Subject of Research. The paper presents the study of a graphite-epoxy composite plate strain detection possibility by the fiber-optic acoustic emission sensor mounted on its surface. Method. The proposed method consisted in additional lowfrequency phase-generated carrier implementation in the impulse Fabry-Perot interferometer and its amplitude evaluation. The phase-generated carrier amplitude depends on the interferometer optical path difference, therefore, its value change can be used for the studied composite strain estimation. VCSEL with a wavelength of 1550 nm was used as a light source. The phase carrier was generated by current modulation of the light source that caused center wavelength shift of the VCSEL. Main Results. The low-frequency phase-generated carrier signal amplitude dependence on the interferometer optical path difference and wavelength shift of the light source were obtained. According to simulation results the sensitivity of the proposed method is 1.6 urad×ppm, 5.3 urad×ppm and 13.3 urad×ppm at different values of the coefficient Kd 30, 100 and 250 pm, respectively. Experimental study of the proposed method and results analysis were performed. According to experimental results, the accuracy of the proposed method was about 110% that corresponds to the sensor relative stretch of 10 e, while the accuracy of the market available fiber optic systems based on fiber Bragg grating sensors equals to 4 ppm. Practical Relevance. The proposed method can be used for strain detection of the graphite-epoxy composite constructions along with its acoustic emission control by one fiber-optic sensor.

http://cyberleninka.ru/article/n/osobennosti-vremennyh-parametrov-transmitralnogo-diastolicheskogo-potoka-pri-serdechno-sosudistoy-patologii.pdf

Особенности временных параметров трансмитрального диастолического потока при сердечно-сосудистой патологии

Abstract The purpose of this study was to clarify the silicon-germanium dioxide (SiGeO2) and Aluminum Indium Gallium Arsenide (AlInGaAs) based acoustic optic modulators for upgrading transmission performance characteristics. The transient time response of these modulators is analyzed and discussed in detail. The 3-dB modulation signal bandwidth, diffraction signal efficiency, signal rise time, and signal quality factor with minimum data error rates are also considered. The proposed models with silicon-germanium dioxide and Aluminum Indium Gallium Arsenide acoustic optic modulators were compared to the previous model with silicon acoustic optic modulators. The results confirmed the high-performance efficiency of the proposed models when compared to the previous model, in both the lowest transient time response and the highest acoustic optic modulators speed response.

/pdf/silicon-germanium-dioxide-and-aluminum-indium-gallium-3y46a6hobq.pdf

Silicon-Germanium Dioxide and Aluminum Indium Gallium Arsenide-Based Acoustic Optic Modulators

Phase generated carrier (PGC) demodulation schemes are widely used in fiber-optic interferometric sensors. All known PGC schemes use carrier signals to obtain in-phase and quadrature components from the interference signal. The unwanted phase delay between the reference carrier signal and the modulation signal in the interference signal might exist. This effect might lead to the incorrect measurement of the phase signal in the PGC scheme. In this paper, the original PGC demodulation scheme with the carrier phase delay compensation based on the basic PGC-Atan scheme is presented. The proposed scheme provides the real-time carrier phase delay compensation over the all possible phase delay range from 0° to 360° without using phase adjustments of the carrier signal. Theoretical analysis and mathematical modeling of the proposed scheme and the basic PGC-Atan demodulation scheme were performed to compare their performance under the same conditions. The proposed scheme, the basic PGC-Atan demodulation scheme, and the PGC synchronous carrier restoration scheme were implemented in the FPGA-based electronic processing circuit of the single interferometric fiber Bragg grating sensor. Experimental results showed that the proposed scheme provides carrier phase delay compensation without using phase adjustments of the carrier signal.

PGC-Atan Demodulation Scheme With the Carrier Phase Delay Compensation for Fiber-Optic Interferometric Sensors

Fiber-optic interferometric sensors (FOISs) are widely used in seismometers, hydrophones, and gyroscopes. The arctangent approach of phase-generated carrier (PGC-Arctan) demodulation algorithm is one of the key demodulation techniques in FOISs. The conventional PGC-Arctan demodulation algorithm requires the specific value of the phase modulation depth C to work properly. However, C will variate with laser wavelength, temperature, and humidity in the actual working environment, which leads to harmonic distortion and even demodulation failure. In this paper, a novel PGC demodulation algorithm called self-calibration PGC-Arctan (PGC-Arctan-SC) demodulation algorithm is presented. The proposed algorithm can jointly estimate the accurate C value by the elliptical parameters and C-related components while suppressing nonlinear distortion by ellipse fitting algorithm (EFA). Then C can be calibrated to the specific predefined optimal value by the closed-loop proportion integration differentiation (PID) module. The simulation results are consistent with theoretical analysis, and the all-digital PGC-Arctan-SC demodulation system is implemented on the embedded SoC. The experimental results show that C can be estimated and calibrated accurately in real time. The signal-to-noise and distortion ratio (SINAD) of the PGC-Arctan-SC demodulation output achieves 61.57 dB.

Real-time self-calibration PGC-Arctan demodulation algorithm in fiber-optic interferometric sensors.

Fiber-optic interferometric sensing is a very attractive approach for creating lightweight, high-sensitive, and fully passive fiber-optic hydrophone arrays. In this paper, results of sea trials of the thin cable fiber-optic hydrophone array for passive acoustic surveillance applications are presented. The performed trials consisted of two parts: the first part was devoted to the estimation of the array acoustic performance and the second part included the direction of arrival (DOA) estimation of the moving acoustic source. The estimation of the array acoustic performance showed that the average measured pressure sensitivity of fiber-optic hydrophones increased as the acoustic frequency increased from −122 dB re rad/ $ {\mu }$ Pa at 20 Hz to −116 dB re rad/ ${\mu }$ Pa at 495 Hz. The average minimum detectable pressure of hydrophones decreased from 78, 1 dB re $1~{\mu }$ Pa at 20 Hz to 28, 5 dB re $1~{\mu }$ Pa at 495 Hz. Obtained values of the minimum detectable pressure were below the sea state zero noise level in the considered frequency range. The average dynamic range of fiber-optic hydrophones was above 120 dB at 495 Hz. The proper capability of the DOA estimation was successfully demonstrated using the motor boat as the moving acoustic source. Trajectories of the moving boat were obtained by using the beamscan DOA estimation algorithm with additional Kalman filtering. Obtained results demonstrated the great potential of using fiber-optic interferometric sensors for hydroacoustic surveillance applications. The presented results might be helpful for the implementation of extended fiber-optic hydroacoustic surveillance systems.

Thin Cable Fiber-Optic Hydrophone Array for Passive Acoustic Surveillance Applications

Phase generated carrier (PGC) demodulation schemes are widely used in fiber-optic interferometric sensors Basic PGC schemes required the certain value of the phase modulation depth to work properly In this paper, a novel phase modulation depth evaluation and correction technique for PGC demodulation schemes based on the integral control feedback is presented The proposed scheme provides the phase modulation depth stabilization to the certain predefined optimal value Detailed theoretical analysis and mathematical modeling of the proposed scheme and the PGC-Atan demodulation scheme were performed to estimate their required parameters The suggested technique with the PGC-Atan demodulation scheme was implemented in the field-programmable gate array-based electronic processing circuit of the single interferometric fiber Bragg grating sensor Experimental results are consistent with theoretical analysis and the proposed scheme provides real-time stabilization of the phase modulation depth to its optimal value 263 rad with the standard deviation less than $5\ast 10^{-4}$ rad

Phase Modulation Depth Evaluation and Correction Technique for the PGC Demodulation Scheme in Fiber-Optic Interferometric Sensors

A lithium niobate (LN) phase modulator is widely spread because ofhigh electro-optic coefficients. Particularly, it is a highly required component for a closed-loop fiber-optic gyroscope (FOG) of navigation and tactical grade. However, low-frequency distortions of LN phase modulator frequency response can degrade the FOG performance. This paper deals with the research and compensation of frequency response of an LN phase modulator. It is a complex task to measure the response of the LN phase modulator in a FOG because of its Sagnac interferometer. Therefore, the special and novel modulation/demodulation algorithm is proposed. To the best of our knowledge and belief, the proposed method is the first published method that provides the measurement of the pulse response of a phase modulator as a part of a closed-loop FOG. The pulse response obtained in the proposed way allows getting appropriate high order transfer function of a phase modulator. For the first time to the best of our knowledge, the humidity dependence of the LN phase modulator frequency response is found. Influence of the phase modulator frequency response on FOG angular random walk, bias drift, and scale factor nonlinearity and instability is theoretically analyzed and mathematically simulated. The algorithmic method of the phase modulator response compensation is proposed and experimentally confirmed. The experimental results show that the proposed measurement technique of the phase modulator transfer function allows creating the compensating inverse filter that provides phase modulator response being close to flat. The application of the proposed method in the FOG operating mode allows reducing unwanted spikes to the noise level.

Research and Compensation of Frequency Response of LiNbO 3 Phase Modulator for High-Performance Fiber-Optic Gyroscope

The investigation is devoted to residual amplitude modulation (RAM) of phase electro-optic modulator, which guides are made in LiNbO3 crystal by Ti diffusion technology. An analysis is presented that shows influence of RAM on the signal of fiber-optic gyroscope. The RAM compensation method is offered.

https://iopscience.iop.org/article/10.1088/1742-6596/735/1/012040/pdf

An investigation of the influence of residual amplitude modulation in phase electro-optic modulator on the signal of fiber-optic gyroscope

The electro-optical modulator is one of the most important parts of the fiber optic gyroscope. Unfortunately, the integral implementation of the modulator has a number of undesirable effects such as parasitic amplitude modulation, phase drift, and acousto-optical resonance effects. Influence of the first two effects on the gyroscope operation has been described in a number of works, but at the moment, there are no published papers aimed at investigating the relationship between the presence of acousto-optic resonances in modulators and changes in the performance of a fiber optic gyroscope. There are several design solutions that provide damping of undesired acoustic waves in electro-optical modulators. However, the use of these solutions requires a method to estimate their effectiveness. The main purpose of the article is to describe such a method and to evaluate the correctness of its application. We also offer an additional way to reverse the effect of the mentioned resonant effects on the characteristics of the fiber gyroscope.

Influence of Acousto-Optic Resonances in Electro-Optical Modulator on Fiber Optic Gyro Performance and Method for Its Compensation

Fiber optic components, such as fiber optic interferometers, fiber sensors and fiber lasers have high level of sensitivity to environmental acoustic and vibration noise due to elasto-optical effect and fiber elongation under pressure. For most applications this effect is undesirable and it should be reduced for proper operation of fiber optic system. The proposed method for reducing the fiber components environmental noise sensitivity level is based on the implementation of two-layer protective construction. The experimental test confirmed its effectiveness of undesirable impact suppression at the level from -3.2 to -19 dB relatively to the acoustic sensitivity level of bare optical fiber sample. The effectiveness appeared to be directly proportional to the acoustic pressure level. This fact allows us to implement proposed construction as an acoustic shock absorber or an acoustic filter with external impact level dependent transfert characteristic for sensitive fiber optic components.

Artem S. Aleynik

Papers

Phase Modulation Depth Evaluation and Correction Technique for the PGC Demodulation Scheme in Fiber-Optic Interferometric Sensors

Research and Compensation of Frequency Response of LiNbO 3 Phase Modulator for High-Performance Fiber-Optic Gyroscope

An investigation of the influence of residual amplitude modulation in phase electro-optic modulator on the signal of fiber-optic gyroscope

Influence of Acousto-Optic Resonances in Electro-Optical Modulator on Fiber Optic Gyro Performance and Method for Its Compensation

The Method for Protection of Sensitive Fiber Optic Components from Environmental Noise and Vibration Impacts