水中音響標準としての超ジュラルミン球放射圧法

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This article concerns a new ultrasonic intensity standard in water, which makes use of the acoustic radiation force on a super duralumin sphere and covers the range of frequency from about 0. 2 to l0 MHz. The radiation force on a sphere of radius a placed freely in a plane progressive sound field is expressed by Eq. (2), where E is the mean energy density in the field and Y_p the radiation force function of the sphere. In the radiation force method of acoustic-intensity measurement, the mean energy density or the local intensity is determined by the measured radiation force and the calculated radiation force function. Y_p was computed from the authors' thory (1969) for a sphere of super duralumin (of physical constants listed in Table 1) as a function of ka, as shown in Fig. 2, k being the wave number in water. Experiments were made on various super duralumin spheres of 3, 4 and 5 mm in diameter suspended by a bifilar arrangement at 470-2250 kHz in an unechoic water tank of 50×80×60 cm^3 in volume. It was proved that in case of small values of ka, the absolute magnitude of acoustic-intensity for the super duralumin sphere was just the same as that for a stainless steel sphere so far used (Fig. 4). and in the range of ka over about 10, the experimental ka-dependence of Y_p agreed almost well with the theoretical one, but with minute discrepancy attributed to the errors in the values of the longitudinal and transversal wave velocities the spheres(Fig. 5-8). As is expected from consideration on the physical constants, super duralumin is one the metals that show the most flat Y_p-Ka curve (except beryllium, which hardly grinds into a ball), and is thus superior to stainless steel as the target metal in the radiation force method. The former gives a more accurate value of intensity than the latter especially in the range of large ka.
社団法人日本音響学会の論文
1974-08-01

水中音響標準としての超ジュラルミン球放射圧法

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