Liangliang Rong

Study of transient electromagnetic method measurements using a superconducting quantum interference device as B sensor receiver in polarizable survey areaTEM measurements using SQUID

Time-domain transient electromagnetic method (TEM) measurements sometimes exhibit a sign reversal in the secondary field during off-time, which is usually attributed to the induced polarization effect. In contrast with the conventional induced polarization method, which employs a current source, TEM with an ungrounded transmitting loop operates using a pure voltage source, which is induced by the primary field switching on and off. We performed TEM measurements in a resistive survey area showing an induced polarization effect, and used a low-temperature superconducting quantum interference device (LT-SQUID) with sensitivity ≈10 fT/√Hz as a magnetic field sensor. A sign reversal in all of our measurements was observed; furthermore, the negative amplitude reached ≈10 pT. In-depth analysis with an extended version of a wire-filament circuit reveals that the large negative signal may be due to discharging of in-ground capacitance, an induced polarization effect. The conduction response of the ground can be re...

Study of transient electromagnetic method measurements using a superconducting quantum interference device as B sensor receiver in polarizable survey area

Time-domain transient electromagnetic method (TEM) measurements sometimes exhibit a sign reversal in the secondary field during off-time, which is usually attributed to the induced polarization effect. In contrast with the conventional induced polarization method, which employs a current source, TEM with an ungrounded transmitting loop operates using a pure voltage source, which is induced by the primary field switching on and off. We performed TEM measurements in a resistive survey area showing an induced polarization effect, and used a low-temperature superconducting quantum interference device (LT-SQUID) with sensitivity ≈10 fT/√Hz as a magnetic field sensor. A sign reversal in all of our measurements was observed; furthermore, the negative amplitude reached ≈10 pT. In-depth analysis with an extended version of a wire-filament circuit reveals that the large negative signal may be due to discharging of in-ground capacitance, an induced polarization effect. The conduction response of the ground can be re...

Initial Results from SQUID Sensor: Analysis and Modeling for the ELF/VLF Atmospheric Noise

In this paper, the amplitude probability density (APD) of the wideband extremely low frequency (ELF) and very low frequency (VLF) atmospheric noise is studied. The electromagnetic signals from the atmosphere, referred to herein as atmospheric noise, was recorded by a mobile low-temperature superconducting quantum interference device (SQUID) receiver under magnetically unshielded conditions. In order to eliminate the adverse effect brought by the geomagnetic activities and powerline, the measured field data was preprocessed to suppress the baseline wandering and harmonics by symmetric wavelet transform and least square methods firstly. Then statistical analysis was performed for the atmospheric noise on different time and frequency scales. Finally, the wideband ELF/VLF atmospheric noise was analyzed and modeled separately. Experimental results show that, Gaussian model is appropriate to depict preprocessed ELF atmospheric noise by a hole puncher operator. While for VLF atmospheric noise, symmetric α-stable (SαS) distribution is more accurate to fit the heavy-tail of the envelope probability density function (pdf).

STUDY OF TEM MEASUREMENTS UTILIZING SQUID AS B SENSOR RECEIVER IN POLARIZABLE SURVEY AREA

Time-domain transient electromagnetic method (TEM) measurements sometimes exhibit a sign reversal in the secondary field during off-time, which is usually attributed to the induced polarization effect. In contrast with the conventional induced polarization method, which employs a current source, TEM with an ungrounded transmitting loop operates using a pure voltage source, which is induced by the primary field switching on and off. We performed TEM measurements in a resistive survey area showing an induced polarization effect, and used a low-temperature superconducting quantum interference device (LT-SQUID) with sensitivity ≈10 fT/√Hz as a magnetic field sensor. A sign reversal in all of our measurements was observed; furthermore, the negative amplitude reached ≈10 pT. In-depth analysis with an extended version of a wire-filament circuit reveals that the large negative signal may be due to discharging of in-ground capacitance, an induced polarization effect. The conduction response of the ground can be re...

Two-Pole Integrator SQUID Readout Electronics With High Slew Rate and Small Closed-Loop Frequency Response Peak

Direct-readout electronics with high slew rate and small closed-loop frequency response peak is described by using a two-pole integrator for superconducting quantum interference device (SQUID) applications. In our experiment, a weakly damped niobium-SQUID magnetometer with a large flux-to-voltage transfer coefhcient ∂V/∂Φ of about 380 μV/Φ0 was used to suppress the contribution of direct-readout preampliher noise. A two-stage preampliher was employed, and integrator parameters were optimized to extend the system slew rate, while minimizing the closed-loop frequency response peak. A slew rate of 2.7 Φ0/μs (at 10 kHz) is achieved with only 1-dB peak at 50 kHz in closed-loop frequency response, which means higher system stability. This system was verihed by recording undistorted transient electromagnetic held bipolar square-pulse signals, which required high slew rate and broad bandwidth.