called “Cowboy Cops Something Something”. This question doesn’t seem to belong there, exactly, but the point of that thread was that high speed chases by the police are dangerous. (At least I think that was the point. It got kind of hard to tell sometimes).
The question is this: is it possible to create a directed electromagnetic pulse strong enough to interfere with the electrical functioning of a car engine? I realize you’re not going to stop the plugs from sparking, but those computers that control the fuel mix must be reasonably sensitive, Yes? I’m no mechanic, nor electrical engineer, but could an EM device render a car, if not immobile, at least incapable of the performance necessary for a HSC?
Perhaps some physicist can enlighten me. Outside of an atomic bomb, what’s the best current technology to produce an EM pulse? Can it be kept local and directed?
Actually, a device for doing just that has been developed. I saw it on Discovery. A small, high speed, radio controlled car is launched from under the front bumper of the police car. It accellerates until it is under the suspect’s car and delivers the pulse via two springs (much like the old curb-feelers). I’m guessing that it hasn’t been proven reliable enough to catch on.
Two SPRINGS? How do you launch an EM pulse via SPRINGS?! I need to learn more physics!
Seriously, though, that’s not what I’m talking about: In that system, something has to come in physical contact with the car to deliver the juice; I don’t think that qualifies as an EM pulse. Since that something is a remote controlled car that has to be run under the fleeing vehicle during a high speed chase, I’m not surprised it hasn’t caught on.
I was thinking of some kind of device that could be aimed and shot. It should be harmless to humans, but muck up electrical systems. A single pulse is the idea, transmitted through space.
I believe the little remote does send out an EMP. It just needs to be close enough that it doesn’t knock out anything else.
Any “gun” fired from a pursuing police cruiser would have to be so strong that the pulse would continue and disrupt non-suspects cars. Sort of like why they don’t always shoot at fleeing suspects; they might hit someone else.
Oh, and the springs are the antennas that emit the pulse. The coil structure probably amplfies the signal because the remote unit can only carry so big of a battery.
So, you’re asking why they don’t just make a gun, capable of firing a focused EMP that would selectively disable the suspect’s car, while leaving the pursuing vehicle (and others on the road) unaffected? Why not just set phasers for stun?
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No, Stephen, I’m not asking why “they don’t just”, I’m asking for intelligent input as to the technical problems here, hopefully from someone who has mastered more electrical engineering than I. It is certainly not crazy to suggest that an EM pulse can be aimed; that’s what a parabolic antenna does. The only question, as I see it, is one of power, and for this application one needs only a single, large pulse. Until you can tell me how one might be produced, or why it can’t, I think your Star Trek reference is out of place.
AWB, yes, I considered that it might affect other cars. But cops sometimes SHOOT at fleeing suspects. Guns. The idea is that they are supposed to aim them, and not shoot when anyone is standing behind the target, of course. Can we not carry over that over? This is why I was careful to emphasize a DIRECTED pulse. In the thread I referenced, the issue was the extreme danger posed to the public by high speed chases. If the greatest objection to the present idea is that it may interfere with the fuel mix in innocent bystanding cars, it’s a very desirable technology.
I do appreciate your responses, but, these are not the sorts of objections I was hoping for. I was more hoping for “you can’t do that because the best current technology produces an EM pulse by … and for a device weight of, say, 500 lbs or less this can only produce power in the range of X watts, and to interfere with a car engine enough to degrade performance you’d need Y watts”.
Or something along those lines.
FYI, Cecil wrote about this (sorta) several years ago. (Actually, it was about burning out a loud car stereo, but he does talk about EMPs.) It’s here: http://www.straightdope.com/classics/a3_294.html
Of course this article is several years old, and it’s hard to say what advances have been made since then.
Well, an EMP gun might stop your modern car in its tracks, but if the evil doers were driving something like a '67 Ford Fairlane, you’d need enough power to melt the car into a puddle. No computerized fuel injection in the old beaters.
I’m also wondering if the metal in the car wouldn’t act as a Faraday cage, shielding the computer from your pulse.
A remote Em gun can and has been made for that specific purpose. I saw a documentary here in Australia about a retired US navy engineer who demonstrated a device built with oridinary parts and junk. He then ‘fired’ it at several models of cars that were stationary but idling.they all stalled. He also ‘shot’ some computers that all crashed.
No, it’s not out of place, you’re ignoring the fact that the pulse generation needs to be in close proximity to avoid collateral damage and you’re asking for science fiction.
An EMP capable of wiping out a vehicle’s electronic system at a distance, isn’t going to be confined, or focused by a parabolic, conic, gaussian, tetrahedral, or other shape, dish. The farther you are from the target, the more power you’re going to need and above a very low threshold (below energies capable of disabling a vehicle at a distance) that pulse is going to radiate right through portable amounts of any shielding known to man.
Further, the required energy in the pulse is going to increase with the distance, at a rate of squares or better. If you want to be 5 feet away, you’ll need at least 25 times the pulse that you needed at 1 foot, at 10 feet, you’d need 100 times the energy. No police cruiser has the trunk space for that sort of power supply. The little RC car on the Discovery special, was actually just frying the computer with a very high voltage discharge directly to the frame. An EMP isn’t going to be generated on portable battery power in our lifetimes.
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APB9999: I do appreciate your responses, but, these are not the sorts of objections I was hoping for. I was more hoping for “you can’t do that because the best current technology produces an EM pulse by … and for a device weight of, say, 500 lbs or less this can only produce power in the range of X watts, and to interfere with a car engine enough to degrade performance you’d need Y watts”.
Or something along those lines.
We do have the technology to create an EMP. But I don’t think it can be focused like a laser. We can get it to go a general direction. But since the pulse would need to have some width to make sure it hits something, it would need to either fan out, or the pulse antenna would need to be as wide as a car.
The collateral damage is one reason that they wouldn’t use it. Even if they could direct it, it would still travel beyond the suspect car and possibly knock out 1/2 mile of cars directly in front of it. Also, other electronics along the street (signal lights, variable traffic signs, store security systems) could be affected. And to top it off, construction blasting caps are set off by radio; having a noisy EM pulse go anywhere near one would be a huge hazard.
The accountability of its use is another issue. Shooting out a $70 tire is one thing; frying $2000 of electronics is another. Plus, what if the suspect’s car was stolen/carjacked. You’d have a really pissed-off citizen suing for damages.
If you’ve seen an EMP that can be ‘directed’ it wasn’t a true EMP.
“EMP is produced by electron motion transverse to the Earth’s magnetic
field. So, electrons moving along the field do not radiate. For a burst at
hlgh geomagnetic latitudes, as would be the case for Europe or North America, there will be a region of near-zero
field strength north of the sub-burst point, where the magnetic field lines
from the burst site intersect the Earth.” – US Army Corps of Engineers
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Yes, its possible, but there are a lot of engineering issues. Directivity is one. To achieve this, you need a pulse which is modulated at some high frequency. The higher the frequency, the more directive the beam can be for a given antenna size. At radio or VHF TV frequencies, wavelengths are many feet, and you’d need a few wavelengths to get substantial directivity. For something which could be held in your hand, you probably need to get into the GHz range (1 GHz has a wavelength of one foot, higher frequencies have smaller wavelengths).
Assuming you have such a device, the issue is how well the energy couples into sensitive components (e.g. the on-board computer). This is going to vary widely, depending on the angle the device is being aimed from. It will also be different for each model of car. You also have to be concerned with what the energy will do to people. Killing or maiming the suspect, or especially any hostages or bystanders, probably isn’t acceptable.
Essentially, as you increase the power, eventually you’ll couple enough in to break something wth a, say, 90 percent probability. You have to look at whether you can generate and radiate that much power without frying the EMP gun. If you can, will the power level be dangerous to people (including the person doing the EMP shooting), can you size it down to where it fits comfortably into a car, and finally how much will it cost.
The problem with an EMP or alternate form of stunning the vehicle is that when all the electronics are fried the power steering becomes inoperative. The driver would invariably loose control of the car. Now the police are responsible for where this out-of-control car is going and sustain many lawsuits. A typical high-speed chaise in LA would inevitably end in certain bystander casualties. Also, as pointed out earlier, the bad guys would start driving old, rebuilt or custom vehicles that circumvent or don’t use electronics for crucial operations.
A more plausible solution might be that automobile manufacturers conform to a standard “chip” that allows authorized authorities to take control of the fleeing auto through an encrypted wireless link. This “control” the officers have to the car might include breaking, acceleration and steering. We could of course dedicate and entire message thread to all the problems this could bring. The only way the aforementioned chip could ever come into existence is through legislation and years of testing. By then cars will be hovering rght?
Thanks to MrKnowItAll. That column was helpful, especially the part about the Aviation Week article. They seem to have produced a non-nuclear pulse, but they had to use explosives. Of course, the types of applications the military would be after would be more extreme than what we’re after, but it looks like more than could be used by the cops. They also seem to have had problems aiming it, though why that should be given that it was “microwave energy” is a puzzle. Microwaves can certainly be aimed easily enough.
It’s still outside the application envisioned, though, since microwaves are harmful to people. The single pulse I was talking about earlier wouldn’t be.
By the way, Stephen, I am not “asking for science fiction”. I am not asking for anything except information, which I’m not getting from you. Among the many assertions you make without backing them up,
is just plain wrong. This is what people learn in high school about energy radiation, and it’s a good place to start. But it applies only to energy radiated spherically. In the case of electromagnetic radiation, there are methods of focusing that can cause the drop in energy to fall off much more slowly than the square of the distance from the source.
This isn’t quite what the OP was talking about, but one time when I was a kid I saw a TV show (I think it was That’s Incredible) that was spotlighting a device that looked like a small square skateboard with some electronics on the top. Anyway, this thing was attached to the front underside of the police car, and in the event of a chase, the police car could jettison this small cart quickly enough to travel underneath the fleeing vehicle, and then some kind of charge would detonate that would render the fleeing vehicle undrivable. My memories of this are real sketchy (I was 9 or 10 when I saw this). It looked like a chemical charge/explosion of some sort. Anyone recall seeing this?