| With the rapid urbanization in China,the construction of underground infrastructure has increased rapidly,but the underground situation in cities is complex and densely packed with pipelines,which will cause huge losses and seriously endanger people’s lives and properties in case of accidents.Therefore,accurate underground environmental information is necessary for the safe and efficient development of various resources in the shallow surface.Frequency domain electromagnetic method as an active detection method,with the advantages of high resolution,non-invasive,strong anti-interference ability,etc.,suitable for detection in complex environments.Most of the current frequency electromagnetic method detection instruments use induction coils as secondary field signal receiving devices,the instrument is large,low positioning accuracy,this paper designs a new frequency domain electromagnetic method detection system,using magnetoelectric sensor arrays instead of traditional receiving coils,and targeted proposed a weak secondary field signal detection method under strong primary field interference at the same frequency,which improves the detection accuracy and efficiency of the instrument.The main work of this paper is as follows.First,according to the principle of frequency domain electromagnetic method detection,the frequency domain electromagnetic method detection system architecture based on magnetoelectric sensor array is proposed,the inductance characteristics of the transmitting coil are studied,the influence of the parameters of the transmitting coil on the transmitting magnetic moment is clarified through theoretical calculations,and a broadband transmitting coil is designed.The frequency domain electromagnetic method metal target detection model is established,and the effects of primary field characteristics,target geometric characteristics,target material properties,and environmental factors on the secondary field response are analyzed.Secondly,the coupling mechanism and operating mode of the stacked magnetoelectric composites are analyzed,the model of magnetoelectric effect at low frequency and resonant state of the magnetoelectric composites under the equivalent circuit method is calculated theoretically,and the effects of material properties,dimensions and external magnetic field on the magnetoelectric response are analyzed.The FeGa/PZT-5A/FeGa three-layer magnetoelectric composites are designed,and the low-frequency magnetoelectric voltage coefficients are calculated and prepared.After testing,the magnetoelectric composite has an optimum bias magnetic field of 200 Oe,resonant frequency of 78.4k Hz,low-frequency magnetoelectric voltage coefficient of 112.3m V/Oe,and good linearity for AC magnetic fields less than 1Oe.The magnetoelectric composite bias magnetic circuit structure is determined by finite element simulation analysis,and a non-magnetic package structure is designed.The signal conditioning circuit of the sensor is designed to achieve broadband amplification of weak signals.The test can obtain a low frequency magnetoelectric voltage coefficient of 1.115V/Oe at 10 x gain,magnetic field resolution better than 1n T and noise equivalent magnetic induction of 24 p T/√Hz at 1k Hz.Since the strong primary field of the same frequency seriously affects the detection effect,the finite element simulation of the primary field of the transmitting coil is carried out to obtain the spatial distribution law of the primary field,and then the differential sensor structure is designed according to the working mode of the magnetoelectric sensor,the primary field rejection ratio is about-40 d B,which basically eliminates the primary field interference,and the secondary field sensitivity is multiplied according to the secondary field characteristics.For the demand of weak secondary field signal detection,the principle of quadrature lock-in amplifier is analyzed and programmed with LabVIEW software to meet the demand of weak secondary field detection in the detection system.Finally,the frequency domain electromagnetic detection system based on magnetoelectric sensor array is built,and the secondary field response of the detection system is tested at different detection depths,and the secondary field sensitivity of each channel is corrected.The secondary field response law of the system under different emission currents and different targets is analyzed.The secondary field response of each channel at different horizontal positions is studied,and a metal target localization method is proposed,with good localization accuracy.An underground metal target detection experiment is designed to verify the effectiveness of the detection system. |
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