I don’t really plan on giving any.
Here in the Twin Cities, they use those for tornado warnings. Whenever they go off, people go outside to see if they can spot the funnel cloud.
High altitude Electromagnetic pulse (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. In more dense atmosphere where the the rays are rapidly absorbed and don’t have much free mean length, this pulse is seriously 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 direct threat to microelectronics, but would likely compromise the power grid the same way a massive geomagnetic storm could (see JSR-11-320 “Impacts of Severe Space Weather on the Electric Grid”, JASON Committee, Nov 2011) resulting in severe long term consequences for the electrical distribution infrastructure.
It is important to understand that EMP is not just a burst of electromagnetic energy; it is a pulse of energy that are quasi-coherent; that is, the wave is in phase as if emitted from a giant free electron maser that is constructed out of the Earth’s magnetosphere. (I’m specifically referring to the E1 component of high altitude EMP, which is what is of concern with regard to damaging semiconductor electronics). EMP is in the radio frequency range and can deliver potentials of up to the 50 kV/m atmospheric saturation range after which the atmosphere will undergo dielectric breakdown as it does with lightning. This pulse develops high potentials in semiconductors that causes them to physically breakdown, regardless of whether they are powered or connected to a power grid. This will affect any device that is not adequately protected, and especially anything with an antenna or other conductive lead that is directly coupled to internal electronics or electrically sensitive components. Much of the effort to make commercial electronics smaller and operate on lower power has also made them much more sensitive to EMP effects.
Military electronic hardware, save for acceptable commercial-off-the-shelf (COTS) components, area built to specific interface standards like MIL-STD-464 (Electromagnetic Effects Requirements for Systems), MIL-STD-461 (Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment), and MIL-STD-2169 (Classified) (High Altitude Electromagnetic Pulse Environment). However, the ugly truth about high altitude EMP is that no amount of shielding, save being buried deep under hundreds of feet of rock or dirt, is really adequate to protect sensitive microelectronics. By their nature, the electronics are delicate and sensitive to small levels of excess voltage, and it is nearly impossible to make a practicable sensor, communication system, or avionics control that has to interface with the outside world and yet is adequately isolated against large pulses.
Previous threads on the topic of EMP:
[POST=11781642]How much EMP shielding does military equipment has?[/POST]
[POST=13967041]Solar flares, EMP, and electronics damage[/POST]
[POST=13919909]how big is the “EMP cannon” for stopping cars?[/POST]
[POST=5931094]Question about Electromagnetic Pulses (EMP)[/POST]
Stranger
The fire station in the town where my parents (in N Ireland) live used a siren up to the mid 90s to alert fire fighters to come to the station. I assume they finally got them pagers or the like after that. It used to get the dog next door howling when it went off.
We still have that alarm here, it’s really loud and about a block away. :mad:
When I was a young fellow in training at a nuclear power plant, we had one of those loud air-raid sirens at the plant. They ran it up once a week, on Saturday afternoons.
One day I was at home an hour before work, on a day that wasn’t Saturday, and I heard a wailing siren in the distance :eek:. My thoughts raced, wondering if I should go to work early, or if there would be work at all … or …?
It turned out to be the siren at a local volunteer fire department. I had never heard of such a thing until that day—I had grown up in a city with a full time fire department.