I ran across this fairly amazing book/article on the web, published by Neumann, which describes in fairly technical terms which I found to be fairly understandable (OK, I didn't even try to figure out any of the equations), how microphones work as well as how and why various capsule designs work the way they do. It also has an extensive section on applications. I don't think I've ever seen so much information on mic principles of operation in one place. (It's 79 pages...I printed it out for bathroom reading.) Check it out.
www.neumann.com/download.php?download=docu0002.PDF