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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...
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... implies that the amplitude of the FID signal can be increased theoretically by 660 times. Figure 4 illustrates the hardware structure of an Over- hauser magnetometer, which can be divided into two parts: (1) the sensor and (2) the instrument host. The sensor consists of high frequency excitation coils, low frequency receiving coils, and the free radical solution sealed in an organic glass bottle. ...
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A co-axial cavity type Overhauser sensor for geomagnetic field measurement has been analyzed. The cavity with free radical solution has inductance of 32 nH. A Radio Frequency (RF) matching network has been designed to couple the RF power at proton polarization frequency of 40 MHz. The tuned circuit has quality factor of 150. The required voltage fo...
Citations
... The output of scalar magnetometers only involves the total strength of the magnetic field [4] . Typically, Overhauser magnetometers with a resolution of 0.01 nT are widely accepted as a standard instrument for measuring the magnetic field [5] . The demand for multi-information measurement accelerates the development of a vector magnetometer. ...
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 magnetometer is constructed, and then, the limit of detection tests and the magnetic anomaly detection tests are performed. The indoor experimental results show that the proposed magnetometer can capture the magnetic anomalies higher than 3.9 nT, with the low-frequency equivalent magnetic noise of 46.89 pT/√Hz@1Hz. The outdoor experimental results show that the proposed magnetometer can effectively detect small-scale magnetic targets such as hammers at a distance of about 1.5 m. With the advantages of small size, low power consumption, and high magnetic measurement sensitivity, the TMR magnetometer has great application prospects for long-term magnetic anomaly monitoring, high-density magnetic imaging, and other fields.
... Magnetometers have been used to perform magnetic resonance imaging (MRI) [3,4] and magnetoencephalography [5,6] (detection of magnetic fields generated by brain activity). In industry, magnetometers have found uses in industrial imaging [7], mechanical stress measurements [8], coal and mineral exploration [9], and in the oil industry. ...
... Lower frequencies could not be explored due to the short measurement duration. The system's response to atom number was also investigated, shown inFigure 5.9. The atom number in the PGC phase (just before the start of magnetometry) was varied by changing the MOT loading time, and the sensitivity recorded. ...
This thesis details progress in radio-frequency atomic magnetometry with ultracold rubidium atoms. Motivations and context are first covered, before an introduction of the main concepts required to understand the underlying physics is given. At first, a cold atom magnetometer is designed, built and characterised. Consistent 20 µK atoms are produced. Radio-frequency (RF) atomic magnetometry (AM) is performed by placing the atoms in a bias magnetic field and generating coherent precession with an external AC field. A noise floor at 330 pT/√Hz defines the sensor’s sensitivity, with a range of applications. RF-AM is then performed with a Bose-Einstein condensate (BEC). The 20 µK atoms are loaded into a magnetic trap, where RF evaporation increases their phase space density (PSD = nλ^3dB, n is the density and λdB is the thermal de Broglie wavelength of the atoms). Next, atoms are transferred into a hybrid dipole trap, collecting in a dimple created at the intersect of two high power laser beams. Production and stabilisation of these beams is described, which are focused down to a 75 µm beam waist at the trap position with a total power of 7 W. Optimisation of the evaporation process in both traps leads to consistent BEC production. A pure condensate with 4x10^4 atoms at 25 nK is reported. Radio-frequency magnetometry is performed at various probe volumes. With systematic optimisation a best AC sensitivity of 24 pT/√Hz with 3.4 × 10^8 atoms in the magnetic trap before evaporation is achieved. This is extended to the BEC with 4 × 10^4 atoms, where an AC sensitivity of 84 nT/√Hz and DC sensitivity of 14 nT/√Hz is reported, bringing previously achieved atomic magnetometry into the micrometer regime. A trade-off must be considered due to reduction in sensitivity at lower probe volumes. Volumes between 1.4×10−7 m^3 and 1.6×10−14 m^3 can be accessed, highlighting the sensors adaptability and tunability for different applications. The results are contextualised in the background of previously achieved magnetometers of various types. Finally, proof-of-concept electromagnetic induction imaging (EMI) measurements are made to confirm the sensor’s viability for high resolution imaging.
... An Overhauser geomagnetic sensor, a kind of high-precision magnetic total field observation device based on the dynamic nuclear polarization effect, plays an important role in the fields of earth and space sciences, mineral resource exploration, earthquake early warning, unexploded ordnance detection, and so on. [1][2][3][4][5] Nevertheless, several problems for magnetic survey applications with an Overhauser geomagnetic sensor still need to be solved. 6,7 For instance, in the marine magnetic survey, how to improve the gradient tolerance of magnetic field measurement, 8 how to suppress the background noise to make sure an available signal-to-noise ratio (SNR) of the sensing signal, 9,10 and so on, 11,12 are still challenges that need to be overcome. ...
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 miniaturized sensor and how to improve the signal quality have become the bottleneck. To address these problems, we came up with an optimal design of the FID signal sensing coil for a miniaturized Overhauser geomagnetic sensor and propose a front-end matching circuit for the sensing coil to inhibit the attenuation of the signal amplitude caused by high impedance, further reducing the overall noise floor of the signal acquisition system. Finally, the field experimental results show that the miniaturized prototype sensor has a smaller volume and mass with an approximate performance compared with the commercial sensor.
... As the cavity cools down to a superconducting condition, the partial ambient magnetic field should be trapped into the radio-frequency cavity. In this case, we can obtain the surface residual resistance variations though measuring the corresponding magnetic field strength [5], [6]. ...
The surface resistance reduction can further suppress the surface power loss of a superconducting radio-frequency cavity. Since the surface resistance of a superconducting radio-frequency cavity is mainly originated from the magnetic flux trapping, and thus the corresponding magnetic field strength could be measured to reflect the residual resistance. A fluxgate magnetometer is always employed to measure the ambient surface magnetic field of a superconducting radio-frequency cavity. However, this kind of equipment is relatively larger than the cavity and always need expensive cost. In this paper, we developed a magneto-inductive (MI) magnetic sensor, which is smaller, lighter weight, and lower cost than the fluxgate magnetometer. The specifications such as the noise floor, resolution, etc., are measured. In addition, a comparative observation of the magnetic field between the proposed MI sensor and a highly precise is conducted. The experimental results identify the capability of the proposed MI sensor in weak magnetic detection.
... Some magnetic field sensors measure only one component of the magnetic field, e.g., Fluxgates and Hall effect instruments which are referred to as single axis devices [38], [39]. Other instruments measure only the total field B, e.g., NMR [40], [41], ESR [42], [43]. Aiming to get more information for engineering geophysical exploration, it is possible to combine three-axis sensors to give three field measurements in a single probe package. ...
Magnetic survey 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, for example, the depth to igneous rock and the thickness of sedimentary rock formations. In this case, the vector magnetic survey method can simultaneously obtain the modulus and direction information of the Earth's magnetic field, which can effectively reduce the multiplicity on data inversion, contribute to the quantitative interpretation of the magnetic body and obtain more precise information and characteristics of magnetic field resource, so as to improve the detection resolution and positioning accuracy of the underground target body. This paper presents a state-of-the-art review of the application situations, the technical features, and the development of the instruments for different application scenarios, i.e., ground, wells, marine, airborne, and satellites, respectively. The potential of multi-survey technique fusion for magnetic field detection is also discussed.
... The proton precession magnetometer (PPM) is a frequently used quantum device for weak geomagnetic detection, 1 and it has several advantages: superior stability, easy operation, etc. 2 Hence, the PPM has been widely employed in the fields of mineral exploration, 3 ferromagnetic target detection, 4 and geological disaster monitoring. 5 Nevertheless, a critical bottleneck for the PPM is still not to be overcome, i.e., how to obtain a high-precision measurement for the weak sensing free induction decay (FID) transversal signal whose corresponding frequency is proportional to the magnetic field strength. ...
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 random noise and power frequency noise. In this study, aiming to boost the SNR of the FID transversal signal, a novel filtering algorithm based on a prewhiten (PW) strategy is proposed and the PW filtering was combined with singular value decomposition (SVD) for further noise reduction. This method aims to generate adaptive PW input data before filtering, further decorrelating the noise to reduce the impact of varying noise levels in the received FID signals. The efficiency of the proposed joint filtering framework, dubbed PW-SVD, was evaluated by comparing with two state-of-the-art methods, i.e., SVD and principal component analysis and decomposition, using the same data. The results demonstrated that the proposed PW-SVD method obtained the smallest root mean square error and the highest signal-to-noise ratio improvement among all the compared methods, especially for the strong-noisy scenario, which enhances the environmental adaptability of a PPM.
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, for example, the depth of igneous rock and the thickness of sedimentary rock formations. In this case, the vector magnetic survey method can simultaneously obtain the modulus and direction information of the Earth's magnetic field, which can effectively reduce the multiplicity on data inversion, contribute to the quantitative interpretation of the magnetic body and obtain more precise information and characteristics of magnetic field resource, so as to improve the detection resolution and positioning accuracy of the underground target body. This paper presents a state-of-the-art review of the application situations, the technical features, and the development of the vector magnetic sensing platform-technical aspects for different application scenarios, i.e., ground, wells, marine, airborne, and satellites, respectively. The potential of multi-survey sensing platform technique fusion for magnetic field detection is also discussed.
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 characteristics of magnetic field resources. This paper is concerned with the possibility of vector magnetic field measurement with a magneto-inductive (MI) magnetic sensor. To evaluate the capability of the MI sensor, a test platform is set up and its performance including the noise floor, the resolution, the sensitivity, etc., are comprehensively characterized. Further, a comparative geomagnetic observation and magnetic anomaly detection among the proposed MI sensor, a high-precision Overhauser sensor, and a commonly used and accepted commercial MI sensor are conducted. The experimental results identify the capability of the proposed MI sensor in weak magnetic detection.
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 (OMPCS-FIDR), is developed and its working principle and implemented strategy are elaborated. By comparing the new sensor tuning approach with the state-of-the-art algorithms, i.e., peak detection, auto-correction, and secondary tuning, the results demonstrate that the proposed tuning method not only retains the performance but also overcomes the drawbacks of the state-of-the-art methods, which accelerates the possibilities of the PPM working in a scenario with a strong gradient magnetic field.
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 interferences such as harmonic noise and random noise. In this study, to boost the SNR of the FID signal, an effective filtering algorithm based on time-frequency peak filtering (TFPF) analyzed with pseudo-Wigner–Ville distribution (PWVD) is proposed. Through pre-treating the collected noisy FID signal with frequency modulation and instantaneous frequency estimation using the peak value of the time-frequency characterization, the embedded noise can be decorrelated and the relative pure FID signal can be detected regardless of the impact of varying noise levels. The superiority of the proposed synaptic noise reduction framework, namely, TFPF-PWVD, was found by comparing it with state-of-the-art approaches under the same conditions. The results illustrated that even though in a strong-noisy scenario, the proposed TFPF-PWVD based approach still achieved the best SNR for the yielded sensing FID and the minimum standard deviation for the observed magnetic field data, which can enhance the geomagnetic measuring performance of a PPM.
