求翻译：目前汽车防撞有微波.激光和超声波等多种方法。超声波的发射和接收是自然界中的普遍现象。频率高于20KHZ的超声波不仅波长短、方向性好、能够呈射线定向传播，而且碰到界面就会有显著反射。这些特性有利于选用超声波做媒体，测定物体的位置、距离甚至形状等。超声波传感器的特性:1在自身特性谐振点40KHZ附近可获得较高的灵敏度；2谐振带宽、波束角可以通过制作工艺控制得很窄，有利于抗声波干扰设计；3不受无线电频谱资源限制，易于抗电磁干扰设计。另外，超声系统成本低、性能稳定可靠，应用前景好。因此,采用的设计的方法为：超声波汽车防撞报警系统。是什么意思？

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At present the automobile anti-collision has the microwave. Laser and ultrasonic wave and so on many kinds of methods.The ultrasonic wave launch and the receive are in the nature universal phenomena.Not only the frequency is higher than 20KHZ well the ultrasonic wave the wave length, the directivity

Current automotive collision microwave. laser and ultrasound and other methods. Ultrasonic transmitting and receiving is a common phenomenon in the natural world. Frequencies higher than 20KHZ of ultrasonic wave length, direction, and not only to rays beaming and touch interface would be a significa

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