### ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

## 1pPA10. Numerical study on particle velocity and sound pressure by circular
flat transducers.

**Tohru Imamura
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*Natl. Res. Lab. of Metrol., 1-1-4, Umezono, Tsukuba, Ibaraki 305, Japan
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During years of investigation on the ultrasonic near field, only the sound
pressure, namely, the spatial distribution of velocity potential, has been
studied. In this report, particle velocity and acoustic impedance density of the
ultrasonic field by circular flat transducers are derived and computed together
with sound pressure. Sound pressure is proportional to the velocity potential of
the ultrasonic field. Its particle velocity is the space differential of the
velocity potential, and the acoustic impedance density is the quotient of the
sound pressure by the particle velocity. On the axis of the transmitting
circular flat transducer, the phase delay of the sound pressure has peculiar
leaps. But, acoustic impedance density has constant leaps from -(pi)/2 to
(pi)/2, where the amplitude is zero. The mean value over a receiving coaxial
circular flat transducer is also computed changing the ratio of the radius (a)
of the circular flat transducer to the wavelength ((lambda)) of the ultrasonic
wave. Mean amplitudes of sound pressure, particle velocity, and acoustic
impedance density are tabulated with the normalized distance (z(lambda)/a[sup
2]) in the computing precision of 0.1%. The mean amplitude of the z component of
the particle velocity is always less than 1.0 and seems to be an appropriate
response for the ultrasonic system of a pair of circular flat transducers.