Charging capacitors using diodes at different temperatures. II. Numerical studies

This study is presented in a series of two papers. The preceding paper [L. L. Bonilla et al., Phys. Rev. E 113, 014123 (2026)10.1103/j22d-1zwg] is an analytical study. In the present paper we numerically study the thermal energy-harvesting capability of two electronic circuits. The first circuit consists of a diode and capacitor in series. We solve the time-dependent Fokker-Planck equation and show that the capacitor initially charges and then discharges to zero. The peak charge on the capacitor increases with temperature, capacitance, and diode quality. The second circuit has two current loops with one small capacitor, two storage capacitors, and two diodes wired in opposition. When the diodes are held at different temperatures we observe that a nonzero steady-state charge is accumulated on both storage capacitors. The magnitudes of the stored charges are nearly equal, but the signs are opposite. When resistors are used in place of diodes there is no transient and no steady-state charge buildup. Numerical studies for the time-independent Fokker-Planck equation are presented and confirm the steady-state charges.