The Evolution of Automotive Ultrasonic Sensors: From ADAS to Autonomous Driving and Beyond

For vehicles to sense their surroundings, one of the longest established methods is ultrasonic sensing. Initially used for park assist to detect nearby objects while parking, these versatile sensors have evolved into many advanced driver assistance systems (ADAS) applications such as blind spot detection, lane change assistance and navigation – as well as driver and occupant monitoring.

This article will look at how ultrasonic sensors have evolved and discuss the associated applications. Additionally, it looks ahead to the future of ultrasonic technology, exploring onsemi innovations that are likely to shape the next generation of sensing systems for automotive and other industrial applications such as autonomous mobile robots (AMR). Through this comprehensive overview, readers will gain a deeper appreciation for the adaptability and versatility of ultrasonic sensors in the context of evolving safety and automation.

A Brief History of Ultrasonic Sensors

Ultrasonic technology was first developed almost a century ago to detect objects and find flaws in solid materials. The technology was first patented in 1931. As electronic technology evolved, ultrasonic transducers were commonly used in intruder alarms.

In the automotive field, ultrasonic sensors were first used in park assist, detecting obstacles that may not be within the driver’s line of sight. Most commonly they were mounted in the rear bumper, although upscale vehicles often deployed ultrasonics in the front bumper as well.

onsemi released its first ultrasonic park assist sensor in 2007 and has continued to evolve the technology. Two decades and six generations later, the development continues with the seventh-generation device targeting even wider applications. A key part of the evolution has been the advance in onsemi proprietary high voltage technology from 700 nm to 65 nm. This has enhanced performance through an improved signal-to-noise ratio (SNR) and increased detection distance.

As a result of these improvements in technology, ultrasonic sensors are more versatile and can be used in more advanced applications both outside the vehicle (e.g., blind spot detection) and emerging in-cabin applications, such as occupant detection and gesture recognition.

The popularity of ultrasonic sensors is rising rapidly. In 2009, onsemi shipped 3 million (M) devices and doubled the shipment to 6 M units in 2010. Within a decade (2018), they were shipping over 100 M every year. By last year (2023) this had doubled to 200 M units per year, with over a billion devices shipped in total.

Modern Automotive Applications of Ultrasonic Sensors

Almost all vehicles have a “blind spot” where the driver cannot see using their mirrors or by turning their head – this is located to the rear and side of the vehicle. The danger occurs when a driver wants to pull out to overtake without seeing the approaching vehicle. Correctly positioned ultrasonic sensors can monitor this area and provide a visual or audible warning to the driver that it is not safe to pull out, thereby avoiding a collision.

Modern automated parking systems (APS) use the ultrasonic sensors in conjunction with automated steering, acceleration and braking to park the vehicle in an available space without the driver doing anything more than stopping the vehicle close to the space and engaging the auto-park system.

Similarly, a driver is often unsighted when reversing out of a parking space. Here, as the driver edges the vehicle out, cross traffic detection using ultrasonic sensors can identify vehicles and provide a warning. If the warning is ignored, many vehicles now have the capability to apply the brakes automatically.

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Figure 2: Ultrasonics can detect static obstructions for APS 

Recently, ultrasonic sensors have expanded their applications inside the cabin. With occupant detection becoming mandated by legislation and programs such as the Euro NCAP, these sensors are now used to detect passengers, trigger seatbelt warnings, and ensure that airbags are safely deployed according to the size and weight of any occupant(s). Additionally, should an infant be left in an unattended vehicle, a warning can be provided. They can also be used to monitor the driver for alertness, detecting breathing and heartbeat.

With the sophisticated infotainment systems in vehicles, there is often little space for buttons and searching for the right button while driving can be dangerous. Using ultrasonics, drivers can control many vehicle functions with a simple gesture (such as rotating their hand to change volume), thereby improving convenience and safety.

Future Trends and Innovations: From Automotive to Industrial

Ultrasonics are not limited to automotive – in the industrial field they provide short range depth sensing to automatic guided vehicles (AGVs) found in warehouses, and AMRs used in delivery/transportation applications. Similar to the automotive use case, ultrasonic sensors can help AMR and AGVs detect objects in close proximity and navigate their working environments. In factories, ultrasonics are found also on production lines, monitoring and controlling process parameters.

Clearly, ultrasonic technology is advancing, and new applications are emerging. If anything, in the future, the pace of change will accelerate. For example, work is being done to co-locate a MEMS microphone with the ultrasonic sensor. As well as receiving the ultrasonic signal, the MEMS microphone can pick up other sounds – such as that of an approaching vehicle. It would also be able to distinguish the siren of an emergency vehicle, alerting the driver to take appropriate action.

Dirt and rain can cause performance issues with ultrasonic sensors as well as forward-facing cameras. By incorporating a piezoelectric device in the housing, the sensor can be vibrated to remove rain, dirt or even ice ensuring that the safety-critical sensor is operating correctly. In some cases, this may not be needed as future ultrasonic sensors are likely to be fitted behind the bumper rather than protruding through it.

As electrification expands throughout the vehicle fleet, knowing the state of the battery is crucial. Nowadays this is done externally by measuring voltage, current and temperature of the battery. However, by mounting ultrasonic sensors within the battery, they will be able to provide a far more accurate assessment of the state of charge and state of health of the battery in every vehicle.

Conclusion

onsemi has been a market leader in supplying custom ultrasonic sensor interfaces for park assist and autonomous driving applications to major automotive OEMs in the past two decades. The NCV75215 from onsemi offers a single chip solution which simply takes external circuitry and a transducer to complete. With highly sensitive, low-noise operation, detection is possible at distances from 0.15 m to 4.5 m for a standard 75 mm pole. Also available is an ultrasonic parking assist evaluation kit that allows designers to prototype and fully debug designs.

Ultrasonic sensing is an established technology that has become more important in the automotive sector as vehicles adopt more intelligence, safety and automation. With the rapid innovation and the continued push towards higher level of ADAS and automated driving, ultrasonic technology is expected to provide higher sensor performance. As sensor performance improves, new use cases in automotive, industrial, medical and consumer applications are emerging.

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