The full name of the reversing radar is "reversing collision avoidance radar", also called "parking assistance device", which is a safety assistance device when a car is parking or reversing. Multi-layer PCB learned that it is composed of ultrasonic sensor (commonly known as probe), controller and display (or buzzer) etc.

      The invention can inform the driver of the surrounding obstacles by voice or more visual display, relieves the troubles caused by front, back, left and right visits when the driver parks, backs up and starts the vehicle, helps the driver to eliminate the defects of blind angle and blurred vision, and improves the driving safety. PCB factory found that ultrasonic wave (refer to mechanical wave with frequency over 20kHz) is a special kind of sound wave with basic physical characteristics such as sound wave refraction, reflection and interference. The ultrasonic ranging sensor sends out ultrasonic waves through the ultrasonic emitting device, and the distance length is measured by the time difference between the time when the ultrasonic waves are received and transmitted through the receiver.

      The ultrasonic transmitter emits an ultrasonic signal to a certain direction outside, and starts timing at the same time of emitting the ultrasonic wave. The ultrasonic wave propagates through the air, and when encountering obstacles during propagation, the ultrasonic transmitter will immediately retroreflect and propagate back, and the ultrasonic receiver will immediately stop timing when receiving the reflected wave. The propagation speed of ultrasonic wave in air is 340 m/s, and the timer can measure the distance length (s) from the emitting point to the obstacle by recording the time t, i.e., s = 340 t/2.

      The energy consumption of ultrasonic wave is relatively slow, the propagation distance in the medium is relatively long, the penetrability is strong, the ranging method is simple, and the cost is low. However, it has certain limitations in measuring distance at very high speed. This is because the transmission speed of ultrasonic wave is easily affected by weather conditions.

      Under different weather conditions, the transmission speed of ultrasonic wave is different and the transmission speed is relatively slow. When the car is running at high speed, the use of ultrasonic distance measurement cannot keep up with the real-time change of the car distance and has large error. 

      The PCB factory found that, on the other hand, the ultrasonic scattering angle is large and the directivity is poor. When measuring long-distance targets, their echo signals will be relatively weak, affecting the measurement accuracy. However, ultrasonic ranging sensors have great advantages in short-range measurement.