A system is disclosed which includes a chamber, one or more transmitters configured to emit EM radiation, one or more power harvesters, one or more EM stirrer, and a processing system configured to a) receive a measure of dimensional characteristics of the chamber b) control the one or more EM stirrers, c) evaluate statistical properties of the statistical EM environment, d) set a new criterion for acceptable statistical properties of the statistical EM environment, e) measure a lowest usable frequency of the chamber below which the statistical properties are not acceptable according to a predetermined criterion, f) determine an efficiency profile of the one or more power harvesters versus frequency, g) select an operating frequency that maximizes efficiencies of the one or more power harvesters, h) measure a collective efficiency of the chamber, and i) return to step d if the measured collective efficiency is below a predetermined efficiency threshold.