Abstract
Nondestructive testing methods are used to inspect and test materials and components for discontinuities or differences in mechanical characteristics. Phased array signal processing techniques have been widely used in different applications, but less research has been conducted on contactless nondestructive testing with passive arrays. This paper presents an application of beamforming techniques analysis using a passive synthetic microphone array to calculate the origin and intensity of sound waves in the ultrasonic frequency range. Acoustic cameras operating in the audible frequency range are well known. In order to conduct measurements in higher frequencies, the arrangement of microphones in an array has to be taken into consideration. This arrangement has a strong influence on the array properties, such as its beam pattern, its dynamics, and its susceptibility to spatial aliasing. Based on simulations, optimized configurations with 16, 32, and 48 microphones and 20 cm diameter were implemented in real experiments to investigate the array resolution and localize ultrasonic sources at 75 kHz signal frequency. The results show that development of an ultrasonic camera to localize ultrasonic sound sources is beneficial.
Highlights
Ultrasonic arrays [1] for nondestructive testing (NDT) are well known in industry to detect defects such as cracks or voids in components, flaws in welded joints, or properties such as thickness variations
Phased array signal processing techniques have been widely used in different applications, but less research has been conducted on contactless nondestructive testing with passive arrays
This paper presents an application of beamforming techniques analysis using a passive synthetic microphone array to calculate the origin and intensity of sound waves in the ultrasonic frequency range
Summary
Ultrasonic arrays [1] for nondestructive testing (NDT) are well known in industry to detect defects such as cracks or voids in components, flaws in welded joints, or properties such as thickness variations. In most of the NDT applications, linear and planar arrays are implemented in which the same elements are active transmitters and passive receivers of ultrasonic signals. Such phased arrays are deployed to create two-dimensional cross-sectional images, and the sensors have to be in contact with the component surface to perform the measurement, or the component has to be immersed in a coupling medium such as water. In the field of air acoustics on the other hand acoustic camera systems are increasingly popular for detection, visualization and analysis of sound sources These systems are based on beamforming, where an array of passive receivers is used to enhance identification of air acoustic emissions by summing the received signals of all microphones with individual delays [2, 3]. It is significant that the array has good performance for the intended beamforming application
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