Signal Demodulation Algorithm Research Articles

Optical fiber weak magnetic sensing system based on strip-ring sensing structure and PGC-Improved algorithm

The detection of weak magnetic fields is integral to applications in geophysical monitoring, biomagnetism, and remote sensing. This paper presents a new sensing unit structure and signal demodulation algorithm for optical fiber weak magnetic sensing system. The system uses a strip-ring sensing unit structure that combines magnetostrictive effects with optical fibers through 3D printing technology. This integration facilitates the conversion of magnetostrictive displacement into optical phase. An improved Phase Generated Carrier (PGC) algorithm is employed to demodulate the phase information, enhancing the signal to noise ratio (SNR) by 4.33 dB compared to the traditional PGC algorithm, and achieving a phase resolution of 29.51 µrad/Hz1/2 at 500 Hz. Experimental results demonstrate that the suggested sensing system can detect a minimum magnetic field of 140 nT, with an AC magnetic field phase resolution of 15.78 nT/Hz1/2 at 500 Hz. The demodulation sensitivity reaches 1.87 × 10−6 rad/nT under a magnetic field of 140–1400 nT. The capability of the proposed system demonstrated great potential as an efficient approach for detecting weak magnetic signals in many practical applications.

Improved Sensorless Control Strategy for IPMSM Using an ePLL Approach With High-Frequency Injection

This paper proposes an improved sensorless control strategy for interior permanent magnet synchronous motor (IPMSM) using high-frequency (HF) rotating signal injection method in the stationary reference frame. Conventional HF rotating signal injection methods face the problems of long convergence time and poor stability, due to the filters used in signal demodulation process. Therefore, an improved signal demodulation algorithm based on an enhanced phase-locked loop (ePLL) is proposed in this paper. This method improves the stability and dynamic response of the system by eliminating additional filters and reducing the resulting delays. This ePLL, in addition to estimating the phase angle of sinusoidal signal, which contains the rotor position inside it, estimates its amplitude. It is shown that the proposed method has a high robustness against the uncertainties of the motor inductances. The proposed sensorless control method is verified by experiments on a 1.8-kW IPMSM drive platform.

Variable-Angle Random High-Frequency Voltage Injection Strategy with Cross-Saturation Effect Compensation for Sensorless Synchronous Reluctance Motor Drives

There are usually noise problems when the position sensorless control of a synchronous reluctance motor (SynRM) is carried out by high-frequency (HF) signal injection method. Due to the special structure, the cross-saturation effect of the SynRM is particularly serious, resulting in reduced position observation accuracy. In this paper, a variable-angle random HF voltage injection strategy with cross-saturation effect compensation is proposed for position sensorless SynRM drives. Random number generation based on the chaotic mapping method is used to generate random HF voltage signals with different frequencies for injection; the current power spectral density (PSD) distribution is extended and the HF noise can be reduced. A control strategy based on variable-angle square-wave injection is proposed to suppress the cross-saturation effect. By measuring the position error curves of different loads off-line and polynomial fitting the curves, the position error is achieved by combining with the corresponding signal demodulation algorithm. The proposed method does not require additional hardware resources and can maintain high control accuracy and robustness. Finally, the effectiveness of the proposed sensorless control strategy is verified on a 3 kW SynRM experimental platform.

Optical Interferometric MEMS Accelerometers

AbstractLaser interferometry is one of the most accurate measurement technologies whose displacement resolution can reach the femtometer (fm) level. With the development of Micro‐Electro‐Mechanical Systems(MEMS) technology, many excellent optical interferometric MEMS sensors have emerged, which play an essential role in intelligent manufacturing, aerospace, and many other fields. Among them, optical interferometric MEMS accelerometers develop rapidly due to their high sensitivity, low noise, and anti‐electromagnetic interference advantages. Lots of research in optical interferometric chip design, micro‐nano fabrication process, signal demodulation algorithm, and range extension technology are performed, and different types of MEMS accelerometers based on the optical interferometric principles are developed, which have been demonstrated and applied in the fields of disaster monitoring, equipment operation and maintenance, and resource exploration. This paper reviews the development status of optical interferometric MEMS accelerometers, mainly focusing on the critical problems and solutions that need to be solved in the development process of optical interferometric accelerometers, and finally introduces the typical application scenarios.

Primary Low-g Shock Acceleration Calibration Using Laser Interferometry

The current situation of low g shock is introduced with three types of shock exciters described. The measuring theory and system set-up using laser interferometry is explained in accordance with ISO 16063-13 with the emphasis on key technology of signal demodulation algorithm and air-bearing shock exciter based on collision. According to calibration results, the primary shock calibration system can achieve expanded uncertainty of 1%,k=2, in the acceleration range from 20m/s2 to 10000m/s2 and pulse duration from 0.5ms to 10ms.

Sensorless Control of IPMSM Using Moving-Average-Filter Based PLL on HF Pulsating Signal Injection Method

As for the sensorless control of interior permanent magnet synchronous motor (IPMSM), conventional high frequency (HF) pulsating signal injection method is widely used, which uses band-pass filter (BPF) and low-pass-filter (LPF) based phase-locked-loop (PLL), however it may face the problems of poor stability and long convergence time. Therefore, an improved signal demodulation algorithm based on moving-average-filter (MAF)-PLL is proposed. MAF, which makes full use of the HF signal periodicity and half-wave symmetry, has higher bandwidth and better harmonics suppression ability than BPF or LPF. Furthermore, a proportional-integral (PI) regulator is used to gain the rotor speed and an integrator is applied to estimate rotor position. Compared with the conventional method, the proposed method gets rid of BPF and LPF, contributing to improving the stability and dynamic performance. Besides, undetermined parameters are reduced to one, i.e., window length of MAF, avoiding complex parameters design and selection. The proposed HF pulsating injection method has simpler signal demodulation process and is easy to implement. Finally, the experimental results have verified the feasibility and effectiveness of proposed method.

Signal Analysis, Signal Demodulation and Numerical Simulation of a Quasi-Distributed Optical Fiber Sensor Based on FDM/WDM Techniques and Fabry-Pérot Interferometers.

In civil engineering quasi-distributed optical fiber sensors are used for reinforced concrete monitoring, precast concrete monitoring, temperature monitoring, strain monitoring and temperature/strain monitoring. These quasi-distributed sensors necessarily apply some multiplexing technique. However, on many occasions, two or more multiplexing techniques are combined to increase the number of local sensors and then the cost of each sensing point is reduced. In this work, a signal analysis and a new signal demodulation algorithm are reported for a quasi-distributed optic fiber sensor system based on Frequency Division Multiplexing/Wavelength Division Multiplexing (FDM/WDM) and low-precision Fabry-Pérot interferometers. The mathematical analysis and the new algorithm optimize its design, its implementation, improve its functionality and reduce the cost per sensing point. The analysis was corroborated by simulating a quasi-distributed sensor in operation. Theoretical analysis and numerical simulation are in concordance. The optimization considers multiplexing techniques, signal demodulation, physical parameters, system noise, instrumentation, and detection technique. Based on our analysis and previous results reported, the optical sensing system can have more than 4000 local sensors and it has practical applications in civil engineering.

Railway monitoring system using optical fiber grating accelerometers

Optimal operation, reduced energy consumption, longer service availability, and high safety level are the major concerns in today’s railway transport systems. Smart monitoring systems should address these issues without interrupting railway operability. Many successful works have been carried out to provide railway monitoring functions using fiber Bragg grating (FBG) sensors on rail. Most of them are based on strain measurement due to the train passage. This paper presents a highly sensitive means for railway monitoring based on vibration measurement. FBG accelerometers placed on sleeper have been employed as sensor heads, which significantly facilitated the field sensor installation work compared to the positioning on the foot of the rail. An optimized signal demodulation algorithm has been effectively used to extract from the accelerometer traces both the axle number and the average speed information. Excellent capability of the developed system to obtain both parameters has been demonstrated by the way of field trials carried out on a Belgian railway line, during its normal operation. Easy installation, multi-function diagnosis, good data integrity, and compatibility with fiber optic sensors make the proposed sensor a good candidate for railway monitoring applications.

Signal demodulation research of a frequency output resonant gyroscope based on instantaneous frequency analysis

Signal demodulation method of a frequency output resonant gyroscope is studied in this study. It has been a major problem of frequency micro gyroscopes. The detection elements of frequency gyroscopes are two double-ended tuning forks (DETF). The vibratory response of DETF is a periodic signal modulated by both amplitude and frequency. According to the characteristic that the amplitude and frequency of the gyro signal vary continuously with time, the signal demodulation algorithm is designed based on instantaneous frequency analysis. Hilbert transform is used to solve the instantaneous frequency. The algorithm is programmed in digital signal processor (DSP) and a test circuit board is made. Experimental test demonstrates that the demodulation circuit has a high precision and linearity, and the correlation coefficient between input signals and demodulation results achieves as much as 0.99999998. The demodulation method is proved to be feasible. This study provides a new train of thought for the study of the signal demodulation method of frequency micro gyroscopes and brings a new direction for the signal analysis of resonant sensors.

Demodulation algorithm design of VHF data broadcast signal

In order to enhance the performance of the synchronization and demodulation,a Very high frequency(VHF) Data Broadcast(VDB) signal demodulation algorithm based on the solution of differential equation was proposed.This algorithm eliminated the synchronization performance deterioration caused by the frequency offset.And frame synchronization,bit synchronization,frequency offset estimation and correction could be completed within a single set of synchronization symbols.The simulation results show that the method is effective to enhance the VDB signal demodulation performance.

Research on Fiber-Optic Strain Signal Processing Based on Demodulation Technique

A higher performance signal processing module is demanded because of the high sensitivity of fiber-optic sensor probe. Excellent signal processing module is expected have the function of restore the sensor signal and very little to the introduction of noise. In this paper, improved demodulation algorithm is proposed based on the general demodulation algorithm through changing certain parameters of the algorithm aimed to improve the quality of the signal after demodulation. The output signals of scene sensor probe is sampling, sampling data through filtering. By using the improved fiber optic sensor signal demodulation algorithm, the system can fully improve the quality of the signal after demodulation under the premise of maintains the minimum sampling rate.

Special Issue of Photonic Sensors for Chemical, Biological, and Physical Parameter Detection

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A polarimetric glucose sensor using a liquid-crystal polarization modulator driven by a sinusoidal signal

Rather than using a conventional Faraday modulator, this study adopts a liquid-crystal based rotator to modulate the azimuth of the linear polarized light in a sinusoidal signal for the measurement of glucose concentrations. The tilt angle of the LC director would vary as a sinusoidal-like function; however the modulating frequency in the sensing system is the double of the driving signal. A new signal demodulation algorithm, therefore, is developed that enables the polarization rotation angle corresponding to the glucose concentration to be derived. The standard deviation in rotation angle level of 0.00551° has been obtained, with a 0.998773 correlation coefficient between the reference and the measured values. The proposed measurement method has a minimum resolvable concentration of 0.2g/dl. Compared to its conventional counterparts, the developed polarimeter potentially has a simpler structure, fewer optical elements, and a cheaper modulator component.

Fiber temperature sensor for high-pressure environment

We describe a fiber optic extrinsic Fabry-Perot interferometer EFPI based temperature sensor that incorporates a pressure isolation fixture. The sensor has high temperature sensitivity and low pressure- induced crosstalk. The detailed analysis and discussion of the sensor design, the signal demodulation algorithm, and the sensor fabrication as well as the sensor performance are presented. © 2005 Society of Photo-Optical