Is it possible to induce brainwaves such as delta waves externally, (Such as using EM waves) and what happens if the brain is flooded with such waves?

see https://en.wikipedia.org/wiki/Delta_wave.

There are various machines sold that appear to alter the delta rhythms (a google search will bring up many sites). that said the science around these machines and their long term benefits is rather weak and the evidence base in somewhat lacking!

You may also want to look at this very recent commentary on the non-medical uses of brain stimulation in Nature - http://www.nature.com/news/brain-power-1.19475