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An agile very low frequency radio spectrum explorer

Research in Astronomy and Astrophysics 2021年第4期21卷 139-148页

作者： Lin-Jie Chen Yi-Hua Yan Qiu-Xiang Fan Li-Hong Geng Susanta Kumar Bisoi Key Laboratory of Solar Activity National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China School of Astronomy and Space Sciences University of Chinese Academy of SciencesBeijing 100049China Institute of Automation Chinese Academy of SciencesBeijing 100190China National Institute of Technology Rourkela 769008India

The very low frequency(VLF)regime below 30 MHz in the electromagnetic spectrum has presently been drawing global attention in radio astronomical research due to its potentially significant science outcomes exploring many unknown extragalactic sources,transients,and so ***,the nontransparency of the Earth’s ionosphere,ionospheric distortion and artificial radio frequency interference(RFI)have made it difficult to detect the VLF celestial radio emission with ground-based instruments.A straightforward solution to overcome these problems is a space-based VLF radio telescope,just like the VLF radio instruments onboard the Chang’E-4 *** building such a space telescope would be inevitably costly and technically *** alternative approach would be then a ground-based VLF radio ***,in the period of post 2020 when the solar and terrestrial ionospheric activities are expected to be in a’calm’state,it will provide us a good chance to perform VLF ground-based radio *** such an opportunity,we built an agile VLF radio spectrum explorer co-located with the currently operational Mingantu Spectra Radio Heliograph(MUSER).The instrument includes four antennas operating in the VLF frequency range 1-70 *** with them,we employ an eight-channel analog and digital receivers to amplify,digitize and process the radio signals received by the *** present in the paper this VLF radio spectrum explorer and the instrument will be useful for celestial studies of VLF radio emissions.

关键词： very low frequency instrumentation:polarimeters methods:data analysis

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SIMULATION STUDY ON very low frequency VECTOR HYDROPHOE APPLICATION PLATFORM’S SUSPENSION SYSTEM

SIMULATION STUDY ON VERY LOW FREQUENCY VECTOR HYDROPHOE APPL...

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2013全国压电和声波理论及器件技术研讨会

作者： Tian-ji ZHAO Hong-juan CHEN Hu ZHANG College of Underwater Acoustic Engineering Harbin Engineering University Science and Technology on Underwater Acoustic Laboratory Harbin Engineering University

Aiming at very low frequency vector hydrophone application platfonn,this paper simulated and analyzed its performance by using finite element analysis *** result of simulation indicates that the dynamic performance of suspension system obviously effect the vector hydrophone’s acoustic *** comparing to the experimental results,this paper realized the anticipation of lower limit frequency of co-oscillating vector *** this basis,this paper designed and simulated a new structural model of vector *** analysis results have reference value for engineering application of vector hydrophone.

关键词： very low frequency Co-oscillating vector hydrophone Finite element simulation Elastic element

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Contaminated Effect of Geomagnetic Storms on Pre-Seismic Atmospheric and Ionospheric Anomalies during Imphal Earthquake

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Open Journal of Earthquake Research 2020年第5期9卷 383-402页

作者： Sagardweep Biswas Subrata Kundu Soujan Ghosh Swati Chowdhury Shih-Sian Yang Masashi Hayakawa Suman Chakraborty Sandip K. Chakrabarti Sudipta Sasmal Indian Centre for Space Physics Kolkata India Institute of Space Science National Central University Chinese Taipei Hayakawa Institute of Seismo Electromagnetics Co. Ltd. UEC Alliance Center Chofu Tokyo Japan Physical Research Laboratory Navrangpura Ahmedabad India

Study of seismo-ionospheric coupling mechanism demands the quiet geomagnetic condition to eliminate any kind of contamination in the lower atmospheric and ionospheric parameters. In this manuscript, we present the effect of back to back two geomagnetic storms before a strong earthquake happened in Imphal, India on January 4, 2016 (M = 6.7). We studied the lower ionospheric irregularities for the duration of 31 days by computing the nighttime fluctuations in very low frequency (VLF) radio signal received transmitter JJI (22.2 kHz) in Japan at Ionospheric and Earthquake Research Centre & Optical Observatory (IERCOO), Sitapur, India. We also studied the presence of Atmospheric Gravity Wave (AGW) in nighttime VLF signal in lower ionospheric heights and the same computed that from SABER/TIMED satellite. Two geomagnetic storms occurred on December 21, and 31, 2015. By the conventional analysis, we found that there is a significant decrease in nighttime trend and an increase in nighttime fluctuations around 15 days before the earthquake and just on the first storm and thus the pre-seismic effects on VLF signal gets contaminated due to the presence of storms. The wave-like structure in VLF fluctuations shows significant increase in intensity by using Fourier and Wavelet analysis before the earthquake. By analysis of SABER data, we found significant enhancement in AGW around 10 days before the earthquake. As the wavelike structures are coming from neutral acoustics reasons from pressure or temperature variations, this paper exhibits a significant example of contamination in ionospheric parameters due to geomagnetic storm where the acoustics parameters remain un-contaminated.

关键词： very low frequency Wave Propagation Earthquake Precursory Atmospheric Gravity Wave Geomagnetic Strom SABER/TIMED

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Review of through-the-earth communication technologies

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Journal of Measurement Science and Instrumentation 2014年第2期5卷 64-67页

作者： HAO Jian-jun GONG Yu-qin College of Electronic Communication and Physics Shandong University of Science and Technology Qingdao 266590 China

In this paper, development of through-the-earth communication technologies is summarized, as well as the operating principles and performances. The propagation loss, frequency band and power efficiency are also analyzed. We can know that among these technologies, the antenna induction method is more popular, but the communication system with ground electrodes is more promising due to its high energy efficiency. The communication with elastic wave （seismic） is not suitable for emergency communication when the accidents of rock burst or land slide occur.

关键词： through-the-earth communication very low frequency transmission attenuation

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