Arduino Tutorial Ping. https://www.arduino.cc/en/Tutorial/Ping (Available at: 2018.12.12)

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The Principle of Doppler. https://baike.baidu.com/item/多普勒原理/1196721?fr=aladdin (Available at: 2018.12.12)

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Ultrasonic Sensor with Arduino. https://jingyan.baidu.com/album/4f34706e23f740e387b56dc7.html?picindex=6 (Available at: 2018.12.12)

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Distance Sensor and Olde. https://create.arduino.cc/projecthub/javier-munoz-saez/distance-sensor-and-oled-ad9e35 (Available at: 2018.12.12)

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Complete Guide for Ultrasonic Sensor. https://randomnerdtutorials.com/complete-guide-for-ultrasonic-sensor-hc-sr04/ (Available at: 2018.12.12)

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Processing Serial. https://www.processing.org/reference/libraries/serial/(Available at: 2018.12.12)