Flat Coil Research Articles

Detection of holes, rivets or screws fixed on a metal sheet using a flat magnetic sensor

We describe a magnetic field sensor in which the sensitive part is a flat coil engraved on a printed circuit. In the presence of a metallic target in the electromagnetic field yielded by the sensor, eddy currents are induced and cause a frequency variation of the transducer output signal. The measurement of this frequency variation is used for detecting holes, screws and rivets fixed on a metal sheet. The experimental characterization and the electronics needed for implementing this sensor are discussed in connection with its applications.

ESR imaging of polymers and solid materials

AbstractEPR imaging was applied to the study of several important processes in polymers and materials. The solvent diffusion and induced swelling was visualized in the water/DMF or toluene/DMF interactions with polycarbonate or polystyrene molded rods. The cross‐sectional images revealed non‐homogeneous solute/solvent diffusion, rod expansion and crack development. The ESR lineshapes in all cases above confirmed that the nitroxide imaging agent did not interact significantly with the polymer matrix; thus the paramagnetic distribution reflected bulk solvent distribution quite well. The diffusion of an electrolyte buffer (Krebs) solution containing a nitroxide spin probe was followed in a cross‐sectional image of a polyacrylamide gel rod. A one‐dimensional radial diffusion constant was calculated for the solvent piperidinol nitroxide spin probe, TEMPOL. Lastly, solid coal rods were monitored during mild pyrolysis at 150°C in air. Here the naturally occurring organic radical composition was imaged. Even with the increase in total ESR signal and subsequent decline to ca. the initial levels, the coal rod cross‐section was essentially homogeneous in paramagnetic centers throughout the heating process. All of the imaging above utilized a homemade L‐band, flat loop surface coil spectrometer.

Temperature insensitive fiber coil sensor for altimeters

A displacement sensor using a pair of flat Panda fiber coils with a 90 degrees connection is demonstrated. The dual coils are squeezed differentially. The phase retardations caused by the compression are constructively added, while the retardations caused by the environmental temperature are destructively added, thereby removing the temperature effect. Both the birefringence and loss effects induced by the deformation of the coils are utilized for high accuracy detection and emergency detection, respectively. In experiments using thirty turn coils, the guaranteed sensitivity of 357 degrees /mm (retardation/displacement) and the long term stability of 4 degrees /h (retardation/period) were obtained.

Shock wave tube for the fragmentation of concrements

First Page

4718431 Surface coil with calibration substance for use in a nuclear magnetic resonance apparatus

Avec une incidence de 5 % de la population féminine, les malformations génitales représentent un problème clinique réel décrit par Oppelt et al. (2007) [1]. Il faut d’abord les diagnostiquer, et en reconnaître les anomalies extragénitales associées et donc savoir quand les rechercher ; penser au diabète maturity-onset-diabetes-of the young 5 (MODY-5) quand il y a une histoire personnelle ou familiale de diabète. Cela est souvent du ressort du diabétologue et notre spécialité peut être mise à contribution dans la recherche de la malformation génitale associée. Nous rapportons le cas d’une patiente de 19 ans présentant un diabète, une néphropathie sous forme de reins micropolykystiques, une cytolyse biologique, un utérus bicorne unicervical cela pouvant s’inscrire dans un diabète MODY-5 confirmé par la découverte de la délétion complète du gène codant pour HNF-1β à l’état hétérozygote.With an incidence of 5% in the female population, genital malformations are a frequent clinical occurrence presented by Oppelt et al. (2007) [1]. First, we have to diagnostic them and search for extra genital malformation when it is necessary. Think about maturity-onset-diabete-of-the young 5 (MODY-5) when there's a personnel or family story of diabetes. This is often within the competence of the diabetologist and our speciality can be put in contribution in the research for the associated genital malformation. We report on the case of a young woman age of 19 with diabetes diagnosed during her adolescence, a nephropathy with polykystic kidneys, biological cytolysis, a bicornuate unicervical uterus while this may be a clinical diabetes MODY-5 confirmed by the discovery of the complete deletion of the gene coding for HNF-1β in the heterozygous state.

Distributed self-capacitance of magnetic resonance surface coils

A theoretical investigation of the capacitive coupling between a round, flat NMR surface coil and a dielectric medium is presented. The change in coil self-capacitance produced by the presence of the medium is calculated. These calculated results are compared with those observed experimentally in a series of NMR surface coils.

High-speed forming of metal sheets by electromagnetic force.

A numerical method to simulate the high-speed free forming of a clamped circular disk in an electromagnetic forming system using a flat spiral coil is presented. The method combines field penetration into the disk and dynamic elasto-plastic deformation of the disk. The spiral coil is approximated by coaxial circular loops carrying the discharge current from a capacitor bank. The penetration of the magnetic field of the coil into the disk is formulated as a boundary-value problem for the diffusion equation. Magnetic field, eddy currents and electromagnetic force density in the disk are calculated. An equation of motion for the disk loaded by the magnetic force is combined with the field equation as well as an equivalent circuit equation. Plane stress condition is assumed. Strain-rate effect on the work-hardening law of the disk material is taken into account. An experiment on the free bulging of annealed aluminum disks is also presented, showing fairly good agreement with the numerical solution.

渦流探傷に用いる空芯回転トランスの開発

渦流探傷に用いる空芯回転トランスの開発

可動へん平コイル形差動変圧器の解析

可動へん平コイル形差動変圧器の解析

Two Magnetic Methods for Articulatory Measurements

We present two magnetic methods for measuring articulatory activities. Unlike previous methods, the magnetic fields are uniform. Three alternating magnetic fields induce voltages in two detectors, a magnetic potentiometer and a flat coil. Thus we are able to measure jaw and tongue movements during speech production. These methods are biologically safe. The miniaturized detectors do not disturb the speech movements. Some preliminary results are presented. These methods can also be applied for other kinds of vectorial distance measurement.

Responses in small hand muscles from magnetic stimulation of the human brain.

1. The magnetic field generated by a brief current in a 9 cm diameter flat circular coil varies rapidly with time and when applied over the human scalp it is capable of exciting motor structures subserving the small hand muscles. With a peak magnetic field at the centre of the coil of 0.9-1.6 Tesla, single scalp stimuli produced twitches in the right abductor digiti minimi (a.d.m.), first dorsal interosseous (f.d.i.) and adductor pollicis muscles. Compound muscle action potentials (c.m.a.p.s) and single motor units from these muscles were recorded. 2. The twitch force and corresponding c.m.a.p. were greatly enhanced by voluntary background contraction of the muscle and depended on the direction and intensity of the magnetic field. Response amplitude was maximal with the stimulating coil centred near the vertex but precise coil position was not critical. 3. When the orthodromic volley set up in the peripheral nerve by magnetic stimulation of the brain collided with a maximal antidromic volley set up by stimulation at the wrist, remaining electromyographic (e.m.g.) activity gave evidence of multiple firing of some spinal motoneurones, provided that the muscle exerted a slight voluntary background contraction and the stimulus intensity was above threshold for relaxed muscle. 4. When the muscle changed from total relaxation to a slightly contracted state the onset latency of the c.m.a.p. was shortened by about 3 ms without further change when the background contraction increased. In slightly contracted muscle, c.m.a.p. onset latency was little affected over a wide range of stimulus intensities and was unaffected by the position of the stimulating coil within an area of 6 X 6 cm over the vertex. 5. Single motor units, recorded with needle electrodes in the a.d.m. or f.d.i. muscle, could be caused to discharge at a constant latency by threshold brain stimuli. Different single motor units had latencies varying from 22.4 to 32.1 ms. The same motor unit was activated from different coil positions up to 7 cm apart. These motor units had the lowest thresholds for voluntary activation. Stronger stimuli caused the same motor unit to discharge 1.5 ms earlier. 6. The threshold for excitation of pathways to the a.d.m. muscle was reduced by voluntary contraction of the contralateral a.d.m. and by contraction of the ipsilateral f.d.i. muscles. Using these procedures, the c.m.a.p. of totally relaxed a.d.m. muscle showed a more than 2-fold amplitude increase, a shortening of onset latency to a similar degree as with contraction of the muscle itself, and single motor units in the a.d.m. muscle discharged 1.5 ms earlier.(ABSTRACT TRUNCATED AT 400 WORDS)

Technical Aspects on Magnetic Resonance Imaging of the Spine at 1.5 Tesla

Technical aspects on surface coil magnetic resonance imaging of the spine using a superconducting system with a field strength of 1.5 tesla are described. By using a flat surface coil instead of the body coil the image quality was markedly improved and the signal-to-noise ratio (S/N) was increased approximately 2.6 times. Small voxels resulted in low S/N. The best image quality was achieved with a slice thickness of 5 mm, a field of view of 20 to 24 cm and a matrix of 256 X 256. Interleaved slices provided superior image quality compared with contiguous slices at the expense of acquisition time. For sagittal images the phase encoding gradient should be in the cranio-caudal direction to minimize motion artifacts. To obtain T1 and T2 images of high quality, spin echo pulse sequences with TR 600/TE 20 ms and TR 2000/TE 40 to 80 ms are useful.

An investigation of the magnetic field in the plane of a circular current loop

The earliest experiment a student performs when studying electromagnetism is the magnetic field at the center of a flat circular coil carrying an electric current. Later he may study the field at points along the axis of the coil. This paper deals essentially with the measurement of the magnetic field at points along a diameter of the coil, which is not generally attempted. The paper focuses on the usefulness of this laboratory exercise from the standpoints of pedagogy and practical application.

Unidirectional, intermittent rotation of the flagellum of Rhodobacter sphaeroides.

The single flagellum of the photosynthetic bacterium Rhodobacter sphaeroides was found to be medially located on the cell body. Observation of free-swimming bacteria, and bacteria tethered by their flagellar filaments, revealed that the flagellum could only rotate in the clockwise direction; switching of the direction of rotation was never observed. Flagellar rotation stopped periodically, typically several times a minute for up to several seconds each. Reorientation of swimming cells appeared to be the result of Brownian rotation during the stop periods. The flagellar filament displayed polymorphism; detached and nonrotating filaments were usually seen as large-amplitude helices of such short wavelength that they appeared as flat coils or circles, whereas the filaments on swimming cells showed a normal (small-amplitude, long-wavelength) helical form. With attached filaments, the transition from the normal to the coiled form occurred when the flagellar motor stopped rotating, proceeding from the distal end towards the cell body. It is possible that both the relaxation process and the smaller frictional resistance after relaxation may act to enhance the rate of reorientation of the cell. The transition from the coiled to the normal form occurred when the motor restarted, proceeding from the proximal end outwards, which might further contribute to the reorientation of the cell before it reaches a stable swimming geometry.

High speed forming of metal sheets by electromagnetic force. 1st report. Measurement of electromagnetic force generated by a spiral flat coil.

In designing effective electromagnetic forming systems, more knowledge on the mutual induction between forming coils and workpieces and on resulting magnetic force are required. Coupling coefficient kc between a spiral flat work coil of 15 turns and different specimens of circular plates in an electromagnetic forming machine is evaluated based on the measurement of effective coil inductance. kc at different circuit frequencies is obtained and shown as a function of the ratio of the thickness of the specimen to the skin depth, h0/δs. If h0/δs is greater than 0.5, kc is about 0.92. Impulses of an electromagnetic force defined by the time integral of the force are measured by accelerating specimens. The impulse depends on the conductivity and the thickness of the specimen. The surface density of a specimen also plays a significant role when kinematic energy gained by the specimen is concerned. It is shown that a frequency range to maximize the impulse at constant initial energy stored in a capacitor bank exists between h0/δs=0.3∼0.8.

High speed forming of metal sheets by electromagnetic force. 2nd report. Analysis of the electromagnetic impulsive force generated by a spiral flat coil.

An analytical method to predict the electromagnetic force in an electromagnetic forming system is presented. A spiral flat coil is approximated by coaxial circular rings carrying the discharge current from a high voltage capacitor bank. The penetration of the magnetic field of the coil into a conductive circular disk is analyzed based on the boundary-value problem for the diffusion equation. The thickness of the disk is assumed to be large compared with the skin depth. Magnetic field, eddy currents and electromagnetic force density in the disk are calculated numerically. Coil current and the magnetic field distribution in the gap between the coil and the disk agree well with the experiment, showing the validity of the analysis.

High speed forming of metal sheets by electromagnetic force. 3rd report. Free bulging of circular aluminum plates by spiral flat coils.

An experiment on the free bulging of circular plates of annealed aluminum alloy by a pancake coil of single layer is presented in the first part. The bulging process is observed in detail by high speed photography. It is shown that the deformation begins at the annular part of the disk and the central part is bulged at the final stage of the process. A method of the simulation of the process is developed in the next part. The penetration of the magnetic field applied by the coil current into the disk is formulated by the diffusion equation to obtain impulsive electromagnetic pressure. The thickness of the disk is assumed to be large enough compared with the skin depth. An equation for the dynamic elastic-plastic deformation of a clamped disk loaded by magnetic pressure is derived. The simultaneous equations are solved numerically. The calculated bulging process agress pretty well with the experimental observation showing the validity of the simulation.

The wrist: a preliminary report on high-resolution MR imaging.

Excellent spatial resolution is required to demonstrate the complex region of the wrist, with its diverse structures comprising bone, cartilage, and ligaments. Magnetic resonance (MR) imaging was done with a Magnetom imaging system operating at 1.0 T. Use of a flat surface coil enabled excellent spatial resolution and a section thickness of 4 mm. Twenty-nine patients with navicular nonunion or pseudarthrosis, rheumatoid arthritis, recent fractures, soft-tissue alterations, and bone tumors were examined. All patients had undergone radiography and bone scintigraphy. In this limited sampling, MR was found to detect and characterize marrow and articular alterations more accurately, and earlier, than either of those modalities.

A surface coil design for a vertical field MRI system and its application in imaging the breast

The general design of a flat surface coil for use with a vertical field MRI system is discussed. A development of the design for imaging the breast is used as a specific illustration. The phenomenon of “sympathetic resonance” is described in which transmission and reception is performed on the standard body coil with the surface coil disconnected, its presence amplifying the signal to the body coil from the region of interest. Results show that better quality images can be obtained with the surface coil than with the standard body coil and that the sympathetic resonance mode overcomes to a large extent the limited field of view problem normally associated with a surface coil. A threefold improvement in signal to noise ratio was obtained using the surface coil.

Stereo phono pick-up and/or cutter

A phonograph pick-up or cutter has a stylus holder carrying a stylus, which cooperates with two transducers, one for each of two orthogonal directions of vibration. Each transducer has a flat coil and an associated magnet having their axes in line. For each transducer the direction of relative movement of the coil to the magnet corresponds to the direction of the coil axis and the magnetic axis. The stylus holder is connected to the moving parts of the two transducers by a coupling member. Preferably, the moving part is arranged on a support connected to the stationary part, to minimize undesired transverse movements.