Police radar and vehicle vibrations?

When speed and red-light cameras were all the rage here in Arizona for about six months some company was selling plastic covers that you could read the plate through if you were directly behind – like a cop following in a car – but reflected the flash back into the camera if it was off-axis.

But did it actually work?
A lot of these types of things are sold and don’t do as advertised.
When LIDAR first came out in the early 90’s companies were selling clear covers that allegedly dispersed the laser beam on the license plate (the most common target) and prevented a reading. Tests showed they didn’t do squat. Companies made money, drivers still got tagged.

I’m waiting for someone to post the virtues of jammers from Rocky Mountain Radar, the biggest scam organization in America.

I was dubious. I saw exactly one when I was walking around and it did do odd things to the plate seen through it as the angle changed.

The key point is that a red light camera (the ones I’ve seen) will fire a photographic flash even in broad daylight (in the somewhat focused direction of he plate, I presume) , to enhance the readability of the plate. Plates are made with reflective material, and the letters are not (or vice versa). Countermeasures can either optically block reading from an angle, or cause the whole plate to reflect equally (blank white result) or like the strobe solution I read about, flood the plate with so much light that it is not exposed properly on the picture.

Also, making your whole plate reflective doesn’t stop hand-held IR units -it may help. The problem with IR plate readers is that they typically rely on the plate reflection, but they can equally pick up any reflections from the rest of the car - plus as “triggered” readers, by the time a detector tells you you are a target, it’s too late - unless it detects a spillover signal from the guy in front of you being targeted. Many of the hand-held radar units are also triggered, so same problem - unless you detect it being used on someone else, by the time you detect and react to it, it’s too late.

Hmmm… which fan speed?

The angular velocity varies linearly from the maximum at the blade tips to zero at dead center. And this velocity is perpendicular to the car’s direction of travel.

So what “fan speed” did the radar read? Unless the radar gun returns results in RPM, I’m highly dubious.

Same principle as those “privacy screens” that prevented reading a computer monitor from an angle, I gather it’s like a tiny (open) venetian blind embedded in plastic. Obviously won’t help against a head-on IR gun looking for a reflection.

I would imagine the radar unit would have to be at quite an angle to pick up the rotating blades. But for head on - If you pick one spot on the fan’s range of rotation, you would get a point that varies from the back of the fan to the front of the fan (then suddenly skips to the back as the next blade comes around to that point). But the return signal is the sum of all points on the fan, plus the rest of the car front profile - the return signal would be essentially a large signal amplitude at the speed of the vehicle, and a fuzzy bit trailing that was the reflection from the fan blades. As I understand, the electronics picks the loudest signal, the peak amplitude, which would be the whole car reflection.