Acoustography is a full-field ultrasonic imaging process where a high resolution 2D acousto-optic sensor based on liquid crystal technology is employed to directly convert the ultrasound into a visual image in near real time. Unprocessed acoustography images typically suffer from non-uniformity due to spatial variations in the optical brightness response of the acousto-optic sensor field to ultrasonic intensity. Additionally, dynamic range of the acousto-optic sensor is limited to approximately 20 to 30 db. The nonuniformity and dynamic range limitation can result in difficulty in acoustography image interpretation, impracticality for large field application, and difficulty for use on samples having a wide range of attenuation. The approach of this ongoing study is to apply various methodologies that address these limitations in hopes of extending the usefulness and applications of acoustoography for nondestructive testing. This article shows initial results of methodologies developed to correct for image non-uniformity and explains the proposed approach to extend the dynamic range of acoustography images.
This paper presents the results of a comparison study of three ultrasonic nondestructive evaluation (NDE) methods applied to polymer matrix composite (PMC) specimens subjected to impact damage. Samples mainly consisted of various thicknesses of graphite/epoxy coupon panels impacted with various energy levels. Traditional pulse-echo and through transmission ultrasonic c-scan techniques were applied to impacted samples and served as the basis for comparison. Specimens were then inspected using acoustography, a large field ultrasonic inspection technique that is analogous to real-time X-ray imaging. Acoustography utilizes a unique, wide area two-dimensional (2-D) detector, called an acousto-optic (AO) sensor, to directly convert ultrasound into visual images; much like an image intensifier in real-time radiography. Finally, a newly developed guided wave scanning system was utilized to inspect the same set of samples. This system uses two transducers in a pitch catch configuration to examine the total (multi-mode) ultrasonic response in its inspection analysis. Several time- and frequency-domain parameters are calculated from the ultrasonic guided wave signal at each scan location to form images. Results are presented for all of the methods demonstrating each technique's detection capabilities and highlighting their advantages and disadvantages.
Many small composite parts undergo manual pulse-echo scan because 1) the set-up time for and automated scan is unjustifiably long and 2) the automated scan does not provide the flexibility to cope with frequent angle changes in a complex geometry part. Manual scans can be time consuming, laborious, and are prone to errors due to operator fatigue and subjectivity. What is required is a full-field ultrasonic inspection system analogous to real time radiography that allows the operator to perform ultrasonic inspection by manipulating the part under a systems field of view. In this paper, we will present an acoustography-based ultrasonic inspection system developed under a SBIR (Small Business Innovation Research) award that is bringing this vision to into reality. Acoustography is the ultrasonic analog of radiography and photography. A unique, wide area 2D detector, called acousto-optic (AO) sensor, is used to directly convert ultrasound into visual images; much like a fluorescent screen is able to convert x-rays into visual images. It offers the potential for providing the NDT engineer with a large field of view (e.g. 6”x 6” or larger) and a capability to inspect complex shaped parts in real time.
The replacement of chemical batteries with composite flywheels offers many potential advantages in space applications. Before such flywheels can be successfully employed, it is imperative to ensure their integrity using NDE techniques. Previously, the use of traditional C-scan for the NDE of flywheels was compared to Scanning Ultrasonic Spectroscopy. However, both C-scan and scanning ultrasonic spectroscopy are point-by-point inspection techniques, and are thus inherently limited in inspection speed. In this paper, the application of Acoustography for the NDE of flywheels is reported. Acoustography provides an efficient and economical alternative to point-by-point ultrasonic scanning; in this approach a novel, wide area (AO) sensor is employed to provide full-field, real time ultrasonic images similar to x-ray imaging, significantly decreasing the required inspection time. Side by side images generated using Acoustography and traditional C-scan techniques for Plexiglas cylinder and a composite ring standard (both with known defects) are presented.
Acoustography is the ultrasonic analog of radiography and photography. A unique 2D detector, called acousto-optic (AO) sensor, is used that is capable of directly converting ultrasound into visual images; much like a fluorescent screen is able to convert x-rays into a visual image. The AO sensor offers exceptionally high resolution and can be fabricated to have a large area. This allows image formation through simple shadow casting (analogous to x-ray image formation) or with acoustic lense (analogous to a photographic or video camera). This paper will report on several new developments, which could allow acoustography to provide a simpler more cost-effective alternative to conventional ultrasonic testing.
Acoustography is a full field, large area ultrasonic imaging method where a novel, wide area acousto-optic (AO) sensor is employed to form ultrasonic images similarly to real-time x-ray imaging. The AO sensor converts ultrasound directly into a visual image due to the inherent acousto-optic property of a proprietary mesophase material contained in the AO sensor. The AO sensor also offers exceptionally high pixel resolution, as a continuous layer of the mesophase material, with sensing molecules on the order of 20 Angstroms in size, senses the ultrasound. This paper will report on progress being made under a SBIR project to develop acoustography as an efficient and economical alternative to conventional point-by-point ultrasonic scanning (e.g. A-scan, C-scan).
Military and commercial aircraft structures are being fielded well beyond their designed life cycle, resulting in escalating maintenance costs. The principle driver behind these costs is the need to nondestructively interrogate large areas to detect and quantify anomalies such as corrosion, cracks, and delaminations. Manual ultrasonic techniques are routinely applied to inspect aircraft structures, but these techniques are time consuming, laborious, and are prone to errors such as operator fatigue and subjectivity. Automated ultrasonic systems require costly, complex scanning systems that are often difficult to adapt to complex shaped structures. Acoustography can provide full-field ultrasonic images in near real-time, making it a suitable method for high-speed, wide area inspection applications. This paper will report on progress being made toward developing acoustography for NDE of aging aircraft structures.
The objective of this study is to provide details on a novel wide area acousto-optic (AO) sensor that can be used to nondestructively evaluate materials and components in near real-time. A description of the technology and how it compares to conventional ultrasonic methods is provided. The results from three experiments provide details on how acoustography compares to conventional ultrasonics when applied to the inspection of composite parts. The first experiment involves performing ultrasonic and acoustography tests on a standard graphite/epoxy composite panel that has embedded inclusions of known sizes. The objective of this experiment is to determine if the capabilities (i.e. resolution) of acoustography are comparable to those of conventional ultrasonic techniques. The second experiment applied acoustography and ultrasonic techniques to evaluate the effects of low impact damage in composite materials. The third experiment involves applying ultrasonics and acoustography to evaluate a complex shaped composite part. The purpose of this experiment is to show the strengths and weaknesses of both techniques as applied to real world problems.
A series of epoxy carbon fiber development panels manufactured as part of a BAE SYSTEMS, Airbus, Composite Wing Development program were evaluated using Acoustography, a new ultrasonic Non Destructive Evaluation (NDE) method being developed by Santec Systems Inc, as an alternative to the conventional point-by-point ultrasonic C-scan. This study provides details on a novel wide area Acousto-optic (AO) sensor that can be used to nondestructively evaluate materials and components in near real-time. A description of the technology and how it compares to conventional ultrasonic methods is provided. The results of 4 experiments are also provided. The first experiment involves performing ultrasonic and Acoustography tests on thick graphite/epoxy composite panels that have embedded inclusions of known sizes. The objective of this experiment is to determine if the capabilities (i.e. resolution) of Acoustography are comparable to those of conventional ultrasonic techniques. The second experiment involves applying ultrasonics and Acoustography to evaluate a 10 mm thick graphite/epoxy composite panel containing defects associated with the manufacturing process. The third and fourth experiments detail the inspection of complex shaped composite parts representative of aerospace applications. Effort has been conducted towards demonstrating the effectiveness of the technology and establishing a baseline for projected inspection times.
Liquid crystals have been investigated for acoustic imaging purposes for more than 20 years, however, their practicality has become apparent only recently through a number of technological developments. This has led to the development of the world's first liquid crystal based acoustic imaging system, which is finding commercial applications. This paper will discuss some of the fundamental technical progress that was needed to make liquid crystal based acoustic imaging a reality. Numerous current and potential uses of the liquid crystal based acoustic imaging approach will be discussed, including nondestructive testing, underwater mine detection, medical imaging, etc.
Acoustography is being developed as an alternative to conventional point-by-point ultrasonic scanning commonly employed for composite inspection. In acoustography, an area detector is used to produce full-field images of the test component in near real time, which makes the method suitable for providing rapid ultrasonic inspection of composites. Although the possibility of using acoustography to inspect composites has recently been demonstrated, a side-by-side comparison of acoustography with conventional ultrasonic scanning has not been made. In this work we will report on studies conducted toward establishing a direct comparison between acoustography and conventional ultrasonic scanning.
Acoustography provides an alternative to the conventional point-by-point ultrasonic scanning approach commonly used for composite inspection. In acoustography, an area detector (sonoplate) is employed for near real-time imaging of composites. In this paper, we report on the application of acoustography for ultrasonic inspection of tight-radii in composite components/specimens, where conventional point-by- point ultrasonic scanning may not be practical and/or cost- effective.
Acoustography provides an alternative to the conventional point-by-point scanning approach employed for ultrasonic inspection of composites. In acoustography, an acousto-optic area detector is employed for direct ultrasonic imaging of composites in near real time. In this work, we will report on the application of this approach for inspecting composites where the point-by-point approach may not be practical and/or cost-effective.
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