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Abstract. This study is focused on a computer simulation-based determination of top electrode voltages associated with the free running oscillator (FRO) radio frequency (RF) heating of soybeans. This is an extension of a previous study that used a single parameter linear regression model to a two-parameter model to better estimate the voltages by considering two different electrode configurations (with/without copper strips) and a wider range of moisture content. Soybeans at four moisture contents (i.e. 4.7%, 7.7%, 9.7% and 11.7% on wet basis, w.b.) and soybean flour (9.7% w.b.) were heated in a 6 kW, 27.12 MHz FRO RF heating system and the corresponding voltages under five electrode gaps were measured using a customized measuring device for model testing. The results demonstrated that the installed copper strips raised both anode and measured currents, and thus two different models were established for each electrode configuration (with/without copper strips). The relative error was less than 5% between voltages predicted by the improved model and the previous model under the same condition used in the previous study. Moreover, under the broader conditions, the voltage predicted by the improved model was much closer to the computer simulated values than observed with the previous model. Therefore, the developed method was more accurate for estimating the voltage for RF heating of soybeans, which can be applied in computer simulations.