From: saekung <[email protected]>On 03/03/2016 21:50, jim bell wrote:> >From:
"[email protected]" <[email protected]>>Here's another one, http://www.nauto.com, which
I mention as the
>> recording of license plates and everything else in the surround,
> Nearly 20 years ago, I first heard of "3M Louvered film", thin plastic sheets
> with opaque black plastic molded perpendicularly to the plane of the sheet.
> It would be very useful to help block the viewing of license plates from the
> side of the road, or above on poles or overpasses. Google-search '3M
> louvered film". http://www.apioptics.com/pdf/3M-Display-Film-Summary.pdf
> http://www.freepatentsonline.com/3919559.html
> http://www.freepatentsonline.com/EP0466460A2.html Two sheets installed
> perpendicularly to each other would render a license plate readable only from
> a limited viewing cone behind, or in front of, the car. Jim Bell
>I would think that is illegal in most countries.
A policeman might, and presumably has, argued that. But go to your typical
car-parts store (in America), and you will see plenty of license-plate covers
which shield the plate from dirt and dust. That doesn't mean that it is
definitely 'legal', merely that most of the time, cops tend to look the other
way if they can easily see the plate itself.
One actually claims that it prevents photographing the plate:
http://www.ontrackcorp.com/original-protector.cfm?id=03
25 years ago, I did some research into making a car 'infrared stealthy'. The
technology of (cheap) laser radar was just coming into play. I learned that
such laser speedgun units used 905 nanometers IR, pulsed at about 25
nanoseconds. I concluded that covering a car's corner-cube plastic
retroreflectors with an IR-absorptive glass (PPG's Azurlite absorbed all but 6%
of 905 nm IR). Azurlite could also be used to cover a license plate, although
it had a distinctive bluish color. Etching the inside surface of the glass
with ammonium bifluoride etchant (art stores) greatly decreased the
retroreflectance from the plate itself.I found an LED, Stanley DN305, (since
discontinued)which had a rise/fall time of about 10 nanoseconds. It would have
made an excellent jammer. Presumably, better ones exist today.
Jim Bell
