is there any powerful microphone which i can install and record voice at about 20 meters clearly?

Answer 1

Go looking for parabolic microphones.

But of you want to do this in secret you need to know these are not small discreet things. They look like a metal dish about a foot across the ones I've seen and it's obvious you are pointing them at your subject.

Also try gun microphones. They are more discreet.