59,942 research outputs found
Non Destructive Surface and Sub-surface Material Analysis using Scanning SQUID Magnetic Microscope
Non Destructive Testing (NDT) based on magnetic technique for the investigation of surface and sub-surface material properties is carried out using a room-temperature sample Scanning Magnetic Microscope. The performances of such instrument are well suited in the field of non destructive evaluation, thanks to the good combination of the spatial resolution and the magnetic field sensitivity of its own superconducting magnetic sensor.
The aim of this work is to show the capability and the advantages of the NDT technique based on Superconducting Quantum Interference Device (SQUID) sensors. We start by describing our Scanning SQUID Microscope in terms of its performances, the different non destructive techniques we can apply to perform the measurements, and the efforts we have done to improve its capability to detect weak magnetic field variations.
Two main applications are presented. On of this is based on the high magnetic field sensitivity of the SQUID sensor at low frequencies, and it consists to excite the sample with an alternating magnetic field (AC). This technique is applied to detect subsurface flaws in paramagnetic samples, for instance, in multilayer structures of aeronautical interest. The other field of application concerns the capability of the sensor to detect, with high spatial resolution, the direct magnetic field (DC) distribution on ferromagnetic samples, due to their residual magnetization. In this way, we can visualize magnetic domain structures of ferromagnetic particles. This capability is also exploited to evaluate the changing of magnetic field distribution in proximity of crack initialization on structural steels, subjected to fatigue cycles
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Magnetic Field Sensing with Nitrogen-Vacancy Color Centers in Diamond
In recent years, the nitrogen-vacancy (NV) center has emerged as a promising magnetic sensor capable of measuring magnetic fields with high sensitivity and spatial resolution under ambient conditions. This combination of characteristics allows NV magnetometers to probe magnetic structures and systems that were previously inaccessible with alternative magnetic sensing technologies. This dissertation presents and discusses a number of the initial efforts to demonstrate and improve NV magnetometry. In particular, a wide-field CCD based NV magnetic field imager capable of micron-scale spatial resolution is demonstrated; and magnetic field alignment, preferential NV orientation, and multipulse dynamical decoupling techniques are explored for enhancing magnetic sensitivity. The further application of dynamical decoupling control sequences as a spectral probe to extract information about the dynamics of the NV spin environment is also discussed; such information may be useful for determining optimal diamond sample parameters for different applications. Finally, several proposed and recently demonstrated applications which take advantage of NV magnetometers' sensitivity and spatial resolution at room temperature are presented, with particular focus on bio-magnetic field imaging.Engineering and Applied Science
Resonant Magnetic Field Sensors Based On MEMS Technology
Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration
Magnetometry with nitrogen-vacancy defects in diamond
The isolated electronic spin system of the Nitrogen-Vacancy (NV) centre in
diamond offers unique possibilities to be employed as a nanoscale sensor for
detection and imaging of weak magnetic fields. Magnetic imaging with nanometric
resolution and field detection capabilities in the nanotesla range are enabled
by the atomic-size and exceptionally long spin-coherence times of this
naturally occurring defect. The exciting perspectives that ensue from these
characteristics have triggered vivid experimental activities in the emerging
field of "NV magnetometry". It is the purpose of this article to review the
recent progress in high-sensitivity nanoscale NV magnetometry, generate an
overview of the most pertinent results of the last years and highlight
perspectives for future developments. We will present the physical principles
that allow for magnetic field detection with NV centres and discuss first
applications of NV magnetometers that have been demonstrated in the context of
nano magnetism, mesoscopic physics and the life sciences.Comment: Review article, 28 pages, 16 figure
Sub-picotesla widely tunable atomic magnetometer operating at room-temperature in unshielded environments
We report on a single-channel rubidium radio-frequency atomic magnetometer
operating in un-shielded environments and near room temperature with a measured
sensitivity of 130 fT/\sqrt{Hz}. We demonstrate consistent, narrow-bandwidth
operation across the kHz - MHz band, corresponding to three orders of magnitude
of magnetic field amplitude. A compensation coil system controlled by a
feedback loop actively and automatically stabilizes the magnetic field around
the sensor. We measure a reduction of the 50 Hz noise contribution by an order
of magnitude. The small effective sensor volume, 57 mm^3, increases the spatial
resolution of the measurements. Low temperature operation, without any magnetic
shielding, coupled with the broad tunability, and low beam power, dramatically
extends the range of potential field applications for our device.Comment: Main text: 6 pages, 9 figures. Supplementary material: 3 pages, 3
figures. Published version can be found at
https://aip.scitation.org/doi/full/10.1063/1.5026769 . V2: Added journal
layout, minor typos fixed. Content unchange
Optical Magnetometry
Some of the most sensitive methods of measuring magnetic fields utilize
interactions of resonant light with atomic vapor. Recent developments in this
vibrant field are improving magnetometers in many traditional areas such as
measurement of geomagnetic anomalies and magnetic fields in space, and are
opening the door to new ones, including, dynamical measurements of bio-magnetic
fields, detection of nuclear magnetic resonance (NMR), magnetic-resonance
imaging (MRI), inertial-rotation sensing, magnetic microscopy with cold atoms,
and tests of fundamental symmetries of Nature.Comment: 11 pages; 4 figures; submitted to Nature Physic
Scanning microSQUID Force Microscope
A novel scanning probe technique is presented: Scanning microSQUID Force
microscopy (SSFM). The instrument features independent topographic and magnetic
imaging. The SSFM operates in a dilution refrigerator in cryogenic vacuum.
Sample and probe can be cooled to 0.45 K. The probe consists of a microSQUID
placed at the edge of a silicon chip attached to a quartz tuning fork. A
topographic vertical resolution of 0.02 micrometer is demonstrated and magnetic
flux as weak as is resolved with a 1 micrometer diameter
microSQUID loop.Comment: submitted to Review of Scientific Instrument
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