Application Of Magnetometers Research Articles

Multi-channel spin exchange relaxation free magnetometer towards two-dimensional vector magnetoencephalography.

Optically pumped atomic magnetometers based on spin exchange relaxation free regime have recently become a powerful tool in the field of magnetoencephalography measurements. For this application of magnetometers, simultaneous multilocation magnetic field measurements are desired. To fulfill the requirement, we develop a multi-channel sensor module based on a single large vapor cell. The probe beam passes through the vapor cell twice by reflection and then records the two-dimensional spatial magnetic field distribution with two 2 × 2 photodiode matrixes. Comparing with the previous multi-channel tangential magnetic field measuring sensors, our magnetometer is sensitive to the normal magnetic field by operating in the longitudinal parametric modulation mode. Measuring the normal component is considered more suitable for magnetoencephalography, because the normal component provides more information. The sensitivities of the channels are approximately 10 fT/Hz1/2 in the normal direction. The auditory evoked magnetic fields of the four adjacent locations perpendicular to the scalp are detected simultaneously. Our magnetometer can measure the normal and tangential magnetic fields simultaneously. The dual-axis vector measurement of magnetic field is very important for magnetoencephalography.

The Application of Magnetometers and Electromagnetic Induction Sensors in UXO Detection

This paper introduces the physical model of unexploded ordnance (UXO) in the magnetization process and the formula derivation of the magnetic dipole model. The application of magnetometers and electromagnetic induction sensors in the detection of UXO is introduced. The magnetometers introduce the total field measurements technology of the CS optical-pump marine magnetometer and the MagSTAR (Magnetic Scalar Triangulation and Ranging) gradient detection technology. The electromagnetic induction sensors introduce the working theories and the popular product models of Geophex company and Geonics Ltd. The method of detecting UXO by MTADS of United States Naval Research Laboratory (The multisensor towed array detection system) compares the difference between the United States Naval Research Laboratory for target recognition.

Constant speed motion analysis using a smartphone magnetometer

This study demonstrated that the constant average speed of a dynamic car could be measured and calculated using the smartphone magnetometer. The apparatus setup was built using a dynamic car, a linear track up to 1.50 m, a bunch of magnets, and a smartphone magnetometer application. The smartphone magnetometer application, ‘Physics Toolbox Suite’, was free for the experiment. The magnet and smartphone magnetometer were attached on a linear track and dynamic car, respectively. When the dynamic car are moving on the car track, the smartphone magnetometer will measure the magnetic field value versus the time relation. The magnetic field value will fluctuate, increasing when close to the magnet or decrease when the distance from the magnet increases. The magnetic field properties (peaks time) versus the magnet distance position were analyzed using linear fitting, and we find the average speed of the dynamic car. We hope that this magnetometer experiment will be valuably used in general physics laboratories.

Magnetoresistive performances in exchange-biased spin valves and their roles in low-field magnetic sensing applications

Abstract The magnetoresistive properties of pinned spin valves (SV) and their roles in low-field sensing applications were characterized. The magnetoresistive parameters were extracted, including the exchange bias (Heb) field as a function of the iron content in the CoFe layer and the antiferromagnetic (AFM) thickness, the magnetoresistance (MR) ratio versus the spacer thickness, the coercivity (Hc) as a function of the seed layer, and the composite layer [NiFe/Co] used. These parameters are crucial in determining the features of the magnetic sensors. Eventually, the selected SV film structure of (Si/SiO2)/Ta(50 A)/[NiFe(30 A)/Co(15 A)]/Cu(24 A)/Co80Fe20(25 A)/IrMn(100 A)/Ta(50 A) was found significant, and the SV elements were patterned using the lithographic lift-off method with the active cell dimensions of 2 μm × 150 μm. To define a pinning axis, a cool-field anneal was applied at 250 °C for 30 min in a magnetic field of 2 kOe. A Wheatstone half bridge was engineered using two SV elements and two external resistors. The operation point of the sensor was well tuned using a tiny permanent magnet. A sensitivity of 5 V/T was observed with a linear range of ±2 mT. To demonstrate the performance of the designed sensor, a measurement of the Earth magnetic field was carried out. The engineered SV sensor finds its usefulness in low-field magnetometer and electronic compass applications.

Drive signal waveform for a fluxgate

One of the obvious applications of magnetometers is a system of magnetic vacuum which is able to minimize the influence of external magnetic fields on the operation of electronic instrumentation. In magnetic field systems, fluxgate magnetometers are commonly used in the capacity of absolute magnetic field sensors. However, the quality improvement of magnetic vacuum requires the improvement of the fluxgate performance, in particular, its sensitivity.

Coherent population trapping with polarization modulation

Coherent population trapping (CPT) is extensively studied for future vapor cell clocks of high frequency stability. In the constructive polarization modulation CPT scheme, a bichromatic laser field with polarization and phase synchronously modulated is applied on an atomic medium. A high contrast CPT signal is observed in this so-called double-modulation configuration, due to the fact that the atomic population does not leak to the extreme Zeeman states, and that the two CPT dark states, which are produced successively by the alternate polarizations, add constructively. Here, we experimentally investigate CPT signal dynamics first in the usual configuration, a single circular polarization. The double-modulation scheme is then addressed in both cases: one pulse Rabi interaction and two pulses Ramsey interaction. The impact and the optimization of the experimental parameters involved in the time sequence are reviewed. We show that a simple seven-level model explains the experimental observations. The double-modulation scheme yields a high contrast similar to the one of other high contrast configurations like push-pull optical pumping or crossed linear polarization scheme, with a setup allowing a higher compactness. The constructive polarization modulation is attractive for atomic clock, atomic magnetometer, and high precision spectroscopy applications.

Magnetometer Application for GAMMA-400 Telescope Switching into the Mode with Increased Low Energy Charged Particles Intensity Registration

GAMMA-400 is an international project of a high apogee orbital astrophysical observatory for studying the characteristics of high-energy gamma-emission, electrons/positrons and light nuclei fluxes. The energy range for γ-rays and electrons/positrons registration in the main aperture is from ∼0.1GeV to ∼3.0 TeV. Also, this aperture allows high energy light nuclei fluxes characteristics investigation. Moreover, special aperture configuration allows registering of gamma-quanta, electrons (positrons) and light nuclei from the lateral directions too.The spacecraft GAMMA-400 orbit will be located in the Earth's magnetosphere and will pass front shock wave from magnetosphere interaction with the solar wind, turbulent-transition region, magnetopause and so on. During the satellite's movement through various Earth's magnetosphere regions its anticoincidence detectors will register high intensity fluxes of low energy charged particles captured by the magnetic field. The working area sections of GAMMA-400 detector systems used as anticoincidence shield are about 1 m2 each. The high intensity low energy charged particles flux influence on anticoincidence detectors should be taken into account during particle identification.This article presents a comparison between Earth's magnetosphere theoretical model according to SPENVIIS package and real data measured by detectors onboard THEMIS series satellites. The differences between these two datasets indicate that the calculated data are not sufficient to make short time predictions of variations of magnetic induction in the outer magnetosphere. A special trigger marker flag will be produced by GAMMA-400 counting and triggers signals formation system accordingly to the data of two onboard magnetometers. This flag's presence leads to special algorithms execution start, putting the plastic detectors into a dedicated working mode taking into account possible high count rates of external detector layers.

The Application of Aerial Magnetometers in Maritime Archaeology

International Journal of Nautical ArchaeologyVolume 43, Issue 2 p. 436-443 Note The Application of Aerial Magnetometers in Maritime Archaeology Jeremy Green, Jeremy Green Department of Maritime Archaeology, Western Australian Museum, Cliff Street, Fremantle, WA, 6160 Western AustraliaSearch for more papers by this author Jeremy Green, Jeremy Green Department of Maritime Archaeology, Western Australian Museum, Cliff Street, Fremantle, WA, 6160 Western AustraliaSearch for more papers by this author First published: 12 August 2014 https://doi.org/10.1111/1095-9270.12062Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume43, Issue2September 2014Pages 436-443 RelatedInformation

Highly Sensitive Superconducting Quantum-Interference Proximity Transistor

Superconducting quantum interference proximity transistors (SQUIPTs) are ultralow-power magnetic interferometers showing impressive magnetic flux response. An optimized nanofabricated geometry realizes a sensitivity so high that it is limited by the noise from room-temperature preamplification. This study demonstrates that SQUIPTs can achieve state-of-the-art sensors for magnetometric applications at micrometer scales.

Measuring the Effects of Lighting Distribution on Walking Speed and Head Pitch With Wearable Inertial Measurement Units

A comparative human performance evaluation of a miner's walking speed and head pitch was conducted on miners wearing two types of LED cap lamps. Walking speed and head pitch are indirect indicators of improved lighting. The better that miners can see the floor, the faster they can walk and the less they pitch their heads downward to illuminate the floor with their cap lamps. NIOSH researchers developed a non-contact way to quantify human performance by using two small wireless, wearable inertial measurement units. Data were collected in the field from nine coal miners in an underground coal mine. The field results showed no statistical difference between the two cap lamps for walking speed. However, there was a trend of 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> lower head pitch for one of the cap lamps. The field testing procedures were then replicated in a controlled laboratory environment and the results indicated a 5-degree lower head tilt when using the same cap lamp and a corresponding difference in walking speed. A novel application of magnetometers for distance flagging is also presented. Finally, study limitations and a follow-up study are discussed.

Roundabout Critical Headway Measurement Based on High-Resolution Event-Based Data from Wireless Magnetometers

Critical headway is an important parameter for roundabout design, particularly with regard to analytical modeling approaches. The models that have been developed over the past 30 years were typically based on data obtained from manually reduced video or field observations. This paper reports on the application of wireless magnetometers to collect point presence detection for calculating the rejected critical headways. Data were collected at a single-lane roundabout in Carmel, Indiana. Carmel has had more than 60 roundabouts in operation for several years: it represented a community that was highly experienced with roundabouts. More than 260,000 entering vehicles were observed at one of the single-lane roundabouts over a 2-week period with more than 45,000 rejected headways analyzed. For the roundabout studied, 75% of the rejected headways were found to be less than 3.0 s. The rejected headway values were somewhat lower than the values reported in NCHRP Report 572, perhaps because of the evolving driver familiarity with roundabouts. Although this community had a particularly large number of roundabouts, the rejected headway characteristics observed suggested that as roundabouts became more common throughout the United States, it was appropriate to revisit some of the basic traffic engineering parameters used for analysis, much as the traffic signal community did with saturation flow rate in the 1990s. The techniques presented in this paper could be scaled to several roundabouts with varying geometrics and traffic to diversify the data set necessary to update some of the values developed during the past decade before roundabouts were common in the United States.

A large sample study of spin relaxation and magnetometric sensitivity of paraffin-coated Cs vapor cells

We have manufactured more than 250 nominally identical paraffin-coated Cs vapor cells (28 mm inner diameter bulbs) for multi-channel atomic magnetometer applications. We describe our dedicated cell characterization apparatus. For each cell we have determined the intrinsic longitudinal, Γ 01, and transverse, Γ 02, relaxation rates. Our best cell shows Γ 01/2π≈0.5 Hz, and Γ 02/2π≈2 Hz. We find a strong correlation of both relaxation rates which we explain in terms of reservoir and spin exchange relaxation. For each cell we have determined the optimal combination of rf and laser powers which yield the highest sensitivity to magnetic field changes. Out of all produced cells, 90% are found to have magnetometric sensitivities in the range of 9 to 30 fT $\sqrt{\mathrm{Hz}}$ . Noise analysis shows that the magnetometers operated with such cells have a sensitivity close to the fundamental photon shot noise limit.

Peculiarities of SQUID magnetometer application in TEM

Due to progress in high‐temperature superconductor (HTS) technology, research in the application of superconducting quantum interference devices (SQUIDs) in time‐domain transient electromagnetics (TEM) has intensified. Several TEM systems using HTS SQUIDs have been developed and tested in numerous field trials. In this paper, the reliability of SQUID TEM data is investigated by comparison with commonly used induction‐coil data. Generally, a good agreement between SQUID and coil TEM data was found. However, two effects were observed with the SQUID TEM system which were not visible in coil measurements. The first effect is a “frequency dependence”: the response signal measured by the SQUID depends on the base frequency of the transmitter signal, decaying faster for higher frequencies. The second effect is a “zero‐crossover”: the SQUID response data becomes negative for late times. We propose a model for magnetometer TEM measurements that provides a possible explanation for these two effects. This model takes into account remnant responses induced in the ground by repetitive transmitter signals. Our simulations of coil and magnetometer responses show that, at moderately conducting ground, the influence of remnant responses is negligible in coil recordings, whereas it leads to a typical frequency dependence of magnetometer recordings. We show also that the influence of remnant responses may lead to the sign reversal of magnetometer data over highly conducting ground structures. To optimize magnetometer TEM measurements, it is advantageous to use lower transmitter frequencies than typical frequencies used for induction coil measurements. A recalculation of the original ground response on the basis of the proposed model may also be of advantage.

Performance of asymmetric superconducting quantum interference devices

Low T c superconducting quantum interference devices with asymmetric shunt resistances (SQUIDARs) have been numerically and experimentally investigated. Numerical simulations show that the flux to voltage transfer coefficient V Φ and magnetic flux noise S Φ are strongly dependent on both the asymmetry parameter ρ and damping parameter γ= R/ R d, where R and R d are the SQUID normal resistance and damping resistance, respectively. For small γ values, SQUIDARs show larger V Φ and smaller S Φ than symmetric devices. Asymmetric SQUIDs can then improve the performance of standard sensors in most of the magnetometric applications. By increasing γ, V Φ several times larger than that of symmetric SQUIDs can be achieved. Therefore, it is possible to couple SQUIDAR magnetometers to an external preamplifier without the need of an external circuit, simplifying the read-out electronics. Experimental values of the magnetic field sensitivity of 6–7 fT/Hz 1/2 have been so far obtained. These results, already suitable for biomagnetic applications, can be further improved by properly optimizing the device parameters.

Improved superconducting quantum interference devices by resistance asymmetry

Direct current superconducting quantum interference devices made by Josephson junctions with asymmetric shunt resistances have been numerically investigated in the low temperature regime. When combined with a damping resistance, the asymmetry leads to a flux to voltage transfer coefficient several times larger than the one typical of symmetric devices, together with a lower magnetic flux noise. These results show that this type of asymmetric device may replace the standard ones in a large number of magnetometric applications, improving the sensitivity performance. The large transfer coefficient may also simplify the readout electronics allowing a direct coupling of asymmetric devices to an external preamplifier, without the need of an impedance matching flux transformer.

Advanced field magnetometers comparative study

The application of flux-gate and search-coil magnetometers for geophysical prospecting is more and more widespread. The physical principle of their operation determines their use for the measurement of weak magnetic fields in the frequency band where their sensitivity threshold is lower: from DC to some tens of Hz for flux-gates and from some fractions of Hz till ∼1 MHz for search-coils. The estimation of the noise level of both types of magnetometers is made and recommendation for choice of ELF band is given. The problems connected with the digital measuring system are analyzed and new errors arising in the digital structure are outlined. The main parameters of recently developed flux-gate and search-coil magnetometers are discussed.

High- Tc SQUIDs: the ultra sensitive sensors for non-destructive testing and biomagnetism

This paper reviews the theory and applications of SQUID magnetometers, in view of recent progress in SQUID technology and since the discovery of high- T c superconductors (HTS). With their unrivalled sensitivity for magnetic flux and, consequently, for magnetic fields, voltages and currents, SQUID magnetometers have succeeded in a variety of applications, particularly in fields where a non-invasive, non-destructive type of detection and measurement is required. However, even with the introduction of HTS SQUID, the commercial impact of SQUID systems has been limited for a number of factors. We review these factors, and discuss few aspects that could contribute to the wider acceptance of SQUID applications.

Design and Optimization of HTC DC Squids for Magnetometric Applications

In order to optimize the magnetic field sensitivity [Formula: see text] we have followed two different approaches. In the former we have analyzed the influence of the quality of YBCO films on the superconducting properties and noise characteristics of bicrystal grain boundary junctions and dc-SQUIDs. For this purpose we have studied and compared three different YBCO deposition processes. In the latter we have reported the different criteria for the design of SQUID magnetometers usable for applicalions in shielded and unshielded environment.

Applications of high-temperature SQUIDs

Using examples from our recent work, we describe the progress toward three types of applications of SQUID magnetometers and gradiometers operating at the temperature of liquid nitrogen, and using high temperature superconductor (HTS) YBa 2 Cu 3 O 7 thin-film sensors. First, we demonstrated usefulness of our magnetocardiographic data for diagnosis of cardiac arrhythmia and determination of risk of sudden cardiac death by means of a new method. This was achieved in a shielded room using our sensitive HTS magnetometer, in a back-to-back comparison with a state-of-theart low-temperature (LTS) magnetometer. Second, using an eddy-current technique in conjunction with our HTS gradiometer in unshielded environment, we demonstrated detection of flaws located very deep, e.g. 36 mm, below the surfaces of stacks of aluminium sheets. This indicated a high potential for nondestructive material evaluation (NDE) of, e.g. aging airplane structures. Third, we showed the applicability of an HTS magnetometer for electromagnetic geological prospecting. A successful field test was conducted using the controlled-source audio magnetotellurics method, with reference to a commercial induction coil system. In these three areas of applications, HTS SQUID systems are expected to soon gain user and market acceptance.

High-temperature Josephson junctions and their applications

Manufacturable Josephson junctions with grain-boundary and proximity barriers made it possible to demonstrate SQUID sensors having energy resolutions approaching those of commercial low-temperature SQUIDs. Results indicate that the field sensitivity of HTS SQUIDs is already adequate for most magnetometer applications.