Megawave ???

Why wait for the future?

blast freezer

"...will there be a Megawave in the future that would reverse the process of microwave?"

Do you mean a Megawave refrigerator or freezer? This sort of exists today as Thermoacoustic Refrigeration. Not too practical (today) for a homeowner...maybe you can find a way to improve this?

The shock freezing and/or thermoacoustic refrigeration is what I meant in similar concept. But it's still taking too long about 90mins to bring temperature of the core down. I wonder if it is possible to bring the timing down to 10 to 20mins in a portable way like a microwave take only couple minute to heat up the item (and of course depend on the size). Microwave uses excited energy to heat up the item. Maybe Megawave is ...i don't know....

The constituent here is not micro but wave

Any wave have to have an energy (hν) associated with it. So this can not be used with cooling. megawaves (or to be precise the Gamma rays if you take the visible spectrum as the base) will have higher energy and hence will heat more, the higher end of the spectrum (Long radio waves) will too generate heat and will heat up sooner or later)

But here you want to suck up the energy and that too from core (presumeably to override the constraints put on by the thermal conductivity) It unfortunately does not look possible, at least now.

UD15

Yes, it is possible, but is it practical?

Review the link in #2, and have a peek at Pulse Tube Refrigeration in Wiki.

Ben and Jerry's Ice Cream gets a plug in both articles... they are as 'Green' as they can be, and they are experimenting with this technology for their freezers.