# Characteristics of Electric Field Induced by Oscillating Metal Underwater Vehicle
## 4 Maritime Verification Experiment  
An at-sea measurement study was carried out to verify the electric field interference characteristics of platforms shaken by metallic vehicles and to provide a basis for the study of electric field detection methods on moving platforms. The experiment uses a high-speed speedboat as a metal navigation body platform; its propulsion system adopts pump-jet propulsion, and the highest speed can reach more than 50 knots; the electric field sensor consists of four Ag/AgCl electrodes, used to measure along the direction of the speedboat and the speedboat transverse direction of the two horizontal components of the electric field; the installation schematic diagram, as shown in Figure 7a, shows two measurements in each direction of the electric field. The electrode distance of the sensor is 0.5 m, and at the same time, in order to reduce the impact of the sensor's connecting wire shaking, the sensor and the wire are fixed on the surface of the hull using a strong adhesive and clamps, and the wire is outside the parcel layer, which not only ensures that the sensor and wire in the movement process itself do not produce shaking (only with the hull of the ship shaking) but also ensures that the sensor and the  
Figure 5: The 0.005\({}^{\circ}\)/s angular velocity shaking output. Figure 6: The 0.5\({}^{\circ}\)/s angular velocity shaking output. wire do not fall off during the high-speed movement of the speedboat. The installation on the real boat is shown in Figure 7b. The water depth of the experimental sea area is about 5 m, and the conductivity of seawater is measured to be 2.8 S/m. The forward direction of the speedboat is defined to be in the \(x\)-axis direction, and the sampling rate of the system is 250 Hz. Figure 8 shows the background electric field of the platform of the speedboat with the engine turned off, and the surface of the sea is in a state of free swaying. Figure 8: Shaking disturbance analysis of the platform at a standstill (offshore). (**a**) Time domain diagram. (**b**) Frequency domain diagram. Figure 7: Installation diagram of speedboat platform. (**a**) Bottom structure and erection diagram. (**b**) Schematic diagram of boat and sensor installation. As can be seen from Figures 8 and 9, when the speedboat platform floats on the sea surface, the total electric field signal can reach the order of mV/m, and most of its energy is concentrated in the low-frequency band, especially in the part of the frequency band below 1 Hz, which is close to the ship's electrostatic field, so there is a larger probability of false alarms when using the ship's electrostatic field to detect it; there is a stronger industrial frequency interference near 50 Hz, which belongs to high frequency in comparison with the ship's low-frequency electric field. There is a strong industrial frequency interference near 50 Hz, which is a high frequency compared to the ship's low-frequency electric field, and the ship's axial frequency electric field signal can be detected in this background. To verify the electric field interference characteristics of the measurement system under uniform motion state. Due to the fact that the propeller rotation frequency of ships at economic speeds is always higher than 1 Hz, which is 60 revolutions per minute, the interference analysis frequency band focuses on the 1-30 Hz; focus on the analysis of the background interference within the frequency band of the axial frequency electric field, the use of the speedboat platform to measure the background electric field interference under the motion speeds of 5, 10, and 20 knots, respectively, and the time domain signals are shown in Figure 10.  
Figure 9: Shaking disturbance analysis of the platform at a standstill (far shore). (**a**) Time domain diagram. (**b**) Frequency domain diagram. As shown in Figure 10, at 0-116 s, the speed is 5 knots; at 126-233 s, the speed is 10 knots; and at 357-476 s, the speed is 20 knots.