Influence of frequency and voltage of electric excitation signal on electric property of fruits

The influences of frequency and voltage of electric excitation signal on electric property of fruits with non-destructive and orthogonal experiment method were studied. The results show that when the voltage is in 0.2～2.5 V, the electric parameters of apple have critical voltage value. If the voltage is less than the critical value, the capacitance, resistance and loss angle tangent keep constant; if it is bigger than the values, with the increase of voltage, the values of capacitance and resistance decrease rapidly and loss angle tangent increases sharply. The critical voltage value is correlated with frequency. During the frequency band of 5～100 kHz, the biggest critical value is at 30 kHz. The electric parameters of kiwifruit and pear also have the same frequency characteristic as apple and different critical voltage values, which are 1 V, 1.8 V and 1.4 V, respectively for apple, kiwifruit and pear under 10 kHz. Based on the differences of critical voltage value, the identification method on species of fruits is proposed. The test result shows that the identification rates for apple, kiwifruit and pear are 100%, 93% and 90%, respectively.