MIT researchers have devised what they call a bias-flip rectifier that can extract about four times more power from low-level energy sources than can full-bridge rectifiers. The control circuit they came up with contains embedded dc-dc converters that can share their filter inductor with the bias-flip rectifier and thus reduce the volume and component count of the necessary circuitry.
MIT Professor Anantha Chandrakasan and alumnus Yogesh Ramadass PhD '09 did the work and described it in a paper at the recent International Solid State Circuits Conference (ISSCC) in San Francisco. Their prototype is implemented in CMOS and works with a piezoelectric transducer. But MIT says their idea could also be applied to temperature transducers and could harness a temperature difference of just one or two degrees. The application they have in mind is biomedical instrumentation. But they also think the idea could get applied in machinery or industrial installations in remote or inaccessible situations. Their paper can be found here: