What is the principle of a reverse radar?

[VonSerenity]

The principle of a reverse radar is: radar detectors are installed on the rear bumper or both front and rear bumpers of the car to detect obstacles in the front and rear, helping the driver to see obstacles around the vehicle or the distance to other cars when parking. In addition to facilitating parking, this device can also protect the car body from scratches and improve driving safety. The full name of the reverse radar is reverse anti-collision radar, also known as a parking assist device. It is a safety assist device for car parking or reversing, consisting of ultrasonic sensors, a controller, and a display, among other components. The reverse radar also has certain blind spots, including obstacles that are too low, too thin, or ditches.

[BarrettFitz]

The reverse radar is actually quite amazing—those small round dots at the rear of the car are its eyes. When you shift into reverse, the radar emits ultrasonic waves that go 'whoosh' and bounce back if they hit an obstacle. The computer calculates the time difference like a stopwatch, knowing sound travels at 340 meters per second, and instantly figures out the distance. When the obstacle is far, it beeps slowly—'beep... beep... beep'—but as you get closer, the beeps turn into rapid 'beepbeepbeepbeep,' and within half a meter, it blares a continuous alarm. I often remind friends not to rely solely on it, as thin poles or slopes can be missed. It's best to use it alongside the rearview mirror. This gadget reacts 0.3 seconds faster than human eyes, especially useful in rain or fog, but remember to clean the sensors regularly—mud splatters can trigger false alarms.

[SanLucas]

I've studied this principle, which is essentially a bionic design. The reversing radar works like a bat's echolocation, with rear sensors emitting 40kHz ultrasonic waves—inaudible to human ears but highly penetrating. After the receiver captures the reflected waves, the chip calculates the distance using the formula: distance = speed of sound × time difference ÷ 2. Different distances trigger a three-level alarm system: intermittent beeps start at 1.5 meters, turn rapid at 0.5 meters, and become continuous at 0.3 meters. Interestingly, the system features a filtering function to eliminate noise like rain sounds. The latest models even support virtual image displays, far more advanced than the simple beeping metal boxes from twenty years ago.

[OBrayden]

It's essentially the principle of ultrasonic ranging. When reversing, the radar emits dozens of ultrasonic pulses per second, which bounce back upon hitting objects. The built-in computer calculates the distance by multiplying the time between emission and reception by the speed of sound and then dividing by two. Typically, four to eight sensors scan blind spots, with the chip fusing the data. The system is quite intelligent, capable of distinguishing between walls and bushes—hard objects produce strong, continuous echoes, while soft objects trigger weaker alerts. However, note that if the sensors are positioned lower than the bumper, they might miss detecting curbs. It's recommended to keep the reversing speed below 8 km/h to allow the system sufficient reaction time.