Re: Police prepare stunning end for high-speed car chases

[jim bell <jimbell@pacifier.com>]

At 02:15 PM 8/12/96 -0700, Timothy C. May wrote:
>At 4:43 AM 8/13/96, jim bell wrote:
>>At 09:54 AM 8/12/96 -0700, Timothy C. May wrote:
>>
>>>
>>>(And I'm not ignorant of such technologies, having attended several of the
>>>Nuclear and Space Radiation Effects Conferences. I also played around with
>
>>Why would you need an "EM Cannon" for this?  Just string a 1-car-sized loop
>>of wire on the surface of a road, and off in the bushes hide a battery,
>>DC-to-Hi voltage DC converter and 20kv+ capacitor, and a vacuum switch or
>>some other switch arrangement.  When the car in question traverses the loop,
>>short the switch and the car will be blasted with 20,000 volt-turns of
>>induction.  Sure, most of it will pass harmlessly through the car's steel,
>>but even iron has a limited "mu" which means that every electrical device in
>>the car will be subjected to a certain amount of induced EMF, probably
>>enough to at least reset a few microprocessors and possibly even destroy 
them.
>
>Well, we're all operating based on speculation, as to intended modes of
>operation, what the contracts may ask for, what may eventually get
>delivered, etc.
>
>Certainly the described mode, that of a police car _pursuing_ another car,
>suggests a car-launched signal. Rewiring the nation's roads to include
>buried cables in anticipation of a future use would be pretty expensive!

Yes, it would be rather impractical for _that_ particular application.  


>(And if the cops can plan for a suspect/fleeing car to pass a specific
>location, low-tech solutions like laying a row of caltrops across the road
>will do much the same thing as "zapping" (which may not even work.))

The one place where this might be practical is on highways where these units 
can be placed fairly sparsely and still have a 

Even so, I think that non-police applications are more "interesting."



>As to high-voltage zapping, on this I am _extremely_ skeptical, at least as
>Jim's proposal above goes. Modern chips are equipped to deal with
>high-voltage, having electrostatic discharge (ESD) provisions. Voltages a
>lot higher than 20kv.

That's based on a certain source model.  You know, a specific capacitor in 
series resistance to limit the current.  However, if the current was induced 
from a low-impedance circuit, damaging currents might flow even if the EMF 
within a certain shielded loop in the car never exceeded a few tens of volts.

>
>And getting this hv signal in to the interior of the engine compartment,
>and past the various thermal and other shields would be a chore. Certainly
>the rubber tires will provide an _awful_ lot of insulation!

No, Tim, remember that I'm postulating an _inductively_ coupled system.  
Loop on ground, loops in the car, etc.  Magnetic coupling.  Conduction 
through car tires would be irrelevant the the functioning of this system. 
Wouldn't hurt it; wouldn't help it.

(Side note:  BTW, car tires are not non-conductive.  Check it out someday 
with a ohmmeter.)


Jim Bell
jimbell@pacifier.com