Stopping Cars With Microwave Radiation

Ponca City, We Love You writes "Researchers have created an electromagnetic system that can quickly bring a vehicle to a stop by sending out pulses of microwave radiation to disable the microprocessors that control the central engine functions in a car. A 200-pound unit attached to the roof of a police car can be used to stop fleeing and noncooperative vehicles. The average power emitted in a single shot is about 10 kilowatts at 100 hertz and since each radiated pulse lasts about 50 nanoseconds, the total energy output is 100 joules at a distance of 15 meters. One concern with the device is that it could cause an accident if a car is disabled and a driver loses steering control. The device could also disable other vehicles in the area so the most practical application may be for perimeter protection at remote areas. Criminals have a work-around too. Since electronic control modules were not built into most cars until 1972, the system will not work on automobiles made before that year."

Comments

Re:Faraday cage

[Technician]

No. Each wire entering into the ECM is another vector, thus inputs into the ECM would have to be protected.

Coaxial feed thru capacitors through a RF gasketed cover followed by a small RF choke and ferrite bead should do the trick.

Concerns are quite valid

[AP2k]

One concern with the device is that it could cause an accident if a car is disabled and a driver loses steering control. This isnt a problem for most of the vehicles on the road today since they use primarilly hydraulically actuated power steering, but you can still steer even without hydraulic pressure. Same thing with standard rack-and-pinion and recirculating ball steering systems. For these three types, only a grandma that doesnt expect to loose hydraulic pressure will have any serious problems controlling the car.

However, steer-by-wire systems are quickly coming into play in America, especially on some of the lower-end GM products. Now I'm no GM engineer yet, but from what I gather the steering system is either on the GMLAN high speed bus or it has its own bus but still gets data off GMLAN.

Now suppose the ECM stops giving out speed information on the GMLAN bus. Hopefully there is a contingency plan in the steering logic so that you can still have some steering I/O even without the vehicle speed information, but if the output isnt on its own bus, I cant say I'd want to be in that car.

Faraday Cage won't necessarily stop this!

[compumike]

I'd like to try to explain why their microwave design might work, and why the "faraday cage" argument isn't enough: Differential vs. Common-Mode Signals. It's because of all the devices connected to the car's central engine controller.

Lots of old school communications protocols are based on single-ended signaling, where one voltage represents a 0 or 1. This includes RS232, Parallel, and even ISA and PCI slots on your motherboard. However, almost everything new that's outside the computer is based on differential signaling -- reading the differential voltage between two wires. This includes 10/100/1000BaseT ethernet over twisted pair, USB, Firewire, etc.

Here's the key difference: when you get noise coupling onto your signal, whether it's a pulse from the engine ignition coil firing or from this car-stopping microwave device, it tends to be the case that the voltage of *both* of the differential wires is increased by the same amount -- so that when the voltages are subtracted, the effect of the noise cancels out.

However, this exploits the fact that no devices have an infinitely large common-mode range. That is, the average voltage of the differential pair must be within some predefined limit, or your circuit won't work. By putting in a big enough pulse, this microwave device might be able to move charges around on the outside of the car body (which happens to be the ground that most devices hook to) enough to move the voltages significantly. This would cause any devices (think an oxygen sensor or a tachometer) to act as though they were momentarily dead.

Thus, even with differential signaling (which cars already use), it's possible to break things by putting too much common-mode noise on top. See Wikipedia article.

--
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My '81

[X86Daddy]

I have a vehicle built in 1981 and I know the electronics on it pretty well. The idle controller is the only part with ICs besides the modern stereo and car PC, and I believe it will simply idle rough without that controller functioning. My steering is rack and pinion, my auto transmission computer has nothing more advanced than a transistor; same for the door lock controller. Everything else is vaccum, steel cable, etc... So the date value for vehicles that are impervious to this attack can be set a little further forward.

Re:'67 AMC Rebel

[jag7720]

That is why AMC is no longer making cars..... and no one but you is still driving them

Re:Steering?

[Dun Malg]

New luxury cars are being developed (some BMW and Mercedes - I don't know if they're being sold) that don't even have a direct connection between the steering wheel and the drive train. Instead, it's all computerized with some type of central bus system. This allows for much smoother/easier handling. So far, only BMW and Lexus have electronic steering planned, but even those are hybrid systems that maintain a direct mechanical linkage. It's not just a safety issue, but an issue of control. Whether you realize it or not, you get quite a bit of feedback about how the tires are interacting with the road through the movement of the steering wheel. Control is actually better with a direct link. This is why they do not plan to go 100% electronic.

Re:The real scoop on RFI suppression

[Technician]

I tried to be informative, but was modded funny as people just thought I was using buzzwords.

RF on a wire can be shorted directly to the case with no way past due to lead inductance when coaxial feed through capacitors are used. They work well and are used on every microwave oven made. They are on the bottom of the magnitron. The fillimant leads come from the bottom inside a box. They then go through feed through capacitors to keep microwave energy from radiating out the wire.

http://www.freepatentsonline.com/7184256.html

photos here at the bottom of the page..
http://www.samwha.co.th/capacitor.htm

RFI suppression on motors..
http://www.freepatentsonline.com/6307344.html

RFI protection for pacemakers.. PDF alert..
http://www.interferencetechnology.com/ArchivedArticles/medical/Article08web.pdf?regid=

A full filter often includes an inductor. Here is an example. PDF alert..
http://www.dearbornelectronics.com/pdf/EMIFilters.pdf
This shows performance curves of various filters. A 3 DB change is the half power point. To have the same effect on a device 3 DB less sensitive would require double the power. Many of these devices have more than 80 DB attenuation at 10 MHZ and above. This would provide a high degree of immunity as the RFI source would need to be very close and very powerful to overcome the attenuation compared to an unprotected device.

Info on ferrite beads is here...
http://www.google.com/search?hl=en&q=ferrite+bead+RFI

Unlike a capacitor or inductor, a ferrite bead doesn't re-direct the RF current. It converts it to heat, and in the process, attenuates it. A capacitor on a wire, may make a tuned antenna at some frequencies. The ferrite bead is to prevent these tuned peaks by eating the power. Used in combination with a feed-through will prevent a tuned standing wave building on the wire.

A capacitor and inductor simply make a tuned circuit with a venurable frequency. Diodes, discharge tubes, resistors, and ferrite beads prevent a high Q tuned circuit.

http://en.wikipedia.org/wiki/Q_factor

For example, a pendulum suspended from a high-quality bearing, oscillating in air, would have a high Q, while a pendulum immersed in oil would have a low one.