Cesium Magnetometer Research Articles

A high-precision and fast-sampling frequency measurement method based on FPGA carry chain for airborne optically pumped cesium magnetometer.

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 method based on carry chains of Field-Programmable Gate Array (FPGA). In order to achieve a fast-sampling rate, an improved equal precision frequency measurement method is proposed to measure the standard signal and the resonance signal continuously. Besides, by using the serial full adder to connect FPGA carry chains to a delay line, the delay line is used to compensate the unsynchronized clock edge, so the counting error can be reduced, and the precision of frequency measurement can be improved greatly. Experiments show that the frequency resolution is 0.014 nT and the relative error is lower than 2 × 10-6 when the sampling rate is 500 Hz. The experimental result indicates that the proposed method improves the precision and sampling rate of resonance frequency measurement greatly. Consequently, the precision and sampling rate of AOPCM can be improved.

Aeromagnetic Investigation of the Central Apennine Seismogenic Zone (Italy): From Basins to Faults

AbstractWe report on a high‐resolution, low‐altitude aeromagnetic investigation of the central Apennine extensional seismogenic zone, hit by destructive historical earthquakes including the 2009 L'Aquila seismic sequence. Central Apennines are predominantly made by thick (>4 and possibly up to 12 km) packages of shelf and deep marine limestones and dolomites of Mesozoic age, unconformably covered by upper Pliocene‐Holocene continental sediments lying on (often active) normal fault hanging walls. Seismogenic faults cut the carbonates down to 10‐ to 12‐km depth, where the brittle‐ductile transition occurs. Aeromagnetic data were collected during June 2014 with a cesium magnetometer, along 200‐m‐spaced flight lines. Apart from a regional 80‐nT anomaly that we modeled at 30‐ to 40‐km depths in the lower crust of the Adria plate, weak magnetic residuals are observed. As expected, normal faults cutting the diamagnetic carbonates lack any magnetic fingerprint. However, shallow continental basins yield clear anomalies of 2‐ to 8‐nT intensity, as they contain both residual soils and tephra erupted after 0.7 Ma by volcanoes from the Tyrrhenian margin of Italy. Basin margins imaged by aeromagnetism mirror the geometry of their causative normal faults. Thus, aeromagnetic residuals document many of the central Apennine normal faults that were active during the last ~3 Ma. Most prominent anomalies reflect basins formed after 0.7 Ma, as their magnetization is significantly higher than that of older continental basins. We conclude that rectilinear boundaries of most prominent anomalies reflect faults formed after 0.7 Ma, thus probably seismogenic.

Historical anthropogenic layers identification by geophysical and geochemical methods in the Old Town area of Krakow (Poland)

In the Middle Ages, trade and craft started developing intensely in Krakow, a significant metropolis of Central Europe. This led to a considerable demand for water, which resulted in the creation of an elaborate network of artificial watercourses. Their course, until today, has not been sufficiently studied. Non-invasive geophysical methods combined with a small diameter borehole drilling technique and geochemical analyses can identify the presence of structures connected with historical moats, millstreams, etc. on the basis of historical sediment recognition. The research carried out in 2010 involved measurements with two geophysical methods, i.e. the ground-penetrating radar (GPR) and the cesium magnetometer. Due to the high attenuation of electromagnetic waves by anthropogenic soil and magnetic disturbances connected with a tram line, additional measurements were undertaken using the electrical resistivity tomography (ERT) technique. This method allowed the detection of structures buried under anthropogenic layers. Based on the use of borehole drilling and the acquisition of ground profiles, it was possible to present a more precise interpretation. In consequence, the location of historical watercourses was determined and the course of their fragments was mapped more precisely. The measurement of the basic physicochemical proprieties of the ground samples (pH, Eh, EC) and determining the metal concentration with atomic absorption spectroscopy (AAS), enabled to identify anthropogenic-origin metals, such as Cu and Pb, and also those of the geogenic origin, like Fe, in the medium. The measured values were correlated with the measurement results of magnetic susceptibility, which allowed for lithological classification of the layers.

An Automatic Wideband 90° Phase Shifter for Optically Pumped Cesium Magnetometers

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 phase deviation of 1° will cause 1 Hz change of the resonant frequency. In order to meet the continuous measurement of the geomagnetic field, an automatic wideband 90° phase shifter based on the all-pass filter has been designed. It can be used to precisely make the phase of the detected signal shifted by 90° in a wide range of frequencies from 50 to 350 kHz. Through the actual test and analysis, the phase shift error of the automatic phase shifter is less than 0.1°, and the relative error less than 0.1%. It has been proved the feasibility of the automatic wideband 90° phase shifter applied to the cesium optically pumped magnetometer.

Study of 3He Rabi nutations by optically-pumped cesium magnetometers

We describe a method for recording the Rabi nutation of nuclear spin polarized 3He by optically pumped cesium magnetometers. The measurement is performed by detecting the time-dependent magnetic field produced by the 3He magnetization. The observed signals are compared to theoretical models and the results are used to precisely trace the evolution of the magnetization. This procedure represents a convenient way to control and measure the Rabi flip angle and the degree of spin polarization in experiments using 3He magnetometers. The method requires only very coarse knowledge of the applied magnetic field’s magnitude.

All-Optical Vector Cesium Magnetometer**Supported by the National Natural Science Foundation of China under Grant Nos U1631239 and U1331114, and the 111 Project to Harbin Engineering University under Grant No B13015.

Based on power modulation of a pump laser and precessional projection detection, we present an all-optical vector magnetometer of cesium, which has a demonstrated magnitude sensitivity of 80 fT/Hz1/2 and an orientation sensitivity of 0.1°/Hz1/2. In the device, four main factors are measured experimentally, which are the Larmor precession frequency of a polarized magnetic moment that depends on the modulus of the measured magnetic field only, two phase shifts and amplitude ratio of the precession projection in the two probe directions relative to the magnetic field orientation. This kind of magnetometer with high sensitivity in the range of the spatial angle is suitable for solving the inverse problem and geomagnetic navigation.

PCB Coil Design Producing a Uniform Confined Magnetic Field

We present a magnetic field confining coil with a sub-$10^{-3}$ field uniformity over a large fraction of the coil. The structure is entirely made out of printed circuit boards (PCBs). The PCB design allows to tailor the path of wires to fit the required geometry. We measure the field uniformity with cesium magnetometers in a field range from 1 to 10 $\mu\mathrm{T}$. Our application uses such a coil for an atomic magnetometry-based current controller.

Absolute Positioning Using the Earth's Magnetic Anomaly Field

Achieving worldwide dependable alternatives to the Global Positioning System is a challenging engineering problem. Current Global Positioning System alternatives often suffer from limitations such as where and when the systems can operate. Navigation using Earth’s magnetic anomaly field, which is globally available at all times, shows promise to overcome many of these limitations. We present a navigation framework that uses Earth’s magnetic anomaly field as a navigation signal to aid an inertial navigation system in an aircraft. The filter utilizes ultra-accurate optically pumped cesium magnetometers to make scalar intensity measurements of Earth’s magnetic field and compare them with a map using a particle filter approach. The accuracy of these measurements allows observability of not only the inertial navigation system errors but also the temporal effects of Earth’s magnetic field, which corrupt the navigation signal. These temporal effects are thoroughly analyzed, and we present a simple model that allows near worldwide use of the navigation filter. We analyze the dependencies on altitude and magnetic storm activity in a realistic simulation using data from test flights and magnetic observatories.

Investigation of the intrinsic sensitivity of a 3He/Cs magnetometer

We report on extensive studies on the intrinsic sensitivity of a combined 3 He/Cs magnetometer. The magnetometer relies on the detection of the free spin precession of nuclear spin polarized 3 He by optically pumped cesium magnetometers. We characterize the relevant processes involved in the detection and quantify their impact on the total sensitivity of the magnetometer. An expression is derived that predicts the sensitivity of this magnetometer scheme and the results are compared to experiments. Excellent agreement is found between theory and experiments, and implications for an application of a 3 He/Cs magnetometer in an experiment searching for a permanent neutron electric dipole moment are discussed.

Measurement of a false electric dipole moment signal from 199Hg atoms exposed to an inhomogeneous magnetic field

We report on the measurement of a Larmor frequency shift proportional to the electric-field strength for $^{199}{\rm Hg}$ atoms contained in a volume permeated with aligned magnetic and electric fields. This shift arises from the interplay between the inevitable magnetic field gradients and the motional magnetic field. The proportionality to electric-field strength makes it apparently similar to an electric dipole moment (EDM) signal, although unlike an EDM this effect is P- and T-conserving. We have used a neutron magnetic resonance EDM spectrometer, featuring a mercury co-magnetometer and an array of external cesium magnetometers, to measure the shift as a function of the applied magnetic field gradient. Our results are in good agreement with theoretical expectations.

Duo- and Quadro-sensor Configuration for High Speed/High Resolution Magnetic Prospecting with Caesium Magnetometer

Duo- and Quadro-sensor Configuration for High Speed/High Resolution Magnetic Prospecting with Caesium Magnetometer

Design and performance of an absolute 3He/Cs magnetometer

We report on the design and performance of a highly sensitive combined $^3$He/Cs magnetometer for the absolute measurement of magnetic fields. The magnetometer relies on the magnetometric detection of the free spin precession of nuclear spin polarized $^3$He gas by optically pumped cesium magnetometers. We plan to deploy this type of combined magnetometer in an experiment searching for a permanent electric dipole moment of ultracold neutrons at the Paul Scherrer Institute (Switzerland). A prototype magnetometer was built at the University of Fribourg (Switzerland) and tested at Physikalisch-Technische Bundesanstalt (Berlin, Germany). We demonstrate that the combined magnetometer allows Cram\'er-Rao- limited field determinations with recording times in the range of $\sim 500\mathrm{s}$, measurements above $500\mathrm{s}$ being limited by the stability of the applied magnetic field. % With a $100\mathrm{s}$ recording time we were able to perform an absolute measurement of a magnetic field of $\approx1\mathrm{\mu T}$ with a standard uncertainty of $\Delta B\sim60\mathrm{fT}$, corresponding to $\Delta B/B<$6$\times$10$^{-8}$.

Chasing aeroplanes: developing a vehicle‐towed caesium magnetometer array to complement aerial photography over three recently surveyed sites in the UK

Aerial photography combined with airborne lidar can often provide information on the location of archaeological sites at a near landscape level of coverage. Ground‐based geophysical techniques may then be deployed to complement the aerial survey, particularly where the soils or land use may not be ideal for either producing crop marks or preserving topographic features. This paper describes the development of a vehicle‐towed caesium magnetometer array, from an original hand‐pushed system, to allow high‐density datasets to be rapidly acquired over large areas required to provide a meaningful comparison at the scale demanded by the aerial survey results. Technical details of the system are presented together with methodological considerations for both data acquisition in the field and appropriate post processing to obtain high‐sensitivity field measurements over more weakly magnetized sites. Results are presented from a number of recent collaborative research projects within the English Heritage Remote Sensing Team to illustrate the benefits of a combined aerial and ground‐based approach to mapping the historic environment.

Identification of UAV Platforms and Payloads for Mineral Exploration and Applications in the Oil and Gas Industry

Donohue V. (2014). Identification of UAV Platforms and Payloads for Mineral Exploration and Applications in the Oil and Gas Industry. International Journal of Unmanned Systems Engineering. 2(3): x-x. This paper identifies UAV platform and sensor suites for use in oil, gas and mineral exploration and monitoring. Platform selection accounts for the extreme weather environments and remote locations where the UAVs are expected to operate. The six platforms considered include four single engine UAVs (Insitu GeoRanger, Insitu Integrator, AAI Shadow 200, Aeronautics Aerostar Tactical) and two twin engine platforms (ROV-1, MA THOR Twin). Sensor suite options include a high-definition (HD) camera with full motion video, scanning light detection and ranging (LiDAR), differential thermal imager, hyperspectral imager, cesium magnetometer, and a quantum cascade laser. Mission requirements include: 1. Reliable operation in arctic, desert and tropical environments; and 2. A minimum 10 kg payload capacity; 3. Fully autonomous function from launch to recovery; 4. Continuous satellite link with ground control station monitoring; 5. A range of 1000 km; 6. Remote launch and recovery capability. Three UAV/sensor suite combinations are considered viable in satisfying the mission requirements. The ROV-1 is selected as the best UAV platform option with the following sensor suite: HD camera, hyperspectral imager, differential thermal imager, cesium magnetometer, and quantum cascade laser. The features making the ROV-1 the best option include its twin engines, 1500 km range and 34 kg payload capacity, which meet or exceed the mission requirements of reliability, range and payload. © Marques Engineering Ltd.

Aeromagnetic surveying using a simulated unmanned aircraft system

ABSTRACTCarleton University and Sander Geophysics are developing an unmanned aircraft system (UAS) for aeromagnetic surveying. As an early indication of the expected performance of the unmanned aircraft system, a simulated unmanned aircraft system (sUAS) was built. The simulated unmanned aircraft system is a T‐shaped structure configured as a horizontal gradiometer with two cesium magnetometers spaced 4.67 m apart, which is the same sensor geometry as planned for the unmanned aircraft system. The simulated unmanned aircraft system is flown suspended beneath a helicopter.An 8.5 km2 area in the Central Metasedimentary Belt of the Grenville Province, near Plevna, Ontario, Canada, was surveyed with the simulated unmanned aircraft system suspended 50 m above ground. The survey site was chosen on the basis of its complex geological structure. The total magnetic intensity (TMI) data recorded were compared to that obtained during a conventional fixed‐wing survey and a ground survey. Transverse magneto‐gradiometric data were also recorded by the simulated unmanned aircraft system.The simulated unmanned aircraft system total magnetic intensity data have a higher resolution than the conventional fixed‐wing data and were found to have a similar resolution to that of the ground survey data. The advantages of surveying with the simulated unmanned aircraft system were: (1) the acquisition of a detailed data set free of gaps in coverage at a low altitude above the terrain and (2) substantial saving of time and effort.In the survey site, the 4.67 m simulated unmanned aircraft system gradiometer measured the transverse magnetic gradient reliably up to an altitude of 150 m above ground.

Analysis of influence of RF power and buffer gas pressure on sensitivity of optically pumped cesium magnetometer

A further study is conducted on two factors which respectively influence the sensitivity of optically pumped cesium magnetometer (CsOPM). The influence of radio frequency (RF) power and the buffer gas pressure on the sensitivity is theoretically analyzed, and some properties are predicted. Based on the established measurement system and the visible Zeeman spectrum, not only is the real influence of these factors studied, but also, under our experimental condition, optimum parameters based on the measured curves are ascertained. The properties of these measured curves match the theoretical result very well. Our research attempts to provide theory reference to help magnetometer designers determine optimum parameters under certain conditions.

The Study of Degaussing Technology for Underwater Vehicle

The underwater vehicle is mainly made of ferromagnetic material, the sensor measured except magnetic field, besides magnetic field that the vehicle of the inherent hard magnetic and soft magnetic materials produce and vehicle magnetic fields produced in mechanical and electrical equipment. At the same time, the precision of the geomagnetic measurements will be affected by sensor manufacturing error and installation error factors. Therefore, how to extract the magnetic field from complex environment is a real time measurement of a difficult problem. In this paper, it is based on soft compensation. The magnetic survey experiment that underwater carrier rotates 360 degrees underwater has been done on this basis, and the effect of underwater carrier on cesium magnetometer in different heading is analyzed. The degaussing algorithm for own magnetic field of carrier is obtained and the real value of underwater magnetic field can be restored. It is the solid foundation of high precision underwater geomagnetic navigation and establishing the underwater geomagnetic map.

Spectrally selective optical pumping in Doppler-broadened cesium atoms

The D1 line spectrally selective pumping process in Doppler-broadened cesium is analyzed by solving the optical Bloch equations. The process, described by a three-level model with the Λ scheme, shows that the saturation intensity of broadened atoms is three orders of magnitude larger than that of resting atoms. The |Fg = 3〉 → |Fe = 4〉 resonance pumping can result in the ground state |Fg = 4, mF = 4〉 sublevel having a maximum population of 0.157 and the population difference would be about 0.01 in two adjacent magnetic sublevels of the hyperfine (HF) state Fg = 4. To enhance the anisotropy in the ground state, we suggest employing dichromatic optical HF pumping by adding a laser to excite D1 line |Fg = 4〉 → |Fe = 3〉 transition, in which the cesium magnetometer sensitivity increases by half a magnitude and is unaffected by the nonlinear Zeeman effect even in Earth's average magnetic field.

Ground Truthing Magnetometer Data Using Soil Coring: Initial Results from Cornesti-Iarcuri, Timis County, Romania

is study uses soil augering to explore a sample of the range of geomagnetic anomalies from magnetometer surveys at the massive fortified site of Corneşti-Iarcuri. e cores focus on the south end of the interior of Enclosure II and a limited area to the east between Enclosures II and III. ese areas were studied during the 2010 campaign when the international team used different techniques to verify the age and type of occupations in this portion of the site. e coring results are presented in standardized descriptions and 1 m section photographs. e cores sample both high contrast anomalies from suspected burned deposits and low contrast areas where archaeological deposits are thought to be absent. ese field data suggest that the local calcareous Chernozem soils vary by depth and thickness of calcitic horizons due to slope, erosion, or impact due to possible use of the slopes for borrow. e low magnetic susceptibility of the carbonates can affect the results of the Cesium Magnetometer, in some cases identifying high contrast anomalies due to the close proximity to CaCO3 horizons and other material. In other cases archaeological deposits result in low contrast areas on the magnetogram due to the absence of burning. e initial auger results suggest that while the geomagnetic data clearly maps the enclosures and other burned features, there is the potential that other types of deposits may go unrecognized in this calcareous soil landscape.

All-Optical Cesium Atomic Magnetometer with High Sensitivity

An all-optical cesium magnetometer with high sensitivity based on absorptive detection is reported. The experiment achieves a polarized rotational spectrum of the probe light which is induced by circular dichroism and a quarter wave plate together. The frequency response of the rotational spectrum is 1.8 mrad/Hz at Larmor precession resonance. Analyzing the signal-to-noise ratio from the experimentally observed spectrum, we predict that the magnetic measurement sensitivity of 0.3 pT/Hz1/2 would be obtained in the responsive range from 20 nT to 2000 nT.