At 04:54 PM 5/8/2001 -0500, Jim Choate wrote:
>On Tue, 8 May 2001, Sandy Sandfort wrote:
>
> > I thought up a similar but stealthier version some time back. The corner
> > cuts would be on bars that rotate about a horizontal axis. The whole
> > assembly would be inside a visual opaque (but radar transparent)
> cylinder on
> > the front bumper of the car. It could be made to look like a water
> > container or heavy-duty bumper or whatever. Either the receding or
> > advancing portion of the bar's rotation could be behind a radar opaque
> > barrier (depending on whether you'd like to subtract or
> > add--ridiculously--to your true speed).
>
>And worthless as long as that big flat radiator is sitting there. The
>total area of the 'reflector' by a 1/r^4 (it's a reflected wave so it goes
>down 1/r^4) needs to be about the same as the front area of the car.
The radiator is not flat, at least in most of today's cars. Also, an
increasing amount of plastic means the exterior is lower in reflectivity
and the complex shapes of the metal under the hood are increasingly
important. In general, only the corners and edges of the body and engine
parts (a relatively small surface) contribute much to the radar return.
The reflector, on the other hand, though smaller has very high equivalent
reflectivity. The situation is similar to small yachts, mostly fiberglass,
which often fly corner-cube reflectors so they can be seen by the radars of
larger passing vessels.
steve
