the upfront cost for something like geothermal is still outrageous, though. anecdotally, i bought my house with an older unit that ended up catastrophically failing after the reversing valve got stuck and destroyed the compressor. only 1 local shop in the area serviced the thing (same people who installed it when the house was built...) and the unit had long been discontinued since the company that made it (hydro delta) went bankrupt years ago. it was over $15k to put in a new updated unit... luckily my home owners insurance (with the help of a rider i added a year earlier that covered home systems) footed the bill, albeit after a long and arduous battle with the 3rd party shits that state farm outsourced it to. now this new system has a 10 year warranty on parts and labor, otherwise, i would have switched to gas in a heart beat. i can put in a new gas unit every year for 10 years at the same price... so while the geo's monthly electric bill is nice, i wouldn't dare install a new residential build with geo... plus add another easy $50k for the loop field if it's a new install.
i'm afraid what's going to happen once then 10 years are up since that always seems to be about the time major home appliances fail... probably try to move by then so it isn't my problem, lol.
and different parts of the body resonate at different frequencies...~~part of the reason ~2.4 GHz was picked for the common household microwave is water molecules resonate there~~ (and other harmonically related frequencies too... it's why a lot of the unlicensed ISM stuff is allocated there: crappy atmospheric propagation). also the necessary magnetron and waveguide for that freq is conveniently sized for a kitchen appliance and not too complicated.
EDIT: see proper principle of operation in reply below