Portable Frequency Domain Electromagnetic Sensor for Shallow Underground Metal Detection
As the received signals in shallow surface electromagnetic exploration are extreme-ly weak and they are easily influenced by such environmental factors as cosmic radiation elec-tromagnetic noise,power frequency,harmonic interference,and industrial electrical noise.When using electromagnetic induction,the coupling between coils inevitably affects the sys-tem,resulting in low signal-to-noise ratio,severe primary field interference,and the re-ceived signals easily getting submerged in noise.In this paper,a mutual inductance modeling analysis of the differential model is proposed,and a combined design scheme of receiver-transmitter coil horizontal coaxial differential configuration is introduced to remove the pri-mary field interference.A secondary field digital orthogonal vector demodulation algorithm is proposed in the system acquisition module to extract the amplitude and phase of the electro-magnetic signal.In the data processing module,a wavelet threshold denoising technique is proposed,which uses the signal-to-noise ratio and root mean square error to compare and an-alyze the denoising effects of the measured data with wavelet transform.Finally,a prototype system of portable frequency domain electromagnetic underground metal detection principle is designed based on the above technologies.The experimental results show that the horizon-tal coaxial differential scheme can effectively suppress primary field interference,and the dig-ital orthogonal vector demodulation algorithm can extract the amplitude and phase of the use-ful signal from the noisy signal.By analyzing and comparing the wavelet transform,the sys-tem signal-to-noise ratio is improved by 27.32 dB.The research findings of this paper have practical applications in extracting secondary field signals and removing noise from the ac-quired signals in frequency domain electromagnetic exploration systems.
frequency domain electromagnetic methodsignal filteringdigital lock-in ampli-fierwavelet transform
NETL
NSTL
万方数据
维普
