Detection of Aircraft Component Defects Using Low Voltage Excitation of Ultrasonic Transducers

Large areas of composite primary structure are now to be found both on civil and military aircraft throughout the world and the inspection of these structures contributes significantly to overall operating costs. Therefore methods to reduce the inspection time, whilst maintaining an acceptable minimum defect detection capability, are required in order to optimize the potential cost saving benefits offered by using that carbon fiber composite material.</p

Frame synchronisation methods for digital satellite systems

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Exploratory study of a non-invasive method based on acoustic emission for assessing the dynamic integrity of knee joints

The paper presents the development of a new measurement system based on acoustic emission (AE) for assessing the dynamic integrity of knee joints, and the evaluation of its efficacy, through an exploratory study using healthy and osteoarthritic knees. For the former, the paper describes the system implemented to acquire joint angle-based AE and the protocol developed to obtain repeatable results. For the latter, the paper reports significant differences between healthy and osteoarthritic knees using statistical analysis of AE occurrence and distribution of AE features in different movement phases. Osteoarthritic knees are found to produce 6–10 times more acoustic emissions than healthy knees, with amplitudes which can be 20 dB higher, and durations which can be 10 times longer. These findings lead to a visual representation method of AE feature profiles based on multidimensional density of AE hits per repeated movement and the use of principal component analysis for objective assessment of the clinical status of knee joints

Analysis of high frequency acoustic emission signals as a new approach for assessing knee osteoarthritis

Acoustic signal analysis offers a potential scientific basis for new, convenient, non-invasive tools to monitor the dynamic integrity of joints. The rationale is that smooth, optimally lubricated surfaces slide quietly against each other whereas rough, suboptimally lubricated surfaces move unevenly, producing acoustic signals. To investigate this, we used wide-band piezoelectric transducers to detect sound waves with frequencies up to 400 kHz (a well-established technique for evaluating the integrity of engineering structures1) emitted during knee movement. The Joint Acoustic Analysis System (JAAS) comprises a laptop controlling a data acquisition system connected to two acoustic emission (AE) sensors and an electrogoniometer. While each AE sensor is fastened inferior to the patella of each knee and anterior to the