mmWave Radar vs. Ultrasonic Sensors: A New Parking Solution?

Park assist sensors are integrated into vehicles to help drivers park more accurately by detecting obstacles around them. These sensors provide real-time feedback, often through visual or audible alerts, guiding drivers as they maneuver into parking spaces. The goal is to reduce the likelihood of collisions, even in challenging conditions with multiple moving objects around the vehicle.

Several types of technology are commonly used in park assist systems, each with their strengths and weaknesses. Currently, one of the most prevalent types are ultrasonic sensors, which detect objects at close range but have several performance drawbacks. Radar sensors, as an emerging technology for parking, offer more advanced capabilities, help overcome performance shortcomings of ultrasound sensors, and bring new features and applications.

Ultrasonic technology

Ultrasonic parking sensors work by emitting high-frequency sound waves that are inaudible to the human ear. When these waves hit an object, such as a wall or another vehicle, they bounce back to the sensor. By measuring the time it takes for the sound wave to return, the sensor calculates the object’s distance based on the known speed of sound. If an object is within a critical distance, the system alerts the driver, usually through an audible alarm. Typically, four or six ultrasonic sensors are integrated into the bumper to cover a 180-degree field of view.

Radar technology

Radar sensors emit electromagnetic waves and analyze the reflected signals to detect objects around the vehicle, their distance, horizontal and vertical angle, and speed of movement. mmWave radar technology uses electromagnetic waves in the millimeter wavelength range where 79 GHz is the standard frequency for exterior automotive applications. Once the sensor emits the waves, they travel through the air and reflect off objects in their path, such as other vehicles, walls, or pedestrians.

The sensor receives reflected waves and, based on the time it took them to return, calculates the distance of each detected object from the vehicle. Today’s radar sensors have MIMO (multiple-input, multiple-output) technology with several transmitters and receivers enabling a larger field of view, detecting in one scan all objects, with distances, angles to the sensor and their relative speed.

Sensor range and angle comparison

When comparing range, mmWave radar outperforms ultrasonic sensors in both minimum and maximum detectable distances. mmWave radar sensors can detect objects as close as 5 centimeters from the vehicle, while ultrasonic sensors typically have a minimum detection distance of 10-20 centimeters. The maximum range for ultrasonic sensors is around 8 meters, with some systems reaching up to 20 meters. In contrast, radar sensors can detect objects up to 60 meters away for a person and up to 100 meters for a vehicle, with 180° degree field of view

The field of view (FoV) describes how wide the view of a sensor is and is mostly measured in angle degrees. Radar parking sensors typically have a 120° horizontal FoV, but the new generation of mmWave radar sensors can have a horizontal FoV of 180°, covering the full area behind the vehicle. 

Four ultrasonic park assist sensors

One 180° radar parking sensor

Using one sensor to cover an entire side of a vehicle results in an affordable system cost.

Ultrasonic sensors have a narrower field of view (typically 60°, up to 75°) and are designed to focus on detecting objects directly in front of or behind the vehicle. To provide full 180° coverage, ultrasonic parking systems require multiple sensors strategically placed next to each other at specific distances. Additionally, they need comprehensive sensor harnessing and an additional signal processing unit, which further increases the cost of a 180° ultrasonic sensor system.

Typical ultrasonic sensor FoV

mmWave NOVELIC radar with 180° FoV and a state-of-the-art radar with 120° FoV

Low-height object detection

Ultrasonic sensors struggle to detect objects less than 50 centimeters above the ground, making it difficult to spot low obstacles such as curbs. This limitation poses safety risks, as small children or pets behind the vehicle may go undetected, potentially leading to tragic outcomes.

In contrast, mmWave radar parking sensors are capable of detecting low-height obstacles and can alert the driver, preventing collisions.

Kick sensor functionality

This feature allows the driver to open the vehicle’s trunk with a simple leg motion, providing hands-free access. mmWave radar parking sensors can provide kick sensor functionality with the same module used for parking, which is more cost-efficient.

Kick sensor enabled by mmWave radar

Tailgate and back door protection

Another functionality that can be achieved with the mmWave radar parking sensor is tailgate and back door protection. The sensor will calculate the critical minimum distance for opening the tailgate or a door and alert the driver if there is a risk of collision in scenarios with low-height garage doors.

Maintenance issues

mmWave radars are more resistant to dirt, and other buildup that typically forms on the bumpers, they require no cleaning or regular maintenance. On the other hand, ultrasonic sensors are sensitive to these, and drivers often report issues like constant beeping alerts after a car wash

Additionally, ultrasonic sensors must be carefully aligned and calibrated, which can be affected by any changes to their mounting or the vehicle’s exterior.

Mounting and aftermarket installation

The complexity and price of aftermarket installation are significant factors for car manufacturers, which may influence the decision to move from ultrasonic to radar technology.

Since ultrasonic sensors are affected by surrounding materials, their installation requires drilling holes in the bumper and repainting it post-installation. Any changes and repairs on the bumper increase the overall installation price of the ultrasonic parking system. There is often no way to discreetly mount ultrasonic sensors without affecting their performance, which can disrupt the vehicle design and aesthetics.

Radar parking sensors don’t require holes in the bumper, making for a more slick design

As long as there are no metal parts nearby, mmWave radar parking sensors can be placed inside the bumper, or above the bumper on the tailgate or back door. This allows for simple, invisible installation that doesn’t change vehicle appearance.

Conclusion

In the debate between mmWave radar and ultrasonic parking sensors, each technology offers distinct technical advantages. In comparison with ultrasonic, radar offers outstanding performance, single hardware installation, small maintenance costs as well as a completely new set of applications that cannot be done with ultrasonic sensors.

If you are interested in learning more about park assist with mmWave technology, NOVELIC offers ASPER, a short-range 79 GHz mmWave radar sensor providing front, rear, and lateral monitoring around the vehicle.