Fig. 1

Schematic diagram of the AECM’s composition. The red and green circles represent positive and negative charges, respectively. The instrument inputs 220 V, 50 Hz AC power, which is converted into DC power (green line) through the power converter to power each module. The yellow circles represent the current detection module (A) and the bias voltage module (U). The red line provides direct current for the outer electrode, which can be converted from − 5 V to + 5 V, but during the testing phase we set it to 5 V. The GND of the current detection module and inner electrode are connected to the ground through the blue line. The control module controls and transmits data to the bias voltage module and weak current acquisition module through the communication line (purple line).