5/18/2023 0 Comments Mac uninstall soundflowerThe FITT principle gives athletes a workable approach to designing workout plans that suit their level of fitness. It also helps them to achieve their fitness goals. The benefits of the approach are that it provides for consistency when designing programmes. The laser self-mixing interference (SMI) occurs when a portion of the light emitted by a laser is reflected from an external target and re-enters the laser active cavity, resulting in the modulation of both the amplitude and frequency of the laser oscillating field. The theoretical model of SMI is the theoretical basis of various measurement techniques. The SMI model analysis methods include compound Fabry–Perot cavity and Lang-Kobayashi equations . The SMI model based on the three-mirror cavity model can accurately describe the power of SMI signal. The model contains two important parameters: the optical feedback level factor ( C) and the laser linewidth enhancement factor ( α). These two parameters together affect the waveform of SMI signal and they are important for the displacement reconstruction. Due to the advantages such as high sensitivity and ease of use, the SMI technology is increasingly used in many measurement areas such as distance , velocity ,, angle ,, acceleration , displacement . The displacement measurement methods based on SMI mainly include fringe counting , phase measurement method ,, beat frequency measurement , phase unwrapping. Similar to the traditional laser interference, when the reflecting target moves half wavelength of the light wave, the output power of the laser in the SMI system fluctuates one fringe. Therefore, the displacement of an object can be measured by calculating the number of fringes, but the accuracy of fringe counting method is not high. According to the phase measurement method, the phase of the SMI signal is modulated with external cavity length and demodulated by the Fourier transform analysis technique. With this method, the measurement accuracy of target displacement can reach λ ∕ 50. However, due to the modulation of the current, the output power of the laser will be unstable and the measurement error will increase. Since the optical feedback effect changes the optical frequency of the LD and the offset of the optical frequency is linearly related to the variation of the length of the external cavity. The beat frequency measurement method is to use this relationship to perform displacement measurement.
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