what do we know about impact of such weapons on passengers’ electronic possessions?
Do any police cars actually carry such devices? Are there even any plans to?
[THREAD=615732]Previous thread[/THREAD] with links to other threads on the topic of EMP.
Stranger
I’ve been hearing about police using EMP devices to stop cars since the 1970s. The current claim is that they can stop cars under controlled conditions, but they still have a few bugs to work out to make the devices work reliably in the field. Funny, that’s exactly what they said in the 70s too.
Real world EMP devices are fighting against a couple of basic principles of physics. The first is the inverse square law, which means the energy of the EMP drops off with the square of the distance. At 2 feet, it’s got 1/4th the power it had at 1 foot. At 4 feet, it’s 1/16th, etc. What this means is that for the EMP to be effective, you need a huge honkin’ amount of energy. Nukes create big EMPs. Anything non-nuclear generates a much smaller EMP, and anything small and portable enough for police use is just too wimpy to be of much use.
The second factor here is the fact that cars are made out of metal, which means that they naturally act like somewhat imperfect Faraday cages (a true Faraday cage can’t have holes in it, and without windows, it’s kinda hard to drive a car). A car’s electronics are protected from interference from things like the electrical noise generated by the spark plugs, which further protects the electronics from EMP devices.
EMP weapons were first seriously tinkered with during WWII. Back then, they promised to make the enemy bombers engines stop, and the planes would just drop out of the sky! They were able to stop plane engines in controlled tests, but in the real world the EMP weapons were of little practical use. So far, police EMP devices are in the exact same category, functioning well enough in controlled conditions to keep conning people into development money, but not working very well in the real world.
An EMP powerful enough to stop a car could easily destroy a watch or a laptop, though the metal body of the car will give some protection to anything inside the passenger compartment.
IIRC the Air Force has a giant EMP test facility. I saw a description of it a while ago (Wired? Popular Science?) There’s a giant trestle made entirely of wood (no metal fasteners), so they can place something the size of a large aircraft 100 feet away from the ground and bombard it with EMP from a huge source surrounding it.
So if you could persuade your perp to drive his car into he airforce base and onto a bridge surrounded by giant electronic antennas, it maight stop car, watches, pacemakers, etc.
There are a few misnomers here. First of all, a Faraday cage (an enclosed conductive cage of metal mesh) insulates against static electrical fields, but may provide only limited protection against electromagnetic radiation (depending on the completeness and fineness of the mesh) and does not insulate at all against magnetic fields. Devices within a cage may be subject to electromagnetic pulses of high frequency even if it is currently enclosed if radiation can enter through gaps such as doors jambs or cableways, and can definitely develop a pulse that enters via a conductor outside the case. It is also subject to induction within the case via a moving or changing magnetic field, which may either be generated directly by the pulse or as a response from conductors outside the case.
Second, the body of a car makes a very poor Faraday cage as it has huge gaps in the conductive surface, and provides almost no protection against radiation in the wavelengths of concern, as it is electromagnetically transparent in those gaps, which you demonstrate any time you use a cellular phone inside a car. Virtually all cars also have a collecting device (antenna) which connects directly to the car’s radio or communication systems. These systems are typically not fully isolated from other electrical systems, i.e. they all connect to a common ground, so any level of voltage developed that exceeds allowable throughput to ground can be delivered to all of the vehicle electrical systems, especially in the high frequency range.
It is true that vehicle control electronics are generally protected against the high frequency noise such as cellular signals and any interaction of other systems, the most powerful of which is generally the starter solenoid, but this is generally done by placing adequate physical separation from the systems, providing adequate ground with isolation against back voltage, providing noise filtering capability within a digital system, and whatever minimal shielding a designer can get away with. These are intended to protect against the milliwatt-range inputs that create noise. An electromagnetic pulse, on the other hand occurs at farfield power densities the high tens of KW/m2 to MW/m2, and basically acts by inducing resonance modes within an electrical system which causes it to accumulate static charge or current at high frequency until it reaches a breakdown limit.
Wit the exception of electronics specifically designed to operate in a high radiation environment (such as spacecraft avionics) the noise-protection, isolation, and physical and logical hardening features of most commercial electronics simply cannot cope with the power densities developed by high energy electromagnetic pulses, and undergo dielectric breakdown well before the 50kV/m atmospheric saturation limit. Indeed, efforts to make commercial electronics more energy efficient have also largely made them more sensitive to external interference and pulse damage. Military avionics and hardened electronics have special design features including elaborate isolation and robustness. In other words, they aren’t protected from experiencing the effects of the pulse so much as assuring that they don’t suffer damage from induced currents and high voltage breakdown.
High altitude EMP (HEMP) devices produce three distinct regimes of pulse, referred to as E1, E2, and E3. Microelectronics are most sensitive to E1, which is due to interaction of x-ray and gamma ray radiation with the rarified upper atmosphere and the geomagnetic field resulting an a nearly coherent, widely distributed pulse, sort of like a very large free electron maser. In more dense atmosphere where the the rays are rapidly absorbed and don’t have much length to deflect, this pulse is serious attenuated, and the amount of damage done but the physical effects of the blast (shock and thermal wave) would likely make E1 effects moot. E2 is more like static electricity, and can typically be shielded by using a protected ground or faraday cage type shielding. E3 is energy that is stored in the Earth’s magnetic field (similar to that which comes from coronal discharges and solar flares) and will cause longer term disruption and very high voltage spikes in large arrays like power grids; again, not much of a threat to microelectronics.
Some work has been done on non-nuclear electromagnetic pulse (NNEMP) generation, mostly by use of explosively pumped flux compression generators (EPFCG), like that portrayed in the remake of Ocean’s 11 (although they are larger than what would fit in a regular passenger van). Much of this work is classified, but the basic physics of it is pretty simple; you use an explosion to compress a large capacitor, vastly amplifying the discharge and obtain a very large flux through its electromagnetic field. The range of these devices are necessarily limited to the local area, unlike HEMP devices that provide coverage for hundreds of thousands of square miles. However, there is no fine control or targeting; it will basically disable electronics forward and aft of the device for some distance without prejudice.
Stranger
Likewise - claims of portable, directional EMP cannons turn up regularly, but I’ve never seen any evidence such a thing exists. I saw a video demo of a prototype some years back of one that was supposed to be able to stop a car. From 2 feet away it made the engine stutter slightly.
EMP is a real phenomenon, but until someone turns up a cite I think portable, directional EMP guns are just fantasy.
My understanding is that most of the research into Explosively pumped flux compression generators is that they use inductors or magnetostrictive devices, not capacitors.
I know this is an old thread, but just recently I had a police car pull up behind me at a red light with no other car around, and my car (which NEVER stalls, before or since) just died like someone turned off the key. I looked at my friend in the passenger seat and said “That cop behind me just killed my car!” To which he said what most of you will probably say. The car started right back up after I re-turned the key, and I drove away knowing those cops just tested something on my car. The car details are not as important to me, but if you want to know, It’s a very clean 91 Dodge Stealth with a healthy dose of go fast mods, but very tasteful and not “Fast and Furious” or “ricer” in any way. But the police do actively test things like this and they did test it out successfully on my car. I wish I could have heard them snickering to each other wishing to hear my reaction. LOL
My understanding of what an EMP would do to solid-state electronics is that it wouldn’t just temporarily turn them off, but permanently fry them. So, if the cop had, indeed, hit you with an EMP, you wouldn’t have been able to start the car back up a few moments later.
When I was using an iPod Nano on a regular basis, I did notice occasional playback oddities if a police car passed me (just driving along, I seriously doubt I attracted any attention just walking down the sidewalk).
an EMP would do that, but especially on an older car (and even especially more if the shielding has degraded) regular old EM radiation at the right frequencies could cause the PCM to go fritzy.
This post is a picture perfect illustration of how belief in the supernatural is never going to go away. Human minds are wired to find patterns and connections even if events are totally random.
Aren’t they working more on a kill switch in the car’s computer nowadays?
The Police have a code that will stall the engine in a chase scenario, but you have to subscribe to On Star or Lo Jack for it to be effective?