NDTnet - August 1997, Vol.2 No.08

Ultrasonic beams focusing in piezoelectric crystals and ferroelectric ceramics by application of a nonuniform electric field

Authors: V.N.Belyi, N.S.Kazak V.K.Pavlenko, A.G.Mashchenko and F.M.Severin

Abstract

1 Introduction

2 Electroacoustic lenses made of electrostrictional ferroelectric ceramics

3 Electroacoustic lenses based on piezoelectric crystals

4 Experimental results and discussion

    The spherical lens, shown in Fig. 1, was designed for experimental study. The working medium of the electroacoustic lens was made of ferroelectric ceramics based on solid solution of lead zirconate-niobate (PbZn1/3Nd1/3O3). The lens had geometrical dimensions 22 x 22 x 50 mm at the working aperture of ~ 17mm.

    A beam of longitudinally polarized ultrasonic waves with a frequency of 10 MHz was excited by plate 20 mm in diameter made of barium titanate piezoceramics and injected into the lens through the glass buffer. After passing through the lens, the ultrasonic beam was introduced through the glass buffer into a cell with distilled water.

    In experiments we measured the amplitude distribution of the acoustic field over the beam section at various distances from the output surface of the lens with various values of the control voltage. For example, Fig. 2 give the result of successive measurement of the acoustic field distribution over the beam section at distances 15 cm from the lens with control voltage values 0 (a) and 5kV (b). The spatial coordinates over the beam section are plotted on the axis x,y, and the ultrasound intensity is plotted along the vertical axis. For a given beam section the ultrasound intensity is normalized to the maximum value of the series dimensions obtained at different values of the control voltage. During the process of distribution measurement the acoustic beam power was held constant for the fixed section. It is seen from Fig. 2 that the cross-sectional dimension of the ultrasonic beam and its spatial distribution depend on the bias voltage value.

    Thus, with increasing control voltage the acoustic field power increases in the central part of the beam and there is a decrease in its diameter as to distribution half-height, which is indicative of controlled spherical focusing. For this type of ceramics and geometric dimensions of the electroacoustic lens, the focal length measured at 5kV is F=15 cm, and the beam intensity at the distribution maximum increases by more than three times compared to the zero control voltage.


Figure 2:
The acoustic field distribution over the beam section at distances 15cm from the lens with control voltage values O (a) and 5 kV (b).

5 References


Authors

V.N.Belyi, N.S.Kazak V.K.Pavlenko, A.G.Mashchenko and F.M.Severin
Stepanov Institute of Physics, Academy of Sciences of Belarus,
70, F.Skaryna Prospect, Minsk 220072, Belarus

International Conference "Computer Methods and Inverse Problems in
Nondestructive Testing and Diagnostics", 21-24 November 1995, Minsk, Belarus
Contact for the proceedings: DGZfP Deutsche Gesellschaft für Zerstörungsfreie Prüfung e.V.
Motardstra├če 54 , 13629 Berlin, Germany
Telephone: + 49 (030) 386 29 911, Fax:.. /29 918,
Email: mail@dgzfp.de


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