A simple method for generating the monopole ultrasonic pulse and its sound field

Abstract

Abslrad -The cycloid function voltage having no resonant component is applied to the piezo-ceramic planar and concave circular transducers to generate the monopole ultrasonic pulse. On-axis pressure characteristics of two kinds of transducer are observed using monopole ultrasonic pulse. As the experimental results, 1) the sound field of monopole ultrasonic pulse is consisted of direct wave and edge wave, and these are separated in time near the transducer, 2) the monopole ultrasonic pulse from a planar transducer becomes bipolar pulse in the large distance from the transducer and 3) in case of the concave transducer, the monopole ultrasonic pulse is gradually changed to the bipolar pulse around the focus, are clearly observed. These experimental results can be explained by the interference between direct wave and edge wave using monopole ultrasonic pulse. A possibilities of the diffraction effect which dominated at the focus of wncave transducer is also suggested. lotductionThe sound field of transient radiation from a piston source has been studied theoraically using impulse response method". Recently, we have developed a simple method for and experimentally using optical" and acoustic generating the monopole ultrasonic pulse radiated from a plane circular piston transducer". Our method have the advantages which are simple and low cost technique for generating the monopole ultrasonic pulse using a conventional piezoelectric transducer without backing, matching layer or any complex electrical circuits. Monopole ultrasonic pulse is needed not only in the field such as imaging or nondestructive inspection of materials hut also in the observation of transient acoustic field". In this paper, onaxis pressure characteristics of monopole ultrasonic pulse radiated from a planar and concave transducer are investigated, The method and system are briefly explained and the experimental results will be demonstrated to clarify the usefulness of monopole ultrasonic pulse in the analysis of field components. *eolyll" 0-7803-4153-8/97/$10.00 0 1997 IEEE System and method planar or concave transducer immersed in the water tank was Fig.1 shows the experimental arrangement. The PZT excited by a cycloid function voltage v,(t) having a finite raise time I as indicated in Fig.2(a). E x -i I Ilt 2 I r Yr (n)Wavebnn ofcyebd h h n @)frsguercy specmm of u r f cycbd 6 r r h Fig2 Cycbid function (a) and its frequency specbum@).Exciting voltage v,(r) can be expressed as,