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Numerical characterization of capacitively coupled plasma driven by tailored frequency modulated radio frequency source

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PLASMA SOURCES SCIENCE & TECHNOLOGY 2024年第5期33卷 055009-055009页

作者： Wang, Yu Zhou, Youyou Chen, Jian Cao, Yong Wang, Zhijiang Huang, Xiaojiang Zhang, Ya Wuhan Univ Technol Dept Phys Wuhan 430070 Peoples R China Huazhong Univ Sci & Technol Sch Phys Wuhan 430074 Peoples R China Harbin Inst Technol Sch Mech Engn & Automat Shenzhen 518055 Peoples R China Huazhong Univ Sci & Technol Sch Elect & Elect Engn Int Joint Res Lab Magnet Confinement Fus & Plasma State Key Lab Adv Electromagnet Engn & Technol Wuhan 430074 Peoples R China Donghua Univ Coll Sci Shanghai 201620 Peoples R China

Capacitively coupled plasma (CCP) is widely used in plasma etching and deposition processes because of its low cost, simple structure, and easy generation of a uniform plasma in large areas. Conventional CCPs are operated under a fixed frequency power source;however, CCPs driven by a variable frequency power source are poorly understood. In this paper, numerical simulations of CCPs driven by frequency modulated (FM) radio frequency (RF) sources within the frequency range of 2 MHz-18 MHz are carried out with a particle-in-cell/Monte Carlo collision model. Our research indicates that the CCP driven by an FM RF source can maintain a stable glow discharge and form a time-dependent plasma. Plasma density, electron and ion current, energy and heating rate, ion flux, and energy on the electrodes fluctuate consistently with the FM period. The electron and ion energy distribution function can also be modulated by the frequency variation of the FM source. A multi-peak structure that varies and shifts with frequency variation is observed in the ion energy distribution function. In addition, by fixing the chirp period while varying the start or end frequency of the chirp signal (start frequency from 0.4 to 6 MHz, or end frequency from 18 to 48 MHz), effective modulations can be produced on the electron density, electron energy, and the shape of the EEPF and IEDF.

关键词： CCP PIC/MCC chirp linear frequency modulation

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Photonic joint radar and communication system using a chirp-polarity coded LFM waveform

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OPTICS COMMUNICATIONS 2024年 552卷

作者： Li, Xuan Zhou, Yixiao Wang, Guodong Zhao, Shanghong Zhu, Zihang AF Engn Univ Informat & Nav Sch Xian 710077 Peoples R China

A photonic joint radar and communication system using a frequency improved, bandwidth doubled, chirppolarity coded linear frequency modulation (LFM) waveform is proposed and demonstrated. In the scheme, a dual-polarization modulator is driven by a repetitive LFM waveform and an RF signal to generate different optical sidebands in two orthogonal polarization directions. Then, the orthogonally polarized optical sidebands are filtered and polarization modulated to achieve chirp-polarity coding. The generated signal is employed to simultaneously perform dual functions. Both the radar echo and the communication reception are processed based on optical de-chirping. The approach is demonstrated by simulation. A chirp-polarity coded LFM waveform with central frequency of 24 GHz, bandwidth of 8 GHz, bit rate of 10 Mbit/s is generated and processed for dual functions. The radar range resolution, unambiguous range, and range-Doppler resolution are investigated. The optical demodulation of the communication is verified, and the speed improvement of communication is discussed.

关键词： Joint radar and communication Chirp-polarity coding linear frequency modulation Optical de-chirping

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Multi-Radar Interference Mitigation in Photonics-Based Radar With Sliding Window LSTM Recurrent Neural Network

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2024年第21期42卷 7567-7576页

作者： Parajuli, Hum Nath Ashimbayeva, Aigerim Nakarmi, U. Ukaegbu, Ikechi Augustine Gaudel, B. Pan, Shilong Molardi, C. Nakarmi, B. Nazarbayev Univ Sch Engn & Digital Sci Dept Elect & Comp Engn Integrated Device Solut & Nanophoton iDSN Lab Astana 010000 Kazakhstan Univ Arkansas Dept Comp Sci & Comp Engn Fayetteville AR 72701 USA Stevens Inst Technol Mech Engn Dept Hoboken NJ 07030 USA Nanjing Univ Aeronaut & Astronaut Key Lab Radar Imaging & Microwave Photon Minist Educ Nanjing 210016 Peoples R China

In this paper, we propose and experimentally demonstrate a technique of mitigating multi-radar interference in a photonic radar using a sliding window long short-term memory (SW-LSTM)-based recurrent neural network. For the proof-of-concept experimental demonstration, a photonics-based victim radar (VR) with an 8 GHz linear frequency modulated (LFM) signal is generated using optical injection in a semiconductor laser. This VR is used to detect two objects separated by 10 cm in the presence of multiple interference sources. To perform the analysis of mitigating interference in the multi-radar environment, we generated random interference LFM signals (IR-LFM) with diverse bandwidths (4 GHz to 10 GHz) and chirp rates (+/- 1 GHz/mu s to +/- 20 GHz/mu s), both experimentally and synthetically. The generated IR-LFM signals consist of both coherent and non-coherent interferences and are added to the echo signal and trained using SW-LSTM. During the training stage, learning rate, stacked layers, nodes, batch size, and window size are optimized. In the test stage, we use signals with both coherent and non-coherent interferences, which are distinct from the interferences in the training stage. The proposed model is evaluated for one, four, and eight interference test scenarios, in which it successively achieves a meanR(2 )value of > 93% for all test scenarios, taken over ten trials in each test scenario. Furthermore, a mean error vector magnitude (EVM) of < 0.07 and a mean signal-to-interference plus noise ratio (SINR) of > 11 dB are obtained. These results indicate a strong similarity between the range profile calculated in the interference-free and the multi-interference environments with our proposed scheme of mitigating interference using SW-LSTM.

关键词： Interference Radar Laser radar Photonics Chirp Optical filters Training Interference mitigation linear frequency modulation LSTM photonic radar RNN

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Multi-Chirp LFM Waveforms Generation With Reconfigurable Chirp Rates Using Optical Injection in a Semiconductor Laser

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2024年第1期42卷 184-193页

作者： Nakarmi, B. Song, Bai Yan Ukaegbu, Ikechi Augustine Parajuli, Hum Nath Ashimbayeva, Aigerim Nakarmi, U. Wang, Xiangchun Pan, Shilong Nanjing Univ Aeronaut & Astronaut Nanjing Univ Aeronaut Astronaut Key Lab Radar Imaging & Microwave Photon Minist Educ Nanjing 210016 Peoples R China Nazarbayev Univ Sch Engn & Digital Sci Elect Engn Dept Integrated Device Solut & Nanophoton Lab Astana 010000 Kazakhstan Univ Arkansas Dept Comp Sci & Comp Engn Fayetteville AR 72701 USA

We propose and experimentally demonstrate a photonics-based technique for generating simultaneous up-down multiple chirp-rate linear frequency modulated (SUDMC-LFM) waveforms using a dual beam injection technique in a distributed feedback (DFB) laser. To generate waveforms with multiple chirps, drive waveforms of different amplitude-time slopes for each sub-interval time are designed in an arbitrary waveform generator (AWG) and fed into the intensity modulator, which in turn, controls the intensity of the injected beam. Consequently, the rate of redshift of the emission wavelength is controlled. In the experiment, the intensity of only one beam is controlled with the designed AWG signal. For the proof-of-concept demonstration, we generate continuous multiple chirps (CMC), simultaneous up-down multiple chirps (SUDMC), and simultaneous up-down frequency hopped multiple chirps (SUDFHMC) LFM waveforms. Furthermore, re-configurability of the generated waveforms in terms of center frequency, bandwidth, number of chirps, and chirp-rates are obtained by either changing the wavelength of the injected beams or by changing the parameters of the AWG signal. In the experiment, the SUDFHMC waveform with four frequency-hopping with sub-interval chirps of 4 GHz/mu s, 1.2 GHz/mu s, 2.4 GHz/mu s, and 2.8 GHz/mu s for both the up-chirps and down-chirps, respectively, is generated. The auto-ambiguity analysis at -3 dB full-width half maximum (FWHM) shows the time-bandwidth product (TBWP) of >4545, and unambiguous Doppler of <0.75 MHz for CMC, SUDMC, and SUDFHMC signals with three chirps. These results indicate that the proposed waveforms have the potential to provide high performance in multi-radar and multi-target applications.

关键词： Chirp Laser beams Laser radar Bandwidth Semiconductor lasers Radar frequency modulation Dual LFM linear frequency modulation microwave photonics multiple chirps optical injection radar

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Free Space Optical Integrated Sensing and Communication Based on LFM and CPM

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IEEE COMMUNICATIONS LETTERS 2024年第1期28卷 43-47页

作者： Wen, Yunfeng Yang, Fang Song, Jian Han, Zhu Tsinghua Univ Dept Elect Engn Beijing 100084 Peoples R China Tsinghua Univ Shenzhen Key Lab Digital TV Syst Shenzhen City Res Inst Shenzhen 518057 Peoples R China Univ Houston Dept Elect & Comp Engn Houston TX 77004 USA

Integrated sensing and communication (ISAC) is a crucial component of future wireless networks, with optical ISAC regarded as a promising complement to its radio-frequency counterpart. In this letter, an ISAC scheme combining linear frequency modulation (LFM) and continuous phase modulation (CPM) is proposed for free space optics. The generalized intermediate frequency, the direct-current bias, and the Hilbert transform are adopted to make the complex LFM-CPM signal compatible with optical intensity modulation and direct detection. Additionally, various performance metrics are derived theoretically to establish an optimization problem that reveals the trade-off between communication and sensing. Furthermore, numerical simulations demonstrate the simultaneous communication and sensing abilities of LFM-CPM and reveal its superiority over other constant-modulus signal.

关键词： Optical ISAC linear frequency modulation continuous phase modulation free space optics

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Monolithic Integrated linear frequency Modulated Dual- Wavelength DFB Laser Chip with High linearity and Its Application in Long Distance Ranging

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ACS PHOTONICS 2023年第7期10卷 2344-2352页

作者： Zhang, Yunshan Xu, Yifan Shi, Jianqin Zhao, Tongfei Li, Pu Guan, Shijian Li, Lianyan Zhang, Xin Zheng, Jilin Fang, Tao Chen, Xiangfei Wang, Yuncai Nanjing Univ Posts & Telecommun Coll Elect & Opt Engn Nanjing 210023 Peoples R China Nanjing Univ Posts & Telecommun Coll Flexible Elect Future Technol Nanjing 210023 Peoples R China Nanjing Univ Coll Engn & Appl Sci Nanjing 210023 Peoples R China PLA Army Engn Univ Coll Commun Engn Nanjing 210007 Peoples R China Guangdong Univ Technol Sch Informat Engn Guangdong Prov Key Lab Photon Informat Technol Guangzhou 510006 Peoples R China Guangdong Univ Technol Guangzhou 510006 Peoples R China Taiyuan Univ Technol Key Lab Adv Transducers & Intelligent Control Syst Minist Educ Taiyuan 030024 Peoples R China

The ranging distance and precision of the coherent frequency modulated continuous wave (FMCW) lidar systems are mainly limited by the modulation linearity and the intrinsic line width of the laser sources. To this issue, we design and experimentally demonstrate a monolithic integrated linear frequency modulated (LFM) dual-wavelength (DW) DFB laser with high frequency sweep linearity and without a complicated predistortion compensation system. Our results show that the nonlinearity of the LFM beat signal from the DW-DFB laser chip can reach 0.0146%. Furthermore, using the LFM DW-DFB laser, we implement an accurate measurement of a single mode fiber (SMF) with a length of 12.6 km, which is hundreds of times the intrinsic coherent length of the DW-DFB laser. Due to the high linearity of the LFM DW-DFB laser, the measurement error does not deteriorate significantly when the target distance increases from 0.43 to 24.24 m.

关键词： linear frequency modulation dual-wavelength DFB laser frequency modulated continuous wave lidar photonic integrated circuits

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Sub-Nyquist Measurement of LFM Pulse Stream Based on Signal Separation and Parameter Matching

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IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT 2023年 72卷 1页

作者： Fu, Ning Yun, Shuangxing Han, Bingtong Qiao, Liyan Harbin Inst Technol Sch Elect & Informat Engn Harbin 150080 Peoples R China

The linear frequency modulated pulse stream (LFMPS) is a finite rate of innovation (FRI) signal that depends on a finite number of parameters within a unit of time, and precise measurement of these parameters holds great significance in the engineering field. However, traditional LFMPS sensing methods face challenges such as complex sampling structures, high sampling rates, and poor parameter estimation accuracy. This article proposes a universal pulse stream sampling structure based on FRI sampling theory to address these issues. The structure utilizes the periodicity of LFMPS to locate pulses from the sub-Nyquist samples of the first signal period. Then, window functions are constructed to separate the LFM pulse in the second period and perceive the related parameter through the parameter matching method. We analyze the effect of the LFM waveform on pulse positioning in the first period and demonstrate the feasibility of estimating the chirp-rate (CR) factor using the parameter matching method. Numerical simulation results show that our proposed algorithm achieves accurate LFM signal measurement at lower sampling rates and has stronger noise immunity during parameter measurement compared to classical sensing approaches.

关键词： Finite rate of innovation (FRI) linear frequency modulation parameter measurement sub-Nyquist sampling

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Advancing Stepped-Waveform Radar Jamming Techniques for Robust False-Target Generation against LFM-CFAR Systems

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SENSORS 2023年第18期23卷 7782页

作者： Wang, Yanqi Wang, Chao Shi, Qingzhan Huang, Jingjian Yuan, Naichang Natl Univ Def Technol Coll Elect Sci & Technol Changsha 410073 Peoples R China Natl Univ Def Technol State Key Lab Complex Electromagnet Environm Effec Changsha 410073 Peoples R China

This study investigates the utilization of a stepped wave frequency modulation jamming technique in radar systems. The objective is to enhance the effectiveness and robustness of false target jamming in the presence of linear frequency modulation (LFM) radars employing constant false alarm rate (CFAR) detection. The proposed method combines stepped frequency modulation with full pulse delay/sum repeat jamming to enhance resilience against uncertainties in target parameters. Theoretical analysis and simulation experiments are conducted to establish relationships between key jammer parameters, such as frequency slope and power compensation, and performance metrics, like false target distribution and CFAR masking. The results demonstrate that the proposed technique effectively maintains a dense distribution of false targets surrounding the protected target, even in the presence of uncertainties in position and signal-to-noise ratio. In comparison to existing methods, the utilization of stepped-waveform modulation enables improved control over target distribution and CFAR masking. Adaptive power allocation compensates for parameter errors, thereby enhancing robustness. Simulation results reveal that the proposed approach significantly reduces the probability of detecting the true target by over 95% under uncertain conditions, while previous methods experienced degradation. The integration of stepped waveforms optimizes false target jamming, thereby advancing electronic warfare capabilities in countering advanced radar threats. This study establishes design principles for resilient jamming architectures and supports enhanced survivability against radars employing pulse compression and CFAR detection. Moreover, the concepts proposed in this study have the potential for extension to emerging radar waveforms.

关键词： radar jamming false target generation stepped waveform modulation linear frequency modulation constant false alarm rate detection

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Trapping of Particles by a Wideband Vortex Ultrasonic Field

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RUSSIAN PHYSICS JOURNAL 2023年第8期65卷 1257-1261页

作者： Sukhanov, D. Ya. Rosliakov, S. N. Natl Res Tomsk State Univ Tomsk Russia

A method for trapping of particles in a wideband vortex acoustic field in air is proposed. The placement of radiators on the surface of a spherical belt with a radial shift, which ensures the formation of a vortex field, is considered. The results of numerical calculations and of experimental studies are presented. It is shown that in a wideband field there is only one point at which a stable trapping of a particle is maintained.

关键词： acoustic trapping vortex acoustic field ultrasonic phased array linear frequency modulation

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Compressed Sampling of LFM Signals Based on Fractional Fourier Domain 24

Compressed Sampling of LFM Signals Based on Fractional Fouri...

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1st International Conference on Image Processing Machine Learning and Pattern Recognition

作者： Liu, Wenping Huang, Kemeng Zheng, Yanxin Zhu, Jubo Sun Yat Sen Univ Sch Artificial Intelligence Guangzhou Peoples R China

ISBN: (纸本)9798400707032

In response to the challenge posed by excessively high sampling rates resulting from the wide bandwidth of linear frequency modulation (LFM) signals, we exploit the inherent sparsity of LFM signals in the fractional Fourier transform (FRFT) domain. By applying a two-step search method to estimate the optimal order, we construct an orthogonal basis dictionary for discrete fractional Fourier transform corresponding to this order. Integrating principles from compressed sensing (CS) theory, we propose a novel LFM signal compressed sampling method based on the FRFT domain. This method compresses and reconstructs LFM echo signals while simultaneously considering the impact of varying digitalizing bit depths during the analog-to-digital converter (ADC) process. Simulation results demonstrate that our approach achieves a favorable sparse representation of LFM signals, enabling signal reconstruction at approximately 10% of the Nyquist rate, while also exhibiting some attenuation of quantization noise and white Gaussian noise.

关键词： linear frequency modulation Fractional Fourier Transform Sparse Representation Compressed Sensing

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