ΔE-Effect Magnetic Field Sensors

Many conceivable biomedical and diagnostic applications require the detection of small-amplitude and low-frequency magnetic fields. Against this background, a magnetometer concept is investigated in this work based on the magnetoelastic ΔE effect. The ΔE effect causes the resonance frequency of a magnetoelastic resonator to detune in the presence of a magnetic field, which can be read-out electrically with an additional piezoelectric phase. Various microelectromechanical resonators are experimentally analyzed in terms of the ΔE effect and signal-and-noise response. This response is highly complex because of the anisotropic and nonlinear coupled magnetic, mechanical, and electrical properties. Models are developed and extended where necessary to gain insights into the potentials and limits accompanying sensor design and operating parameters. Beyond the material and geometry parameters, we analyze the effect of different resonance modes, spatial property variations, and operating frequencies on sensitivity. Although a large ΔE effect is confirmed in the shear modulus, the sensitivity of classical cantilever resonators does not benefit from this effect. An approach utilizing surface acoustic shear-waves provides a solution and can detect small signals over a large bandwidth. Comprehensive analyses of the quality factor and piezoelectric material parameters indicate methods to increase sensitivity and signal-to-noise ratio significantly. First exchange-biased ΔE-effect sensors pave the way for compact setups and arrays with a large number of sensor elements. With an extended signal-and-noise model, specific requirements are identified that could improve the signal-to-noise ratio. The insights gained lead to a new concept that can circumvent previous limitations. With the results and models, important contributions are made to the understanding and development of ΔE-effect sensors with prospects for improvements in the future

The Effect of Temperature and Partial Melting on Velocity and Attenuation in a Simple Binary System

A possible explanation of the low-velocity, low-Q zone in the upper mantle is partial melting, but laboratory data are not available to test this conjecture. As a first step in obtaining an idea of the role that partial melting plays in affecting seismic variables, we have measured the longitudinal and shear velocities and attenuations in a simple binary system that is completely solid at low temperatures and involves 17% melt at the highest experimental temperature. The system investigated was NaCl • H_2O. At temperatures below the eutectic the material is a solid mixture of H_2O (ice) and NaCl • 2 H_2O. At higher temperatures the system is a mixture of ice and NaCl brine. In the completely solid regime the velocities and Q change slowly with temperature. There is a marked drop in the velocities and Q at the onset of melting. For ice containing 1% NaCl, the longitudinal and shear velocities change discontinuously at this temperature by 9.5 and 13.5%, respectively. The corresponding Q's drop by 48 and 37%. The melt content of the mixture at temperatures on the warm side of the eutectic for this composition is about 3.3%. The abrupt drop in velocities at the onset of partial melting is about three times as much for the ice containing 2% NaCl; for this composition, the longitudinal and shear Q's drop at the eutectic temperature by 71 and 73%, respectively. If these results can be used as a guide in understanding the effect of melting on seismic properties in the mantle, we should expect sharp discontinuities in velocity and Q where the geotherm crosses the solidus. The phenomena associated with the onset of melting are more dramatic than those associated with further melting

Seismic Absorption and Modulus Measurements in Porous Rocks in Lab and Field: Physical, Chemical, and Biological Effects of Fluids (Detecting a Biosurfactant Additive in a Field Irrigation Experiment)

We have been exploring a new technology that is based on using low-frequency seismic attenuation data to monitor changes in fluid saturation conditions in two-fluid phase porous materials. The seismic attenuation mechanism is related to the loss of energy due to the hysteresis of resistance to meniscus movement (changes in surface tension, wettability) when a pore containing two fluids is stressed at very low frequencies (< 10 Hz). This technology has potential applications to monitoring changes in (1) leakage at buried waste sites, (2) contaminant remediation, and (3) flooding during enhanced petroleum recovery. We have concluded a three year field study at the Maricopa Agricultural Center site of the University of Arizona. Three sets of instruments were installed along an East-West line perpendicular to the 50m by 50m inigation site. Each set of instruments consisted of one three component seismometer and one tiltmeter. Microseisms and solid Earth-tides served as strain sources. The former have a power peak at a period of about 6 seconds and the tides have about two cycles per day. Installation of instruments commenced in late summer of 2002. The instruments operated nearly continuously until April 2005. During the fall of 2003 the site was irrigated with water and one year later with water containing 150 ppm of a biosurfactant additive. This biodegradable additive served to mimic a class of contaminants that change the surface tension of the inigation fluid. Tilt data clearly show tidal tilts superimposed on local tilts due to agricultural irrigation and field work. When the observed signals were correlated with site specific theoretical tilt signals we saw no anomalies for the water irrigation in 2003, but large anomalies on two stations for the surfactant irrigation in 2004. Occasional failures of seismometers as well as data acquisition systems contributed to less than continuous coverage. These data are noisier than the tilt data, but do also show possible anomalies for the irrigation with the surfactant. The quantity of data is large and deserves careful analysis. Detailed analyses of the two data sets are ongoing

Die solvothermale Synthese von Thioantimonaten(III), Kupfer(I)- und Silber(I)haltigen Thioantimonaten(III)

Die Arbeit bestand darin, unter solvothermalen Bedingungen offene Netzwerkstrukturen aus Übergangsmetallhaltigen-Thioantimonaten und Aminen als Strukturdirektoren zu synthetisieren und zu charakterisieren. Zunächst wurden reine Thioantimonate(III) der allgemeinen Formel RSbxSy (R = Amin) wie (C6N3H17)Sb6S10 und (C6N2H18)Sb4S7 hergestellt. Sie sind in die Reihen der Thioantimonate(III) mit dem Sb:S-Verhältnissen 1:1.667 und 1:1.75 einzureihen. Im Unterschied zu diesen Verbindungen sind in der Literatur nur wenige auf Kupfer und Silber basierende Thioantimonate(III) beschrieben. Unter nahezu gleichen Versuchsbedingungen gelang es, Kupfer(I)-Thioantimonate(III) der allgemeinen Formeln RCu2SbS3 und RCu3Sb2S5 (R = Amin) zu synthetisieren. Die fünf hergestellten Verbindungen (C4N2H14)0.5Cu2SbS3 [C4N2H12 = 1,4-Diaminobutan], (C6N2H18)0.5Cu2SbS3 [C6N2H16 = 1,6-Diaminohexan], (C4N3H15)0.5Cu2SbS3 [C4N3H13 = Diethylentriamin] und (C8N4H22)0.5Cu2SbS3 [C8N4H20 = 1,4-bis(2-aminoethyl)-Piperazin] kristallisieren in der monoklinen Raumgruppe P21/n und weisen alle die gleiche Topologie des Cu2SbS3-Netzwerkes auf und können als anorganisch-organische Hybridverbindungen aufgefasst werden. Die Sb-S- , Cu-S- , Cu-Sb- und Cu-Cu-Abstände, sowie die entsprechenden Winkel unterscheiden sich nur geringfügig. Dagegen weisen die Verbindungen (C4N3H14)Cu3Sb2S5 [C4N3H13 = Diethylentriamin] und (C6N4H20)0.5Cu3Sb2S5 [C6N4H18 = Triethylentetramin] trotz des identisches Cu:Sb:S-Verhältnisses völlig verschiedenartige Strukturen auf. Alle Verbindungen zeigen eine sandwichartige Anordnung der Anionenschicht und des protonierten Amins auf. Dabei variieren die Schichtabstände zwischen 4.4 und 8.8 Å. Schichtverbindungen sind ebenfalls die beiden Silber(I)-Thioantimonate(III) (C4N2H14)Ag3Sb3S7 (C4N2H12 = 1,4-Diaminobutan) und (C2N2H9)2Ag5Sb3S8 (C2N2H8 = Ethylendiamin). Sie kristallisieren in der orthorhombischen Raumgruppe Pnma bzw. der monoklinen Raumgruppe P21/n. Um Kenntnis über weitere Materialeigenschaften zu erhalten, wurden zusätzlich Messungen zur magnetischen Suszeptibilität χ, der diffusen Reflexion und der Impedanzspektroskopie durchgeführt

Dural Arteriovenous Fistula on the Brain Stem and Upper Cervical Spinal Cord - A Case Report -

A 53-year-old man abruptly developed headache and unconsciousness. Brain computed tomography (CT) and CT angiography showed subarachnoid hemorrhage, intraventricular hemorrhage, and multiple tortuous vascular structures on the brain stem and upper cervical spinal cord. Four-vessel angiography displayed intradural ventral arteriovenous fistula, supplied by the left vertebral and occipital arteries. Drainage was via both sigmoid sinus and cervical venous plexus. He had been treated with transarterial coil embolization of the left vertebral artery. Subsequently, he suffered from left hemiplegia and cognitive problem. Brain magnetic resonance (MR) and MR angiography performed 4 weeks later revealed multiple infarctions on the left cerebellum, left upper cervical spinal cord, and both medial thalamus, as well as occlusion of the left vertebral artery with reduction in varix size. After rehabilitative management, his muscle strength and cognitive function improved. We report a very rare case of dural arteriovenous fistula on the brain stem and upper cervical spinal cord

The Role of Mobile Point Defects in Two-Dimensional Memristive Devices

Two-dimensional (2D) layered transition metal dichalcogenides (TMDCs) are promising memristive materials for neuromorphic computing systems as they could solve the problem of the excessively high energy consumption of conventional von Neumann computer architectures. Despite extensive experimental work, the underlying switching mechanisms are still not understood, impeding progress in material and device functionality. This study reveals the dominant role of mobile defects in the switching dynamics of 2D TMDC materials. The switching process is governed by the formation and annihilation dynamics of a local vacancy depletion zone. Moreover, minor changes in the interface potential barriers cause fundamentally different device behavior previously thought to originate from multiple mechanisms. The key mechanisms are identified with a charge transport model for electrons, holes, and ionic point defects, including image-charge-induced Schottky barrier lowering (SBL). The model is validated by comparing simulations to measurements for various 2D MoS$_2$-based devices, strongly corroborating the relevance of vacancies in TMDC devices and offering a new perspective on the switching mechanisms. The insights gained from this study can be used to extend the functional behavior of 2D TMDC memristive devices in future neuromorphic computing applications

Frequency Dependency of the Delta-E Effect and the Sensitivity of Delta-E Effect Magnetic Field Sensors

In recent years the delta-E effect has been used for detecting low frequency and low amplitude magnetic fields. Delta-E effect sensors utilize a forced mechanical resonator that is detuned by the delta-E effect upon application of a magnetic field. Typical frequencies of operation are from several kHz to the upper MHz regime. Different models have been used to describe the delta-E effect in those devices, but the frequency dependency has mainly been neglected. With this work we present a simple description of the delta-E effect as a function of the differential magnetic susceptibility χ of the magnetic material. We derive an analytical expression for χ that permits describing the frequency dependency of the delta-E effect of the Young's modulus and the magnetic sensitivity. Calculations are compared with measurements on soft-magnetic (Fe90Co10)78Si12B10 thin films. We show that the frequency of operation can have a strong influence on the delta-E effect and the magnetic sensitivity of delta-E effect sensors. Overall, the delta-E effect reduces with increasing frequency and results in a stiffening of the Young's modulus above the ferromagnetic resonance frequency. The details depend on the Gilbert damping. Whereas for large Gilbert damping the sensitivity continuously decreases with frequency, typical damping values result in an amplification close to the ferromagnetic resonance frequency

Part I. The Effect of Temperature and Partial Melting on Velocity and Attenuation in a Simple Binary System. Part II. Effect of Temperature and Pressure on Elastic Properties of Polycrystalline and Single Crystal MgO

A possible explanation of the low-velocity, low-Q zone in the upper mantle is partial melting, but laboratory data has not been available to test this conjecture. As a first step in obtaining an idea of the role that partial melting plays in affecting seismic variables, the longitudinal and shear velocities and attenuations were measured in a simple binary system that is completely solid at low temperatures and involves 17% melt at the highest experimental temperature. The system investigated was NaCl•H2O. At temperatures below the eutectic the material is a solid mixture of H2O (ice) and NaCl•H2O. At higher temperatures the system is a mixture of ice and NaCl brine. In the completely solid regime the velocities and Q change slowly with temperature. There is a marked drop in the velocities and Q at the onset of melting. For ice containing 1% NaCl, the longitudinal and shear velocities change discontinuously at this temperature by 9.5 and 13.5%, respectively. The corresponding Q's drop by 48 and 37%. The melt content of the mixture at temperatures on the warm side of the eutectic for this composition is about 3.3%. The abrupt drop in velocities at the onset of partial melting is about three times as much for the ice containing 2% NaCl; for this composition, the longitudinal and shear Q's drop at the eutectic temperature by 71 and 73%, respectively. If these results can be used as a guide in understanding the effect of melting on seismic properties in the mantle, we should expect sharp discontinuities in velocity and Q where the geotherm crosses the solidus. The phenomena associated with the onset of melting are more dramatic than those associated with further melting. The theory for randomly oriented fluid-filled penny-shaped cracks satisfactorily explains the velocity data. The anomalous behavior on the warm side of the eutectic temperature is attributed to thermochemical effects associated with interaction of the sound wave with the phase equilibria. This phenomenon is not observed when supercooling is possible. A laboratory has been constructed to measure the elastic properties of solids to 12 kbar and 1200°K by ultrasonic interferometry techniques. The elastic constants and their temperature and pressure derivatives have been measured to high temperature and pressure for both single crystal and polycrystalline MgO. A pseudoresonance technique involving pulse superposition and a lapped buffer rod without bond were used in order to obtain the necessary precision. The results for the single crystal are tabulated below.</p

Multi-Mode Love-Wave SAW Magnetic-Field Sensors

A surface-acoustic-wave (SAW) magnetic-field sensor utilizing fundamental, first- and second-order Love-wave modes is investigated. A 4.5   μ m SiO2 guiding layer on an ST-cut quartz substrate is coated with a 200 n m (Fe90Co10)78Si12B10 magnetostrictive layer in a delay-line configuration. Love-waves are excited and detected by two interdigital transducers (IDT). The delta-E effect in the magnetostrictive layer causes a phase change with applied magnetic field. A sensitivity of 1250 ° / m T is measured for the fundamental Love mode at 263 M Hz . For the first-order Love mode a value of 45 ° / m T is obtained at 352 M Hz . This result is compared to finite-element-method (FEM) simulations using one-dimensional (1D) and two-and-a-half-dimensional (2.5 D) models. The FEM simulations confirm the large drop in sensitivity as the first-order mode is close to cut-off. For multi-mode operation, we identify as a suitable geometry a guiding layer to wavelength ratio of h GL / λ ≈ 1.5 for an IDT pitch of p = 12   μ m . For this layer configuration, the first three modes are sufficiently far away from cut-off and show good sensitivity