Abstract : This paper analyzes and discusses the working principle and design method of a novel angular acceleration sensor. This sensor directly converts the angular acceleration signal into an electrical signal output based on the flow potential effect. Compared with other types of angular acceleration sensors, it has the advantages of simple structure, low cost, high reliability, and high stability. Keywords : Flow potential; double layer; angular acceleration; sensor Traditional angular acceleration sensors used in some fields are mainly modified designs based on angular rate gyroscopes, belonging to the differential electromechanical type of angular acceleration sensors. The acceleration signal of this type of sensor is obtained by connecting a differentiator in series at the output of the angular rate gyroscope, resulting in poor signal quality and reliability. Alternatively, several linear accelerometers are used for measurement, followed by information processing to obtain the angular acceleration signal. However, this method is relatively complex to implement, expensive, and not very accurate. The angular acceleration sensor introduced in this paper directly converts the angular acceleration signal into an electrical signal output based on the flow potential effect. Therefore, it has the characteristics of simple structure, light weight, low cost, good signal quality, and high reliability. It can be widely used in navigation, attitude control, and system stability of moving objects such as satellites, aircraft, warships, strategic missiles, and rockets. 1 Flow Potential [1-3] When any solid comes into contact with any liquid, the solid surface will exhibit a charged phenomenon. The main reasons are as follows: (1) Adsorption of ions on the solid surface; (2) Dissolution of ionic crystals; (3) Ionization of the solid surface; (4) The solid has n-type (hole-type) or p-type (electron-excess-type) defects; (5) The two phases have different affinities for electrons. Regardless of the cause, when the solid surface is charged, it will inevitably attract an equal amount of opposite polarity charge around it. This creates a special surface layer—the electric double layer—just in front of the charged solid surface. There are three classic theories of the electric double layer: the Debye-Yuge theory, the Gouy-Chapman theory, and the Stern theory. The Stern theory, in particular, remains largely correct in interpreting experimental results. The theoretical model of the Stern double layer is shown in Figure 1. As can be seen from the figure, the double layer is divided into two parts by a plane called the Stern plane (actually an imaginary plane): the inner layer is the Stern layer, and the outer layer is the diffusion layer, in which anti-charged ions are enriched. When the liquid is forced through a capillary (or porous plug) by pressure (or angular acceleration), the diffusion layer in the double layer near the capillary wall carries anti-charged ions and flows towards one end of the tube, thus creating a current and generating a potential difference. This potential difference generates a conduction current in the opposite direction to the flow direction, and the two quickly reach equilibrium. In a steady state, the flow current, proportional to the pressure difference P, and the conduction current, proportional to the potential difference E, are equal in magnitude. Therefore, the flow potential E is directly proportional to the pressure P, and their linear relationship is given by equation (1), where E is the flow potential, p is the pressure difference between the two ends of the capillary or porous plug, ε is the dielectric constant of the liquid, η is the viscosity of the liquid, k is the specific conductivity of the liquid, and ζ is the potential at the sliding surface (also known as the shear surface) in the double layer. From equation (1), it can be seen that the flow potential is a linear function of the pressure on the liquid. Liquids with low specific conductivity, low viscosity, and high dielectric constant will generate a considerable flow potential when passing through a capillary or porous plug. 2 Schematic Structure The schematic structure of the liquid ring angular acceleration sensor made based on the flow potential effect is shown in Figure 2. Among them, the liquid ring is blown from a glass tube; the porous plug is made of microsphere glass powder with a diameter of about 10 μm; the ring electrode is made of platinum wire; and the liquid in the liquid ring is prepared with high-purity acetone. 3. Working Principle Experimental results show that after filling the liquid ring with high-purity acetone solution, the inner surface of the micropores in the glass stopper becomes negatively charged. This result can be explained by the different electron affinities of glass and acetone. When glass and acetone come into contact, the different electron affinities cause electrons to flow from the side with the higher dielectric constant to the side with the lower dielectric constant. The dielectric constant of glass is 6, and that of acetone is 20.7. Therefore, electrons flow from acetone to glass, causing the inner surface of the micropores in the glass stopper to become negatively charged. Under the influence of electrostatic force, the negative ions in the acetone solution repel the negative charge on the inner surface of the micropores in the glass stopper, while the positive ions attract the negative charge on the inner surface. As a result, positive ions in the acetone solution accumulate near the inner surface of the micropores. When subjected to an external angular acceleration, the pressure exerted on the acetone solution at both ends of the glass stopper is given by the formula: p is the pressure; m is the inertial mass of the liquid; ω is the angular velocity; and c is the proportionality constant. Under the pressure, the acetone solution is forced through the porous stopper. As a result, the diffusion layer in the double layer near the micropore wall will carry positive charges and flow towards one end of the tube, thus generating a current and causing a potential difference. Substituting equation (2) into equation (1), we get equation (3). It can be seen from equation (3) that the flow potential E is a linear function of the acceleration dω/dt. Therefore, the magnitude of the angular acceleration can be measured instantly based on the amplitude of the flow potential. As shown in Figure 2, when the liquid ring rotates clockwise, the positive charges in the diffusion layer near the micropore wall in the microporous glass stopper flow from A to B, resulting in a potential difference between A and B. The polarity of the potential difference is positive at B and negative at A. Conversely, when the liquid ring rotates counterclockwise, the polarity of the potential difference generated between A and B is positive at A and negative at B. Thus, the direction of angular acceleration can be determined instantly based on the sign (positive or negative) of the flowing potential. 4. Discussion The two key components of the liquid ring angular acceleration sensor are the microporous glass plug and the liquid within the liquid ring. The micropores in the microporous glass plug must be uniformly distributed. Because the flowing potential is only related to the properties of the diffuse layer (the movable part) in the double layer, the flowing charge only occurs near the micropore wall. If the pore size is too large, the zeta potential will decrease, and the flowing potential will also decrease accordingly; if the pore size is too small, when an external angular acceleration is applied, the liquid cannot pass through smoothly, still affecting the generation of the flowing potential. The liquid in the liquid ring must have stable temperature and chemical properties, and no chemical reaction should occur within the liquid ring cavity. In addition, the solution should have a wide melting and boiling point range, low viscosity, and high purity. Experimental results show that only by properly designing and processing these two key components can an angular acceleration sensor with good stability and high accuracy be manufactured. References: [1] Kitahara A, Watanabe A. Interfacial electrical phenomena [M]. Translated by Deng Tong and Zhao Xuefan. Beijing: Peking University Press, 1992. [2] DJ Xiao. Introduction to Colloid and Surface Chemistry (3rd Edition) [M]. Translated by Zhang Zhonglu and Zhang Renyou. Beijing: Chemical Industry Press, 1989. [3] Sparnaay MJ. The Electrical Double Layer [M]. New York: Porgamon Press, 1972.