Anti-electromagnetic Interference Research Articles

A dual-channel microwave photonic mixer with large dynamic range

A microwave photonic mixer has the advantages of large transmission bandwidth, good frequency tunability, high isolation, and anti-electromagnetic interference. For the practical application of the multi-input multi-output (MIMO) communication system, a dual-channel, large dynamic range microwave photonic mixer is proposed in this paper. By controlling the bias angle of the modulator and applying a dual-polarization coherent receiver, the quadrature modulation and demodulation of the dual-channel radio frequency (RF) signal is realized. By constructing a heterodyne polarization light source and adjusting the laser power difference, the third-order intermodulation distortion (IMD3) component in the dual-channel frequency conversion signal can be suppressed. Moreover, due to the balanced detection technology, the second-order spurious-free dynamic range (SFDR2) and the third-order spurious-free dynamic range (SFDR3) of the system are simultaneously improved. Simulation results show that this scheme can obtain local oscillator-radio frequency (LO-RF) isolation of more than 40 dB, SFDR2 of more than 98 dB·Hz1/2, and SFDR3 of more than 115 dB·Hz2/3. In the 16quadrature amplitude modulation (QAM) vector signal test with 450 MHz bandwidth, the adjacent channel power ratio (ACPR) of the system is up to 53 dB and the error vector amplitude (EVM) is as low as 0.3%. Finally, the error analysis of the system is also carried out.

Fiber bragg grating sensors to monitor strain response of epoxy resin during curing and cryogenic temperature

The epoxy resin is one of the critical components of large-scale superconducting magnets which find wide applications in magnetic confinement fusion, high energy accelerator and magnetic resonance imaging. In general, magnetic confinement fusion, high energy accelerator and magnetic resonance will be used at cryogenic temperatures. An approach with respect to real-time monitor of epoxy curing and cryogenic process is practically significant for magnetic reliability, maintainability as well as future mass production. Fiber Bragg Grating (FBG) sensors are excellent candidates of this measurement for their anti-electromagnetic interference characteristics and high sensitivity. The aim of this work is to use the embedded Fiber Bragg Gratings (FBG) to obtain real-time strain response of curing epoxy, and the strain change of the epoxy at cryogenic temperature from 4.2K to 300K. An FBG pre-tensioning device was designed to keep the FBG embedded in the epoxy in a stretched state during the epoxy curing process. Moreover, strain gauge sensors were also embedded to monitor the curing process at the same time. There are subtle differences in strain values obtained by the two sensors, which illustrate higher sensitivity of FBGs. This work verifies the reliability of FBG monitoring the strain response of epoxy during curing process as well as the cryogenic service.

Ultrahigh Sensitive Flexible Piezoresistive Sensor with Carbonized Metal–Organic Framework Fe3O4@MIL-100(Fe)

The piezoresistive sensor is an important device for sensing pressure and strain in flexible electronics. The application of composite conductive nanomaterials is helpful to obtain high-performance and multifunctional flexible piezoresistive sensors. Herein, using carbonized Fe3O4@MIL-100(Fe) as a composite conductive nanomaterial, an ultrahigh-sensitivity flexible piezoresistive sensor was achieved by a laser-processed template. Due to the porous Fe3O4@MIL-100(Fe) conductive nanomaterials and microridges on the styrene–isoprene–styrene substrate, the sensitivity of the sensor reaches 1727.46 kPa–1 in the pressure range of 0–50 Pa, which has a significant advantage over the reported sensors. Meanwhile, the sensor exhibits good cycling stability (>1500 cycles), a fast response of 24 ms, an instant recovery of 15 ms, excellent reversibility, and an antielectromagnetic interference capability. For practical applications, the sensor was applied for monitoring body physiological signals such as speech and artery pulses, indicating that the sensor is suitable for health monitoring. Moreover, using carbonized metal–organic frameworks with functional nanoparticles as conductive nanomaterials in the sensing unit provides a feasible way to develop multifunctional flexible piezoresistive sensors.

Cost-effective microabsorbance detection based nanoparticle immobilized microfluidic system for potential investigation of diverse chemical contaminants present in drinking water

The measurement of the concentration of different heavy-metal ions present in the water environments is becoming increasingly essential as water-pollution concerns worsen. The optical sensor has become a good platform for detecting heavy-metal-ion concentration due to its compact size; chemical inertness; and anti-electromagnetic interference. Here, we propose to fabricate a simple and cost-effective microfluidic device for the detection of aqueous-heavy-metal ions such as lead(II), chromium(III) and mercury(II) using an optical-micro-absorbance-spectroscopy/LSPR based principle. Firstly, a disposable-PDMS-micro-device with a rectangular “Z-shaped microfluidic channel” integrated with micro-lens-structure and optical-fibre-coupler-structure was fabricated via cost-effective soft-lithography-technique using a microfabricated SU8 master. Further, the synthesized-Silver-Nanoparticles were also immobilized inside the microchannel structure in some of the micro-devices for nanoparticle-based-sensing studies. The real-time presence of heavy metal ions in the minuscule sample volume was analyzed by passing different-sample concentrations intermittently through the abovementioned microfluidic structure and measuring the bulk-micro-absorbance across its enhanced optical path length coupler-structure. The results specify that the fabricated micro-device can be easily utilized for label-free detection of a minimum of 0.5 ppb for all the aforesaid sample-heavy metal ions. The absorbance-change observed per unit concentration-change of Lead ion, mercury ion and chromium ion (from 0.001 to ∼50 μg/ml) is found on average-1.8 × 10−2 ΔA/μg/ml, 1.1 × 10−2 ΔA/μg/ml, 4.2 × 10−3 ΔA/μg/ml, respectively. For silver nanoparticle-based studies, the absorbance-change observed per unit concentration change of aforesaid heavy-metal-ions (i.e. the sensitivity) was found on average ∼2 times higher in comparison to simple micro-absorbance-based studies. Additionally, the micro-device has a capability for simplistic incessant(real-time)investigation, a preset-analyte-quantity-interface, and management over the injected analyte-evaporation.

A Compact Optical MEMS Pressure Sensor Based on Fabry-Pérot Interference.

Pressure sensors have important prospects in wind pressure monitoring of transmission line towers. Optical pressure sensors are more suitable for transmission line towers due to its anti-electromagnetic interference. However, the fiber pressure sensor is not a suitable choice due to expensive and bulky. In this paper, a compact optical Fabry–Pérot (FP) pressure sensor for wind pressure measurement was developed by MEMS technology. The pressure sensor consists of a MEMS sensing chip, a vertical-cavity surface-emitting laser (Vcsel), and a photodiode (PD). The sensing chip is combined with an FP cavity and a pressure sensing diaphragm which adopts the square film and is fabricated by Silicon on Insulator (SOI) wafer. To calibrate the pressure sensor, the experimental platform which consists of a digital pressure gauge, a pressure loading machine, a digital multimeter, and a laser driver was set up. The experimental results show that the sensitivity of the diaphragm is 117.5 nm/kPa. The measurement range and sensitivity of the pressure sensor are 0–700 Pa and 115 nA/kPa, respectively. The nonlinearity, repeatability, and hysteresis of the pressure sensor are 1.48%FS, 2.23%FS, and 1.59%FS, respectively, which lead to the pressure accuracy of 3.12%FS.

Analysis and Optimization of Acoustic Sensor Based on Fiber Fabry-Pérot Etalon

Fiber optic sensors have been extensively studied in recent years. Due to the advantages of high sensitivity, compact structure, and anti-electromagnetic interference, the sensors based on the Fabry-Pérot (FP) cavity have become a research hotspot. The Fabry-Pérot etalon (FPE) acoustic sensor consists of two Plano-Concave Lenses coated with a highly reflective film, the Graded Index Lenses (GRIN) lenses, the optical fibers and a glass tube. Acoustic detection is realized by detecting the small change in the refractive index of the cavity medium caused by sound pressure, and the phase modulation technology realizes the modulation and demodulation of the acoustic signal. Matlab is used to analyze the influence of refractive index changes on the resonance spectrum and sensitivity curve, so the cavity mirrors with the reflectivity of 99% are selected. The structure of the FPE sensor is optimized using Zemax software. The optimal length of the sensor is 29.973 mm and the diameter is 6 mm. The high quality factor values of experiment and simulation are both 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> . At the same time, the experimental results show that the sensor has a response in the range of 50 Hz-20 kHz, with a high Signal-to-Noise Ratio (SNR) of 61.97 dB when the sound pressure is 19.795 Pa, and the sensitivity response is linear, reaching 0.19013 V/Pa. The research results provide useful guidance for the optimal design of the sensor, and the correctness of the theory is verified by the performance test of the optical acoustic sensor.

Progress on Optical Fiber Biochemical Sensors Based on Graphene.

Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing has also been a hotspot in cross-research in biology, materials, medicine, and micro-nano devices in recent years, owing to prospective benefits, such as high sensitivity, small size, and strong anti-electromagnetic interference capability and so on. Here, the progress of optical fiber biochemical sensors based on graphene is reviewed. The fabrication of graphene materials and the sensing mechanism of the graphene-based optical fiber sensor are described. The typical research works of graphene-based optical fiber biochemical sensor, such as long-period fiber grating, Bragg fiber grating, no-core fiber and photonic crystal fiber are introduced, respectively. Finally, prospects for graphene-based optical fiber biochemical sensing technology will also be covered, which will provide an important reference for the development of graphene-based optical fiber biochemical sensors.

Recent Advances and Tendencies Regarding Fiber Optic Sensors for Deformation Measurement: A Review

Deformation is a crucial factor to be employed for evaluating the health state of the equipment structure. Electrical-based sensors have been widely used for structural deformation monitoring. However, they are difficult to achieve accurate measurements in some harsh environments, such as those with strong magnetic fields, corrosion, and high-speed rotations. Compared with electrical-based sensors, fiber optic sensors (FOSs) possess the inherent advantages of being small and having passive sensing, anti-electromagnetic interference, etc., which endows them with great potential for deformation sensing. In this review, fiber optic deformation sensors (FODSs) are divided into contact and non-contact types according to the spatial location relationship between them and the objects being monitored. Related FOS sensing principles, including wavelength, phase, and intensity modulations are introduced. Also, cutting-edge designs of contact and non-contact FODS are discussed. Recent achievements in applying FODS are investigated and their limitations and development prospects analyzed.

Verification and Analysis of Lumped-Circuit Approximate Models of Twisted-Stranded Cables for High-Speed Railway Signaling Systems

To evaluate the transmission characteristics, anti-electromagnetic interference performance, and cable channel fault detection of multi-core twisted-stranded cables used in high-speed railway signaling systems, this study established a model for accurate twisted cable physical simulations. With the LEU-BSYYP cable, the finite element method (FME) software constructed a one twisted cycle length model and calculated the per-unit-length (pul) distribution parameters of the cable under high-frequency pulses. The purpose is to simulate long-distance twisted cables physically and analyze the factors affecting the transmission quality and transmission distance of high-frequency signals quantitatively by constructing a lumped equivalent circuit comprising cascaded T-type circuits. Additionally, by analyzing the relationship between the working frequency and the characteristic impedance error, where the characteristic impedance error is the difference in characteristic impedance between a lumped equivalent circuit and a lossy uniform transmission line, the number of T-type cascaded circuits that fulfill the accuracy requirements of the physical simulation is determined. Finally, the model output is compared with the measured waveforms using a 500 m LEU-BSYYP twisted pair cable as an example to verify the correctness of the equivalent modeling of the lumped circuit in the paper.

Polymer Optical Fiber Liquid Level Sensor: A Review

Polymer optical fiber (POF) level sensors have a lot of potential in liquid level sensing because of their inherent safety, chemical corrosion resistance, anti-electromagnetic interference, electrical isolation, compactness, high coupling efficiency, and flexibility. In this context, a review of POF liquid level sensing is presented. Several POF materials are introduced, including polymethyl methacrylate (PMMA) and perfluorinated polymer (CYTOP). In addition, the operation principles of intensity modulation and wavelength modulation are described in general. Thereafter, contemporary POF liquid level sensing applications are discussed. For intensity modulation, the bending or polishing type and coupling type sensors are introduced. There are also some extrinsic POF level sensors based on intensity modulation. For wavelength modulation, a POF fiber Bragg grating (POFBG) and a special structure grating based POF liquid level sensors are introduced.

A broadband optical fiber transmission-based time domain measurement system for nanosecond-level transient electric field.

A novel nanosecond transient electric field (E-field) measurement system is developed in this paper to measure the E-field pulse caused by the operation of the high-voltage switch (switching E-field pulse) in the substation. An electrically small rod antenna is used as the receiving antenna and is matched by the operational amplifier with high input impedance to achieve broadband frequency response and stable working performance. A broadband analogoptical fiber transmission system is further designed based on the high-frequency circuit model of the electronic components. Unlike the traditional frequency domain E-field measurement methods, the developed measurement system can directly output the time domain waveform of the switching E-field pulse. It also has the advantages of adjustable sensitivity, portability, and anti-electromagnetic interference. The calibrated measurement bandwidth ranges from 200Hz to 680MHz. Furthermore, the switching E-field pulse in an ultra-high voltage substation is measured and analyzed to verify the effectiveness of the fabricated measurement system.

Three-Fingers FBG Tactile Sensing System Based on Squeeze-and-Excitation LSTM for Object Classification

As one of the important sensing technology, tactile sense has been the focus of attention in recent years. Because of its small, light and anti-electromagnetic interference, fiber Bragg grating (FBG), as an advanced tactile sensor, can be encapsulated on any type of industrial manipulator. Based on the three-dimensional characteristics of the grabbed object, this paper designs a three-fingers FBG tactile sensing system. The structure of wavelength-swept optical coherence tomography is built to collect high sensitivity three-channels FBG tactile sensing signal. The obtained tactile signal is one-dimensional small volume data, which has fast transmission rate and occupies a small bandwidth. The system is suitable for application in any places especially in industrial with complex environment and precious bandwidth. FBG tactile signal is demodulated into a time-correlation sequence representing the grasping process, as the input of neural network. The classification results of two neural networks for processing time-correlation signal: WaveNet and LSTM are compared. For three-channels of the obtained tactile signal, Squeeze-and-Excitation module, which increases the correlation between channels, is added to the better performance LSTM model. The accuracy of classification is further improved. The Squeeze-and-Excitation LSTM (SE-LSTM) classification result shows that the classification accuracy of SE-LSTM for six types of objects with similar size and shape reaches 95.97%, which proves the effective of FBG tactile sensing technology for object classification. The time of single recognition can reach 1.2ms, which meets the requirements of real-time.

Development of Sapphire Optical Temperature Sensing System Used in Harsh Environment Sensing

A sapphire optical fiber blackbody radiation sensor based on the high temperature multilayer structure of wolfram and aluminum oxide has been developed. Through the analysis of Planck&#x2019;s law, the linear relationship between the temperature and the square root of the voltage is theoretically deduced. Radio frequency magnetron sputtering method is used to sputter and deposit high-temperature wolfram metal film and aluminum oxide film on sapphire fiber. In order to meet the needs of real-time temperature measurement, an online acquisition system of optical signals is designed to complete the demodulation and storage of signals. The high-temperature experiment results show that the temperature response sensitivity is 0.00113V1/2/&#x2103; between 300&#x2103; and 1750&#x2103;, and it can work stably for more than 10 hours. The sensor is calibrated in the metrology institute where a maximum quoted error of 0.84% within a range between 900 &#x2103; and 1600&#x2103; is proved. Compared with the traditional high temperature measurement method, the sensor has the advantages of compact structure, anti-electromagnetic interference, large measuring range, and good linearity, which can be widely used in the sensing and measurement of extreme high temperature environments such as aero-engine tail injection temperature monitoring, combustion chamber temperature monitoring of aero-engine simulation test benches.

Constructions of Optimal Uniform Wide-Gap Frequency-Hopping Sequences

In frequency hopping (FH) communication systems, frequency hopping sequences (FHSs) are crucial in determining the system’s anti-jamming performance. If FHSs can ensure a wide-gap between two adjacent frequency points to avoid the frequency points with high interference probability, it will significantly improve the FH communication system’s anti-interference ability. Moreover, if each frequency point appears at the same number of times in a sequence period, the system’s anti-electromagnetic interference will be enhanced. Therefore, it is desirable to employ FHSs with low Hamming autocorrelation, wide frequency-hopping gap, and good uniformity in practical applications. However, to the best of our knowledge, no such infinite classes of FHSs have been reported in the literature to date. This paper aims to present two constructions of uniform wide-gap frequency-hopping sequences (WGFHSs) by concatenating two or three adequately designed sequences. For the first time, we obtain two infinite classes of WGFHSs, which are optimal with respect to the well-known Lempel-Greenberger bound.

Background Noise Suppression for DAS-VSP Records Using GC-AB-Unet

Distributed acoustic sensing (DAS) is one of the most popular sensors for seismic acquisition. Compared with traditional seismic acquisition technology, DAS has the advantages of full-well coverage, high density, high efficiency, high sensitivity, low cost, strong resistance to high temperature and high pressure, and anti-electromagnetic field interference. However, the DAS vertical seismic profile (VSP) data are contaminated by strong noise interference, which brings challenges for practical applications and difficulties to seismic inversion and interpretation. A deep learning method named U-net with Global Context Block and Attention Block (GC-AB-Unet) is proposed to suppress the background noise and increase the data quality for DAS-VSP records without knowing any prior information. In GC-AB-Unet, several dropout layers are added to the U-net to avoid overfitting. Meanwhile, to speed up the network training, the residual units are set as the output of the network. Furthermore, GC-Block is introduced for better capturing shallow and deep features by extracting global context information. In addition, Attention Block is used to emphasize seismic event features and restrain irrelevant details in seismic data. We also construct a training dataset by utilizing the synthetic data and real noise of DAS-VSP data. The denoising results for both synthetic data and field DAS-VSP data show that compared to original U-net and Damped Rank Reduction (DRR) method, the GC-AB-Unet network is able to preserve the effective signals with almost no energy leakage while suppressing a large amount of background noise.

The Study on a New Method for Detecting Corona Discharge in Gas Insulated Switchgear

Partial discharge (PD) is the main cause of insulation deterioration and failure of gas-insulated switchgear (GIS). Corona discharge (CD) is a typical type of PD in gas-insulated switchgear. Accurate and sensitive measurement of CD in GIS is of great significance for theoretical research in the laboratory and fault prediction of GIS in the actual operation. A novel method for detecting CD in GIS is proposed in this article. A coaxial structure model for simulating GIS is established. The CD detecting sensor based on the proposed method is designed for this model. An artificial tip defect is designed on the internal high voltage conductor of the coaxial model to simulate CD in GIS. A 50 Hz ac power supply, a dc negative power supply, and a dc positive power supply are applied as excitations to generate the CD at the defect, respectively. The discharge pulse signal is detected by the proposed sensor. The results show that the proposed sensor can completely obtain the information of the CD pulse signal. The proposed method has the same anti-electromagnetic interference ability as the ultrahigh-frequency method and has a high sensitivity to CD in GIS.

An Optimized Lightweight Ultrasonic Liquid Level Sensor Adapted to the Tilt of Liquid Level and Ripple

Ultrasonic liquid level measuring technology has been extensively applied in the industrial field, which is characterized by its high accuracy, strong ability of anti-electromagnetic interference and simple structure. However, its measurement results are easily affected by the tilt of liquid level and ripple. In this study, the traditional gas-liquid interface was transformed into a solid-liquid interface based on the acoustic scattering by a rigid sphere and a circular waveguide, and the liquid level was measured with the stable reflecting surface by complying with the liquid level in the duct. Such a method could overcome the effect of the tilt of liquid level and ripple on the measurement results. In this study, a signal processing method to improve the signal to noise ratio of the direct wave was proposed. To improve the sound intensity of the direct wave and reduce the effect of high-order mode waves on the signal, the transceiver was applied with a matching layer, and the appropriate waveguide material should be selected to absorb a portion of high-order mode waves. As revealed from the experimentally achieved results, an optimized lightweight ultrasonic liquid level sensor was proposed to eliminate the effect of ripple, and the tilt of liquid level increased from 20° to 60°.

Anti-electromagnetic interference method based on high-order cumulant method and PRI sorting

Facing the increasingly complex electromagnetic environment, how to make the detection instrument still have better detection performance is one of the current research hotspots. This paper proposes an anti-electromagnetic interference method based on high-order cumulant and PRI sorting. The former identifies the modulation type of the signal, the latter sorts the signals with different modulation parameters of the same modulation type, and finally selects the signal to be processed. The simulation results show that the algorithm is accurate and effective.

Sensitivity Criterion and Law on a Navigation Receiver under Single Frequency Electromagnetic Radiation

To objectively assess the anti-electromagnetic interference ability of the navigation receiver, the sensitivity criterion of a certain type of navigation receiver is tested under single-frequency continuous wave electromagnetic radiation with an optimized testing method. The experimental results show that it is difficult to guarantee the accuracy of the measurement value of the sensitivity level by using the carrier-to-noise density ratio (C/N0) as the sensitivity criterion, but the initial C/N0 of each satellite can be used as the basis for identifying whether the navigation system has recovered from the interference. The experimental error is dramatically decreased when the sensitivity criterion of “the sensitive phenomenon appears within the first 4 s, and the loss of positioning lasts for 30 s” is employed, the variable interference power step size is adopted and all of the satellites C/N0 are required to recover to the initial value after an interference. The critical interference field intensity error can be controlled within 1 dB by using all these measures. The sensitivity law of the navigation receiver is the same under different working signal intensities. It is significantly sensitive in the working frequency bandwidth. It is also quite sensitive in −11.5 MHz~55.5 MHz of the frequency offset range. The positive sensitive bandwidth is about 5 times that of the negative sensitive bandwidth.

Temperature controllable optical switch for erbium-doped random fiber laser

Different from the conventional optical switches, a rapid response and simple structure of erbium-doped random fiber laser for optical switch is presented. The random fiber laser (RFL) was achieved by pumping an erbium-doped fiber connected with tens of kilometers of single-mode-fiber (SMF). Meanwhile, the 1 cm-long photonic crystal fiber (PCF) filled with a liquid crystal (LC), which is spliced after the reflected output port of a 980/1550 nm wavelength division multiplexing (WDM) coupler, is used as the sensing unit. A high-extinction ratio more than 36 dB over a wavelength range from 1529.00 nm to 1533.16 nm can be observed when the temperature increases from 60 °C to 61 °C. The high-extinction ratio RFL is caused by the reduction of refractive index of the LC-filled PCF (LCPCF). Under the action of the band gap guiding mechanism, the LC molecules in PCF change from each anisotropic to each isotropic when the temperature increases from 60 °C to 61 °C, which induces thermo-optical switch of the LCPCF. The optical switch of erbium-doped fiber random fiber laser has the best comprehensive performance with low cost, high sensitivity, strong anti-electromagnetic interference ability based on control of the temperature.