3B-5 Development of an Ultrasonic Array Technique for LSAW Measurement

Abstract

An ultrasonic method of leaky surface acoustic waves measurement employing focused transducer and linear array mounted in a pitch-catch arrangement is considered. We present the wave theory of the system and demonstrate that the spatiotemporal spectrum of the output data set can be expressed as a product of the reflectance function of the liquid-specimen interface and overall transfer function of the system. By processing data in the spectral domain, it is possible to obtain parameters of dispersive waves. Using the wave model, it was shown that the angular resolution of the system increases with increasing of the number of the elements of the array and depends on the tilt angle of the array. Also, the problem of spatiotemporal spectrum aliasing was considered, and the maximal value of the pitch of the array was estimated at a given tilt angle of the array and directivity of the transmitting and receiving transducers. The results of the theoretical consideration were confirmed by the test experiments carried out in the 20 MHz frequency range Keywords-array; leaky surface wave; angular resolution spectrum aliasing. I. INTRODUCTIONRecently, various immersion ultrasonic material characterization (UMC) systems based on mechanical scanning of focused transducers has been developed for measurement of parameters of leaky surface acoustic waves (LSAW). The experimental arrangements with longitudinal movement of the transducer (the V(z) scheme) [1] and lateral translation of the receiving transducer (the V(x) scheme) [2] are typical UMC systems. The disadvantages of these methods are obvious: the mechanical scanning of the transducer is associated with slow data acquisition, and precision mechanics is required. A new UMC system based on recording of the LSAW field distribution with a motionless ultrasonic array has been developed for measurement of the velocity and attenuation of a separate, non-dispersive leaky wave [3]. In this system, the mechanical scanning of the transducers is not used any more, and the measurement time is only limited by the time of the wave propagation and speed of the electronic data acquisition system. Based on the ray model, it was previously shown that the velocity and attenuation factor of the non-dispersive wave can be obtained by processing the output waveforms of the array. In this work, we present the wave theory of the method, develop the inversion algorithm for the general case, analyze the angular resolution, and consider the problem of spatiotemporal spectrum aliasing.

Detection of plate components defects by surface wave based on transducer arrays

“…Multi-channel detection software has been built to measure the amplitude or phase-angle changes. Amplitude response is proportional to defect size in the plate [5,6].…”