摘要:

This paper describes a wireless demonstrator system designed for generation and detection of fundamental symmetrical Lamb waves (S0) characterized by high velocity and low attenuation. The demonstrator comprises two piezoceramic transducers embedded within an epoxy plate, drive and pre‐amplification electronics, a microcontroller and a communications interface. This arrangement can be configured to operate in an active pitch‐catch or pulse‐echo interrogation mode or as a passive acoustic emission (AE) sensor. The history of AE incidents, for example, may then be transmitted by wireless link. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570324

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A sensor based on the change in the magnetic field‐induced microwave absorption due to the presence of ferrous corrosion products on steel is described. This type of sensor for detection of corrosion under structural coatings is unique in that its sensitivity is to chemical, rather than physical alterations, to steel surfaces by corrosion processes. Preliminary results suggest that this sensor may be particularly sensitive to ferrous corrosion products found in the initial phases of the corrosion process. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570325

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In ultrasonic diffraction grating spectroscopy, the grating surface is in contact with the liquid or slurry. The ultrasonic beam, traveling in the solid, strikes the back of the grating and produces a transmitted m = 1 beam in the liquid. The angle of this beam in the liquid changes with frequency and the so‐called critical frequency occurs when the angle is 90°. At this point, the signal of the reflected m = 0 wave—the signal observed in the experiment—increases and this increase is used to characterize the liquid or slurry. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570326

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Rapid, on‐line determination of particle size and concentration is required for the efficient process measurement and control of many processes in government and industrial applications such as waste remediation for the Department of Energy sites and process control for chemical and pharmaceutical manufacturing. However, existing methods based on ultrasonic attenuation can become inaccurate for highly concentrated suspensions due to careful transducer alignment and the complicated mathematics required to describe multiple scattering, which controls the attenuation. Two measurements that help to overcome these difficulties are the ultrasonic backscattering and diffuse field. Backscattering is attractive because the single scattering theories typically used to describe backscattering are mathematically simpler than attenuation theories and lend themselves to more stable inversion processes. Also, the measurements of backscattering and diffuse fields do not require long travel distances and can be made with a single transducer thus eliminating alignment problems. We will present ultrasonic measurements on solid liquid suspensions designed to elucidate the particle size and concentration at high concentrations. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570327

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Damages like cracks, delaminations, etc., in composite parts have traditionally been evaluated using manual methods like acoustic impact (using measurements in the audio frequencies). This technique is currently used during manufacturing for product quality testing and later for maintenance and assurance of structural integrity. The automation of this technique will significantly improve the reliability of inspection. The signals obtained from the composites are analyzed using signal‐processing techniques in the time‐frequency domain to build a robust algorithm for detection and identification of defects. A feature vector is constructed using these techniques and then applied to a neural network for defect identification. Comparative studies are conducted to search for the best and most comprehensive feature vector. Results using different signal processing techniques are presented. Similarly comparative results are presented between two different kinds of neural networks (namely Radial Basis functions and MLP) and various architectures in each kind. A low cost data acquisition system has also been developed for acquiring audio signals using the sound card and the microphone in a multi‐media PC. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570328

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

This paper investigates the use of phenomenological models of viscoelasticity to simulate ultrasonic compression wave propagation in a curing thermoset. Kelvin‐Voigt and Maxwell models do not give physical results whilst the anelastic solid (Debye) formulation and its Cole‐Davidson (CD) extension provide a qualitative match to experiment, although with some inconsistencies. The CD model when fitted to experimental phase velocity data gave parameters that could be used to track molecular polydispersity in the curing thermoset. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570329

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

For the paper industry, stiffness properties are an important parameter for producing more efficiently a fibrous material like paper. Some stiffness properties of paper webs can be obtained in a non‐contact fashion using two lasers. The authors have developed an automated laboratory laser‐ultrasonics instrument for paper, described here. The results of non‐contact laser generation and detection of ultrasound are also presented. The paper grades investigated were heavy grades like linerboard, as well as copy paper. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570330

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The development of prognostic capabilities that predict the condition and remaining service life for key industrial systems has the potential to significantly impact performance and the economics of operation for both current and next generation plants. This paper describes an on‐line real‐time ultrasonic meter that can be used to monitor both fouling and cleaning in reverse osmosis filters. It provides a measure for the degree of fouling. A suit of ultrasonic transducers is mounted to operate through the filter‐housing wall on a pilot‐scale service water system. A “Degree of Fouling” index is given during both fouling and cleaning for the filters during operation for processing of saline solutions (simulated sea and brackish waters) and solids contamination. The fouling index is transmitted to a central computer where it is integrated in a system level prognostic algorithm. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570331

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Laser‐ultrasonic measurements are performed during the annealing of cold‐worked low‐carbon steel at temperatures between 590°C and 610°C. During annealing, the ultrasound velocity behaves in a peculiar way, first decreasing and then increasing to a final value. The recrystallized fraction evaluated by metallography indicates that recrystallization occurs during both the decrease and the increase in longitudinal velocity. Texture evaluated using laser ultrasonics suggests that the peculiar behavior of the velocity might be due to two different regimes of texture evolution. Internal friction, investigated through ultrasound absorption measurements, is also revealed to be very sensitive to the annealing process. This internal friction is attributed to magnetomechanical effects that are also known to decrease the ultrasonic longitudinal velocity and probably contribute to the observed peculiar behavior of the velocity. From this work, we conclude that, although there remains much work to do to explain our observations, both the longitudinal velocity and internal friction measurements are promising approaches for the development of an online sensor to characterize annealing using laser‐ultrasonics. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570332

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Air‐coupled NDE has been used to perform measurements on food containers. This relies on the broad bandwidth available from polymer‐filmed capacitive transducers, combined with pulse compression techniques. The first experiments involve liquids within cylindrical polymer containers. It will be demonstrated that transmission through the drinks bottles can be used to measure liquid level, either from monitoring the through‐transmitted signal directly, or by observation of a reflection from the liquid surface. This can be achieved without contact to the container. By scanning the transducers around the container, it is also possible to collect tomographic data. It will be demonstrated that this can be used to reconstruct air‐coupled cross‐sectional images of such containers, so that contaminants can be located. It is also shown that the temperature of a liquid can be estimated successfully, using time‐of‐flight measurements. The result is a powerful method for the NDE of such materials, which could be applied to production‐line situations. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570333

出版商:AIP    

年代:1903

数据来源: AIP