I kind of get op's point. It's not straight up debunked, but it's so few microwatts that they can power the sensor but they can't store log data.
It requires a close proximity powered base station nearby to fire a signal out to get reflected back somehow.
I'm having a hard time picturing any viable setup outside of a laboratory experiment. If you've got a powered base station within a few inches of it why not just power it with that?