I have built an EMP and it works. All it is, is a capacitor bank that discharges into a coil of wire. The coil produces a very powerful magnetic pulse. A strong magnet pulse will generate high voltages in semiconductor devices causing them to burn out.
I have a bridge rectifier that I can plug into the wall with a cord. I have a current limiting resistor in the 120 Volt AC line to keep surge current from killing the bridge rectifier. This converts the 120 VAC into 120 x 1.414 = 169.7 volts DC. I use this to charge 2 capacitors that are wired in parallel. The 2 electrolitic caps are rated 200 volt DC about 7400 uf.
I wound my own pancake coil with #24 enamel coated copper wire. The coil is 1/4" thick 5" diameter about 1000 turns of wire coated with polyurethane varnish.
Discharge the cap bank into the coil it produces a very powerful magnetic pulse. I have a very high amp push button switch to dischaged the cap bank into the coil. A low amp switch will weld the contacts together.
The charger circuit inside of a (throw away camera) can be used to charge the cap bank too and make this device portable. A D cell battery works best instead of the intended AAA battery. It is a slow charge. If you can get your hands on about 10 of these throw away camera circuit board use 10 of those charger circuit boards in parallel to charge the cap bank 10 times faster.
Charge the cap bank, push the button and discharge it through the coil, it will kill any cell phone within 3 feet. It will kill a calculator, transistor radio and any solid state transistor device within 3 feet.
There is lots of hostility to ill mannered people using cell phones in public places! I totally despise mindless gabbling, where you can't escape, or the bad manners of people of all ages who seem to think their affairs (literal as well as figurative) will interest all within hearing range. They even raise their voices, so everyone can hear. How nice! Just walk past some loud mouth jerk with a cell phone and push the kill button it solves the problem every time.
I think a large diameter pancake coil and a larger cap bank will give this a longer range.