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linear frequency modulation INFRARED THERMAL IMAGING DETECTION TECHNOLOGY FOR GFRP/PMI FOAM SANDWICH STRUCTURE DEFECTS

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THERMAL SCIENCE 2023年第1B期27卷 483-490页

作者： Song, Ya-Fei Tang, Qing-Ju Bu, Chi-Wu LI, Yu-Mei Xi, Peng Heilongjiang Univ Sci & Technol Sch Mech Engn Harbin Peoples R China Harbin Univ Commerce Coll Light Ind Harbin Peoples R China

As one of the important structures of composite materials, polymethacrylimide (PMI) foam sandwich structure is prone to debonding and delamination defects during manufacturing and service, which seriously affects the mechanical prop-erties of materials. Therefore, it is necessary to detect the defects of foam sand-wich structure. A linear frequency modulation infrared thermal wave nondestruc-tive testing system was built to study the correlation between the geometric char-acteristics (diameter and depth) of the defect and the surface temperature signal and its influence on the detection effect. The image sequence is processed by principal component analysis, discrete Fourier transform, thermal wave signal reconstruction, and other algorithms. Studies have shown that the larger the de-fect diameter, the shallower the depth, easy to detect defects, detection effect is good. The detection system can effectively detect and identify debonding and de -lamination defects. The thermal wave signal reconstruction method is superior to the principal component analysis method and the discrete Fourier transform method in the signal-to-noise ratio index, which improves the quality of the image and is conducive to the effective identification of the image surface defect infor-mation.

关键词： PMI foam sandwich structure linear frequency modulation image sequence processing signal to noise ratio

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A new spatial modulation scheme exploiting linear frequency modulation

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ANNALS OF TELECOMMUNICATIONS 2024年 1-7页

作者： Slimani, Chellali Ghanem, Khalida Ghanem, Farid Nedil, Mourad EMP AT Algiers Algeria CDTA Algiers Algeria Independent Consultant Montreal PQ Canada UQAT Rouyn Noranda PQ Canada

In forthcoming 6 G wireless networks, spatial modulation (SM) has established itself as a technique in massive MIMO setups. In this letter, a novel SM architecture embedding linear frequency modulation (LFM) principle is proposed. In the resulting SM-LFM scheme, the data block is split into the signal and the antenna index parts, and prior to its transmission, distinctly assigns a different LFM chirp (up or down) to be mixed up with the SM block, depending on the index of the antenna to be activated. When the antenna index is even, the associated chirp is up, while the down chirp is retained otherwise. Similarly, the proposed SM-LFM receiver part consists of two main parts: the LFM chirp recognizer and the tuned SM detector. In the former, the received signal is fed to the two up and down LFM chirp-correlators, and the chirp selected at the transmitter is retrieved by an energy comparator. The target behind the incorporation of the LFM chirps, between each adjacent antennas-pair, is to mitigate the miss-estimation of the antenna indices at the receiver side. Depending upon the detected chirp, in the tuned SM detector, only the signals (indices and symbols) emanating from even- or odd-indexed antennas are processed. The performance of the resulting scheme is investigated by adopting a channel model, which considers the effects of estimation errors and antenna correlation. Two modified detectors which adapt to the LFM signaling are investigated, namely the iterative maximum ratio combining (i-MRC) and the maximum likelihood (ML) detectors. The improvement provided, by adopting LFM concept in SM, is shown in terms of data reliability and complexity reduction.

关键词： Spatial modulation linear frequency modulation MIMO systems

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Deception Jamming Method for Wideband linear frequency modulation Radar Based on Time-Modulated Array

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IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS 2024年第12期23卷 4408-4412页

作者： Yang, Liu Zhang, Yuehang Zhao, Xiaonan Liu, Zhenji Geng, Junping Chen, Jingfeng Jin, Ronghong Shanghai Jiao Tong Univ Shanghai 200000 Peoples R China China Ship Develop & Design Ctr Wuhan 430205 Peoples R China Wuhan Maritime Commun Res Inst Wuhan 430205 Peoples R China

A deception jamming method for wideband linear frequency modulation radar based on time-modulated array (TMA) is proposed in this letter. Different from other real-time modulation jamming methods using metasurface, the real-time modulated method based on TMA, where the system consists of discreet components of passive antenna, low-noise amplifier (LNA), analogy switches etc., shows merits of wide system bandwidth and extra gain for false targets. Hence, in view of the TMA-based method, this letter establishes the real and false targets' amplitude model under nonuniform and uniform modulation. The situation of switches' opening instant linearly varying with antenna order is introduced to manipulate false targets' energy distribution in both observed angle and range directions. Numerical simulations are conducted to discuss the false-target characteristics under different modulation parameters. In the experiment, a two-element wideband jamming system covering 6 GHz to 18 GHz is constructed to demonstrate the proposed method's feasibility.

关键词： Jamming modulation Radar frequency modulation Radar antennas Wideband Real-time systems Deception jamming linear frequency modulation time-modulated array

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Interferometric Fiber-Optic Hydrophone System Based on linear frequency modulation

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2022年第20期40卷 6769-6777页

作者： Zhao, Mengyuan Mao, Ying Wang, Zexu Yin, Feifei Xu, Kun Dai, Yitang Beijing Univ Posts & Telecommun Sch Elect Engn State Key Lab Informat Photon & Opt Commun Beijing Peoples R China

Microwave photonic sensing is an emerging technology that uses broadband analog optical signal processing to help traditional optical sensor achieve higher detection speed, sensitivity, and resolution. In this article, we use microwave photonic approach to improve the performance of a long-range, relay-free fiber-optic hydrophone system. Specifically, we use linear frequency modulated (LFM) optical pulses as a new light source for the interferometric hydrophone system. Compared with conventional heterodyne-type techniques, the above innovation improves the sensitivity of the sensing receiver, meanwhile effectively increases the excitation threshold of the fiber nonlinearity and then increases the optical power at the transmitter. As a result, the hydrophone system will have a larger maximum tolerable loss. In theory, we show that with a high-repetition-rate LFM optical pulse train, the echo beating frequency is strictly an integer multiple of the repetition rate, which is no longer determined alone by the chirp rate multiplied by arm length difference of interferometer. This feature ensures accurate phase demodulation of the hydrophone system. We experimentally compare with typical heterodyne-type hydrophone scheme, and confirm that the use of LFM source brings a 3-dB improvement in reception sensitivity, and completely suppresses the stimulated Brillouin scattering (SBS) effect within the fiber. At an incident optical power of 10 dBm, the LFM source brings larger than 10-dB improvement in the carrier-to-noise ratio (CNR). This article provides a thorough analysis of the noise performance of sensing system using LFM light source, and concludes that this technology can significantly extend its relay-free transmission distance and expand the network scale, and thus will become a competitive solution for future interferometric fiber-optic hydrophone system.

关键词： Optical fiber sensors Optical interferometry Optical fiber networks Optical pulses Sonar equipment Optical fiber theory Optical transmitters Carrier-to-noise ratio fiber-optic hydrophone linear frequency modulation microwave photonics phase noise

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DEFECT DETECTION OF GFRP/NOMEX HONEYCOMB SANDWICH STRUCTURE BY linear frequency modulation INFRARED THERMAL IMAGING

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THERMAL SCIENCE 2021年第6期25卷 4611-4619页

作者： Tang, Qing-Ju Fan, Wei-Ming Ji, Juan Song, Ya-Fei Heilongjiang Univ Sci & Technol Sch Mech Engn Harbin Peoples R China

Honeycomb sandwich material is a new material widely used in many fields, but it is easy to produce defects such as delamination and ponding in the process of manufacturing and service. First, a honeycomb sandwich sample containing delamination defects and water accumulation was built. Then, a linear frequency modulated driving halogen lamp is used as the excitation source. Finally, the surface thermal image sequence of the test sample is acquired by infrared thermal imager. Image sequences are processed by inter-frame difference-multi-frame cumulative average method, principal component analysis, Fourier transform method, and logarithmic polynomial fitting method, respectively. Define and calculate the signal-to-noise ratio of the heat map processed by each algorithm. Compared with the other three algorithms, the principal component analysis method processed the image with the highest signal-to-noise ratio and high contrast. This algorithm achieves effective identification of delamination defects and water accumulation in GFRP/Nomex honeycomb sandwich structure.

关键词： GFRP Nomex linear frequency modulation signal-to-noise ratio analysis image sequence processing

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Multi-Band linear frequency modulation in External Cavity FP-LD Subjected to Multi-Input Injection

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IEEE PHOTONICS TECHNOLOGY LETTERS 2021年第11期33卷 565-568页

作者： Lee, Muyoung Chen, Hao Nakarmi, Bikash Pan, Shilong Won, Yong Hyub Korea Adv Inst Sci & Technol Convergence Optoelect Device Engn Lab Dept Elect Engn Daejeon 34141 South Korea Nanjing Univ Aeronaut & Astronaut Key Lab Radar Imaging & Microwave Photon Minist Educ Nanjing 210016 Peoples R China

In this letter, we experimentally demonstrate multi-band linear frequency modulation (LFM) signal generation subjected to multi-input optical injection in an external cavity-based Fabry-Perot laser diode (ECFP-LD). The ECFP-LD is a specially designed FP-LD with a self-injected single longitudinal mode tuned up to 10 nm. The non-linear dynamics in period-one oscillation in ECFP-LD subjected to multi-input optical injection shows unique characteristics for multi-band linear frequency modulation. In the proposed scheme, four external input beams are injected to ECFP-LD, among which one is power modulated with the saw-tooth like waveform, and others are with the constant power. The varying power beam red-shifts the self-injected mode of ECFP-LD and mode-hopping on attaining a particular power level. Hence, multi-band LFM signals are generated by beating self-injected and multi-input injected beams with a large time-bandwidth product (TBWP). The total bandwidths of 12GHz (LFM1: 33-36 GHz, LFM2: 29-32 GHz, LFM3: 25-28 GHz, LFM4: 22-25 GHz) for four-band linear frequency modulation signals with a TBWP of 12000 is measured. The generated multi-band LFM signal provides flexibility on central frequency tunability and dynamic chirp rate for a multifunctional radar system.

关键词： Optical beams Particle beam injection Optical fibers Bandwidth Radar Optical amplifiers frequency modulation External cavity based FP-LD linear frequency modulation optical injection period-one oscillation

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Ka Band Holographic Imaging System Based on linear frequency modulation Radar

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SENSORS 2020年第22期20卷 6527.-6527.页

作者： Meng, Yang Lin, Chuan Zang, Jiefeng Qing, Anyong Nikolova, Natalia K. Univ Elect Sci & Technol China Sch Phys Chengdu 611731 Peoples R China Southwest Jiaotong Univ Sch Elect Engn Chengdu 611756 Peoples R China McMaster Univ Dept Elect & Comp Engn Hamilton ON L8S 4K1 Canada

Millimeter wave (MMW) technology is expanding rapidly into security screening for dangerous items concealed under clothing. It uses safe non-ionizing radiation and penetrates clothing well. We present a new planar system at Ka band for the three-dimensional simultaneous imaging of both sides of an inspected person where the images are produced in real time by a recently proposed generalized holographic reconstruction algorithm. Low-cost linear frequency modulation (LFM) radar technology is used along with a simple but efficient method for system calibration. Experimental characterization of the spatial resolution and the sensitivity of the system prototype has been carried out. It is established that the achieved spatial resolution is 6 mm or better if the item is not obscured by clothing and it may deteriorate to 7 mm depending on the clothing hiding the item. The spatial sensitivity is confirmed to be at least 2 mm.

关键词： holographic imaging linear frequency modulation millimeter wave security check

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Numerical Simulation of linear frequency modulation Infrared Thermal Wave Detection for GFRP/Nomex Honeycomb Sandwich Structure 5

Numerical Simulation of Linear Frequency Modulation Infrared...

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5th International Conference on Mechanical, Control and Computer Engineering (ICMCCE)

作者： Tang Qingju Fan Weiming Heilongjiang Univ Sci & Technol Sch Mech Engn Harbin Heilongjiang Peoples R China

ISBN: (纸本)9781665423144

In order to explore the effectiveness of linear frequency modulation continuous light-excited infrared thermal waves to detect defects in GFRP/Nomex honeycomb sandwich structure, a three-dimensional heat conduction model of heat flow in the component was established and a finite element simulation study was carried out. By setting different detection parameters, the changes in contrast of the internal components with defects such as debonding, water accumulation and glue blocking are explored. The results show that the larger the debonding diameter and the smaller the thickness, the easier it is to detect;the higher the water accumulation height, the easier it is to detect;the thicker the plugging thickness is, the easier it is to detect. At the same time, the greater the initial frequency of the excitation signal, the earlier the first contrast peak will appear;the change in the stop frequency and the scan period will have less influence on the contrast.

关键词： GFRP/Nomex honeycomb sandwich structure infrared thermal wave linear frequency modulation numerical simulation

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Real-Time Recognition and Parameters Estimation of linear frequency modulation Microwave Signal Based on Reservoir Computing

Real-Time Recognition and Parameters Estimation of Linear Fr...

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International Topical Meeting on Microwave Photonics (MWP)

作者： Jing, Ning Wang, Chao Univ Kent Sch Engn & Digital Arts Canterbury Kent England North Univ China Sch Informat & Commun Engn Taiyuan Peoples R China

ISBN: (纸本)9784885523311

Real-time waveform recognition and parameter evaluation for linear frequency modulated (LFM) pulse waveform is crucially important while challenging in microwave detection systems. To address this issue, in this work, we proposed a new artificial intelligence enabled classification method based on reservoir computing (RC). A sampled sequence, generated by random concatenation of LFM signals with different chirp rates and initial frequencies, is used to training the designed reservoir with 200 nodes. The testing result shows that the RC can recognize individual LFM signals in the sequence, and estimate the instantaneous frequency of an LFM signal within the sequence. Compared to conventional computing methods for instantaneous frequency identification such as Hilbert transform or short-time Fourier transform, RC-based approach features faster speed and great potential for hardware implementation using photonic devices.

关键词： linear frequency modulation signal recognition parameters estimation reservoir computing microwave photonics

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Progress Review of General Holographic Millimeter Wave Imaging System Based on linear frequency modulation for Safe Personnel Screening

Progress Review of General Holographic Millimeter Wave Imagi...

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IEEE International Symposium on Antennas and Propagation / North American Radio Science Meeting

作者： Qing, Anyong Southwest Jiaotong Univ Sch Elect Engn Chengdu 610031 Peoples R China

ISBN: (纸本)9781728166704

Millimeter wave imaging (MMWI) has proven itself an irresistible revolutionary technology for safe personnel screening. The progress of in-house research on general holographic MMWI based on linear frequency modulation (LFM) is summarized in this paper. Major innovations including distinctive system framework, staggered transceiver antenna array (STAA), inventive calibration, and novel imaging algorithm are highlighted. Prototype evaluation has also been presented.

关键词： Millimeter wave holographic imaging linear frequency modulation personnel screening

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