I think its better to say:
My goal is producing a sound
ON the metalic surfaces. Formerly, I thought that making spark on metalic surfaces is a good solution. but now I have many problems with the dimesion and of course, the electromagnic noise
I want to produce the sound on the surfaces with a probe and calculate the travelling distance to three microphones. thereby, the coordinate of that point on the surface is specified. I call this project "Sonic CMM".