Power Receiver for Extracting Power from Electric Field Energy in the Earth
https://patents.google.com/patent/US20150102675A1/en
From a quick scan there is NO evidence that the applicant actually tested any of his 'patent'.
So this is just here for reference (circuit Diagram) atm.
I NB that Thermoacoustic devices are light. Hollow tubes mostly that might be part of a car or bike chassis. (Weight Saving. Increased power to weight ratio of the whole system..?)
With them there is much resonance matching required.
I also NB Quarter Wave (and Helmholtz?) Resonators that kill the frequencies of highest amplitude in engine exhaust remain 'cold' at their closed ends as there is no flow in them.
That means a normal speaker might be used in them to harvest noise energy via a similar resonant circuit..? (and a MPPT..?)
The trick will be to find (or tune) a speaker that happens to also resonate at the desired frequency.
An efficient low-frequency acoustic energy harvester [38%]