This paper describes an improvement of ultrasonic environment-sensors for autonomous land vehicle (ALV). Scanning ultrasonic sensor has very simple structure, but the sensing time is long and the longitudinal detectable range is very short. Therefore, we shortened the sensing time by using a multi-receiver method instead of the scanning method and expanded the detectable range by increasing the power of emitted sound waves. Since the sound pressure was increased extremely, a large audible click noise was generated at the transient time of burst-wave. We decreased this audible noise by modifying the waveform of the burst wave. In order to simplify the discriminating circuit of Doppler shift, a method to modulate the frequency of emitted sound wave is proposed. Basic experiments were carried out and useful results were obtained.
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