Huan Liu

China University of Geosciences · School of Automation

Composite materials have been widely used in the aerospace industry and are critical for safe operations. However, the delamination, caused by cyclic loads and corrosive service environment, poses a serious threat to the structural integrity of composite laminates. The acoustic emission technique has been adopted to assess the structural integrity...

Geomagnetic data forecasting plays a critical role for natural disaster institutions to respond promptly or to make decisions for the magnetic storm warning, earthquake early warning, etc. However, the forecasting accuracy is not always reliable due to the spatial correlations among different sites and the temporal correlations from each site measu...

The free induction decay (FID) signal output by a proton precession magnetometer (PPM) is usually only of the micro-volt level, and its frequency is proportional to the magnetic field strength. Therefore, obtaining a high signal-to-noise ratio (SNR) FID signal crucial for improving the measurement accuracy of the magnetometer. The current gold stan...

Magnetic target positioning methods that use magnetic gradient tensors have wide application prospects in unexploded ordnance detection, moving magnetic target tracking, etc. However, the commonly used positioning methods, such as Nara, Frahm, and Scalar Triangulation and Ranging (STAR), still have some problems. Namely, these methods cannot avoid...

Geomagnetic data is vital for predicting earthquakes and magnetic storms. In this regard, a new Bayesian exponential regularized tensor completion framework for sparse geomagnetic data, i.e. BERTC, is proposed to address this problem in the study. First, the spatiotemporal geomagnetic data is reshaped into a 3D tensor with days and hours that featu...

Surface defects directly affect the mechanical properties of industrial strip steel products. To evaluate the integrity of the strip steel surface, a channel-wise global Transformer-based dual-branch network (CGTD-Net) for strip steel surface defect detection, dubbed CGTD-Net, is proposed in this study. First, the strip steel surface images are pre...

Radio Frequency Identification (RFID) technology, is expected to provide a new way for accurate, and convenient localization of underground pipelines. However, a new passive RFID localization method that is closely coupled with complex underground environments is still an unsolved challenge. Firstly, this work analyzes in detail the inductive coupl...

Magnetic field sensing is of great significance for marine geoscience research and industrial engineering. This article proposes a high-precision and dual-mode Overhauser marine magnetometer, which integrates base station monitoring mode and towed mobile survey mode. To accurately extract the frequency of weak free induction decay (FID) signals in...

For proton precession magnetometers, the influence of FID signal noise on the frequency measurement procedure is a significant impediment to improving the precision of geomagnetic field measurements. However, the existing noise suppression methods treat the noise as a system, aiming to reduce its impact on frequency estimation without directly addr...

The wide-range vector magnetic field measurements (up to the order of mT) have been employed for many years to measure currents, and displacements or detect magnetic anomalies in space applications. In recent years, solid-state-based magnetic sensors, such as Hall or magnetic-induction, have been extremely regarded for space missions because of the...

Magnetic anomaly detection (MAD) is one of the most effective methods for engineering and environmental geophysical exploration, and plays an important role in scientific research and human technological innovation. Although numerous systematic and valuable articles have been published on the topic of MAD, they only briefly summarized relevant rese...

In recent years, moderate-strong earthquakes have brought indelible disasters to the safety of people's lives and properties. Hence, exploring the connection between geomagnetic fields and earthquakes, obtaining precursor information, and then realizing the prediction of moderate-strong earthquakes are vital issues that need to be solved urgently....

Magnetic anomaly detection technologies have been widely used for tracking moving targets. In this paper, we present a fast-tracking method for magnetic abnormalities using a distributed Overhauser magnetometer system based on the genetic algorithm. Our proposed framework of the Overhauser magnetometer system employs multiple sensors to eliminate b...

The information on the high-precision and multidirectional magnetic gradient is highly relevant to detecting and locating shallow subsurface unexploded ordnance (UXO). In this article, the design of a 3-D Overhauser magnetic gradiometer is presented. Taking the sensor array interferences and working efficiency into account, a time slice overlapping...

The magnetic anomaly signal tends to be contaminated by ambient environmental noise due to the complexity and diversity in the field of magnetic anomaly detection (MAD). The current denoising methods are effective in improving the signal-to-noise ratio (SNR). However, most of them are only applicable to the Gaussian noise and perform poorly for the...

Directionality problem caused by the rolling of microtag with flowing fluid seriously affects the reliability of an oilwell downhole radio frequency identification (RFID) system. In this article, we propose a novel RFID reader antenna structure using multiple tubular coils for reduced orientation sensitivity. The conventional solenoid coil and sadd...

In the field of magnetic anomaly detection (MAD), the anomaly signal is easy to be submerged by ambient electromagnetic interference. Though the existing noise suppression methods can effectively improve the signal-to-noise ratio (SNR), there are still some intractable problems, such as signal distortion and boundary blur. To solve these problems,...

Multimodal imaging with visible and thermal sensors attracts much attention due to its robustness under challenging illumination conditions. Due to spectral differences, the visible and thermal images are typically misaligned, where image registration is necessary before high-level vision tasks such as information fusion, multimodal object detectio...

The frequency of a free induction decay (FID) signal from an industrial proton precession magnetometer (PPM) is proportional to the magnetic field strength. To achieve high-precision frequency estimation for an FID signal with a low signal-to-noise ratio (SNR), a long estimation period is always required which limits the application scenarios of th...

The real estate market has a significant impact on people’s daily life. Therefore, it is crucial to understand the real estate market from both spatial and temporal perspectives, while there is still a lack of research in real estate industries. In this paper, a regional house price mining and forecasting (RHPMF) framework is proposed to help peopl...

In the field of magnetic anomaly detection (MAD), the anomaly signal is easily submerged by ambient electromagnetic interference. Though the existing noise suppression methods can effectively improve the signal-to-noise ratio (SNR), there are still some intractable problems, such as signal distortion and boundary blur. To solve these problems, a no...

The free induction decay (FID) signal of Overhauser geomagnetic sensors may suffer from saturation distortion in the mobile magnetic survey, which results in the loss of signal envelope information. Aiming to suppress the negative effects of saturation, this paper proposes a recovery method for the FID signal from saturation based on segmented line...

The development of high-performance and miniaturized magnetometers is important for small-scale target magnetic anomaly detection. In this work, a miniaturized three-axis vector magnetometer based on the tunnel magnetoresistance (TMR) technique is investigated for magnetic anomaly detection. First, the miniaturized three-axis TMR vector magnetomete...

The RF excitation coil is an important component of the Overhauser magnetic sensor, which determines whether the dynamic nucleation polarization of the free radical solution can be carried out smoothly. A capacitance-loaded resonant cavity structure is proposed as the RF excitation of the Overhauser magnetic sensor. The structure and equivalent cir...

The effective imaging of metal workpieces is of great significance in the field of nondestructive testing. However, most commonly used detection methods, including radiographic, magnetic flux leakage, and electromagnetic techniques, are easily affected by environmental influences and have small detection ranges. Therefore, a new active imaging appr...

The magnetic anomalies generated by the ferromagnetic targets are usually buried within uncontrollable interference sources, such as the power frequency and random noises. In particular, the variability of the geomagnetic field and the low signal-to-noise ratio (SNR) of the magnetic anomalies cannot be avoided. In this paper, to improve the perform...

Fluxgate sensors are currently widely used for weak magnetic field measurement because of their relatively great performance, such as resolution, power consumption, and measurement of vector magnetic fields directly. Since the analog fluxgate sensor has some drawbacks, e.g., it would be influenced by the noise of the analog circuit. Hence, in recen...

There is a growing demand for a reliable and comprehensive measurement of critical quantities in modern industry. As any individual sensor or measurement does not reflect the overall properties of the object, the use of multiple sensors becomes essential. The industrial Internet of Things finds a diverse range of applications. Accordingly, the abil...

There is a growing demand for a reliable and comprehensive measurement of critical quantities in modern industry. As any individual sensor or measurement does not reflect the overall properties of the object, the use of multiple sensors becomes essential. The industrial Internet of Things finds a diverse range of applications. Accordingly, the abil...

Magnetic sensing platform techniques have been used in many years in an attempt to better evaluate the likelihood of recoverable hydrocarbon reservoirs by determining the depth and pattern of sedimentary rock formations containing magnetic minerals, such as magnetite. Utilizing airplanes, large-area magnetic surveys have been conducted to estimate,...

The measurement while drilling (MWD) system in underground coal mine currently uses wire for signal transmission. However, it has shortcomings such as strict technical requirements for cable drill pipe processing and high cost of use. Electromagnetic measurement while drilling (EM-MWD) is a new technology has a high rate of information transmission...

As a very important part of the RFID system, the tag antenna directly affects the performance of the whole RFID system. In this paper, the design strategies for a high sensitivity ferrite-core RFID tag antenna using in oil well downhole applications is presented. Based on the derived formula of voltage sensitivity for the ferrite-core tag coil ante...

The mission of detecting and locating unexploded ordnance (UXO) such as the landmine, the improvised explosive devised, etc., is still a challenge to be overcome. In this paper, a new active approach for UXO detection through measuring electromagnetic (EM) response with a magnetic sensor is proposed. To further enhance the magnetic field strength o...

The low magnetic field measurement has been utilized since ancient times in order to find economic resources, to detect magnetic anomalies, etc. In this case, the vector magnetic survey can simultaneously obtain the modulus and direction information of the magnetic field, which can contribute to obtaining more precise information and characteristic...

Metal pipe is a key factor affecting the performance of oil well downhole radio frequency identification (RFID) system. This study investigates the optimum separation for coping with the impact of metal pipe on the solenoid coil antenna so as to improve the performance of downhole RFID system. Through the equivalent circuit model of RFID communicat...

The optically pumped cesium magnetometer is a quantum magnetometer based on the Zeeman effect. The frequency of the output Larmor signal is proportional to the magnetic field intensity. Therefore, improving the measurement accuracy of the Larmor frequency can make the magnetic field measurement more accurate. However, the Larmor signal is easily co...

Mutual inductance is a crucial parameter in the design and optimization of coupled antennas in underground radio frequency identification (RFID) systems. In this paper, a simple and accurate modeling method for determining the mutual inductance between two coaxial solenoid antennas with a large ferrite core is proposed. This proposed model is verif...

An Overhauser geomagnetic sensor is a precise instrument commonly employed for geomagnetic field observation, magnetic surveys, and so on. Currently, the miniaturization of the Overhauser geomagnetic sensor is limited due to the lower signal-to-noise ratio. Thus, how to effectively extract weaker free induction decay (FID) signal from a miniaturize...

The diversity of magnetic field information obtained in marine geomagnetic measurements is of great relevance to defining detailed features of the targets. In this article, a solution algorithm based on the combination of scalar and vector fields is proposed. The magnetic direction of the geomagnetic field was obtained by repeatedly applying bias f...

Achieving effective detection of unexploded ordnance (UXO) is of great significance for ensuring the safety of human lives and regional economic development. Differential magnetic tensor gradient systems have strong application prospects for UXO detection because of their low orientation requirements and exceptional sensitivity to weak magnetic fie...

In this Note, we develop a real-time magnetic field imaging system by employing a multi-magneto-inductive (MI) sensor array. The sensor array consists of 3 × 3 tri-axial MI sensors, which we constructed by using three sensor coils. Outputs from several rows of sensors are routed to a master-controller responsible for data pre-processing and data re...

Pipelines serve as the major infrastructure for transmission and distribution in oil and gas and water industries. The health condition of a metallic pipe is determined mainly by the extent to which it is corroded. Thus, the quantification of pitting corrosion in terms of metal loss is required for the understanding of pipe condition. There are dif...

Magnetic flux leakage (MFL) is one of the most popular in-line inspection techniques to detect pipeline corrosion defects. However, the measurement limitation and random error associated with the individual MFL could introduce observable variations to the inspection. One potential way to reduce such variation is to fuse the inspection data from axi...

Earth magnetic field sensors are used to detect the geomagnetic field and are critical for research in the geosciences and in prospecting for mineral resources. Today, the Overhauser sensor is the most accurate scalar sensor among widely applied geomagnetic field sensors. However, the Overhauser sensor shows severe orientation sensitivity due to it...

Corrosion is one of the significant reasons for oil and gas pipeline failures. In pipeline integrity management programmes, the magnetic flux leakage (MFL) technique is widely used to detect and quantify corrosion defects. The inspection results of MFL list the profiles of individual corrosion defects; however, the structural safety of a pipeline n...

High-density resistivity meter is a common instrument used in shallow geophysical exploration. At present, the structure of the centralized high-density resistivity meter is bulky, while the distributed instrument needs more than 7 core cables, and the long measuring line needs to relay power supply to the intelligent electrode to provide enough vo...

The self-oscillating loop is an important part of the optically pumped cesium magnetometer, and its working characteristics directly determine the accurate measurement of external magnetic field. The design of the self-oscillating loop has been discussed in this paper, including a signal conditioning circuit, a phase shifter and a frequency meter....

The traditional aeromagnetic compensation model does not consider the negative effects of the gradient of the geomagnetic background field. Especially in emergency aeromagnetic surveys, this gradient effect is obvious and can reduce the performance of magnetic compensation. To solve this problem, we propose a method of reducing the gradient effect...

Background: the proton precession magnetometer based on dynamic nuclear polarization (DNP) effect, dubbed Overhauser magnetometer, is a high-precision device for weak magnetic field measurement. The Larmor precession of excited protons around the geomagnetic field can generate a free induction decay (FID) signal. The strength of the magnetic field...

The initial orientation error of a coil vector magnetometer directly determines the measurement accuracy of the magnetic field direction. The traditional initial orientation method requires auxiliary manually operated instruments. To solve this problem, we propose an electrical orientation method based on applying bias fields. To analyze quantitati...

In aeromagnetic surveys, poor aircraft heading and weather may frequently cause a classical optically-pumped sensor to enter into or close to its dead zone, which results in unavoidable outliers that seriously reduce aeromagnetic compensation. To address these problems, a method to identify rapidly and pre-cull magnetic outliers based on the gray s...

In this Note, a new compressed sensing-based tuning algorithm has been developed to boost the sensor tuning performance of the proton precession magnetometers (PPMs). An end-to-end framework for the PPM’s sensing free induction decay (FID) signal resonance based on orthogonal matching pursuit compressed sensing (OMPCS), dubbed OMPCS-FID resonance (...

Aiming to overcome the problem of the frequency error between the reference signal and the measured signal in an analog lock-in amplifier, this paper presented a digital lock-in amplifier (DLIA) with accurate frequency automatic tracking to improve its performance. In this paper, a modular design approach based on DSP Builder was employed to develo...

Using a prior data to solve for the characteristic parameters of a moving magnetic target is crucial in its detection. For this purpose, we developed a real-time detection method using distributed scalar sensor networks based on a hybrid algorithm combining particle swarm optimization and the Gauss- Newton method. The magnetic anomaly fitting model...

The proton precession magnetometer (PPM) is a commonly used device to measure the varying magnetic field. Since the frequency of the PPM sensing free induction decay (FID) signal is proportional to the magnetic field, the signal-to-noise ratio (SNR) is always a critical issue that influences the measurement accuracy severely due to the external int...

A towed Overhauser marine geomagnetic magnetometer used for weak magnetic anomaly detection in severe ocean conditions is studied to investigate means to reduce the negative effect of dynamic behavior and magnetic noise associated with ocean waves. For the dynamic effect, a continuous polarization workflow is proposed to enhance the free-induction-...

A miniature magnetic gradient tensor system may be used in small spacecraft for mineral prospecting and detection of unexploded explosive ordnance. The system consists of a magneto-inductive (MI) sensors array, a signal extraction circuit, and a micro-controller. A magnetic gradient full-tensor configuration utilizes four MI sensors arranged in a p...

Concealed metallic object detection is one of the critical tasks for any security system. It has been proved that different objects have their own magnetic fingerprints, which are a series of magnetic anomalies determined by shape, size, physical composition, etc. This study addresses the design of a low-cost power security system for the detection...

The proton precession magnetometer (PPM) is always employed for geomagnetic observation, magnetic anomaly detection, etc., while the tuning performance of the PPM determines the signal-to-noise ratio (SNR) of the free induction decay (FID) signal output from the sensing coil. A tuned circuit was always used for the PPM sensing coil because of its n...

Marine electromagnetic (EM) methods can be used for marine geophysical exploration. We proposed an all-solid-state porous Ag/AgCl electrode with high stability and a long service life as a marine electric field sensor with the ability to withstand deep sea high pressures while improving the accuracy of electric field measurements for long-period ma...

A magnetic sensor of the optically pumped magnetometer may enter a dead zone during an aeromagnetic survey, resulting in unavoidable abnormal data and seriously affecting the effect of aeromagnetic compensation. We propose a fast discrimination and culling method based on the Hough transform to prevent abnormal data from participating in the coeffi...

The free induction decay (FID) transversal signal is always employed by a proton precession magnetometer (PPM) to evaluate the time-domain geomagnetic field. Nevertheless, the signal-to-noise ratio (SNR) is an important factor that severely affects the detection accuracy of the magnetic field due to uncontrollable interference sources, including ra...

The sensor tuning of a proton precession magnetometer determines the signal-to-noise ratio (SNR) of induced free induction decay (FID) signal, while the quality of the FID influences the measurement accuracy of the geomagnetic field. Even though numerous methods have been proven to be effective in improving the tuning precision, how to efficiently...

Proton precession magnetometer (PPM) is a potential device to measure the low-frequency geomagnetic field in the time domain. Nevertheless, the uncontrollable noise such as power frequency noise, random noise, etc., severely affects the detection results. In this paper, aimed to boost the performance of the PPM, a novel real-time processing algorit...

The outliers of magnetic sensor that are inevitable in special aeromagnetic surveys reduce the robustness of ordinary least-squares (OLS), which is widely used for aeromagnetic compensation. To address this problem, we propose an aeromagnetic compensation algorithm based on Huber loss method that is robust to outliers. In the proposed method, diffe...

Aimed to interpolate the geomagnetic data from under-sampled or missing traces, this paper presented an approach based on recurrent neural network (RNN) techniques to avoid the time & labor-intensive nature of the traditional manual and linear interpolation approaches. In this study, a deep learning algorithm, long short-term memory (LSTM) was empl...

The free induction decay (FID) transversal data determines the measurement accuracy of time-dependent geomagnetic fields, whereas the conservation of clean components and removal of noise cannot be easily achieved for this kind of data. Even though numerous techniques have been proven to be effective in improving the signal-to-noise ratio by filter...

In practical applications of electromagnetic measurement while drilling (EM-MWD) in underground coal mine, the signal-to-noise ratio (SNR) of receiver cannot always meet the requirements of reliable communication conditions due to the earth-attenuation, interfering signal from well site, etc. Aimed to solve these problems, this paper presents a low...

Aeromagnetic surveys using unmanned aerial vehicles (UAV) can be used in low-altitude detailed detection of small-scale magnetic anomalies and offers an auxiliary means for geomagnetic survey on land. However, excessive weight of the detection instruments and strong magnetic interference remain problems. To address them, an aeromagnetic system for...

The polarization frequency of free radical solution in Overhauser geomagnetic sensor determines the quality of the Larmor precession signal generated by the sensor. To obtain the polarization frequency accurately, a test apparatus was designed in this paper, which can overcome existing problems in the presently used apparatuses, such as lower resol...

Pulsed eddy current (PEC) technique has been applied as a viable method to detect hidden discontinuities in metallic structures. Conventionally, selected time-domain features are employed to characterize the PEC data, such as peak value, lift-off point of intersection, rising point, crossing time, and differential time to peak. The research present...

If the continuous-wave electromagnetic induction (EMI) method is used to detect plastic anti-personnel (PAP) landmines in strongly mineralized soil, background noise may interfere with and further submerge the weak secondary field generated by the landmine. To analyze quantitatively the characteristics of this noise, a semi-space homogenous medium...

The measurement precision or uncertainty of proton precession magnetometer (PPM) depends on the signal-to-noise ratio (SNR) of the free induction decay (FID) signal induced in the sensing coil. A diversity of weak magnetic measurement applications has benefited from various coils through a more comprehensive and reliable design. Likewise, numerous...

Improving the precision and sampling rate of the resonance frequency of cesium atoms is the key to enhancing the same factors of an airborne optically pumped cesium magnetometer (AOPCM). Aiming at the existed problems of AOPCM and characteristics of resonance signal, this paper proposes a high-precision and fast-sampling frequency measurement metho...

The integrity of geomagnetic data is a critical factor for understanding the evolutionary process of Earth's magnetic field, as it can provide useful information for near-surface exploration, unexploded explosive ordnance (UXO) detection, etc. Aimed to reconstruct geomagnetic data from under-sampled or missing traces, this paper presented an approa...

The parameters in a nuclear magnetic resonance (NMR) free induction decay (FID) signal contain information that is useful in magnetic field measurement, magnetic resonance sounding (MRS) and other related applications. A real time sampled FID signal is well modeled as a finite mixture of exponential sequences plus noise. We propose to use the Hilbe...

Resonant cavity is an important component of Overhauser magnetometer sensor. Its function is to make the working substance generate dynamic nuclear polarization effect in the sensor. An alternative design of resonant cavity based on the birdcage coil structure is proposed to make the resonant frequency in accordance with the polarization frequency...

The measurement accuracy of the larmor frequency of the Overhauser magnetic sensor directly determines the magnetic accuracy of the Overhauser magnetometer. We propose a multi-channel interpolation method for marine magnetic measurements, addressing specifically the deficiencies in traditional measurement methods. The quantization error of the coun...

An automatic wideband 90° phase shifter for optically-pumped cesium magnetometer has been investigated experimentally. As an important part of the self-oscillating optically-pumped cesium magnetometer detecting circuit, the band and automation of the phase shifter directly affect the continuous measurement of the magnetic field. At the same time, a...

The proton precession magnetometer with single sensor is commonly used in geomagnetic observation and magnetic anomaly detection. Due to technological limitations, the measurement accuracy is restricted by several factors such as the sensor performance, frequency measurement precision, instability of polarization module, etc. Aimed to improve the a...

Proton precession magnetometer is a high-precision device for weak magnetostatic field measurement. The measurement accuracy depends on the frequency measurement of free induction decay (FID) signal, while the signal to noise ratio (SNR) is an important factor affecting the results. Many signal processing methods have been proposed to improve the S...

The excitation frequency of radical solution in Overhauser magnetometer probe directly determines the quality of larmor precession signal,which is generated by the probe.In order to obtain the excitation frequency accurately,a test apparatus for measuring the excitation frequency of Overhauser magnetometer probe was designed.In view of the existing...

This paper presents the experimental results of capacitive imaging sensors for structural integrity assessment. The capacitive sensor is based on the measurement of capacitance change due to the anomaly or discontinuity in structures and materials. A number sensor prototypes are investigated in the study. The observation of the scanned image of a A...