1958 年 14 巻 1 号 p. 36-48
An approximate theoretical calculation is performed in obtaining the ultrasonic field near the circular plane source, vibrating with uniform normal velocity. As shown by Schoch, the Reyleigh surface integral giving the field reduces to a line integral when the coordinates are suitably chosen. By employing a simple approximation in calculating the above integral, it is shown that the pressure amplitude at the observed point is given as the sum of two terms, besides the constant term. Each of them, varying simply with the observed position, consists of the product of the so-called 'phase factor' and the 'amplitude factor'. Both factors given above can be easily obtained by a simple numerical calculation and the distribution figures of the values of them are shown for the near filed. The results obtained are in reasonable agreement with the author's experimental data for a 6. 9 mc quartz crystal described in his previous paper.