| Superconducting quantum interference device(SQUID)is the most sensitive weak magnetic field measurement sensor in the world.Compared with the traditional induction coil,it has the characteristics of low noise,large bandwidth,direct magnetic field measurement and low frequency response linearity,so it is an ideal transient electromagnetic method(TEM)receiving sensor.The high-temperature superconducting magnetometer made by SQUID is mainly used in the ground TEM detection technology.After receiving the TEM secondary field signal processing,the underground resistivity distribution is obtained.The later the signal received reflects the deeper underground information,the detection depth can be improved by optimizing the low frequency noise of the high-temperature superconducting magnetometer.This dissertation focuses on the low-noise optimization method of the high-temperature superconducting magnetometer.The noise optimization is mainly carried out from the two parts of the magnetometer probe and the readout circuit.After the high-temperature superconducting magnetometer is optimized,the indoor and field performance tests are carried out.The main research contents and results of this dissertation are as follows:(1)Research on low noise technology of high-temperature superconducting magnetometer probe.Through the selection of Dewar materials and the special design of the structure,a non-magnetic Dewar with low noise,wide frequency band and high thermal insulation performance has been developed.According to the SQUID device structure and experimental requirements,the probe holder was designed and the performance test of the assembled magnetometer probe was carried out.Based on electromagnetic shielding theory,an electromagnetic shielding device is designed and manufactured,including an electromagnetic shielding box that can be used flexibly and an electromagnetic shielding barrel that is convenient to carry in field experiments,which effectively reduces the interference of external radio frequency noise to the system.(2)Research on low noise technology of high-temperature superconducting magnetometer readout circuit.A low-noise preamplifier circuit is designed by matching the impedance between the preamplifier and SQUID.The relationship between the total input noise of the preamplifier,the collector current and the source resistance in the low frequency band is studied,and the conclusion of the corresponding low-noise optimization is given.Low-noise design is carried out on the power supply circuit,integral circuit,differential circuit and feedback circuit in the readout circuit,and the noise test of the readout circuit is carried out with a dynamic signal analyzer.The measured input voltage noise is reduced from the original1 n V/√Hz@1k Hz is reduced to 0.6n V/√Hz@1k Hz.(3)Indoor and field test of high-temperature superconducting magnetometer.An indoor test environment was constructed and various indicators of the high-temperature superconducting magnetometer were tested indoors and in the field.The test results showed that the system was stable and the static noise level has been improved from 1p T/√Hz to 200 f T/√Hz.Finally,the developed high-temperature superconducting magnetometer in the lead-zinc ore exploration joint experiment conducted with TEM in the Huzhong area of Heilongjiang shows that it is for the purpose of carrying out accurate detection of urban underground space,observation of complex effects of multiple physical fields,and the accurate detection of shallow surface targets in the field of geophysics,and satisfies the demand for the precise exploration of deep underground resources and it also provides new technical means for achieving high-resolution and large-depth exploration of complex underground geological structures. |
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