Research on MEMS Fluid Gyroscope

Introduction

The development of MEMS technology has led to a profound change in the field of inertial technology. Inertial sensors are a type of sensor that uses the inertial properties of an object to measure the motion of an object, including accelerometers and gyroscopes. Among them, micro-gyroscopes play an increasingly important role in inertial navigation systems such as aerospace and navigation. In addition to traditional mechanical vibration gyroscopes, various new gyroscopes have also emerged in an endless stream, such as electrostatically supported gyroscopes, magnetically supported gyroscopes, microfluidic gyroscopes, superconducting gyroscopes, etc. These new gyroscopes have their own advantages in performance and size. The following is an introduction to the research, development and application prospects of fluid gyroscopes.

1 Introduction to various fluid gyroscopes

Compared with traditional gyroscopes, fluid gyroscopes have greatly simplified structures and reduced manufacturing difficulty due to the lack of suspended mass blocks. More importantly, they eliminate complex moving parts, greatly improve their impact and vibration resistance, and are particularly suitable for use in high-impact and high-vibration environments.

There are two basic principles of fluid gyroscopes: one is that the fluid itself generates angular momentum under external control. The fluid acts as a conventional rotor to form angular momentum for measuring external angular velocity. When there is an angular velocity input from the outside, the relative motion between the rotating fluid and the shell is used to generate a sensitive output signal. The other is to use the Coriolis acceleration of the fluid system to generate a sensitive output signal.

1.1 Gas convection gyroscope

Figure 1 is a microfluidic gyroscope designed by Tsinghua University and processed by the 13th Institute of China Electronics Group. It uses the principle that the direction of gas flow velocity deflects under the action of Coriolis acceleration and is made using micromachining technology. This microfluidic sensor consists of an insulated cavity, a heater and two pairs of symmetrical temperature sensors. The heater and the temperature sensor are suspended above the cavity. The heater heats the surrounding gas to increase its temperature and reduce its density. Under the action of gravity acceleration, the gas in the cavity convects. A pair of temperature sensors located at equal distances from the heater are used to measure the temperature difference on both sides of the heater. The device is encapsulated in a sealed insulated tube shell to prevent the influence of external airflow and temperature on the device. When there is no Coriolis acceleration in the sensitive direction, the heated gas in the cavity convects only under the action of gravity acceleration, such as the temperature at equal positions on both sides of the heater in the horizontal direction is equal, and the outputs of the two pairs of temperature sensors are equal. When there is Coriolis acceleration in the sensitive direction, the gas in the cavity expands alternately under the combined action of gravity acceleration and external angular velocity, and a temperature difference appears at equal positions on both sides of the heater, and the outputs of the two pairs of temperature sensors differ. If the two pairs of temperature sensors use thermistors, they can form a resistance bridge with two pairs of external reference resistors, so that the value of the external input angular velocity can be measured by the change of the output voltage signal of the bridge.



1.2 Jet micro-gyroscope

The jet gas gyroscope uses the airflow beam (laminar flow) of forced convection gas and the thermal resistance effect of the sensitive element to measure the angular velocity. At present, there are not many jet micro-gyroscopes made using MEMS technology. The reported jet gas micro-gyroscopes are mainly composed of piezoelectric drive pumps, circulating airflow channels and chambers, micro-nozzles and thermal sensitive elements. It has a simple structure, no active detection mass, strong overload resistance, low cost and long life. It was invented based on the Coriolis force theorem. It drives the gas circulation through a piezoelectric pump. When the gyro has an angular velocity signal input, the Coriolis force is used to deflect the circulating gas flow beam to achieve the measurement of angular parameters. The circulating gas flow is a gas laminar flow beam (jet) generated by the excitation of the piezoelectric pump. The signal is sensed by two parallel thermistors R1 and R2. When the input angular velocity is ∞, due to the action of the Coriolis force, the jet beam deviates from the center position of the original cavity (see Figure 2). The angle and direction of the deviation are determined by the input angular velocity. In this way, the corresponding acceleration value can be measured by measuring the change in the voltage of the peripheral circuit.



The traditional gyro uses the fixed axis and precession of the high-speed rotor to sense the angular velocity, while the jet gyro uses the deflection of the gas flow beam under the action of inertial force to sense the angular velocity. Since the mass of the gas is very small and there are no rotating parts, the piezoelectric jet gyroscope can withstand high impact and has advantages that other gyroscopes cannot match, such as long life and low cost. Piezoelectric jet gyroscopes can be used in missiles, aircraft, ships, industrial automation, robots and other technical fields. They are key components for measuring and controlling angular parameters such as angular velocity, angular acceleration and angle. They are also indispensable inertial devices for terminally guided projectiles and robot attitude control.

1.3 ECF fluid gyroscope

ECF (electro-conjugate fluid) fluid is a new type of fluid material. When a voltage of several thousand volts is applied to the electrodes at both ends of the fluid, the ECF fluid can generate a strong flow. This characteristic of the ECF fluid can be used to make a fluid gyroscope based on ECF. The fluid gyroscope made by Tokyo Institute of Technology in Japan is shown in Figure 3. Its basic principle is as follows: the container is filled with ECF liquid. When a voltage of more than a thousand volts is applied to the electrodes as shown in Figure 3, a strong ECF liquid impact flow will be generated and flow in the direction shown in Figure 3 (a). When the gyroscope is given an angular velocity that rotates clockwise as shown in Figure 3 (b), the flow of the ECF will shift to the left. The flow change of the left and right fluids causes the thermal resistance value of the top to change, and then the change of the external voltage value can be detected. By measuring the change of the external voltage, the value of the external input angular velocity can be measured.



The characteristics of ECF fluids have opened up new avenues for the study of fluid gyroscopes, but the high voltage used in ECF fluid gyroscopes may limit their application scenarios. Trying to find new ECF materials or taking other approaches to reduce the voltage value used is the key to expanding the application of ECF fluid gyroscopes.

1.4 Superfluid gyroscopes

The study of superfluid gyroscopes is based on a low-temperature physical effect, superfluid. The gyroscopes using superfluids. The design of its working principle, feasibility verification, and the determination of its accuracy level all require a lot of exploratory theoretical research and experimental analysis. However, because the unique physical properties of superfluids have good potential for maintaining inertia, researchers are actively carrying out related work to develop inertial gyroscopes based on superfluids. Since the flow of superfluids can basically be considered to have no resistance, when the carrier container moves tangentially with it, the superfluid will not follow the movement due to the viscosity of the liquid like a normal fluid, but will maintain its original state. In other words, low resistance makes it possible to present very good inertia for rotation. In this way, relative flow occurs between the superfluid and the carrier container, and the information of the rotation speed can be obtained by detecting the movement speed or its amplification.

Since the viscosity coefficient of superfluid is very low, the damping of fluid movement and fluid movement around it is very small, and it has good inertia. The inertial navigation system requires the gyroscope to maintain a good inertial system. The detection of angular velocity using the superfluid effect has a performance potential far higher than that of conventional gyroscopes in principle, and is suitable for all kinds of occasions that require high-precision gyroscopes. However, since research in this direction has just begun, there are still many immature links. How to combine the principle with practical applications, explore more effective high-precision solutions, and improve supporting technologies to reduce manufacturing costs and reduce volume and weight are all issues that need further research.

2 Conclusion

This paper introduces several common MEMS microfluidic gyroscopes based on the different principles of microfluidic gyroscopes, and briefly introduces their basic principles, advantages and disadvantages, and application prospects. These MEMS microfluidic gyroscopes have unique advantages such as small size, light weight, low cost, and high impact resistance, making them more suitable for application in inertial navigation, automatic control and other related fields, and therefore have broad application prospects. With the development of micro-electromechanical technology and the application of new materials, the types of fluid gyroscopes will be further diversified, and microfluidic gyroscopes will play an increasingly important role in inertial navigation and automatic control.