Let me word it again.
I want the pulse to have a radius of 20 cm. Meaning that all electronics within 20 cm would be disabled, outside of that is fine.
How would I go about making that.
Also, I don't want the design that involves explosives.
You can not confine to range to just 20 cm, unless you shield it. Which makes your design super easy, and readily available, it's called a MICROWAVE OVEN.
You need a certain level of power to disable electronics at 20 cm, but it doesn't just stop right there, since it's much stronger than communication signals, it's disruptive influence will be seen much further.
You mentioned a Tesla coil, but not how large. Mine is about 250,000 volts, and I stop using it about 15 years ago, as it seemed to have a bad effect on electronics, like computers, TV, stereo, camera. Could have been coincidence, but haven't had the same problems since ending my experiments. There is a concrete block wall, and an entire room, separating the Tesla Coil, and most sensitive electronics. Even had neighbors comment on poor TV reception.
Electromagnetic waves just don't stop short, once they reach their target.
How can anyone design this for you, if it's not been done, nor likely be realized. Most people wouldn't want to invest the time and money for such a short range anyway, unless it was something they could carry in their pocket.