h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hello there!

Just a quick note about the above (which I left on your sub-ed's space as the credits got mixed up, how annoying!). I got stuck into reading the entries on radar and was pretty fascinated by them - great writing.

There were a few things which struck me as being not quite true in your automotive radar section, and as I used to work in that area (well, the parking aid bit of it particularly) I wondered if you wanted any more info?

If you do, just drop me a line. If your info was from a better source then I'll happily shut up!

Cheers,

Rains

Well, there was a wee bit of guesswork and interpretation involved there Apparently none of the manufacturers want to spill their beans. Most of them wouldn't even specify which type of antenna they are going to use.

Sometimes it appeared that someone has published their dreams rather than their plans. For example, one of them reported (or rather, proposed) a system utilising two radars,
- one system operating at 27MHz for side/all round coverage
- the second at 77GHz for cruise control etc.

Anyway, if you know better then please feel free to fire away and point out the flaws! Y'know, the original Guide was well known for its wild inaccuracies

No worries - this sort of thing tends to be very secretive even amongst manufacturers. And as I work for one I can't give too much away :o)

However....

Ultrasonic parking aids (the ugly little circles in the bumper) operate at about 38kHz and have a maximum range of about 2 metres. They're also being used for parking slot detection, which tells you if the gap you've gone past is long enough for your car.

There is a radar parking aid system, which utilises a 27MHz (or about that range) sensor behind the bumper. Some systems are purely this type, with two sensors to get full bumper coverage, or a hybrid system which uses one 27MHz and two 38kHz sensors at the corners. The 27MHz sensors give about 5 metres of coverage.

These as well as the ultrasonic ones are beginning to be used for pre-crash sensing, like you say. Radar sensors do have some issues with bumper contruction and paint, though.

The 77GHz ones are longer range (typically 100m or so, if not longer) and used primarily for adaptive cruise control.

I think that's about it, however I only really worked on the ultrasonics bit of it! This is an area which is actually moving quite fast and I don't doubt that I've missed things out. But then I'm probably not supposed to say anything anyway!

Besides, inaccuracies leave something for people to argue about :o)

Thanks for that!

As to ultrasonics - I've got a hobby project at 40kHz and I'm aiming at a max range of 8 metres against objects the size of a post card. Well I have to add that there's a transmit array of 17 elements

Ta!

17!!!! Impressive! You'll have to let me know how that goes on.

Incidentally, the ISO standard for parking aid detection includes a square 40cm by 40cm, a 10cm diameter pipe (I think), all at a height of 1m off the ground and a distance of 2m from the centreline of the bumper, so if you can detect a postcard I'll be very impressed!