I think may be a very good time to review this interesting Apple patent and the article I wrote in 2013:
"AUTONOMOUS BATTERY-FREE MICROWAVE FREQUENCY COMMUNICATION SYSTEM"
Passif technolog —ready.
Cue the balloons

#AppleEventhttps://qr.ae/TWKTPy
Daniel, thank you. Indeed some has been. However radio frequency harvesting has not been deployed to any great effect and this patent has amazing potential. We will soon.