| 摘要 |
A high frequency continuous wave capable of achieving sufficient lateral resolution is produced by a wave transmitting device (20) to constitute a transmitted ultrasonic wave. A frequency of the continuous wave is alternated in a rectangular wave manner by a frequency modulator (15) so as to be frequency-modulated. An alternating time period of the frequency modulation is set to such time two times longer than such delay time which is defined from a time instant when a signal voltage is applied to a piezoelectric transducer element (1) up to another time instant when an ultrasonic wave originated from the piezoelectric transducer is reflected from a focal point 5 and then is reached to the piezoelectric transducer element. In a delay circuit (35), a delay equal to the delay time is applied to the transmitted ultrasonic wave so as to be used as a reference signal. A mixture signal produced by mixing the transmitted ultrasonic wave with the received ultrasonic wave is lock-in-detected (55), so that a reflection signal reflected from the checking object is selectively detected. As a result of increasing a total wave number of transmitted/received waves per unit time, since the continuous wave ultrasonic wave is irradiated onto the checking subject, for instance, in the case that living body tissue is imaged with high resolution at a cell level, S/N is improved.
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