宽频带时频电磁接收机关键技术研究
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摘要
时频电磁法包括大地电磁法、可控音频大地电磁法和瞬变电磁法，是通过天然或人工产生的电磁场研究地球内部介质的电性结构的地球物理方法，被广泛应用于金属与非金属矿床、油气田、地下水等资源和能源的勘查以及地震等自然灾害的监测。本文以宽频带、低噪声采集为研究目标，以高精度模数转换技术（Δ-Σ技术）、GPS授时同步技术、大规模可编程逻辑技术（FPGA）、固态硬盘存储技术、高性能低功耗处理器、信号处理技术为基础，参考国外先进多功能电磁法仪器设计，研制出宽频带时频电磁法接收机样机。利用全波采集、双极性叠加方法，实现时频电磁法接收机的瞬变电磁接收；利用自动扫描、整周期采集技术，实现可控音频大地电磁法高效率施工、相关参数准确获取；利用高采样率采集、数字滤波抽取的方法，实现大地电磁宽频带、长周期的采集。自主研制的科研样机应用于松江河地热勘探、大台沟铁矿探测等可控音频大地电磁野外实验，取得了与地质结构相符的结果；进行了室内瞬变电磁模型实验以及室外对比实验，验证了仪器的低噪声，并与商业化瞬变电磁仪的指标进行了对比；在长春孙更屯进行了大地电磁测量，与早期凤凰公司的V5产品所测得的结果一致。
The current situation is that geophysical equipment such as electromagnetic instrument heavily depends on imports, and instrument developed has not been given attention for a long time. Development Plan Outline for Medium and Long Term Science and Technology Development (2006—2020) suggest that the demand of time‐frequency electromagnetic Instrument will be a further increase, so it is pressing to develop it with freedom knowledge property right and excellent performance for the healthy development of geophysical exploration in our country. The rapid development of high‐precision analog‐digital conversion technology, GPS timing technology, solid‐state disk storage technology, high performance processor, signal processing technology will help to deal with key technologies such as high‐frequency weak signal detection and extraction,1/f low‐frequency noise removed, synchronization trigger for remote sending and receiving, real‐time storage of large data amounts, so it is feasible to develop broadband electromagnetic receiver.
Started with the principle of TEM, CSAMT, MT, collected and compared with technical specifications of the foreign instrument, designed by modular concept, electromagnetic receiver is made of a control board, five high‐frequency board, five low‐frequency board. The control board is based on USB2.0transfer protocol, and control FPGA controller through microcontroller bus, which includes SLAVE controller, large‐capacity FIFO controller, SPI bus converter, GPS information converter, synchronization trigger and calibration signal transmitter. The control board has solved the problem of high‐speed data transmission by combination of slave FIFO and large‐capacity FIFO. Slave FIFO is combined with USB2.0microcontroller and main controller simulated by FPGA. Large‐capacity FIFO is made of SRAM and small scheduled FIFO which is integrated in FPGA. In order to decrease crosstalk, the communicate of each functional board and control board is completed by magnetic coupling isolation, and reasonable layout, shielded, ground handing, power isolation is used too, which can decrease interference and reduce noise.
On the basis of analyzing how to decrease1/f noise by chopper technology and Δ‐∑technology, the low‐frequency board achieve targets that1/f noise corner frequency is lower than0.1Hz, and amplitude spectrum of frequency lower than corner frequency is less than10‐8uV. Through the experiment of signal test, short circuit test, sensor matching test, the low‐frequency board can be used in the acquisition of a large dynamic range, which includes MT, LOTEM and CSAMT. It also verify the long‐term reliability and standability of the low‐frequency board. After designed high‐frequency acquisition boards based on AD7763and AK5394, it verify the advantages of the AK5394through noise test and sensor matching test.The final design of the high‐frequency board has achieved these target that the peak‐peak value of noise is less than10~(‐7) uV and amplitude spectrum less than10~(‐7)uV, so the acquisition of AMT, TEM and CSAMT can use high‐frequency board. The successful design of the low and high frequency board laid the foundation of broadband low noise acquisition.
Because of non‐consisitency caused by component differences, the calibration souce and synchronous clock board generates1V peak value by GPS PPS trigging benchmark source chopper and analog amplifier operation circuits, in order to providing calibration source for low and high frequency acquisition. It also integrates circuit of OXCO synchronization and GPS synchronization, which is combinationed with FPGA to achieve line trig, gps trig and OXCO trig.
Three electromagnetic methods of Data recording and storage strategy has been analyzed in detail. On the basis of thorough analysis of the TEM signal characteristics, TEM data recording is achieved by binary full waveform records and bipolar overlay method of handing. A series of basic logarithmic interval frequencies used for CSAMT is designed by the advantages of the whole cycle of acquisition. CSAMT sweep data is automatically recorded by tbl table completed by own TBLEditor softeware. After analysis of the relevant characteristics of the MT signal,the MT recording method is full‐wave acqusisition by2000Hz, and then PC104generates time series data of125/2Hz,125/64Hz and125/2048Hz by digital filter and extract.
The right of time‐frequency electromagnetic design is verified by the experiment in Jilin Changbaishan geothermal resource exploration, Liaoning Dataigou iron mine explortation, Changchun Cultural Square, Changchun Sungengdun and so on. Compared with similar instruments on the market today, it has a great advantage.
The current situation is that geophysical equipment such as electromagnetic instrument heavily depends on imports, and instrument developed has not been given attention for a long time. Development Plan Outline for Medium and Long Term Science and Technology Development (2006—2020) suggest that the demand of time‐frequency electromagnetic Instrument will be a further increase, so it is pressing to develop it with freedom knowledge property right and excellent performance for the healthy development of geophysical exploration in our country. The rapid development of high‐precision analog‐digital conversion technology, GPS timing technology, solid‐state disk storage technology, high performance processor, signal processing technology will help to deal with key technologies such as high‐frequency weak signal detection and extraction,1/f low‐frequency noise removed, synchronization trigger for remote sending and receiving, real‐time storage of large data amounts, so it is feasible to develop broadband electromagnetic receiver.
Started with the principle of TEM, CSAMT, MT, collected and compared with technical specifications of the foreign instrument, designed by modular concept, electromagnetic receiver is made of a control board, five high‐frequency board, five low‐frequency board. The control board is based on USB2.0transfer protocol, and control FPGA controller through microcontroller bus, which includes SLAVE controller, large‐capacity FIFO controller, SPI bus converter, GPS information converter, synchronization trigger and calibration signal transmitter. The control board has solved the problem of high‐speed data transmission by combination of slave FIFO and large‐capacity FIFO. Slave FIFO is combined with USB2.0microcontroller and main controller simulated by FPGA. Large‐capacity FIFO is made of SRAM and small scheduled FIFO which is integrated in FPGA. In order to decrease crosstalk, the communicate of each functional board and control board is completed by magnetic coupling isolation, and reasonable layout, shielded, ground handing, power isolation is used too, which can decrease interference and reduce noise.
On the basis of analyzing how to decrease1/f noise by chopper technology and Δ‐∑technology, the low‐frequency board achieve targets that1/f noise corner frequency is lower than0.1Hz, and amplitude spectrum of frequency lower than corner frequency is less than10‐8uV. Through the experiment of signal test, short circuit test, sensor matching test, the low‐frequency board can be used in the acquisition of a large dynamic range, which includes MT, LOTEM and CSAMT. It also verify the long‐term reliability and standability of the low‐frequency board. After designed high‐frequency acquisition boards based on AD7763and AK5394, it verify the advantages of the AK5394through noise test and sensor matching test.The final design of the high‐frequency board has achieved these target that the peak‐peak value of noise is less than10~(‐7) uV and amplitude spectrum less than10~(‐7)uV, so the acquisition of AMT, TEM and CSAMT can use high‐frequency board. The successful design of the low and high frequency board laid the foundation of broadband low noise acquisition.
Because of non‐consisitency caused by component differences, the calibration souce and synchronous clock board generates1V peak value by GPS PPS trigging benchmark source chopper and analog amplifier operation circuits, in order to providing calibration source for low and high frequency acquisition. It also integrates circuit of OXCO synchronization and GPS synchronization, which is combinationed with FPGA to achieve line trig, gps trig and OXCO trig.
Three electromagnetic methods of Data recording and storage strategy has been analyzed in detail. On the basis of thorough analysis of the TEM signal characteristics, TEM data recording is achieved by binary full waveform records and bipolar overlay method of handing. A series of basic logarithmic interval frequencies used for CSAMT is designed by the advantages of the whole cycle of acquisition. CSAMT sweep data is automatically recorded by tbl table completed by own TBLEditor softeware. After analysis of the relevant characteristics of the MT signal,the MT recording method is full‐wave acqusisition by2000Hz, and then PC104generates time series data of125/2Hz,125/64Hz and125/2048Hz by digital filter and extract.
The right of time‐frequency electromagnetic design is verified by the experiment in Jilin Changbaishan geothermal resource exploration, Liaoning Dataigou iron mine explortation, Changchun Cultural Square, Changchun Sungengdun and so on. Compared with similar instruments on the market today, it has a great advantage.
引文
[1]中国科学院矿产资源领域战略研究组.中国至2050年矿产资源科技发展线路图[M].北京：科学出版社,2009.
[2]滕吉文．强化第二深度空问金属矿产资源探查，加速发展地球物理勘探新技术与仪器设备的研制及产业化[J]．地球物理学进展，2010，25(3)：729-748，
[3]董树文,李廷栋. SinoProbe—中国深部探测实验[J]．地质学报,2009,83(7):895-909.
[4]中国地球物理学会.2008-2009地球物理学学科发展报告[M].北京：科学出版社,2009.
[5]卓贤军,陆建勋.“极低频探地工程”在资源探测和地震预测中的应用与展望[J].舰船科学技术,2010,32(6):3-7.
[6]林君,王言章,刘长胜.高端地球物理仪器研究及我国产业化现状[J].仪器仪表学报,2010,31(8):174-180.
[7]林君.电磁探测技术在工程与环境中的应用现状[J].物探与化探，2000,24(3):165-177.
[8]Louis Cagniard. BASIC THEORY OF THE MAGNETO-TELLURIC METHOD OFGEOPHYSICAL PROSPECTING[J]. Geophysics,1953,18:605-635.
[9]Goldstein M A, Strangway D W. Audio-frequency magnetotellurics witha grounded electric dipole source[J]. Geophysics,1975,40(4):669-683.
[10]P. Turberga, I. Müllera, F. Fluryb. Hydrogeological investigation ofporous environments by radiomagnetotelluric-resistivity (RMT-R12–240kHz)[J].Geophysics,1994,31:133–143.
[11]严良俊,胡文宝,陈清礼,胡家华.长偏移距瞬变电磁测深法在碳酸盐岩覆盖区落实局部构造的应用效果[J],2001,23(2):271-276.
[12]刘国栋.我国大地电磁测深的发展[J].地球物理学报,1994,37(A01):301-310.
[13]Carlos Torres-Verdin, Francis X, Bostick. Principles of spatialsurface electric field filtering in magnetotellurics:Electromagnetic array profiling (EMAP)[J]. GEOPHYSICS,57(4):603-622.
[14]Bruce Hobbs,Anton Ziolkowski, David Wright. Multi-TransientElectromagnetics (MTEM)–controlled source equipmentfor subsurfaceresistivity investigation.IAGA WG1.2on Electromagnetic Inductionin the Earth Extended Abstract18th Workshop El Vendrell,2006.
[15]张文秀.大深度分布式电磁探测接收系统原理样机研究[D].长春：吉林大学，2009.
[16]程德福,王君,李秀平等.混场源电磁法仪器研制进展[J].地球物理学进展,2004,19(4):778-781.
[17]林品荣,郭鹏,石福升等.大深度多功能电磁探测技术研究[J]．地球学报,2010,31(2),149-154.
[18]何继善.广域电磁法和伪随机信号电法[M].北京:高等教育出版社,2010.
[19]李金铭.地电场与电法勘探[M].北京：地质出版社，2005：216-227
[20]Nabighian N编著，赵经祥等译.勘查地球物理电磁法[M].第一卷，北京：地质出版社，1992.
[21]底青云，王若等．可控音频大地电磁数据正反演及方法应用[Ｍ]．北京：科学出版社，2008．
[22]陈明生，闫述.CSAMT勘探中场区、记录规则、阴影及场源复印效应的解析研究[J].地球物理学报，2005，48(4):951-958.
[23]牛之琏．时间域电磁法原理[M]．长沙：中南工业大学出版社，1992．15-20．
[24]嵇艳鞠.浅层高分辨率全程瞬变电磁系统中全程二次场提取技术研究[D].长春：吉林大学,2004.
[25]王世隆.基于VIETS的类VXI总线研究与开发[D].长春：吉林大学,2008.
[26]陈健,凌振宝,陈鹏飞等.近红外光谱仪数据采集系统的研制[J].电子测量与仪器学报,2012,26(1):72-77.
[27]吴继华,王诚. Altera FPGA/CPLD设计（高级篇）[M].北京:人民邮电出版社,2009.
[28]宁伟超,程东方,张春燕等. CMOS磁场传感器芯片中斩波放大器的设计[J].仪表技术与传感器,2007(4):53-55.
[29]李冬梅,高文焕.用于过采样∑—△A／D转换器的∑—△调制器[J].微电子学,2000年30(2):72-75.
[30]康华光，邹寿彬.数字电子技术基础[M].北京：高等教育出版社，2000.
[31]高印寒,吴保军,江游等.四极质谱数据采集控制技术的设计及FPGA的实现[J].吉林大学学报(工学版),2009,39(增1):206-209.
[32]王淑玲，林君，段清明.基于GPS的瞬变电磁系统同步测量控制器研究.石油仪器，2001，15(1):13-15
[33]陈健,林君,张文秀等基于直接数字频率合成技术的类激发极化信号源研制[J].物探与化探,2010,34(5):600-609.
[34]郑采君,肖原.新型磁耦合隔离电路设计电子设计工程201119(4):162-166.
[35]孙肖子,邓建国等.电子设计指南[M].北京:高等教育出版社,2006.
[36]程德福,林君.智能仪器[M].北京：机械工业出版社，2005.
[37]王忠,林君. TEM接收机低噪声抗饱和前放电路设计[J].吉林大学学报(信息科学版),2002,20(4):1-4.
[38]王世隆,林君,王言章.等直升机式航空时间域电磁法全波收录[J].吉林大学学报（工学版）201141(3)：776-781.
[39]严家斌.大地电磁信号处理理论及方法研究[D].长沙：中南大学,2003.
[2]滕吉文．强化第二深度空问金属矿产资源探查，加速发展地球物理勘探新技术与仪器设备的研制及产业化[J]．地球物理学进展，2010，25(3)：729-748，
[3]董树文,李廷栋. SinoProbe—中国深部探测实验[J]．地质学报,2009,83(7):895-909.
[4]中国地球物理学会.2008-2009地球物理学学科发展报告[M].北京：科学出版社,2009.
[5]卓贤军,陆建勋.“极低频探地工程”在资源探测和地震预测中的应用与展望[J].舰船科学技术,2010,32(6):3-7.
[6]林君,王言章,刘长胜.高端地球物理仪器研究及我国产业化现状[J].仪器仪表学报,2010,31(8):174-180.
[7]林君.电磁探测技术在工程与环境中的应用现状[J].物探与化探，2000,24(3):165-177.
[8]Louis Cagniard. BASIC THEORY OF THE MAGNETO-TELLURIC METHOD OFGEOPHYSICAL PROSPECTING[J]. Geophysics,1953,18:605-635.
[9]Goldstein M A, Strangway D W. Audio-frequency magnetotellurics witha grounded electric dipole source[J]. Geophysics,1975,40(4):669-683.
[10]P. Turberga, I. Müllera, F. Fluryb. Hydrogeological investigation ofporous environments by radiomagnetotelluric-resistivity (RMT-R12–240kHz)[J].Geophysics,1994,31:133–143.
[11]严良俊,胡文宝,陈清礼,胡家华.长偏移距瞬变电磁测深法在碳酸盐岩覆盖区落实局部构造的应用效果[J],2001,23(2):271-276.
[12]刘国栋.我国大地电磁测深的发展[J].地球物理学报,1994,37(A01):301-310.
[13]Carlos Torres-Verdin, Francis X, Bostick. Principles of spatialsurface electric field filtering in magnetotellurics:Electromagnetic array profiling (EMAP)[J]. GEOPHYSICS,57(4):603-622.
[14]Bruce Hobbs,Anton Ziolkowski, David Wright. Multi-TransientElectromagnetics (MTEM)–controlled source equipmentfor subsurfaceresistivity investigation.IAGA WG1.2on Electromagnetic Inductionin the Earth Extended Abstract18th Workshop El Vendrell,2006.
[15]张文秀.大深度分布式电磁探测接收系统原理样机研究[D].长春：吉林大学，2009.
[16]程德福,王君,李秀平等.混场源电磁法仪器研制进展[J].地球物理学进展,2004,19(4):778-781.
[17]林品荣,郭鹏,石福升等.大深度多功能电磁探测技术研究[J]．地球学报,2010,31(2),149-154.
[18]何继善.广域电磁法和伪随机信号电法[M].北京:高等教育出版社,2010.
[19]李金铭.地电场与电法勘探[M].北京：地质出版社，2005：216-227
[20]Nabighian N编著，赵经祥等译.勘查地球物理电磁法[M].第一卷，北京：地质出版社，1992.
[21]底青云，王若等．可控音频大地电磁数据正反演及方法应用[Ｍ]．北京：科学出版社，2008．
[22]陈明生，闫述.CSAMT勘探中场区、记录规则、阴影及场源复印效应的解析研究[J].地球物理学报，2005，48(4):951-958.
[23]牛之琏．时间域电磁法原理[M]．长沙：中南工业大学出版社，1992．15-20．
[24]嵇艳鞠.浅层高分辨率全程瞬变电磁系统中全程二次场提取技术研究[D].长春：吉林大学,2004.
[25]王世隆.基于VIETS的类VXI总线研究与开发[D].长春：吉林大学,2008.
[26]陈健,凌振宝,陈鹏飞等.近红外光谱仪数据采集系统的研制[J].电子测量与仪器学报,2012,26(1):72-77.
[27]吴继华,王诚. Altera FPGA/CPLD设计（高级篇）[M].北京:人民邮电出版社,2009.
[28]宁伟超,程东方,张春燕等. CMOS磁场传感器芯片中斩波放大器的设计[J].仪表技术与传感器,2007(4):53-55.
[29]李冬梅,高文焕.用于过采样∑—△A／D转换器的∑—△调制器[J].微电子学,2000年30(2):72-75.
[30]康华光，邹寿彬.数字电子技术基础[M].北京：高等教育出版社，2000.
[31]高印寒,吴保军,江游等.四极质谱数据采集控制技术的设计及FPGA的实现[J].吉林大学学报(工学版),2009,39(增1):206-209.
[32]王淑玲，林君，段清明.基于GPS的瞬变电磁系统同步测量控制器研究.石油仪器，2001，15(1):13-15
[33]陈健,林君,张文秀等基于直接数字频率合成技术的类激发极化信号源研制[J].物探与化探,2010,34(5):600-609.
[34]郑采君,肖原.新型磁耦合隔离电路设计电子设计工程201119(4):162-166.
[35]孙肖子,邓建国等.电子设计指南[M].北京:高等教育出版社,2006.
[36]程德福,林君.智能仪器[M].北京：机械工业出版社，2005.
[37]王忠,林君. TEM接收机低噪声抗饱和前放电路设计[J].吉林大学学报(信息科学版),2002,20(4):1-4.
[38]王世隆,林君,王言章.等直升机式航空时间域电磁法全波收录[J].吉林大学学报（工学版）201141(3)：776-781.
[39]严家斌.大地电磁信号处理理论及方法研究[D].长沙：中南大学,2003.