Imagine that you’re slowly making your way down a dark highway as your wipers struggle to keep up with the downpour that is assaulting your windshield. As you squint to make out the yellow lines painted on the road, a car traveling next to you suddenly changes into your lane and cuts you off. Before you have time to react and hit the brakes, your car automatically slows down, avoiding a serious accident.
This is a common scenario with newer cars fitted with pre-collision avoidance systems. These active safety systems use Doppler radar to detect objects that come into a vehicle’s path, triggering the brakes before impact. Typically, a radar detector is placed towards the front of a vehicle, such as within the grill. This detector sends out high frequency waves and then interprets the signals that bounce back, which would indicate object location, speed, and the direction it is traveling.
In order for the system to process all of this information and take action in a matter of milliseconds, a delay needs to be introduced. Linear Surface Acoustic Wave (SAW) delay lines are typically used in collision avoidance systems because they are smaller and less expensive than other delay line options. SAW delay lines used in collision avoidance systems operate across public frequency bands, and system designers would typically down mix the radar frequencies in order to process them through one channel with a constant delay.
This gives the system all of the information it needs to determine if a collision is imminent, and allows it to respond by automatically deploying the brakes, tensing seatbelts, or taking other safety precautions rapidly enough to avoid impact.