Creating a temporary EMP device

I'm new in this site. Anyhow, I want to create a EMP that can temporary disable electronic devices. I read some articles that producing one can  permanently destroy any electronic devices when activated.  I don't know if its real in the Dark Knight Rises where Bruce used a device to disable the cameras or even the lights and vehicles in the tunnel but I want one. The purpose of its creation is for killing some time and having experience in making one. Technically, I found a way to make a step by step temporary EMP however it does not show much like how much power produce or some voltage adjuster when you want to increase or decrease its potential. 

In such case, if i happened to make one, how can I determine the radius of its effects? Does the voltage produce counts to determine its radius?

You face a major problem: Using an EMP device is illegal in almost any country, no matter what the size of the device is unless it happens in a secure lab conditions.

The other problem is that building one takes not just a lot of wire but also quite a bunch of electronics and there is no such thing as "temporary" when it comes to an EMP....