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

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

Whoa there, speederpunks!

I've let a couple of these messages go past me without comment, but I
think I'd like to throw in a couple cents on this one.

1) I'd like to assure y'all, as someone who has had a run in with a
   couple bad alternators, that loosing electrical power will not 
   cause you to go careening off the side of the road.

   Granted, you might be a in fix if your a nine year old kid running
   from the cops in a '64 volvo, or some other arian super-car, and the
   power steering went out. But if that were to ever happen, it would be
   because you ran over a few curbs at ludicrus speed -- not because
   Johnny Flatfoot hosed ya down with an EM cannon.

2) Someone was curious why they don't just throw some high voltage
   cables across road and wait for the fire works. Well, this is a
   no-brainer too. In order for that to work, you sorta have to get me
   to do two things 1) drive down your street and 2) drive over your
   wires. Assuming that I have a reson for not being caught, I might
   not be too cooperative at doing that either. And of course the last
   consideration is that the guy putting down the wires might not get
   out of the way fast enough -- y'all come down to texas and ask the
   armadillo's why thats a problem.

3) It is really pointless to bicker about this. To quote from a not so
   popular Mark Hamel flick, "Radio, kid. Faster then rubber." Use the
   force, luke.

4) I would think that y'all would be happy that someone is doing all
   the tough work of constructing these devices. I think we all know
   that the first space cadet to haul one of these things into Kabrini
   Park is gonna loose it. From there its just a matter of time until
   every speed racer has one of these "inventions" mounted on his car
   and junior is wanting to order one from the 'Amazing Devices' ad in
   the back of Popular Science (in fact, I think you already can).

   From there, I think that a practical and portable EM cannon could
   become the HOT urban warfare weapon of the next decade. Bonnie and
   Clyde are going to look like amateurs when any rank and file with a
   mortage can buzz the bank and take them off-line for a day. Not to
   mention what you could do to a hospital, police station, air plane,
   traffic signal, grocery store, U-FO, and anything else that uses 1s 
   and 0s. All safely and anonymously I might add -- a concealed EM 
   cannon isn't gonna draw any attention, even when you fire it.

Thats my two cents,
Bye y'all.

Christopher