In this question, I found out that a single EMP is not enough to stop all mobile phones from working. So as a follow-up question: how many EMPs would you need, and how expensive would this be?
To be clear, it is ok when other things become disabled too, if that makes it easier.
Also, both nuclear and non-nuclear EMPs are allowed.
The US Department of Health and Human Services has some literature on that.
According to this page from them, Electromagnetic Pulse (EMP) Following a Nuclear Detonation:
Although experts have not achieved consensus on expected impacts, generally they believe that the most severe consequence of the pulse would not travel beyond about 2 miles (3.2 km) to 5 miles (8 km) from a ground level 10 KT IND detonation.
Also:
Cell phones and handheld radios have relatively small antennas, and if they are not connected to electrical power supplies during the electromagnetic pulse (EMP) they may not be affected, but they do rely on an intact infrastructure for communications.
So basically you'd need to make sure that every single cell tower in the world is hit by a nuke.
I am going out on a tentacle here and assume that there is a strong correlation between the presence of an electric grid and cell phone towers. So if you want to know which areas you need covered by a blast, that's basically everywhere in a world map except for oceans and some major deserts/forests.
In another question I showed some actual calculations made by boffins that show we'd need all the uranium on Earth's crust combined, most of which is unreachable with current tech, to approximate the blast from the dino killing asteroid. That impact had a radius of less than half the surface of the world... If you spread it carefully you could hit all continental areas, but at this point I am thinking that you would need an interstellar economy in order to procure all that uranium. So I am guessing it would cost more than the annual global GDP per year for wvery year you spend on this project.
And that is just considering materials. Your total implementation cost would be much greater due to three factors:
So there's too many factors to consider that could affect the final cost, but I will say it should approximate to between 0 and 1 Au Bon Pain lawsuits.
The starfish test of a 1.5M ton warhead in 1962 caused an EMP pulse in Hawaii which was 900 miles away. It shut down their phone system. Starfish test
This was not a weapon designed to cause an emp pulse. the EMP was a side affect. A high altitude detonation can easily cover a million square miles (1000 miles by 1000 miles). To cover the continental US would only take about 4 weapons.
The effects of EMP are very brief. In some cases the currents generated ae high enough to damage the device. In other cases they probably can be restarted. The biggest issue would not be cell phones, but power lines. With the long wires, enormous amounts of current would be created destroying transformers and switching equipment. Basically the entire electrical grid would have to be rebuilt, if we can power the equipment needed to make the new components.
Besides nuclear weapons we can also get a EMP event from a solar flare. look up the Carrington Event in 1859 which shut down the telegraph system and even started a few fires from the overloaded lines. Carrington Event
