Abstract
Air-coupled ultrasonic techniques are being increasingly used for material characterization, non-destructive evaluation of composite materials using guided waves as well as for distance measurements. Application of those techniques is mainly limited by the big losses of ultrasonic signals due to attenuation and mismatch of the acoustic impedances of ultrasonic transducers and air. One of the ways to solve this problem is by application of novel more efficient piezoelectric materials like lead magnesium niobate-lead titanate (PMN-PT) type crystals. The objective of this research was the development and investigation of low frequency (<50 kHz) wide band air-coupled ultrasonic transducers and arrays with an improved performance using PMN-32%PT crystals. Results of finite element modelling and experimental investigations of the developed transducers and arrays are presented. For improvement of the performance strip-like matching elements made of low acoustic impedance, materials such as polystyrene foams were applied. It allowed to achieve transduction losses for one single element transducer −11.4 dB, what is better than of commercially available air-coupled ultrasonic transducers. Theoretical and experimental investigations of the acoustic fields radiated by the eight element ultrasonic array demonstrated not only a good performance of the array in a pulse mode, but also very good possibilities to electronically focus and steer the ultrasonic beam in space.
Highlights
Air-coupled ultrasonic techniques are already used for range finding and surface profile measurements [1,2], material characterization, non-destructive evaluation (NDE) [3,4,5,6,7,8,9,10,11] and even for secure wireless transmission of data [12].The frequency range of the air-coupled transducers used depends on a particular application and properties of the materials under investigation and environment
We have shown that this kind of excitation and reception may be achieved using low frequency (
Development of relatively low frequency efficient air-coupled ultrasonic transducers and arrays is important for NDE of composite materials using guided waves, as well as for distance measurement applications
Summary
Air-coupled ultrasonic techniques are already used for range finding and surface profile measurements [1,2], material characterization, non-destructive evaluation (NDE) [3,4,5,6,7,8,9,10,11] and even for secure wireless transmission of data [12]. Development of relatively low frequency efficient air-coupled ultrasonic transducers and arrays is important for NDE of composite materials using guided waves, as well as for distance measurement applications. In order to generate and pick up relatively low-frequency (
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