Ultrasonic detectors are already in widespread use. The technology has been used to scour the bottom of lakes for artefacts, to sense unwanted intruders and now to help us park our cars. As well as taking care of the awkward parts of driving, ultrasonic obstacle detection is proving to be an important boon to road safety.
How does it work?
By using ultrasonic acoustic waves of a very high frequency. Humans can hear sound waves between about 20Hz and 20kHz, so ultrasound – sound beyond human hearing – is generally above 20kHz. It works rather like a bat’s echo-location ability, in that these sound waves are emitted, bounced off objects and then picked up again at source. It’s just like radar – the shorter the gap between waves being fired off and picked up again, the closer an object is.
The reason ultrasonic waves are so suited to obstacle detection of the sort employed by car makers is they are highly directable. It’s also noiseless to us, which is just as well since a typical car’s ultrasonic sensor would need to generate sonic pressure of around 100 decibels to ensure crystal clear reception – about the same pressure the ears would be hit with if you stood next to a jet engine.
Ultrasound’s high frequency means that it can be aimed almost like a precise jet of water. This is why the technology has long been in use as a means of breaking down kidney stones within the body – the energy level required is so low, it does no damage to us.
Since ultrasonic waves are caused by the vibration of matter, the sound creates an ‘image’ of the object it bounces off. It’s this detailed information that allows bats to ‘see’ in the pitch black of night, and why obstacle detecting camera systems are so accurate on many cars now.
What does this mean for cars and road safety?
Ultrasonic waves travel at much the same speed through the air as other sound types, typically around 34m/s. Low speed signalling processing – such as that performed by obstacle detection technology – is therefore possible. Parking sensors and collision sensors use sonar, the detection technology used by ships. An acronym for sound navigation and radar, it can very quickly and accurately ascertain the distance and direction of an object – and very often the size and shape of the object itself.
Often taking the form of a small sound-emitting speaker mounted around the rear bumper of a car, an obstacle detector will send out its inaudible sound beam and a connected microphone will pick it up. Some obstacle detectors use combined speaker-receiver devices.
Increasing numbers of new vehicles are equipped with obstacle detectors. More than half of brand new cars in Europe and Asia are equipped with such devices, while the number is on the rise in the USA too. As well as as the obvious safety benefits (blind spot reduction, early warning and so on), obstacle detectors may help to drive down the cost of your car insurance premium.