Harmonic Detection Research Articles

Laser Linewidth Analysis and Filtering/Fitting Algorithms for Improved TDLAS-Based Optical Gas Sensor.

Tunable Diode Laser Absorption Spectroscopy (TDLAS) has been widely applied in in situ and real-time monitoring of trace gas concentrations. In this paper, an advanced TDLAS-based optical gas sensing system with laser linewidth analysis and filtering/fitting algorithms is proposed and experimentally demonstrated. The linewidth of the laser pulse spectrum is innovatively considered and analyzed in the harmonic detection of the TDLAS model. The adaptive Variational Mode Decomposition-Savitzky Golay (VMD-SG) filtering algorithm is developed to process the raw data and could significantly eliminate the background noise variance by about 31% and signal jitters by about 12.5%. Furthermore, the Radial Basis Function (RBF) neural network is also incorporated and applied to improve the fitting accuracy of the gas sensor. Compared with traditional linear fitting or least squares method (LSM), the RBF neural network brings along the enhanced fitting accuracy within a large dynamic range, achieving an absolute error of below 50 ppmv (about 0.6%) for the maximum 8000 ppmv methane. The proposed technique in this paper is universal and compatible with TDLAS-based gas sensors without hardware modification, allowing direct improvement and optimization for current optical gas sensors.

Adaptive PI + VPI Harmonic Current Compensation Strategy under Weak Grid Conditions

With the increase of the penetration rate of renewable energy power generation in the power system, the power grid gradually tends to be weak. Under the scenario of nonlinear load connecting to weak power grid, the grid-side voltage will produce unbalance, distortion and frequency deviation due to the influence of large internal impedance, insufficient inertia, three-phase current unbalance and harmonics of weak power grid. The operation of active power filters (APF) under above conditions can lead to significant degradation in harmonic compensation performance. An adaptive proportional integral (PI) + vector PI (VPI) harmonic compensation strategy for a three-phase APF is proposed for use in complex conditions of weak grid. The strategy consists of an adaptive notch filter based synchronous phase-locked loop (ANF-PLL) and an adaptive PI + VPI current control method. In this strategy, a series of adaptive lattice notch filters are introduced to improve the accuracy of grid phase and frequency estimation under the condition of voltage unbalance, distortion and a large range of frequency deviation. Then the phase and frequency information are used in the Park transformation of harmonic detection and current compensation control and the update of PI + VPI current control law parameters. A VPI current tracking controller with adaptive resonant frequency is constructed, which can improve the gain of the resonant frequency point and ensure that the APF can maintain the best compensation performance under the above weak grid conditions. Finally, the simulation and experimental results indicate that the ANF-PLL shows a better phase and frequency estimation performance under complex conditions of weak grid than the conventional and notch filter based methods, and the harmonic compensation strategy presented in this paper achieves a significant performance improvement under complex conditions of weak grid compared with Fixed VPI/SRF-PLL strategy and adaptive VPI/NF-PLL strategy.

The effect of laser repetition rate in second harmonic generation imaging and intensity detection

Here we revealed that lasers with lower repetition rates (5 kHz and 50 kHz) from an amplifier were more efficient in SHG imaging than a laser with high repetition rate (80 MHz) from an oscillator, demonstrating that peak power played a more important role than the repetition rate for high SHG yield. Although lasers with relatively high peak power damaged the cancer cells used in the imaging at a relatively lower laser power, better signal/noise ratio was achieved before the occurrence of the adverse damage. It was also revealed that photobleaching was avoided with the lower repetition rate lasers. Furthermore, the three lasers were applied in analyzing the scattered SHG intensity from colloidal BaTiO3 nanoparticles using photon counting method. All tests with the three lasers reached satisfactory results. Importantly, the lasers with low repetition rates showed great potential in the detection of weak nonlinear scattering.

Harmonics and intermodulation products-based fuzzy logic (HIPBFL) algorithm for vital sign frequency estimation using a UWB radar

The ultra-wide band (UWB) radar can achieve non-contact measurement of human vital sign including respiration and heartbeat. This can be applied in the fields of healthcare, security and search-rescue mission. At present, most studies adopt the relationship between harmonics and fundamental frequency to estimate the frequency of vital sign. In this work, the harmonics and intermodulation products-based fuzzy logic (HIPBFL) algorithm for vital sign frequency estimation is proposed. For the first time, to the best of our knowledge, intermodulation products information is considered to locate possible heart rates. Then a fuzzy logic system is designed to select the optimal heart rate from them. 120 s measurement experiment on human beings was carried out at the hospital. Compared with the commonly used chirp Z-transform and moving target indicator (CZT-MTI), the harmonic multiple loop detection (HMLD) and the variational mode decomposition (VMD), the proposed HIPBFL algorithm obviously improves the estimation accuracy of heart rate. This work paves a way for the investigation of non-contact vital signs monitoring via UWB radars.

Recognition of Whistle-like Signals Based on FM Harmonic Characteristics

While human hearing can easily identify whistle-like sounds made by dolphins and whales, manually identifying them from the increasingly variety and quantity of underwater acoustic signals (such as other marine life sounds and underwater acoustic communication signals) is undoubtedly laborious. To solve this question, a recognition method based on the frequency modulated feature and harmonic characteristic is analyzed in this paper. A harmonic energy analysis algorithm is proposed and is compared to a harmonic detection method. The experimental results prove that the proposed method could identify the whistle-like sounds with an accuracy over 90% and the traditional one could only reach 50%. The recognition method may be applied to the investigation of marine biological habits and the monitoring of marine ecological environment, and can also potentially be further applied to the detection of bionic communication signal.

Leveraging Symmetry for an Accurate Spin–Orbit Torques Characterization in Ferrimagnetic Insulators

AbstractSpin–orbit torques (SOTs) have emerged as an efficient means to electrically control the magnetization in ferromagnetic heterostructures. Lately, increasing attention has been devoted to SOTs in heavy metal (HM)/magnetic insulator (MI) bilayers owing to their tunable magnetic properties and insulating nature. Quantitative characterization of SOTs in HM/MI heterostructures is, thus, vital for the fundamental understanding of charge–spin interrelations and designing novel devices. However, the accurate determination of SOTs in MIs is limited due to low electrical signals and dominant spurious thermoelectric effects caused by Joule heating. Here, a simple method based on harmonic Hall voltage detection and macrospin simulations is reported that accurately quantifies the damping‐like and field‐like SOTs, and thermoelectric contributions separately in MI‐based systems. Experiments on the archetypical Bi‐doped YIG/Pt heterostructure using the developed method yield precise values for the field‐like and damping‐like SOTs, reaching −0.14 and −0.15 mT per 1.7 × 1011 A m−2, respectively. It is further revealed that current‐induced Joule heating changes the spin transparency at the interface, reducing the spin Hall magnetoresistance and damping‐like SOT, simultaneously. These results and the devised methodology can be beneficial for the fundamental understanding of SOTs in MI‐based heterostructures and device designs where accurate SOTs knowledge is necessary.

Locating mutation damage based on the zero-frequency component of nonlinear Lamb waves

Degradation, such as micro-voids, dislocation, persistent bands, and micro-cracks, can give rise to local material nonlinearity and cause early-stage material local damage. The material nonlinearity of a plate can be represented as a distribution function. Depending on whether the nonlinearity distribution function of a plate is smooth or not, early-stage material local damage can be divided into gradual and mutation damage. Gradual damage is usually caused by lattice distortion, and the nonlinearity distribution function is smooth. In contrast, mutation damage is usually induced by a discontinuous interface, and the nonlinearity distribution function is not smooth but stepped. Mutation damage is more harmful than gradual damage. To ensure safety, it is important to locate and evaluate mutation damage. The conventional nonlinear Lamb wave technique has limitations in resolving the location and spatial distribution of mutation damage owing to several reasons. To address these issues, a novel method for locating mutation damage based on the zero-frequency component is proposed in this paper. The theoretical solution of the zero-frequency component generated by the Lamb wave pulse is derived based on certain ideal assumptions. Other complex behaviors of the zero-frequency component can be understood by the contribution of this theory. The region of mutation damage is modeled by enhancing local three-order elastic coefficients, and mutation damage can be located simply and efficiently by using the proposed zero-frequency component-based method. The proposed damage detection based on the zero-frequency component of nonlinear Lamb waves has significant advantages compared to the second harmonic and mixing-wave detection techniques.

Optimization of Photoacoustic Cell for Trace Acetylene Detection in Transformer Oil

This paper presents the development of a highly sensitive gas detection system based on a resonant photoacoustic cell for detecting dissolved gases in transformer oil. A simulation model of the resonant photoacoustic cell was studied and optimized the buffer chamber volume while ensuring signal enhancement. The volume of the photoacoustic cell was reduced by about 80% compared to the classical model. A resonant photoacoustic cell was then fabricated based on the optimized simulation optimization. The dual-resonance photoacoustic system was constructed by combining the resonant PA cell with a handmade cantilever fiber acoustic sensor. The system’s sensitivity was further improved by using an erbium-doped fiber amplifier, wavelength modulation, and harmonic detection technology. The experimental results showed that the system achieved a detection limit of 6 ppb and an excellent linear range under 1000 ppm for C2H2 gas. The developed gas detection system has potential applications for monitoring the condition of power transformers in power grids.

Development of a Stable Oxygen Sensor Using a 761 nm DFB Laser and Multi-Pass Absorption Spectroscopy for Field Measurements.

An optical sensor system based on wavelength modulation spectroscopy (WMS) was developed for atmospheric oxygen (O2) detection. A distributed feedback (DFB) laser with butterfly packaging was used to target the O2 absorption line at 760.89 nm. A compact multi-pass gas cell was employed to increase the effective absorption length to 3.3 m. To ensure the stability and anti-interference capability of the sensor in field measurements, the optical module was fabricated with isolation of ambient light and vibration design. A 1f normalized 2f WMS (WMS-2f/1f) technique was adopted to reduce the effect of laser power drift. In addition, a LabVIEW-based dual-channel lock-in amplifier was developed for harmonic detection, which significantly reduced the sensor volume and cost. The detailed detection principle was described, and a theoretical model was established to verify the effectiveness of the technique. Experiments were carried out to obtain the device's sensing performances. An Allan deviation analysis yielded a minimum detection limit of 0.054% for 1 s integration time that can be further improved to 0.009% at ~60 s. Finally, the reliability and anti-interference capability of the sensor system were verified by the atmospheric O2 monitoring.

Diode Laser Overtone Spectroscopy of Methyl Iodide at 850 nm

Using Tunable Diode Laser Absorption Spectroscopy (TDLAS), 82 CH3I overtone absorption lines were detected for the first time in the range between 11,660 and 11,840 cm−1 (844–857 nm), with strengths estimated around 10−27–10−26 cm/molecule. The lines were measured utilizing commercial heterostructure F–P type diode lasers, multipass cells, and wavelength modulation spectroscopy with the second harmonic detection technique. A high modulation amplitude approach was adopted for the analysis of the line shapes. Self-broadening coefficients were obtained for two lines.

Photoacoustic spectrometry and resonant frequency tracking based dual-mode gas sensor

Photoacoustic spectrometry has excellent advantages in trace gas detection. However, due to the influence of gas saturation absorption, when the gas concentration spikes to a certain level, this technology is difficult to achieve accurate detection. Therefore, a dual-mode gas sensor based on photoacoustic spectroscopy and resonant frequency tracking is developed by the features of both detection technologies. A tunable DFB diode laser in the 1654 nm wavelength range and a loudspeaker are used for the photoacoustic detection, and the resonant frequency tracking, respectively. A resonant photoacoustic cell is used as the sensing element to work in dual-mode by time-division multiplexing technology. The wavelength-modulated photoacoustic detection is enabled in the methane concentration below 30%. When the gas concentration exceeds 30%, it will be automatically switched to the measurement-mode of resonant frequency tracking by the fast Fourier transform. The double-range gas detection is realized by a single sensor with dual-mode detecting functionality. With the wavelength modulation and lock-in harmonic detection method, the minimum detectable limit (1σ) of 3.5 ppm CH4 was demonstrated under the photoacoustic detection mode. The response time of the sensor is about 10 s within the measurement range of double-range.

A novel Ethernet based processing system for remote source harmonic detection

This work is carried out to objectively establish a new method to detect harmonics and measure the total harmonic distortion (THD) in a remote source, such as a high voltage transformer. The proposed approach utilized embedded design techniques to construct an embedded processor system with Ethernet intellectual property core to acquire data from a remote harmonics source. The designed system has several notable merits, namely, it is portable that can be applied in the work field, and it avoids workers from being subject to a hazard high voltage shock as well as its simplicity and high accuracy. The harmonics detection and analysis are achieved by inserting a microcontroller system near the high voltage transformer to acquire the necessary data and transmit it to a remote embedded processor system that is used to detect and analyze the harmonics. The microcontroller and the processor systems are connected by a wide-area network (WAN) through Ethernet and transmission control protocol/internet protocol (TCP/IP) protocols. The processor system is accommodated to perform 128 points fast Fourier transform for harmonics detection. Matlab simulations are used to validate the results. It is found that the results match very accurately the simulation results with an error of less than 0.02%.

Highly Sensitive Capacitive MEMS for Photoacoustic Gas Trace Detection.

An enhanced MEMS capacitive sensor is developed for photoacoustic gas detection. This work attempts to address the lack of the literature regarding integrated and compact silicon-based photoacoustic gas sensors. The proposed mechanical resonator combines the advantages of silicon technology used in MEMS microphones and the high-quality factor, characteristic of quartz tuning fork (QTF). The suggested design focuses on a functional partitioning of the structure to simultaneously enhance the collection of the photoacoustic energy, overcome viscous damping, and provide high nominal capacitance. The sensor is modeled and fabricated using silicon-on-insulator (SOI) wafers. First, an electrical characterization is performed to evaluate the resonator frequency response and nominal capacitance. Then, under photoacoustic excitation and without using an acoustic cavity, the viability and the linearity of the sensor are demonstrated by performing measurements on calibrated concentrations of methane in dry nitrogen. In the first harmonic detection, the limit of detection (LOD) is 104 ppmv (for 1 s integration time), leading to a normalized noise equivalent absorption coefficient (NNEA) of 8.6 ⋅ 10-8 Wcm-1 Hz-1/2, which is better than that of bare Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS), a state-of-the-art reference to compact and selective gas sensors.

Research on Harmonic Management of Single-Phase AC Charging Pile Based on Active Filtering

Nowadays, AC charging piles are widely used, and with the increasing number of charging piles, the harmonic pollution generated by them becomes more serious and affects the power quality of the grid. Aiming at the problem of harmonic control of the single-phase AC charging pile, it is decided to apply the active filter technology. The single-phase parallel active filter (PAPF) is selected according to the characteristics of the charging pile. The single harmonic detection method is studied based on instantaneous reactive power theory, and a new adaptive low-pass filter with fixed-step size is proposed to improve the performance of harmonic detection by combining the least mean square (LMS) and the least fourth-order moment (LMF) adaptive algorithms. The PAPF control part adopts the composite control strategy of inner and outer loop combined with repetitive control to complete the voltage stabilization control, harmonic tracking, and compensation. Based on MATLAB/SIMULINK, the output waveforms of the low-pass filter link are simulated and analyzed, and the prototype experiment is carried out. The results verify that the algorithm can improve the performance of harmonic detection. Finally, the single-phase PAPF system simulation is established and the harmonic compensation capability of system is analyzed by the Fast Fourier Transform (FFT). The results demonstrate that single-phase PAPF can effectively manage harmonics and the total harmonic distortion (THD) is reduced to less than 5%.

An FCS-MPC Strategy for Series APF Based on Deadbeat Direct Compensation

Aiming at the delay caused by the phase-locked loop (PLL) and harmonic detection in the traditional control of a series active power filter (SAPF), a deadbeat direct control (DBDC)-based finite control set model predictive control (FCS-MPC) strategy for the SAPF is proposed in this work. Firstly, a reference voltage generation mechanism based on direct control is established, which avoids the delay in harmonic detection, thus improving the dynamic response performance of the system. Secondly, the reference current generation mechanism suitable for the SAPF is derived and established using the deadbeat control (DBC) in the αβ coordinate system, based on which the FCS-MPC system is constructed. It eliminates the complex coordinate transformation and PLL and effectively compensates for the full-frequency harmonic voltage. Finally, the proposed control strategy is verified by a simulation and an experiment. The results suggest that the proposed control strategy can effectively compensate for the load voltage and suppress harmonic distortion for the temporary swell and sag of the grid voltage, sudden load changes, and harmonic distortion conditions.

Electron Paramagnetic Resonance Implemented with Multiple Harmonic Detections Successfully Maps Extracellular pH In Vivo.

Extracellular acidification indicates a metabolic shift in cancer cells and is, along with tissue hypoxia, a hallmark of tumor malignancy. Thus, non-invasive mapping of extracellular pH (pHe) is essential for researchers to understand the tumor microenvironment and to monitor tumor response to metabolism-targeting drugs. While electron paramagnetic resonance (EPR) has been successfully used to map pHe in mouse xenograft models, this method is not sensitive enough to map pHe with a moderate amount of exogenous pH-sensitive probes. Here, we show that a modified EPR system achieves twofold higher sensitivity by using the multiple harmonic detection (MHD) method and improves the robustness of pHe mapping in mouse xenograft models. Our results demonstrate that treatment of a mouse xenograft model of human-derived pancreatic ductal adenocarcinoma cells with the carbonic anhydrase IX (CAIX) inhibitor U-104 delays tumor growth with a concurrent tendency toward further extracellular acidification. We anticipate that EPR-based pHe mapping can be expanded to monitor the response of other metabolism-targeting drugs. Furthermore, pHe monitoring can also be used for the development of improved metabolism-targeting cancer treatments.

Temperature Measurements by Wavelength Modulation Diode Laser Absorption Spectroscopy with Logarithmic Conversion and 1f Signal Detection

A new version of a sensor for temperature measurements in the case of strong laser intensity fluctuation was developed. It was based on tunable diode laser absorption spectroscopy (TDLAS) with wavelength modulation, logarithmic conversion of the absorption signal, and detection of the first harmonic of the modulation frequency. The efficiency of the technique was demonstrated under experimental conditions with excess multiplicative noise. Temperature was evaluated from the ratio of integrated absorbance of two lines of the water molecule with different lower energy levels. Two algorithms of data processing were tested, simultaneous fitting of two spectral ranges with selected absorption lines and independent fitting of two absorption lines profiles. The correctness of the gas temperature evaluation was verified by simultaneous measurements with a commercial thermocouple. An error in temperature evaluation of less than 40 at 1000 K was achieved even when processing a single scan of the diode lasers.

Error Correction Method of Transformer Harmonic Detection Based on the Improved BP Neural Network

In the case that the harmonic problem has threatened the safe operation of user equipment, the requirements of power quality are constantly improving, and the error correction method of harmonic detection has become a key concern in the field of power. Due to the complexity of the power structure, some of the transformer harmonic detection error correction methods have the defect of too large an error. In this demand, a transformer harmonic detection error correction method based on an improved BP neural network is designed. The open-circuit mode of the damper is converted into the connected mode, and the key parameters of the transformer are obtained. Based on the improved BP neural network, the harmonic voltage content is extracted, and the transfer relationship between the currents is obtained. The reverse propagation path of the fault component is clarified, and the detection error correction method is designed. The experimental results show that the average error rate of the error correction method of transformer harmonic detection is 37. 437%, which proves that it has more advantages in accuracy after combining with the improved BP neural network. The research results not only have high academic value but also help improve the user’s electricity experience.

Harmonic current variation characteristics of shunt capacitors based on full-phase FFT algorithm

Abstract Shunt capacitors can effectively improve the system voltage level and increase the economy of grid operation. However, under the effect of harmonics, the capacitor bank is prone to harmonic resonance, which causes overcurrent and overvoltage and threatens the safe operation of the capacitor itself and the system. To avoid damage to capacitors due to harmonics, the harmonic current variation characteristics of shunt capacitors are investigated. Based on the established mathematical model of shunt capacitors, the characteristics of harmonic current amplification under different harmonic states are analyzed. Based on the amplification characteristics and sampling law, the harmonic current signal is acquired using the full-phase fast Fourier transform algorithm. The full-phase fast Fourier transform algorithm is improved by the phase difference algorithm to complete harmonic current detection. The experiments show that the dynamic response time is 1.6 cycles with minimum steady-state error before and after the load current jump. When the capacitor changes from unit power factor to 0.89 inductance, the harmonic current at point A changes from 17.59A to 21.34A and 11.65 to 22.38A, respectively. The deviation values are 3.75A and 10.73A, respectively. It shows that the algorithm has good tracking ability for load currents and can effectively detect the harmonic currents of shunt capacitors and obtain accurate variation characteristics. It can ensure that the harmonic content of the shunt capacitor in the distribution system is relatively reasonable, and realize the safe, stable and economic operation of the equipment.

Waveform Correlation Based Harmonic Voltage Contribution Determination of Iron and Steel Plants Supplied From PCC

This paper presents a new waveform correlation based method which determines the individual harmonic voltage contributions of Electric Arc Furnace (EAF) plants supplied from a point of common coupling (PCC). The method is based on the waveform correlation computations between the PCC voltage and the feeder current at the individual harmonic frequency. PCCs supplying multiple EAF plants usually suffer from high voltage harmonic components due to their operation principles. A relationship between the correlation coefficient of the PCC voltage and the feeder current waveforms, and the harmonic voltage contribution of each plant is derived and this relationship is used to derive the individual contributions to the PCC voltage. The main idea of the method is based on the fact that harmonic voltage at the PCC is a result of the additive effect of voltage drops on the source side impedance of the power system caused by the individual feeder currents. No real-time impedance measurements are required in the proposed method and no need for the measurements of the other feeders to compute the contribution of a specific feeder in contrast to some previously proposed methods for the same problem. The proposed method is further expanded in order to reveal the effects of the compensation systems of the EAF plants, which identifies the harmonic current sinking problem of a victim plant with a powerful compensation system using further correlation computations between the feeder currents and in-plant current measurements. The proposed method can be easily adapted as a real time harmonic contribution detection tool for the already-installed power quality analyzers, most of which employ synchronized voltage and feeder current waveform measurements.