High-resolution Acoustic Imaging Research Articles

Imagerie ultrasonore haute résolution

High resolution acoustical imaging involves hard constraints for the ultrasonic probes which are used: a high resonance center frequency, a very wide bandwidth, a good sensitivity and a strong focusing of the beam. The system which is described uses two kinds of focused transducer: a very broad band 17 MHz center frequency transducer (PZT), and a 45 MHz copolymer transducer. The focal distances are respectively 7 mm and 6 mm in water. The movement of the transducer provides a 6 mm wide and 5 mm deep echographic cross-section with at the rate of 15 images/s. The resolution is respectively at 17 MHz and 45 MHz, 80 μm and 60 μm in axial and 250 μm and 60 μm in lateral in the focal zone. The device was tested on fantoms in water and in vivo with applications in Dermatology

High resolution images in acoustic microscopy

A novel scanning acoustic microscopy technique for achieving high resolution acoustic images by employing thermal effects and image subtraction has been studied and demonstrated. Experiments were performed on a perspex block patterned with a machined grid on the reverse surface, and on a buried channel in similar material. It was found that using the image subtraction technique, short periods of sample heating can lead to a stronger pattern selectivity, because of the strong temperature dependency of the elastic parameters of the polymer. In previous SAM techniques improvement in resolution has been achieved through the use of special liquids as acoustic coupling media between the acoustic lens and the sample. The reported technique retains water as the coupling medium and the acoustic impedance matching is performed by varying the elastic parameters of the sample itself through direct heating. The temperature increase in the sample decreases the velocity of propagation of acoustic waves in the solid, and brings the acoustic impedance close to that of water. A theoretical model, including expressions for the acoustic aberrations, depth dependence, and acoustic impedance matching, has been derived. Examples of the results obtained are presented.

Quantitative performance analysis of the phase-only technique for high-resolution acoustical imaging

The phase-only technique is commonly used in holographic imaging. It utilizes only the phase information of the resultant complex wave field for image reconstruction. The amplitude information is either unavailable due to the limited data acquisition capability or removed for wave-field data compression purposes. From the perspective of signal processing, phase-only image formation is an extreme case of signal reconstruction from partial information. In the past, the capability of high-resolution imaging with only the phase information and the superior resolving capability over the counterpart, amplitude-only method have been demonstrated. However, the previous study was limited to several selected cases, and the resolution analysis was largely qualitative. It is highly desirable to conduct a quantitative performance evaluation and theoretical resolution analysis for the phase-only technique. Image reconstruction with partial wave-field information often involves nonlinearity because of the loss of wave-field information. Therefore, resolution analysis becomes a difficult task for the conventional measure. In this paper, the problem is approached with an alternative resolution formula and is extended to include the effects of wave-field information loss. As a result, it is now possible to quantitatively evaluate the resolving capability of the phase-only method. With this technique, one can also numerically compare the performance with that of the amplitude-only case, and theoretically support the experimental findings. In addition, this approach can also be applied to a quantitatively performance evaluation of various low bit-rate imaging schemes.

High-resolution acoustical imaging

High-resolution acoustical imaging

Casing Corrosion Evaluation Using Wireline Techniques

Abstract Corrosion control in the oil industry is a matter of economics. Up to 1% of the over-all operating costs could be saved through corrosion management. All too often, this is not considered and corrosion monitoring only occurs on a need to know basis, after an unscheduled shutdown or actual casing failure. Corrosion management involves casing inspection and periodic monitoring, corrosion rate prediction and cathodic protection evaluation. Today's corrosion wireline logging tools offer a technique to predict and detect potentially disastrous corrosion problems. Current wireline measurements utilize electromagnetic, flux leakage, ultrasonic and mechanical techniques. They can predict, detect and delineate corrosion in the form of metal loss, holes, pits, and mechanical deformation. Furthermore, external problems can be distinguished from internal ones, These measurement systems will be briefly described along with examples of multiple measurement diagnostics. Introduction Corrosion control in the oil industry is essentially a cost containment exercise; the likely cost of a failure being balanced against the expenditure on a corrosion control program. The oil and chemical processing industries, which have to live with their corrosion problems, have a better record of corrosion control than most. In oil production, some 3% of the over-all operating costs can be attributed to corrosion. Up to one third or this could be saved through a planning scheme involving corrosion detection, evaluation and management in downhole casings. This generally involves three areas: casing inspection and periodic monitoring, corrosion rate prediction and corrosion protection evaluation. These can be accomplished through the application of current wireline measurements in addition to corrosion protection techniques. All too often, corrosion is not considered during the planning stages of a field. Most corrosion programs result from an adverse inspection report, an unscheduled shutdown or an actual failure. Cathodic protection systems of both surface and downhole tubulars are becoming the only realistic solution to a field's corrosion problems. Simply pm, monitoring casing corrosion is a function of dollars and cents. Today's corrosion logging tools offer oil companies the best chance of detecting and correcting the potentially disastrous effects of corrosion. These wireline measurement systems consist of three basic principles. Electromagnetic Tools Cathodic Protection Profile Tool Location of anodic corrosion cells - a device to evaluate external casing corrosion cell activity and determine cathodic protection needs. Flux Leakage Tool Localized corrosion - a high resolution flux leakage and eddy current multi-pad device to evaluate the extent of internal and external localized pitting and holes. Multifrequency Electromagnetic Thickness Tool General wall loss - electromagnetic device which determines wall thickness, inner diameter and casing wall electromagnetic properties measurement. Ultrasonic Tools Acoustic Corrosion Tool General wall loss - an acoustic device which determines wall thickness, inner radii and internal roughness, using eight fixed ultrasonic transducers. Borehole Televiewer Casing wall imaging - a high-resolution acoustic imaging device to evaluate internal surfaces and determine pipe geometry. Mechanical Tools Mechanical Calipers Inner wall loss - a multifingered mechanical caliper system with, 16 to 60 fingers to evaluate inner pipe wall for wear or deform

Non-linear signal processing for high-resolution acoustical imaging

Non-linear signal processing for high-resolution acoustical imaging