computer-predicted speech transmission index

An acoustic survey was conducted in a church with a modern architectural style in Curitiba, southern Brazil. The investigation used acoustic measurement methods to assess the acoustic quality of the nave and the results were compared with the NBR 12179 Brazilian National Standard, ISO 3382-1 international standard and IEC 60268-16 Standard. Integrated impulse responses were measured to determine two acoustic objective parameters: (1) Reverberation Time (RT), (2) Definition ( D 50) according to the international ISO/3382 and ISO/3382-1 standards. The Speech Transmission Index (STI) inside the church was calculated by computer simulation. The measured and calculated values were consistent with those proposed by the standards for speech auditoria (RT 500Hz = 1.18 s, D 50 > 50% and STI > 0.45), and are in line with the music and speech intelligibility requirements resulting from the Second Ecumenical Council of the Vatican in 1965, whose liturgical reforms involved the adoption of vernacular languages in place of Latin for religious service.

Forage density effect on sound insulation properties

AbstractOne of the main parameters affecting forage management and quality is density. Existing methods used for measuring physical properties of forage involve costly destructive analysis. A frequent and appropriate control of the forage density is required for optimizing the management of silage, hay and straw production; therefore, there is a need to develop a new measurement method. The sound insulation properties of a material are governed by its physical structure. Based on this, an inexpensive, non‐destructive acoustic measurement method using sound insulation properties was developed to determine forage density. The method has been used to analyse the correlation of the density with the sound insulation spectra produced by small‐scale models of hay, silage and straw. Results show that the sound insulation spectra of forage have a high correlation with the density and a significant congruence with the physical structure of the targeted forage types. The findings are highly relevant for innovative applications in agriculture, animal nutrition and bio‐energy production in terms of material properties monitoring, materials classification and quality determination.

Acoustic Transmission and Measurement Method for Near-bit Dynamic Force Signal of Bottom Drill String

A straight beam strain gauge sensor and a virtual instrument-based dynamic force wireless measurement device of simulated drill string are developed to study the near-bit bottom drill string dynamics in measurement while drilling.The structure and working principle of the measurement system are expressed.The axial forces,radial forces and torsional moments for rotating simulated drill string are detected multithreadedly in the laboratory.By comparing downhole data transmission methods,an acoustic transmission experimental device is established via longitudinal waves along simulated drill string.Then,the on-off keyed(OOK) modulation of time-delayed pulses is designed.The narrow pulse modulated signal transmission experiments are performed by applying the longitudinal excitation to the length-limited simulated drill string in the axial direction of pipes.The results show that the pulse time-delayed and OOK modulated dynamic force data transmission of bottom drill string is implemented by using low frequency acoustic waves along the simulated drill string channel in the laboratory,which provides the theoretical and experimental basis for the application of low-frequency acoustic transmission system of near-bit sensor measurement data.

Calibration of the two microphone transfer function method with hard wall impedance measurements at different reference sections

In many acoustic simulations, particularly when using lumped parameter models or electrical analog circuits, the acoustic impedance of a component needs to be determined accurately. A widely used acoustic impedance measurement method is the “two microphone transfer function method”, which is standardized in ISO-10534-2. When the acoustic impedance is needed over a wide frequency band with a high impedance magnitude range, this method faces some limitations. In this paper, a calibration method is proposed which uses hard wall impedance measurements at different positions of the reference section. The measured hard wall impedance is used to calibrate the microphone positions, to compensate the microphone mismatch and to estimate the wave guide damping. Also, the measured hard wall impedance can be used as performance criterion. It can be used to select frequency bands from different load impedance measurements where the accuracy is maximum and to assemble them in a load impedance measurement. As a result, impedances with a high ratio with respect to the characteristic duct impedance can be accurately measured. The capability of the presented calibration method is illustrated by the impedance measurement of an open duct end and a closed tube.

Acoustic measurement of bubble size and position in an ink jet printhead

An acoustic measurement method of the volume and position of a bubble in an ink jet print head, is presented. The system is driven by a piëzo actuator. The actuator is also used as a sensor by measuring the current through the piëzo. The method used to determine the volume and position of the bubble is based on a linear model of the investigated system. This model predicts the current for a given position and volume of the bubble. The inverse problem is to infer the position and volume of the bubble from the measured current through the piëzo actuator. The solution of the inverse problem is demonstrated. Thus, an acoustical measurement method of these properties is obtained. The results from the acoustical measurement method correspond closely with results from optical measurements. This indicates validity of the presented method.

Imaging Method for Acoustic Impedance Difference for Puncture Needle-Type Ultrasonography using a Thin Rod with Focusing End Face

In this paper, we propose an imaging method for acoustic impedance difference for puncture needle-type ultrasonography. The difference in acoustic impedance between benign and malignant tissues will provide valuable diagnostic information. In this experiment, a thin rod that has a concave polished end face was constructed using a fused quartz with a diameter of 1 mm and a focus length of 0.3 mm. An ultrasonic wave emitted from the concave end face of the rod is focused on a tissue. The difference in acoustic impedance was determined by the reflection-type interference-based acoustic impedance measurement method. We confirmed that the image shows the difference in impedance between the polyethylene (PE) plate and acrylic rod with a diameter of 3.5 mm embedded therein. The experimental results show that the method is useful for puncture needle-type ultrasonography.

Field measurements of acoustic performance in buildings: a Round Robin Test

This paper presents the experimental results of a round robin test performed on the same building by different teams working with three independent bodies: a research body, ITC‐CNR, a university laboratory DISAT and the Regional Agency for Environment Protection of Lombardy, ARPA. A partition wall (the airborne sound insulation between rooms), a floor (the impact sound insulation between rooms) and a facade (the insulation of the facade against outdoor sound) were tested, using the measurement methods given in the relevant parts of the ISO 140 series. The accuracy of acoustic measurement methods in buildings depends on many factors. In this round robin test, the situation (varying from straightforward rectangular rooms to half open spaces with all kind of shapes) and the construction details were kept fix. The analysis was aimed at investigating the influence of the operating condition of the equipment (repeatable settings) and the reproducibility, using different types of acoustic instrumentation and var...

Study of Partial Discharge Measurement in Power Equipment Using Acoustic Technique and Wavelet Transform

This study proposes a noncontact type of acoustic measurement system and applies wavelet transform to noise suppression in order to raise the correct partial discharge (PD) signal identification rate. We first investigate an acoustic measurement method in the laboratory and apply the wavelet transform to suppress noise. A wavelet mother function most similar to the acoustic PD signals is chosen to set the filtering threshold value for the wavelet transform. Finally, the proposed acoustic measurement system is applied on line to epoxy-resin transformers, power distributors and the like. The superior measurement results we obtained will be able to help maintenance personnel eliminate field noise to correctly identify the PD fault types of power equipment.

Measurement Methods Adapted to Wood Frame Lightweight Constructions

When building elements of wood-frame lightweight constructions are considered, laboratory acoustic measurement methods have to be rethought. Indeed, because lightweight elements are often highly damped, the vibrational fields are no longer reverberant and existing standards often lose relevance, particularly in the case of mechanical excitation (such as in impact noise measurements or in vibration reduction index measurements of junctions). In this paper, standardized methods are identified or new methods are proposed for characterizing lightweight elements in order to obtain input data for prediction models such as that adapted from the standards EN 12354-1 and −2 and described in a companion paper. Moreover, it is shown that a new parameter (the radiation efficiency) is required when predicting the performance of lightweight buildings. Measurement results are shown for both wall and floor elements and the results are discussed, particularly in comparison with heavy building elements.

A method for acoustic parameter measurement of viscoelastic material

A method for acoustic parameters measurement of viscoelastic material, using the directivity pattern of scattering field of spherical sample made by that material, had been presented. Aluminum spheres had been used for verification of the accuracy of this method, and the measurement results of a kind of rubber had been given. It shows that this method can be used to measure parameters of viscoelastic material in sufficient wide frequency range.

Acoustic measurement method and apparatus

Method and apparatus for simultaneous acoustic measurement at a point (M) in space of the three components of the sound intensity vector. A preferred omnidirectional vector probe ( 40 ) includes a central ring ( 42 ) with four small, microphones on tubes attached to the ring spaced from one another in a regular tetrahedral arrangement. The tubes are parallel to the axis of the ring, two on one side ( 58 ) and two on the reverse side ( 60 ) of the ring, with two of the microphones pointing in one direction and two in the opposite direction. The microphone signals are processed by an analog-to-digital converter feeding a digital signal processor ( 68 ) and employing a cross-spectral formulation to compute a sound intensity vector at the measurement point (M). Sound velocity and pressure can also be determined at this point. The resulting data may be outputted on a computer screen or other device ( 70 ). Additional related features and methods are disclosed.

Device and method for acoustic diagnosis and measurement by pulse electromagnetic force

A device and a method for acoustic diagnosis and measurement by pulse electromagnetic force capable of surely diagnosing and measuring, without destruction, the corrosion, adhesive force, cover depth, and diameter of the reinforcements of a reinforced concrete structure; the method, comprising the steps of installing a coil (12) on the surface of a structure (11) comprising a conductor (11a) and a nonconductive substance (11b) covering the conductor (11a), applying current pulses to the coil (12) to generate magnetic field pulses, inducing an eddy current in the conductor (11a) by the magnetic field pulses to excite the conductor (11a) by an interaction between the eddy current and the magnetic field pulses, converting the acoustic signals generated from the conductor (11a) into electric signals by an acoustic transformer (14) for converting acoustic signals into electric signals installed on the surface of the structure (11), and measuring the electric signals by a measuring part (15) to diagnose and measure the position of the conductor (11a) or the state of the structure (11).

Acoustic method and device for distance measurement

An acoustic method for measuring of a distance between an emitter of acoustic energy and a target object provides for an accurate measurement by having the measurement’s outcome invariant to the speed of sound variations along the acoustical path between the emitter and the target. One emitter (40) and one receiver are located in a spatial region such that the sent and the reflected acoustic energy passes along substantially the same vertical line between the emitter and the target (12). Another emitter (48) sends acoustic energy at an angled direction to the same area (10) on the target’s reflecting surface as the first emitter does. The corresponding echo travels to another receiver (52). The sought distance between the first emitter and the target’s reflecting area is calculated by a function of the radio between the travel time measurements, whereby, possible variations of the speed of sound to the result of the distance calculations are irrelevant.

Acoustic mixing and measurement system and method

An acoustic measurement system detects solids within a fluid includes a sample cell 10 for containing the fluid, a first transducer 20 for outputting a first acoustic detection signal at a first frequency, a first acoustic receiver 20 responsive to the first acoustic detection signal, and a second acoustic transducer 20 for outputting an acoustic second mixing signal at a second frequency to mix the solids in the fluid within the sample cell. Controller 40 may vary the “on” time of the second transducer with respect to the measurement of the first acoustic signal. The fluid within the cell may be tested under a wide range of temperatures and pressures. The acoustic measurement system may also be used to measure the bulk modulus of the liquid. The method of the invention allows for the detection of crystallization for a portion of the fluid in the sample cell under widely varying conditions.

Measurement of Acoustoelastic Effect of Surface Wave with an Improved Acoustic Transducer

ABSTRACTA new acoustic transducer and measurement method have been developed for precise measurements of surface wave velocity. This technique is used to investigate the acoustoelastic effect of surface waves in polymethylmethacrylate (PMMA). The transducer utilizes two miniature conical PZT elements for surface wave transmitter and receiver, and hence can be viewed as a point-source/point-receiver (PS/PR) surface wave transducer. Surface waves are excited and detected with the PZT elements and the surface wave velocity can be accurately determined over a small measurement area. Improvement has been made so that the transducer can be used for both conductive and non-conductive materials. The transducer is then applied to measure the acoustoelastic effect of surface wave in a PMMA specimen. The acoustoelastic coefficients are experimental determined.

A method for Doppler acoustic measurement of black smoker flow fields

A method is developed for using multibeam sonar to map the flow velocity field of black smoker plumes. The method is used to obtain two‐dimensional cross‐sectional maps of vertical velocity, but is capable of mapping velocity in three dimensions. This is in contrast to conventional current meters, which measure only at several points and acoustic Doppler current profilers, whose diverging beams cannot readily map the interior of a plume. Geometric corrections are used to estimate the vertical component of velocity, compensating for ambient current. The method is demonstrated using data from the main plume at the Grotto vent complex in the Main Endeavour Field, Juan de Fuca Ridge, and the errors due to noise, signal fluctuations, and fluctuations in plume structure are estimated.

An acoustic method for in-line particle size measurement in flowing bulk solids

The propagation velocity of acoustic waves through a packed bed of particles depends on, among other things, the wave frequency and the size of the particles. In this paper, theory is developed to describe the propagation velocity based on consideration of viscous interactions between the gas and solid phases. Experimental measurements in the frequency range 50–10 000Hz, and for particles ranging in mean size from 65 to 6000μm, agree well with the theory, particularly at low frequencies. The propagation velocity also correlates strongly with measurements of the surface mean particle diameter, independently of changes in particle density, and a method is described using this relationship as the basis of an in-line particle size measurement instrument for flowing bulk solid systems. Measurements using different size fractions of sand suggest that changes in mean particle size of less than 1.5 per cent can be resolved using the simple prototype developed for this work.

An investigation of the role of cavitation in low-frequency ultrasound-mediated transdermal drug transport.

Low-frequency ultrasound (20 kHz) has been shown to increase the skin permeability to drugs, a phenomenon referred to as low-frequency sonophoresis (LFS). Many previous studies of sonophoresis have proposed that ultrasound-induced cavitation plays the central role in enhancing transdermal drug transport. In this study, we sought to definitively test the role of cavitation during LFS, as well as to identify the critical type(s) and site(s) of cavitation that are responsible for skin permeabilization during LFS. Pig full-thickness skin was treated by 20 kHz ultrasound and the effect of LFS on the skin permeability was monitored by measuring the increase in the skin electrical conductance. A high pressure LFS cell was constructed to completely suppress cavitation during LFS. An acoustic method, as well as chemical and physical dosimetry techniques, was utilized to monitor the cavitation activities during LFS. The study using the high-pressure LFS cell showed definitively that ultrasound-induced cavitation is the key mechanism via which LFS permeabilizes the skin. By selectively suppressing cavitation outside the skin using a high-viscosity coupling medium, we further demonstrated that cavitation occurring outside the skin is responsible for the skin permeabilization effect, while internal cavitation (cavitation inside the skin) was not detected using the acoustic measurement method under the ultrasound conditions examined. Acoustic measurement of the two types of cavitation activities (transient vs. stable) indicates that transient cavitation plays the major role in LFS-induced skin permeabilization. Through quantification of the transient cavitation activity at two specific locations of the LFS system, including comparing the dependence of these cavitation activities on ultrasound intensity with that of the skin permeabilization effect, we demonstrated that transient cavitation occurring on, or in the vicinity of, the skin membrane is the central mechanism that is responsible for the observed enhancement of skin permeability by LFS. LFS-induced skin permeabilization results primarily from the direct mechanical impact of gas bubbles collapsing on the skin surface (resulting in microjets and shock waves).