Fiber Accelerometer Based On Frequency Modulation

Optical fiber accelerometer is a kind of optical fiber sensors essentially, which is used to measure accelerations of objects. The accurate measurement of accelerations often play a very important role whether in the automotive industry, aerospace industry or military industry. Optical fiber accelerometers can just meet those needs. Compared with the common electronic and mechanical accelerometers, fiber optic accelerometers have many advantages, such as superior ability to resist electromagnetic interference, light weight and small volume, water resistant, high temperature resistant, corrosion resistant, low transmission loss and large transmission capacity, high response speed and so on. They almost have satisfied us all the requirements and standards. These unique advantages have been widely researched and rapidly developed since it was put forward for the first time in 1980. There have been hundreds type of optical fiber accelerometers until now. The basic principle of fiber optic accelerometers is to make a block which quality is M do variable motion in inertial space. Then use sensors to perceive the motion when an inertia force or displacement happen. The acceleration can be measured when we get the inertia force or displacement. However, there are still many problems of fiber optic accelerometers which need to overcome in the future, such as, the stability is easily affected by the light source power; the phase demodulation method which is the most common method can be vulnerable to environmental interference because of its high sensitivity; Some excellent fiber optic accelerometers cannot be put into production just because the cost is huge. Sometimes what we need is an instantaneous acceleration but the sensor usually give us an average acceleration. A kind of fiber Michelson accelerometer based on frequency modulation is designed in this paper. The phase modulation is converted to frequency modulation. To solve those problem of fiber optic accelerometers, we propose some new adjustment and improvement which are analyzed and validated from theory and experiment.The main content of this article is divided into the following four parts.Chapter one mainly introduces the technology principle and development status of fiber optic sensors, including classification, application, different types and different characteristics of them. Then the background of fiber optic accelerometer research is explained in detail. The existing problems of fiber optic accelerometers are summarized. Innovations of fiber Michelson accelerometer based on frequency modulation are proposed.Chapter two mainly introduces optical fibers, including the structure, classification and characteristics of fibers; The application of total reflection principle; Deducing the transmission characteristics and the interference characteristics of light waves in fibers theoretically; Introducing the strain effect of fibers though the photoelastic effect and poisson effect. All these analyses set a concrete foundation for the research and study in later chapters.Chapter three mainly introduces the principle of fiber optic accelerometer and related theoretical basis. Put fiber optic accelerometers into different types and emphatically introduces the principle of Michelson fiber optic accelerometer and its development. The output and the phase difference formulas of interference light waves of optical fiber Michelson interferometer is obtained by theoretical derivation. All of those lay establishes foundations for the following chapters.Chapter four mainly introduces the theoretical analysis and experimental research of Michelson accelerometer based on frequency modulation. A new system of fiber interferometer is demonstrated and a new type of sensing elements is designed in this chapter. According to the theory of light interference in optical fibers and some mechanical basic theory, the theoretical formula between sensitivity and modulated frequency is derived and verified by experiment. A kind of reticular fiber optic sensor is designed based on that. The formula between sensitivity and modulated frequency is obtained in theory and will be verified in the next working.