1. Introduction With the rapid development of space science and technology, the detection of the space environment has attracted increasing attention in order to ensure the safe launch and operation of spacecraft. The atmospheric electric field is a crucial parameter in space physics and the space environment. When a spacecraft passes through a region with a strong electric field, it may be struck by lightning or induced by lightning, causing damage. Monitoring and detecting the values ​​and changes of the electric field is of great significance for spacecraft launch. Various electric field detection devices have been developed both domestically and internationally to monitor the atmospheric electric field, mainly including dual-sphere electric field meters, rocket electric field meters, and rotating plate electric field sensors. The detection direction is generally parallel or perpendicular to the main axis of the sensor, enabling the detection of one or two components of the vector electric field in the air. However, the atmospheric electric field exists in a three-dimensional vector form; when only one or two components of the vector electric field are detected, the detected electric field value may have a significant deviation. This paper first introduces the unique sensitive structure design of a novel three-dimensional vector electric field sensor in the air; then, based on the structural characteristics and signal processing methods of the three-dimensional electric field sensor, a theoretical analysis of the sensor output results is conducted; and a computer simulation of the calibration method of the three-dimensional electric field sensor is performed, and a dedicated calibration device for the sensor is designed to calibrate the three-dimensional electric field sensor's sensing electrodes in each of the three directions, ensuring the measurement accuracy of the three-dimensional electric field sensor. 2 Three-dimensional Electric Field Sensor 2.1 Working Principle This three-dimensional electric field sensor is based on the principle of induced charge in a conductor in an electric field. It utilizes the alternating shielding effect of a grounded shielding conductor on the sensing electrodes, causing the sensing electrodes to be alternately exposed to the external electric field. The induced charge on the sensing electrodes undergoes periodic changes, forming an alternating current signal whose magnitude is proportional to the external electric field. The electric field strength is detected by detecting the magnitude of this current. The structure of the sensor is shown in Figure 1, mainly including three pairs of sensing electrodes (axial Z-sensing electrode, radial X-sensing electrode, and radial Y-sensing electrode), a shielded rotor, and a drive motor. Three pairs of sensing electrodes are distributed perpendicularly in three-dimensional space. The axial Z sensing electrode consists of a pair of rotating blades, while the radial X and Y sensing electrodes each consist of a pair of rectangular copper plates. When the sensor is working, the drive motor drives the shielded rotor to rotate. The shielded rotor alternately shields the sensing electrodes in the three-dimensional direction, generating an induced current on the surface of the sensing electrodes. The magnitude of this induced current is proportional to the external electric field. For the axial sensing electrode (1): iZ(t) is the induced current; QZ is the induced charge on the sensing electrode; EZ is the external electric field; ε is the dielectric constant of air; r1 and r2 are the inner and outer radii, respectively; f is the electrode rotation frequency; and T/2 is the time when the shielded rotor exposes the entire sensing electrode. For the radial sensing electrode (2): A0 is the area of ​​the radial (X) sensing electrode, and other parameters are the same as in equation (1). From equations (1) and (2), it can be seen that when the motor speed frequency f is constant, the amplitude of the induced current on the electrode is linearly related to the external electric field. Therefore, the external electric field can be detected by detecting the induced current. 2.2 Theoretical Analysis of Sensor Output Signal Since the electric field sensor outputs a weak alternating current signal on the order of nA from its sensing electrodes, directly detecting this current signal is very difficult. Therefore, a signal processing circuit is used to convert the weak current signal into an easily detectable voltage signal. In the signal processing section, the current signals output from the three pairs of sensing electrodes in the three-dimensional direction are first converted to IV values. Then, the voltage signals output from each pair of sensing electrodes are differentially amplified. The differential amplification section is used to reduce noise and improve the signal-to-noise ratio. Finally, the amplitude values ​​of the amplified voltage signals are extracted, and three DC voltage signals that are linearly related to the external electric field are output. In the theoretical analysis, the linear relationship between the induced current output by the electrodes and the external electric field strength is based on the premise that the motor speed is constant. In actual sensor operation, it is difficult to guarantee that the motor speed remains constant. Disturbances in the motor speed introduce nonlinearity between the external electric field and the sensor output, which can easily cause measurement errors in the sensor. Here, in the IV conversion section of the signal processing circuit, a capacitor is used as the load of the feedback loop. Since the axial sensing electrode is alternately shielded by the four blades of the rotor, the frequency of its electrode output signal is four times the motor speed; the radial sensing electrode is alternately shielded by the two blades of the rotor, and the frequency of its electrode output signal is twice the motor speed. Then the capacitive reactances corresponding to the axial signal ZC(Z) and the radial signal ZC(X, Y) are respectively. In equation (5), AZ is the axial coefficient, which is a fixed value; in equation (6), AX(Y) is the radial coefficient, which is also a fixed value. From equations (5) and (6), it can be seen that the output voltage signal is linearly related to the external electric field, thus solving the influence of motor speed disturbance. Although the coefficient between the sensor output voltage and the external electric field can be calculated theoretically, since the structure of each electric field sensor and the parameters of each component in the signal processing section are not exactly the same, the linear coefficient between the output voltage and the external electric field of each electric field sensor needs to be determined by calibration. 3. Research on Calibration Method of Three-Dimensional Electric Field Sensor 3.1 Calibration Principle Accurate calibration of the electric field sensor is a prerequisite for its precise detection. Calibration is generally performed in a uniform electric field with known values. Typically, a stable voltage is applied to two plate electrodes spaced a certain distance apart, generating a uniform electric field between the electrodes, as shown in Figure 2. Currently, electric field boxes designed based on this principle are commonly used. During calibration, the sensor's sensing head is placed in the electric field box, with the sensor's sensing surface perpendicular to the direction of the electric field. Due to the unique structure of the three-dimensional electric field sensor, with three pairs of sensing electrodes in three dimensions, a dedicated calibration device must be designed. The entire sensor is placed in the electric field box, and each pair of sensing electrodes is calibrated separately. The design of this calibration device should ensure that the sensing electrodes are all in a relatively uniform electric field during calibration, and the smaller the volume of the calibration device, the better. 3.2 Simulation Calculation and Analysis of the Calibration Device The calibration device was analyzed and designed using extensive simulation calculations with ANSYS software. The main calculations and analyses focused on determining the distance between the upper and lower plates and the area of ​​the plates. (1) Determine the distance between the plates. A three-dimensional electric field sensor is established, and the model placed in a uniform electric field is calculated and analyzed. Figure 3(a) shows the electric field line distribution of the sensor in the electric field, and Figure 3(b) shows the potential cloud diagram of the sensor in the electric field. It can be seen that the three-dimensional electric field sensor in a uniform electric field is distorted due to the influence of its structure, resulting in the equipotential surface close to the sensor not being a plane. Since the upper and lower plates of the calibration device are generally made of flat metal plates and an electric potential is applied to them, in order to ensure that the electric field distribution is consistent when the sensor is placed between the plates of the calibration device and in a uniform electric field, the upper and lower plates should be located on a flat equipotential surface. In Figure 3(b), two planes above and below the sensor are selected based on the simulation calculation results. The potential error between the center of the plane and the edge is about 3%, which is taken as the plane where the upper and lower plates are located. In this way, the distance between the two plates is determined, and the position of the sensor between the plates is also determined. (2) Determine the area of ​​the plates. When the area of ​​the plates is relatively small, the edge effect on the electric field between the plates may lead to non-uniformity of the electric field in the area where the sensor is located during calibration at the center of the plates. Therefore, the size of the plate area must be determined through simulation calculation. To facilitate modeling and calculation, a cylindrical electric field box is used for simulation. The half-section of the cylindrical electric field box model is shown in Figure 4(a). The upper and lower plates are placed in parallel, and the plates are shielded by a shielding box. To reduce the influence of the edge effect on the electric field, 19 metal wires are used to divide the voltage between the upper and lower plates. The dashed box in the middle is the sensor placement area. Since the electric field sensor is placed in the middle of the calibration device, it is sufficient to ensure that the electric field in the middle part is uniform. Therefore, the central area of ​​the calibration device is selected for analysis, which is slightly larger than the sensor volume. Since the spacing between the plates has been determined by calculation, models with different areas are established for calculation and analysis. After a large number of simulation calculations, a reasonable electric field box area is determined, and the potential cloud diagram of the central area of ​​the calibration device is shown in Figure 4(b). The calculation results show that the maximum error of the electric field strength in this area is less than 1%, which meets the requirements for the calibration device of this electric field sensor. [align=center] [/align] 3.3 Calibration Device Structure Design and Test Results Based on the above calibration principles and simulation results, a dedicated calibration device for a three-dimensional electric field sensor was designed. This device consists of two high-voltage power supplies (positive and negative) and an electric field box. The electric field box comprises three parallel plates and a shielding box. Polytetrafluoroethylene (PTFE) pillars are used for insulation between the plates and between the plates and the shielding box. The sensor is placed on the middle plate during calibration. When calibrating the axial sensing electrode, the electric field sensor is placed upright on the middle plate, with the sensing surface perpendicular to the direction of the electric field strength. When calibrating the radial sensing electrode, the electric field sensor is placed sideways on the middle plate, with the radial electrode to be calibrated symmetrically exposed in the electric field and perpendicular to the direction of the electric field strength. Calibration tests were conducted on the three-dimensional electric field sensor using this calibration device. Figure 5 shows the relationship curves between the output voltage of the axial and radial sensing electrodes and the external electric field. The calibration data shows that the data curves in the three-dimensional directions all have good linearity, and the external electric field and the sensor output have a linear relationship, which is consistent with the theoretical analysis. 4. Conclusion This paper introduces a three-dimensional electric field sensor that enables three-dimensional detection of aerial vector electric fields, effectively reducing the error in aerial electric field measurement. The proposed calibration method, suitable for the sensor's structural characteristics, ensures the accuracy of its detection of aerial vector electric fields. Calibration using a dedicated calibration device shows good linearity in the test data, consistent with theoretical analysis, proving the rationality and feasibility of the three-dimensional electric field sensor design and calibration method. Furthermore, this electric field sensor has advantages such as small size, light weight, and simple operation, and can be widely used for electric field detection during spacecraft launches, as well as for meteorological research departments to monitor and warn of lightning and charged cloud activity.