The reverse parking radar, also known as the reversing collision avoidance radar or parking assistance device, is like an invisible ruler that measures the distance to the obstacles behind the vehicle and safeguards the safety of both the vehicle and pedestrians. The reverse parking radar was invented in the 1970s and was first used in the military field. In 1982, Toyota equipped the new Corona model with a rear reverse parking radar. The radar installed at the rear of the vehicle uses lights and beeping sounds to prompt the driver about the distance to the objects behind. The emergence of the reverse parking radar effectively solved the problem of the blind spot in the driver's vision when reversing the car. And this important milestone marked the entry of the reverse parking radar into the civilian automotive field.
How does the reverse parking radar measure the distance?
The ultrasonic sensor, controller, display, and other components work together to form a complete reverse parking radar system:
Corresponding to the above three components, the working process of the reverse parking radar is mainly divided into three steps:
Ultrasonic emission and reception: The controller controls the ultrasonic sensor to emit ultrasonic waves and simultaneously receives the reflected wave signals.
Signal processing: Calculate the time difference between the emission and return of the ultrasonic waves. According to the known speed of sound (340 m/s), calculate the distance.
Display and alarm: Intuitively feedback the distance and direction of the obstacles to the driver through the display.
What does the ultrasonic wave emitted by the reverse parking radar look like?
Ultrasonic waves are invisible, intangible, and even inaudible to the human ear. So, how can we visually display the ultrasonic signals of the reverse parking radar? Obviously, this is not a problem for a professional acoustic measurement company like Aoyinbei. Our company's engineers used a Q041H-T-2 data acquisition instrument that supports a sampling rate of 192kHz, and paired it with an MNP4120 microphone with a frequency range of 4-100kHz to build a simple and portable ultrasonic measurement system. And we selected two vehicle models, a certain brand of SUV (left picture) and a sedan (right picture), for actual testing.
A long-time collection of 2 seconds was carried out on the reverse parking radars of the two vehicle models. By comparing the time-domain data, it can be found that the ultrasonic ranging signal is a fast transient strong signal. The emission frequency of the ultrasonic signal of the SUV is 12 times in 2 seconds, while that of the sedan is 18 times in 2 seconds. The data of both vehicle models contain approximately 23Hz of low-frequency noise from the car engine and exhaust pipe.
It can be seen from the time-frequency diagrams of the two vehicle models that the main frequency of the ultrasonic ranging signal is approximately 51kHz, and the energy is relatively strong.
By randomly extracting a set of ultrasonic ranging signals from the two vehicle models for observation, it can be found that the originally mysterious ultrasonic ranging signal is actually an ultrasonic wave with 16 cycles and a frequency of approximately 51kHz. When comparing the signals of the two vehicle models, there is no obvious difference.
Our company, based on the convenient and professional measurement system, has uncovered the secrets of the reverse parking radar. We have visualized the intangible ultrasonic signals, enabling us to have an intuitive understanding of them and providing a data foundation for the research of reverse parking radars. In the future, our company will continuously optimize the measurement system, delve deeper into the field of acoustics, provide accurate data support for the development of more related technologies, and drive the continuous progress of the industry.
