The Applied Physics group at the Pacific Northwest National Laboratory (PNNL) in Richland, WA has evaluated a
method for waterless/liquidless coupling of ultrasonic energy from planar ultrasonic contact transducers to irregular test
surfaces for ultrasonic non-destructive evaluation applications. Dry couplant material placed between a planar
transducer face and a curved or uneven steel or plastic surface allows for effective sound energy coupling and preserves
the integrity of the planar transducer sound field by serving as an acoustic impedance matching layer, providing good
surface area contact between geometrically dissimilar surfaces and conforming to rough and unsmooth surfaces. Sound
fields radiating from planar ultrasonic contact transducers coupled to curved and uneven surfaces using the dry coupling
method were scanned and mapped using a Pinducer receiver connected to a raster scanner. Transducer sound field
coverage at several ultrasonic frequencies and several distances from the transducer contact locations were found to be in
good agreement with theoretical beam divergence and sound field coverage predictions for planar transducers coupled to
simple, planar surfaces. This method is valuable for applications that do not allow for the use of traditional liquid-based
ultrasonic couplants due to the sensitivity of the test materials to liquids and for applications that might otherwise require
curved transducers or custom coupling wedges. The selection of dry coupling material is reported along with the results
of theoretical sound field predictions, the laboratory testing apparatus and the empirical sound field data.
A sound field beam mapping exercise was conducted to further understand the effects of coarse-grained microstructures
found in cast austenitic stainless steel (CASS) materials on phased array ultrasonic wave propagation. Laboratory
measurements were made on three CASS specimens with different microstructures; the specimens were polished and
etched to reveal measurable grain sizes, shapes, and orientations. Three longitudinal, phased array probes were fixed on
a specimen's outside diameter with the sound field directed toward one end (face) of the pipe segment over a fixed range
of angles. A point receiver was raster scanned over the surface of the specimen face generating a sound field image. A
slice of CASS material was then removed from the specimen end and the beam mapping exercise repeated. The sound
fields acquired were analyzed for spot size, coherency, and beam redirection. Qualitative analyses were conducted
between the resulting sound fields and the microstructural characteristics of each specimen.
Ultrasonic nondestructive examination (NDE) has a long and successful history of application across a wide array of
industries, including nuclear, aerospace, and transportation sectors. In coarse-grained, cast Manganese (Mn) steel frog
components, NDE/inspection challenges are encountered both in-field (after the frogs have been installed on a rail line)
and at the manufacturing facilities during post-fabrication QA/QC activities. Periodically inherently flawed frogs are
received from a manufacturer, and put into service, as most railroad operators do not have a means to conduct pre-service
examinations on received components. Accordingly, there is a need for a pre-service inspection system that can
provide a rapid, cost-effective and non-intrusive inspection capability for detection of defects, flaws, and other
anomalies in frog components, in order to avoid premature initiation of cracks or failures of these components during
service. This study focused on evaluating use of a volumetric phased-array ultrasonic testing (PA-UT) method to
monitor fabrication quality assurance. In this preliminary assessment of using PA-UT, data were acquired at a frequency
of 2.0 MHz on a known, flawed Mn steel frog component directly from a manufacturing facility. The component
contained flaws commonly found as a result of the manufacturing process of these cast rail components. The data were
analyzed and the anomalies were detected, localized and characterized. Results were compared against baseline
radiographic data. A detection metric was reported in the form of signal-to-noise values.
KEYWORDS: Signal to noise ratio, Ultrasonics, Signal processing, Inspection, Interference (communication), Acoustics, Scattering, Phased arrays, Data fusion, Laser scattering
Cast austenitic stainless steel (CASS) that was commonly used in U.S. nuclear power plants is a coarse-grained,
elastically anisotropic material. In recent years, low-frequency phased-array ultrasound has emerged as a leading
candidate for the inspection of welds in CASS piping, due to the relatively lower interference in the measured signal
from ultrasonic backscatter. However, adverse phenomena (such as scattering from the coarse-grained microstructure,
and beam redirection and partitioning due to the elastically anisotropic nature of the material) result in measurements
with a low signal-to-noise ratio (SNR), and increased difficulty in discriminating between signals from flaws and signals
from benign geometric factors. There is therefore a need for advanced signal processing tools to improve the SNR and
enable rapid analysis and classification of measurements. This paper discusses recent efforts at PNNL towards the
development and evaluation of a number of signal processing algorithms for this purpose. Among the algorithms being
evaluated for improving the SNR (and, consequently, the ability to discriminate between flaw signals and non-flaw
signals) are wavelets and other time-frequency distributions, empirical mode decompositions, and split-spectrum
processing techniques. A range of pattern-recognition algorithms, including neural networks, are also being evaluated for
their ability to successfully classify measurements into two or more classes. Experimental data obtained from the
inspection of a number of welds in CASS components are being used in this evaluation.
KEYWORDS: Liquids, Acoustics, Signal attenuation, Ultrasonics, Temperature metrology, Transducers, Distance measurement, Signal to noise ratio, Inspection, Explosives
Work at the Pacific Northwest National Laboratory has demonstrated that ultrasonic property measurements
can be effectively employed for the rapid and accurate classification/discrimination of liquids in small, carry-on,
standard "stream-of-commerce" containers. This paper focuses on a set of laboratory measurements
acquired with the PNNL prototype device as applied to several types of liquids (including threat liquids and
precursor chemicals) to the manufacture of LEs in small commercially available plastic containers.
The increase of terrorism and its global impact has made the screening of the contents of liquid-filled containers a
necessity. The ability to evaluate the contents of a container rapidly and accurately is a critical tool in maintaining global
safety and security. Due to the immense quantities and large variety of containers shipped worldwide, there is a need for
a technology that enables rapid and effective ways of conducting non-intrusive container inspections. Such inspections
can be performed utilizing "through-transmission" or "pulse-echo" acoustic techniques, in combination with multiple
frequency excitation pulses or waveforms. The challenge is combining and switching between the different acoustic
techniques without distorting the excitation pulse or waveform, degrading or adding noise to the receive signal; while
maintaining a portable, low-power, low-cost, and easy to use system.
The Pacific Northwest National Laboratory (PNNL) has developed a methodology and prototype device focused on this
challenge. The prototype relies on an advanced diplexer circuit capable of rapidly switching between both "through-transmission"
and "pulse-echo" detection modes. This type of detection requires the prototype to isolate the pulsing circuitry from the receiving circuitry to prevent damage and reduce noise.
The results of this work demonstrate that an advanced diplexer circuit can be effective; however, some bandwidth issues
exist. This paper focuses on laboratory measurements and test results acquired with the PNNL prototype device as
applied to several types of liquid-filled containers. Results of work conducted in the laboratory will be presented and
future measurement platform enhancements will be discussed.
Maritime security personnel have a need for advanced technologies to address issues such as identification, confirmation
or classification of substances and materials in sealed containers, both non-invasively and nondestructively in field and
first response operations. Such substances include items such as hazardous/flammable liquids, drugs, contraband, and
precursor chemicals used in the fabrication of illicit materials. Our initial efforts focused specifically on a commercial
portable acoustic detector technology that was evaluated under operational conditions in a maritime environment.
Technical/operational limitations were identified and enhancements were incorporated that would address these
limitations. In this paper, application-specific improvements and performance testing/evaluation results will be
described. Such enhancements will provide personnel/users of the detector a significantly more reliable method of
screening materials for contraband items that might be hidden in cargo containers.
KEYWORDS: Transducers, Ultrasonics, Prototyping, Signal attenuation, Velocity measurements, Inspection, Signal to noise ratio, Signal processing, Distance measurement, Liquids
Government agencies and homeland security related organizations have identified the need to develop and establish a wide range of unprecedented capabilities for providing scientific and technical forensic services to investigations involving hazardous chemical, biological, and radiological materials, including extremely dangerous chemical and biological warfare agents. Pacific Northwest National Laboratory (PNNL) has developed a prototype portable, handheld, hazardous materials acoustic inspection prototype that provides noninvasive container interrogation and material identification capabilities using nondestructive ultrasonic velocity and attenuation measurements. Due to the wide variety of fluids as well as container sizes and materials encountered in various law enforcement inspection activities, the need for high measurement sensitivity and advanced ultrasonic measurement techniques were identified. The prototype was developed using a versatile electronics platform, advanced ultrasonic wave propagation methods, and advanced signal processing techniques. This paper primarily focuses on the ultrasonic measurement methods and signal processing techniques incorporated into the prototype. High bandwidth ultrasonic transducers combined with an advanced pulse compression technique allowed researchers to 1) obtain high signal-to-noise ratios and 2) obtain accurate and consistent time-of-flight (TOF) measurements through a variety of highly attenuative containers and fluid media. Results of work conducted in the laboratory have demonstrated that the prototype experimental measurement technique also provided information regarding container properties, which will be utilized in future container-independent measurements of hidden liquids.
KEYWORDS: Transducers, Ultrasonics, Prototyping, Signal attenuation, Velocity measurements, Signal to noise ratio, Inspection, Signal processing, Distance measurement, Liquids
Government agencies and homeland security related organizations have identified the need to develop and establish a wide range of unprecedented capabilities for providing scientific and technical forensic services to investigations involving hazardous chemical, biological, and radiological materials, including extremely dangerous chemical and biological warfare agents. Pacific Northwest National Laboratory (PNNL) has developed a prototype portable, hand-held, hazardous materials acoustic inspection prototype that provides noninvasive container interrogation and material identification capabilities using nondestructive ultrasonic velocity and attenuation measurements. Due to the wide variety of fluids as well as container sizes and materials encountered in various law enforcement inspection activities, the need for high measurement sensitivity and advanced ultrasonic measurement techniques were identified. The prototype was developed using a versatile electronics platform, advanced ultrasonic wave propagation methods, and advanced signal processing techniques. This paper primarily focuses on the ultrasonic measurement methods and signal processing techniques incorporated into the prototype. High bandwidth ultrasonic transducers combined with an advanced pulse compression technique allowed researchers to 1) obtain high signal-to-noise ratios and 2) obtain accurate and consistent time-of-flight (TOF) measurements through a variety of highly attenuative containers and fluid media. Results of work conducted in the laboratory have demonstrated that the prototype experimental measurement technique also provided information regarding container properties, which will be utilized in future container-independent measurements of hidden liquids.
The inspection of sealed containers is a critical task for personnel charged with enforcing government policies, maintaining public safety, and ensuring national security. The Pacific Northwest National Laboratory (PNNL) has developed a portable, handheld acoustic inspection device (AID) that provides non-invasive container interrogation and material identification capabilities. The AID technology has been deployed worldwide and user’s are providing feedback and requesting additional capabilities and functionality. Recently, PNNL has developed a laboratory-based system for automated, ultrasonic characterization of fluids to support database development for the AID. Using pulse-echo ultrasound, ultrasonic pulses are launched into a container or bulk-solid commodity. The return echoes from these pulses are analyzed in terms of time-of-flight and frequency content (as a function of temperature) to extract physical property measurements (acoustic velocity and attenuation) of the material under test. These measured values are then compared to a tailored database of materials and fluids property data acquired using the Velocity-Attenuation Measurement System (VAMS). This bench-top platform acquires key ultrasonic property measurements as a function of temperature and frequency. This paper describes the technical basis for operation of the VAMS, recent enhancements to the measurement algorithms for both the VAMS and AID technologies, and new measurement data from laboratory testing and performance demonstration activities. Applications for homeland security and counterterrorism, law enforcement, drug-interdiction and fuel transportation compliance activities will be discussed.
KEYWORDS: Acoustics, Signal attenuation, Inspection, Ultrasonics, Velocity measurements, Transducers, Personal digital assistants, Liquids, Temperature metrology, Solids
The Pacific Northwest National Laboratory (PNNL) has developed a portable, battery-operated, handheld ultrasonic device that provides non-invasive container interrogation and material identification capabilities. The technique governing how the acoustic inspection device (AID) functions, involves measurements of ultrasonic pulses (0.1 to 5 MHz) that are launched into a container or material. The return echoes from these pulses are analyzed in terms of time-of-flight and frequency content to extract physical property measurements (the acoustic velocity and attenuation coefficient) of the material under test. The AID performs an automated analysis of the return echoes to identify the material, and detect contraband in the form of submerged packages and concealed compartments in liquid filled containers and solid-form commodities. An inspector can quickly interrogate outwardly innocuous commodity items such as shipping barrels, tanker trucks, and metal ingots. The AID can interrogate container sizes ranging from approximately 6 inches in diameter to over 96 inches in diameter and allows the inspector to sort liquid and material types into groups of like and unlike; a powerful method for discovering corrupted materials or miss-marked containers co-mingled in large shipments. This manuscript describes the functionality, capabilities and measurement methodology of the technology as it relates to homeland security applications.
KEYWORDS: Inspection, Ultrasonics, Transducers, Scanners, Ultrasonography, Calibration, Signal to noise ratio, Corrosion, Backscatter, Signal detection
A laboratory system was developed that utilized an ultrasonic pulse-echo technique to detect very small cracks emanating from the thread root of a tensile-stressed fastener. Primary benefits were (1) the ability to inspect the fastener without its removal from the structure, (2) much improved detection sensitivity to small cracks, and (3) easy interpretation of data. The fastener of interest had threads with nominal inner and outer diameters of 1.8 cm (0.73 in.) and 2.2 cm (0.86 in.), respectively, and a thread pitch of 3.1 threads per centimeter (8.0 threads per in.). A plastic washer was placed over the fastener nut to shield the nut from ultrasound and thereby eliminate spurious signals. B-scan images provided feedback to align the ultrasonic scanner and fastener for optimal detection sensitivity. A tone-burst pulser-receiver controlled excitation frequency and bandwidth to maintain focal properties, minimize backscatter noise from the base material, and increase penetration into the coarse-grained Inconel. A custom ultrasonic transducer was used to optimize the focal properties over the inspection zone of 2.3 cm to 3.3 cm (0.9 in. to 1.3 in.) from the threaded end of the fastener. A calibration part with four 1.0-mm (0.040-in.) deep notches spanning the length of the inspection zone was used to calibrate distance-amplitude correction and system sensitivity. Custom B-scan and C-scan views were used to present data to the inspector and optimize the signal-to-noise ratio. A direct comparison was made between ultrasonic and destructive test images. Details of system hardware, data- acquisition procedure, analysis, and plans for a portable hand-held system for field inspection are provided.
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