Abstract-A simple and accurate model is presented for computation of the electromagnetic induction (EMI) resonant frequencies of canonical conducting and ferrous targets, in particular, finite-length cylinders and rings. The imaginary resonant frequencies correspond to the well known exponential decay constants of interest for time-domain EMI interaction with conducting and ferrous targets. The results of the simple model are compared to data computed numerically, via method-of-moments (MoM) and finiteelement models. Moreover, the simple model is used to fit measured wideband EMI data from ferrous cylindrical targets (in terms of a small number of parameters). It is also demonstrated that the general model for the magnetic-dipole magnetization, in terms of a frequency-dependent diagonal dyadic, is applicable to general rotationally symmetric targets (not just cylinders and rings).
Tiltmeters on the Arctic Ocean were used to measure flexure of the ice forced by an energetic packet of internal waves riding the crest of diurnal internal bores emanating from the Yermak Plateau, north of the Svalbard Archipelago. The waves forced an oscillatory excursion of 36 microradians in tilt of the ice, corresponding to an excursion of 16 micrometers per second in vertical velocity at the surface and of 3.5 millimeters in surface displacement. Strainmeters embedded in the ice measured an excursion of 3 x 10(-7) in strain, consistent with ice flexure rather than compression. The measured tilt is consistent with direct measurements of excursions in horizontal current near the surface (12 centimeters per second) and in vertical displacement (36 meters) of the pycnocline 100 meters below the surface.
Quantum Magnetics (QM), in collaboration with the Coastal Systems Station (CSS), Naval Surface Warfare Center, Florida, is developing a magnetic real-time tracking vector gradiometer (RTG) for incorporation into an unmanned underwater vessel (UUV) built by Bluefin Robotics as part of the United States Navy buried mine hunter program.The UUV-RTG will detect the presence of mines in conjunction with the buried object scanning sonar (BOSS) system being developed by Florida Atlantic University (FAU).Both the RTG and the BOSS systems will be placed in the same UUV; used together, they will improve mine detection and reduce hits on clutter.The RTG uses high-resolution fluxgate magnetometers.Based on the three-sensor gradiometer (TSG) concept invented by IBM, it comprises three primary threeaxis sensors and one three-axis reference sensor.The configuration cancels the large ambient magnetic f i el d at the primary sensors, thus mitigating dynamic range and linearity requirements. An earlier version of the RTG has been demonstrated on land and used for preliminary at-sea measurements. The new RTG is more compact and designed to fit inside a 12" diameter UUV. The RTG sensor unit is oil-filled and is sealed from the UUV, which is flooded with seawater. The RTG electronics resides in a sealed air-tilled container. The RTG is placed in the nose section of the UUV in order to minimize electromagnetic interference from noise sources such as batteries, motors and actuators at the rear. To achieve further noise mitigation, magnetic field and electric current sensors placed at appropriate locations inside the UUV gather signals from noise sources for noise mitigation in post-processing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.