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| Marine controlled-source electromagnetics-based technology for generating arbitrary-frequency waveforms |
WANG Jie1( ), WANG Meng1,2(), REN Zhi-Bin1, WANG Chen-Tao1, WANG Hui-Min1 |
1. School of Geophysics and Information Technology, China University of Geosciences (Beijing), Beijing 100083, China
2. Key Laboratory of Intraplate Volcanoes and Earthquakes, Ministry of Education, China University of Geosciences (Beijing), Beijing 100083, China |
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Abstract Marine controlled-source electromagnetics (MCSEM) is used to explore resources such as oil and gas hydrates, as well as deep geological structures, by revealing resistivity differences below the seabed. Different excitation frequencies correspond to varying detection depths. To enhance the resistivity imaging of targets beneath the seabed, this study investigated the MCSEM-based technology for generating arbitrary-frequency waveforms to flexibly alter the excitation frequency and improve the exploration effectiveness and efficiency. Using the direct digital frequency synthesis (DDS) chip AD9833 and the joint control of a microcontroller and a complex programmable logic device (CPLD), this study achieved the generation of arbitrary-frequency waveforms with limited precision. The test results indicate that this technology can effectively enhance the spectral adaptability and flexibility of MCSEM.
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Received: 15 April 2024
Published: 08 January 2025
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Schematic diagram of the basic structure of the AD9833
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Overall system diagram
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Block diagram of the system composition
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Circuit diagram of signal generation
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Overall program flow chart
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| D15 | D14 | D13 | D12 | D11 | D10 | D9 | D8 | | 0 | 0 | B28 | HLB | FSEL
ECT | PSEL
ECT | 0 | RESET |
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D15 to D8 control bit functions
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| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 | SLE
EP1 | SLE
EP12 | OPBI
TEN | 0 | DIV2 | 0 | MODE | 0 |
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D7 to D0 control bit functions
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| OPBITEN位 | MODE位 | DIV2位 | VOUT脚 | | 0 | 0 | X | 正弦波 | | 0 | 1 | X | 三角波 | | 1 | 0 | 0 | 方波(DAC数据MSB/2) | | 1 | 0 | 1 | 方波(DAC数据MSB) | | 1 | 1 | X | 保留 |
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VOUT waveform output logic
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Upper computer interface
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Test physical diagram
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Direct frequency test results at different frequencies points
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1.00 Hz adjustment frequency step value test results
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| 主要参数 | 技术指标 | | 输出频率范围/Hz | 0.01~100 | | 频率分辨率/Hz | 0.01 | | 频率步进值/Hz | 0.01 | | 频率稳定度(常温) | ±20 ppm(25±2 ℃) |
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Performance specifications
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