Imaging Of Acoustic Fields Research Articles

Acoustic Field Imaging of Pipeline Turbulence for Noninvasive and Distributed Gas Flow Measurement

Precise control and measurement of the flow are essential for pipeline safety monitoring and economic accounting. Nowadays, the measurement of pipeline flow relies on point measurement schemes such as mechanical flowmeters, which invade the pipeline and can irreversibly damage the fluid pressure, especially when multipoint measurements are required. To overcome these problems, we have explored a novel technique in which the acoustic field properties of pipeline turbulence are reflected by distributed backscattering light field, from which the flow can be measured via acoustic field imaging. The acoustic field information is recorded by a helical deployment scheme using backscattering-enhanced optical fiber (BEOF) encapsulated in the polyethylene anticorrosive layer, thereby achieving highly sensitive, noninvasive, and distributed online monitoring of gas flows. We obtained 24-h flow fluctuation distributions with only one sensing fiber for two operating gas pipelines, and the flow measurement accuracy reached higher than 98% within the error range of −15% to 15%. Moreover, the minimum detectable flow is evaluated and it is demonstrated that the proposed scheme is extremely sensitive to weak flows. We successfully demonstrated noninvasive and distributed online measurement of operational pipeline flow, which will exhibit great potential for pipeline integrity management in the future.

Multi-View Acoustic Field Imaging With Digital Color Holography

This paper proposes an approach for acoustic field imaging using simultaneous multi-view digital holography based on three-color digital off-axis holography. Considering spatio-chromatic multiplexing and the recording with a monochrome sensor, the numerical processing of time-sequences of holograms yields both the amplitude and phase of the acoustic field along three different directions of observation. Distortion analysis is presented and the acousto-optic interaction along the optical beam is discussed using a theoretical modelling. Experimental results with an emitter at 40 kHz establish the proof-of-concept of the proposed multi-view imaging for acoustic fields.

Imaging of acoustic fields using optical feedback interferometry.

This study introduces optical feedback interferometry as a simple and effective technique for the two-dimensional visualisation of acoustic fields. We present imaging results for several pressure distributions including those for progressive waves, standing waves, as well as the diffraction and interference patterns of the acoustic waves. The proposed solution has the distinct advantage of extreme optical simplicity and robustness thus opening the way to a low cost acoustic field imaging system based on mass produced laser diodes.

Excitation of regular convective motions in liquids and liquid crystals by an acoustic wave

A possibility of exciting steady convective motions in isotropic and anisotropic liquids under the action of a force produced by the radiation pressure of an acoustic wave with a spatially periodic transverse intensity distribution is investigated theoretically and experimentally. Cells both with two rigid boundaries and with one free surface are studied. The flows lead to reorientation of the director of liquid crystal in the case of anisotropic liquid. As a result, it acquires a periodic distribution in the transverse plane. The phenomenon can be utilized for the imaging of acoustic fields of microwatt power.

Optical Bragg imaging of acoustic fields after reflection

Bragg diffraction of x-rays occurs when the rays interact with a crystalline lattice at the appropriate angle. Bragg diffraction of visible light occurs when the light interacts at the Bragg angle with an ultrasonic field of the appropriate frequency. (The spacing between acoustic condensations and rarefactions acts like the planes in an atomic lattice.) If a beam of light is Bragg diffracted by an ultrasonic beam that previously has passed through an object, an image of the structure of the object is made visible in the diffraction field of the optical beam since there is a one-to-one mapping of the ultrasonic field onto the diffraction order. In many acoustic Bragg imaging applications, the sound field must pass through the object which is to be imaged. Ultrasonic attenuation at the very high acoustic frequencies needed for Bragg imaging (typically approximately 25-30 MHz) severely limits the nondestructive testing (NDT) applications of traditional acoustic Bragg imaging. In this paper, a reflection-based application of acoustic Bragg imaging is discussed which may have useful industrial and biomedical NDT applications.

Optical Bragg imaging of acoustic fields after reflection.

If visible light is incident at the Bragg angle on an acoustic wave of the appropriate frequency, the light will undergo Bragg diffraction from the acoustic wavefronts in a manner analogous to the Bragg diffraction of x-rays in a crystalline lattice. If the acoustic beam has previously passed through an object before having light diffracted from it, the structure of that object will be imaged in the optical diffraction orders. In traditional Bragg imaging applications, the sound is first transmitted through the object. In this presentation a new reflection-based method of Bragg imaging (where light is reflected from rather than transmitted through the object) will be discussed. This technique is capable of imaging structures at or near the surface of the object and may have potential industrial and biomedical NDT applications.

Imaging of acoustic fields in bulk acoustic-wave thin-film resonators

By using an atomic-force-microscope-based technique, we image the vibration of high-frequency, bulk-mode, thin-film resonators. Our experimental technique is capable of monitoring the vibration of these devices over a broad frequency range, from 1 MHz to beyond 10 GHz, allowing us to obtain quantitative measurements of the piezoelectric properties of thin-film materials in that frequency range. This technique allows us to map the complex vibration modes of a new generation of high-frequency bulk piezoelectric resonators, revealing the presence of vibration patterns of very different characteristic lengths.

Acoustic field imaging by light reflection at the free surface of a liquid

In this paper we present a novel technique for acoustic field imaging. This technique is based on reflection of a collimated laser beam at the free surface of a liquid. The reflected beam becomes phase modulated by the acoustic wave as in acoustical holographic systems. We do not use a reference acoustical beam for holographic reconstruction but we observe this phase modulation using dark-field techniques. It gives a measurement of the acoustic field power as a function of the position. The authors have built an optical imaging system and carried out experiments with piezocomposite transducers. The technique presented in this work is able to give fast quantitative information about the performance of individual ceramic rods of the piezocomposite.

Optical generation and detection of elastic waves in solids

In this paper we review optical methods suitable to generate and to detect elastic waves in solids without any mechanical contact. The mechanisms underlying elastic wave generation by the impact of a pulsed laser beam are outlined. The principles of optical techniques able to detect surface displacements of amplitude less than one angstrom are described. Examples of applications in domains such as nondestructive testing and acoustic field imaging are given.

Ultrasonic evaluation of the resistance to hydrogen induced cracking of line pipe steel

In this paper we present a novel technique for acoustic field imaging. This technique is based on reflection of a collimated laser beam at the free surface of a liquid. The reflected beam becomes phase modulated by the acoustic wave as in acoustical holographic systems. We do not use a reference acoustical beam for holographic reconstruction but we observe this phase modulation using dark-field techniques. It gives a measurement of the acoustic field power as a function of the position. The authors have built an optical imaging system and carried out experiments with piezocomposite transducers. The technique presented in this work is able to give fast quantitative information about the performance of individual ceramic rods of the piezocomposite.