超声波发射器向某一方向发射超声波，在发射时刻的同时开始计时，超声波在空气中传播，途中碰到障碍物就立即返回来，超声波接收器收到反射波就立即停止计时。-Ultrasonic transmitter emitting an ultrasonic wave in one direction, at the same time start the launch timing, ultrasonic propagation in the air, on the way encounter obstacles