| 摘要 |
PROBLEM TO BE SOLVED: To increase the security of the generation of subharmonic echo by transmitting ultrasonic waves in which waves having an instantaneous acoustic pressure at which a microballoon is destructed exist, respectively, in the front and rear of at least one wave having an instantaneous acoustic pressure at which a microballoon is not destructed. SOLUTION: An acoustic pressure wave form is composed of a plurality of continuous waves, and wave height values of a wave in the second cycle and a wave in the fourth cycle exceed a destruction limit of a shell of a microballoon. The shell of the microballoon is destructed when an acoustic wave form exceeds the destruction limit due to the irradiation of ultrasonic beams. The shell of a microballon is destructed sequentially by two waves across one cycle so that the acoustic emission generated due to the destruction has a frequency of 1/2 of a basic frequency of an ultrasonic wave to be sent, for example, as shown in Fig. (b). That is, an echo having a frequency of 1/2 of the basic frequency of the ultrasonic wave to be transmitted, namely, a subharmonic echo, is generated.
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