961 research outputs found
Non-Invasive Hall Current Distribution Measurement in a Hall Effect Thruster
A means is presented to determine the Hall current density distribution in a closed drift thruster by remotely measuring the magnetic field and solving the inverse problem for the current density. The magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned just outside the thruster channel on a 1.5 kW Hall thruster equipped with a center-mounted hollow cathode. In the sensor array location, the static magnetic field is approximately 30 G, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is approximately tens of milligauss, which is within the sensitivity range of the TMR sensors. Because of the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field does provide the current density distributions. These distributions are shown as a function of time in contour plots. The measured ratios between the average Hall current and the average discharge current ranged from 6.1 to 7.3 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 1.5 kW exhibited a breathing mode frequency of 24 kHz, which was in agreement with temporal measurements of the discharge current
Miniaturized magnetic sensors for implantable magnetomyography
Magnetismâbased systems are widely utilized for sensing and imaging biological phenomena, for example, the activity of the brain and the heart. Magnetomyography (MMG) is the study of muscle function through the inquiry of the magnetic signal that a muscle generates when contracted. Within the last few decades, extensive effort has been invested to identify, characterize and quantify the magnetomyogram signals. However, it is still far from a miniaturized, sensitive, inexpensive and lowâpower MMG sensor. Herein, the stateâofâtheâart magnetic sensing technologies that have the potential to realize a lowâprofile implantable MMG sensor are described. The technical challenges associated with the detection of the MMG signals, including the magnetic field of the Earth and movement artifacts are also discussed. Then, the development of efficient magnetic technologies, which enable sensing picoâTesla signals, is advocated to revitalize the MMG technique. To conclude, spintronicâbased magnetoresistive sensing can be an appropriate technology for miniaturized wearable and implantable MMG systems
Entwicklung eines magnetoresistiven Biosensors zur Detektion von BiomolekĂŒlen
Schotter J. Development of a magnetoresistive biosensor for the detection of biomolecules. Bielefeld (Germany): Bielefeld University; 2004.Diese Arbeit prĂ€sentiert eine neue Nachweismöglichkeit fĂŒr BiomolekĂŒle, in deren Rahmen Sub-Mikrometer groĂe magnetische Marker and magnetoresistive Sensoren in einen magnetischen Biochip integriert werden. Die interessierenden MolekĂŒle werden an OberflĂ€chen-immobilisierte Proben hybridisiert und spezifisch mit magnetischen Partikeln markiert. Im Folgenden werden die Streufelder der magnetischen Marker als WiderstandsĂ€nderung in einem eingebetteten magnetoresistiven Sensor nachgewiesen. Jedes einzelne Sensorelement deckt die FlĂ€che eines typischen Proben-DNA Spots ab, und ĂŒber 200 Sensorelemente sind in einen magnetischen Sensor-Prototypen integriert, wodurch er kompatibel zu DNA-Microarray Applikationen ist.
Die Eigenschaften verschiedener kommerziell erhĂ€ltlicher magnetischer Partikel werden verglichen und hinsichtlich ihrer Eignung als Marker fĂŒr magnetische Biosensoren untersucht. Sensoren, welche entweder auf dem Riesen-Magnetowiderstand oder dem Tunnel-Magnetowiderstand basieren, werden prĂ€sentiert, und ihre Reaktion auf lokale Streufelder, welche von magnetischen Markern auf ihrer OberflĂ€che induziert werden, wird untersucht.
DNA-Hybridisierungsexperimente werden prĂ€sentiert, die zeigen, dass unser Prototyp eines magnetischen Biosensors komplexe DNA-Sequenzen mit einer LĂ€nge von tausend Basen bis herab zu einer Konzentration von etwa 20 pM nachweisen kann. Ein direkter Vergleich unserer magnetoresistiven und einer Fluoreszenz-basierten Detektionsmethode zeigt, dass unser magnetischer Biosensor bei dem Nachweis geringer DNA-Konzentrationen ĂŒberlegen ist. AuĂerdem weist der magnetische Biosensor eine kompakte GröĂe auf und ĂŒbersetzt die vorhandene Menge einer bestimmten Sorte BiomolekĂŒle direkt in ein elektronisches Signal, wodurch dies eine sehr vielversprechende Wahl fĂŒr die Detektionseinheit eines zukĂŒnftigen Lab-on-a-Chip GerĂ€tes darstellt.In this thesis, a new sensing scheme for biomolecules is presented that combines sub-micron sized magnetic markers and magnetoresistive sensors into a magnetic biochip. The molecules of interest are hybridized to surface-immobilized probes and get specifically labeled by magnetic markers. Afterwards, the stray fields of the magnetic markers are detected as a resistance change by an embedded magnetoresistive sensor. Each sensor element covers the area of a typical probe DNA spot, and over 200 sensor elements are integrated into a magnetic biosensor prototype, thus making it compatible to standard DNA microarray applications.
The properties of different commercially available magnetic particles are investigated and compared with respect to their suitability for magnetic biosensor applications. Sensors based both on giant and tunneling magnetoresistance are presented, and their response to local stray fields induced by magnetic markers on their surface is studied.
DNA hybridization experiments are presented that prove that our prototype magnetic biosensor can detect complex DNA with a length of one thousand bases down to a concentration of about 20 pM. A direct comparison of the magnetoresistive and a fluorescent detection methods shows that our magnetic biosensor is superior to standard fluorescent detection at low DNA concentrations. Furthermore, the magnetic biosensor has compact size and directly translates the abundance of desired biomolecules into an electronic signal, thus making it a very promising choice for the detection unit of future lab-on-a-chip devices
Magnetic biosensors: modelling and simulation
In the past few years, magnetoelectronics has emerged as a promising new platform technology in various biosensors for detection, identification, localisation and manipulation of a wide spectrum of biological, physical and chemical agents. The methods are based on the exposure of the magnetic field of a magnetically labelled biomolecule interacting with a complementary biomolecule bound to a magnetic field sensor. This Review presents various schemes of magnetic biosensor techniques from both simulation and modelling as well as analytical and numerical analysis points of view, and the performance variations under magnetic fields at steady and nonstationary states. This is followed by magnetic sensors modelling and simulations using advanced Multiphysics modelling software (e.g. Finite Element Method (FEM) etc.) and home-made developed tools. Furthermore, outlook and future directions of modelling and simulations of magnetic biosensors in different technologies and materials are critically discussed
Engineering Electromagnetic Systems for Next-Generation Brain-Machine Interface
MagnetoElectric Nanoparticles (MENPs) are known to be a powerful tool for a broad range of applications spanning from medicine to energy-efficient electronics. MENPs allow to couple intrinsic electric fields in the nervous system with externally controlled magnetic fields. This thesis exploited MENPs to achieve contactless brain-machine interface (BMIs). Special electromagnetic devices were engineered for controlling the MENPsâ magnetoelectric effect to enable stimulation and recording. The most important engineering breakthroughs of the study are summarized below.
(I) Metastable Physics to Localize Nanoparticles: One of the main challenges is to localize the nanoparticles at any selected site(s) in the brain. The fundamental problem is due to the fact that according to the Maxwellâs equations, magnetic fields could not be used to localize ferromagnetic nanoparticles under stable equilibrium conditions. Metastable physics was used to overcome this challenge theoretically and preliminary results show the potential of single neuron localization in neural cell culture. 3D electromagnetic sources generated a time varying magnetic field pattern which effectively kept the nanoparticles in a metastable diamagnetic state.
(II) Electromagnetic Systems to Locally Stimulate Neurons: Assuming a magnetoelectric coefficient of 1 V/cm/Oe, application of a 1000 Oe field can lead to a local electric field of 1000 V/cm, which can be sufficient to induce stimulation. Two approaches for achieving local stimulation relied on localization of nanoparticles and field profiles, respectively. The nanoparticles were localized via the aforementioned metastable physics. As for the field profiles, they were controlled by specially designed electromagnetic sources. Both approaches were used to achieve sub-mm firing in hippocampal cell cultures. This controllably induced neural firing was confirmed via standard calcium ion imaging and electroencephalography.
(III) Engineering Electromagnetic Systems to Record Neural Activity with MENPs: A theoretical model was developed to use MENPs for contactless recording of local neural activity. With MENPs, neural firing from a 1 mm3 depth could generate a magnetic field of 100 pT a few millimeters above the skull. For comparison, this value is approximately 3 orders of magnitude higher than the field generated by the same brain volume without using MENPs, i.e., on the order of 100 fT. Such amplification of the magnetic field generated by MENPs has the potential to enable cost-effective magnetoencephalography (MEG) based brain imaging systems which could operate at room temperature in a shield-free environment
Magnetoresistive and Thermoresistive Scanning Probe Microscopy with Applications in Micro- and Nanotechnology
This work presents approaches to extend limits of scanning probe microscopy techniques towards more versatile instruments using integrated sensor concepts. For structural surface analysis, magnetoresistive sensing is introduced and thermoresistive sensing is applied to study nanoscale phonon transport in chain-like molecules. Investigating with these techniques the properties of shape memory polymers, a fabrication method to design application-inspired micro- and nanostructures is introduced
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